Chapter 44

Regional Anesthesia

Spinal and Epidural Anesthesia

R. Lee Olson, Joseph E. Pellegrini and Beth Ann Movinsky

Spinal and epidural blocks are known collectively as central neuraxial blockade (CNB) because they involve the placement of local anesthetic solution onto or adjacent to the spinal cord. Both spinal and epidural blocks share much of the same anatomy and physiology but are distinct from one another due to their unique anatomic, physiologic, and clinical features.

The person most credited with introducing spinal anesthesia is Augustus Bier, who in 1898 described the injection of cocaine into the spinal column and its potential for use as a surgical anesthetic technique. When cocaine was introduced into the subarachnoid space, anesthesia lasted approximately an hour. With the development of newer and safer anesthetic drugs, needles, and techniques, regional anesthesia expanded to include many neural blocks for the enhancement of surgery and obstetrics and the management of pain.1,2 Modern procedures have simplified, refined, and increased the safety and success of regional anesthesia techniques.²

Applied Anatomy and Physiology of the Central Neuraxis

Knowledge of anatomic landmarks and underlying structures aids the anesthetist in forming a three-dimensional “mind’s-eye” picture. This picture, coordinated with the “feel” of the structures and tissues against the needle and a steady, sensitive hand, facilitates accurate placement of the needle tip and administration of appropriate techniques and medications. Although anatomy is the oldest of medical sciences (with detailed descriptions of the spinal column dating from the nineteenth century), modern imaging methods such as computed tomography (CT), magnetic resonance imagining (MRI), and endoscopic examination have permitted in vivo investigations that further our understanding of spinal anatomy. The following is therefore a current review of applied anatomy of the central neuraxis.

The sequential interconnectivity of the 33 bones called vertebrae form the spinal, or vertebral, column, which anesthetists use as a bony reference during the placement of various anesthetics or analgesics. This column is located in the posterior midline of the trunk and allows for truncal flexibility because movable joint surfaces and cartilaginous vertebral bodies exist between 24 of the 33 vertebrae (Figure 44-1). The vertebral column extends from the base of the skull and the foramen magnum to the tip of the coccyx. The vertebral bodies are stacked on top of one another, separated by fibrocartilaginous intervertebral disks that provide support for the cranium and trunk. In general, each vertebra can be visualized as having two parts. The anterior, cylindric portion of the vertebra is solid and called the body. This heavier portion of the vertebra forms the anterior portion of the vertebral arch. The body of each vertebra is contiguous with two pedicles that stretch in a posterior and slightly lateral direction, joining to two laminae that stretch posteriorly and medially to complete an arch, creating an oval-triangular foramen. This foramen, known as the vertebral foramen, allows for the passage and protection of the spinal cord. Transverse processes on both sides of the pedicles allow for muscular attachments and the control of movement. A spinous process projects along the median plane from the union of the laminae in a posteroinferior direction. The spinous process is the long, slender, bony prominence that can often be seen and felt along the midline of the back. The spinous process also provides a place for muscular attachment and movement control. In addition, the inferior angle of the bone creates an overlap that further protects the spinal cord (Figure 44-2).³

FIGURE 44-1 The spinal, or vertebral, column with its 33 vertebrae.

FIGURE 44-2 Articular surfaces, transverse processes, and spinous process. Inf, Inferior; Sup, superior.

The pedicles and processes of each vertebra have superior and inferior articular surfaces and lateral notches. The superior notch is shallow when compared with the deeper inferior notch. When the vertebrae are stacked, the notches and the articulating surfaces, known as zygapophyseal or facet joints, form the intervertebral foramina. The intervertebral foramina provide safe passage for spinal nerves passing from the spinal cord to the rest of the body. The articular surfaces of the facet joints are covered with hyaline cartilage, which permits a gliding motion between the vertebrae. Because the facet joints are innervated by branches from closely associated spinal nerves, these joints often become clinically important. When the joint is injured, the associated spinal nerves also may be affected, leading to pain along associated dermatomes or muscle spasm along associated myotomes.³

The size and shape of vertebral lamina and spinous processes differ among the thoracic, lumbar, and sacral regions, and variation exists within each region. Knowledge of these variations is important in the practice of regional anesthesia and in selection and administration of spinal and epidural anesthesia. For instance, cervical and thoracic vertebrae have spinous processes that angle acutely in a caudad direction such that the process of the superior vertebra overlaps the inferior vertebra and its process. This construction adds protection to the spinal cord when an individual stands erect. When attempts are made to insert a needle into the cervical or thoracic regions, the tight construction and angles of the vertebral column must be considered.

In the lumbar region the vertebrae are larger, and the spinous processes become shorter and broader and have a posterior orientation with less overlap than in other vertebrae. Relatively large gaps, bridged by ligaments, exist between the spinous processes in the lumbar area. This provides the anesthesia practitioner easier access for needle placement, catheter passage, and the instillation of anesthetic into the epidural or subarachnoid space for surgical or obstetric procedures.

The sacrum is a triangle-shaped section of fused bodies of vertebrae. The broader portion is the base, which tapers as it approaches the coccyx. The sacrum is shaped so the weight of the body forces the base of the sacrum downward and forward. It is wedged tightly between the two iliac crests by the downward forces exerted on the spinal column. The lamina of the last sacral vertebra is incomplete and bridged only by ligaments. This area is known as the sacral hiatus (Figure 44-3). The coccyx is composed of four small segments of bone that become fused into two bones as an individual ages; between the ages of 25 and 30 years, fusion is complete. The bodies of the vertebrae can be identified with the transverse processes and articular processes. No pedicles or spinous processes are present. The last, or fourth, bone is small and is similar to a nodule. The changing size of the bone from the first to the fourth vertebra gives the coccyx the appearance of a triangle. The projections of the rudimentary articular processes are known as the cornua, and the superior pair is the most pronounced. These sacral cornua are the “horns” or bony protuberances that guard the area of the sacral hiatus.³ Because they can be easily palpated in children and in most adults, they are important surface anatomic landmarks for the performance of a caudal anesthetic procedure.

FIGURE 44-3 Sacrum and coccyx.

