Is preemptive analgesic effect of ketamine dose dependent? Effect of increasing dose on post septorhinoplasty pain

Objective: To find out the effect of increasing the dose of preemptive ketamine on ketoprofen requirement in first 24 hours after surgery. Methodology: 120 patients, scheduled for elective septorhinoplasty were randomly divided in to four groups. At the time of induction of general anesthesia one test drug was given. Group1 received placebo, group 2, 3 and 4 received I.V ketamine, 0.5 mg kg-1, 1.0 mg kg-1 and 1.5 mg kg-1 respectively. The total postoperative consumption of ketoprofen and pethidine as rescue analgesia in 24 hours was recorded. The incidence of common side effects was recorded. Results: There was no difference in ketoprofen requirement between group 1 2(P=0.108).Patients in group 1 2 required more ketoprofen than patients in group 3 and 4 (P=0.00). Group 4 patients required significantly less ketoprofen compared to group 3 patients (P=0.01). Time to first request analgesia was longer in the groups 2, 3 and 4 compared to group 1 (P=0.00). Time to discharge from PACU was found to be longer in patients where ketamine was used (P=0.018). No patient in any group required pethidine as rescue analgesia. There was no significant difference in the common side effects among the groups. Conclusion: Ketamine in the doses of 0.5 mg kg-1 failed to produce reduction in ketoprofen requirement. However, the dose of 1.0 mg kg-1 and 1.5 mg kg-1 resulted in reduction in post operative ketoprofen requirement and prolonged the time to first request analgesia without any increase in side effects.