An evaluation of the effect of vasodilatation on oxygen saturations measured by pulse oximetry and venous blood gas analysis.

Measurements of arterial oxygen saturation were estimated using a pulse oximeter under conditions of reactive hyperaemia in the arms of 10 volunteers. Oxygen saturation measured by pulse oximetry was significantly lower, and venous oxygen saturation measured by co-oximetry was significantly higher, in the hyperaemic arm than in the other arm. Pulse oximeters analyse the pulsatile component of blood flow and exclude nonpulsatile causes of absorption in estimating arterial oxygen saturation. The pulsatile component is assumed to be purely of arterial origin. However, other vessels may pulsate when vasodilatation occurs and pulse oximeter saturation readings taken under these conditions may not give a true reflection of arterial saturation.