Of the more than 35 pairs of muscles and ligaments in the back, the supraspinous ligaments, the interspinous ligaments, and the ligamentum flavum (yellow ligaments) are of special significance to the anesthesia practitioner. These three structures act as landmarks that help in identification of and access to the epidural and subarachnoid spaces. The supraspinous ligament is a strong cordlike ligament that connects the apices of the spinous processes; it is thick and serves as the major ligament in the cervical and upper thoracic regions. The supraspinous ligament consists of three layers: the superficial layer extends over several vertebral spinous processes, the middle layer connects two or three spinous processes, and the inner layer connects only the neighboring spinous processes. The ligament blends at all levels with the thin interspinous ligaments that run between adjacent spinous processes. The interspinous ligaments are usually absent or of poor quality in the cervical region and can be exceptionally thin in the lumbar area, even in young people. The ligamenta flava are the strongest of the posterior ligaments. These broad elastic bands join the vertebral arches through vertical extensions from adjacent lamina. The ligamenta flava are paired flat ligaments that run caudad from the inferior border of one lamina to the upper border of the lower lamina on both sides of the midline. The two ligaments almost fill the space, leaving only a separation in the midline and thereby creating a V or wedge that points posteriorly to align with the interspinous and supraspinous ligaments. The V is thin on the lateral edge and thickest midline—in an adult approximately 3 to 5 mm at the L2-L3 interspace. The ligaments extend from each lamina with an overlapping of fibers that creates the appearance of a contiguous ligament from one vertebral body to the next. The ligament is thicker in the lumbar area than in the cervical area and is responsible for maintenance of upright posture. The ligaments’ color comes from their high content of yellow elastic tissue.⁴

The spinal cord itself is a cylindrical structure extending from the medulla oblongata through the spinal foramen to the level of the L2 vertebra in most adults and ranges from 42 to 45 cm in length (Figure 44-4). Because the vertebral column grows more rapidly than the spinal cord, the spinal cord in children extends initially to the level of the third lumbar vertebra. In approximately 1% of adults, the spinal cord may extend below L2 and rarely to the level of L3. The spinal cord tapers to the conus medullaris, and nerve pathways continue in a collection of rootlets called the cauda equina or horse’s tail, which extends from L1 to S5. The spinal cord is enlarged in two regions. The first, called the cervical enlargement, extends from the spinal segments C4 to T1. The ventral rami of the spinal nerves in this enlargement form the brachial plexus of nerves that innervates the upper limbs. The second enlargement stretches from segments L2 to S3. This lumbosacral enlargement contributes corresponding nerves to create the lumbar and sacral plexuses. It is important to note that the spinal cord levels do not directly correspond with vertebral levels. For example, in adults the lumbosacral enlargement (L2 to S3) usually extends from the body of the T11 vertebra to the body of the L1 vertebra.³

FIGURE 44-4 Extension of the spinal cord to the second lumbar vertebra.

The spinal cord is enveloped by the same three membranes that line the cranium, and they are collectively called the meninges. The meninges are nonnervous support tissues that provide a protective covering for the cord and nerve roots from the foramen magnum to the base of the cauda equina. The linings are identified as the dura mater, the arachnoid mater, and the pia mater. The dura mater is the outermost layer. It is a thick, tough membrane that provides most of the protection for the central cord structures. The nerve roots are covered with dura mater while inside the spinal canal. As the roots exit the canal via the intervertebral foramen, the dura blends into the root at a junction referred to as a dural cuff or root sleeve. The arachnoid mater is a thin, spiderweb-like covering that forms the middle layer. Beneath the arachnoid mater is a space that is continuous with the central canal of the cord and the ventricles. This space, which is filled with cerebrospinal fluid (CSF), is known as the subarachnoid space. This mater and the fluid protect the spinal cord from shock injuries and are the medium for the interaction with local anesthetics and opioids that occurs during the administration of regional anesthesia. The innermost layer, the pia mater, is thin and is in direct contact with the outer surface of the spinal cord (Figure 44-5).³

FIGURE 44-5 The linings of the spinal cord and the posterior ligaments of the spinal column.

The epidural space is a potential space outside the dural sac but inside the vertebral canal and is continuous from the base of the cranium to the base of the sacrum at the sacrococcygeal membrane. The epidural space contains epidural veins, fat, lymphatics, segmental arteries, and nerve roots. Fat in the epidural spaces is physiologically fluid, acting as a pad and lubricant for the movement of neural structures within the canal. The posterior epidural space, as it is approached by the anesthetist’s advancing needle, is protected by the ligamenta flava, the lamina, and the spinous processes. It is easy but inaccurate to depict the epidural space as a uniform column surrounding an equally uniform and tapering spinal cord. A better mental picture is provided by a “look” along the longitudinal axes. The epidural space can be envisioned as a series of lateral, posterior, and anterior compartments existing among the vertebral body, lamina, and pedicles. The compartments, occupied mostly by fat but also by nerves and fibrous tissue, repeat at each segment in a metameric fashion. Of greatest interest to the anesthetist, the posterior epidural space is a series of fat-filled tripodial pads, shaped like a three-sided sand dune. The pad stretches and narrows in a caudad direction as it approaches the next inferior lamina. In areas of the vertebral canal surrounded by bone, the dura actually contacts bone, leaving only a potential epidural space that physically separates the epidural fat-containing compartments. The posterior epidural space, therefore, is a discontinuous group of tapering fat pads that repeat throughout the length of the spinal canal and are separated by a potential space that allows the passage of fluids or small catheters.4–7

The distance from the skin to the epidural space and the depth of the epidural space, or the distance to the dura, is of interest to one wishing to avoid needle injury of neural and vascular tissues. The distance to the epidural space varies with vertebral level and is loosely correlated with patient weight. The distance from skin to the lumbar epidural space using a midline approach varies from 2.5 cm to 8 cm, with an average of 5 cm. Because the space itself is not uniform in shape, the depth of the epidural space from the ligamenta flava to the dura varies considerably. Given the tripodial, dunelike shape of the epidural space, expect the space to narrow considerably when approaching laterally to the midline and in more caudad areas in the space. The depth of the epidural space is also relative to the vertebral level of approach and angle of needle entry, but some clinical generalizations can be made. The epidural space is largest (posterior to anterior) in the midline of the midlumbar region, at 5 to 6 mm. The midline thoracic region epidural space may be 3 to 5 mm deep and is narrower there (lateral width). Caution must be exercised when one approaches the lower cervical region because the epidural space is very small (only 1.5 to 2 mm), leaving little room for error.⁵

In addition to a larger epidural space, another anatomic reason to stay midline with an approaching anesthetic needle is the presence of the epidural veins. The epidural veins are valveless veins that form a plexus draining the blood from the spinal cord and the linings of the cord. The plexus is most prominent in the lateral portion of the epidural space. In pregnant or obese patients, the epidural veins become engorged and swollen as increased intraabdominal pressure results in venous congestion of the lumbar and sacral vessels. The potential for injury or accidental cannulation of these vessels is increased because of this physiologic compensation.3,4,6

