Effects of a loading dose of morphine before i.v. morphine titration for postoperative pain relief: a randomized, double-blind, placebo-control study

Background. I.V. morphine titration (MT) allows adjustment of the dose needed for pain relief in the post-anaesthesia care unit (PACU). However, MT has limitations such as a delay to achieve pain relief. We thus assessed the effect of a fixed intraoperative loading dose of morphine administered before titration. Methods. One hundred patients who were undergoing major orthopaedic surgery were included in a double-blind, randomized study comparing a loading dose of morphine (0.15 mg kg(-1)) with placebo administered intraoperatively. MT was then administered in the PACU followed by patient-controlled analgesia (PCA) over 24 h. Data are expressed as mean (sd). Results. The initial VAS [41 (36) vs 52 (35), NS] was not decreased in the morphine group. The VAS was lower in the morphine group in the PACU and PCA periods. The time to achieve effective pain relief was not decreased in the morphine group. The total dose of morphine administered in the PACU (including the loading dose) was significantly increased in the morphine group (+31% in mg kg(-1), P < 0.05). Morphine requirements during the PCA period were not different between groups. The incidence of sedation was increased and a severe episode of ventilatory depression occurred in the morphine group. Conclusions. A loading dose of morphine administered at the end of surgery slightly decreased the VAS but did not reduce the time to pain relief or morphine consumption within the first 24 h. This slight improvement in analgesia was obtained at the expense of morphine-related adverse events.