Haemodynamic changes associated with thermodilution cardiac output determination during myocardial ischaemia or pulmonary oedema in dogs

Since the technique of thermodilution (TD) cardiac output measurements per se causes haemodynamic alterations, the authors examined whether the alterations elicited by iced injectate are augmented in the presence of myocardial ischaemia (MI) or pulmonary oedema (PE), compromised conditions frequently associated with critically ill patients. MI (N = 7) or PE (N = 7) was induced by clamping the anterior descending coronary artery or by a slow infusion of oleic acid into the right atrium, respectively, in anaesthetized dogs. Injection of iced injectate, 3 ml, caused similar changes in heart rate, mean systemic and pulmonary arterial pressures, pulmonary blood flow, right ventricular dP/dt, and right atrial pressure in dogs with and without MI or PE. Cardiac output estimated by TD correlated closely with pulmonary blood flow measured by electromagnetic flowmeter in both MI and PE (r>0.9). No profound alterations in haemodynamics were observed at any injection during TD cardiac output measurements under MI or PE. These results indicate that TD cardiac output determination does not cause serious haemodynamic alterations, and can estimate right ventricular output accurately under MI and PE.