Spinal anesthesia is frequently the preferred technique for parturients requiring cesarean delivery. In an effort to prevent pooling of the local anesthetic onto the left side of the parturient who is positioned with left uterine displacement, the right lateral (RL) decubitus position is generally preferred to the left for the induction of spinal anesthesia for cesarean delivery (1–6). Russell (7) compared the injection of hypobaric bupivacaine in the RL and left lateral (LL) positions and found that more patients in the LL group required postural manipulation and intraoperative analgesic supplement than the RL group. Although hyperbaric bupivacaine is currently the most commonly used drug (2), there are no randomized controlled trials to compare the effect of RL and LL decubitus position on its intrathecal spread in obstetric patients. We hypothesized that the use of the LL decubitus position for the induction of spinal anesthesia might lead to pooling of hyperbaric bupivacaine onto the left side of the body. Primary outcomes were the loss of cold sensation at the fourth thoracic dermatome (onset time), the maximum sensory level to loss of cold and sharp pinprick sensation, and the time taken to achieve them. Secondary outcomes were the intraoperative hemodynamic status, the amount of ephedrine required, and fluid administered.
The study was performed with the approval of the local institutional ethics committee and written informed consent was obtained from all parturients. Sixty ASA physical status I parturients with singleton full-term pregnancy presenting for elective cesarean delivery under spinal anesthesia were recruited. The parturients were assigned to the RL or LL decubitus position group for performance of the block using a random number table. Those with a history of injuries, diseases, or previous surgery affecting the spinal cord or vertebral column were excluded. The anesthetic management was standardized apart from the parturient position during intrathecal injection. As per customary practice at this institution, premedication with 2 separate doses of ranitidine 150 mg orally the night before and on the morning of surgery and 30 mL 0.3 M sodium citrate orally on arrival at the operating room were used. A 16-gauge IV cannula was inserted, and each parturient received an IV crystalloid fluid preload of 10 mL/kg before induction. Monitoring consisted of continuous electrocardiogram, pulse oximetry (Spo2), and intermittent noninvasive blood pressure. A 27-gauge Whitacre needle (Becton Dickinson, Franklin Lakes, NJ), with the side-hole facing cephalad, was used for midline dural puncture at the L3-4 intervertebral space. The needle was inserted perpendicular to the skin and any deviations in the order of 10 degrees were noted. Hyperbaric bupivacaine (2.2 mL, 0.5%) and 15 μg of fentanyl at room temperature were given over a period of 15 s without barbotage. Parturients were then immediately laid supine and the bed was tilted 20 degree to the left as measured by a protractor to reduce the risk of aortocaval compression. Surgery was commenced once the loss of cold sensation at T4 was reached bilaterally. Blood pressure was monitored every minute until the baby was delivered and then every 3 min until completion of surgery. The mother was returned to the supine position after delivery, and the total duration of LL tilt was recorded. Five international units (IU) of oxytocin was given IV, with or without an infusion of 8 IU/h depending on uterine tone. A blinded observer assessed the extent of sensory blockade bilaterally at 5-min intervals for 30 min. These levels were determined by loss of cold sensation to ice and by loss of sensation to sharp pinprick. The time from injection of local anesthetic to achieving bilateral loss of cold sensation at the fourth thoracic dermatome (T4) was defined as the onset time. Hypotension, defined as a systolic blood pressure <100 mm Hg or 20% less than baseline, was treated with ephedrine and IV fluids. Surgical operating conditions and the incidence of intraoperative complications (e.g., nausea, vomiting, shivering, pain) were noted. IV fentanyl 50 μg could be given for any intraoperative discomfort after delivery of the fetus. Nausea and vomiting were treated with IV metoclopramide 10 mg once hypotension had been excluded. All parturients were followed up the next day for postdural puncture headache, backache, pruritus, or urinary retention.
