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Model of pCO2 gap during hypothermic cardiopulmonary bypass
1Ension, Inc., Pittsburgh, Pennsylvania 15238, USA.
Insights
A new mathematical model estimates tissue pCO2 levels during cardiopulmonary bypass. This model may help predict tissue ischemia and improve perfusion adequacy in pediatric cardiac surgery patients.
Area of Science:
- Biomedical Engineering
- Cardiovascular Surgery
- Pediatric Critical Care
Background:
- Perfusion adequacy during cardiopulmonary bypass is critical for minimizing postoperative complications.
- The pCO2 gap (blood-to-tissue pCO2 difference) indicates ischemia in pediatric patients during deep hypothermic cardiac arrest.
- Direct tissue pCO2 measurement is complex, necessitating indirect methods.
Purpose of the Study:
- To develop and evaluate a mathematical model for indirectly assessing the pCO2 gap.
- To examine the relationship between tissue pCO2, plasma pCO2, and CO2 removal during extracorporeal circulation.
- To provide a potential tool for monitoring tissue perfusion during hypothermic cardiopulmonary bypass.
Main Methods:
- A three-compartment mathematical model was developed.
- CO2 generation and mass transfer coefficients were estimated using patient height and weight correlations.
- Model predictions were compared against oxygenator exhaust measurements during hypothermic procedures.
Main Results:
- The model predicts carbon dioxide accumulation in tissues during hypothermia.
- The model indicates CO2 equilibration between tissues and blood upon rewarming.
- Qualitative agreement was observed between model predictions and measured CO2 removal rates.
Conclusions:
- The developed mathematical model shows potential for predicting tissue pCO2 levels during and after hypothermic cardiopulmonary bypass.
- Further refinement and validation are needed.
- This model could aid in optimizing perfusion strategies and reducing ischemia in pediatric cardiac surgery.
Abstract:
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.
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