Thorax 1987;42:892-896 Evaluation of the Ohmeda 3700 pulse oximeter

ABSTRACT Arterial oxygen saturation values (Sao2) from 60 % to 98 % were measured by the Ohmeda 3700 pulse oximeter with the three types of probe available and compared with values of oxygen saturation estimated from direct arterial sampling (arterial oxygen and carbon dioxide tensions and pH) on 65 occasions. The response time of the oximeter was measured after a sudden rise in inspired oxygen concentration. Artefact rejection was assessed by arterial compression prox-imal to the probe site, and by simultaneous recordings of overnight Sao2 on opposite hands. The ability to recreate patterns of oscillating Sao2 from the data stored in the oximeter was also investigated. With the best probe system the oximeter measured Sao2, relative to arterial values estimated from Pao2, with a mean (SD) difference of-0 4 % (1 8%). The response time was com-parable with those of previous oximeters. It was not possible to generate artefactual dips in excess of2 % Sao2, and the dual overnight recordings rarely showed even small dips on one tracing alone. The stored data can recreate oscillating Sao2 signals with wavelengths down to about 35 seconds, but not below. The Ohmeda 3700 pulse oximeter appears to be suitable for unattended overnight recordings of Sao2. The Ohmeda Biox 3700 pulse oximeter is a new con-tinuous monitor of arterial oxygen saturation and pulse rate. Its easy portability, the availability of finger as well as ear probes, eight hours of internal memory, and apparently better ability to reject low quality signals should constitute important advan-tages over previous oximeters, particularly for unattended overnight recordings of arterial oxygen saturation (Sao2). We have tested aspects of the machine's per-formance with particular attention to inaccuracies that might occur during unattended ovemight record-ings. These include comparison of the oximeter Sao2 with values obtained from arterial sampling, speed of response, artefact rejection, and the ability of the stored data to recreate the original pattern of Sao2 oscillations