Accuracy sensitivity to carboxyhemoglobin, and speed of response of the Hewlett-Packard 47201A ear oximeter.

We have shown that the Hewlett-Packard 47201A ear oximeter measures arterial O2 saturation within 95 per cent confidence limits of +/- 4 per cent when arterial blood saturation is more than 65 per cent, but at lower saturations the oximeter consistently provides a reading that is too low. The oximeter is sensitive to carboxyhemoglobin, progressively overestimating arterial saturation as carboxyhemoglobin concentration increases from 0 to 18 per cent. The time response is exponential, with a normal time constant of 3 sec, but this is halved in the fast mode or operation.