Transcutaneous Pco2 monitoring during initiation of noninvasive ventilation

Background: To assess the efficacy of transcutaneous Pco(2) (Pteco(2)) measurements for monitoring alveolar ventilation in patients requiring noninvasive positive-pressure ventilation (NPPV). Methods: In a prospective study on method agreement pairs of Paco(2) and Ptcco(2) (SenTec Digital Monitor; SenTec AG; Therwil, Switzerland), measurements were performed every 10 min during the establishment of NPPV over a 4-h period in 10 patients (8 patients with COPD) presenting with acute-on-chronic hypercapnic respiratory failure, thus providing 250 pairs of measurement. Results: Mean (+/- SD) Paco(2) decreased from 67.2 +/- 11.9 mm Hg (Ptcco(2), 65.5 +/- 13.9 mm Hg) to 54.6 +/- 8.8 min Hg (Ptcco(2), 47.8 +/- 8.8 mm Hg), and mean pH increased from 7.36 +/- 0.03 to 7.44 +/- 0.04. Following Ptcco(2) assessment, Ptcco(2) in the ensuing 2-min period was the strongest predictor for Paco(2) compared to Ptcco(2) in the ensuing 5-min period and to real-time measurements. Ptcco(2) was highly correlated with Paco(2) (r = 0.916; p < 0.001), as determined by linear regression analysis. The mean difference between PaCo2 and Ptcco(2) was 4.6 mm Hg, and the limits of agreement (bias +/- 1.96 SDs) ranged from -3.9 to 13.2 mm Hg, following the Bland and Altman analysis. Retrospective drift correction produced an even higher correlation (r = 0.956; p < 0.001) with lower limits of agreement (-1.7 to 7.5 mm Hg). Conclusions: Ptcco(2) measurements provide a sensitive, continuous, and noninvasive method for monitoring alveolar ventilation in patients who are receiving short-term NPPV therapy. Drift correction Of Ptcco(2) measurements improves the accuracy of Ptcco(2) monitoring compared to the gold standard Paco(2) assessment. A lag time of approximately 2 min is present for reliable Ptcco(2) values compared to PaC02 values. However, individual variance between Paco(2) and Ptcco(2) cannot be excluded. Trial registration: www.uniklinik-freiburg.de/zks/live/uklregister/Oeffentlich.html Identifier: UKF001271.