///2009 Abstract Details
2009 Abstract Details2019-08-03T15:55:31-06:00

Intrathecal Bupivacaine Requirements in Morbidly Obese Patients Undergoing Cesarean Delivery

Abstract Number: 1
Abstract Type: Original Research

Lindsey M Atkinson MD1 ; Jeremy Collins FRCA2; Ed Riley MD3; Vicki Ting MD4; Scott Harter MD5; Brendan Carvalho FRCA6


Morbidly obese patients may have a lower local anesthetic requirement for spinal and epidural anesthesia.(1) The aim of this study was to determine the effective dose (ED50/ED95) of intrathecal (IT) bupivacaine with opioids for cesarean delivery in morbidly obese patients.


Morbidly obese parturients (BMI ≥ 40) undergoing elective cesarean delivery were enrolled in this randomized, double-blinded, IRB-approved study. Anesthesia was administered using a combined spinal-epidural technique. 42 patients were randomized to receive IT hyperbaric bupivacaine in doses of 5, 6, 7, 8, 9, 10, or 11 mg (n=6 per group), and co-administered with IT 200 mcg morphine and 10 mcg fentanyl. The epidural catheter was not dosed unless inadequate anesthesia was determined. Success(induction) was defined as a peak sensory block height to pinprick at ≥ T6 within 10 minutes; and success (operation) defined as success(induction) plus no requirement for epidural supplementation throughout surgery. ED50/ED95 values for success(induction and operation) were determined using a logistic regression model.


40 of 42 patients have been enrolled in this ongoing study. The ED50/ED95 for success(operation) were 9.6 and 14.4 mg respectively (Figure 1). We were unable to measure the ED50 and ED95 for success(induction) because there were so few initial block failures even in the low dose range. This produced an indeterminate logistic regression curve transition point (Figure 1). The meanSD surgical time was 6520 min with no differences among the dosage groups. There were no differences with regard to secondary outcomes (hypotension, vasopressor use, nausea, vomiting, or maternal satisfaction).


The ED50/95 for success(operation) was higher than expected and greater than the ED50/95 of a non-obese population determined in a previous study using similar methodology.(2) Reasons for a greater dose requirement are unclear but possibilities include increased stimulation from difficult surgical exposure, slower assumption of the supine position after block placement due to body habitus, and longer surgical duration. This study suggests that IT dose reduction is not necessary; similar or larger IT doses may be required in obese patients undergoing cesarean delivery. Adequate initial sensory block heights obtained with low doses do not guarantee adequate cesarean anesthesia.


1. Obesity Surgery 2007;17:1146-49

2. Anesthesiology 2004;100:676-82

SOAP 2009