Obesity and the cephalad spread of analgesia following epidural administration of bupivacaine for Cesarean section.

Epidural anesthesia using 20 ml of 0.75% bupivacaine at L3-4 with the patient in the left lateral position and the table horizontal was employed for cesarean section in 147 A.S.A. class 1 or 2 parturients under the age of 35 with a single fetus. The height of the analgesia was positively correlated with the body mass index (BMI) (weight in kilograms divided by the height in square meters), a measure of adiposity, and with body weight. Both correlations were statistically significant (p less than 0.001). There was no statistically significant correlation with the patients' height or age. It is concluded that higher levels of epidural block should be anticipated in obese obstetrical patients in proportion to their obesity. Twenty milliliters of 0.75% bupivacaine must frequently be augmented to provide adequate analgesia for cesarean section in thin parturients (BMI below 28) whereas it is too high a dosage for obese patients.