Anesthesia is a medical treatment that prevents patients from feeling pain during procedures like surgery, certain screening and diagnostic tests, tissue sample removal (e.g., skin biopsies), and dental work. It allows people to have procedures that lead to healthier and longer lives.

To produce anesthesia, doctors use drugs called anesthetics. Scientists have developed a collection of anesthetic drugs with different effects. These drugs include general, regional, and local anesthetics. General anesthetics make patients unconscious during the procedure while local and regional anesthetics just numb part of the body and allow patients to remain awake.

Depending on the type of pain relief needed, doctors deliver anesthetics by injection, inhalation, topical lotion, spray, eye drops, or skin patch.

General anesthesia affects the whole body, making patients unconscious and unable to move. Surgeons use it when they operate on internal organs and for other invasive or time-consuming procedures such as back surgery. Without general anesthesia, many major, life-saving procedures would not be possible, including open-heart surgery, brain surgery, and organ transplants.

Doctors provide general anesthetics either directly into the bloodstream (intravenously) or as an inhaled gas. General anesthesia delivered intravenously will act quickly and disappear rapidly from the body. This allows patients to go home sooner after surgery. Inhaled anesthetics may take longer to wear off.

General anesthetics typically are very safe. But they can pose risks for some patients, such as the elderly or people with chronic illnesses such as diabetes. Also, side effects may linger for several days in some patients, especially the elderly and children.

Serious side effects—such as dangerously low blood pressure—are much less common than they once were. Still, as with any medical procedure, some risks exist. To minimize these risks, specialized doctors called anesthesiologists carefully monitor unconscious patients and can adjust the amount of anesthetic they receive.

Doctors use local and regional anesthetics to block pain in a part of the body. With these anesthetics, patients stay conscious and comfortable. Usually, patients may go home soon after surgery.

Local anesthetics affect a small part of the body, such as a single tooth. They are often used in dentistry, for eye surgeries such as cataract removal, and to remove small skin growths including warts and moles.

Regional anesthetics affect larger areas, such as an arm, a leg, or everything below the waist. For example, this sort of anesthesia is used for hand and joint surgeries, to ease the pain of childbirth, or during a C-section delivery.

Until recently, we knew very little about how anesthetics work. Scientists are now able to study how the drugs affect specific molecules within cells. Most researchers agree that the drugs target proteins in the membranes around nerve cells. Because inhaled anesthetics have different effects than intravenous ones, scientists suspect that the two types of drugs target different sets of proteins.

Every day, people undergo surgery. Some operations require going deep into the body. Some can take many hours to finish.

Many of these procedures are possible only because of anesthesia. Different types of anesthesia may be used depending on the procedure.

Local anesthesia numbs a small part of the body, such as a tooth. Regional anesthesia is used for larger areas of the body such as an arm, a leg, or everything below the waist. People remain awake during local and regional anesthesia, but pain is reduced or blocked.

General anesthesia uses drugs that make people unconscious and unable to feel pain or move. It’s used for long or invasive procedures. Every year, millions of people in the nation undergo general anesthesia.

“Doctors and nurses have used general anesthesia for over 170 years,” explains Dr. George Mashour, an NIH-funded anesthesia expert at the University of Michigan.

Since that time, new drugs and advances in how patients are monitored have helped make administering anesthesia safer. We know a lot about how general anesthesia affects the heart, lungs, and many other organs. Clinicians can use machines to track how these organs are functioning while people are unconscious. This lets them precisely adjust anesthesia doses to keep people as safe as possible.

But how general anesthesia affects the brain is still not fully understood. NIH-funded researchers are studying ways to track brain activity during anesthesia. This may help them better understand anesthesia’s effects on the brain in general. It may also help them develop safer and more effective drugs.

General anesthesia does come with some risks. A rare complication is awareness under anesthesia. This is when a person gains some awareness during surgery, when they should be unconscious. Most often, this awareness is only of sounds. But sometimes it can include pain.

A more common unwanted effect of surgery and anesthesia is delirium. In delirium, a person is confused and often unclear about what is happening to them. Many people over the age of 60 experience delirium in the days following surgery. It’s also common in children when they awake from anesthesia.

“Ideally, we want to ensure that we are providing enough anesthesia to the brain to suppress consciousness and memory. But we don’t want to provide so much that we induce unwanted effects on brain function after surgery,” says Mashour.

Mashour and his team recently used thin wires placed on the scalp to measure electrical activity in the brain during anesthesia. They saw several shifts in the way areas of the brain communicated while people were unconscious.

Different shifts were seen during different stages of anesthesia, such as going under and waking up. Understanding such brain activity patterns may help scientists develop a brain monitor for anesthesia, Mashour says. Studying anesthesia could also yield insight into consciousness itself and conditions where consciousness is impaired, such as sleep or coma.

If you’re afraid of having general anesthesia, talk with your doctor. They can give you more information about the drugs used. Some procedures can also be done with types of anesthesia where you remain awake.

Ask Your Doctor

Before going under anesthesia, ask:

• Which type of anesthesia will I have? Do I have more than one option?
• Do I need to stop taking any of my medications before anesthesia?
• Do I need to do anything special before I have anesthesia?
• Will I be awake or aware of what is happening during anesthesia?
• Will I feel any pain?
• How soon will I wake up after anesthesia?
• Will I have any side effects from the drugs used?
• How long will I need to stay in the hospital afterward?

Introduction

Epidural anesthesia is a method of neuraxial pain control in which anesthetic medications are injected into the epidural space to block sensory and motor spinal nerve roots in the thoracic, abdominal, pelvic, and lower extremity areas. This epidural technique can be used for anesthesia during procedures, chronic pain, or muscle spasticity as a primary anesthetic or pain management adjuvant. Epidural anesthesia has been an effective modality for pain control for more than 100 years, with many proven advantages over other forms of anesthesia. A primary advantage epidural anesthesia offers is the ability for clinicians to tailor the medication used and the type of administration (ie, intermittent or continuous infusion) to meet the clinical need.[1] Additionally, this technique can reduce the opioid requirement during and after a procedure, lowering the incidence of associated side effects. This is particularly relevant in pediatric anesthesia, where the potential negative impact of certain anesthetic drugs on neurodevelopment is debated. The epidural technique is also valuable for postoperative pain management as part of a multimodal approach. A recent benefit of epidural anesthesia was providing an alternative to aerosol-generating general anesthesia during the COVID-19 pandemic.

However, recent studies have argued that alternative anesthesia techniques may benefit more and are less invasive than epidural anesthesia. Furthermore, several complications and risks are also associated with the epidural procedure. Therefore, healthcare professionals need enhanced competence in recognizing the indications and contraindications for epidural anesthesia and the risks, benefits, and complications involved. Additionally, clinicians should have knowledge of the current techniques recommended for performing epidural anesthesia and the role of the interprofessional team in caring for patients who undergo the procedure to optimize outcomes.

Anatomy and Physiology

The Spinal Cord and Epidural Space

The adult spinal cord is approximately 45 cm shorter than the spinal canal. The spinal cord ends at the L1 vertebra in 50% of adults and at the L2 vertebra in about 40%. Although it was previously believed that the newborn's spinal cord extended to the L2 or L3 vertebrae, recent studies have shown that the average neonate's conus medullaris is also at the L2 vertebra. Below this level, the lumbar and sacral nerves converge to form the cauda equina. The spinal cord is suspended in cerebrospinal fluid and surrounded by the arachnoid mater. The arachnoid mater and subarachnoid space extend caudally to S2 in adults, S3 in children, and S4 in newborns. The arachnoid mater is closely approximated to the dura mater, which is attached to the spine by its outer endosteal portion. The arachnoid mater envelopes the brain intracranially and the spinal cord and extends through the foramina intervertebral to the epineural connective tissues of the spinal nerves.

The spinal epidural space extends from the foramen magnum at the base of the skull to the sacral hiatus and contains fatty and connective tissues, blood vessels, and lymphatics. The blood vessels may dilate with pregnancy or ascites, increasing the risk of a traumatic or bloody puncture. The epidural space is further divided into the anterior and posterior epidural spaces. The anterior epidural space contains the ventral spinal nerves, the basivertebral veins, and the internal vertebral venous plexus. In contrast, the posterior epidural space contains the dorsal spinal nerves, the intervertebral veins, and the sinuvertebral nerves.

The boundaries of the epidural space are formed by the dura mater and arachnoid mater internally, the ligamentum flavum and the vertebral periosteum externally, and the intervertebral foramina laterally. The distance between the skin and the spinal epidural space is variable. Depending on a patient's age and amount of subcutaneous fat, this distance can range from 4 cm in normal BMI adults to >8 cm in obese patients. The dorsal border of the spinal epidural space is the ligamentum flavum. Moving superficially, the remaining layers are the interspinous ligament located between the spinous processes, the supraspinal ligament situated on the surface of the spinous processes, subcutaneous tissue, and the skin.

