Age predicts effective epidural morphine dose after abdominal hysterectomy.

To determine whether there is a relation between patient age and the effective dose of epidural morphine for relief of incisional pain after abdominal hysterectomy, experience treating 66 patients between the ages of 22 and 84 years was retrospectively examined. Linear regressions were plotted for age vs effective 24-hr morphine dose, age vs pain at rest, and age vs pain during coughing. To evaluate the frequency of side effects, the population was classified into three age groups (less than 40, 40-60, greater than 60 yr) and examined by Fisher's exact test for possible differences. Although there was wide interpatient variability, there was a correlation between patient age and effective 24-hr morphine dose (r = -0.40, P less than 0.01). The relation is described by the following equation: 24-hr morphine dose (mg) = 18-age(0.15). The quality of analgesia did not diminish with the smaller doses administered to the older patients. The frequency of side effects did not differ significantly in the three age groups. These observations may be related to higher CSF morphine concentrations or to a greater analgesic effect from morphine absorbed systemically from the epidural space in older patients.