The purpose of this investigation was threefold: (1) could the perfusionist accurately estimate oxygen transfer (VO2/minute) while on CPB; (2) could this estimate, and its position on the oxygen transfer slope (OTS), predict resultant PaO2 values within a specific range; and (3) could previously derived performance 'normals' be used during this study. Fifty-four sets of samples (both arterial and venous) from 27 oxygenators were used in this study. Each oxygenator provided one normothermic and one hypothermic set of samples. In 48 of the 54 samples (88.9%) the predicted VO2/minute was within +/- 10% of the actual VO2/minute. Thirty-nine of these 48 (81.25%) had resultant PaO2 values within our target range of 140 +/- 30 mmHg. The PaO2 for these 39 samples ranged from 110 to 168 mmHg with a mean of 133 mmHg. The percentage of predicted shunt (POPS) ranged from 59.0 to 192.4% with a mean of 109.3% (SD = 23.81%). With this degree of variability, we concluded that the perfusionist must assess VO2/minute as well as POPS in order to predict the resultant PaO2.

Oxygen transfer performance of the Sorin Monolyth membrane oxygenator was evaluated. Similar to previous oxygen transfer performance studies conducted at this institution, our purpose was sixfold: (1) to construct an oxygen transfer slope (OTS); (2) to find the maximum extrapolated oxygen transfer; (3) to calculate the oxygenator performance index (OPI); (4) to generate a shunt fraction line; (5) to determine the percentage of predicted shunt (POPS); and (6) to compare the Monolyth's performance to several previously studied membrane oxygenators. From the OTS, the maximum extrapolated oxygen transfer was 346.4 ml O2/min. This absolute value was the lowest of the four oxygenators compared. When maximum oxygen transfer was compared relative to membrane surface area, the Monolyth ranked third (157.5 ml O2/min). The Monolyth produced a relatively narrow range for the OPI (81.64-130.47%) and had the lowest standard deviation (SD) in this group. The Monolyth exhibited higher shunt fractions over the range of clinical blood flows when compared to our three previously studied oxygenators. The range of POPS values (71.65-128.77%) was relatively narrow and the SD was the lowest of the four. We concluded from our evaluation that the Monolyth had relatively low top end oxygen transfer capabilities, but provided very consistent and predictable oxygen transfer performance.

During cardiopulmonary bypass (CPB), the perfusionist must be able to differentiate between: (1) a normal oxygenator with oxygen transfer reserve; (2) a normal oxygenator without O2 transfer reserve; and (3) a failing or suboptimal oxygenator. The purpose of this paper is to report on the use of the oxygen transfer slope, as well as other evaluation techniques previously described, which aided in the differential diagnosis of suboptimal oxygenator performance. We were able to determine the presence and extent of the dysfunction, follow the progression over time, and assess the effectiveness of our intervention. As a direct result of our ability to carefully monitor the oxygenator, replacement was not necessary despite severe dysfunction.

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