Relevance to Epidural Anesthesia

The anatomy of the epidural space is of paramount importance to the administration of epidural anesthesia. By targeting specific spinal segments and structures within the epidural space, anesthesiology clinicians can achieve targeted pain relief and minimize the risk of complications. In addition, understanding the anatomical variations and the location of blood vessels, spinal nerves, and other structures within the epidural space is essential for safe and effective epidural catheter placement.

Techniques to Locate the Epidural Space

Various techniques have been developed to locate and access the epidural space safely and accurately. The traditional landmark-based approach relies on identifying anatomical landmarks, including the spinous processes, interspinous spaces, and the midline, to guide epidural needle insertion. In addition, the loss-of-resistance technique is commonly employed to confirm the location of the epidural space, which involves feeling resistance to the gentle injection of air or saline with the epidural needle when not in the epidural space and the sudden loss of resistance when the space is entered.

The caudal epidural block is a specific technique that involves the administration of local anesthetic agents into the caudal epidural space located at the sacral hiatus. This technique is often used in pediatric anesthesia and specific lower extremity and perineal procedures in adults. The most common shape of the sacral hiatus is an inverted U shape, seen in both males and females. The length from the apex of the sacral hiatus to the first sacral spine is slightly longer in females compared to males; however, the sacral cornua's width is similar in both sexes. Understanding these morphometric parameters is crucial for successful epidural anesthesia procedures. Variations in the sacrum can contribute to lower backache and may impact surgical procedures. The sacral canal is formed by the union of the pedicle and lamina of the 5 sacra and contains important structures such as the cauda equina and sacral nerves.Correct needle placement can only be achieved by identifying anatomical landmarks (eg, the sacral cornu, the lateral sacral crests, and the apex of the sacral hiatus). Even with identifying anatomical landmarks, clinicians fail to place a caudal epidural block 30% of the time, secondary to anatomical variations; often, ultrasound is used to guide placement.Therefore, clinicians must have a good understanding of the anatomy of the sacral region to have any chance of successfully administering a caudal epidural block.

Indications

The primary indications for epidural anesthesia include obstetrical anesthesia during labor and surgical anesthesia for thoracic, major intra-abdominal, or spine surgeries, provided there is no need for muscle relaxation. Epidural anesthesia may also be used as an adjunct in intraoperative or postoperative pain management. Patients at higher risk for postoperative complications, such as those affected by ischemic heart disease, have demonstrated increased benefits (eg, decreased postoperative pulmonary complications and faster intestinal return to function) with epidural anesthesia in the past.

A systematic review with a meta-analysis comparing intravenous and epidural routes of patient-controlled analgesia (PCA) in abdominal surgery demonstrated that epidural PCA was associated with better postoperative pain relief, reduced opioid consumption, and fewer postoperative complications than intravenous PCA.] Additionally, it has been shown that combined epidural anesthesia and analgesia reduced postoperative cognitive impairment in patients receiving general anesthesia. Furthermore, investigations have been conducted on the effects of perioperative epidural analgesia on cancer recurrence and survival, suggesting a potential association between epidural analgesia and improved survival outcomes. However, recent studies have shown that the benefits of epidural analgesia during surgery compared to current alternative types of anesthesia (eg, catheter wound infusions and peripheral nerve blocks) are not as great and carry a higher risk of complications. In limited studies, epidural anesthesia demonstrated slightly more effective postsurgical pain control than systemic medications. Therefore, other than for obstetrical indications, epidural anesthesia may be more indicated as an adjuvant therapy; further research is needed before definitive conclusions can be reached.

Contraindications

Epidural anesthesia is considered relatively safe for most patients; however, alternative types of anesthesia may be more appropriate for some individuals.

Absolute Contraindications

• Patient refusal
• Local infection at the puncture site
• Increased intracranial pressure
• Traumatic spinal cord injury

Relative Contraindications

• Hemodynamic instability
• Obstructive cardiomyopathy
• Uncorrected coagulopathy or therapeutic anticoagulation
• Thrombocytopenia
• Inability to maintain positioning for epidural placement
• Anatomic spinal abnormalities

Equipment

Epidural Needles

Multiple types of epidural needles have been designed (eg, Tuohy, Hustead, Crawford, and Weiss). However, the Tuohy epidural needle is most often used. These epidural needles are usually 17 G or 18 G and are 3.5 in long; epidural needles up to 6 in are available and can be used in patients with increased subcutaneous adiposity.

Loss of Resistance Syringe

Loss of resistance syringes are made of glass or plastic and have very low friction between the plunger and the barrel to detect the change in resistance at the epidural space. Syringes may be loaded with air, saline, or both; the injected medium does not affect the success of identifying the epidural space, nor does it change the complication rate.

Epidural Catheters

Epidural catheters are used for continuous epidural anesthesia or analgesia. The catheters may be flexible or stiff and may have single or multiple perforations for the perfusion of the analgesic agent. In most commercially available kits, syringe-catheter connections (eg, Luerlock or Luer-slip connectors) are also included.

Epidural Procedure Site Preparation

Aseptic technique when placing an epidural catheter and dressing the insertion site is critical for infection prevention. Supplies required include:

• Sterile gloves
• Surgical cap and mask
• Sterile draping
• Individualized skin preparation solution packet (eg, chlorhexidine with or without alcohol or povidone-iodine with or without alcohol)
• Sterile occlusive dressing

Medications

The preference of anesthesiology clinicians will dictate which medications are used in a patient's epidural anesthesia. However, a combination of local anesthetic (eg, bupivacaine, ropivacaine, and an opioid (eg, fentanyl, sufentanil). IV fluids are also typically administered before an epidural is performed to prevent hypotensive episodes. Additionally, IV ephedrine or phenylephrine should be available to treat hypotension during neuraxial anesthesia.

Ultrasound-Guided Epidural Anesthesia

Clinicians may choose to place an epidural catheter with ultrasound guidance. Ultrasound technology allows real-time visualization of the relevant anatomical structure, potentially improving the accuracy and safety of epidural catheter placement. The advantages of using ultrasound guidance for epidural anesthesia include better identification of the epidural space, fewer needle passes and attempts, and a lower incidence of complications such as unintentional dural puncture, infection, and hematoma formation. Recent advancements in ultrasound-guided techniques have shown promise in improving the safety and efficacy of epidural anesthesia. Ultrasound guidance can reduce complications and improve the procedure's success by providing real-time visualization of the relevant anatomical structures. However, further research is needed to establish the superiority of ultrasound-guided epidural anesthesia over traditional landmark-based techniques.

Personnel

• Anesthesiologist or Nurse Anesthetist
• Assisting personnel

Preparation

Before an epidural anesthesia procedure, the patient should be positioned and the area prepared appropriately. Emergency equipment and medications need to be readily available in the room. Furthermore, intravenous access must be placed for fluid and medication administration. Standard American Society of Anesthesiologists (ASA) preanesthesia guidelines should be followed (eg, preoperative testing, hemodynamic monitoring). The patient may be positioned in a sitting or lateral decubitus position; back arching is advised for better exposure to intervertebral interspaces. Aseptic technique and field preparation must be used throughout epidural placement.

With any technique used to place an epidural, the patient should be positioned, prepped, and draped in the standard sterile fashion. The correct intervertebral space is then identified using anatomic landmarks, a loss of resistance needle, and sometimes ultrasound guidance. A systematic review of random controlled trials to evaluate preprocedural lumbar neuraxial ultrasound compared to the traditional landmark-based approach demonstrated that ultrasound guidance reduced the number of needle passes, attempts, and traumatic procedures. Additionally, ultrasound-guided techniques were associated with a shorter procedure time and a higher success rate. A recent literature review on ultrasonography for lumbar neuraxial block, including epidural anesthesia, reported similar findings. Ultrasound-guided techniques were also associated with improved procedural outcomes, such as increased first-attempt successes, fewer needle passes, and a decreased incidence of complications.

Technique or Treatment

The clinician's approach to performing epidural anesthesia depends on which area of the spine the epidural space will be accessed. Due to the difficult angulation of the thoracic spinous processes, epidural anesthesia performed above the T11 vertebra generally uses the paramedian approach. Those performed below the T11 level typically use the midline approach.

