Small-dose neuraxial block: heading toward the new millennium.

Abstract

I n this issue of Anesthesia & Analgesia, Vercauteren et al. (1) report that a single IV dose of 5 mg of ephedrine decreases the occurrence and severity of postspinal hypotension in women undergoing cesarean delivery. Although the many anesthesiologists who are accustomed to using much larger doses of ephedrine to treat or prevent hypotension during cesarean delivery may be surprised by this finding, it should be emphasized that these authors used a much smaller dose of spinal anesthetic than is usual, as part of a combined spinal-epidural (CSE) technique. The prevention of hypotension associated with spinal anesthesia for cesarean delivery is an important goal that merits study. The debates regarding the use of colloid versus crystalloid and the optimal intravascular volume of preload to prevent hypotension continue to rage. Unless current practice changes, however, this study will not resolve these controversies, because these findings are limited to patients who receive much smaller doses of spinal local anesthetic than commonly administered for cesarean delivery. It is possible, however, that as the CSE technique for cesarean delivery increases in popularity and smaller doses of spinal agents are used, hypotension and its sequelae will disappear, as will the debates about its prophylaxis and treatment. Winston Churchill once said, “The further backward you look, the further forward you can see.” However, to foresee the techniques of neuraxial blockade, which will take us into the new millennium, one needs to go back less than 20 yr to the classic observations of Wang et al. (2) and Behar et al. (3) that neuraxial opioids were effective analgesics in humans. These reports opened a remarkable chapter of development of small-dose local anesthetic neuraxial blockade techniques. The introduction of fine-gauge, pencil-point spinal needles in the 1980s led several researchers to rediscover the CSE technique, first used successfully for surgical anesthesia in the 1920s (4) and reported in Anesthesia & Analgesia in 1937 (5). The article by Vercauteren et al. (1) published in this issue is a further illustration of the advantages of this exciting technique. At first sight, readers might conclude that here is yet another study illustrating the successful antagonism of unwanted effects of sympathetic blockade using prophylactic ephedrine. However, prophylactic ephedrine has been used before, and results have been disappointing (6). Why have these authors discovered a dramatic decrease in the incidence and severity of hypotension after such a small dose of ephedrine? The answer lies in the fact that these authors were able to achieve satisfactory anesthesia with a fraction of the spinal local anesthetic dose that is currently used for this surgery (7). It appears that hypotension occurs less frequently and is easier to treat if less spinal drug is administered. This study illustrates clearly how surgical anesthesia to the upper thoracic levels is readily achievable when small doses of intrathecal bupivacaine (6.6 mg) are combined with an opioid. Although not reported in the study, any deficiencies in the extent of the block were readily corrected with small incremental doses of epidural local anesthetic. Such is an advantage of the CSE method. If this small-dose spinal anesthetic were used as part of a single-shot spinal technique, there would be no way to easily remedy an inadequate level. After the application of a CSE technique, the epidural catheter is available, should this task become necessary. The use of CSE in this sequential fashion was first reported by Rawal (8) in 1988. Subsequent refinements and clinical studies have led to the CSE method’s being used increasingly for many types of surgical and obstetric anesthesia (9). In addition to its use in providing surgical anesthesia for orthopedics and cesarean delivery, CSE has achieved remarkable popularity for labor analgesia, proving very successful even with Accepted for publication October 20, 1999. Address correspondence and reprint requests to David J. Birnbach, MD, Department of Anesthesiology, St. Luke’s-Roosevelt Hospital Center, 1000 Tenth Ave., New York, NY 10019.