[Preanalytical errors on the determination of arterial O(2)-partial pressure and their impact on the AaDO(2)]

The paO(2) and AaDO(2) are routinely measured for evaluating pulmonary gas exchange. The normal value of the AaDO(2) amounts 10 mmHg when breathing atmospheric air and is said to increase with rising FIO(2). This increase is discussed controversially. One possible reason for incongruities in AaDO(2) measurement may be the impact of so called preanalytical errors during paO(2) measurement, which are often neglected. Therefore, the aim of this study was to evaluate the relevance of preanalytical errors on the AaDO(2) under hyperoxic conditions.

Arterial blood gas analysis was performed on twenty patients without known pulmonary disease after tracheal intubation and 30 min of ventilation with pure oxygen. All preanalytical paO(2) errors (sampling technique, transport and storage of samples, aspirated air bubbles) were assessed and all paO(2) measurements were corrected by applying respective predetermined correction factors. Calculation of the AaDO(2) was performed with corrected and uncorrected paO(2) values.

The average amount of the AaDO(2) under ventilation with FIO(2)=1.0 was 118.9+/-41.1 mmHg, calculated from uncorrected paO(2) values, and 13.4+/-7.5 mmHg calculated from paO(2) values corrected for preanalytical errors, respectively.

The present results show that the assumption of an increasing AaDO(2) with rising FIO(2) is questionable. It could be proved that neglecting preanalytical paO(2) errors leads to a significant overestimation of the AaDO(2). The consequence would be a misinterpretation of the patient's condition in relation to a reduced pulmonary gas exchange, which should in fact be attributed solely to the preanalytical errors.