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The Effects of Maternal Position During Induction of Combined Spinal-Epidural Anesthesia for Cesarean Delivery

Yun, Esther M. MD; Marx, Gertie F. MD; Santos, Alan C. MD

doi: 10.1213/00000539-199809000-00023
Obstetric Anesthesia

Combined spinal-epidural anesthesia (CSE) is a popular technique for cesarean delivery. Regional blocks in obstetrics are often performed with the parturient in the sitting position because the midline may be recognized more easily than in the lateral decubitus position. When conventional spinal anesthesia is performed in the sitting position, the patient is placed supine immediately after drug injection. In contrast, when CSE is performed with the woman sitting, there is a delay in assuming the supine position because of epidural catheter placement, which may affect the incidence of hypotension. Healthy women, at term of pregnancy, about to undergo an elective cesarean section under CSE, were randomly assigned to the sitting or lateral recumbent position for initiation of the block. All parturients were given 1000 mL of lactated Ringer's solution in the 15 min preceding induction and an additional 300-500 mL while the actual block was being performed. On completion of the CSE, they were turned to the supine position with left uterine displacement. A second anesthesiologist, blinded to the woman's position during CSE, evaluated the sensory level of anesthesia, maternal heart rate, blood pressure, oxygen saturation, need for ephedrine, and occurrence of nausea and vomiting. Results are expressed as mean +/- SD. Twelve women were studied in the sitting group and 10 were studied in the lateral recumbent group. The severity and duration of hypotension were greater in those parturients who had CSE induced in the sitting (47% +/- 7% and 6 +/- 3 min, respectively) compared with the lateral recumbent position (32% +/- 14% and 3 +/- 2 min, respectively). Women in the sitting group also required twice as much ephedrine (38 +/- 18 mg) to correct hypotension compared with the other group (17 +/- 12 mg). In conclusion, the severity and duration of hypotension were greater when CSE was induced in the sitting compared with the lateral decubitus position. Implications: We studied the induction of combined spinal-epidural anesthesia (CSE) in the sitting versus lateral recumbent positions in healthy women undergoing a scheduled cesarean delivery. The severity and duration of hypotension were greater when CSE was induced in the sitting position. Thus, the position used for induction of CSE should be among the factors considered when there is greater maternal or fetal risk from hypotension.

(Anesth Analg 1998;87:614-8)

Departments of (Yun, Marx, Santos) Anesthesiology and (Santos) Obstetrics and Gynecology, Albert Einstein College of Medicine/Montefiore Medical Center, Bronx, New York.

Presented in part at the annual meeting of the Society for Obstetric Anesthesia and Perinatology, Tucson, AZ, May 1-4, 1996 and the Post-Graduate Assembly of the New York State Society of Anesthesiologists, New York, NY, December 7-11, 1996.

Accepted for publication April 29, 1998.

Address correspondence to Dr. E. Yun, Department of Anesthesiology, Jack D. Weiler Hospital, 1825 Eastchester Rd., Brunx, NY 10461.

Of all cesarean sections in the United States, 40% are performed under spinal anesthesia [1]. However, a spinal block has a fixed duration of action, occasionally requiring the systemic administration of adjuvants or even general anesthesia if the operation is unexpectedly prolonged. Because of this and other factors, the popularity of combined spinal-epidural anesthesia (CSE) for cesarean section has increased because it combines the benefits of both techniques. The advantages of CSE are the ease, predictability, and rapidity associated with the spinal component, in conjunction with the ability to provide anesthesia of long duration with the epidural catheter once the initial subarachnoid block begins to recede. In addition, the epidural catheter may also be used for prolonged postoperative analgesia.

Induction of regional anesthesia can be performed with the patient in either the sitting or lateral recumbent position. It has been argued that the sitting position facilitates the technical aspects of performing a block, particularly in the obese patient, because the midline may be easier to recognize [2]. Thus, the sitting position may be preferable for cases in which there is urgency in delivering the infant. However, whereas after conventional spinal anesthesia parturients are immediately placed supine, there is a delay in assuming the recumbent position (because of epidural catheter placement) when CSE is performed in the sitting position. This may increase the incidence of hypotension after intrathecal injection of the local anesthetic. The current study was performed to compare the incidence and severity of hypotension when CSE was induced in the sitting versus the lateral recumbent position.

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Healthy women (GSA physical status I or II) with a singleton gestation who were scheduled for elective cesarean delivery were enrolled in the study, which was approved by our institutional review board. Parturients were asked to participate if their height was between 4[prime]10[double prime] and 5[prime]10[double prime] and they weighed <300 labs. Those receiving antihypertensives or other medications that may affect arterial blood pressure (UP) or heart rate were excluded. Having given their informed consent, the women were assigned to either the sitting (seated perpendicular to the operating room Table withlegs dangling) or the lateral recumbent position for CSE placement using a Table ofrandom numbers. All were given 1000 ML of lactated Ringer's solution via an indwelling IV cannula in the 15 min preceding anesthetic induction. An additional 300-500 ML of crystalloid was infused while the block was being performed. UP, heart rate (JR), and oxygen saturation (SPO2) were monitored before CSE and throughout the operation.

