Determination of cardiac output based on breath-holding

A breath-holding method for determination of cardiac output is described. It is based on the indirect Fick principle applied to carbon dioxide. Mixed venous PCO2 (PvCO2) is measured noninvasively using a CO2 breath-holding technique and PaCO2 is obtained by arterial puncture. Partial pressures are converted into contents using each patient's CO2 dissociation curve, taking into account temperature, hemoglobin, arterial and venous pH. The authors have applied this method to the determination of cardiac output in 20 patients, in whom cardiac output was also measured invasively using either direct Fick or thermodilution method. Mean cardiac output determined using the breath-holding method was 5.48 +/- 2.95 (SD) L/min, compared to 5.54 +/- 2.88 L/min as determined by the direct Fick or thermodilution method. Good correlation was found between the invasive and breath-holding method (r = 0.97, p < 0.001). The authors conclude that cardiac output at rest may be estimated with considerable accuracy from the measurements of PaCO2, CO2 production and the breath-holding mixed venous PCO2 without right-sided cardiac catheterization.