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Small-Dose Neuraxial Block: Heading Toward the New Millennium

Crowhurst, John A. MD*; Birnbach, David J. MD

doi: 10.1213/00000539-200002000-00002
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Departments of *Queen Charlotte’s Hospital, Imperial College School of Medicine, London, United Kingdom; and †St. Luke’s-Roosevelt Hospital Center, Columbia University College of Physicians and Surgeons, New York, New York

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.

In 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 smaller doses of opioid and local anesthetic than are commonly used (10). The use of neuraxial small-dose opioids alone, or more commonly with small-dose local anesthetic, has become a de facto gold standard for selective neural blockade. In this context, the true selectivity of neuraxial block is readily apparent, with most parturients able to walk, sit, void, and bear down normally. Such ambulatory analgesic blocks are now in common use in many countries (11). 1 Experience with these analgesic blocks is now beginning to reveal that not only are they more rapidly effective and satisfying than epidurals alone, but that the CSE technique offers a truly objective sign of correct placement of the epidural needle—the dural ‘click’ as dura is penetrated (12,13). Several recent clinical series confirm that overall failure rates of CSEs are significantly less frequent than epidurals or single-shot spinals alone, and the rate of accidental dural puncture is likewise decreased (14,15).

The CSE technique is not perfect, but it offers many advantages for both labor analgesia and operative delivery. Although single-shot spinal and conventional epidural anesthesia techniques have their proponents, the popularity of CSE continues to grow. Perhaps, a new spinal microcatheter will eventually become available and replace CSE. But this will only occur if ongoing research (16) proves that they can be safely, economically, and effectively used without fear of cauda equina syndrome, neurotoxicity, broken catheters, or postdural puncture headaches. For now, CSE can be readily used wherever spinals and epidurals are performed, whereas spinal microcatheters are not available in most countries.

Sam Goldwyn, the old movie mogul, said, “Never prophesy, especially about the future.” However, it is doubtful that he would have said this about the future of small-dose neuraxial blockade via CSE. This is one of the new techniques that will lead us into the new millennium.

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FOOTNOTES

1 Rawal N. European trends in the use of combined spinal epidural technique: a 17 nation survey [abstract]. Reg Anesth 1995;20:A162.
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References

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© 2000 International Anesthesia Research Society