The pO2 of Samples Drawn from the Shiley S-100A Arterial Reservoir Is Not an Accurate Indicator of Arterial Line pO2

While conducting clinical bypass with the Shiley S-100A bubble oxygenator, an observation was made that arterial pO2 values reported by the laboratory were routinely inconsistent with inline arterial blood oxygen saturation measurements. It was also noted that the blood in the arterial reservoir in the vicinity of the arterial sampling port was often darker in color than the blood in the arterial line. Sixty-four simultaneously drawn pairs of arterial blood gas samples were drawn from the arterial reservoir sampling port and from the purge line of the arterial line filter (ALF). In all instances, the pO2 of the sample drawn from the arterial line filter exceeded the pO2 of the corresponding sample drawn from the arterial reservoir. The percentage difference between the pO2 of samples drawn from the ALF and from the arterial reservoir correlated strongly (p < .01) with the arterial blood temperature and moderately (p < 0.2) with the reservoir level. No significant differences were found between the pCO2, pH and base excess of the ALF and the arterial reservoir. The authors postulate that the discrepancy in pO2 between the arterial reservoir sampling port and the ALF is a result of rapid channelling of partially oxygenated blood through the defoamer into the vicinity of the arterial sampling port. The rapidly channelled blood is, therefore, deprived of the additional oxygenation that occurs in the defoamers of bubble oxygenators. It is recommended that Shiley reposition the S-100A’s arterial sampling port closer to, the arterial reservoir outlet port and that a unidirectional valve be inserted to prevent inadvertent introduction of air to the arterial reservoir. Until this design modification is carried out, the authors recommend that clinical users of the S-100A draw arterial blood gas samples directly from the arterial line or from the ALF purge line.