Study Objective: To investigate the effects on the autonomic nervous system of anesthesia induction with a combination of midazolam and barbiturate using plasma catecholamine concentration and heart rate (HR) variability in comparison with the induction with barbiturate alone. Design: Prospective study. Setting: Operating room of a university hospital. Patients: 40 ASA physical status I and II patients aged 30 to 70 years, who were scheduled for general anesthesia. Interventions: Anesthesia was induced with 0.1 mg/kg midazolam followed by 3 mg/kg thiopental sodium (Midazolam-Barbiturate group) or thiopental 5 mg/kg (Barbiturate group) with 6 L/min oxygen. Measurements: Arterial blood pressure (BP), HR, HR variability, and plasma concentrations of epinephrine and norepinephrine were measured. Main Results: Blood pressure and HR increased in response to tracheal intubation in both groups, but the increase was significantly larger in the Barbiturate group. In the Barbiturate group, the high-frequency component (HF) in HR variability increased significantly during intubation, whereas in the Midazolam-Barbiturate group, HF decreased continuously. The low-frequency component (LF)/HF ratio increased in both groups, with significantly higher values noted in the Barbiturate group. Plasma epinephrine concentrations decreased before intubation and increased in response to tracheal intubation in the Barbiturate group. Finally, plasma norepinephrine concentrations increased in response to tracheal intubation only in the Barbiturate group. Conclusions: Anesthesia induction with a combination of midazolam-thiopental was effective in reducing hemodynamic and cardiac autonomic nervous system responses to tracheal intubation in comparison with the conventional induction with thiopental alone.
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