BACKGROUND: Thiopental and propofol are commonly used intravenous induction agents and entropy is a new method of assessing depth of anesthesia. In this study we evaluated the entropy responses to endotracheal intubation during anesthetic induction with thiopental or propofol.

METHODS: Forty ASA class I and II adult female patients undergoing elective surgeries were enrolled into this randomized, prospective study. At 1 minute after fentanyl 2 µg/kg, thiopental 5 mg/kg (group T) or propofol 2 mg/kg (group P) was administered for induction. And endotracheal intubation was performed following succiny choline 1 mg/kg. From pre-induction till post-intubation 10 minutes, the entropy and hemodynamic variables were measured and compared.

RESULTS: The entropy following intubation increased significantly in both groups. But entropy changes in group T were greater than those in group P remained below 65.

CONCLUSIONS: Our results using the entropy to monitor anesthetic depth during induction and intubation, suggest that thiopental 5 mg/kg is more likely to be associated with lighter planes of anesthesia and consequent risk of arousal reaction following endotracheal intubation than propofol 2 mg/kg.