Non-invasive measurement of cardiac output during induction of anaesthesia and tracheal intubation: thiopentone and propofol compared.

We have investigated the haemodynamic changes in response to induction of anaesthesia and tracheal intubation in patients who received either thiopentone 5 mg kg-1 or propofol 3 mg kg-1 followed by atracurium 0.5 mg kg-1 and fentanyl 1.5 micrograms kg-1. Anaesthesia was maintained with 0.6% enflurane and 50% nitrous oxide in oxygen with assisted ventilation. Cardiac output and heart rate (HR) were monitored continuously with a transthoracic impedence monitor. Mean HR did not change after induction in each group, but increased after tracheal intubation in both groups (P less than 0.01). Mean cardiac index (CI) decreased after induction (P less than 0.05) and decreased further after tracheal intubation in both groups (P less than 0.05). There was no difference between the two groups with respect to changes in CI and HR. Mean arterial pressure (MAP) and systemic vascular resistance (SVR) did not change significantly after induction in the thiopentone group. Both variables increased from preinduction values 1 min after tracheal intubation (P less than 0.001). In contrast, both MAP and SVR decreased after induction in the propofol group (P less than 0.001) and did not differ from preinduction values 1 min after tracheal intubation. MAP and SVR were greater in the thiopentone group compared with the propofol group after induction and tracheal intubation (P less than 0.01).