Is morphine-induced sedation synonymous with analgesia during intravenous morphine titration?

Background. Postoperative morphine titration frequently inducessedation. The assumption is made that patients sleep when theirpain is relieved. Some patients complain of persistent painwhen they awake. We studied the time-course of sedation andanalgesia to understand the determinants of patients’sleep during morphine titration. Methods. Seventy-three patients requiring morphine titrationin a post-anaesthetic care unit after major surgery, were studied.Fifty-two patients slept (Sleep group) and 21 did not (Awakegroup). When a patient slept during titration, morphine wasdiscontinued. Visual analogue pain scale (VAS), Ramsay score(RS), and the bispectral index (BIS) were recorded at the beginningof titration (STonset), at sleep onset (STsleep), then 5, 10,20, and 30 min afterwards (ST4). Results. In the Sleep group, mean (SD) RS increased from 1.7(0.4) to 2.4 (0.6) (P<0.05 vs STonset) and BIS decreasedfrom 95 (5.0) to 89.8 (10.2) between STonset and STsleep (P<0.05),RS remained stable thereafter. Conversely, RS and BIS remainedunaltered in the Awake group. The reduction in VAS was comparablebetween groups (from 78 (17) to 39 (21), and from 64 (16) to30.4 (11), respectively). Even though mean (SD) VAS was 39 (21)at ST4 in the Sleep group, 13 patients (25%) maintained a VASabove 50 mm. Conclusion. We observed dissociated effects of morphine on thetime-course of sedation and analgesia with sedation occurringfirst, followed by analgesia. Therefore, morphine-induced sedationshould not be considered as an indicator of an appropriate correctlevel of analgesia during i.v. morphine titration. Br J Anaesth 2002; 89: 697–701