The effect of preoperative sedation on postoperative analgesia level in patients undergoing total knee replacement surgery under spinal anesthesia

The effect of preoperative sedation on postoperative analgesia level in patients undergoing total knee replacement surgery under spinal anesthesia Purpose: It was aimed to investigate the postoperative analgesic activity of low dose of ketamine added to midazolam sedation in patients undergoing spinal anesthesia. Primary goal of the study is to evaluate the effect of preop ketamine on the ananlgesia consumption and nausea - vomiting incidence in the first 24 hours postoperatively. Materials and methods: After approval from the ethics committee of our hospital, 48 adult patients of ASA I-II risk group who would undergo knee replacement surgery were included in this prospective, randomized and double-blind study. Study patients were divided into 2 groups; ketamine and control, each containing 24 patients. Written consent were taken from all patients preoperatively. Control group patients received 0.03 mg/kg midazolam, while ketamine group patients 0.01 mg / kg midazolam and 0.3 mg/kg ketamine (10 min) for sedation. Both groups underwent spinal anesthesia with 15 mg of 0.5 % hyperbaric bupivacaine between L3-4 or L4-5. In case of need for intraoperative sedation (to keep the patient at Ramsey Sedation Scale 3), 0.5 mg i.v midazolam doses (with 3-5 min intervals) were applied to both groups. Sensory block, sympathetic block and motor block was evaluated by hot - cold discrimination, Pin-prick test and Bromage scale, respectively. The surgery started when the sensory block reached T10 level. Preoperative, intraoperative and postoperative hemodynamic parameters were monitored and recorded. Postoperatively, both groups received i.v morphine for 24 hours with patient - controlled analgesia method. Postoperative Visual Analogue Scale, total morphine consumption, complications, side effects and patient satisfaction were evaluated. Results: Three patients were excluded from the study due to surgical complications. The average age of the 45 patients was 66 ± 7. There was no statistically significant difference in terms of demographic data, duration of anesthesia and surgery time, sensory block onset time, motor block regression time, sleep quality and patient satisfaction between the two groups. Total morphine consumption, 2, 4, 6, 12, and 24. hour VAS levels were statistically significantly low in the ketamine group (p < 0.05). Conclusion: Low doses of preoperative ketamine reduces VAS scores the incidence of nausea and vomiting and postoperative morphine consumption significantly. Key words: ketamine, spinal anesthesia, morphine, patient controlled analgesia.