Medial and Paramedian Approach

In the medial (ie, midline) approach, the needle insertion site is midline between the spaces created by the vertebral spinous processes. Upon locating the desired spot, lidocaine 1% must be injected into the skin and underlying tissues to decrease the discomfort with the advancement of the epidural needle. Once localized anesthesia is achieved, the epidural needle is advanced with a stylet in place and with its bevel point cephalad, ultimately guiding the epidural catheter to the proper location. The epidural needle must be advanced through the skin, subcutaneous tissue, supraspinous, and interspinous ligaments. Once there, the stylet is removed, and the loss of resistance syringe that is filled up with saline, air, or both must be attached to the needle. As the needle advances, the clinician applies pressure to the plunger so that once the ligamentum flavum is pierced, a loss of resistance pressure is noted, confirming entry into the epidural space. On average, the distance from the skin to the ligamentum flavum is approximately 4 cm. The anesthesiology clinician will usually inject 5 to 10 cc of saline to expand the epidural space and decrease the risk of vascular injury.

In the paramedian approach, the needle insertion site is 1 cm lateral to the vertebral interspace. Local anesthetic is injected along the predicted path of the epidural needle as described for the medial approach. The epidural needle is then advanced through the paraspinal tissues. Given this location, the needle will not transverse the supraspinous or interspinous ligaments. The advancement of the needle must stop upon feeling the engagement in the ligamentum flavum. The loss-of-resistance syringe is attached, and the epidural space is located similarly to the median approach.

Once the epidural space is reached by either the midline or paramedian approach, the epidural catheter is advanced through the introducer needle after removing the loss-of-resistance syringe. The epidural catheter should be advanced to the 20-cm mark on the outside of the catheter. The epidural needle is removed after noting the distance from the skin to the epidural space as indicated by the marked epidural needle. The epidural catheter is then partially withdrawn, leaving approximately 5 to 6 cm of the tip in the epidural space. However, no consensus exists on the precise catheter length that should be left within the epidural space. The clinician can calculate the length by adding 5 to 6 cm to the distance previously measured by the epidural needle; the resulting total is the number up to which the epidural catheter should be withdrawn.

Once the catheter is in its final position, a 3-cm syringe is used to see if cerebral spinal fluid can be gently aspirated. Aspiration of cerebral spinal fluid indicates the epidural catheter is within the intrathecal space and should be relocated. A test dose to exclude a misplaced catheter is then performed by injecting 3 mL of 1.5% lidocaine with 5 mcg/mL of epinephrine. An increase in a patient's heart rate of 20 to 30 bpm or 15 to 20 mm Hg in systolic blood pressure may indicate intravascular positioning.

Caudal Anesthesia

Caudal anesthesia is a variation of epidural anesthesia widely used in children for procedures performed on areas under the umbilicus (eg, circumcision, herniotomy, or orchiopexy). Typically, patients are placed in a lateral decubitus position, and after the site is sterilely prepped, the sacral hiatus is identified. The sacrococcygeal membrane is pierced with a 22 to 25 G venous catheter at a 45-degree angle relative to the body's longitudinal axis, and the epidural catheter advanced until a loss of resistance is felt. No additional advance must be attempted since the distance between the sacrococcygeal membrane and the caudal end of the dural sac may be less than 10 mm. If CSF or blood is noted, the catheter is repositioned. Once properly located, a common test dose with epinephrine 0.5 mcg/kg is given to exclude a malpositioned catheter.

Complications

Spinal cord injuries (SCI) resulting from anesthesia procedures are rare but significant concerns for surgical patients. These injuries can have devastating effects on the quality of life and may even lead to mortality. Complications associated with anesthesia-induced SCI include temporary or permanent neurological symptoms, epidural hematoma or abscess, direct traumatic spinal injury, and adhesive arachnoiditis. These complications can manifest as motor deficits, sensory loss, pain, paraesthesia, and even permanent paralysis or anesthesia.

High-risk patients for anesthesia-induced SCI include those with spinal canal malformations, extremes of age, obesity, diabetes, immunocompromised or critically ill individuals, and those with previous neurological diseases. It is essential to carefully evaluate these patients preoperatively to identify any clinical conditions that may increase the risk of complications associated with neuraxial techniques. However, managing traumatic SCI patients in emergency rooms can be challenging due to existing tissue damage. Other complications associated with epidural anesthesia include:

• Hypotension
• Nausea and vomiting
• Bronchoconstriction
• Postpuncture headache after dural perforation
• Transient neurological syndrome
• Nerve injury with possible neuropathy; paralysis is rare
• Epidural hematoma
• Epidural abscess
• Meningitis
• Accidental intrathecal injection with total spinal anesthesia
• Osteomyelitis

Clinical Significance

The epidural technique is one of the earliest performed in the field of anesthesia. When correctly performed, epidural anesthesia is a safe technique that provides multiple benefits, including decreasing the need for general anesthesia, exposure to volatile anesthetics, and the associated risks. In addition, this technique can reduce the opioid requirement during and after a procedure, lowering the incidence of side effects associated with these medications. This is particularly relevant in pediatric anesthesia, where the potential negative impact of certain anesthetic drugs on neurodevelopment is debated. The epidural technique is also valuable for postoperative pain management as part of a multimodal approach. A recent benefit of epidural anesthesia was providing an alternative to aerosol-generating general anesthesia, which was restricted during the COVID-19 pandemic.

Studies have critically examined the balance between the benefits and risks associated with epidural analgesia for postoperative pain management, concluding that while epidural analgesia offers superior pain relief and improved postoperative outcomes, it also carries inherent risks. Therefore, careful patient selection and close monitoring are essential to minimize complications. Despite potential complications, neuraxial techniques, including epidural anesthesia, remain among the best opioid-sparing pain prevention and management options. These techniques can reduce patients' morbidity, improve outcomes, shorten hospital stays, and decrease the risk of chronic pain, ultimately providing economic benefits. Consequently, epidural anesthesia is a valuable technique for pain management, but it is not without risks. Careful patient selection, close monitoring, and timely interventions are essential to minimize the risk of anesthesia-induced SCI and associated complications. Further research and improvement of anesthesia protocols are necessary to enhance patient safety in neuraxial procedures.

Enhancing Healthcare Team Outcomes

A growing body of evidence demonstrates that using epidural anesthesia has positive effects like faster return in bowel function, decreased hormonal stress response to pain, decreased postoperative pulmonary complications, shortening in the length of in-hospital stay, and patient satisfaction. However, the safe and effective use of epidural anesthesia requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, and pharmacists collaborating across disciplines to monitor and manage patients during the perioperative period.

Collaboration between interprofessional and multidisciplinary teams is essential in the choice of the locoregional anesthesia technique as the chosen technique must take into account various factors, in particular, the opinion of the patient, the surgeon, and the preferences of the anesthesiology clinician who must be able to perform the nerve block without difficulty for patient safety it is advisable to follow specific guidelines and protocols to conduct adequate regional anesthesia procedures. Furthermore, maintaining continuous closed-loop communication between all members of the perioperative care team regarding the need, technique, and potential management issues associated with the regional anesthetic utilized is essential to optimizing patient outcomes. In addition to obtaining thorough informed consent from either the patient or their authorized legal guardian before the placement of any regional anesthesia, all health team members are responsible for voicing their concerns as needed throughout the perioperative period based on their professional discretion.

Introduction

The development of regional anesthesia started with the isolation of local anesthetics, the first being cocaine (the only naturally occurring local anesthetic). The first regional anesthetic technique performed was spinal anesthesia, and the first operation under spinal anesthesia was in 1898 in Germany by August Bier. Before this, the only local anesthetic techniques were topical anesthesia of the eye and infiltration anesthesia.

The central nervous system (CNS) comprises the brain and spinal cord. Neuraxial anesthesia refers to the placement of local anesthetic in or around the CNS. Spinal anesthesia is a neuraxial technique where local anesthetic is placed directly in the intrathecal (subarachnoid) space. The subarachnoid space houses sterile cerebrospinal fluid (CSF), the clear fluid that bathes the brain and spinal cord. An adult human has roughly 130 to 140 mL of CSF, which continually cycles throughout the day. Approximately 500 mL of CSF is produced daily.

Other neuraxial techniques include epidural and caudal anesthesia, each having its particular indications. Spinal anesthesia is only performed in the lumbar spine and is used for surgical procedures involving the lower abdomen, pelvis, and lower extremities.

Anatomy and Physiology

The administration of spinal anesthesia requires appropriate positioning and understanding of neuraxial anatomy. The goal is to deliver appropriately dosed anesthetic into the intrathecal (subarachnoid) space.

The spine comprises 7 cervical, 12 thoracic, 5 lumbar, and 5 fused sacral vertebral bones. The different vertebral bones earn their names based on their relative positions and structural differences. The vertebrae are stacked end-to-end with articulating joints and ligaments with a hollow space called the spinal canal. This canal houses the spinal cord. The spinal nerves exit the spinal canal via lateral spaces between pedicles from adjacent vertebrae.

