Spinal Anesthesia in the Parturient with Severe Preeclampsia: Time for Reconsideration

In this issue of Anesthesia & Analgesia, Aya et al. (1) report that severely preeclamptic patients experience less hypotension during spinal anesthesia for cesarean delivery than normotensive women. Although individual patients may vary, this study also suggests that adequately prepared preeclamptic women require no more volume preload than normotensive controls to prevent catastrophic hypotension under subarachnoid block. The latter may not apply to women with placental abruption where significant retroplacental hemorrhage may occur. In designing their study, it is notable that only women with severe hypertension, and thus at greatest risk of hypotension from sympatholysis, were enrolled. Furthermore, women who were in labor were excluded because labor itself, due to periodic augmentation of circulating blood volume during rhythmic uterine contractions, has been shown to reduce the incidence of hypotension during regional block for cesarean delivery (2). Aya et al’s study did, however, have several limitations, including that the severely preeclamptic women were not a homogenous group. For instance, women with a mean arterial blood pressure (MABP) greater than 130 mm Hg could be treated at the discretion of the anesthesiologist with antihypertensive medications. This is important for two reasons. First, bias may have been introduced into the study by the potential for aggressive blood pressure reduction in the most hemodynamically severe patients before the induction of subarachnoid block; thus resulting in an apparently lower incidence of hypotension among preeclamptic women as compared with the normotensive group. Although the authors state that there was no significant difference in the percent reduction in MABP between the treated and untreated preeclamptic women, this comparison may have lacked adequate statistical power. Second, there was no standardized protocol for control of blood pressure. For instance, a majority of the treated women were given nicardipine, but some received urapidil. It is important to note that this contrasts with clinical practices in the United States where hydralazine and labetalol are the mainstays of antihypertensive therapy in preeclamptic women. Interpreting hemodynamic responses to spinal anesthesia may be further complicated by the fact that some but not all of the preeclamptic women were also treated with magnesium sulfate. The latter is important because laboratory studies have shown that magnesium may increase the frequency and severity of hypotension under regional block (3). Another potential confounding variable in the Aya et al. study was that preeclamptic women had babies of lower weight than term pregnant controls. A smaller uterine mass may result in less aortocaval compression and potentially decrease the risk of hypotension. Furthermore, the criteria for hypotension were arbitrary and we really do not know what would be an acceptable short-term reduction in MABP in individual patients. In addition, whereas the reduction in MABP was less in preeclamptic as compared with normotensive women, there was no difference between the groups in systolic arterial blood pressure, which is the value that clinicians use at the point of care in making decisions as to whether or not to administer a vasopressor. Hypotension may be deleterious for the fetus as well. Unfortunately, without umbilical cord blood pH, gas tensions, and base excess, it is difficult to determine if the reductions in MABP observed in this study were associated with any adverse fetal effects. Despite its limitations, taken with the results of earlier studies (4,5) and an National Institute of Health Consensus Opinion (6), the current study by Aya et al. indicates that subarachnoid block may be an appropriate anesthetic choice for women with severe preeclampsia having a cesarean delivery. Furthermore, because of its simplicity and rapidity, we also believe that spinal anesthesia should be considered as an alternative to general anesthesia for emergency cesarean delivery in preeclamptic women who have been adequately prepared with judicious amounts of IV preload. This will obviously necessitate the early involvement of the anesthesiologist in the care of the preeclamptic woman but avoiding general anesthesia is important because airway catastrophes remain the leading cause of anesthesia-related mortality in pregnant women (7). The potential for serious airway events may be even greater in preeclamptic women due to increased airway edema/friability and heightened cardiovascular responses to laryngoscopy and intubation (8). In those preeclamptic women who are in labor, it would seem prudent that consideration be given to early placement of an epidural catheter for several reasons. Regional analgesia provides more effective pain relief during labor than systemically administered opioids but without the attendant risks of sedation/obtundation. Although not intended for primary blood pressure control, regional analgesia may attenuate the wide fluctuations in blood pressure, which can be particularly exaggerated in preeclamptic parturients, due to painful uterine contractions. Epidural analgesia also improves placental blood flow in preeclamptic women (9). But perhaps most important, a well-functioning epidural catheter for labor can be rapidly converted to an anesthetic suitable for cesarean delivery, thus precluding the need for general anesthesia (10,11). This is significant because preeclamptic women may be at risk for emergency cesarean delivery due to nonreassuring fetal status, and a preexisting epidural catheter will avoid the need to choose between spinal and general anesthesia. Preeclamptic women, in addition to hypertension, may have reduced platelet count and function. The choice of anesthetic for these women must balance the risk of epidural/spinal hematoma associated with regional anesthesia techniques as compared with the potential for airway catastrophes with general anesthesia. Although there are no studies supporting the practice, intuition leads many anesthesiologists faced with this clinical scenario to choose a spinal anesthetic with a small-gauge needle rather than using a larger gauge needle and catheter required for an epidural block. Indeed, it has been suggested that the overall risk of spinal hematoma in surgical patients is lower, 1:220,000, with subarachnoid block as compared with epidural anesthesia, 1:150,000 (12). In summary, Aya et al. have demonstrated that severely preeclamptic women receiving spinal anesthesia for cesarean delivery are at no greater risk of catastrophic hypotension than normotensive women when using standard spinal doses (1). It is possible that the use of even smaller doses of spinal anesthesia or sequential combined spinal-epidural technique (very small dose local anesthetic for the initial spinal component followed by epidural supplementation as required) may reduce the incidence of hypotension in severely preeclamptic women even further (13). Does the parturient with severe preeclampsia benefit from spinal anesthesia? Probably. Do these patients have a lower incidence of hypotension following spinal anesthesia? Further investigation will be necessary to answer this question, as well as to better understand the compensatory mechanisms that might be responsible for a decreased incidence of hypotension.