Chapter 14 Spinal and Epidural Anesthesia
1. What term is used to collectively describe spinal and epidural anesthesia?
2. Where is medicine deposited during performance of spinal anesthesia? With epidural anesthesia? With caudal anesthesia?
3. What are some advantages of spinal anesthesia when compared with epidural anesthesia?
Anatomy
5. What is the relative clinical significance of the curvatures of the spinal canal with respect to spinal and epidural anesthesia?
6. What is the number of each type of vertebrae composing the vertebral column?
7. Describe the anatomic parts of a vertebra by answering the following questions: What are the two parts that make up a vertebra? From what parts of the vertebra does the transverse process arise? From what parts of the vertebra does the spinous process arise?
8. How do the different characteristic features of the spinous processes and laminae of the thoracic and lumbar vertebrae impact clinical performance of neuraxial blocks?
10. What are some important surface landmarks used to identify specific spinal interspaces to guide placement of a spinal or epidural needle?
11. How are the laminae of adjacent vertebrae connected?
12. How are the tips of the spinous processes of adjacent vertebrae connected?
13. What passes through the intervertebral foramina?
14. What are the rostral and caudal limitations of the spinal canal? What accounts for the disparity between the vertebral level and spinal level?
15. What is the cauda equina, and what characteristic features are relevant to spinal anesthesia?
16. What are the three meningeal layers surrounding the spinal cord?
17. Where is cerebrospinal fluid relative to the meningeal layers? What are two interchangeable terms for this space?
18. What structures form the boundaries of the epidural space?
19. What structures are contained within the epidural space?
20. As the nerves pass through the intervertebral foramen they become encased by the dura, arachnoid, and pia, forming what three components of a peripheral nerve?
21. Where do the preganglionic nerves of the sympathetic nervous system originate, and what is their course of travel after leaving the spinal cord?
22. What is the plica mediana dorsalis? What might be its clinical significance?
23. Describe the blood supply of the spinal cord. Which area of the cord is most vulnerable to ischemic insult?
Preoperative preparation
25. What are the potential complications that should be discussed with the patient before proceeding with a spinal or epidural anesthetic?
26. What are the common indications for spinal anesthesia?
27. What are the common indications for epidural anesthesia?
28. What are the absolute contraindications to neuraxial anesthesia?
29. Does bacteremia preclude performance of a neuraxial technique?
30. Does chronic back pain preclude performance of a neuraxial technique?
31. What cardiac disorders warrant specific concern with respect to neuraxial anesthesia?
32. Do coagulation abnormalities preclude performance of a neuraxial anesthetic?
Spinal anesthesia
33. What are the common positions patients are placed in for administration of a spinal anesthetic?
34. What are some advantages and disadvantages of having a patient in a sitting position during performance of a spinal anesthetic?
35. Why might an anesthetist choose to administer a spinal with a patient in the lateral decubitus position?
36. What vertebral level is crossed by a line drawn across the patient’s back at the level of the top of the iliac crests? What interspace is located directly above this line? What interspace is located directly below this line?
37. What is the reason for placing a spinal anesthetic at a level below the L2 vertebra?
38. On what basis are spinal needles generally classified?
39. Which characteristics of a spinal needle will result in the lowest incidence of postdural puncture headache?
40. What are the two approaches used for spinal anesthesia, and what are their relative advantages and disadvantages?
41. When a midline approach is chosen, what are the tissue planes that will be traversed as the needle is advanced toward the subarachnoid space?
42. What accounts for the “pop” the anesthetist may feel when advancing a spinal needle into the subarachnoid space?
43. How is subarachnoid placement of the spinal needle confirmed?
44. How can the spinal needle be handled to stabilize the needle after proper placement in the subarachnoid space is confirmed?
45. After the syringe containing the local anesthetic solution for administration into the subarachnoid space is attached to the spinal needle, how can continued subarachnoid placement of the spinal needle be confirmed?
46. What should be done if blood-tinged cerebral spinal fluid (CSF) appears at the hub of the needle?
47. Describe the lumbosacral (Taylor) approach. When is this approach advantageous?
48. What are the three factors that most influence the distribution of the local anesthetic solution in cerebrospinal fluid after its administration into the subarachnoid space?