As mentioned earlier, spinal anesthesia is only performed in the lumbar area, specifically the mid to low lumbar levels, to avoid damage to the spinal cord and also to prevent intrathecally injected medications from having any activity in the upper thoracic and cervical regions. The caudal end of the spinal cord is the conus medullaris and usually is at the lower border of the first or sometimes the second lumbar vertebral body. It is a little inferior in pediatric patients, generally ending around L3. In the adult population, the mean conus position is the lower third of L1 (range: the middle third of T12 down to the upper third of L3). The variation in conus positions follows a normal distribution. No significant difference in conus position is seen between male and female patients or with increasing age. The dural sac usually extends to S2/3. For these reasons, the insertion of the spinal needle for spinal anesthesia is usually at the L3/4 or L4/5 interspace. Spinal cord trauma is more likely when choosing higher interspaces, especially in obese patients.On entry and starting at the skin, the needle traverses several structures. The structures traversed depend on the approach.

Understanding dermatomal anatomy is imperative for understanding the blockade level of target structures. For example, the incision is usually made below the T10 dermatome for lower abdominal cesarean sections. However, coverage of up to T4 dermatome is required to prevent discomfort or pain from peritoneal tugging, especially with uterine manipulation. Patients complain of "pulling on their inside." Some corresponding dermatomal landmarks are:

• C8: 5th finger
• T4. Nipple
• T7: Xiphoid process
• T10: Umbilicus

Indications

Neuraxial anesthesia is used as a sole anesthetic or in combination with general anesthesia for most procedures below the neck. As mentioned in the introduction, spinal anesthesia is in common use for surgical procedures involving the lower abdomen, pelvis, perineal, and lower extremities; it is beneficial for procedures below the umbilicus.

Patient counseling regarding the procedure must be provided and signed informed consent is necessary. Since the procedure is usually performed on awake or slightly sedated patients, the indication for spinal anesthesia and what to expect during placement of neuraxial, risks, benefits, and alternative procedures are some of the discussions that can help allay anxiety. It is crucial to let patients understand that their ability to move their lower extremities is reduced until the resolution of the block.

Spinal anesthesia is best for short procedures. For more extended procedures or procedures that would compromise respiration, general anesthesia is usually preferable.

Contraindications

There are major known contraindications to neuraxial anesthesia (spinal and epidural). The absolute contraindications are lack of consent from the patient and elevated intracranial pressure (ICP), primarily due to intracranial mass and infection at the site of the procedure (risk of meningitis).

Relative contraindications are

• Preexisting neurological diseases (particularly those that wax and wane, eg, multiple sclerosis)
• Severe dehydration (hypovolemia) due to the risk of hypotension - risk factors for hypotension include hypovolemia, age greater than 40 to 50 years, emergency surgery, obesity, chronic alcohol consumption, and chronic hypertension
• Thrombocytopenia or coagulopathy (especially with epidural anesthesia due to the risk of epidural hematoma)

Other relative contraindications are severe mitral and aortic stenosis and left ventricular outflow obstruction, as seen with hypertrophic obstructive cardiomyopathy. In the setting of coagulopathy, the placement of the neuraxial block requires re-evaluation. The American Society of Regional Anesthesia (ASRA) publishes updated guidelines that detail timing for neuraxial anesthesia for patients on oral anticoagulants, antiplatelets, thrombolytic therapy, unfractionated, and low molecular weight heparin. Review the latest guidelines before proceeding with the procedure. Overall because these are elective procedures, it is imperative to undergo a risk/benefit analysis before proceeding.

Equipment

Since the performance of neuraxial procedures is under an aseptic technique, the clinician is expected to maintain a sterile environment. Cap, masks, hand wash, and sterile gloves are required. For a successful procedure, adequate preparation is requisite. There should be adequate equipment count and space to accommodate patients and personnel. Monitors should be set up and ready to assess the patient's circulation (blood pressure, continuous EKG), oxygenation (continuous pulse oximetry), and temperature. The clinician performing the process must be proficient in using and interpreting monitors. If planning sedation, means to assist patient ventilation, oxygenation, and circulatory support should be in place. Intravenous access should be established before starting. A certified anesthesiologist should be present if the patient requires general anesthesia.

There are commercially available spinal anesthesia kits. Contents of kits usually include chlorhexidine with alcohol, drape, and local infiltrating anesthetic (usually 1% lidocaine). Other contents include the spinal needle (Quincke, Whitacre, Sprotte, or Greene), 3 mL and 5 mL syringes, and preservative-free spinal anesthetic solution. Solutions may range from lidocaine, ropivacaine, bupivacaine, procaine, or tetracaine.

Personnel

Spinal anesthesia should only be performed by highly trained and certified medical personnel; this is typically by a board-certified anesthesiologist or anesthesiologist in training under the supervision of an anesthesiologist. Other fellowship-trained spinal anesthesia staff are pain management physicians with training in physical medicine and rehabilitation (PM&R), neurology, and emergency medicine.

Like in any other procedure, an assistant is always helpful. Since the patient's back faces the physician performing the procedure, another staff member is typically present to assist with equipment. The supporting staff also helps support the patient from the ventral side to help them maintain their posture and keep them safe in their position, especially if the patient has undergone sedation.

Preparation

Before the induction of neuraxial anesthesia, a thorough history and physical examination should take place. Pertinent in history is an understanding of previous exposure to anesthetic medication, a review of allergies, and a family history of any anesthetic problems.

The physical exam generally focuses on the site of spinal anesthesia placement. The back should receive a full examination. A check for systemic or local skin infections, spine abnormalities (eg, scoliosis, spinal stenosis, previous back surgery, spina bifida, history of tethered cord), and the pre-procedural neurological exam for strength and sensation are also crucial for assessment and documentation. A procedural time-out should be performed, confirming the patient's identity, planned procedure, allergy, check for consent, and verbal statement of coagulation status.

Drugs used:

• Lidocaine (5%): onset of action occurs in 3 to 5 minutes with a duration of anesthesia that lasts for 60 to 90 minutes
• Bupivacaine (0.75%): one of the most widely used local anesthetics; onset of action is within 5 to 8 minutes, with a duration of anesthesia that lasts from 90 to 150 minutes
• Lidocaine 5%
• Tetracaine 0.5%
• Mepivacaine 2%
• Ropivacaine 0.75%
• Levobupivacaine 0.5%
• Chloroprocaine 3%

Technique or Treatment

Once the patient has undergone appropriate selection, the optimal patient position for the procedure must be established. The procedure is usually carried out with the patient sitting or lateral decubitus. The patient's comfort is tantamount. Positioning aims to help establish a straight path for needle insertion between the spinal vertebrae. The most commonly used position is the sitting position. This is because the spinal anatomy is usually not laterally symmetrical in the lateral decubitus position as in the sitting position. With the patient positioned in the sitting position and leg hanging from the side of the bed, he/she should be encouraged to maintain a flexed spine position to help open up the interspace. The sitting position is appropriate for spinal anesthesia with a hyperbaric solution. Either left or right lateral decubitus positions are viable options as well.

The access site is identified by palpation after the patient is properly positioned. This is usually very difficult to achieve with obese patients because of the amount of subcutaneous fat between the skin and the spinous process. The space between 2 palpable spinous processes is usually the site of entry. The patient should wear a hat or cover for his/her hair to maintain asepsis.

A strict aseptic technique is always necessary, achievable with chlorhexidine antiseptics with alcohol content, adequate hand-washing, mask, and cap. Cleaning always starts from the chosen site of approach in circles and then away from the site. Allow time for the cleaning solution to dry. In the spinal kit, the drape placement is on the patient's back to isolate the access area. Local anesthetic (usually about 1 mL of 1% lidocaine) is used for skin infiltration, and a wheal is created at the site of access chosen, either midline or paramedian.

In the midline approach, the spinal approach to the intrathecal space is midline with a straight line shot. After infiltration with lidocaine, the spinal needle is introduced into the skin, angled slightly cephalad. The needle traverses the skin, followed by subcutaneous fat. As the needle courses deeper, it engages the supraspinous and interspinous ligaments; the practitioner notes this as increased tissue resistance. The practitioner approaches the ligamentum flavum, and this would present like a "pop." On popping through this ligament is the approach to the epidural space, which is the point of placement for epidurally administered medications and catheters. This also presents the point where the loss of resistance is felt to the injection of saline or air. For spinal anesthesia, the clinician proceeds with needle insertion until penetration of the dura-subarachnoid membranes, which is signaled by free-flowing CSF. It is at this point that the administration of spinal medication takes place.

For the paramedian approach, the skin wheal from the local anesthetic is placed about 2 cm from the midline, and the spinal needle advances at an angle toward the midline. In this approach, the supraspinous and interspinous ligaments are usually not encountered. Hence, there is little resistance encountered until reaching the ligamentum flavum.

