Subarachnoid

Question 1

State two other names for spinal anesthesia.

Answer 1

(1) Subarachnoid and (2) intrathecal. [Reese, Clinical Techniques of Regional Anesthesia and Spinal and Epidural Blocks, p6]

Question 2

Between which two meningeal layers is a local anesthetic administered for a spinal?

Answer 2

Between the pia and the arachnoid. [Millen Antes, 1994, pp1506‐1607]

Question 3

A line drawn between the left and right iliac crest crosses the spine of what lumbar vertebra?

Answer 3

The fourth. [Stoelting and Miller, Basics, 1994, p167]

Question 4

What is the highest curve of the spinal column in the supine position?

Answer 4

The highest curve of the spinal column in the supine position is at the apex of the lumbar curve (L3‐L4). [Davison, Eckhardt, and Perese, Mass Geni, 1993, p20]

Question 5

Where is the largest interlaminar interspace of the vertebral column found? The approach using this interspace to the subarachnoid compartment is avariation of what approach?

Answer 5

The LS-Sl interspace is the largest interlaminar interspace of the vertebral column. This lambosacral approach to the subarachnoid space is a variation on the paramedian approach. [Miller, Anes, 1994, p1516; Stoelting and Miller, Basics, 1994, pp346, 351]

Question 6

Name six structures traversed by the needle for midline spinal anesthesia?

Answer 6

(1) The skin and subcutaneous tissue, (2) the supraspinous ligament, (3) the interspinous ligament, (4) the ligamentum flavum, (5) the dura, and (6) the arachnoid. [Miller Anes, 1994, pp1506~1507]

Question 7

What is the last structure the needle passes before entering the epidural space?

Answer 7

The ligamentum flavum. [Morgan and Mikhail, Clin. Anes, 1996, p230; Stoelting and Miller, Basics, 1994, p173]

Question 8

As the needle is being inserted for subarachnoid block, you feel a pop. What has occurred?

Answer 8

The dura has been penetrated. Penetration of the dura produces a subtle “pop” that is most easily detected with pencil‐point needles. [Barash, Clin. Anes., 2001, p693]

Question 9

⚡️Name the common spinal needles shown in the figure below.

Answer 9

⚡️A: Sprotte B:Whitacre C:Greene D: Quincke.

[Brown, Atlas of Regional Ane5., 4e. 2010; Barash, Clin. Anes., 6th. 2009]

Question 10

⚡️Identify which common spinal needles are pencil-point, which are cutting, and which are non-cutting.

Answer 10

⚡️Sprotte and Whitacre Spinal needles are pencil-point, Quincke (and Pitkin) are cutting spinal needles, and the Greene is a non-cutting needle. [Hadzic, Reg. Aries, . 2007 p211f;]

Question 11

The patient will be “sympathectomized” when local anesthetic reaches what level after spinal or epidural anesthesia?

Answer 11

Sympathetic outflow will be completely interrupted when local anesthesia spreads up to T1 or higher. [Authors]

Question 12

Where do local anesthetics work after administration into the intrathecal space?

Answer 12

Local anesthetics work on the spinal nerve root, spinal nerve rootlets and the spinal cord. [Barash, Clin. Anes., 1997, p660]

Question 13

⚡️What is the result of blocking each of the nerve fiber types (B, C, A-delta, A-gamma, A-beta, A-alpha)?

Answer 13

⚡️B fibers—venodilation with hypotension; C fibers and A-delta fibers—loss of pain and temperature; A-gamma—loss of muscle tone; A-beta—loss of motor function and proprioception (position sense); A-alpha—loss of motor function and proprioception (position sense). [Barash, Clin. Anes, 1997,p415;Miller,Aries, 1994,p493]

Question 14

⚡️What nerve fibers are responsible for proprioception (position sense)?

Answer 14

⚡️Proprioception is conveyed by A-alpha and A-beta fibers. [Stoelting, PPAP, 4e. 2006 p673t; Nagelhout 81Plans, N A , 4c. 2009 p1049; Barash, Clin. Aries, 6th. 2009 p533t; Miller, Anes., 7e. 2009 p917t; Boron & Boulpaep, Mea1 Physiol, 26. 2009 p319t; Hall & Guyton, T M P, 12th. 2011 p563]

Question 15

The mechanism(s) of differential block of sensory and motor nerve fibers by local anesthetics is a controversial topic, at best. State the clinical progression
of fiber block and list 6 mechanisms that contribute to the differential block produced by local anesthetics.

