The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

COMPARISON OF CUTANEOUS CARBON DIOXIDE TENSION AND OXYGEN SATURATION MEASUREMENTS USING A NEW COMBINED DIGITAL SENSOR WITH ARTERIAL BLOOD GAS VALUES

Prashant N Chhajed, MD, FCCP 1, Ludwig Heuss, MD 2, Michael Tamm, MD 1Divisions of Respiratory Medicine1 and Gastroenterology2, University Hospital Basel, Switzerland

Background: Various medical procedures are commonly performed using conscious sedation. Oxygen saturation measured with a pulse oximeter does not completely reflect hypoventilation and carbon dioxide monitoring is desirable. Recently, a new digital device which measures both oximetry and cutaneous carbon dioxide tension (PcCO2) has been developed. Having the possibility to measure a reliable non invasive surrogate marker of arterial carbon dioxide tension along with pulse oximetry might improve patient safety during medical procedures such as bronchoscopy and thoracoscopy carried out under conscious sedation. The other areas where this might have potential application is the intensive care unit to monitor non invasive ventilation, weaning from mechanical ventilation or post extubation, in the sleep laboratory to titrate non invasive ventilation pressures using continuous carbon dioxide tension monitoring as opposed to only diurnal blood gas measurements to check the arterial carbon dioxide tension.

Aim: Assess the accuracy of a newly developed combined PcCO2 and oximeter (SpO2) monitor.

Method: A new combined digital earlobe sensor (Sentec AG, Therwil, Switzerland) measuring SpO2 (%) and PcCO2 (mm Hg) was used. This device measures the PcCO2 using a Severinghaus-type electrochemical sensor and the SpO2 using conventional optical pulse oximetry sensors. The sensor is heated to a constant surface temperature of 42 degrees Celsius. It undergoes regular automatic calibration when it is placed on the docking station in between procedures. The calibration and equilibration time are about five minutes each.

Results: Accuracy of the combined SpO2/PcCO2 earlobe sensor was compared in 86 patients with 106 PaCO2 and SaO2 blood gas values obtained by arterial puncture. In the lung function laboratory (90 samples) an average of two blood-gas analyzers (ABL 500 and ABL 725, Radiometer, Copenhagen, Denmark) was used and in the intensive care unit (16 samples) values were available from one blood gas analyzer (ABL 735, Radiometer, Copenhagen, Denmark). The correlation coefficient for carbon dioxide tension and oxygen saturation comparing measurements of the combined earlobe sensor and arterial blood gas analysis were r = 0·95 and r = 0·91 respectively.

Conclusion: This combined SpO2/PcCO2 sensor showed good correlation with measurements obtained with arterial blood gas analysis. This novel approach to detect and monitor both hypoxemia and hypoventilation has potential applications in patient management in the ICU, in the sleep laboratory to quantify hypoventilation and to enhance patient safety during procedures performed under conscious sedation such as bronchoscopy and medical thoracoscopy.

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