A final anatomic consideration for neuraxial anesthesia is the existence of normal and abnormal curvatures of the spinal column. A median-plane longitudinal view of the vertebral column reveals four curvatures in the normal adult. The thoracic and sacral curvatures have posterior curvatures (concave anteriorly), whereas the cervical and lumbar regions have anterior curvatures (concave posteriorly). In a supine patient, the apex of the lumbar curve is usually at L3 to L4, and the trough of the thoracic curve is at T4.⁸ Scoliosis, the most common abnormal curvature, is a lateral curvature of the spine, and kyphosis is an excessive posterior curvature or hump, usually of the thoracic region. Excessive lordosis, or hollowing of the back, may occur as a result of obesity as the body attempts to restore the center of gravity. A temporary lordosis may also occur during pregnancy. Changes in these anatomic curves will challenge the anesthesia practitioner during the performance of epidural or spinal anesthetic techniques. Clear knowledge of the curves is also important when anticipating the spread of local anesthetics in the subarachnoid space relative to the site of injection and the patient’s position.⁹

Neuroanatomic Mapping and Evaluation of Neuraxial Anesthesia

The goal of neuraxial anesthesia is to block pain transmission from areas of injury, disease, or surgical intervention. Therefore, it is clinically useful to have knowledge of the innervations of body structures being operated on in relation to spinal nerve location within the vertebral column. Anatomic maps have been generated based on cutaneous sensation alone. These sensation maps are referred to as dermatomal maps, charts, or levels. A dermatome is defined as the area of cutaneous sensation supplied by a spinal nerve that is anatomically identified as it passes through an intervertebral foramen. For example, the umbilical area is directly anterior to the L3 vertebra but receives cutaneous innervations from T7 to T11, depending on the dermatomal map consulted (Figure 44-6).

FIGURE 44-6 Dermatomes.

For the practical clinician, use of accepted anatomic landmarks and test methods is perhaps the best method for documenting the functional level of blockade—the level of the loss of sensation achieved. The level of anesthetic can be evaluated in many ways, and tests can be used to evaluate several components of the neuraxial anesthetic. For motor function, a straight leg raise or a request to “step on the gas” works well as a clinical measure. Cutaneous sensation can be evaluated through use of a Wartenberg pinwheel, a Semmes-Weinstein monofilament aesthesiometer, or (more practically and simply) with the stylet from the spinal or epidural needle, a portion of a broken wooden tongue blade, or even a peripheral nerve stimulator. Such “pressure” or “scratch” tests are done using two surface-anatomy points for comparison. Inform the patient that the sensation on a normal area, such as the skin surface of the shoulder, is scratchy or sharp. Next, scratch or press an area expected to be numb, such as the lateral thigh. Gradually work cephalad in 2- or 3-inch bands until the patient notices a change in sensation. Note the level of the change in sensation relative to a dermatomal map. This approximates the upper level of sensory loss. Skin refrigerant, ice cubes, and alcohol pads can be used in a similar manner to identify changes in temperature sensation.

Physiology and Mechanisms of Action

Despite more than 90 years of research and experience with spinal and epidural anesthesia, much speculation remains regarding the exact cellular locations and molecular mechanisms involved when local anesthetics, opioids, and other pharmacologically active agents bind to produce spinal analgesia and anesthesia.10,11 For a thorough review of local anesthetics and details on mechanism of action please see Chapter 10. What is known and clinically important about spinal and epidural anesthesia is that the primary site of action for local anesthetics is on the nerve roots within the spinal cord. When a drug is injected directly into the CSF, the drug distributes through the subarachnoid space based on the physical and chemical properties of that injectant and the characteristics of the space in which it must spread. When the drug concentration reaches a minimal effective concentration, neuronal transmission is altered in a manner that clinically provides anesthesia. Neurons—some myelinated, others not; some relatively large, others smaller—differ in susceptibility to drugs such as local anesthetics, and these pharmacodynamic relationships are not easily explained (Table 44-1). The processes involved at the cellular level are complex, and blockade is perhaps a confusing term. It is more accurate to say that anesthetic drugs alter nerve transmission, predominantly by affecting sodium ion channels and inhibiting the units of information that are transferred along the spinal cord. Complete blockade or a “chemical transection” of the cord is an oversimplification. For example, somatosensory evoked potentials have been recorded in individuals made functionally insensate from lidocaine epidural anesthesia. This suggests that neural transmissions are reaching the brain without causing sensory perceptions.4,12

TABLE 44-1

Classification of Nerve Fibers

When a local anesthetic interrupts nerve transmission of autonomic nerves but not sensory nerves or motor nerves (because of a variation in susceptibility), a “differential block” is said to have occurred. A differential block is seen in the more rostral spinal segments of a spinal anesthetic. As the spinal anesthetic spreads from the epicenter of injection, the distal reaches of drug distribution are presumably of lesser concentrations. A differential block is clinically important when sensory anesthesia is desired at a specific level; however, sympathetic blockade could be deleterious in a patient with coexisting disease. The level of sympathetic blockade could be as high as six or more dermatomal levels above the level of sensory blockade and therefore contribute to hypotension and bradycardia.¹¹

Drug injected into the epidural space is distributed to the same sites of action as a spinal anesthetic but in a slightly different manner. The drug must first distribute along the epidural space then diffuse through the meninges and dural cuffs to reach the nerve roots or reach the spinal cord through absorption into the radicular arteries.¹³ Data exist to support the clinical impression that spinal anesthesia is generally more effective or complete from the patient’s perspective than epidural anesthesia and therefore referred to as a more “dense” anesthetic. Epidural local anesthetics first act at sites such as the dural cuffs, at which spinal nerves pass through the peridural spaces. This is consistent with the segmental onset often associated with epidural anesthesia. If the concentration and volume of the anesthetic agent are increased, or if time is allowed for the drug to diffuse into the CSF or pass via radicular arteries into the spinal cord, the epidural anesthetic can become more dense.^4,8

Central Neuraxial Blockade: Indications and Preoperative Considerations

Spinal and epidural anesthesia (central neuraxial blocks) can be used successfully for a variety of inpatient or ambulatory surgical procedures involving the lower extremities, perineum, and abdomen. In addition, spinal and epidural anesthesia or analgesia is used for the treatment of acute and chronic pain syndromes, for obstetric procedures and labor analgesia, and can be applied in patients at the extremes of age.¹⁴ Spinal anesthesia techniques also may be used in combination with other techniques, such as epidural catheter techniques, general or intravenous anesthetic techniques, and with the use of a laryngeal mask airway, to provide anesthesia during surgery. Such combinations, or balanced techniques, minimize the side effects of any one anesthetic technique, maximize the benefits, and offer options in the selection of anesthesia or analgesia for surgical or obstetric procedures.¹⁵

As with any anesthetic plan, proper preparation, patient selection, education, and collaboration with surgeons and nurses are the keys to success. Often the best time to obtain a truly informed consent is during the preoperative visit. It is important to establish rapport with patients to gain their trust and cooperation. Patients eager to be involved in their own care often have the emotional maturity to understand the benefits of their anesthetic options and make rational choices. Anticipate patients’ fears and anxieties; they are often easily dealt with through education and the reassurance provided by the calm voice of a confident and competent anesthetist.