Answer 15

The clinical progression of differential nerve block by local anesthetics, from first blocked
to last blocked, is autonomic fibers, sensory fibers and motor fibers. At least 6 factors contribute to differential nerve block by local anesthetics: (1) the anatomic and geometric arrangement of the individual fibers in a nerve bundle; (2) the size (diameter) of the individual nerve fibers; (3) the inherent impulse activity (firing rate, frequency) of the individual nerve fibers; (4) the variability in longitudinal spread of agent along the nerve fibers; (5) the effects on ion channels other than the sodium channel, and (6) the choice of local anesthetic. Sensory nerve fibers fire more often than motor fiber and this may explain to a large extent why sensory fibers are blocked before motor nerve fibers (Nagelhout). [Stoelting 8t Miller, Basics, 5e, 2007, p128; Nagelhout 8rZaglaniczny, N A , 3e, 2004, p128, Barash, Clin. Aries, Sc. 2006, p456]

Question 16

What nerves are least likely to be blocked during spinal anesthesia?

Answer 16

A‐alpha fibers are most difficult to block, A‐beta next most difficult, and A-gamma next most difficult. Recall that B-fibers are easiest to block. [Hurford et al, Mass G e n , 1998, p245; Authors]

Question 17

What sensations are lost first after injection of a spinal anesthetic?

Answer 17

The first sensations to be lost are pain and temperature which are carried by C and A‐delta fibers. [Stoelting and Miller, Basics, 1994, p75]

Question 18

The sympathetic response to spinal anesthesia occurs because local anesthetics act on what neurons?

Answer 18

The sympathetic outflow is inhibited during spinal anesthesia because local anesthetics are blocking conduction in sympathetic preganglionic efierents. [Authors]

Question 19

Why does the blood pressure fall with spinal anesthesia?

Answer 19

Venodilation leads to a decrease in cardiac output. Sympathetic nervous system blockade produces venodilation and venous pooling, with a subsequent decrease in venous return (preload), decreased cardiac output, and decreased arterial blood pressure. During a spinal block, systemic vascular resistance is only slightly decreased. With high spinal block (T1-T4), bradycardia can contribute to the hypotension. [Stoelting and Miller, Basics, 1994, p171]

Question 20

What reflex best explains bradycardia during spinal anesthesia?

Answer 20

The Bainbridge reflex relates to the characteristic but paradoxical slowing of the heart rate seen with spinal anesthesia. The usual mechanism given for bradycardia with spinal anesthesia is blockade of the sympathetic efferents from T1-T4 (cardioaccelerator fibers) with subsequent unopposed parasympathetic stimulation (bradycardia). However, bradycardia during spinal anesthesia is more clearly related to the development of arterial hypotension than to the height of the block. The primary deficiency in the development of spinal hypotension is a decrease in venous return. The reduced venous pressure is sensed by low pressure venous baroreceptors, resulting in a reflex bradycardia. [Barash, Clin. Anes., 4e, 2001, p281]

Question 21

What are the two most common physiologic changes associated with spinal anesthesia?

Answer 21

Hypotension and bradycardia. [Barash, Clin. Anes., 1997, p661; Duke and Rosenberg, Secrets, 1996, p431]

Question 22

What effect does spinal anesthesia have on the intestines? Why?

Answer 22

Spinal blockade above T5 inhibits sympathetic nervous system innervation of the gastrointestinal tract, which results in contracted intestines and relaxed sphincters and increased peristalsis. The parasympathetic nervous system is unopposed. [Stoelting and Miller, Basics, 1994, p171]

Question 23

Spinal anesthesia is administered and the patient reports tingling in the little finger of the right and left hand. What is the level of block?

Answer 23

Dermatome charts show that sensory block is at C8 if the little finger and ring finger have abnormal sensation. Note: Sensory block at C6 results in paresthesia of the thumb and index finger, and sensory block at C7 results in paresthesia of the middle fingers. [Stoelting, PPAP, 1999, p597; Morgan and Mikhail, Clin. Anes., 1996, p883]

Question 24

The patient complains of numbness of the fingers and thumb with a subarachnoid block. What level is the anesthetic?

Answer 24

C6, C7, C8. [Stoelting and Miller, Basics, 1994, p165]

Question 25

What level of spinal block would be appropriate for a patient with kidney pain?

Answer 25

The kidneys receive sensory innervation from spinal levels T10-L1/L2, therefore ablock to T10 ‐ L1 is usually sufficient for kidney pain relief and referred pain to the kidneys. [Miller, Anes., 5th ed. 2000, p1935t; Morgan, Mikhail, and Murray, Clin. Anes., 36ed. 2002, pp312, 693‐694]

Question 26

A patient received a subarachnoid block for a TURP. What dermatome level needs to be reached?

