Use of Maximum End-Tidal CO2 Values to Improve End-Tidal CO2 Monitoring Accuracy

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Abstract:

BACKGROUND: The arterial partial pressure of CO2 (PaCO2) can be grossly estimated by the end-tidal partial pressure of CO2 (PETCO2). This principle is used in SmartCare (Dräger, Lübeck, Germany), which is an automated closed-loop system that uses PETCO2 to estimate alveolar ventilation during mechanical ventilation. OBJECTIVE: To assess whether the maximum PETCO2 value (instead of the averaged PETCO2 value) over 2-min or 5-min periods improves PaCO2 estimation, and determine the consequences for the SmartCare system. METHODS: We continuously monitored breath-by-breath PETCO2 during ventilation with SmartCare in 36 patients mechanically ventilated for various disorders, including 14 patients with COPD. Data were collected simultaneously from SmartCare recordings, every 2 min or 5 min, and through a dedicated software that recorded ventilation data every 10 s. We compared the maximum and averaged PETCO2 values over 2-min and 5-min periods to the PaCO2 measured from 80 arterial blood samples clinically indicated in 26 patients. We also compared SmartCare's classifications of patient ventilatory status based on averaged PETCO2 values to what the classifications would have been with the maximum PETCO2 values. RESULTS: Mean PaCO2 was 44 ± 11 mm Hg. PaCO2 was higher than averaged PETCO2 by 10 ± 6 mm Hg, and this difference was reduced to 6 ± 6 mm Hg with maximum PETCO2. The results were similar whether patients had COPD or not. Very few aberrant values (< 0.01%) needed to be discarded. Among the 3,137 classifications made by the SmartCare system, 1.6% were changed by using the maximum PETCO2 value instead of the averaged PETCO2 value. CONCLUSIONS: Use of maximum PETCO2 reduces the difference between PaCO2 and PETCO2 and improves SmartCare's classification of patient ventilatory status.

Keywords: alveolar ventilation; capnometry; closed loop systems; mechanical ventilation; monitoring; weaning

Document Type: Research Article

DOI: http://dx.doi.org/10.4187/respcare.00837

Affiliations: Réanimation Médicale, l’Assistance Publique-Hôpitaux de Paris, Hôpital Henri Mondor, France

Publication date: March 1, 2011

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