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Sensors 2010, 10(1), 491-500;

Optimal Clinical Time for Reliable Measurement of Transcutaneous CO2 with Ear Probes: Counterbalancing Overshoot and the Vasodilatation Effect

Pneumology Service, Hospital de Sabadell, Corporació Parc Taulí, Sabadell 08208, Spain
Department of Medicine, Autonomous University of Barcelona (UAB), Cerdanyola del Valles, Barcelona 08193, Spain
Author to whom correspondence should be addressed.
Received: 23 November 2009 / Revised: 20 December 2009 / Accepted: 21 December 2009 / Published: 11 January 2010
(This article belongs to the Section Chemical Sensors)
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OBJECTIVES: To determine the optimal clinical reading time for the transcutaneous measurement of oxygen saturation (SpO ) and transcutaneous CO2 (TcPCO2) in awake spontaneously breathing individuals, considering the overshoot phenomenon (transient overestimation of arterial PaCO2). EXPERIMENTAL SECTION: Observational study of 91 (75 men) individuals undergoing forced spirometry, measurement of SpO2 and TcPCO2 with the SenTec monitor every two minutes until minute 20 and arterial blood gas (ABG) analysis. Overshoot severity: (a) mild (0.1–1.9 mm Hg); (b) moderate (2–4.9 mm Hg); (c) severe: (>5 mm Hg). The mean difference was calculated for SpO2 and TcPCO2 and arterial values of PaCO2 and SpO2. The intraclass correlation coefficient (ICC) between monitor readings and blood values was calculated as a measure of agreement. RESULTS: The mean age was 63.1 ± 11.8 years. Spirometric values: FVC: 75.4 ± 6.2%; FEV1: 72.9 ± 23.9%; FEV1/FVC: 70 ± 15.5%. ABG: PaO2: 82.6 ± 13.2; PaCO2: 39.9.1 ± 4.8 mmHg; SaO2: 95.3 ± 4.4%. Overshoot analysis: overshoot was mild in 33 (36.3%) patients, moderate in 20 (22%) and severe in nine (10%); no overshoot was observed in 29 (31%) patients. The lowest mean differences between arterial blood gas and TcPCO2 was –0.57 mmHg at minute 10, although the highest ICC was obtained at minutes 12 and 14 (>0.8). The overshoot lost its influence after minute 12. For SpO2, measurements were reliable at minute 2. CONCLUSIONS: The optimal clinical reading measurement recommended for the ear lobe TcPCO2 measurement ranges between minute 12 and 14. The SpO2 measurement can be performed at minute 2. View Full-Text
Keywords: transcutaneous CO2; optimal reading time; overshoot phenomenon transcutaneous CO2; optimal reading time; overshoot phenomenon
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Domingo, C.; Canturri, E.; Moreno, A.; Espuelas, H.; Vigil, L.; Luján, M. Optimal Clinical Time for Reliable Measurement of Transcutaneous CO2 with Ear Probes: Counterbalancing Overshoot and the Vasodilatation Effect. Sensors 2010, 10, 491-500.

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