Accuracy of fiberoptic central venous saturation catheter below 50%

The fiberoptic central venous flotation catheter has gained widespread clinical acceptance for continuous monitoring of mixed venous oxyhemoglobin saturation. There are obvious research applications to this device, especially in monitoring very low central venous saturations in response to hypoxic challenge and cardiopulmonary exercise testing. However, the accuracy of this device has not been established in such low saturation ranges in humans. This study examines the tracking characteristics of the Opticath (Oximetrix, Mountain View, CA) pulmonary arterial catheter in comparison to simultaneously drawn blood specimens in which oxyhemoglobin saturation was determined by direct spectrophotometric oximetry. The results show that the catheter follows saturation established by bench oximetry quite closely between 50 and 80%, the range most commonly encountered in the clinical setting. However, at saturations below this range, the catheter consistently underestimates direct spectrophotometry. Since accuracy is extremely important for research purposes, two equations that can be used to correct catheter readings for mixed venous saturations less than 50% are presented.