Bloodless evaluation of blood oxygenators

Evaluation of blood oxygenators using whole blood is inconvenient and expensive, although it is the ultimate preclinical test. Sodium sulfite solutions have advantages over blood for studying oxygen uptake: They are inexpensive, fewer variables need control, and deoxygenation is unnecessary. Assays and interpretation of results are easy. The kinetics of sulfite oxidation must be fast and the concentration of sulfite must be low to emulate oxygen uptake by blood. The kinetics were studied yielding a first order rate constant in sulfite, zero order in oxygen, of 740/min. Limitations of the technique were evaluated using the experimental rate constant and an adaptation of Lightfoot's approximation. While the reaction of hemoglobin is reversible and essentially instantaneous, that for sulfite is irreversible and finite. Thus if the approach to saturation is not monotonic or if the mass transfer resistance is significantly lowered, e.g., when blood film thicknesses are thinner than a few hundred microns, deviations may occur. Two TMO oxygenators and several prototypes were tested, with both sulfite and bovine blood. Uptakes of oxygen were comparable and the effect of parameter variations were similar. The use of sulfite for early evaluation of oxygenators is concluded to be very useful.