Power analysis (Sample Power R1.0 by SPSS, Chicago, IL) was based on the result of an earlier study using hypobaric bupivacaine (7) in which the within group standard deviation for the mean maximum sensory level was approximately 2–3 dermatomes. Assuming the same standard deviation for our study, we calculated that a total sample size of 60 would give our intended study a 96.8% power to detect a difference of 3 dermatomal levels at the 5% significance level. Statistical analysis was performed using SPSS (version 9.0, SPSS, Chicago, IL). Unpaired Student’s t-tests were used for continuous and Fisher’s exact test for discrete variables. Nonparametric data were analyzed using the Mann-Whitney U-test. The Kaplan Meier test was used for survival analysis.
Demographic data and physical factors, including weight, height, needle angle, and room temperature, that might have influenced the intrathecal spread of bupivacaine were similar for the two groups (Table 1). More parturients in the LL group acquired a loss of cold sensation at the fourth thoracic dermatome at 5 min after the intrathecal injection on the right (87% versus 57%, P = 0.01) and left side (90% versus 63%, P = 0.015) of the body. However, all parturients obtained a T4 level by 15 min (Fig. 1). There was no delay in the commencement of surgery as this was within the time taken for urinary catheterization and draping. The maximum upper sensory levels to loss of temperature and sharp pinprick sensation on both sides of the parturients, and the time required to achieve them were similar for the groups (Table 2).
The sensory level to loss of cold sensation was significantly higher than that of sharp pinprick in both groups (Table 3). However, the difference between the two sides was not significant. The average duration of LL tilt (the time from the injection of bupivacaine until returning to the horizontal supine position after delivery of the baby) was approximately 19 min in both groups. There was no significant change in sensory levels after being placed supine after delivery.
One parturient (3%) in each group developed pain with peritoneal traction after delivery of the fetus, and both were successfully treated with 50 mcg of IV fentanyl. The patient in the RL group, despite a bilateral loss of cold sensation to C6, had a loss of sharp pinprick sensation at T4 and T8 on the right and left side respectively. The one in the LL group had bilateral loss of cold and pinprick sensation to T4 and T6 respectively.
Systolic blood pressure decreased by an average of 12% less than baseline in both groups within 10 min of intrathecal injection. The amount of IV fluid (34 ± 13 mL/kg versus 30 ± 9 mL/kg; P = 0.19) and ephedrine administered (median 18.0 and range 0–30 versus median 13.5 and range 0–30 mg; P = 0.134) were comparable between groups. The number of parturients (13 versus 11, P = 0.40) given oxytocin infusion, and the number of parturients with shivering (10 versus 12, P = 0.66), nausea (14 versus 18, P = 0.54), vomiting (1 versus 6, P = 0.23), and requiring antiemetics (8 versus 11, P = 0.56) were similar in both groups.
None of the parturients developed features of postdural puncture headache postoperatively. The frequency of mild lumbar backache (4 versus 6, P = 0.15) and urinary retention needing catheterization (3 versus 3, P = 1.00) was similar in both groups. One parturient in the RL group developed pruritus in the postpartum period (0 versus 1, P = 0.50).
We found no evidence that the use of LL decubitus position during injection of 0.5% hyperbaric bupivacaine followed by a 20 degree left lateral tilt for cesarean delivery would lead to pooling of hyperbaric bupivacaine onto the left side of body. Indeed, more parturients in the LL group than the RL group obtained a loss of cold sensation at the T4 level at 5 minutes. We postulated that changing from the RL decubitus to the LL tilt position might cause a portion of the local anesthetic to diffuse laterally and hence reduce the initial mass of local anesthetic available for cephalic spread. Post hoc power analysis showed that our study had an 87% power to detect a between group difference of 3 dermatomes in the maximum upper sensory levels.
