Midazolam and ketamine as premedication in colonoscopies: a pharmacodynamic study

As colonoscopy is often painful, a premedication appears to be indispensable. Commonly, benzodiazepines, i.e. midazolam, alone or in combination with analgesic drugs are used. Besides all advantages, midazolam especially is known to have the risk of oversedation and respiratory depression. Therefore it should be used at minimal dose. In a double-blind, randomized study, three premedication-schedules of midazolam (mid) plus ketamine (ket) were compared in 33 patients, aged between 8 and 60 years, with regard to safety and acceptance by patients and endoscopist. I: ket 1 mg/kg+mid 0.1 mg/kg, max. 5 mg II: ket 1 mg/kg+mid 0.05 mg/kg, max. 2.5 mg III: ket 0.75 mg/kg+mid 0.1 mg/kg, max. 5 mg Oxygen-saturation, heart rate and blood pressure were recorded as well as the evaluations of sedation, cooperation and complaint of pain. To assess the recovery-time of the patients, the reaction time and the attention were evaluated by "Wiener's determination apparatus" and "test d2", respectively, before and at 1, 2, 3 and 4 hours after premedication. Medication I resulted in heavy sedation, good cooperation and amnesia but had the strongest tendency towards hypoxemia. Under schedule III, reduced cooperation and acceptance were seen due to a strong experience of pain. The best conditions during the examination with regard to cooperation, experience of pain and acceptance were found after premedication II without relevant depression of vital parameters. It can be concluded that midazolam can be used at minimal recommended doses as premedication for colonoscopy if combined with ketamine in a sufficient analgesic dosage.