Maternal HR rate and SPO2 at the start of the study were 102 +/- 15 bpm and 100% +/- 0.5%, respectively, in the sitting group. The corresponding values for the lateral recumbent group were 93 +/- 12 bpm and 99% +/- 0.5%. There were no significant changes from control in HR or SPO2 at any time during the study. However, BP was affected by the position used for induction of CSE (Table 2). Before CSE, there were no significant differences between groups in the systolic and diastolic blood pressures-141 +/- 14 and 70 +/- 10 mm Hg, respectively, in the sitting group and 130 +/- 14 and 73 +/- 12 mm Hg, respectively, in the lateral recumbent group. All women had some degree of hypotension. Because hypotension occurred at different time periods in individual parturients, there were no significant differences between the two groups in the mean systolic and diastolic blood pressures at each interval. However, the severity of hypotension, measured by the maximal percent decrease in SBP from control, as well as its duration, were significantly greater in the sitting group (P < 0.05) (Table 2). With the exception of one woman in the lateral recumbent group, all patients required ephedrine to treat hypotension. However, parturients in the sitting group required twice as much ephedrine to treat hypotension than those in the lateral recumbent group (P < 0.05) (Table 2). The incidences of nausea or vomiting were not significantly different between the two positions (Table 2). All infants had an Apgar score >7 at 1 min and >8 at 5 min.
The position used for spinal-epidural placement varies among anesthesiologists . However, proponents of the lateral recumbent position believe that it is associated with a lower risk of orthostatic hypotension and syncope [4,5]. Others suggest that the lateral decubitus position provides greater patient comfort than the sitting position , although in one study, neither position was deemed to be more comfortable by term parturients . Interestingly, women who favored the lateral recumbent position tended to be leaner than those who preferred the sitting position for the procedure . However, inability to perform spinal puncture because of lateral placement of the epidural needle is more common when CSE is performed in the lateral position . The sitting position, however, facilitates identification of midline structures  and allows better spinal flexion , thus making it preferable for obese patients or when technical difficulty in performing the block is anticipated. Furthermore, hypoxemia may develop in morbidly obese parturients in the lateral recumbent position .
The efficacy of IV fluids administered before subarachnoid block has been questioned. In a study in which patients were randomized to receive prehydration (lactated Ringer's solution 20 mL/kg) versus no IV fluid before subarachnoid block for cesarean delivery, the incidence of hypotension was 55% versus 71%, respectively . Despite prehydration before CSE, all parturients in the current study had some degree of hypotension. There are two possible reasons for this. First, the strict adherence to preselected blood pressure criteria resulted in parturients with a SBP decreasing to only 98 or 99 mm Hg being considered as having hypotension. Second, the women in our study received a slightly smaller volume of crystalloid (approximately 15-17 mL/kg) by the time subarachnoid injection was performed, compared with the 20 mL/kg used in the previous study . However, a study of spinal anesthesia for cesarean section demonstrated no significant reduction in the incidence of hypotension with IV fluids >10 mL/kg .
Our data suggest that the position used during induction of CSE for cesarean delivery should not be based solely on patient or physician preferences, because hypotension was more severe and more difficult to treat when CSE was induced in the sitting position. This could not be attributed to differences in the amount of IV fluid administered or the level of sensory block, because these were similar for both groups. Others found that the maximal sensory level is lower and takes longer to achieve when CSE for cesarean delivery is performed with 10 mg of 0.5% hyperbaric bupivacaine . Furthermore, a greater number of women in the sitting group required reenforcement of the initial subarachnoid block using the epidural catheter . In contrast, all of the women in our study had a sensory level of at least T4 and did not require epidural supplementation with local anesthetic or narcotic adjuvants. There was no significant difference between the two positions in the maximal number of dermatomal segments blocked. We may not have detected a statistically significant difference in block height and onset times because of the relatively small number of women studied and the insufficient power of statistical analysis (power in the current study was set to determine differences in the magnitude of hypotension). However, the reason for the apparent differences between the studies with respect to sensory level and onset time could be related to the fact that we used a larger dose of hyperbaric bupivacaine (12 mg). All of the women in our investigation had a sensory level of T4 or greater and would be expected to have a complete sympathectomy. Thus, small differences in block height between groups, even if statistically significant, should not result in greater hypotension. It is also interesting to note that bradycardia did not occur, although the sensory level was at least T4 in every case. Although the reason for this is unclear, it could be related to partial aortocaval compression and the fact that almost every woman required ephedrine.