Answer 26

T10 sensory level. [Barash Handbook, Clin. Anes , 1997, p517]

Question 27

Spinal anesthesia to what dermatome level would be required for testicular surgery?

Answer 27

T10 sensory level. [Iaffe and Samuels, Anesthesiologist Manual of Surgical Procedures, 1994, p576; Stoelting and Miller, Basics, 1994, p170]

Question 28

Spinal anesthesia to what dermatome level would berequired for lower abdominal surgery? Upper abdominal surgery?

Answer 28

T6 for lower abdominal and T4 for upper abdominal. [Stoelting and Miller, Basics, 1994, p170]

Question 29

Blockade to which spinal segments will take away urinary bladder tone and inhibit the reflex to void?

Answer 29

Blockade of lower lumbar and sacral spinal segments (S2‐S4) will take away urinary bladder tone and inhibit the reflex to void. [Morgan, Mikhail, and Murray, Clin. Anes, 3eed. 2002, p261]

Question 30

Compared with the level of sensory block associated with spinal anesthesia, motor blockade and sympathetic blockade occurs where?

Answer 30

Motor blockade occurs 2-3 segments lower than sensory block and sympathetic blockade 2‐6 segments higher than sensory block. [Millen Aries, 1994,p1519]

Question 31

The surgical procedure requires a tourniquet on the lower extremity. What is the minimum sensory level required for cutaneous anesthesia in this case?

Answer 31

For a procedure requiring a tourniquet on the lower extremity, a minimum sensory level of T8 is required for adequate cutaneous anesthesia. NB : Nagelhout states: “high-quality block of sacral roots is more important than thoracic sensory level…” [Hurford, Clin. Anes. Mass Gen, 6e, 2002, p232t; Nagelhout 8t Zaglaniczny, N A , 3e, 2004, pp908‐910]

Question 32

Explain why a patient with a sensory block to T5 has a heart rate of 50 after producing a subarachnoid block?

Answer 32

Sympathetic block can be 2 to 6 dermatomes higher that sensory blockade. Since the cardioaccelerators arising from T1-T4 can be blocked when sensory block is at the T5 level, a decrease in heart rate can occur. [Barash, Clin.Anes., 1997,p661;MorganandMikhail,Clin.Anes., 1996,p227]

Question 33

⚡️Define barbotage.

Answer 33

⚡️Barbotage is a method of spinal anesthesia in which a portion of the anesthetic solution is injected into the cerebrospinal fluid, which is then aspirated back into the syringe and reinjected, sometimes repeating the process. With modern thin spinal needles, barbotage is diflicult because of the very slow flow rates through the needle and difficulties in aspirating large volumes. [Cousins, Neural Blockade, 4e. 2009 p221]

Question 34

As fluid is aspirated after placement of the needle for spinal anesthesia, blood-tinged cerebrospinal fluid appears first and is followed by clear cerebrospinal fluid. What should you do?

Answer 34

If blood-tinged cerebrospinal fluid is followed by clear cerebrospinal fluid, proceed with the spinal anesthetic. The blood probably was derived from tissue damage during needle insertion. [Stoelting and Miller, Basics, 1994, p167; Miller, Anes, 2000, p172]

Question 35

As fluid is withdrawn during placement of the needle for spinal anesthesia, blood-tinged cerebrospinal fluid appears in the hub of the needle initially. If blood‐tinged cerebrospinal fluid continues to flow, what should you do?

Answer 35

If blood-tinged cerebrospinal fluid continues to flow, remove the needle and reinsert it at a different interspace. [Stoelting and Miller, Basics, 1994,p167]

Question 36

After withdrawing blood-tinged cerebrospinal fluid during placement of the needle for a spinal anesthetic, the needle is withdrawn and reinserted at a different interspace. Blood-tinged fluid is seen again. What should you do?

Answer 36

Should blood-tinged cerebrospinal fluid persist after reinserting the needle at a different interspace, terminate the attempt to produce spinal anesthesia and further evaluate the patient. [Stoelting and Miller, Basics, 1994, p167]

Question 37

How is the baricity of alocal anesthetic determined?

Answer 37

The measure of baricity is specific gravity. Specific gravity is the density of the local anesthetic solution divided by the density of CSF at 37° C. [Stoelting and Miller, Basics, 1994, p168; Barash Handbook, Clin. Anes, 1997, pp343‐345]

Question 38

What is the specific gravity of cerebrospinal fluid (CSF)? What are the specific gravities of hypobaric and hyperbaric solutions?

