Does preoperative night pulse oximetry provide a reliable baseline?

Background: Postoperative hypoxaemia may be detected by pulse oximetry moni toring of the arterial haemoglobin saturation (SpO2). The SpO2-values obtai ned on the preoperative night are presumed to represent baseline values for the patients. The aim of this study was to evaluate the possible differenc e between nocturnal SpO2-values in the patient's home and in the hospital b efore operation. Methods: We included 20 patients, 60 years or older, who underwent continuo us monitoring of SpO2 on one night in the patient's home and on the night f ollowing hospitalisation before surgery. The alarms were turned off and the values were not accessible to the hospital staff. The SpO2 value was store d every 10 s. We described the general oxygen saturation level using the me dian of all valid values and we calculated the number of valid SpO2-values at 3 levels: above 90%, between 86 and 90%, and below 86%. Results: The number of valid SpO2-values at home and in the hospital were 2 186 and 2330, respectively; the median value was 96% on both occasions. Onl y 0.36% of the values were below 91% on the two occasions and there were no statistically significant differences between the number of SpO2-values at any of the considered levels. Conclusion: Arterial oxygen saturation values measured on the preoperative night in the hospital seem reliable as baseline values for elderly patients .