Complications

Appropriate patient selection and care should be established to help obviate common complications associated with neuraxial anesthesia. While many of the complications are of very low incidence, it’s worth being aware of them. Severe complications are believed to be extremely rare, but the frequency is probably underestimated. Some common complications include the following

• Backache (more common with epidural anesthesia)
• Postdural puncture headache (as high as 25% in some studies): non-cutting needle should be utilized for patients with a high risk for postdural puncture headaches, and the smallest gauge needle available is recommended for all patients[9]
• Nausea, vomiting
• Hypotension
• Low-frequency hearing loss
• Total spinal anesthesia (most feared complication)
• Neurological injury
• Spinal hematoma
• Arachnoiditis
• Transient neurological syndrome (especially with lidocaine)

Clinical Significance

Neuraxial anesthesia offers many benefits that are not available with general anesthesia. Neuraxial anesthesia has made it possible to perform many major procedures on an awake patient. For example, cesarian sections can be better and safely performed via neuraxial anesthesia than with general anesthesia, which allows the establishment of bonding between a mother and her neonate to take place immediately.

Neuraxial anesthesia has demonstrated itself as a useful adjunct to general anesthesia. The use of thoracic epidurals as a postoperative pain modality in post-thoracotomy patients has helped to improve patient's respiratory status. Other beneficial effects are better pain control than intravenous narcotics, less need for systemic opioids, earlier recovery of bowel functions, and easier participation in physical therapy.

Enhancing Healthcare Team Outcomes

Neuraxial anesthesia is a beneficial anesthesia modality that has helped with a wide range of surgical procedures. It does come with risks that healthcare providers need to be aware of. Patient selection is critical and should be driven by a careful history and physical examination. The indication for neuraxial anesthesia needs to match the patient's surgical needs. After surgery, the post-op team needs to be aware of the procedure, and the patient needs to be monitored by well-trained personnel. The patient's hemodynamics require monitoring in the immediate post-op period until the resolution of the anesthetic. Healthcare members from other fields managing the patient must be aware of the nature of the patient's anesthesia.

Upon discharge home, the patient should be able to be contacted by personnel who performed the procedure, and the patient should receive a list of possible complications. The patient should be asked about headaches, backaches, return of bowel and bladder function, and checked for any neurological deficits post-procedure. The patient should be reassured and evaluated regarding any complications that may have resulted. A visit to the anesthesia clinic and appropriate specialist is recommended in the event of any complications.

Anesthesiologists are doctors who carefully monitor patients throughout surgery and during recovery. They use highly advanced electronic devices that constantly display patients’ blood pressure, blood oxygen levels, heart function, and breathing patterns. These devices have dramatically improved the safety of general anesthesia. They also make it possible to operate on many patients who used to be considered too sick to have surgery.

Anesthesiologists also provide pain relief for less invasive procedures, such as those used to examine blood vessels and internal organs (endoscopy) and during labor and delivery.

As experts in pain management, anesthesiologists may advise patients and their doctors on how to manage pain.

Like all medical doctors, anesthesiologists earn a college degree, often in a life sciences field, then a medical degree (M.D. or D.O.). After that, they complete a 4-year residency program in anesthesiology. Many also train for an additional year or more in a specialty such as pain management, pediatric anesthesiology, or critical care medicine.

When you face surgery, you might have many concerns. One common worry is about going under anesthesia. Will you lose consciousness? How will you feel afterward? Is it safe?

Every day about 60,000 people nationwide have surgery under general anesthesia. It’s a combination of drugs that’s made surgery more bearable for patients and doctors alike. General anesthesia dampens pain, knocks you unconscious and keeps you from moving during the operation.

“Prior to general anesthesia, the best ideas for killing pain during surgery were biting on a stick or taking a swig of whiskey,” says Dr. Emery Brown, an anesthesiologist at Massachusetts General Hospital in Boston. Things improved more than 150 years ago, when a dentist in Massachusetts publicly demonstrated that the anesthetic drug ether could block pain during surgery. Within just a few months, anesthesia was being used in Australia, Europe and then around the world.

“General anesthesia changed medicine practically overnight,” says Brown. Life-saving procedures like open-heart surgery, brain surgery or organ transplantation would be impossible without general anesthesia.

General anesthesia affects your entire body. Other types of anesthesia affect specific regions. Local anesthesia—such as a shot of novocaine from the dentist—numbs only a small part of your body for a short period of time. Regional anesthesia numbs a larger area—such as everything below the waist—for a few hours. Most people are awake during operations with local or regional anesthesia. But general anesthesia is used for major surgery and when it’s important that you be unconscious during a procedure.

General anesthesia has 3 main stages: going under (induction), staying under (maintenance) and recovery (emergence). NIH-funded scientists are working to improve the safety and effectiveness of all 3.

The drugs that help you go under are either breathed in as a gas or delivered directly into your bloodstream. Most of these drugs act quickly and disappear rapidly from your system, so they need to be given throughout the surgery. A specially trained anesthesiologist or nurse anesthetist gives you the proper doses and continuously monitors your vital signs—such as heart rate, body temperature, blood pressure and breathing.

“When patients are going under, they experience a series of deficits,” says Dr. Howard Nash, a scientist at NIH’s National Institute of Mental Health. “The first is an inability to remember things. A patient may be able to repeat words you say, but can’t recall them after waking up.”

Next, patients lose the ability to respond. “They won’t squeeze your fingers or give their name when asked,” Nash says. “Finally they go into deep sedation.”

Although doctors often say that you’ll be asleep during surgery, research has shown that going under anesthesia is nothing like sleep. “Even in the deepest stages of sleep, with prodding and poking we can wake you up,” says Brown. “But that’s not the case with general anesthesia. General anesthesia looks more like a coma—a reversible coma.” You lose awareness and the ability to feel pain, form memories and move.

Once you’ve become unconscious, the anesthesiologist uses monitors and medications to keep you that way. In rare cases, though, something can go wrong. About once in every 1,000 to 2,000 surgeries, patients may gain some awareness when they should be unconscious. They may hear the doctors talking and remember it afterward. Worse yet, they may feel pain but be unable to move or tell the doctors.

“It’s a real problem, although it’s quite rare,” says Dr. Alex Evers, an anesthesiologist at Washington University in St. Louis. “Anesthesia awareness can lead to post-traumatic stress disorder,” a severe anxiety disorder that can arise after a terrifying ordeal.

Scientists have developed strategies to identify and prevent anesthesia awareness. Small studies suggested that brain monitors might help. But in 2008, Evers and his colleagues reported the results of the largest study to compare different techniques. Brain monitoring did no better than standard monitoring in preventing anesthesia awareness.

Addiction to alcohol or drugs increases the risk for anesthesia awareness, but doctors can’t accurately predict who will be affected. A research team in Canada identified variations in a gene A stretch of DNA, a substance you inherit from your parents, that defines characteristics such as eye color, your risk for disease and your likely response to different medications. that may allow animals to form memories while under anesthesia. Ongoing studies are exploring whether this gene plays a role in anesthesia awareness in people.

Other researchers are searching for genes that may affect how anesthetic drugs are processed, or metabolized, by the body. Genetic differences might affect the proper dosage or the selection of drugs for each patient.

Nash and his colleagues have found that studies of the common fruit fly may offer clues to how genes affect anesthesia. When certain repeating segments—called copy number variations—are snipped from the fly’s genome, it affects the insect’s response to anesthesia. Copy number variations are known to affect human responses to other drugs. Nash suspects that these gene segments may also affect how patients react to anesthesia. “As researchers learn more, I expect genetic screening will become more common in the clinic,” says Nash.

After surgery, when anesthesia wears off, you may feel some pain and discomfort. How quickly you recover will depend on the medications you received and other factors like your age. About 40% of elderly patients and up to one-third of children have lingering confusion and thinking problems for several days after surgery and anesthesia.

Right now, the best cure for these side effects is time. Brown and his colleagues are working to develop drugs to help patients more quickly emerge and recover from general anesthesia.

Anesthesia is generally considered quite safe for most patients. “Anesthetics have gotten much safer over the years in terms of the things we’re most worried about, like the patient dying or having dangerously low blood pressure,” Evers says. By some estimates, the death rate from general anesthesia is about 1 in 250,000 patients. Side effects have become less common and are usually not as serious as they once were.

Don’t delay important surgery because of fear of anesthesia. If you have concerns, talk with your doctor. It might help to meet in advance with the person who will give you anesthesia. Ask what kind of anesthesia you will have. Ask about possible risks and side effects. Knowing more might help you feel less concerned about going under.

When You Go Under

General anesthesia has 5 major effects on your body. Researchers are working to develop drugs that target each of these characteristics:

• Lack of Consciousness. Keeps you from being aware of your surroundings.
• Analgesia. Blocks your ability to feel pain.
• Amnesia. Prevents formation of memories.
• Loss of Movement. Relaxes your muscles and keeps you still during surgery.
• Stable Body Functions. Stabilizes your heart rate, blood pressure, temperature, breathing and kidney function.

