To see whether continuous
intravenous infusion of
opiates provides more effective postoperative relief of
pain than conventional
intramuscular injection these regimens were compared in a prospective double blind trial. Thirty patients undergoing elective
cholecystectomy were allocated randomly to receive an infusion of
morphine or an infusion of placebo (control group) for 24 hours. Both groups were allowed supplementary
morphine boluses as requested. During the first 48 hours after operation the degree of
pain was almost identical between the groups. Surprisingly, the group that was given the infusion of
morphine received as much supplementary
morphine as the control group during the first 24 hours and appreciably more during the 24 hours after the infusion had been withdrawn.
Nausea and
vomiting were more prevalent among the patients given the infusion of
morphine. These results suggest that continuous infusion of
morphine may be an inferior regimen to intermittent bolus administration in the relief of
postoperative pain. This may be explained by the development of tolerance in patients who received the infusion of
morphine.