Improved ear oximetry with a rubefacient ointment

Abstract

Arterial blood oxygen saturation measurements were compared with those calculated from arterial blood samples in 51 adult cardiac surgery patients studied in the immediate postoperative period. Each patient's ears were arterialized on a random basis, either by 20 sec of brisk rubbing (control ear), or by the topical application of 0.05 ml of Finalgon Strong Ointment (Boehringer Ingelheim, West Germany) (experimental ear). Oximeter determined control ear measurements averaged 1.69% saturation lower than those calculated from arterial blood gases, whereas the difference averaged 0.38% higher on the ear treated with the rubefacient. A paired sample two-tailed Student's t-test showed significant difference between measurements made on the untreated ear and the calculated controls (p less than 0.001). No difference was found between measurements made on the treated ear and calculated controls (0.05 less than p less than 0.10). Thus, test ointment is useful for noninvasive oxygen saturation measurements with the Hewlett-Packard oximeter, particularly in cold or peripherally vasoconstricted patients in whom ear blood flow would be otherwise inadequate.