Scientists are learning more about how anesthetics work at the most basic level. They are also studying the short- and long-term effects of these drugs on specific groups of people, such as the elderly and cancer survivors. These studies will reveal whether certain anesthetics are better than others for members of those groups.

Research on how a person's genetic makeup affects how he or she responds to anesthetics will allow doctors to further tailor drugs for each patient. In the future, scientists hope to design anesthetics that are safer, more effective, and more personalized.

Knowing how anesthetics affect pain and consciousness could also lead to new treatments for conditions that affect consciousness, such as epilepsy or coma. Studies of anesthesia may even help us better understand the nature of consciousness itself.

Anesthesia helps many of us during our lives, whether we need a local painkiller at the dentist, numbing eye drops for laser vision correction or general anesthesia for major surgery. But even though anesthetics have been used in many procedures for more than 150 years, doctors and scientists still don't know exactly how these medicines work in the body.

Finding a Safe Way to Go Under

Before anesthesia, doctors and dentists operated on patients only in extreme circumstances and largely without the use of painkillers or sedatives.

Then, in 1846, dentist William T. G. Morton demonstrated the use of ether to put patients "to sleep" during surgery. The practice soon spread, but because doctors couldn't control the amount of ether inhaled, patients could wake up during surgery—or never wake again. Ether was also highly flammable.

The next few decades saw the introduction of less flammable anesthetic gases as well as the discovery of intravenous anesthetics with controllable dosage. Still, well into the 1950s, dangerous side effects were common and included heart rhythm abnormalities, breathing problems, lowered blood pressure, nausea and vomiting.

Modern anesthetic techniques allow millions of Americans to safely undergo surgery with fewer and less serious side effects. New inhaled and intravenous general anesthetics act quickly and dissipate rapidly when stopped, while local and regional anesthetics that block specific nerves provide an alternative to general anesthesia.

Researchers funded by the National Institutes of Health have helped identify and explore several components of general anesthesia—including sedation, unconsciousness, immobility, analgesia (lack of pain) and amnesia (lack of memory). And they have developed medicines that can provide one or more elements separately, allowing anesthesiologists to tailor painkiller regimens to individual procedures and patients.

An Anesthesiologist's Job Isn't Easy

Since anesthesia can still cause complications and have body-wide effects, anesthesiologists carefully monitor patients throughout surgery using a variety of devices that display blood pressure, blood oxygen levels, heart function and respiration. They adjust medications throughout the procedure to make sure each patient remains safe.

Anesthesiologists' jobs have expanded beyond the operating room as well, including caring for patients as they recover from surgery and providing anesthesia for nonsurgical procedures such as colonoscopy and childbirth. They also advise other specialists on how to manage pain.

"I think it is fair to say that most people have no idea how complex our jobs are and how attentive we must be," says Daniel Kohane, an anesthesiologist at Harvard Medical School and Children's Hospital Boston.

The Future of Anesthesiology

Advances in cell biology, genetics and molecular biology have spurred scientists to learn more about anesthesia and develop better anesthetics.

For instance, Max B. Kelz at the University of Pennsylvania found that the processes of going under and waking up from anesthesia are different. Knowing more about how the brain transitions between conscious and unconscious states could improve our understanding of sleep disorders and states of impaired consciousness such as comas. Daniel Sessler at the University of Louisville School of Medicine found that red-haired women need 20 percent more anesthetic than dark-haired women, and he may have pinpointed a genetic variant that explains why. And Kohane created a slow-release anesthetic that lasted several days in rats and didn't cause nerve damage or other side effects in the animals. This could be a step on the path to improved treatment for chronic pain.

The researchers' ultimate goal is to design anesthetics that are more targeted within the body and personalized to work safely and effectively in each patient. Plus, research into anesthesia could reveal more about pain, memory, conditions such as epilepsy and coma, and the nature of consciousness itself.

What is anesthesia?

Anesthesia is the use of medicines to prevent pain during surgery and other procedures. These medicines are called anesthetics. They may be given by injection, inhalation, topical lotion, spray, eye drops, or skin patch. They cause you to have a loss of feeling or awareness.

What is anesthesia used for?

Anesthesia may be used in minor procedures, such as filling a tooth. It could be used during childbirth or procedures such as colonoscopies. And it is used during minor and major surgeries.

In some cases, a dentist, nurse, or doctor may give you an anesthetic. In other cases, you may need an anesthesiologist. This is a doctor who specializes in giving anesthesia.

What are the types of anesthesia?

There are several different types of anesthesia:

• Local anesthesia numbs a small part of the body. It might be used on a tooth that needs to be pulled or on a small area around a wound that needs stitches. You are awake and alert during local anesthesia.
• Regional anesthesia is used for larger areas of the body such as an arm, a leg, or everything below the waist. You may be awake during the procedure, or you may be given sedation. Regional anesthesia may be used during childbirth, a Cesarean section(C-section), or minor surgeries.
• General anesthesia affects the whole body. It makes you unconscious and unable to move. It is used during major surgeries, such as heart surgery, brain surgery, back surgery, and organ transplants.

What are the risks of anesthesia?

Anesthesia is generally safe. But there can be risks, especially with general anesthesia, including:

• Heart rhythm or breathing problems
• An allergic reaction to the anesthesia
• Delirium after general anesthesia. Delirium makes people confused. They may be unclear about what is happening to them. Some people over the age of 60 have delirium for several days after surgery. It can also happen to children when they first wake up from anesthesia.
• Awareness when someone is under general anesthesia. This usually means that the person hears sounds. But sometimes they can feel pain. This is rare.

What is a nerve block?

A nerve block uses a medicine called an "anesthetic" (pronounced an-is-THET-ik) to numb the nerves so that you do not feel pain for a little while. Anesthetics are the same kind of medicine dentists use to numb teeth and gums. The nerve block will make a part of your body numb for a little while.

Your doctor might use a nerve block to help ease your pain if you cannot take medicines like NSAIDs or opioids. Nerve blocks may be used before, during, or after an operation.

There are many types of nerve blocks. They are named for the part of the body where the doctor injects the anesthetic. Your doctor (or anesthesiologist or nurse anesthetist) may inject these medicines into more than one place in your body to give you the most pain relief. For a broken hip, injections are often given around the hip and groin area.

What are the benefits of using a nerve block?

Some research shows that nerve blocks used before, during, or after an an operation may ease short-term pain more than the usual treatment of opioid or NSAID pain medication. Nerve blocks may help you avoid "delirium," or confusion and cloudy thinking, which can be caused by pain or by opioid pain medicines.

Are there any side effects from using a nerve block?

Researchers cannot say if nerve blocks cause more or less side effects than other treatments for the pain from a broken hip.

Introduction

Recent advances in various surgical techniques and the development of more minimally invasive procedures have spurred an increase in outpatient procedures. With these developments, it requires that analgesic techniques keep pace with these surgical advancements. Studies have shown that peripheral nerve blocks are usually well-tolerated and provide regional analgesia superior to other modalities such as oral pain medications or general anesthesia.

Anatomy and Physiology

Anatomy and landmarks depend on the type of block being performed. Please refer below to techniques for specifics to the more common peripheral nerve blocks performed.

Indications

There is no strict set of guidelines for the use of peripheral nerve blocks. However, the general rationale is to implement regional blocks in cases where conservative measures have failed or to avoid the side effects and complications of general anesthesia and oral medications. The following include examples of where peripheral nerve blocks may be preferable:

• Patients who are at high risk of respiratory depression related to general anesthesia
• Patients who want to avoid systematic medications
• Patients intolerant or not responsive to oral medications

Contraindications

Absolute contraindications to the use of peripheral nerve blocks include allergy to local anesthetics, inability to cooperate, or patient refusal. It is advised to postpone or reconsider a nerve injection when there is an active infection at the injection site, pre-existing neural deficits along with the distribution of the block, and in patients with coagulopathies or on antithrombotic drugs.

Equipment

Equipment that is used is dependent upon the type of technique utilized. The following is a list of equipment used based on technique.

• Nerve stimulator guidance: peripheral nerve stimulator that delivers an adjustable electrical current to the tip of a hollow insulated disposable needle. The needle has specific tubing attached to a syringe that allows for aspiration and injection of a local anesthetic. A wire runs between the needle and an electrode and allows the electrical pulse to be transmitted to stimulate the nerve.
• Ultrasound guidance: portable ultrasound machines with both high and low-frequency probes that can identify superficial and deeper nerves
• Continuous catheter: numerous kits available, which usually contain a needle and catheter. A standard epidural kit can often be utilized.

