Is Continuous In-line Blood Gas Monitoring Reliable During Cardiopulmonary Bypass When PaO2 and PaCO2 Are Calculated Rather Than Measured?

The accuracy and precision of continuous in-line blood gas monitoring (CILBGM) are crucial for optimal blood gas management during cardiopulmonary bypass (CPB) and improved patient outcome. CILBGM devices, such as the CDI 500/550 system measures PaO2 and PaCO2 and B-Capta measures PaO2 through direct contact with arterial blood. However, the Quantum perfusion system with Quantum Ventilation2 (Quantum System) does not measure but calculate PaO2 and PaCO2 using several non-invasive sensors and proprietary formulas. We have observed that the calculated in-line PaO2 and PaCO2 values from Quantum System are frequently significantly higher than those obtained from iSTAT, a point-of-care blood analyzer, exceeding acceptable targets. We conducted a retrospective study involving 81 patients who underwent cardiac surgery using Quantum System with its own CILBGM and the FX05 oxygenator. The aim was to identify the degree, timing and possible patterns of error of the calculated in-line PaO2 and PaCO2. Our study showed that the errors of calculated in-line PaO2 exceed the acceptable target at the 1st blood gas series and during the rewarming and rewarmed periods, correlating with patient weight. The calculated in-line PaCO2 exhibited an upward drift during the rewarming period, correlating with the temperature gradient rather than patient weight. Based on several correlations identified, we derived a formula to predict FiO2 based on patient weight, which would achieve the target PaO2 at the 1st blood gas series when using the FX05 oxygenator.We identified when and how the errors of calculated in-line PaO2 and PaCO2 occurred and developed several recommendations to minimize significant deviations from actual PaO2 and PaCO2 during CPB. Our results suggest that achieving acceptable PaO2 and PaCO2 calculations throughout CPB using a single universal formula for each, embedded in Quantum System, is challenging due to the variety of oxygenators available, different patient sizes, and changing conditions during CPB.