More accurate capillary pO₂(a) measurement

The standard sample for measurement of blood gases is arterial blood. Arterial puncture is painful and, because of inherent dangers, is usually only performed by qualified medical staff. Arterialized earlobe capillary blood sampling provides a less painful and safer alternative, which can be reliably performed after training by all healthcare professionals. 

The technique involves application of a vasoactive cream to the earlobe to "arterialize" capillary blood. Although many studies have demonstrated acceptable agreement between the two kinds of sample for measurement of pH and pCO₂(a), that is not always the case when measuring pO₂(a). 

 Potential sources of error associated with using arterialized capillary blood for pO₂(a) include introduction of unseen contaminating air bubbles during collection and failure to adequately arterialize capillary blood prior to sampling. 

According to the results of a recent study a possible solution to the problem of identifying discrepant capillary blood pO₂(a) results is to monitor SpO₂ by pulse oximetry at the same time as capillary blood is being sampled for blood gases. 

The approach is based on the notion that there should be concordance between oxygen saturation measured by pulse oximetry and that calculated from measured parameters by a blood gas machine (sO₂(a)) during capillary blood analysis. If there is discordance (defined by the study as > 2 % difference between SpO₂ and sO₂(a)), then an error in sampling can be assumed and the pO₂(a) result identified as unreliable. In such cases repeat sampling is indicated.