A comparison of transmittance and reflectance pulse oximetry during vascular surgery

BACKGROUND: 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. METHODS: Patients with peripheral vascular disease undergoing vascular surgery under general anesthesia were monitored with both a transmittance earlobe probe and a reflectance forehead probe. Spo₂ 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. RESULTS: 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 Sao2 closely matched both Spo₂ probe values at the time of sampling. Compared with Sao2, analysis demonstrated limits of agreement of -4.7% to 6.1% for ear and -3.3% to 3.4% for forehead sites. CONCLUSIONS: The new reflectance forehead Spo2 probe tested has acceptable agreement with the older transmittance probe placed on the earlobe for pulse oximetry within typical ranges of Spo₂ in patients undergoing vascular surgery.