Effect of varying intravenous patient-controlled analgesia dose and lockout interval while maintaining a constant hourly maximum dose

Study Objective: To investigate the effect on the use of intravenous patient-controlled analgesia (PCA) of varying the dose (D) and lockout interval (LI) while keeping the hourly maximum dose constant. Design: Randomized, prospective study. Setting: Teaching hospital. Patients: 75 patients scheduled to receive PCA morphine following abdominal surgery. Interventions: Postoperatively, patients were randomly assigned to receive PCA morphine with the following parameters: D = 1 mg, LI = 6 min (Group 1-6), D = 1.5 mg, LI = 9 min (Group 1.5-9), or D = 2 mg, LI = 12 min (Group 2-12), so that each group could receive a maximum hourly dose or 10 mg. Inadequate analgesia was managed by increasing the dose and lockout interval, while excessive sedation or respiratory rate less than 10 breaths/min resulted in decreasing the dose and lockout interval. Measurements and Main Results: Patients were assessed for pain [visual analog scale (VAS), verbal rating scale (VRS)] and side effects at 1, 2, 4, and 24 hours. The number of doses administered, missed attempts, and morphine used for the first 24 hours wets recorded by automatic printout from the PCA machine. There was no difference in the total 24-hour morphine consumption, analgesia, or incidence of side effects among the three groups at any of the measurement limes. Two patients, one each in the 1.5-9 and 2-12 groups, required naloxone for respiratory depression. The number of PCA injections, attempts, missed attemps, and the incidence of dosage adjustment were all significantly higher for the 1-6 group (p < 0.05). Conclusion: The use of 1.0 mg with a 6-minute lockout may represent appropriate dose titration because this group obtained equivalent analgesia, morphine use, and side effects as the two larger dose and lockout groups. However, the increased number of PCA attempts and missed attempts may reflect lower satisfaction with PCA therapy.