Changes in transcutaneous oxygen tension during capillary blood-gas sampling.

With a Radiometer TCM-1 oxygen monitor, we followed the fluctuations in transcutaneous oxygen tension (ptcO2) during capillary blood collection from a heel prick. Thirty premature infants who presented with some respiratory compromise showed unpredictably increased (43 of 125 observations) or decreased (82 of 125 observations) values during this blood-sampling process. The fluctuation exceeded 10 mmHg in 61 observations and represented as much as -67% relative change. In general, ptcO2 values exceeded capillary pO2 values determined by standard blood-gas analysis. We investigated several aspects of capillary blood sampling to explain these observations. Because the induced response is a dynamic change, which continues throughout the collection process, we conclude that successive specimens will have different O2 tensions. Even if the capillary blood pO2 truly reflected paO2, the magnitude and direction of deviation from the patient's uncompromised O2 tension could lead to inappropriate management. We conclude that capillary blood specimens should not be used for pO2 determinations in newborns.