Answer 38

The specific gravity of CSF is 1.003‐1.008. If the specific gravity of a solution is less than 1.003 it is hypobaric, and if greater than 1.008 it is hyperbaric. [Morgan and Mikhail, Clin. Anes , 1996, p224; Authors]

Question 39

How is a hypobaric anesthetic solution prepared? How is an isobaric solution prepared? How is a hyperbaric solution prepared?

Answer 39

Local anesthetic is mixed with : (1) sterile water to make a hypobaric solution, (2) CSF or a commercially prepared solution to make an isobaric solution, and (3) an equal volume of 10% dextrose to make a hyperbaric solution. [Stoelting and Miller, Basics, 1994, p169]

Question 40

Why is dextrose added to spinal drugs?

Answer 40

To make the solution hyperbaric. Dextrose makes the specific gravity of the solution to be injected greater than the specific gravity of the spinal fluid. [Davison, Eckhardt, and Perese, Mass G e n , 1993, p193]

Question 41

The anesthetic level reached after subarachnoid block is determined by what four factors?

Answer 41

Distribution of local solution in CSF is principally influenced by (1) baricity of the solution; (2) concentration (increasing concentration will increase the spread); (3) contour of the spinal canal; (4) position of the patient in the first few minutes after placement of drug into subarachnoid space. [Stoelting and Miller, Basics, 1994, p168; Barash Handbook, Clin. Anes, 1997,pp343‐345]

Question 42

What factor most influences the level of block achieved with ahyperbaric spinal?

Answer 42

Position. Since a hyperbaric solution is heavier than CSF, hyperbaric spinal solution settles to the dependent aspect of the subarachnoid space which is determined by position. [Stoelting and Miller, Basics, 1994, p169]

Question 43

State the maximum dose (mg) of agent for spinal anesthesia with lidocaine, bupivacaine, ropivacaine, or tetracaine.

Answer 43

Maximum doses of local anesthetics, in milligrams, typically used for spinal anesthesia are: lidocaine—60 mg; bupivicaine—9‐15 mg; ropivacaine—15-22.5 mg; and, tetracaine—hypobaric is 10 mg, hyperbaric is 12mg, and isobaric is 15mg. [Hurford, Clin. Anes. Mass Gen, 6e, 2002, pp2267227t]

Question 44

Why do relatively small amounts of local anesthetic produce profound blockade when administered intrathecally?

Answer 44

Spinal nerve roots are bathed in cerebrospinal fluid making them readily accessible to injected local anesthetics. [Barash, Handbook, Clin. Anes., 1997, p348]

Question 45

Of the local anesthetics administered intrathecally, which produces the most profound motor block?

Answer 45

Tetracaine produces the most profound motor block when administered intrathecally. [Barash, Clin. Anes., 1997, p433]

Question 46

What type of drug is injected with local anesthetics to prolong their action? Why?

Answer 46

Drugs that have alpha-1 adrenergic agonist properties (phenylephrine or epinephrine) are injected with local anesthetics to prolong their action. Alpha-1 agonists produce vasoconstriction, which slows the washout of local anesthetic from the injection site. [Barash, Clin. Anes, 1997, p660]

Question 47

What vasopressor would be safest to use on patients with coronary artery disease during epidural anesthesia? Why?

Answer 47

Phenylephrine, a pure alpha-adrenergic agonist might be appropriate. Absorbed phenylephrine will not directly stimulate the heart. In contrast, if epinephrine (an alpha and beta-receptor agonist) were given, beta-1 receptor stimulation of the heart might occur. [Authors]

Question 48

At what level is the spinal anesthetic usually injected? Why is local anesthetic injected at this level?

Answer 48

Spinal anesthetic is usually injected between L3 and L4 or L4 and L5 vertebral interspaces. The spinal cord is not in danger of needle trauma when local anesthetic is injected below the conus medullaris, which ends at L1-L2 in adults. [Miller, Anes, 1994, p1514; Stoelting and Miller, Basics, 1994,p67]

Question 49

What is the duration of action of lidocaine used for spinal anesthesia with and without epinephrine?

Answer 49

For spinal anesthesia, the duration of sensory block by lidocaine is 45-60 minutes without epinephrine and 60‐90 minutes with epinephrine. [Stoelting and Miller, Basics, 1994, p169; Miller, Anes, 1994, p1526]

Question 50

Assessment of subarachnoid (spinal) blockade should begin how long after the local anesthetic is injected?

