Model of pCO2 gap during hypothermic cardiopulmonary bypass.
Perfusion adequacy during cardiopulmonary bypass is important in reducing postoperative morbidity. The pCO2 gap (defined as the difference between blood and tissue pCO2 levels) has been shown to be a sensitive measure of ischemia resulting from inadequate perfusion in pediatric patients undergoing deep hypothermic cardiac arrest. The complexity of measuring tissue pCO2 levels has motivated development of a mathematical model to provide an indirect indication of pCO2 gap. The model allows us to examine relations between tissue pCO2, plasma pCO2, and the rate of CO2 removal through the extracorporeal oxygenator. Three compartments have been modeled with CO2 generation and mass transfer coefficients estimated on the basis of published correlations with height and weight. Model predictions have been compared with oxygenator exhaust measurements taken during a hypothermic cardiac procedure. The model predicts carbon dioxide buildup in the tissues during hypothermia followed by equilibration with the blood on rewarming. The model appears to qualitatively predict CO2 removal rates observed during deep hypothermic cardiac arrest. Refinement and validation of the model may lead to a tool for predicting tissue pCO2 levels during and after hypothermic cardiopulmonary bypass.
Johnson
Greg
G
Ension, Inc., Pittsburgh, Pennsylvania 15238, USA.
Tamblyn
Joseph
J
D002245:Carbon Dioxide / Q000378:metabolism*; D002315:Cardiopulmonary Bypass / Q000009:adverse effects; D050792:Circulatory Arrest, Deep Hypothermia Induced / Q000009:adverse effects; D015199:Extracorporeal Membrane Oxygenation / Q000009:adverse effects; D006801:Humans; D007511:Ischemia / Q000378:metabolism*; D008955:Models, Cardiovascular
D002245:Carbon Dioxide