49. How is the baricity of a local anesthetic solution to be administered into the subarachnoid space defined? Why is this clinically important?
50. What are the two things that most influence the duration of a spinal anesthetic?
51. What is the baricity of the most commonly used spinal anesthetics? What is added to local anesthetics for spinal anesthesia to make the solution hyperbaric? What is the principal advantage of these solutions?
52. What role does the contour of the vertebral canal play in anesthetic distribution, and hence, level of spinal block?
54. What situations might warrant use of a hypobaric solution?
55. What are the relative advantages and disadvantages of isobaric solutions?
56. What is the purpose of adding a vasoconstrictor to the local anesthetic solution used for spinal anesthesia? What is their mechanism of action?
57. What are the two potentially useful effects derived from adding an opioid to the local anesthetic used for spinal anesthesia? What is their mechanism of action?
58. How do spinal anesthetics regress during the recovery from spinal anesthesia?
59. What recent events have led to concern regarding the use of lidocaine for spinal anesthesia? What are some modifications in practice that have been suggested should lidocaine be used for this purpose?
60. What is TNS, and what are the factors that increase the risk of its occurrence following spinal anesthesia with lidocaine?
61. List the rank order for the relative incidence of TNS with the following local anesthetics used for spinal anesthesia: bupivacaine; chloroprocaine; lidocaine; mepivacaine; prilocaine; and procaine.
62. What are some important restrictions with respect to the anesthetic solution if using chloroprocaine off-label for spinal administration?
63. What are some distinguishing characteristics between bupivacaine and tetracaine with respect to spinal anesthesia?
64. What is the temporal order of blockade of the motor, sensory, and sympathetic nerves after the administration of a spinal anesthetic?
65. What is a useful way to gain an early indication of the level of spinal anesthesia?
66. How do the ultimate dermatomal levels of motor, sensory, and sympathetic block compare during spinal anesthesia?
67. How is the extent of motor block produced by a spinal anesthetic generally assessed?
68. What surface landmarks are used to determine the approximate level of spinal anesthesia?
69. What are some advantages and disadvantages of a continuous spinal technique?
70. Why were microcatheters used for spinal anesthesia withdrawn from the U.S. market?
71. What is the likely mechanism of injury associated with microcatheters?
72. Has removal of microcatheters eliminated the risk of neurologic injury?
73. What elements of the continuous spinal technique are important to prevent neurologic injury?
74. What dose of anesthetic should be used when repeating a spinal because of a failed block?
75. What are the physiologic effects on the respiratory system of an appropriately instituted spinal anesthetic?
76. What are some physiologic effects on the gastrointestinal tract and the genitourinary system that result from a spinal anesthetic?
77. What is the effect of spinal anesthesia on blood pressure and what accounts for this effect?
78. How is spinal anesthetic-induced hypotension treated?
79. What is the effect of spinal anesthesia on heart rate, and what is believed to be the underlying mechanism?
80. How are spinal anesthetic-induced perturbations in heart rate treated?
81. What is the cause and typical onset of a postdural puncture headache?
82. What is the hallmark feature of a postdural puncture headache?
83. What are some of the other characteristic features of a postdural puncture headache?
84. What serious complications may result from a postdural puncture headache?
85. Which patients are most at risk for development of a postdural puncture headache?
86. What features of a spinal needle will impact the incidence of a postdural puncture headache?
87. What are some of the commonly used treatment options for a postdural puncture headache?
88. What are the likely predominant mechanism(s) by which an epidural blood patch may relieve a postdural puncture headache?
90. How should a total spinal be managed?
91. What are two possible causes of nausea that present soon after the administration of a spinal anesthetic?
92. What might contribute to backache occurring in a patient who has received a spinal for surgical anesthesia?
Epidural anesthesia
93. Is it acceptable to place a lumbar epidural after the induction of general anesthesia?
94. Is it acceptable to place a thoracic epidural after the induction of general anesthesia?
95. What are the advantages and disadvantages of epidural catheters that have an inner stainless steel core?
96. What are the comparative advantages and disadvantages of epidural catheters with a closed versus open tip?
97. Which approach (midline or paramedian) is most often used for placement of a thoracic epidural, and why is it chosen?
