Morphine after tubal ligation with bupivacaine: dosage versus body weight

We investigated whether there was a statistically significant difference in patient need for postoperative analgesia based on adjusted body weight between heavier and lighter women who underwent laparoscopic tubal ligation with bupivacaine injection at the skin incision. We examined 49 records of women who underwent laparoscopic tubal ligation at Oklahoma State University Medical Center between 2000 and 2005 and received an injection of bupivacaine at the surgical site during the procedure. Postsurgical morphine was measured as doses per kilogram of body weight against total body weight and as total milligrams per kilogram of body weight against total body weight. A regression was performed for each measurement. Heavier women required significantly fewer total milligrams of morphine per kilogram of body weight and fewer total doses of morphine per kilogram of body weight than lighter women (2-tailed P = .0035 and P = .0018, respectively). Our data may suggest that lipophilic bupivacaine injected at a surgical site is held in place better and works for a longer period when more fat is present.