Before presenting the option of a regional anesthetic to the patient, the anesthesia practitioner should answer the following three important questions about the procedure:

1. Will the patient be comfortable having this surgical procedure performed with the proposed regional anesthetic technique?

2. Will the patient be able to remain in the required position without difficulty for the length of the procedure?

3. Does this regional anesthetic technique outweigh the risks of performing this procedure using an alternate anesthetic technique?

The answers to these questions directly affect the choice of anesthetic techniques offered to the patient. When recommending any anesthetic technique to the patient, the practitioner has a responsibility to educate the patient, the patient’s family, and other interested parties about the anesthesia procedure and the potential outcomes. One can then obtain an informed consent and garner the trust of the patient before performing any technique. Without this trust, even the best anesthetic technique may be a failure.

Potential advantages of neuraxial anesthesia include less nausea, vomiting, and urinary retention; a reduced total opioid requirement; and greater mental alertness compared with patients who have received general anesthesia alone. After regional anesthesia, patients are quick to eat, void, and ambulate. Ambulatory surgical patients may or may not be discharged any sooner after spinal anesthesia when compared with those who have undergone general anesthesia, but they can avoid unnecessary overnight admissions resulting from complications of general anesthesia. A growing body of evidence also supports improved outcomes for selected patients and situations. Spinal and epidural anesthesia blunt the body’s stress response to surgery and may offer preemptive analgesia. In addition, studies have shown neuraxial anesthetics to decrease intraoperative blood loss, lower the incidence of postoperative thromboembolic events and postoperative ileus, increase patency of vascular grafts, improve respiratory function and cardiac stability, and improve outcome in high-risk surgical patients.16–20 “Walk-in, walk-out” spinals with a low dose of lidocaine and opioids for ambulatory surgery created the concept of selective spinal anesthesia. Because lidocaine spinals are no longer used, single lower limb anesthesia can be produced with a low dose of hyperbaric bupivacaine. Spinal techniques produce a reliable block, with low incidence of side effects and rapid home-readiness. Reintroduction of chloroprocaine may provide a solution for bilateral, short-acting spinal anesthesia in the future.²¹ Although headache remains a small concern, this risk is greatly reduced.^22,23

Another group of patients well known to benefit from the use of CNB techniques are patients who require anesthesia for obstetric procedures. One primary example is the administration of an epidural anesthetic to the patient in labor. No other modality can provide the parturient with relative relief from the most severe discomfort and still permit the baby and mother to interact immediately after delivery, all with minimal possibility of respiratory distress or depression. Also, epidural techniques in labor allow a safe conversion of the analgesia to a surgical anesthetic if a cesarean section becomes necessary.24,25

Patient safety also may be increased with spinal or epidural anesthesia. Urologic procedures such as cystoscopic examinations and transurethral resections of the prostate (TURP) are most often performed with the use of spinal anesthesia. When awake and anesthetized to the level of the dome of the bladder (T10), the patient may verbally respond to bladder overdistention, thereby helping the urologist minimize the potential for bladder rupture. In addition, the mental status and sensorium of a responsive patient can easily be monitored and the development of conditions associated with TURP syndrome such as hypervolemia, hyponatremia, and ammonium toxicity are more readily detected.19,26

Safety is also an issue when the patient is placed in the prone or jackknifed position as for perianal procedures. A patient in such a position under general anesthesia is at risk for inadvertent extubation and positioning injury. A hypobaric spinal anesthesia technique offers several advantages. The anesthetic procedure can be performed after the patient is positioned and has verbalized that he or she is comfortably padded. With hypobaric spinal anesthesia, the spread of the local anesthetic is controlled, and spontaneous ventilation is maintained.

Additionally, patients often fear postoperative discomfort.²⁷ Therefore, another advantage of spinal anesthesia is the ability to administer long-acting opioid analgesics or clonidine. Epidural catheter placement allows for opioids, low concentrations of local anesthetics, or mixtures containing both solutions to be continuously infused or administered by patient-controlled devices, thereby keeping patients comfortable well into the postoperative period. Because the total doses of opioids and local anesthetics are small, the patient remains alert and possibly ambulatory while receiving analgesia with minimal side effects.^4,8 The patient’s right to be fully informed also necessitates a discussion of the disadvantages of CNB. Consider the patient’s perspective, and keep in mind that the disadvantages and risks inherent in any anesthetic plan are relative only to those of another anesthetic option. For example, patients with a history of headaches or backaches are at increased risk for experiencing these problems after spinal and epidural analgesia but also may have exacerbations of these problems after a general anesthetic. Such patients should be evaluated and counseled regarding this potential problem before the administration of any anesthetic. A thorough history of the patient’s previous pattern of headaches or backaches is essential when faced with the challenge of evaluating similar symptoms in the postoperative period.

To many patients, the risk of paralysis is the most important concern, despite the extreme rarity of any neurologic sequela. The incidence rate of persistent paresthesia and sensory or motor dysfunction is less than 0.1%.4,28–30 Common patient questions also may include the following:

• “Will the injections hurt?”

• “How long will I be numb?”

• “I am afraid of hearing (or smelling or feeling) the surgery. Can I be asleep?”

Patient perceptions can be corrected with thoughtful explanation and discussion of the clinician’s expectations regarding the patient’s case. Additional discussion should include the topic of intraoperative risks, such as the inability to obtain adequate anesthesia, paresthesia, hypotension, dyspnea, high or total spinal anesthesia, nausea and vomiting, use of additional sedation, and allergic reactions. Postoperative complications may include backache, postdural puncture headache (PDPH), hearing loss, transient neurologic symptoms, infection, and peridural abscess or hematoma formation.5,22,31–34

Before administration of any anesthetic, a thorough preoperative history and physical examination must be conducted. During this part of the preoperative patient visit, any concerns regarding administration of spinal anesthesia can be identified. Often the terms absolute and relative contraindications are used; the definition of these categories varies, and their use is therefore controversial. It is more important to think of the anesthetic risks and associated complications relative to the possible benefits of the proposed anesthetic technique. An obvious example is patient refusal or lack of cooperation. Other preoperative concerns include increased intracranial pressure, significant preexisting or therapeutic coagulopathy, skin infection at the site of injection, hypovolemia, spinal cord disease, patients with a fixed-volume cardiac state such as hypertrophic cardiomyopathy or severe atrial stenosis, and an anticipated lengthy surgical time. Finally, if a difficult airway is anticipated, the plan of care must be discussed with both patient and surgeon.

