Abstract

Arterial blood gas tensions, pH, and carboxyhaemoglobin were measured on 322 occasions in 165 patients and the actual oxygen saturation of the haemoglobin (Sao2) was compared with the ear oxygen saturation (SEO2) recorded during the arterial sampling with a Biox IIA ear oximeter. The overall agreement between SEO2 and Sao2 was good, with a mean difference in saturation (SEO2-Sao2) of + 1.5% (SD 3.0). The difference in saturation remained similar at all levels of arterial saturation observed and was unaffected by carboxyhaemoglobin concentration. On four occasions (1% of readings), however, SEO2 and Sao2 differed by more than 10% and such occasional errors might be misleading in clinical practice.