• Serge Kocher, Roman Rohling, and Andres Tschupp.
• SenTec Inc., Ringstrasse 39, CH-4106 Therwil, Switzerland. kocher@sentec.ch
• J Clin Monit Comput. 2004 Apr 1; 18 (2): 75-9.

ObjectiveFor determining the adequacy of ventilation, conventional pulse oximetry should be amended by PaCO2 (= arterial carbon dioxide partial pressure). This study investigates the precision of carbon dioxide measurements of the first digital ear-clip sensor providing continuous non-invasive monitoring of PaCO2, SpO2 (= functional arterial oxygen saturation as estimated with a pulse oximeter) and pulse rate and compares it to two conventional analog oximeters.Methods30 hypoxemia episodes in 6 adult volunteers were investigated in a standardized protocol.EquipmentMasimo analog finger sensor, Nellcor analog ear sensor, SenTec digital ear sensor.ResultsThe difference between PCO2 data (= PaCO2 estimated from the measured PcCO2 based on an algorithm by Severinghaus) (PcCO2 = cutaneous carbon dioxide pressure) and the PaCO2 is clinically unimportant. Therefore, we suggest, the two methods of estimating patient's carbon dioxide status can be used interchangeably.ConclusionsCombined digital SpO2/ PcCO2 ear sensors are very promising to allow for a fast and reliable monitoring of patient's oxygenation, hyper-/hypocapnia and ventilation with one single non-invasive probe. Optimal primary signal processing--amplification and digitalisation within the probe--allow for fast and reliable downstream signal processing algorithms. The resulting short SpO2 response times give the medical staff more time to take appropriate actions.

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