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Effect of Obesity on Epidural Ropivacaine Consumption During Labor
Abstract Number: S-20
Abstract Type: Original Research
Obese parturients have more complicated pregnancies and a higher risk of cesarean section(1), and difficult intubation. Early placement of epidural anesthesia is very important in the management of the obese parturient to avoid morbidity during a crash general anesthetic. However, the literature is controversial on the effect of obesity on epidural dosing. One study(n=32) suggested that obese parturients require less epidural local anesthetic(2). However, another study found no difference in the spread of epidural analgesia in obese parturients(3). We examined the effect of obesity on epidural ropivacaine consumption during labor.
After IRB approval, a retrospective chart review was performed for the year 2008. Inclusion criteria was primigravid women aged >18 years who were admitted with a gestational age >36 weeks and who delivered vaginally. The obese group was body mass index (BMI) > 30 kg/m^2 and non-obese group was BMI < 30 kg/m^2. At our institution epidural analgesia is provided by a 0.2% ropivacaine infusion without narcotic and anesthesiologist administered boluses of either ropivacaine, bupivacaine, lidocaine, or chloroprocaine with or without fentanyl. Total epidural medications were calculated as ropivacaine area under the curve (AUC) as both infusion and bolus dosing. Epidural boluses were converted to ropivacaine equivalent dose in mg by minimal local anesthetic concentration equivalency(4). Unpaired t-test was performed to compare ropivacaine usage in the two groups, p<0.05 was considered statistically significant.
567 patients met the inclusion criteria; the obese group (n=143) and the non-obese group (n=424). The obese group consumed 22.45±7 mg/hr ropivacaine compared to 22.75±7.6 mg/hr ropivacaine in the control group, P=0.6. The duration of epidural infusion was 8.9±4.7 h and 8.03±4.5 h P=0.05, and duration labor 15.4±7.6 h and 13.7±6.8 P=0.01 for obese and non-obese groups. To further examine this effect, we used linear regression analysis of BMI vs. ropivacaine AUC, which was not correlated, r^2 =0.016.
Obstetrical studies have shown obesity leads to complications of pregnancy including a slower labor (5), as well as an increase in cesarean rate, preeclampsia, and postpartum hemorrhage(6). While a previous study found reduced MLAC in obese parturients(2), we found obese and non-obese parturients had the same epidural requirements for labor analgesia. Our study is the first large study examining epidural local anesthetic requirements in primiparous obese parturients completing vaginal delivery. The correct dosing requirements for obese parturients is important to help manage their labor and especially if the need for cesarean arises.
1. Anesthesiology 1993; 79: 1210–8.
2. Br J Anaesth 2006; 96 : 106–10.
3. Int J Obstet Anesthesia 1993:2:134-6.
4. Br J Anaesth 1999;82:371-3.
5. Obstet Gynecol 2004:104:943-51.
6. Int J Gyn Obstet 2006:95:242-247.