Clinical investigation of a new combined pulse oximetry and carbon dioxidetension sensor in adult anaesthesia

Objective. To test the accuracy of a new combined oxygen saturation and cut aneous carbon dioxide tension (SPO2-PCO2) sensor in a routine adult clinica l environment. This probe provides a non-invasive and continuous monitoring of the arterial oxyhaemoglobin saturation, arterial carbon dioxide tension and pulse rate at the ear lobe. The sensor is intended to measure both rel evant respiration/ventilation parameters in one single probe. Methods. Ten adult patients were consecutively studied during general anaesthesia. Durin g the first 5 min after sensor placement at the ear lobe, arterial blood sa mples were drawn each minute. Carbon dioxide tension and oxygen saturation measurements were obtained simultaneously at 1-min intervals. After this pe riod, patients were hyper-, normo- and hypoventilated. After 15 min at each setting, the simultaneously obtained cutaneous and arterial carbon dioxide tension values were compared. Results. A total of 80 comparisons between e ar lobe SpO(2)-PCO2 measurement, finger clip pulse oximetry and arterial bl ood gas values were analysed. Three minutes after sensor placement, there w ere no significant differences between ear probe (cutaneous) and arterial c arbon dioxide tensions (p = 0.367). Comparison of arterial with cutaneous c arbon dioxide values demonstrated an excellent linear correlation (r(2) = 0 .92), and showed a standard error of estimate (SDEE) of 0.26 kPa (1.95 mm H g) only. The mean difference was -0.08 kPa ( -0.60 mm Hg) with a limits of agreement range of -0.38 kPa to + 0.22 kPa ( -2.85 mm Hg to + 1.65 mm Hg). Concerning oxygen saturation measurements, the absolute SpO(2) value deviat ed 1% or less from standard pulse oximetry. Conclusions. During general ana esthesia, postoperative recovery and critical care treatment, both monitori ng of oxygenation and ventilation is important. Since pulse oximetry estima tes only arterial oxygen saturation, periodic blood sampling is still neces sary to determine the patient's arterial carbon dioxide status. We could de monstrate that the difference between cutaneous and arterial PCO2 was clini cally unimportant, and therefore we conclude that the two methods of estima ting the patient's carbon dioxide status may be used interchangeably. Our r esults demonstrated that 3 min after sensor placement, the new SpO(2)-PCO2 sensor prototype proved to be a reliable tool for continuous non-invasive m onitoring of oxygenation and ventilation.