98. What is the “loss-of-resistance” technique?
99. What is the “hanging-drop” technique?
100. What are the potential advantages and disadvantages of the single-injection versus catheter technique for epidural anesthesia?
101. What is the technique used for placement of a catheter following identification of the epidural space?
102. What is the “test dose” for an epidural catheter? What is it testing for? How long must the anesthetist wait after administering the test dose to make this determination?
103. Why is the anesthetic administered in incremental doses?
104. Complete the following table of local anesthetics used for epidural anesthesia:
105. Why are tetracaine and procaine rarely used for epidural anesthesia?
106. How is the caudal epidural space identified?
107. What anatomic variations may impact success and complications with caudal anesthesia?
108. What are the major factors affecting the spread of epidural anesthesia?
109. What patient-related factors might influence spread of epidural anesthesia?
110. How do patient position and anesthetic baricity influence the spread of epidural anesthesia?
111. What are the principal factors affecting the duration of epidural anesthesia?
112. What are some of the potential advantages of adding epinephrine to an anesthetic solution used for epidural anesthesia?
113. What is the effect of sodium bicarbonate when added to the local anesthetic solution used for epidural anesthesia?
114. For which local anesthetics is sodium bicarbonate commonly used as an additive?
115. How does lipophilicity affect the choice of opioids used for epidural administration?
116. What are some potential causes of failure of an epidural block?
117. What are the options for managing a failed epidural block?
118. What is the major site of action of local anesthetics administered epidurally?
119. How do the risks of epidural anesthesia compare with that of spinal anesthesia?
120. What are the commonly used management options following a “wet-tap”?
121. What are the risks associated with accidental subarachnoid injection of an epidural dose of anesthetic, and how should this complication be managed?
122. How do the hemodynamic effects of an epidural compare with those of spinal anesthesia?
123. Why does epidural anesthesia differ from spinal anesthesia with respect to systemic local anesthetic toxicity?
124. What are the clinical characteristics of an accidental subdural injection of anesthetic intended for the epidural space?
125. What is the significance of a paresthesia occuring during performance of an epidural anesthetic?
126. What is “combined spinal-epidural” anesthesia, and in what clinical setting is it commonly used?
127. What are the potential advantages of a combined epidural-general technique?
Answers*
1. Spinal and epidural anesthesia are collectively referred to as central neuraxial block. These procedures are subcategories or specific types of regional or conduction anesthesia. (253)
2. In spinal anesthesia, medicine is deposited into the cerebrospinal fluid within the subarachnoid space, with very rare exception at the lumbar level. In epidural anesthesia, the drug is deposited within the epidural space, and is commonly performed at both the lumbar and thoracic level. In caudal anesthesia, medicine is also deposited in the epidural space but the needle used to inject the medicine approaches the epidural space via the sacral hiatus. (253)
3. When compared with epidural anesthesia, spinal anesthesia takes less time to perform, causes less discomfort during placement, requires less local anesthetic, and produces more intense sensory and motor block. In addition, correct placement of the needle in the subarachnoid space is confirmed by a clearly defined endpoint (appearance of cerebral spinal fluid). (253)
4. Advantages of epidural anesthesia include a decreased risk of a postdural puncture headache (assuming a negligible incidence of inadvertent dural puncture), a lower incidence of systemic hypotension, the ability to produce a segmental sensory block, and greater control over the intensity of sensory anesthesia and motor block achieved by adjustment of the local anesthetic concentration. The routine placement of catheters for epidural anesthesia imparts additional benefit by allowing titration of the block for the duration of surgery. Additionally, maintenance of a catheter provides a means for long-term administration of local anesthetics or opioid-containing solutions (or both), which are highly effective for control of postoperative or obstetric pain. (253)
Anatomy
5. On a lateral view, the vertebral canal exhibits four curvatures, of which the thoracic convexity (kyphosis) and the lumbar concavity (lordosis) are of major importance to the distribution of local anesthetic solution in the subarachnoid space. In contrast, these curves have little effect on the spread of local anesthetic solutions in the epidural space. (253, Figure 17-1)
