Deep Hypothermia and the Vascular Response to Thiopental

Objective: The vascular response to intravenous thiopental in patients on cardiopulmonary bypass during deep hypothermia was examined.Design: This was a prospective observational study.Setting: A university teaching hospital.Participants: Twenty-one consecutive adult patients undergoing pulmonary thromboendarterectomy during which deep hypothermic circulatory arrest was instituted.Interventions: Immediately before circulatory arrest, each patient was administered a 500-mg dose of thiopental intravenously. Arterial blood pressure was monitored and recorded by using a femoral artery catheter and serum electrolytes, acid-base status and arterial hematocrit were determined immediately before the administration of thiopental.Measurements and Main Results: Thiopental was associated with a dose-related increase in mean arterial pressure of 32 ± 11 mmHg (p < 0.0001). Thiopental also resulted in an increase in arterial pH of 0.08 ± 0.03. A positive correlation between the magnitude of the pH change and the magnitude of the hypertensive response was suggested but did not reach statistical significance (p = 0.066). Of the other factors investigated, only serum-ionized calcium had a statistically significant association with the vascular response in that higher ionized calcium was associated with less hypertensive response (p = 0.014).Conclusions: The administration of thiopental to deeply hypothermic patients during cardiopulmonary bypass is associated with a dramatic increase in mean arterial blood pressure. The mechanism responsible for this vasoconstrictive response may involve thiopental’s potentiation of the effects of norepinephrine in the peripheral vasculature.