Neurologic diseases are often listed as potential, absolute, or relative contraindications for neuraxial anesthesia, but data are often mixed. A dural puncture by a spinal needle or a larger epidural needle creates a rent in dural tissue that may or may not leak CSF. In patients with a preexisting increase in intracranial pressure, the risk of brain herniation is increased. In the case of epidural catheter placement or epidural blood patch, the addition of large volumes of fluid into the epidural or subarachnoid spaces could increase already elevated intracranial pressures.4,8

Musculoskeletal deformities such as severe kyphoscoliosis, arthritis, osteoporosis, and fusion and scarring of the vertebrae are considered relative contraindications to neuraxial anesthesia. The location of the epidural or subarachnoid spaces by needle tip may be technically difficult, and spread of anesthetic agents may be limited by anatomic alterations.²⁸ However, a large retrospective study surmises that osteoporosis may be an important risk factor for CNB complications.³⁵

Peripheral neuropathies can be the result of metabolic, autoimmune, infectious, or hereditary etiologies. A presumption is that patients with preexisting neural compromise are more susceptible to and less able to recover from injury when exposed to a secondary insult, compared with patients with healthy tissues. Also, abnormal tissues may not respond to pharmacologic agents in predictable ways. Secondary insults might stem from needle or catheter trauma, ischemic injury from the use of vasoconstrictors, or direct local anesthetic neurotoxicity. For example, diabetes mellitus (DM) is the most prevalent cause of peripheral polyneuropathy, with most patients having some abnormalities in nerve conduction. A study by Hebl et al.³⁶ supports the increased risk of the “double-crush” phenomenon, finding that 0.4% of patients with diabetic polyneuropathy experience new or progressive changes in their neurologic deficits. This suggests that spinal or epidural anesthesia may worsen or exacerbate conditions such as a gradually progressive diabetic neuropathy. However, the same group of investigators also took a retrospective look at central nervous system (CNS) diagnoses such as post-poliomyelitis, multiple sclerosis, traumatic spinal cord injury, and amyotrophic lateral sclerosis. The nature of their study did not permit definitive recommendations, yet they found no patients with exacerbations or deterioration of symptoms. Additionally, they note that their results suggest the safety of CNB in these patients and that their findings were supported by other studies. Until further prospective study can support definitive conclusions, the decision to perform a CNB technique must be made by weighing the relative risks to the individual patient’s neurologic disease against the potential benefits of minimizing the anesthetic effects on their coexisting diseases.³⁶ Because few objective data are available, use of CNB in such patients becomes a medicolegal risk, especially if blame is incorrectly placed on the anesthetic. If a neuraxial block is the appropriate anesthetic choice, then precise documentation of the patient’s preexisting disease state and existing neurologic compromise is a mandatory precaution, as is attentive follow-up care.^4,8,28,31,37

The existence of a significant preexisting or therapeutic coagulopathy increases the risk of spinal or epidural hematoma formation in a patient receiving a CNB. Spinal or epidural hematoma is a rare but devastating complication, possibly resulting in permanent neurologic injury. Therefore, central neuraxial anesthesia should be avoided in any patient with a known coagulopathy. Insufficient data are available to quiet the controversy surrounding absolute laboratory values below which the practitioner should avoid CNB. To determine whether a CNB technique should be avoided, it has been suggested that the following arbitrary values be used as a guide: platelet counts of less than 100,000 and prothrombin time (PT), activated partial thromboplastin time (aPTT), and bleeding times that are greater than two times normal values. For a spinal anesthetic, this is perhaps an overly conservative guide.³⁸ However, severe bleeding with or without symptomatic hypovolemia or the potential for severe bleeding is a possible contraindication to the administration of a regional anesthetic because the sympathectomy caused by CNB further aggravates severely contracted volume states.

Much discussion has arisen regarding the use of spinal and epidural anesthesia when coagulopathy for thromboprophylaxis or for therapeutic treatment of coexisting disease has been initiated, planned, or is ongoing because the therapies, timing, and the effects on coagulation are highly varied. For example, the use of platelet inhibitors, such as aspirin or nonsteroidal antiinflammatory drugs (NSAIDs), is not a contraindication to spinal and epidural anesthesia. Even planned intraoperative anticoagulation with heparin is reasonably safe after atraumatic dural puncture if the patient presents with a normal coagulation profile. Traditionally, a patient’s bleeding time was obtained prior to administration of neuraxial anesthesia, but the predictive value of bleeding time has not been established in patients taking aspirin and NSAIDs.39,40 Also, with the increased use of natural and herbal medicines, anesthetists must be alert to the possibility of drug interactions. Alone, herbal supplements appear not to increase the risk of spinal hematoma; however, data on combinations of herbal and other anticoagulants are not available. Herbal medications that effect hemostasis and some perioperative concerns are listed in Table 44-2. If basic precautions are followed, many thromboprophylaxis strategies have had an extensive safety record when co-administered with neuraxial anesthetics. The surgeon and anesthesia practitioner should consider the potential benefit versus risk before neuraxial intervention for patients who have been or will be anticoagulated for thromboprophylaxis. The number, variety, and indications for the use of anticoagulants and thrombolytics continue to increase.

TABLE 44-2

Herbal Medications Affecting Hemostasis ^∗

^∗At this time, it is not deemed necessary to discontinue herbal medications and allow resolution of their effects on hemostasis before surgery or anesthesia.

Adapted from Horlocker TT, et al. Regional anesthesia in the anticoagulated patient: defining the risks (the second ASRA Consensus Conference on Neuraxial Anesthesia and Anticoagulation). Reg Anesth Pain Med. 2003;28:172-197.

The incidence of neurologic dysfunction resulting from hemorrhagic complications resulting from neuraxial blockade is unknown. Although the incidence cited in the literature is estimated to be less than 1 in 150,000 epidural and less than 1 in 220,000 spinal anesthetics, recent epidemiologic surveys suggest that the frequency is increasing and may be as high as 1 in 3000 in some patient populations. Overall, the risk of clinically significant bleeding increases with age, associated abnormalities of the spinal cord or vertebral column, the presence of an underlying coagulopathy, difficulty during needle placement, and an indwelling neuraxial catheter during sustained anticoagulation, particularly with standard heparin or low-molecular-weight heparin. The American Society of Regional Anesthesia and Pain Medicine (ASRA) convened its Third Consensus Conference on Regional Anesthesia and Anticoagulation. Practice guidelines were formulated. Many international anesthesia societies have also issued guidelines.41–43 Guidelines for the use of regional blocks in patients receiving thromboprophylaxis are given in Table 44-3.

