• A Risch, A Biedler, and F Mertzlufft.
• Klinik für Anaesthesiologie und Intensivmedizin der Universitätskliniken des Saarlandes, Homburg/Saar.
• Anaesthesist. 1999 Aug 1;48(8):533-7.

ObjectiveA variety of influences reduce the validity of the measured oxygen partial pressure (paO(2)). Most errors occur when obtaining the blood sample and preparing it for analysis. Unfortunately, there is great controversy concerning the relevance and extent of these pre-analytic errors. Apart from this, the exact estimation of influencing factors under hyperoxic conditions has been neglected. Therefore, the objective of this study was to assess pre-analytic measuring errors for paO(2) under the condition of hyperoxia as completely as possible and to work out solutions to eliminate these errors.MethodspaO(2) analysis was performed on more than 2000 blood samples. Errors analyzed were the technique of sample taking (direct puncture or from an indwelling catheter), aspirated air bubbles (0.05-0.35 ml), time and temperature of sample storage, and the material, size and manufacturer of the analyzing syringe.ResultsThe paO(2) was on average 41 mmHg lower in samples taken from the indwelling catheter than by direct puncture. An air bubble size of 0.1-0.25 ml caused a decrease of 17-41 mmHg. Storage time of 2 min accounted for an paO(2) reduction of 6-67 mmHg depending on the type of syringe used. Glass syringes turned out to be more accurate than plastic syringes. The best results were obtained not from commercial "blood gas syringes" but from a simple plastic injection syringe. For all pre-analytic errors correction factors were established.ConclusionAll pre-analytic errors investigated caused a significant paO(2) decrease. Even an ideal procedure (almost no air bubble, short storage on ice) contributes a significant error. Only the appropriate correction factors as calculated from this study for routine use lead to the correct results. If they are not taken into account the paO(2) values will be falsely low, potentially leading to misinterpretation and misjudgement of a patient's condition.

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