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Preterm gestation is associated with an increased failure rate of spinal anesthesia for cesarean delivery
Abstract Number: S-52
Abstract Type: Original Research
Pregnancy is associated with an increased spread of spinal anesthesia. While studies have examined the relative spread of spinal block for surgical anesthesia in pregnant versus non-pregnant women, there is limited data reviewing adequate spinal dosing for preterm (gestational age <37 weeks) versus term parturients. The purpose of this study was to investigate the hypothesis that preterm gestation is associated with an increased incidence of failed spinal anesthetics for cesarean delivery (CD) compared to term gestation.
After IRB approval, we searched the perioperative database for women who underwent CD under spinal or combined spinal epidural anesthesia from 2003-2012. We included patients who received our standard doses of local anesthetic (≥10.5mg of 0.75% hyperbaric bupivacaine with fentanyl 15mcg and morphine 0.1-0.2mg) and were 152-183cm tall. Inadequate surgical anesthesia (failure) after initial spinal dose was the primary outcome. Failure was defined as need to repeat the spinal technique to obtain adequate block height; convert to general anesthesia secondary to pain; supplement intravenously with at least two of the following: fentanyl (>100 mcg), ketamine, midazolam or propofol; use nitrous oxide; or augment the initial block with epidural lidocaine within 30 minutes if the combined spinal epidural technique was used. Chi-square test was used to compare failure rate between preterm and term parturients. We also performed a multivariable regression analysis with failure as the outcome and age, height, weight, ethnicity, gestational age and hyperbaric bupivacaine dose as predictors.
5041 patients (3404 term and 1637 preterm) fulfilled the inclusion criteria and were included in the analysis. There were no clinically significant differences between the groups in patient demographics or dose of hyperbaric bupivacaine used. The most common dose administered was 12mg (62%). Overall, there were 150 failed spinal anesthetics (3.2%). The incidence of failure was significantly higher in preterm compared to term patients (4.5% vs. 2.2%, p<0.0001). Failure rate was 6.8% for those ≤30 weeks and 3.6% for those >30 weeks and <37 weeks gestation. In the multivariable model, gestational age was a significant predictor of failure [adjusted odds ratio (95% confidence interval) = 0.91 (0.88, 0.94), p<0.0001] while none of the other predictors was statistically significant.
At standard spinal doses of hyperbaric bupivacaine, there is a higher likelihood of inadequate surgical anesthesia in parturients undergoing CD at preterm gestational ages. Early preterm parturients (gestational age <30 weeks) have the highest risk. These findings suggest that an increased spinal dose may be necessary to reliably ensure adequate anesthesia in this population or, preferably, a combined spinal epidural technique allowing epidural augmentation of inadequate spinal blocks would be recommended.