TABLE 44-3

Regional Anesthesia in the Patient Receiving Thromboprophylaxis

Medication	Clinical Management
Antiplatelet medications	No contraindication with aspirin or NSAIDs; discontinue ticlopidine (generic) 14 days, clopidogrel (Plavix) and prasugrel (Effient) 7 days prior to block; GP 11b/111a inhibitors tirofiban (Aggrastat) and eptifibatide (Integrilin) 8 hours, abciximab (ReoPro) 24-48 hours to allow return of normal platelet function
Unfractionated heparin
Subcutaneous	No contraindication with twice daily dosing of less than 10,000 units; consider delay until after block if technical difficulty anticipated Safety of doses greater than 10,000 units or more than twice daily dosing has not been established
Intravenous	Heparinize 1 hour after block; remove catheter 2-4 hours after last heparin dose; document normal aPTT; sustained heparinization with an indwelling catheter associated with an increased risk; monitor neurologic status aggressively
LMWH	Delay procedures at least 12-24 hours after last dose of LMWH; regardless of technique, remove all catheters 2 hours before first LMWH dose; no additional hemostasis-altering drugs to be administered
Warfarin	Normal INR before neuraxial technique (usually requires 4-5 days); remove catheter when INR is 1.5 or less
Thrombolytics	Absolute contraindication
Thrombin inhibitors	Bivalirudin (Angiomax); desirudin (Iprivask) Avoid regional block, insufficient information
Fondaparinux (Arixtra)	Until additional clinical information is obtained, neuraxial techniques should involve only single needle pass, atraumatic needle placement, no indwelling catheters; if this is not feasible, an alternate method of prophylaxis should be used
Dabigatran (Pradaxa)	Discontinue 7 days prior to regional block; for shorter time periods, document normal thrombin time (TT) or ecarin clotting time (ECT); first postoperative dose 24 hours after needle placement and 6 hours post catheter removal, whichever is later
Herbal medicine	No evidence for discontinuation; be aware of potential drug interactions

NSAIDs, Nonsteroidal antiinflammatory drugs; aPTT, activated partial thromboplastin time; INR, international normalized ratio; LMWH, low-molecular-weight heparin.

Adapted from Horlocker TT, et al. Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: American Society of Regional Anesthesia and Pain Medicine Evidence Based Guidelines. 3rd ed. Reg Anesth Pain Med. 2010;35(1):64-101; Horlocker TT. Regional anaesthesia in the patient receiving antithrombotic and antiplatelet therapy. Br J Anaesth. 2011;107(suppl 1):i96-i106; Chelly JE. Thromboprophylaxis and regional anesthesia in the ambulatory setting. Int Anesthesiol Clin. 2011;49(4):166-173.

By following evidence and consensus-based precautions, the low incidence of permanent neurologic complications can be decreased. A meta-analysis by Brull et al.⁴⁴ identified the risk of permanent neurologic injury after spinal anesthesia at 1 to 4.2:10,000 and after epidural anesthesia at 0 to 7.6:10,000. Because complications are very infrequent, risk factor identification is difficult, and vigilant care must be maintained for all patients. Analysis of known case reports found the median time to onset of neurologic dysfunction after initiation of low-molecular-weight heparin (LMWH) therapy to be 3 days. Scrupulous postoperative nursing surveillance is also required to support patient safety. The initial complaint may be of new-onset weakness to the lower limbs and sensory deficit, although bowel and bladder dysfunction and new-onset back pain may occur. If emergent neurosurgical care is required, recovery is unlikely if surgical decompression of the hematoma is delayed more than 8 hours.30,35,44

The etiology of neuraxial infection is based on the theory that needle placement disrupts the body’s physiologic protective mechanisms and deposits infectious or noxious agents beyond the skin into underlying tissues and the peridural space and past the blood-brain barrier into subarachnoid spaces. Indeed, skin infection at the site of injection increases the risk of meningitis or epidural abscess formation. Infectious complications include, but are not limited to, epidural, spinal, or subdural abscess; paravertebral, paraspinous, or psoas abscess; meningitis; encephalitis; sepsis; bacteremia; viremia; fungemia; osteomyelitis; or discitis. Although colonization of the catheter may be considered a precursor to infection, colonization per se is not considered an infection. A recent advisory committee published guidelines noting several factors to consider to minimize infections. They included conducting a history, physical examination, and preprocedure laboratory evaluations, use of prophylactic antibiotic therapy as indicated, and use of strict aseptic techniques including the use of proper antiseptic solution. The use of sterile occlusive dressings at the catheter insertion site, a bacterial filter during continuous epidural infusion, limiting disconnection and reconnection of neuraxial delivery systems, and limiting the duration of catheterization were also encouraged.³⁴

Although infectious complications of CNB are rare, the practitioner must maintain aseptic technique during the preparation and administration of any regional anesthetic to minimize the potential for infection. Septic meningitis or epidural abscess due to bacterial contamination, and the consequences of persistent neurologic deficits such as loss of bowel and bladder control, chronic pain, and lower extremity weakness or paraplegia, can be devastating. Other factors that increase the risk of infection include dermatologic conditions such as psoriasis that prevent aseptic skin preparation, underlying sepsis, diabetes, immunologic compromise, steroid therapy, and the preexistence of chronic infections such as human immunodeficiency virus (HIV) or herpes simplex virus (HSV). Because meningitis after spinal or epidural anesthesia is so rare, it has been difficult to directly attribute causality to the anesthetic or to identify significant risk factors. In fact, based on the limited data available, it would appear that regional anesthesia is safe in cases of secondary HSV infection and reasonable for patients in the early stages of HIV infection. Again, vigilance must be emphasized. Known predisposing factors include advanced age, diabetes, alcoholism, cancer, and AIDS. Patients are monitored for signs of meningeal irritation, fever, increasing back pain, neurologic changes, and local tenderness to injection sites. Although classic symptoms such as high fever, nuchal rigidity, and severe headache may be present, less alarming symptoms can occur, resulting in misdiagnosis. Although α-hemolytic streptococci is commonly seen in spinal block meningitis, Staphylococcus aureus is the most common causative organism in epidural abscesses, and iatrogenic methicillin-resistant. S. aureus is a growing concern. Epidural abscess, like epidural hematomas with evidence of neurologic deficit, can best be diagnosed by MRI. Early, aggressive surgical intervention and antibiotic administration are vital.4,28,35,45–47

Arachnoiditis and aseptic meningitis are rare but can occur when foreign substances irritate the meninges. As the needle is inserted, precautions must be taken to avoid introduction of glass or metal particles, highly concentrated local anesthetics or dextrose solutions, detergents or antiseptics, and a core of epidermis. Indwelling catheters, previous myelography, and hemorrhages into the subarachnoid or epidural space also have been associated with meningeal irritation and scarring. Modern technology and techniques incorporate the use of disposable equipment, needles with matched stylets, filter needles, and improved pharmacologic agents that make this complication rare.⁴⁸

Shock and severe uncorrected hypovolemia are contraindications to spinal or epidural anesthesia, because both techniques cause sympathetic blockade. The resulting vasodilation prevents physiologic compensation and may worsen hypotension. In addition, management of shock and hypovolemia often requires aggressive fluid therapy and multisystem treatments that are often physiologically and psychologically uncomfortable for the aware patient.4,8,28

