A comparison of transmittance and reflectance pulse oximetry during vascular surgery

New reflectance pulse oximetry probes placed on the forehead may be an improvement over transmittance probes placed on a finger, toe, or earlobe in patients with compromised perfusion. We compared the reliability and accuracy of the 2 types of probes in patients undergoing vascular surgery.

Patients with peripheral vascular disease undergoing vascular surgery under general anesthesia were monitored with both a transmittance earlobe probe and a reflectance forehead probe. Spo(2) was recorded continuously from both probes, and arterial blood gas samples were analyzed when clinically indicated. The average values from both probes over each minute were compared using Bland-Altman analysis.

Twenty patients were included yielding a total of 3993 1-min averaged data pairs. Neither probe failed to report a value for more than 1 min. A Bland-Altman plot showed the limits of agreement between the probes of -4.0% to +2.6%. Twenty-eight arterial blood samples were analyzed for 14 patients and Sao(2) closely matched both Spo(2) probe values at the time of sampling. Compared with Sao(2), analysis demonstrated limits of agreement of -4.7% to 6.1% for ear and -3.3% to 3.4% for forehead sites.

The new reflectance forehead Spo(2) probe tested has acceptable agreement with the older transmittance probe placed on the earlobe for pulse oximetry within typical ranges of Spo(2) in patients undergoing vascular surgery.