Personnel

A well-versed medical professional that is highly familiar and experienced with the type of block being performed should be performing the specific injection.

Preparation

Taking a detailed medical history is necessary to determine conditions like coagulopathy or respiratory compromise that may impact the decision to perform a block. A thorough physical exam is prudent as well to determine preexisting sensory or motor deficits in the distribution of the block. Studies show that patients with preexisting sensory or motor deficits may be more likely to develop new deficits following a block than patients without preexisting deficits. Following the history and physical, the patient should be made familiar with the risks, benefits, and care needed during the recovery phase of the block.

For patients that are receiving a nerve block for a surgical procedure, they should follow the same fasting guidelines for the surgery as it may be necessary for deep sedation to be used in cases of an inadequate block. Also, intravenous access should be obtained due to the risk of potential complications like vasovagal events, local anesthetic toxicity, and the possible use of general anesthetics.

Technique or Treatment

The technique for peripheral nerve blocks is based on the type of block. A quick summary of some of the more common blocks is listed below.

• Interscalene block: anesthetizes nerve roots from the cervical plexus (C3, C4, supraclavicular nerve) and upper and middle trunks of the brachial plexus (C5-C7). For positioning, the patient is placed in a supine position with the head turned away from the side of the block. Sternal notch, the sternal and clavicular heads of the sternocleidomastoid muscle, and clavicle are identified and marked. A probe is placed in a transverse position with its long axis across the neck just above the clavicle if using ultrasound. The carotid artery and internal jugular vein are visualized. The subclavian artery is identified by directing the beam towards the first rib. Nerves are then traced to cephalad. At the C6 nerves of the brachial plexus are visualized in a vertical orientation within the interscalene groove. A needle is then placed in-plane or out-of-plane and directed toward the nerves. A needle tip is placed next to the nerve roots. A total of 12 cc to 30 cc of local anesthetic is injected.
• Supraclavicular block: the patient is placed in the supine position with arms by the sides and the head turned away from the side of the block. The probe is placed in a transverse position just above the clavicle using ultrasound. The carotid artery and internal jugular vein are visualized. The needle is inserted in-plane (parallel to the probe), and a local anesthetic is injected to hydro dissect between the nerves until the tip reaches an area bordered by the first rib, subclavian artery, and brachial plexus. 20 cc to 30 cc of local anesthetic is injected. Before injection, however, aspiration should be performed to ensure there is no blood.
• Infraclavicular block: the patient is placed in the supine position with the head turned away from the side of the block. The arm is abducted with the elbow flexed to identify the coracoid process. The axillary artery is identified, and the cords of the brachial plexus are visualized adjacent to the artery using ultrasound. The needle is placed adjacent to the axillary artery in the cranio-posterior quadrant, and 30 to 40 cc of local anesthetic is administered. Before injection, however, aspiration should be performed to ensure there is no blood
• Axillary block: block anesthetizes nerves of the brachial plexus at the level of the individual nerves and often requires multiple injections. The patient is positioned supine with the arm abducted 90 degrees, and the elbow is flexed. The transducer is placed transversely in the axilla using ultrasound. The needle is introduced perpendicular to the skin and advanced until the tip is next to each nerve.
• Intercostobrachial block: the patient is positioned supine with the arm abducted to expose the axillary fossa. The intercostobrachial nerve runs in the subcutaneous tissue of the medial upper arm. The needle is advanced subcutaneously across the medial aspect of the arm while injecting 5 cc to 10 cc of local anesthetic.
• Radial nerve block: radial nerve emerges between the brachioradialis tendon and the radius, just proximal to the styloid process. The needle is inserted subcutaneously, just proximal to the styloid process of the radius, aiming medially, and 3 cc to 5cc of local anesthetic is injected.
• The median nerve block is located between the tendons of the flexor palmaris longus and the flexor carpi radialis. The need is inserted between the two tendons until it penetrates the fascia and advanced until contact is made with bone. The needle should be redirected and local anesthetic injected in lateral and medial directions.
• Ulnar nerve block: ulnar nerve runs between the ulnar artery and flexor carpi ulnaris tendon. The tendon is just superficial to the ulnar nerve. A needle is placed under the tendon close to its attachment just above the styloid process of the ulna and advanced 5 mm to 10 mm, and 3 cc to 5 cc of local anesthetic is injected at this location.
• Lumbar plexus block: The patient is placed in the lateral decubitus position operative side up with the leg flexed at the hip and knee. It is placed longitudinally adjacent to the spine at the second to third lumbar level using the ultrasound probe. The needle is inserted at the cephalad edge using the in-plane technique. The length of the needle should be seen as it approaches the target structure, which is the posterior third of the psoas major muscle.
• Femoral nerve block: The patient is placed in a supine position. Using ultrasound, the nerve is visualized, which is lateral to the artery. An in-plane or out-of-plane approach can be used where the needle is inserted, and the tip is placed adjacent to the nerve, and 20 cc to 50 cc of local anesthetic is injected in 5 cc increments. Before injection, however, aspiration should be performed to ensure there is no blood.
• Fascia iliaca block: the patient is placed in a supine position where using ultrasound, the probe is placed transversely to the leg at the junction of the middle and lateral thirds (between the ASIS and pubic tubercle) to identify the fascia lata, iliacus muscle, and fascia iliaca. The needle is introduced in-plane inferior to the inguinal ligament and guided beneath the fascia iliaca, and 30 cc of local anesthetic is injected in 5 cc increments. Before injection, however, aspiration should be performed to ensure there is no blood.
• Obturator nerve block: the patient is placed in the supine position with the leg externally rotated. Using an ultrasound probe, it is placed in the inguinal crease, and the femoral vein is identified. The probe is then moved medially to visualize the pectineus and adductor longus muscles. The needle is inserted in-plane or out of plane and is directed to the fascial plane between the adductor brevis and magnus, and 5 cc to 10 cc of local anesthetic is injected. Before injection, however, aspiration should be performed to ensure there is no blood.
• Sciatic nerve block: can be approached anteriorly or posteriorly. The patient is placed in the lateral decubitus position with the hip flexed at 45 degrees and the knee at 90 degrees for the posterior approach. In the anterior approach, the patient is positioned in the same manner. Using an ultrasound probe, it is held transverse to the course of the nerve. The nerve is found lateral to the ischial tuberosity and deep to the gluteus maximus muscle. The needle is inserted in-plane from the lateral aspect of the transducer and positioned with the tip of the needle adjacent to the nerve. Approximately 20 cc of local anesthetic is injected in 5 cc increments with gentle aspirations between injections. Before injection, however, aspiration should be performed to ensure there is no blood.
• Popliteal nerve block: the patient can be placed in either prone, lateral decubitus or supine. There are two approaches. For the posterior approach, the biceps femoris and semitendinosus/semimembranosus tendons are palpated. The ultrasound probe is placed transverse to the thigh and in the popliteal crease. The popliteal artery is used as the landmark, and the tibial nerve is found superficial and lateral to the popliteal artery. The nerve is then followed cephalad to the point where the common fibular nerve joins the tibial nerve from the lateral side to form the sciatic nerve. The sciatic nerve is blocked proximal to this to ensure that both the common fibular and tibial nerves are anesthetized.
• Saphenous nerve block: the patient is positioned supine with the leg straight. Using the ultrasound probe, it is placed perpendicularly to the thigh at the midpoint between the anterior superior iliac spine and the distal end of the femur. The nerve is identified as it exits from the adductor canal adjacent to the femoral artery. As it is followed distally, it becomes more superficial, traveling with an arterial branch just deep to the sartorius muscle. Using an in-plane approach 10 cc of local anesthetic is injected deep into the sartorius muscle at the lateral border of the artery.
• PENG block: The pericapsular nerve group (PENG) block is an interfascial plane block aiming to block articular branches supplied by femoral, obturator, and accessory obturator nerves. PENG block is indicated for anterior hip arthroplasties, lateral hip arthroplasties, and for hip fractures. It is performed in supine position by depositing 15-20 ml of local anesthetic in the plane between the psoas tendon and the pubic ramus under direct ultrasound visualization. Femoral nerve block, fascia iliaca compartment block, or lumbar plexus block have been used to manage post-operative analgesia in hip surgeries. These blocks result in weakness of quadriceps muscles and thus predispose to fall. These blocks also result in incomplete analgesia to the hip as here is sparing of few articular branches to the hip. The main advantage of PENG block is that it provides better analgesia of the hip without causing any muscle weakness. As there is no muscle weakness so the patient can participate in physical therapy early.
• iPACK block: IPACK block is an acronym for infiltration of local anesthetic into the interspace between the popliteal artery and the posterior capsule of the knee. This technique was first introduced by Dr. Sanjay K Sinha at the American Society of Regional Anesthesia (ASRA) meeting in 2012. iPACK block is used for postoperative analgesia for total knee arthroplasty and cruciate ligament repair. Posterior knee pain is mediated by articular branches arising mainly from the tibial nerve with contributions from the obturator nerve. In iPACK block, 15-20 ml of local anesthetic is deposited under ultrasound guidance in tissue plane femoral artery and posterior aspect of the capsule of the knee joint. The main advantage of iPACK block is that it is a muscle strength sparing block and doesn't result in foot drop or loss of sensorimotor function of leg and foot.

