Chapter 27: Regional Anesthesia
Midazolam is a useful premedication for regional anesthetic procedures because it:
(A) decreases the incidence of hallucinations
(B) elevates the seizure threshold
(C) produces a retrograde amnestic effect
(D) does not interact with anticholinergics
(E) is synergistic with opioids for respiratory depression
The answer is B. The benzodiazepine midazolam is a very common anxiolytic administered prior to regional anesthetic procedures. In addition to being short-acting (half-life of 2 hours) and providing a titratable level of sedation, midazolam produces a dose-dependent anterograde amnesia that can be helpful in eliminating recall during the procedure. However, one of the principal advantages of midazolam is that it is a potent anticonvulsant, raising the seizure threshold and increasing the plasma concentration of local anesthetic required to cause seizures. This is likely to be most valuable in preventing signs and symptoms of mild CNS toxicity. Some have suggested that its use can in fact mask the early premonitory signs of severe toxicity. This has not been evaluated rigorously, and most regional anesthesiologists use midazolam for all of the reasons cited above, including alteration of seizure thresholds.
Ref: Hadzic A. Hadzic's Peripheral Nerve Blocks and Anatomy for Ultrasound Guided Regional Anesthesia, 2nd ed. New York, NY: McGraw Hill; 2012.
Which of the following pairs of spinal levels best identifies where the spinal cord terminates in adults and infants, respectively?
(A) L1 in adults, S1 in infants
(B) L1 in adults, S3 in infants
(C) L1 in adults L3 in infants
(D) L3 in adults, S1 in infants
(E) L3 in adults, S3 in infants
The answer is C. The spinal cord normally extends from the foramen magnum to the level of L1 in adults and L3 in infants and children (Figure 27-1). The dural sac continues for several more levels so that it ends at S1 in adults and S3 in children (these are convenient numbers to remember: L1, L3; S1, S3). Based on this anatomical knowledge, it would be reasonable to suggest that a spinal needle could be safely placed below the L1 level without fear of contacting the conus medullaris of the spinal cord.
FIG. 27-1. Sagittal view through the lumbar vertebrae and sacrum. Note the end of the spinal cord rises with development from approximately L3 to L1. The dural sac normally ends ...