Anaesthesia time/dose curves IX: the use of hydromorphone in surgical anaesthesia and postoperative pain relief in comparison to morphine.

Seventy unselected subjects were anaesthetized for major surgical operations with intravenous hydromorphone, nitrous oxide and muscle relaxants as required. The results were compared with earlier observations made with morphine under similar conditions on 44 other subjects from the same hospital population. Hydromorphone was found to be 8.5 times as potent as morphine in terms of the median surgical loading dose, and its median therapeutic half-life was 4.07 hours against morphine's 5.28 hours. It proved to be superior to morphine in its greater consistency of action. The mid-90 per cent variance of its loading dose was 30% less and the same variance of its therapeutic half-life was 65% less than that of morphine. All the differences were statistically significant or highly significant. Observations concerning the fraction of the surgical loading dose of hydromorphone required by the patients to prevent post-operative discomfort also revealed great consistency. This is taken to indicate that psychological factors play only a subordinate role in modulating the intensity of postoperative pain.