Patients with a fixed-volume cardiac state such as hypertrophic cardiomyopathy or severe atrial stenosis do not tolerate bradycardia, decreases in systemic vascular resistance, or decreases in venous return and left ventricular filling—all physiologic changes that can be anticipated with neuraxial block by local anesthetics. In these patients, even transient episodes of hypotension can cause serious coronary hypoperfusion and cardiac arrest. Therefore spinal, and usually epidural, anesthesia, are avoided; however, few things in anesthesia are truly absolute. For example, epidural administration of opioids has been used to provide obstetric analgesia and may provide cardiac benefit for these patients. Precautions in such a scenario might include close hemodynamic monitoring with an arterial line and pulmonary artery catheter, careful titration of the anesthetic, intravascular volume expansion, and use of ephedrine or phenylephrine to treat hypotension.³⁰

Spinal anesthesia is typically a singular deposit of local anesthetic and therefore provides anesthesia for a fixed duration. If uncertainty exists about the anticipated length of surgery, epidural catheter placement is more appropriate to allow for the additional administration, or continuous infusions, of anesthetic agents. If the extent of the surgery is unknown, a neuraxial anesthetic may be initiated only to be converted at a later time to a general anesthetic when the surgeon exceeds the limits of the anesthetic block. This is rarely an ideal situation; the patient may experience discomfort, albeit brief, and the anesthesia practitioner must contend with less-than-ideal intubating conditions. Despite the advantages of neuraxial anesthesia, many patients such as the elderly and those with arthritis or musculoskeletal limitations of the neck and upper extremities poorly tolerate prolonged immobility. The judicious use of conscious sedation can quickly devolve into a “room air general,” placing the patient at risk for hypoventilation, hypoxia, and hypercarbia. To avoid such circumstances, combined neuraxial and general anesthetic techniques are advocated and offer advantages by minimizing the total dose of general anesthetic used. Such techniques lower the risk of secondary effects of general anesthesia (e.g., nausea and vomiting) while gaining the advantages associated with neuraxial anesthesia, such as attenuation of the stress hormone response and improved postoperative pain relief.⁸

The administration of spinal or any regional anesthesia to patients with a difficult airway or full stomach requires careful consideration. The use of spinal anesthesia permits the patient to retain upper airway and pharyngeal reflexes that block the sympathetic nervous system. This theoretically results in increased gastric and intestinal motility, causing the stomach to empty. However, such benefits may be negated by the perception of pain and anxiety that accompanies illness or injury. If sedation is used to counter such perceptions, the airway may again become compromised. Furthermore, if hypotension develops from the resulting sympathectomy, the patient may experience nausea and vomiting. When an injury has occurred after the ingestion of alcohol or if the patient received opioid analgesics, the pain caused by the injury may be the only stimulus for consciousness.

When spinal or other regional anesthesia is instituted, the reticular activating centers in the brain receive less input. This often results in somnolence in a normal patient but can result in unconsciousness in the overly sedated or inebriated patient. In addition, spinal or epidural anesthesia may reach an undesirably high level that is physically and psychologically intolerable for the patient and can even become a “total spinal.” A total spinal is characterized by unresponsiveness accompanied by cardiac and respiratory compromise. In such situations, airway support is required, and the emergent management of any airway can severely compromise patient safety. Therefore, regional anesthesia is not an alternative to a secure airway. For patients identified as potentially difficult to intubate, equipment should be immediately available to secure the airway in a safe manner. Advances in airway management such as the laryngeal mask airway, improved fiberoptics, laryngoscopes, and adjunct airway equipment may tip the risk-benefit scale in favor of regional anesthesia.8,11,48

Spinal Anesthesia

Spinal anesthesia became popular after the discovery of the local anesthetic properties of cocaine, the invention of the hollow needle and syringe, and the written descriptions of the first lumbar puncture. The first clinical application of the technique was reportedly performed in the late 1890s. However, spinal anesthesia’s prominence was short lived. The introduction of specific, reversible, neuromuscular blocking drugs and concurrent improvements in inhalation agents for general anesthesia soon displaced its popularity. It has regained popularity, in large part because of the introduction of newer agents, equipment, and techniques to employ it safely in the ambulatory setting.

Equipment and Techniques

Preparation for spinal anesthetic procedures, like that for any other regional technique, requires the immediate availability of emergency equipment and supplies should emergent resuscitation be required. Usually spinal anesthetics are administered in the operating room where the minimal requirements—functional laryngoscopes, endotracheal tubes, induction agents, cardiovascular drugs including atropine and ephedrine or phenylephrine, suction, oxygen and ventilation equipment, a noninvasive blood pressure monitor, and pulse oximetry and electrocardiographic monitoring equipment—are readily available.

The original spinal technique, performed by August Bier in 1898, has been continually examined and modified in hope of reducing the incidence of complications—primarily that of PDPH. The goal of needle design has been to create a needle that minimally rends, tears, or cuts dural tissues. As technology has improved, the use of sterile, disposable procedure trays containing needles, syringes, catheters, and drugs has virtually eliminated problems previously associated with dull needles or contaminated equipment and has allowed for the development of innovative needles. Currently, two main types of needles are available for use in spinal anesthesia. Needles such as the Quincke-Babcock or Pitkin have a cutting bevel tip. These needles have matching stylets, which minimizes tissue coring, and the tip’s cutting angle is blunter than that of a standard needle. The newer noncutting-tip needles are either pencil-point shaped with lateral openings (e.g., Sprotte, Whitacre, or Pencan needles) or have the rounded bevel tip of the Greene-type needle and an opening at the needle’s end. Several of the more popular types of spinal needles are shown in Figure 44-7. Spinal needles also have matched stylets and are marketed for spinal anesthesia use in sizes ranging from 22- to 29-gauge and in lengths of approximately 3.5 inches (88 mm) and 5 inches (120 mm). Most blocks are performed using 25- to 27-gauge, 3.5-inch (88-mm) needles.^28,48

FIGURE 44-7 Graphic representations of spinal needle design features. A, Cutting-point tips. B, Pencil-point tips. C, Stylet-point tip. (A and B, Chestnut DH. Obstetric Anesthesia: Principles and Practice. 4th ed. Philadelphia: Mosby, 2009; C, CSEN International. Eldor Spinal Needle. Available at: http://www.csen.com.)

