Effect of Ambient Light on Near Infrared Spectroscopy

Background: Concerns have been raised about the ability of Near Infrared Spectroscopy (NIRS) to monitor skeletal tissue regional oxygen saturation (rSO2) in excessive light conditions, as are found under the overhead lights of the operating room. This study seeks to determine whether varying intensities of ambient light exert an influence on NIRS measurements of skeletal tissue rSO2. Methods: Thirty people were recruited from the staff of a local surgical center to participate in the study. Three separate NIRS devices (Covidien INVOS Cerebral Oximeter 510°C, Nonin EQUANOX Model 7600, and a CASMED MC-2030C Cerebral Oximeter) were used to obtain readings from the anterior compartment of the leg. Illuminance was recorded simultaneously with oximetry data in an operating room with (1) no lights on, (2) room lights, and (3) surgical lamps set to maximal intensity. Results: No differences were seen in rSO2 values under the different lighting conditions while using the Nonin device. There was a statistically significant difference between rSO2 for lights off versus room lights (-0.933, p=0.0045) as well as for lights off versus operating room (OR) lamps (level 5) (-0.50, p=0.0035) for the INVOS device, although the INVOS device was not always able to produce a reading in the presence of high-intensity OR light. While there was no difference found between lights off and room lights when using the CASMED device, it was unable to display a value in the presence of high-intensity OR lamp light. Conclusions: The results indicate that the presence of light has an effect on oximetry readings; however, the presence of such an effect is dependent upon the device being used. While other applications of the device, such as cerebral oximetry, may allow for drapes to cover the areas being monitored, monitoring for compartment syndrome of the leg would not be as forgiving. This application would be best served by a device capable of monitoring at all light levels.