Is continuous in-line blood gas monitoring reliable during cardiopulmonary bypass when PaO2 and PaCO2 are calculated rather than measured?

Abstract

Background: 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 outcomes. CILBGM devices, such as the CDI 500/550 system, measure PaO₂ and PaCO_2, 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 calculates 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.

Methods: We conducted a retrospective study involving 81 patients who underwent cardiac surgery using the 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.

Results: 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.

Conclusion: We identified when and how the errors in calculating 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 the Quantum System, is challenging due to the variety of oxygenators available, different patient sizes, and changing conditions during CPB.