Influence of barbiturate anesthetic induction on circulatory responses to morphine

Circulatory responses to morphine (1 mg/kg, 10 mg/min) following a barbiturate anesthetic induction (thiamylal 4 mg/kg) were determined in 7 patients with coronary artery disease. Compared with awake measurements, the mean arterial pressure and cardiac index were decreased 16 and 42 percent, respectively (p less than 0.05) and systemic vascular resistance increased 35% (p less than 0.05) at the end of morphine infusion. The same dose of morphine, but without prior barbiturate, has been previously reported not to significantly alter these measurements. Therefore, the assumption that morphine is associated with minimal circulatory changes may be invalidated by the prior administration of thiamylal.