A comparison of midazolam and diazepam for conscious sedation during colonoscopy in a prospective double-blind study

Midazolam and diazepam are commonly used for conscious sedation, but their comparative respiratory depressive effects have not been accurately studied. We used a novel real-time, on-line, computerized data acquisition system to compare the two agents in a randomized double-blind study.

One hundred patients undergoing colonoscopy were studied. The maximum end-tidal carbon dioxide tension (PetCO2) and the minimum oxygen saturation by pulse oximetry (SpO 2) were recorded by computer every minute. Patients received meperidine (25 to 50 mg) and incremental doses of either midazolam or diazepam to an identical end point of slurred speech and/or ptosis. Sedation was scored from 1 (unarousable) to 5 (wide awake).

Sedation scores were 3.6 +/- 0.1 (mean +/- standard error) after each agent. The doses of midazolam and diazepam were 0. 031 +/- 0.002 and 0.106 +/- 0.009 mg/kg, respectively. In the first 45 minutes (PetCO2) was significantly higher with midazolam than with diazepam (p < 0.05). SpO2 was significantly depressed for 80 minutes after each agent, and the number of minutes when the minimum Sp O2 was less than 90% did not differ between the two agents.

Midazolam was 3.4 times more potent than diazepam. The duration of oxygen desaturation emphasizes the importance of monitoring SpO2 until ventilation and oxygenation have recovered. Although the degree of hypoxemia was comparable, midazolam led to higher end-tidal carbon dioxide tensions.