Date Published: June 20, 2012
Publisher: Hindawi Publishing Corporation
Author(s): Yu-Ying Tang, Jie Zhou, Xiao-Hui Ren, Xue-Mei Lin.
Background. It was suggested that labor may influence the spread of intrathecal bupivacaine using combined spinal epidural (CSE) technique. However, no previous studies investigated this proposition. We designed this study to investigate the spinal block characteristics of plain bupivacaine between nonlaboring and laboring parturients using CSE technique. Methods. Twenty-five nonlaboring (Group NL) and twenty-five laboring parturients (Group L) undergoing cesarean delivery were enrolled. Following identification of the epidural space at the L3-4 interspace, plain bupivacaine 10 mg was administered intrathecally using CSE technique. The level of sensory block, degree of motor block, and hemodynamic changes were assessed. Results. The baseline systolic blood pressure (SBP) and the maximal decrease of SBP in Group L were significantly higher than those in Group NL (P = 0.002 and P = 0.03, resp.). The median sensory level tested by cold stimulation was T6 for Group NL and T5 for Group L (P = 0.46). The median sensory level tested by pinprick was T7 for both groups (P = 0.35). The degree of motor block was comparable between the two groups (P = 0.85). Conclusion. We did not detect significant differences in the sensory block levels between laboring and nonlaboring parturients using CSE technique with intrathecal plain bupivacaine.
Combined spinal epidural (CSE) anesthesia is commonly used for cesarean delivery. It has been suggested that nonlaboring parturients have a higher sensory block level than those in labor during CSE anesthesia . This proposition was derived from combining two independent randomized studies on spinal block levels designed separately for laboring and nonlaboring parturients [2, 3]. There was a 5-dermatome level difference between nonlaboring (C6)  and laboring (T3)  parturients using 10 mg hyperbaric bupivacaine with CSE technique. However, there has been no previous study examining the effect of labor on the level of the subarachnoid block during CSE. The effect of CSE technique on the spinal block level of hyperbaric bupivacaine in nonlaboring parturients was not consistent. Horstman et al. reported that sensory block level was at T3 with CSE in nonlaboring parturients using 20% higher dose of hyperbaric bupivacaine . We speculate that baricity of the hyperbaric bupivacaine used by Ithnin et al. could be a confounding factor, because the block level could be easily manipulated with the positioning of the parturients when hyperbaric local anesthetic was used. The effect of labor on the spread of local anesthetics may be better examined by using plain or isobaric agents which hold the least gravity-generated flow dynamics in cerebrospinal fluid (CSF). This study was therefore designed to compare the spinal block characteristics between the laboring and nonlaboring parturients using plain bupivacaine injected intrathecally with the needle-through-needle CSE technique.
This research was conducted at the West China Second Hospital of Sichuan University, Chengdu, Sichuan Province, China. With median two-segment dermatome blockade level difference to be clinically significant and variability (interquartile range) of two dermatomes in sensory block, 20 parturients in each group were required in each group to address a 2-segment difference with a power of 0.9 and a level of significance of 5%.
All 50 parturients enrolled completed the study. No technical difficulty or inadvertent dural puncture was encountered. Demographical data including age, weight, height, and gestation weeks were presented in Table 1.
Ithnin et al. attributed the significantly higher block level in nonlaboring parturients with CSE technique to the neutralization of the negative pressure of the epidural space and reduction of the dural sac volume . Researchers from the same institution also concluded that labor-induced variable increase of epidural pressure countered the above effects . Combining the aforementioned two studies, Macarthur suggested that CSE might generate higher block level in nonlaboring parturients . However, we demonstrated that there was no statistical difference in the level of sensory blockade to either pinprick or cold between laboring and nonlaboring parturients with CSE technique. Neither did the block level relate to cervical dilation nor did the severity of labor pain. Within the same line of out findings, Horstman et al. confirmed that, compared to simple spinal technique, the change of epidural pressure from CSE technique was negligible to cause significant change of intrathecal anesthetic spread . We believe that with the relatively fixed size and low compliance nature of the skeletal spinal canal, physiological labor contraction would only generate hydraulic pressure evenly transmitted along the spinal dural sac, leaving little fluid dynamic alteration to the intrathecally administered local anesthetics. This was also confirmed by Dubelmanand Forbeswho found that vigorous coughing had no influence on the cephalad spread of spinal anesthesia .