Inhaled Nebulised S(+)-Ketamine for Postoperative Analgesia

Ketamine has been administrated via the intravenous, intramuscular, subcutaneous, rectal, oral, transdermal, intranasal, sublingual, transmucosal, epidural, intrathecal, and intra-articular routes. Pharmacokinetic properties of inhaled ketamine have not been studied officially, but one of the investigators researchers has tested nebulized ketamine on himself with repeated painful stimulus and monitoring applied. Based on this experiment, analgesic effect is roughly estimated to begin in 3 minutes.Ketamine has been used successfully to treat acute pain in intranasal form. The primary purpose of this study is to evaluate whether nebulised S(+)-ketamine carries potential as a an analgesic bypassing first pass metabolism and without the need for intravenous access. Secondary aim is to assess the duration of analgesia obtained by nebulized S-ketamine. Thirdly, the aim is to evaluate whether inhaled nebulized ketamine decreases the need for rescue analgesia during PACU care. The subjects are recruited among patients coming in for a surgical intervention (orthopedic, gastrointestinal, plastic or urologic surgery) and needing further observation in postoperative care unit (PACU). It was calculated that sample size of 8 subjects per group would be required to achieve statistical power of 80% and detect a difference of 3 units in NRS-values with standard deviation of 2 units and type I error of 5%. To prepare for possible dropouts, total of 20 subjects will be recruited (10 in each group). Patients will receive either nebulized placebo (i.e. saline) or ketamine (Ketanest-S) when they require pain alleviation in the PACU. Dosage of ketamine is 1 mg/kg. Patients will be randomized into two groups so that other group's first inhalation contains ketamine and second inhalation placebo and in the opposite order.