In many endoscopy units midazolam is replacing diazepam as the intravenous sedative of first choice. Midazolam is approximately twice as potent as diazepam. Although generally considered a safe drug, there have been a number of recent reports, particularly in the elderly, of the drug causing hypotension, respiratory depression and even death. There have been at least ten studies comparing diazepam with midazolam for upper gastrointestinal endoscopy but many have involved relatively small numbers and none have adequately addressed the question of dosage in the elderly. We have carefully recorded the dose of intravenous midazolam used to produce adequate sedation prior to upper gastrointestinal endoscopy in 800 consecutive patients. The dose of midazolam decreased markedly with age in both male and female patients. There was a highly significant correlation in both sexes between age and the dose of midazolam (rho -0.787, P < 0.001 for males and rho -0.768, P < 0.001 for females). There was only a small difference in dose in men and women, an average of 1 mg; and no difference in dose over the age of 70 years. In patients over 70 years of age the dose of midazolam necessary for endoscopy is often so small that overdosage is all too easy.
Intravenous midazolam (mean dose of 6.3 mg) was given to 100 consecutive patients coming to endoscopy. All patients had an ear oximeter attached throughout the procedure to record continuously their levels of oxygen saturation. Eighty‐five of the 100 patients had pre‐ endoscopy respiratory function tests measured, and 82 wore an induction plethysmograph vest to get a continuous qualitative estimate of respiratory rate and excursion throughout the procedure. Following intravenous midazolam a reduction in respiratory excursion was observed in 80% of patients. The initial baseline oxygen saturation of 95.4% fell 3.3% (P less than 0.0005) following intravenous midazolam to 92.1%. During the endoscopic procedure there was a further 3.1% decrease in oxygen saturation to 89.0% (P less than 0.0005) and in 7% the level fell to below 80%. Age, sex, dose of midazolam given and pre‐ endoscopy respiratory function tests failed to identify those patients at risk of hypoxia during the endoscopy.
1 One hundred and two consecutive patients undergoing upper gastrointestinal endoscopy were randomised to be sedated with either intravenous diazepam (Diazemuls-Kabi Vitrum) or intravenous midazolam (Hypnovel-Roche). It was assumed that midazolam was likely to be approximately twice as potent as diazepam on the basis of previous work. 2 All patients had an ear oximeter attached throughout the procedure to record continuously their level of oxygen saturation. 3 All 102 patients had pre-endoscopy respiratory function tests measured and 100 wore an induction plethysmograph vest to allow continuous estimation of respiratory rate and excursion. The plethysmograph was calibrated using a pneumotachygraph, so baseline, post-injection and post-endoscopy minute volumes could be estimated. 4 The age, sex ratio and pre-endoscopy respiratory function tests of the 51 patients given intravenous diazepam in a mean dose (s.d.) of 11.5 (5.8) mg over a mean of 3.4 (0.9) min) were similar to that of the 51 patients sedated with intravenous midazolam (mean dose 6.0 (2.8) mg over 3.3 (0.9) min. 5 Both drugs significantly reduced minute volume (P < 0.001) and oxygen saturation (P < 0.001). Midazolam appeared to produce slightly greater hypoxaemia with 57% having falls in oxygen saturation of greater than 2.5% compared with only 35% given an equivalent dose of diazepam. 6 Ventilation was still less than baseline when re-checked some minutes after removal of the gastroscope. The speed of recovery appeared faster after diazepam sedation which is in contrast to its longer pharmacological half-life. 7 Potentially dangerous falls in oxygen saturation were observed in five cases (three following diazepam and two midazolam), necessitating supplementary oxygen administration. The implications of these findings are discussed.
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