Stoelting Study 12 Epidural B

Front 1

50. Describe the lumbosacral approach to a spinal anesthetic. When is this approach advantageous?

Back 1

50. The lumbosacral approach to a spinal anesthetic involves introducing the spinal needle 1 em medial and 1 em caudad to the posterior iliac spine. The needle is then directed in a medial, caudal direction where the LS-S 1 interspace is accessed. The L5-S1 interspace is generally the largest interlaminal interspace in the vertebral column. This approach, like the paramedian approach, is advantageous when the patient is unable to flex the back.

Front 2

51. What are the three things that most influence the distribution of the local anesthetic solution in cerebrospinal fluid after its administration into the subarachnoid space?

Back 2

51. The three things that most influence the distribution of local anesthetic . solution in the cerebrospinal fluid in the subarachnoid space are the baricity of the solution, the contour of the spinal canal, and the position of the patient during and for the first few minutes after its administration.

Front 3

52. What are the two things that most influence the duration of a spinal anesthetic?

Back 3

52. The two things that most influence the duration of a spinal anesthetic are the drug selected and whether or not a vasoconstrictor is present in the local anesthetic solution, such as epinephrine or phenylephrine.

Front 4

53. What is the relative motor blockade versus sensory blockade that results from the administration of each local anesthetic for spinal anesthesia?

Back 4

53. The administration of local anesthetics in the subarachnoid space may lead to a denser blockade of motor or sensory nerves. For example, bupivacaine motor than sensory blockade. It theoretically follows thllt hllniv~~~ine may motor than sensory blockade. It theoretically follows that bupivacaine may be a more appropriate choice of local anesthetic for spinal anesthesia for lower extremity, vascular, or orthopedic operations. Tetracaine may be a more appropriate choice of local anesthetic for spinal anesthesia for abdominal operations in which skeletal muscle relaxation is necessary to optimize surgical results. Spinal anesthesia that results after the administration of lidocaine is of Slort duration and does not appear to have any preferential blockade of the motor or sensory neJVes. The short duration of lidocaine spinal anesthesia dictates in which surgical cases its use would be appropriate.

Front 5

54. How do spinal anesthetics regress during the recovery from spinal anesthesia?

Back 5

54. During recovery from spinal anesthesia, regression of the anesthetic is from the highest dermatome to a caudad direction.

Front 6

56. How is the baricity of a local anesthetic solution to be administered into the subarachnoid space defined? Why is this clinically important?

Back 6

56. Baricity is a ratio that compares the density of two solutions. The baricity of a local anesthetic solution to be administered in the subarachnoid space is the density of the local anesthetic divided by the density of cerebrospinal fluid at 37°C. Local anesthetics are characterized as hyperbaric, hypobaric, or isobaric relative to cerebrospinal fluid. The clinical importance of knowing the baricity of a local anesthetic solution for administration into the subarachnoid space is that, by understanding the baricity, the medicine can be guided to the desired spinal nerves for a given surgical procedure.

Front 7

57. What is the baricity of the most commonly used spinal anesthetics? What is added to local anesthetics for spinal anesthesia to make the solution byperbaric?

Back 7

57. Most administered spinal anesthetics are hyperbaric. Local anesthetics for spinal anesthesia are made hyperbaric by the addition of dextrose to the solution. Dextrose is added to bupivacaine 0.75% and lidocaine 5% commerdally. A hyperbaric solution of tetracaine can be made by adding 10% dextrose to equal volumes of 1% tetracaine. The resulting solution will be 0.5% tetracaine plus 5% dextrose.

Front 8

58. How do hyperbaric solutions diffuse in the subarachnoid space?

Back 8

58. Hyperbaric solutions diffuse in the subarachnoid space by settling to the most dependent portion of the space. The ma;t dependent portion of the subarachnoid space is contingent on the position of the patient at the time of and shortly after the administration of the local anesthetic.

Front 9

59. Where would the resultant hyperbaric spinal anesthetic block be most dense for a patient seated upright and for a patient supine just after its admilistration?

Back 9

59. A patient given a hyperbaric spinal anesthetic in the seated upright position ). A patient given a hyperbaric spinal anesthetic in the seated upright position level. This type of spinal anesthesia block is appropriate for genitourinary procedures, such as transurethral resection of the prostate. A patient who was placed in the supil1e position just after the administation of a hyperbaric spinal anesthetic would have an anesthetic block that would be most dense at the kyphotic thoracic level, approximately T6. This level of spinal anesthesia is appropriate for an intra·abdominal surgical procedure.

