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Monitoring Carbon Dioxide Tension and Arterial Oxygen Saturation by a Single Earlobe Sensor in Patients With Critical Illness or Sleep Apnea^*

^* From the Pulmonary Division (Drs. Senn, Clarenbach, and Bloch) and Medical Intensive Care Unit (Drs. Kaplan and Maggiorini), University Hospital of Zurich, Zurich, Switzerland.

Correspondence to: Konrad E. Bloch, MD, FCCP, Pneumologie, Universitätsspital Zürich, Rämistrasse 100, CH-8091 Zürich, Switzerland; e-mail: pneubloc{at}usz.unizh.ch

Objectives: The purpose of the study was to evaluate a novel, combined sensor for transcutaneous monitoring of arterial oxygen saturation and carbon dioxide tension.

Design: The new monitoring technique was compared to established reference methods.

Setting: ICU and sleep laboratory of a university hospital.

Patients: Eighteen critically ill adult patients with acute respiratory failure or heart failure, and 12 patients with sleep apnea (mean [± SD] apnea/hypopnea index, 43 ± 24 events per hour).

Measurements: Continuous measurements were performed over several hours by the novel heated (temperature, 42°C) earlobe sensor (TOSCA; Linde Medical Sensors; Basel, Switzerland), incorporating electrochemical and optical elements for carbon dioxide measurement (PtcCO₂) and pulse oximetry (SpO₂), respectively. The data were compared to the results of repeated arterial blood gas analyses in critically ill patients and to simultaneous nocturnal pulse oximetry performed with different devices with earlobe or finger sensors in sleep apnea patients.

Results: In critically ill patients, the mean difference and limits of agreement (bias ± 2 SDs) of transcutaneous PtcCO₂ vs arterial PaCO₂ were 3 ± 7 mm Hg; the corresponding values for changes in PtcCO₂ vs PaCO₂ were 1 ± 6 mm Hg. The bias ± 2 SDs for pulse oximetric SpO₂ vs arterial oxygen saturation (SaO₂) were 1 ± 4%. In sleep apnea patients, the combined earlobe sensor identified more transient oxygen desaturations, and the rate of change in oxygen saturation during events was greater compared to those with other tested pulse oximeters, indicating a faster response.

Conclusions: Due to its ability to accurately assess both ventilation and oxygenation by a single transcutaneous sensor, the described noninvasive monitoring technique is a valuable tool for respiratory monitoring with potential applications in critical care and sleep medicine.

Key Words: capnometry • carbon dioxide • critical care • oxygenation • physiologic monitoring • pulse oximetry • sleep apnea • sleep medicine • ventilation

This article has been cited by other articles:

				O. Senn, T. Brack, E. W. Russi, and K. E. Bloch A Continuous Positive Airway Pressure Trial as a Novel Approach to the Diagnosis of the Obstructive Sleep Apnea Syndrome Chest, January 1, 2006; 129(1): 67 - 75. [Abstract] [Full Text] [PDF]