1997 OPEN FORUM Abstracts
ASSESSMENT OF OXYGEN SATURATION WITH EAR VS FINGER OXIMETRY IN PATIENTS WITH CYSTIC FIBROSIS
Sandra Strizek, RRT, Tim Hallberg, MS, Nancy Hordvik, RRT, Gerald Judy, MD, Paul Sammut, MD, John Colombo, MD
Department of Pediatrics, University of Nebraska, Omaha, Nebraska Ear or finger oximetry measurements are often utilized in patients with cystic fibrosis (CF). We have previously reported that oximetry values obtained from the ear may be significantly higher than from the finger and that the amount of difference between the two is more closely associated with deterioration in pulmonary function (rho= 0.259, p < 0.01) and decreased oxygenation (rho=0.876, p < 0.001) rather than the magnitude of clubbing (rho=0.164, p=ns) (1). In order to determine which measurement site more closely reflects "true" oxygen saturation, we simultaneously obtained 11 arterial blood gas samples (ABGs) and oximetry readings in 9 patients with CF on 11 different occasions. All patients had at least a 4% difference in ear vs. finger readings. Oximetry on the ear and finger was measured with the Ohmeda 3700 oximeter and arterial blood was analyzed with a Radiometer (ABL 500 or 520), all are accurate within 2% of the reading. The measurements of pO2 and sO2 were comparable for either the ABL 500 or 520. The mean (range) of SaO2 by ABG was 91.7 (88.7-95.6%), by ear was 94.0 (90-98%), and by finger was 89.7 (86-93%). All three mean values were significantly different from each other (paired t >= 3.86, p < =0.002). Although finger oximetry readings more closely correlated with oxygen saturation obtained by ABG (r=0.77, p=0.005) than ear oximetry (r=0.63, p=0.039), the mean finger and ear correlated the best (r=0.84, p=0.001). We conclude that: 1) Neither ear nor finger oximetry readings accurately reflect "true" arterial oxygen saturation as obtained by ABGs as ear readings tend to overestimate the "true" value and finger readings, although closer, tend to slightly underestimate the value. 2) The average of the two site values most closely approximate "true" arterial saturation. 3) Inaccurate measurement of arterial saturation may lead to erroneous estimation of a patient's need for oxygen supplementation.
1. Strizek S, Hordvik N, Hallberg T, Colombo J. Comparison of ear vs. finger probes in cystic fibrosis (CF). Respir Care, 40(11): 1165, 1995.