Safety of mixture of morphine with ketamine for postoperative patient-controlled analgesia: an audit with 1026 patients.

BACKGROUND: Adding ketamine to morphine for patient-controlled analgesia (PCA) may be useful. However, data on this drug combination have been collected on small sample sizes. In order to evaluate the safety of the combination morphine- ketamine, we conducted a prospective study on a large patient population.
METHODS: Patient-controlled analgesia was performed with 1026 patients using morphine and ketamine in a dose ratio of 1:1. All patients were treated in the ward. Prospectively collected data included incidence of complications and side-effects, verbal pain scores at rest and during mobilization (0 = no pain to 4 = very strong pain), consumption of morphine and ketamine and patient satisfaction (0 = very un-satisfied to 3 = very satisfied).
RESULTS: The study included 462 women and 564 men who underwent, on average, 71.8 h (+/-56.1) of PCA. There were 698 orthopaedic, 160 abdominal, 96 thoracic, 20 vascular, 16 plastic, 15 neurosurgical, 11 urologic and 10 other surgical procedures. No complication was observed. Incidence of side-effects was: 1.2% respiratory depression, 23.5% nausea, 6.2% vivid dreams and/or hallucinations, 21.4% sedation and 10.3% pruritus. Reasons for discontinuing the PCA were side-effects (7.0%) and other (0.5%). Mean pain scores over the whole period were 0.44 (+/-0.54) at rest and 1.36 (+/-0.62) during mobilization. Mean satisfaction score was 2.52 (+/-0.69).
CONCLUSION: Patient-controlled analgesia with morphine and ketamine is safe. It produces side-effects which, however, are infrequently a reason for discontinuing the regimen. It is also associated with low pain scores and high patient satisfaction.