Answer 50

Five minutes are allowed to elapse before the anesthesia block is tested. [Brown, RegionalAnes. eivAnalg., 1996, p333]

Question 51

The adequacy of the blockade after administering local anesthetic into the subarachnoid space is assessed how?

Answer 51

Inability to raise the leg is a good indicator of motor block in the lumbar dermatomes. For sensory block (analgesia), a dull needle (pinprick) is used at the operative site. The pinprick is advanced cephalad (headward) up the back until a sharp sensation is elicited. This sensation should be equivalent to the sensation elicited by a pinprick at a high, unanesthetized dermatome such as C4. The dermatome immediately caudad to the dermatome in which the sharp sensation is elicited is the dermatome representing the highest level of analgesia. Main point: Analgesia is assessed with apinprick. [Brown,RegionalAries. e’r Analg, 1996,p333]

Question 52

How long does it take for subarachnoid block to reach its highest (most cephalad) level? What is the significance of this?

Answer 52

Subarachnoid (spinal) block usually reaches its highest level 20 minutes after spinal injection, although the level may move cephalad for 30 minutes. Knowing when analgesia reaches its highest (most cephalad) level is significant because if the level of analgesia is above T5, the probability of hypotension and bradycardia increase. [Brown, Regional Anes. e’r Analg, l996,p333]

Question 53

When performing an epidural, what should alert the anesthetist to the fact that an intrathecal (subarachnoid) injection has occurred?

Answer 53

A profound motor block and sensory block (numbness in hands,for example) soon after an intended subarachnoid injection should alert the anesthetist to the fact that asubarachnoid injection has occurred. The next signs and symptoms suggesting subarachnoid injection are associated with high spinal or total spinal anesthesia: (1) dyspnea caused by absence of proprioceptive input from afferent nerves of the abdominal and intercostal muscles; (b) respiratory arrest if the block spreads to the cervical segments (C3, C4, and C5 blocked so the diaphragm becomes paralyzed); and (3) if high concentration of local anesthetic reaches the cranium, total neural paralysis leads to loss of consciousness, respiratory arrest, and hypotension. [Brown, Regional Anes. (“a Analg, 1996, p454; Longnecker, Tinker and Morgan, Prin. Pract. of Aesth, 1998, p1404]

Question 54

During anepidural block the patient’s blood pressure drops precipitously to 80/35, the heart rate falls to 50 bpm, and Sa02 falls to 85%. What has probably happened?

Answer 54

Severe hypotension, bradycardia, and respiratory insufficiency during an epidural block are signs and symptoms of subdural injection of the anesthetic agent. You have noticed that these are the same signs and symptoms of a “high spinal,” that is, sympathetic block with unopposed parasympathetic effects. Other possible signs and symptoms of a subdural injection include patchy and markedly asymmetric extensive spread of analgesia. (Morgan, et al., Clin. Aries, Be. 2002 p277; Cousins & Bridenbaugh,NeuralBlockade,36. 1998p303]

Question 55

What are seven absolute contraindications to spinal anesthesia?

Answer 55

(1) Patient refuses or is uncooperative. There is: (2) infection at site of injection, (3) high intracranial pressure, (4) a clotting defect or anticoagulation problem (coagulopathy), (5) a brain tumor, (6) spinal cord disease, and (7) severe hypotension. [Miller, Anes, 1994, p1506]

Question 56

Why is a spinal anesthetic contraindicated in a patient with increased intracranial pressure?

Answer 56

A spinal block in a patient with increased intracranial pressure can predispose the patient to brain stem herniation. [Miller, Anes, 1994, p1506]

Question 57

What are the two main differences between spinal and epidural anesthesia?

Answer 57

(1) The onset of sympathetic block is slower with epidural, so the likelihood of abrupt hypotension is lessened. (2) Sympathetic block is at the same level assensory block for epidural anesthesia (compared with 2‐6 segments higher for spinal) and motor block is 4 segments lower than sensory block for epidural anesthesia (compared with 2 segments lower for spinal). [Stoelting and Miller, Basics, 1994, p175]

Question 58

How does the half‐life of a local anesthetic administered intrathecally compare with the half-life when administered epidurally?

Answer 58

Half‐life is the time it takes for the amount of drug in the body to fall by one‐half. The site of injection from which the local anesthetic washes out fastest will be the site which gives the drug the shortest half-life. Hence, the half‐life of alocal anesthetic is longer when injected intrathecally compared with epidurally. [Authors]