Front 10

60. What can be added to a local anesthetic solution to make it hypobaric?

Back 10

60. Local anesthetics can be made hypobaric by the addition of sterile water to the solution. Another method to achieve hypobaric-like effects is to warm 0.5% bupivacaine. Lidocaine 2% is also believed to have hypobaric-like effects

Front 11

61. How do hypobaric solutions diffuse in the subarachnoid space?

Back 11

61. Hypobaric solutions float in the subarachnoid space, bathing nerves in the nondependent portion of the subarachnoid space. The nondependent portion of the space is contingent on the position of the patient at the time of and shortly after the administration of the local anesthetic.

Front 12

62. What type of procedures might make the administration of a hypobaric spinal anesthetic most convenient?

Back 12

62. The administration of a hypobaric spinal anesthetic is useful in procedures such as a hemorrhoidectomy in the jackknife prone position or hip arthroplasty in the lateral position. in both these cases the hypobaric spinal anesthetic is useful because the patient can be placed in the position necessary to perform the otmtive procedure before the administration of the anesthetic

Front 13

63. What local anesthetic is most commonly administered for isobaric spinal anesthesia?

Back 13

63. The local anesthetic most commonly administered for isobaric spinal anesthesia is 0.5% and 0.75% bupivacaine. Tetracaine can be made isobaric by diluting it with cerebrospinal fluid

Front 14

64. What two vasoconstrictors can be added to local anesthetic solution! to prolong the duration of action of a spinal anesthetic?

Back 14

64. Two vasoconstrictors that can be added to spinal local anesthetic solutions tc prolong heir duration of action are epinephrine and phenylephrine. The dose used for this purpose is 0.1 to 0.2 mg epinephrine or 2 to 5 mg phenylephrinl There are conflicting data regarding which vasoconstrictor produces the greatest prolongation of the duration of a spinal anesthetic.

Front 15

65. What are the two ways in which vasoconstrictors are thought to prolong the duration of action of spinal anesthesia?

Back 15

65. One way in which vasoconstrictors are thought to prolong the local anesthetic duration of action in the subarachnoid space is by causing localized vasoconstriction. The localized vasoconstriction results in decreases in spinal blood flow and therefore a decrease in the vascular absorption of the local anesthetic. This allows the local anesthetic to remain in the subarachnoid space and in contact with the nerves for a prolonged period of time. The second way in · which epinephrine is thought to prolong the duration of action is through antinociceptive action by direct stimulation of spinal cord alpha-adrenergic receptorsw

Front 16

66. What is a concern regarding the addition of vasoconstrictors to local anesthetic solutions for spinal anesthesia?

Back 16

66. A concern regarding the addition of vasoconstrictors to local anesthetic solutions for administration in the subarachnoid space is that t~e vasoconstriction that results might compromise the vascular supply to the spinal cord. I Studies evaluating spinal cord blood flow after the administration of vasoconstrictors to the subarachnoid space in dogs has not shown this to be the case, nor is there known to be any unfavorable outcomes in humans

Front 17

70. What is the temporal order of blockade of the motor, sensory, and sympathetic

Back 17

70. Sympathetic nerves are blocked before both motor nerves and sensory nerves after the administration of a spinal anesthetic. A useful way to gain an early indication of the level of spinal anesthesia is by testing the patient's ability for temperature discrimination in the relevant dennatomes. For example, in an unblocked area an alcohol sponge will produce a cold sensation, whereas in the blocked areas the same alcohol sponge will feel wann or neutraL

Front 18

71. From highest to lowest, what is the dermatomal order of blockade of the motor, sensory, and sympathetic nerves produced by a spinal anesthetic?

Back 18

71. The dermabmal order of blockade produced by a spinal anesthetic, from highest to lowest, is sympathetic nerves, sensory nerves, then motor nerves. Sympathetic nervous system blockade from spinal anesthesia exceeds the level of sensory nerve blockade by at least two dennatomes and sometimes by as many as six dermatomes. For this rea&ln, hypotension may accompany a spinal anesthetic whose sensory level is

Front 19

72. Explain in physiologic terms two reasons why sympathetic nerve fibers undergo I conduction blockade from spinal anesthesia before sensory and motor fibers.

Back 19

72. There are two reasons why sympathetic nerve fibers undergo conduction blockade from spinal anesthesia before sensory and motor fibers. First, the nerves of the sympathetic nervous system are small-diameter, u~elinated fibers, as compared with the larger, myelinated fibers of the sensory and motor nerves. Second, the small-diameter unmyelinated nerve fibers of the sympathetic nerves are closest to the surface of the nerve bundle and hence are the first nerve fibers exposed to the local anesthetic solution.

