Lack of pre-emptive analgesic effect of low-dose ketamine in postoperativepatients. A prospective, randomised double-blind study

NMDA receptors are assumed to play an important role for neuronal plasticit y. In vitro and animal experiments confirmed that NMDA antagonistic drugs c an prevent hyperexitability of dorsal root neurons after strong pain stimul i. Clinical data, however, are more or less controversial in this respect. It was the aim of the present prospective, randomised, double-blind study t o verify if low-dose preoperative ketamine, an NMDA antagonist, provides re levant postoperative analgesia in surgical patients and to re-examine posit ive results published by other investigators. 80 ASA I-II patients undergoing elective laparoscopic or proctologic surger y received at induction of general anaesthesia a single i.v. bolus dose of either ketamine 0.15 mg/kg or placebo (0.9% NaCl). Postoperative analgesia was provided by i.v.patient-controlled analgesia (PCA) using the opioid pir itramide. Cardiovascular parameters, respiration, sedation, cumulative piri tramide consumption and pain scores (visual analogue scale 1-10, verbal rat ing scale 0-4) were monitored at 1, 2, 3, 4, 5, 6, 12 and 24 hours after su rgery. Additionally, a retrospective pain score was documented after the 24 hours observation period. There was no statistically significant difference in any study parameter. C umulative PCA piritramide consumption after 24 hours was 25.0 +/- 16.2 mg i n the ketamine group and 29.5 +/- 20.4 mg in the placebo group. Ketamine-sp ecific side effects such as hallucinations or bad dreams were not observed. It is concluded that under the study conditions used, low dose ketamine, co ntrary to previously reported results [30], does not provide a clinically r elevant pre-emptive analgesic effect in postoperative patients.