The actual placement of CSE was performed by an attending obstetric anesthesiologist in the same manner regardless of the woman's position. After local infiltration (1% lidocaine), the epidural space was identified at the L2-3 or L3-4 interspace using an 18-gauge Hustead needle and the loss of resistance to air technique. Thereafter, a 24-gauge, 127-mm Gertie Marx[registered sign] needle (International Medical Development, Inc., Park City, UT) was passed through the epidural needle (needle through needle technique), and on free flow of cerebrospinal fluid (CSF), 0.75% hyperbaric bupivacaine 12 mg with fentanyl 10 [micro sign]g was injected intrathecally. The spinal needle was removed and an epidural catheter was inserted 2.5-3 cm into the epidural space and secured with tape. Immediately thereafter, the parturient was placed in the supine position with left uterine displacement. For both groups, a woman was excluded if the time interval from the start of intrathecal injection to placement in the supine position exceeded 3 min.

Once in the supine position, a different anesthesiologist, blinded to the woman's position during CSE placement, evaluated and recorded maternal BP, HR, and level of anesthesia. Cephalad spread of the sensory block to cold and pinprick was assessed at 2-min intervals for 15 min. BP was measured every minute for the first 15 min after the woman was placed supine and every 3 min thereafter. Hypotension was defined as a systolic blood pressure (SBP) <100 mm Hg or a 30% decline from baseline. Ephedrine, in 5-mg increments, was administered by IV injection to treat hypotension. Maternal weight, height, and parity, as well as the total dose of ephedrine used and the occurrence of nausea and vomiting, were recorded. The infant's birthweight was also noted, and the neonatal condition was assessed by using 1- and 5-min Apgar scores.

All data are expressed as the mean +/- SD. Two-way analyses of variance for repeated measures were used to detect statistically significant changes in physiologic variables and oxygen saturation. Student's t-test for unpaired data (or the Mann-Whitney U-test for data not approximating normal distribution) were used to compare the two groups with respect to demographic characteristics, the total dose of ephedrine used, the number of dermatomal segments blocked, and the time to achieve the maximal spread of anesthesia. The incidences of nausea and vomiting were compared using a chi squared test. A P value <0.05 was considered significant. It was estimated that 10 women per group would be required to detect a 20% difference in the maximal percent decrease in SBP using a two-sided t-test (beta = 0.2, [alpha] = 0.05).

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Twenty-seven women were enrolled in the study. Two parturients in the sitting position group and three in the lateral position group were excluded before analysis. In the sitting group, exclusions were due to a violation of the protocol (IV fluid administration totaling 2000 mL before CSE) in one case and to uncontrollable emesis resulting in unreliable BP determinations in the other. In the lateral recumbent group, there was one case of inadvertent dural puncture with the epidural needle, one case of inability to obtain CSF, and one case of uneven spread of the regional block requiring the induction of general anesthesia. Thus, data for 22 parturients were analyzed: 12 in the sitting group and 10 in the lateral recumbent group.

Demographic characteristics of the two study groups are shown in Table 1. There were no significant differences between the groups with respect to maternal age, height, weight, and parity or the infant's birthweight. The blocks were generally accomplished on the first attempt. One parturient in each group required a second pass of the needle to identify the epidural space. A similar number of dermatomal segments (assessed by pinprick) was blocked in both groups (range T3-C7 in the sitting group and T4-C6 in the lateral recumbent group) (Table 2). The mean time interval from intrathecal injection to the highest sensory block achieved was not significantly different between the two groups (Table 2).

Table 1

Table 1

Table 2

Table 2

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.

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The position used for spinal-epidural placement varies among anesthesiologists [3]. 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 [6], although in one study, neither position was deemed to be more comfortable by term parturients [7]. Interestingly, women who favored the lateral recumbent position tended to be leaner than those who preferred the sitting position for the procedure [7]. 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 [8]. The sitting position, however, facilitates identification of midline structures [9] and allows better spinal flexion [10], 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 [11].

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 [12]. 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 [12]. However, a study of spinal anesthesia for cesarean section demonstrated no significant reduction in the incidence of hypotension with IV fluids >10 mL/kg [13].

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 [14]. Furthermore, a greater number of women in the sitting group required reenforcement of the initial subarachnoid block using the epidural catheter [14]. 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 [16]. 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 [17]. Nonetheless, hypotension lasting <4 min is generally well tolerated by the healthy fetus [18].

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 [19]. 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 [20]. 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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