Recent data support the use of noncutting-tip needles over cutting needles for several reasons. Cadaver lumbar punctures performed with sharp cutting needles show piercing of the cauda equina roots without resistance appreciated by the practitioner. This does not occur with pencil-point needles. The bevel of cutting-tip needles encourages tip deviation on insertion, whereas symmetric noncutting needles stay midline. The use of a beveled needle requires holding the bevel direction parallel to longitudinal dural tissue fibers to minimize the risk of PDPH. Noncutting needles may drag fewer skin contaminants into subdermal tissue than cutting needles. Pencil-point needles pierce the dura with a clearly perceptible “click” or “pop” not as easily noticed with cutting needles. Newer, thin-walled noncutting needles have improved CSF flow rates without compromise to strength. This allows for their use for CSF diagnostic procedures and helps simplify the identification of the intrathecal space by permitting quick return of CSF after stylet removal. Finally, unless prohibitively small cutting needles are used, the incidence of PDPH is clearly reduced with the use of noncutting needles. Pencil-point needles are associated with less than a 1% risk of PDPH and a failure rate of approximately 5%.8,28,49,50

After the patient arrives in the surgical or obstetric preoperative area, the consents for surgery and anesthesia should be checked, and any further patient questions or concerns should be addressed. Review of the anesthetic preoperative history and physical examination should include the addition of any last-minute changes in patient status and notation of recently obtained diagnostic results. Intravenous access is achieved, and a continuous crystalloid infusion is begun. Preoperatively, most patients benefit from low-dose anxiolysis. With the increased emphasis on same-day admission, surgery, and discharge, long-acting agents are avoided. A rapid-acting benzodiazepine with a relatively short duration, such as midazolam, is highly titratable in 0.5- to 1-mg increments given intravenously and minimally alters the patient’s hemodynamic status when used in low doses. The drug’s effects can be reversed with flumazenil.

Monitors appropriate to the patient’s physical status should be applied and at minimum include blood pressure monitoring, a continuous electrocardiogram, and pulse oximetry. For the purpose of baseline comparisons, vital signs must be assessed with the patient in both the supine position and the position in which the block will be administered.

The surgical or obstetric procedure to be performed helps determine the patient’s position for the administration of the block. For example, if vaginal or urologic surgery is planned, a “saddle” block with the patient in a sitting position may be indicated. The prone position is useful for rectal surgery, because the patient can be placed in position before the block is implemented. This reduces the time required for positioning by permitting the patient to move with minimal assistance and to personally verify comfort and adequacy of padding. A lateral position favors spinal drug spread for right- or left-sided extremity or abdominal procedures. When the patient is in the lateral position, a pillow placed under the head and perhaps shoulders helps maintain neutral alignment of the spinal column. Surgical table height or patient position may need to be adjusted to compensate for variations in anatomic structure or physiologic limitations and to maximize anesthetist ergonomics. To maximize the space between spinous processes, the patient should arch the back (with assistance from the clinician) into a C shape or “like a Halloween cat.” Once the patient is positioned, anatomic surface landmarks are used to identify the lumbar region of the back to be used for dural puncture, a point below the end of the spinal cord (L2). The line formed between the tops of the iliac crests, called the intercristal line or Tuffier’s line, crosses the vertebral column as high as the L3 to L4 disk or as low as the L5 to S1 disk (Figure 44-8). The accuracy of predicting the precise level of needle insertion is at best 50%. This fact may account for variability in the spinal anesthesia level ultimately achieved, yet this landmark has been clinically useful since the advent of spinal anesthesia.⁷ The skin overlying a prominent spinous process at this level is marked for easy identification after the skin is prepared and draped. A surgical skin-marking pen is useful for this purpose, with caution exercised to avoid scratching the skin surface and predisposing the patient to infection.

FIGURE 44-8 Patient positioning and identification of landmarks in the lumbar region of the back.

Next, the spinal anesthesia tray is opened, and sterile gloves are donned. The patient is prepared with an antiseptic solution such as Betadine, a povidone-iodine solution that releases a concentration of 1% free iodine as it dries on a surface. The solution must remain in contact with the skin for at least 1 minute to be effective, and then the dry residue can be wiped away with sterile gauze to help prevent a chemical arachnoiditis. Do not use alcohol to remove residue because alcohol neutralizes the iodine solution and minimizes its antiseptic effect. Maintain aseptic technique, and apply the sterile drape to the back. Many spinal and epidural drapes have a circular window that is placed over the area of anticipated injection and adhesive strips to simplify application to the patient’s back. Avoid touching the adhesive, because this has been shown to create small holes in gloves, which increases the risk of infection in both the patient and anesthesia practitioner.⁵¹

A rapid-acting local anesthetic such as 1% lidocaine is used for local infiltration of the area just caudad to the identified spinous process. Approach the skin of the back with the bevel of the needle facing away from the skin and at a 15- to 30-degree angle from the skin. Start injecting before the bevel of the needle is completely through the skin, and raise a skin wheal to place local anesthetic into subdermal tissues most likely to contain nociceptors. Deep tissues, including the supraspinous ligament, can be anesthetized by spreading 3 to 5 mL of local anesthetic through the tissues in a fan pattern.8,28

Larger 22- to 25-gauge spinal needles and epidural needles (used for continuous spinal anesthetic techniques) have tensile strength sufficient to permit introduction of the needle without additional support. However, spinal needles smaller than 25 gauge often require an “introducer” needle to help stabilize the needle during insertion and minimize infection in the surrounding dermis. The introducer is typically an 18- or 20-gauge needle with a “B” or blunt bevel. Introducer needles are approximately 3.8 cm long and matched to the spinal needles. The introducer is inserted through the skin and supraspinous ligament and into the interspinous ligament. Care must be taken, especially in thin individuals, not to enter the subarachnoid space with the introducer needle; the dura may be only 2.5 cm beneath the skin. Depth to the epidural space and the nearby dura correlates with weight but typically averages approximately 4 to 5 cm and rarely exceeds 9 cm. An introducer needle placed into the subarachnoid space would be likely to cause a PDPH.4,8,15,28

Several common spinal anesthesia techniques can be used, including a straight midline approach. With this easy-to-learn technique, the anesthesia practitioner inserts the needle directly midline between the spinous processes and toward the umbilicus perpendicularly to all planes or at the lumbar level with a slight cephalad angle (Figures 44-9 and 44-10). If bone is encountered early, the needle is withdrawn into the introducer and subcutaneous tissue. The introducer is then redirected in small angular increments in a cephalad direction. If bone is encountered when the needle is deeply inserted, the needle should be withdrawn and redirected caudad. As the tip of the spinal needle passes through the ligamenta flava, the sensation is similar to that felt when a needle is passed through a pencil eraser. As the needle tip passes through the dura, the anesthesia practitioner may sense a “pop” or “click.” The stylet is removed, and several seconds are given for CSF to return through the small-gauge needle. Once CSF return is confirmed, some authors recommend rotating the needle 360 degrees in 90-degree increments to ensure that the needle tip is seated well within the subarachnoid space (see Figure 44-10). Other authors suggest that such needle manipulation risks a larger dural rent or needle dislodgement. Whichever method is used, secure needle handling is important. As shown in Figure 44-11, firmly place the dorsum of one’s nondominant hand against the patient’s back and below the spinal needle. Grasp the needle hub between the thumb and index finger. With this Bromage type of grip, the patient’s body then acts as a firm support for the needle-stabilizing hand and helps prevent advancement or withdrawal of the needle tip from the subarachnoid space when the syringe is applied to inject the anesthetic agent.