The effect of cardiac output changes on end-tidal volatile anaesthetic concentrations

Cardiac output is a major determinant of the rate of uptake of volatile ana esthetic agents. Theoretical work suggests a 30% change in cardiac output w ill produce a measurable change in end-tidal volatile agent. We present thr ee patients in whom significant changes in haemodynamic parameters, consist ent with a large fall in cardiac output, were accompanied by an increase in end-tidal volatile agent concentrations. The changes in end-tidal volatile agent concentrations were comparable in magnitude but in the opposite dire ction to the changes in end-tidal CO2. Clinically, an unexplained change in end-tidal concentration of a volatile agent may signify a large change in cardiac output.