6. The vertebral column is composed of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae, as well as the 5 fused sacral and 4 fused coccygeal vertebrae. (253, Figure 17-1)
7. A vertebra is made up of the vertebral body and the bony arch. The transverse process arises from the junction of the pedicle and laminae. The spinous process arises posteriorly from the joining of the laminae. (253, Figure 17-2)
8. The nearly perpendicular orientation of the spinous process in the lumbar area and the downward angular orientation in the thoracic area define the angle required for placement and advancement of a needle intended to access the vertebral canal. The wide interlaminar space in the lumbar spine reflects the fact that the lamina occupies only about half the space between adjacent vertebrae. In contrast, the interlaminar space is just a few millimeters wide at the level of the thoracic vertebrae. (254, Figure 17-5)
9. The opening between the unfused lamina of the fourth and fifth sacral vertebrae is called the sacral hiatus. There is considerable anatomic variability in the features of the dorsal surface of the sacrum. Indeed, the sacral hiatus is absent in nearly 8% of adult subjects, thereby preventing entry through the sacrococcygeal ligament into the sacral canal and performance of caudal anesthesia. (255, Figure 17-4)
10. Surface landmarks are used to identify specific spinal interspaces. The most important surface landmarks include a line drawn between the iliac crests, which generally traverses the body of the L4 vertebra and is the principal landmark used to determine an appropriate level for insertion of a spinal needle; the C7 spinous process appreciated as a bony knob at the lower end of the neck; and a line drawn between the lower limits of the scapulae roughly correlating with the T7-8 interspace that is often used to guide needle placement for passage of a catheter into the thoracic epidural space. (255, Figure 17-6)
11. The laminae of adjacent vertebrae are connected by the ligamentum flavum. (256, Figure 17-3)
12. The tips of the spinous processes of adjacent vertebrae are connected by the supraspinous ligaments. (256, Figure 17-3)
13. The spinal nerves pass through the intervertebral foramina and supply a specific dermatome. (258, Figure 17-3)
14. The spinal cord begins at the rostral border of the medulla and, in the fetus, extends the entire length of the vertebral canal. However, because of disproportionate growth of neural tissue and the vertebral canal, the spinal cord generally terminates around the third lumbar vertebra at birth and at the lower border of the first lumbar vertebra in adults. As a further consequence of this differential growth, the spinal nerves become progressively longer and more closely aligned with the longitudinal axis of the vertebral canal. (256)
15. The cauda equina—so named because of its resemblance to a horse’s tail—is the collection of lumbar and sacral nerves that extend beyond the end of the spinal cord as a collection of nerves in the spinal canal before exiting via the intervertebral foramina at their respective vertebral column levels. The nerve roots of the cauda equina move relatively freely within the CSF, a fortunate arrangement that permits them to be displaced rather than pierced by an advancing needle. (256)
16. The outermost meningeal layer, the dura mater, is a tough fibroelastic membrane that provides structural support. It originates at the foramen magnum and continues caudally to terminate between S1 and S4. Closely adherent to the inner surface of the dura lies the arachnoid membrane. Though far more delicate than the dura, the arachnoid serves as the major pharmacologic barrier preventing movement of the drug from the epidural to the subarachnoid space. The innermost layer of the spinal meninges, the pia, is a highly vascular structure closely applied to the cord that forms the inner border of the subarachnoid space. (258, Figures 17-9 and 17-10)
17. Cerebrospinal fluid is contained between the pia and arachnoid, consequently referred to as the subarachnoid space. Another term for this anatomic compartment is the intrathecal space. (258, Figure 17-10)
18. The epidural space lies between the dura and the wall of the vertebral canal. It is bounded cranially by the foramen magnum, caudally by the sacrococcygeal ligament, anteriorly by the posterior longitudinal ligament, laterally by the vertebral pedicles, and posteriorly by both the ligamentum flavum and vertebral lamina. (259)
19. Although often referred to as a “potential space,” the epidural space is actually an irregular column of fat, lymphatics, and blood vessels. It is not a closed space but communicates with the paravertebral spaces by way of the intervertebral foramina. (259)
20. The dura, arachnoid, and pia encasement of the peripheral nerve are the origins of the epineurium, perineurium, and endoneurium, respectively. (258, Figure 17-10)