Complications

Potential complications and side effects are dependent upon the type of block performed. However, complications include peripheral nerve injury (although not common, the rate may be as high as 8% to 10%), hematoma, local anesthetic systemic toxicity, allergic reaction, infection, and a secondary injury, which includes reduced sensation after nerve block.

Enhancing Healthcare Team Outcomes

Peripheral nerve blocks are often performed by anesthesiologists, surgeons, and emergency department physicians. However, a dedicated nurse must monitor the patient's vital signs during the procedure. More important, resuscitation equipment must be in the room before starting the procedure. A protocol should be established to conduct a peripheral nerve block to ensure patient safety and improve patient outcomes.

Introduction

The purpose of peripheral nerve blocks is to inhibit impulse transmission distally in a nerve terminal, thus terminating the pain signal perceived by the cortex. Nerve blocks can be used to treat acute pain (e.g., procedural anesthesia and perioperative analgesia), as well as for diagnosis and treatment of chronic pain. Impulse blockade can be brief (hours) or prolonged (months), depending on the medication used in the block and the technique (e.g., single-shot block versus catheter). Nerve blocks are also useful in the emergency department for the following indications: Acute pain management of the extremities.

• Anesthesia of the extremity for procedures
• Alternative to procedural sedation
• Alternative to opioids in certain patient populations (e.g., a head injury patient, patients with concomitant mental status change, patients on buprenorphine)

Many nerves can be blocked depending on the injury. These include the following upper or lower extremities:

• Brachial plexus roots at the interscalene location block the shoulder, upper arm, elbow, and forearm.
• Brachial plexus trunks at the supraclavicular location block the upper arm, elbow, wrist, and hand.
• Brachial plexus cords at the infraclavicular location block the upper arm, elbow, wrist, and hand.
• Brachial plexus branches at the axillary location block the forearm, wrist, hand, and elbow, including the musculocutaneous nerve.
• The median nerve at the elbow blocks the hand and forearm.
• The radial nerve at the elbow blocks the hand and forearm.
• The ulnar nerve at the elbow blocks the hand and forearm.
• The femoral nerve at the femoral crease blocks the anterior thigh, femur, knee, and skin anesthesia over the medial aspect of the leg below the knee.
• The sciatic nerve at the subgluteal location or anterior approach below the femoral crease blocks the posterior aspect of the thigh and the anterior, lateral, and posterior lower leg, ankle, and foot.
• The sciatic nerve at the popliteal location blocks the anterior, lateral, and posterior lower leg, ankle, and foot.
• Ankle block of five separate nerves to the ankle and foot (saphenous nerve, deep peroneal nerve, superficial peroneal nerve, posterior tibial nerve, and sural nerve) blocks the entire foot.

Etiology

Peripheral nerve blocks have gained widespread acceptance as technological advancements have improved accuracy, efficacy, and safety. Nonetheless, in-depth knowledge of peripheral nerve anatomy remains an essential component of a successful and safe peripheral nerve blockade. Peripheral nerve blocks were originally performed by eliciting paresthesias to localize peripheral nerves, followed years later by nerve stimulation techniques. More recently, ultrasound guidance has improved anesthesiologists’ and emergency physicians' abilities to visualize nerve structures and other surrounding structures (e.g., vasculature and pleura).

Epidemiology

Peripheral nerve blocks offer many advantages to traditional anesthetic and analgesic techniques. Patients who would otherwise have excessive risks with general anesthesia can safely undergo surgery painlessly with regional anesthesia. Additionally, perioperative opioid analgesia's adverse effects can be minimized or avoided entirely while still providing superior pain control. If a prolonged blockade is a goal, peripheral nerve catheters can remain for several days to provide more extended analgesia than a single-shot block alone.

Pathophysiology

Although peripheral nerve blocks are overall safe when performed correctly, there are rare but serious risks associated with them. Risks include block failure, bleeding, infection, damage to surrounding structures, permanent nerve injury, and intravascular uptake of local anesthetic resulting in systemic toxicity. Contraindications include an inability to cooperate with placement (sometimes seen in pediatric patients, combative patients, or those with severe dementia), pre-existent neurologic deficit, systemic or active local infection at the site of the block, body habitus, or obesity obscuring optimal ultrasonographic visualization. Relative contraindications include the presence of coagulopathy.

Toxicokinetics

Local anesthetics have a significant risk of systemic toxicity when administered intravascularly. Symptoms usually manifest in the central nervous system first (metallic taste, auditory changes, circumoral numbness, blurred vision, agitation, seizures), followed by cardiovascular effects (hypotension, decreased cardiac contractility, dysrhythmias, complete heart block, cardiovascular collapse). Bupivacaine is particularly cardiotoxic, and reports of cardiovascular collapse in the absence of antecedent neurologic symptoms exist. Neurolytic blocks with alcohol and phenol have utility in chronic pain but are usually the last resort in cancer pain. They cause semi-permanent destruction of the nerve, which blocks impulse transmission and improves pain. Risks with neurolytic destruction of a nerve include the development of central or deafferentation pain syndromes, which are very difficult to treat.

Contraindications include an allergy to aminoesters (procaine, cocaine, tetracaine).

Amides-lidocaine/bupivacaine/mepivacaine/ropivacaine (usually preservative).

History and Physical

Before performing a peripheral nerve block, a complete history and physical exam are essential. The emphasis in the patient's history should be on the existence of underlying severe cardiac or pulmonary disease, opioid intolerance, pre-existing neurologic deficit, easy bleeding or bruising, and anticoagulation medications. The physical exam should direct its focus to the sensory and motor function of the extremity undergoing blockade, evidence of coagulopathy (e.g., widespread bruising), evidence of systemic infection (fever or elevated white blood cell count), and infection at the site of the block (redness, swelling, warmth).

Evaluation

A thorough risk/benefit analysis and informed consent are necessary when evaluating a patient for peripheral nerve blockade. If block administration is in the emergency department, discussion with the anesthesiology can help direct preference toward a catheter if a longer block duration is preferable. Each patient’s maximum local anesthetic dose must be calculated before performing the block and never exceeded.

Treatment / Management

Emergency airway equipment, resuscitation drugs (including lipid emulsion 20%), supplemental oxygen, and hemodynamic monitoring must be immediately available where blocks are performed. Blocks should be administered with a strict sterile technique. Anxiolytic medications may be used to facilitate patient comfort. Awake patients reduce the risk of nerve injury by reporting paresthesias so the needle can be redirected before injection of local anesthetic. Additionally, an awake patient can report early symptoms of local anesthetic systemic toxicity (i.e., tinnitus, circumoral numbness, and tachycardia with epinephrine) to avoid more serious complications that can occur a large volume local anesthetic injection (seizures, coma, and cardiac collapse). Recommended maximum dosages for local anesthetics are widely available, but practitioners should always use the lowest dose necessary to achieve the desired result due to the significant risk of systemic toxicity.

Point of care, bedside ultrasound, can be used to locate and visualize the nerve.

Differential Diagnosis

• Anaphylaxis

• Anxiety disorders

• Cocaine toxicity
• Conversion disorders

Complications

Potentially serious complications resulting from peripheral nerve blocks include nerve injury, infections at the catheter site, bleeding, and local anesthetic systemic toxicity (LAST). Other effects can include elevations of blood sugar, itching, rash, and injection site soreness.

Deterrence and Patient Education

Patients should receive explanations about the potential adverse effects of the procedure. They should also be told what to expect from the procedure, including discomfort at the site of catheterization, numbness of the body part affected, and the nerve block duration. The clinician can also answer any other patient questions.

Enhancing Healthcare Team Outcomes

Peripheral nerve blocks can be performed by any physician as long as they are familiar with the anatomy. However, if a complication occurs, early recognition and treatment are essential to reduce long-term morbidity to the patient. Intravenous lipid emulsion 20% must immediately be available in locations that perform peripheral nerve blocks. Patients with a suspected local anesthetic overdose should be treated immediately with intravenous lipid emulsion 20% (Intralipid) 1.5 mL/kg (lean body mass) given over one minute, followed by a 0.25 mL/kg/min infusion. Refractory cases of local anesthetic systemic toxicity may require cardiopulmonary bypass/extracorporeal membrane oxygenation until the metabolism of the drug is complete.