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

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.

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.

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.

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.