Parturients were also similar in height and weight. The slightly greater mean maternal weight in the sitting group could be explained by one woman who weighed 280 lbs. This woman did not have a SBP <89 mm Hg at any time during the study. Infant birthweights were also similar in both groups.
The time interval from assuming the initial study position to spinal injection was not measured but could have been important if the legs were left dangling in the sitting position for a long period of time because of repeated attempts at placement of CSE. However, all CSEs were placed quickly, and there was no difference between the two groups in the technical difficulty encountered in initiating the block.
Thus, the reason for the differences in the incidence and severity of hypotension between the two positions is unclear. It could be related to a slower recovery from sympathectomy-induced venous pooling in the lower extremities on assuming the supine position when CSE was initiated in the sitting position. Indeed, others have found the incidence of syncope caused by orthostasis, as well as decreases in cardiac output and uterine blood flow, to be greater in the sitting than in the lateral recumbent position in unanesthetized pregnant women [5,15]. Unfortunately, we did not investigate whether the use of elastic stockings, wrapping of the legs in elastic bandages, or a small-degree head-down tilt would have decreased the severity of hypotension noted in the sitting group.
Nausea and/or vomiting usually accompany maternal hypotension in the interval between induction and delivery of the infant . Although there were no differences in the incidence of nausea and/or vomiting between the two groups, each of the blind observers noted that the severity of vomiting was greater in patients randomized to the sitting group. As previously mentioned, one woman in the sitting group was excluded from the study because of severe vomiting and the unreliability of automated BP determinations. We did not quantify the severity of nausea and/or vomiting using a visual analog scale. However, such measurements may not have been accurate because the patients knew that we were studying the effects of position, and they could have been influenced by past experiences in rating their current symptoms.
Despite the greater severity and duration of hypotension in patients undergoing CSE performed in the sitting versus the lateral recumbent position, all infants had good Apgar scores 1 and 5 min after delivery. This may be explained by the fact that only healthy women who were not in labor and who were presumed to have normal uteroplacental perfusion were enrolled in the study. Furthermore, although the Apgar score is widely used in assessing immediate neonatal condition, it is imprecise in detecting mild to moderate changes in fetal acid-base status. Unfortunately, we did not obtain umbilical cord pH and blood gas tensions at the time of delivery because it is the practice at our institution to obtain these only when the Apgar score is <7 at 1 or 5 min. Others have shown that even brief episodes of mild maternal hypotension can result in small decreases (0.02-0.04 pH units) in umbilical artery pH when regional anesthesia is used for scheduled cesarean section . Nonetheless, hypotension lasting <4 min is generally well tolerated by the healthy fetus .
In the current study, the duration of hypotension was twice as long and patients required more ephedrine in the sitting group (6 +/- 3 min and 38 +/- 17 mg, respectively) compared with the lateral recumbent group (3 +/- 2 min and 17 +/- 12 mg, respectively). Ephedrine is an indirect acting amine that readily crosses the human placenta . The administration of small doses of ephedrine (approximately 20 mg) to the mother results in higher umbilical cord blood catecholamine levels and transient neonatal electroencephalographic effects (a shift to waking state) compared with infants whose mothers were not given the drug . Larger doses of ephedrine have been associated with low umbilical artery pH, although Apgar scores were unaffected [18,21].
In conclusion, hypotension was more severe and more difficult to treat when CSE for cesarean section was induced in the sitting versus the lateral position. Thus, all other factors being equal, the position used for induction of CSE should be considered, particularly in cases associated with greater maternal or fetal risk from hypotension.
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© 1998 International Anesthesia Research Society
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