Abstract
Errors in measurement by pulse oximeters were thought to be caused by electric warming blankets in patients with peripheral hypoperfusion. This hypothesis was tested experimentally on healthy volunteers. Large fluctuations (0-99%) of oxygen saturation (SpO2) were observed with peripheral hypoperfusion experimentally induced by compression of the upper arm. An oscilloscope displayed cyclic noises of 50Hz from light absorbance signals when the blanket was on. The mean noise voltage decreased by 99% when the blanket was shielded with a conductive cover, and decreased by 5-63% when the probe of the pulse oximeter was shielded.
No fluctuations of SpO2 were recorded after changing the frequency of light absorbance measurements from intervals of 3.3msec to 4.4msec. These results demonstrated that pulse-oximetric errors induced by an electric blanket can be avoided by changing the frequency of light absorbance measurements.
