A new method to measure oxygenator oxygen transfer performance during cardiopulmonary bypass: clinical testing using the Medtronic Fusion oxygenator

Abstract

Background: There is no acceptable method of testing oxygen transfer performance in membrane oxygenators quickly and easily during cardiopulmonary bypass. Pre-clinical testing of oxygenators is performed under controlled situations in the laboratory, correlating oxygen transfer to blood flow using 100% oxygen. This laboratory method cannot be used clinically as oxygen transfer values vary significantly at each blood flow and the FiO₂ is not kept at 1. Therefore, a formula was developed which corrects the existing FiO₂ to attain a PaO₂ of 150 mmHg: the corrected FiO₂ at 150 mmHg. In graph form, this corrected FiO₂ (x-axis) is correlated to the patient's oxygen consumption levels (y-axis), which determines the membrane oxygenator oxygen transfer performance.

Methods: Blood gas and hemodynamic parameters taken during cardiopulmonary bypass using the Medtronic Fusion were used to calculate the oxygen consumption (inlet conditions to the oxygenator) and the corrected FiO₂ for a PaO₂ of 150 mmHg. Validation of the formula "FiO₂-PaO₂/(Pb-pH₂O)+0.21" was carried out by plotting the calculated values on a graph using PaO₂ values between 145 to 155 mmHg and then, using the corrected FiO₂ for PaO₂s outside of this range.

Results: All trend-lines correlated significantly to confirm that the Medtronic Fusion had an extrapolated oxygen transfer of 419 milliliters O₂/min at an FiO₂ of 1 to achieve a PaO₂ of 150 mmHg.

Conclusions: Use of the corrected FiO₂ correlated to the oxygen transfer conditions of the membrane oxygenator can easily be used on a routine basis, providing valuable information clinically. When used by the manufacturer under laboratory conditions, further clinically relevant data is provided in terms of FiO₂ and resultant PaO₂s instead of the present limitations using blood flow. In this way, a clinically justifiable method has been developed to finally establish a standard in testing membrane oxygenator performance.

Keywords: FiO2; PaO2; cardiopulmonary bypass; membrane oxygenator; oxygen consumption; oxygen transfer.