Front 20

73. Name a useful test for the evaluation of the level of sympathetic nerve blockade

Back 20

73. A useful test for the evaluation of the level of sympathetic nerve blockade is the evaluation of the patient's ability to discern between temperature changes at various levels with an alcohol sponge.

Front 21

74. Name a useful test for the evaluation of the level of sensory nerve blockade.

Back 21

74. A useful test for the evaluation of the level of sensory nerve blockade is the evaluation of the patient's ability to discriminate sharpness produced by an object touching the patient's abdomen or chest at various levels.

Front 22

75. Narne a useful test for the evaluation of the level of motor nerve blockade.

Back 22

75. A useful test for the evaluation of the level of motor nerve blockade is the evaluation of the patient's ability to do various motor tasks, such as dorsiflexion of the foot (Sl-S2), raising the knees (L2-L3), and tensing the abdominal rectus muscles (T6-Tl2). (17S)

Front 23

76. What are the physiologic effects on the respiratory system of an appropriately instituted spinal anesthetic?

Back 23

76. Appropriately instituted spinal anesthesia has little effect on alveolar ventilation when evaluated by arterial blood gases. There is no change in tidal volume, but the expiratory reserve volume may decrease slightly owing to the inability of paralyzec abdominal muscles to perform forced exhalation. Levels of spinal anesthesia that produce paralysis of the abdominal and intercostal muscles can also result in a decrease in the patient's ability to cough and expel secretions. From the perspective of the patient, however, high levels of spinal anesthesia often produce a sensation of difficulty breathing, or dyspnea. This results from decreased sensorY input from the thoracoabdominal muscles during regular breathing. Exaggerated hypoventilation might result after the administration of sedatives to patients who are undergoing surgery with a spinal anesthetic simply because of the lack of external stimulation. The judicious administration of sedatives to these patients is indlcated for these reasons

Front 24

77. What are some physiologic effects on the gastrointestinal tract that can result from a spinal anesthetic?

Back 24

77. When spinal anesthesia results in sympathetic nervous system blockade above T5, the sympathetic nerves that innervate the gastrointestinal tract are blocked. This results in unopposed parasympathetic nervous system activity in the gastrointestinal tract, whose effect may lead to contracted intestines and relaxed sphincters.

Front 25

78. What are the physiologic effects on the genitourinary system of an appropriately instituted spinal anesthetic?

Back 25

78. The effects of sympathetic nervous system blockade on the genitourinary system include contraction of the ureters and relaxation of the ureterovesical orifice.

Front 26

79. What is the adrenocortical response to painful stimulation in a patient when the Surgical site has been anesthetized with spinal anesthesia?

Back 26

79. The adrenocortical response to surgical stimulation that can occur is blocked in a patient whose surgical site is anesthetized by spinal anesthesia. This is a result of the blocked afferent impulses from the surgical site.

Front 27

80. What are some side effects associated with spinal anesthesia?

Back 27

80. Some side effects associated with spinal anesthesia include hypotension, bradycardia, pos~dural puncture headache, total spinal, nausea, urinary retention, backache, neurologic sequelae, and hypoventilation.

Front 28

81. Explain in physiological terms some reasons why a patient may become hypotensive after the sympathetic nervous system blockade that results from the administration of a spinal anesthetic. Which of these is thought to predominate when the hypotension is modest? Which of these is thought to predominate when the hypotension IS severe?

Back 28

81. As a result of the sympathectomy caused by spinal anesthetics, as many as one third of patients receiving a spinal anesthetic become hypotensive with a systolic blood pressure less than 90 nun Hg and 10% to 15% of patients become bradycardic. There are several reasons why hypotension can occur I with spinal a1J.esthesia. First, it may be due to decreases in systemic vascular resistance. Second, it may be due to decreased venous return to the heart and subsequent decreases in cardiac output. Finally, if blockade of the cardioaccelerator fibers occurs, bradycardia results and there are even greater decreases in cardiac output. Blockade of the cardioaccelerator fibers occurs when the dermatomal level of the sympathetic nervous system blockade is at or above the Tl level since the cardioaccelerator fibers originate from Tl to T4. When the hypotension is modest it is probably due to decreases in systemic vascular resistance. When hypotension is severe, it is believed to be due to decreases in cardiac output

Front 29

82. What influences the degree of hypotension that can occur with a spinal anesthetic?

Back 29

82. The degree of hypotension that can accompany a spinal anesthetic is most influenced by the level of spinal anesthesia and the intravascular fluid volume status of the patient

Front 30

83. What are two nonpharmacologic methods that can be used to treat the hypotension that can occur with a spinal anesthetic?

