Comparison of three transmittance oximeters

Estimates of oxygenation from three transmittance oximeters, Hewlett-Packard 47201A, Nellcor, and Biox III, were obtained simultaneously in ten healthy human subjects during isocapnic progressive hypoxia and under conditions of episodic hypoxemia. In the oxygen saturation range studied (approximately 95-75%), results showed that values from the Nellcor finger oximeter were 2-4% lower than values from the Hewlett-Packard ear oximeter. Values from the Biox III oximeter, using either the ear or finger probe, were 3-7% higher than those from the Hewlett-Packard, and the biggest discrepancies were seen as oxygen saturation fell below 80%. This often resulted in an estimation of the ventilatory response to hypoxia as measured using the Biox III oximeter that was higher than estimates using the Nellcor or the Hewlett-Packard (P less than 0.005). Hypoxic ventilatory responses using the Nellcor and the Hewlett-Packard oximeters gave similar values. During rapidly changing oxygenation, the distribution of values for oxygen saturation were significantly different for the three oximeters. For example, the median of the distribution for Nellcor values was 89 +/- 1.5% (mean +/- SEM); for the Hewlett-Packard, it was 92 +/- 1.3%; and for the Biox III, it was 93 +/- 0.8% (finger) and 95 +/- 1.6% (ear). The authors conclude that differences between the three non-invasive transmittance oximeters will affect clinical measurement of the ventilatory responsiveness to hypoxia and the estimation of the stimulus for hypoxic complications in respiratory diseases.