Proceedings

Prediction of Arterial Blood pCO₂ by Measuring the Ventilating Gas Exhaust pCO₂ from a Bubble Oxygenator

Emory University Clinic Atlanta, Georgia

^* Address reprint requests to Jeffrey B. Riley, CCT, 2459 Big Creek Terrace, Stone Mountain, GA 30087.

Abstract

Ventilating gas exhaust pCO₂ (P_exCO₂) was continuously monitored by a mass spectrometer during hypothermic, total heart lung bypass employing a bubble oxygenator. The hypothesis that the arterial blood pCO₂, temperature corrected to the arterial blood temperature (pCO₂, T_Bo) is in equilibrium with the P_exCO₂ was tested.

While the P_exCO₂ trends well with the pCO₂, T_Bo during rapid cooling, it assumes a lower value compared to the arterial pCO₂ corrected to the nasopharyngeal temperature (pCO₂, T_NP) because the blood temperature is much less than nasopharyngeal.

During warming, P_exCO₂ reads consistently lower than pCO₂, T_Bo apparently due to increased blood CO₂ removal (V̇_CO2) and an inability of the P_exCO₂ to come to equilibrium with pCO₂, T_Bo in the oxygenator. During low V̇_CO2 and steady state conditions, P_exCO₂ predicts pCO₂, T_Bo well (r = .803, p <.01 ). The percent disagreement of P_exCO₂ and pCO₂, T_Bo is a linear function of the V̇_CO2 (r = −.606, p <.01).