Our results differed from those of Russell (7), who used an equal dose of hypobaric bupivacaine (11 mg) and found that more parturients in the LL decubitus position required intraoperative supplemental analgesia when compared with the RL decubitus position. This may be related to the dose and baricity of bupivacaine used (8) and the adjuvant added (9). Generally, hyperbaric bupivacaine produces a more reliable cephalic spread than does hypobaric bupivacaine in the horizontal supine position (10). In nonobstetric patients, when a modest dose of 3 mL 0.25% of hypobaric, isobaric, or hyperbaric bupivacaine (7.5 mg) was given through a spinal catheter to patients lying in the supine position, the cephalad spread was highest in the hyperbaric group (11). Even a smaller dose of hyperbaric bupivacaine (6.6 mg) combined with sufentanil (3.3 μg) could produce a more reliable cephalic spread than the hypobaric bupivacaine/sufentanil mixture in a cesarean delivery study (4). However, no such differences were found when larger dosages of hypobaric and hyperbaric bupivacaine were compared in cesarean deliveries. Russell compared hypobaric and hyperbaric bupivacaine 12.5 mg given in the RL position and found that the maximum block height and onset time were the same (12). Similar results were obtained when hypobaric bupivacaine 15 mg was compared with an equal dose of hyperbaric bupivacaine given in the sitting position (13). Choi et al. (9) found that the optimal dose of hyperbaric bupivacaine for cesarean delivery was 12 mg; whereas 12.5–15 mg hypobaric bupivacaine has been generally recommended for similar procedures (14,15). It thus appears that when the dose of local anesthetic is smaller than 12 mg, a difference in the anesthetic block height will be more likely to be seen between hyperbaric and hypobaric bupivacaine unless intrathecal opioid is used. Intrathecal fentanyl is known for its bupivacaine-sparing effect. A smaller dose of hyperbaric bupivacaine can be used when fentanyl is added to the intrathecal mixture. Choi et al. (9) reported that the optimal dose of hyperbaric bupivacaine was reduced from 12 to 8 mg when 10 μg of intrathecal fentanyl was added. The maximum block height after intrathecal fentanyl/bupivacaine mixture was reported to be the same as that of local anesthetic alone, but the quality of anesthesia was improved (16,17). Although we had not determined the density of the bupivacaine/fentanyl mixture, published data indicated that the addition of 0.3 mL fentanyl (density, 0.99959 g/mL at 37°C) to 2.2 mL of 0.5% bupivacaine/dextrose 8.0% (1.00155 g/mL) (18) reduced the density of this solution slightly (1.00131 g/mL), and it remained highly hyperbaric (18,19).
Although our patients had been tilted for an average of 19 minutes, the maximum level of sensory block remained unchanged after return to the supine position. This contradicts other studies on the effects of duration of sitting (20) or lateral decubitus position (21) after induction of spinal anesthesia, where the levels of sensory block increased after returning to the supine position. On the basis of these data, it appears that a 20-degree LL tilt was insufficient to cause significant pooling of hyperbaric bupivacaine.
Our findings were similar to the results of studies looking at the effects of sitting position during injection of spinal anesthetic for cesarean delivery. Patients were immediately laid supine with LL tilt after the injection. It was found that when more than 12 mg of hyperbaric bupivacaine was used, the onset time to T4, maximum block height or degree of motor block in the sitting group was similar to the lateral group (22,23). However, using the combined spinal epidural technique, significantly more patients in the sitting group than the LL decubitus group required epidural top-up when a smaller dose of hyperbaric bupivacaine (10 mg) was used (24).
In conclusion, these data suggest that there is no clinical difference between RL and LL positioning during placement of the spinal anesthesia coupled with a 20-degree left lateral tilt regarding height of sensory block or the time required to achieve the block when hyperbaric bupivacaine 11 mg and fentanyl 15 μg were used. It is likely that the effect of posture or baricity of the local anesthetic on the anesthetic block height only becomes more obvious when the dose of local anesthetic used is small. Based on these results, we have changed our practice and now successfully use the LL position for the induction of spinal anesthesia for all of our cesarean deliveries. When clinically indicated, there appears to be no disadvantage to the LL decubitus position during placement of spinal anesthesia for cesarean delivery using hyperbaric bupivacaine plus fentanyl.
We thank Ms. Willy Sung, Statistical Officer at Tuen Mun Hospital, for her helpful advice on statistic methods.
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