Back 30

83. There are at least two nonpharrnacologic methods that can be used to treat the hypotension that can occur with a spinal anesthetic. One is providing the patient with adequate hydration before administering the spinal anesthetic so . as to minimize the effects of the decreased systemic vascular resistance that results fran the anesthetic. The second is placing the patient in a modest head-down position to provide for an increased venous return of intravascular fluid that may be pooling in the lower extremities. This may not be appropriate in patients who cannot handle the increased intravascular fluid volume load or the dilutional anemia it may cause, such as patients with ischemic cardiac disease and poor cardiac function.

Front 31

84. What pharmacologic methods can be used to treat the hypotension that can occur with a spinal anesthetic?

Back 31

84. Sympathomimetics such as ephedrine or phenylephrine can be administered to treat the hypotension that can occur with a spinal anesthetic. Ephedrine in
doses of 5 to 10 mg intravenously is the preferred method of treatment · because it has positive inotropic as well as venoconstrictor effects, thus correcting the factors responsible for the decrease in blood pressure. Phenylephrine, on the other hand, increases systemic blood pressure by increasing systemic vascular resistance but does not necessarily increase venous return . and may m fact result in a reflex bradycardia. For hypotension that is accompanied with bradycardia, atropine may be administered to increase the heart rate. There are reports of hypotension and bradycardia after a spinal anesthetic leading to asystole that does not respond to atropme. For this reason, when hypotension is not easily reversed with standard treatment the prompt administration of epinephrine must follow.

Front 32

85. What are two potential benefits of the decrease in systemic vascular resistance that accompanies spinal anesthesia for the patient in the perioperative period?

Back 32

85. There are at least two potential benefits of the decrease in systemic vascular resistance that accompanies spinal anesthesia. First, there may be decreased bleeding during certain types of surgery, such as hip surgery. This is a result of the decreases in arterial blood pressure in the surgical areas anesthetized by a regional anesthetic. Second, there is a decreased incidence of thromboembolic complications after hip surgery when a regional anesthetic technique is used. This is believed to be due to the increased blood flow to the lower extremities that results from regional anesthesia.

Front 33

86. Describe the hallmark features of a postdural puncture headache. Which feature of a headache must be present to qualify it as a postdural puncture headache?

Back 33

86. The Hallmark features of a postdural puncture headache include its postural component and the fact that the headache gets worse with sitting or standing and better in the supine position. The headache must have a postural component to be a postdural puncture headache. The second hallmark of the postdural puncture headache is the location of the headache in the frontal or occipital region. Diplopia, tinnitus, and decreased hearing acuity may also accompany a puncture headache

Front 34

87. Give a physiologic explanation for a postdural puncture headache.

Back 34

87. A postdural puncture headache is believed to occur as a result of leakage of cerebrospinal fluid from the hc1e in the dura mater caused by the needle. The loss of cerebrospinal fluid results in decreased ,erebrospinal fluid pressures and less "cushion" around the brain in the skull. This in turn leads to tension on the meningeal vessels and l1erves, causing the headache. It is believed that the diplopia may result from tension on the abducens nerve.

Front 35

88. What are the risk factors for a postdural puncture headache?

Back 35

88. Risk factors for a postdural puncture headache include patient characteristics and procedure technique. Patients most at risk for a postdural puncture headache include patients who are young, female, and, in particular, parturients. With regard to technique, the larger the needle gauge, the cutting spinal needles, and multiple dural punctures all increase the risk. To minimize the risk of a postdural puncture headache the anesthesiologist may select a 25gauge or smaller pencil-point spinal needle.

Front 36

89. What are some conservative treatment methods for a postdural puncture headache?

Back 36

89. Some conservative methods of treatng a postdural pmcture headache include bed rest, analgesics, caffeine, and hydration of 3 L or more a day. Hydration may be via the oral or intravenous route and is intended to exceed the rate at which the cerebrospinal fluid is leaking through the hole in the dura mater. Caffeine intake can be by the oral route or intravenous route. If caffeine consumption orally does not provide any relief, the administration of 500 mg intravenously has been shown to provide some benefit.

