Cardiovascular Responses to Induction of Anaesthesia with Thiopentone and Suxamethonium in Infants and Children

Cardiac output, systolic blood pressure and heart rate were measured with non-invasive techniques before, during and after induction of anaesthesia with thiopentone (7.5-8.5 mg/kg) and suxamethonium (1.4-1.7 mg/kg), and after intubation in unpremedicated infants and diazepam-atropine premedicated children. Cardiac output was measured with a combination of M-mode and pulsed doppler echocardiography. Significant decreases in systolic blood pressure, cardiac index and stroke volume index were observed during induction in both infants and children. Intubation caused increases above pre-induction levels of heart rate, blood pressure and cardiac index in both infants and children. Stroke volume index increased marginally in infants but remained depressed in children after intubation. Left ventricular shortening fraction decreased significantly in five other children during induction. It is concluded that thiopentone causes significant reduction in cardiac output by depression of myocardial contractility manifested by depression of blood pressure and stroke volume. Premedication with atropine may ameliorate reduction in cardiac output by permitting an increase in heart rate during induction. Induction of anaesthesia with thiopentone and premedication with diazepam does not prevent hypertension and tachycardia occurring with intubation.