Induction Dose of Midazolam for General Anesthesia

Min, Kyeong Tea; Lee, Myeong Hee; Kang, Yong In; Kim, Jong Rae

Abstract

Midazolam, a new water-soluble benzodiazepine, has a few important advantages over diazepam which are lack of vascular irritation and rapid onset and short duration of action. So it has been used for an induction agent for anesthesia. But there were many different reports about the effective dose of midazolam as an induction agent for anesthesia, and which showed intersubject variability. Therefore, this study was aimed to verify the effective induction dose of midazolam comparing with thiopental 5 mg/kg for general anesthesia. The patients were divided into 6 groups. The patients of group 1, 2, 3, 4, and 5 were injected midazolam 0.15, 0.20, 0.25, 0.30, and 0.35 mg/kg, respectively, and, of group 6, thiopental 5 mg/kg for induction of anesthesia. Induction of anesthesia was defined as complete with loss of eyealsh reflex and failure to verbal commands. Unless induction was attained within 3 minutes, it was considered as failure of induction, and further steps of study were discontinued. After anesthesia was induced, stimulus to trapezius muscle relevant to endotracheal intubation was applied. The blood pressure, heart rate and arterial oxygen saturation were recorded before induction, at induction, and 1, 2, and 3 minutes after a stimulus to trapezius muscle. The incidences of pain on injection, venous irritations and antegrade amnesia were evaluated. The results were as follows; 1) Induction fractions of group 1, 2, 3, 4, 5, and 6 were 21.5, 57.2, 81.9, 100, and 100%, respectively. Induction times of group 1 to 5(midazolam groups) were 74.7-87.9 sec.(raanges, 40 -150 sec.) and, of group 6, 39.5 sec.(ranges, 33-55 sec.). But there was no relationship between midazolam doses and induction times. 2) At induction, systolic blood pressures of patients in group 3, 4, 5, and 6 decreased 6.1%, 5.8%, 10.5%, and 8.8%, respectively, and remained so after stimulus to trapezius muscle, but in group 6, which returned to preinduction value. Changes in sytoiic blood pressure were statistically insignificant among groups. 3) At induction, diastolic blood pressures of patients in group 5 and 6 decreased 11.0% and 11.3%, respectively, and, after stimulus to trapezius muscle, diastolic blood pressures did not change in group 3, 4, and 5, but, in group 6, returned to preinductuin value. Changes in diastolic blood pressure were statistically insignificant among groups. 4) At induction, heart rates of patients in group 3, 4, 5, and 6 increased 10.0%, 13.8%, 7.5%, and 25.8%, respectively. Changes in heart rate were significantly different between group 6 and other groups. 5) Arterial oxygen saturations decreased 0.25%, 0.3%, and 0.35% in group 3, 4, and 5 at induction, respectively, but, in group 6, decreased 3.4% after stimulus to trapezius muscle. Changes in arterial oxygen saturation were statistically insignificant among groups. 6) There were no differences in incidences of pain on injection, venous irritations, and antegrade amnesia among groups. In summary, midazolam can be used to induce general anesthesia safely with dose of 0.25 mg/ kg to 0.35 mg/kg, although there remains intersubject variability.