Front 37

90. How effective is an epidural blood patch for a postdural puncture headache? How is it thought to work?

Back 37

90. An epidural blood patch is highly effective fOI the treatment of a postdural puncture headache. Over 90% of patients experience relief from their headaches with the administration of the epidural blood patch. A second blood patch will provide relief to over 90% of patients who did not respond to the epidural blood patch on the first attempt. Resolution of a postdural puncture headache after the administration of all epidural blood patch is almost immediate. An epidural blood patch for treatment of a postdural puncture headache is thought to work by providing a "patch" over the hole in the dura mater, thus preventing the further leakage of cerebrospinal fluid through the hole. The sealed dura mater allows for reestablishment of appropriate pressures in the subarachnoid space to support the brain in its confined space, relieving the traction on the meningeal vessels

Front 38

91. Describe the epidural blood patch procedure.

Back 38

91. An epidural blood patch is performed first by having the patient appropriately positioned for an epidural anesthetic. The lumbar epidural space is found using the loss of resistance technique, just as with an epidural anesthetic. ce the lumbar epidural space has been located, 10 to 20 mL of blood is drawn sterilely from the patient's vein, most commonly from a cubital vein. I The blood is then, still sterilely, administered into the lumbar epidural space through the needle. The epidural blood patch is most commonly administered at the interspace o~ one interspace below the interspace at which the dura mater was punctured. Radiographic studies of radiolabeled red blood cells have shown that 15 mL of blood in the epidural space spreads about 9 segments, with the greatest degree of spread in the cephalad direction. An epidural blood patch should be perfonned no sooner than 24 to 48 hours after the du·al puncture to achieve the best results

Front 39

92. How effective is the administration of saline in lieu of blood as an epidural patch in patients with postdural puncture headaches?

Back 39

92. An epidural patch performed with saline is not as effective as an epidural patch perfonned with blood.

Front 40

93. What is a total spinal? How does it present?

Back 40

93. A total spinal anesthetic is a spinal anesthetic whose level of sympathetic, sensory, and motor nerve blockade is higher than intended and results in hypotension and difficulty breathing or apnea. Nausea and agitation may also accompany the difficulty breathing seen in a total spinal. Apnea associated with a total spinal will begin to manifest soon after the deposition of the local anesthetic solution into the subarachnoid space. For those whose level of spinal anesthetic leads to apnea pupils appear dilated.

Front 41

94. What is the physiologic explanation for the apnea that occurs with a total spinal? What level of a total spinal will begin to interfere with breathing?

Back 41

94. A total spinal anesthetic that begins to interfere with breathing is usually a high thoracic level of anesthesia, and it approaches the lower cervical levels. Usually the cervical nerves are spared, as are the nerves to the diaphragm. The physiologic explanation for why a total spinal causes apnea without affecting the phrenic nerves is related to the hypotension caused by the total spinal. The profound hypotension caused by the total spinal results in hypoperfusion of the medullary ventilatory centers along with a decrease in cerebral blood flow

Front 42

95. What is the treatment for a total spinal?

Back 42

95. The treatment for a total spinal anesthetic is supportive. The patient's ventilation can be supported by face mask and hand ventilation with oxygen. The patient's hemodynamic status can be supported by the intravenous administration of fluids and sympathomimetics as indicated. When a total spinal results from the administration of local anesthetic solution in the subarachnoid space, the patient should not be placed in a head-up position in an attempt to i decrease the level of the spinal anesthesia. Placing the patient in a head-up position further decreases venous return and exacerbates the hypotension, jeopardizing cerebral blood flow. This further contributes to hypoperfusion of the medullary ventilatory centers. Instead, patients should be placed in a head-down position :o facilitate venous return to the heart and possibly reverse medullary ischemia. Patients with a total spinal should have their tracheas intubated for ventilatory support if necessary. Tracheal intubation is also indicated if they are at an increased risk of aspiration, as is a parturient.

Front 43

96. What is the duration of a total spinal relative to the duration of the local anesthetic administered ?

Back 43

96. The duration of a total spinal anesthetic is usually short because the concentration of local anesthetic is low at the higher thoracic or lower cervical levels.

Front 44

97. What are two possible causes of nausea that presents soon after the administration of a spinal anesthetic?

Back 44

97. Two pos9ble causes of nausea that presents soon after the administration of a spinal anesthetic include hypotension sufficient to produce cerebral ischemia and predominant parasympathetic nervous system activity on the gastrointestinal tract rtsulting in contracted intestines and relaxed sphincters

Front 45

98. How can the nausea after the administration of a spinal anesthetic be treated?

Back 45

98. The anesthesiologist should suspect possible hypotension when nausea occurs just after the administration of a spinal anesthetic. In these cases the administration of a sympathomimetic may reverse the hypotension and the nausea. Nausea occurring in the absence of hypotension can be treated by the adminisrraton of 0.4 mg of atropine, a muscarinic antagonist, intravenously.