Pre-emptive analgesia using intravenous fentanyl plus low-dose ketamine for radical prostatectomy under general anesthesia does not produce short-term or long-term reductions in pain or analgesic use

The aim of the study was to evaluate post-operative pain and analgesic use after pre-operative or post-incisional i.v. fentanyl plus low dose i.v. ketamine vs. a standard treatment receiving i.v. fentanyl but not ketamine. Men undergoing radical prostatectomy under general anesthesia were randomly assigned in a double-blinded manner to one of three groups. Patients received i.v. fentanyl before incision followed by an i.v. bolus dose (0.2 ml kg−1) and an i.v. infusion (0.0025 ml kg−1 min−1) of 1 mg ml−1 ketamine (group 1) or normal saline (groups 2 and 3). Seventy minutes after incision, patients received i.v. fentanyl followed by an i.v. bolus dose (0.2 ml kg−1) and an i.v. infusion (0.0025 ml kg−1 min−1) of saline (groups 1 and 3) or ketamine (group 2). Pain, von Frey pain thresholds, and cumulative morphine consumption using patient-controlled analgesia (PCA) were assessed up to 72 h after surgery. 143 patients completed the study (group 1, n=47; group 2, n=50; group 3, n=46). Cumulative PCA morphine (mean±SD) did not differ significantly among groups (group 1, 92.3±45.9 mg; group 2, 107.2±58.4 mg; group 3, 103.6±50.4 mg; P=0.08 for groups 1 vs. 2, and groups 1 vs. 3). On day 3, the hourly rate (mean±SEM) of morphine consumption was significantly lower (P<0.0009) in group 1 (0.61±0.013 mg h−1) than group 2 (0.86±0.011 mg h−1) and group 3 (0.89±0.008 mg h−1). Pain scores and von Frey pain thresholds did not differ significantly among groups. Two-week and 6-month follow-ups did not reveal significant group differences in pain incidence, intensity, disability or mental health. Pre-operative, low-dose administration of i.v. ketamine did not result in a clinically meaningful reduction in pain or morphine consumption when compared with post-incisional administration of ketamine or a saline control condition