Transcutaneous PCO2 monitoring: Does it really help when initiating noninvasive ventilation in acute-on-chronic respiratory failure?

Abstract

Background

To assess the efficacy of transcutaneous Pco2 (Ptcco2) measurements for monitoring alveolar ventilation in patients requiring noninvasive positive-pressure ventilation (NPPV).

Methods

In a prospective study on method agreement pairs of Paco2 and Ptcco2 (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) Paco2 decreased from 67.2+/−11.9 mm Hg (Ptcco2, 65.5+/−13.9 mm Hg) to 54.6+/−8.8 mm Hg (Ptcco2, 47.8+/−8.8 mm Hg), and mean pH increased from 7.36+/−0.03 to 7.44+/−0.04. Following Ptcco2 assessment, Ptcco2 in the ensuing 2-min period was the strongest predictor for Paco2 compared to Ptcco2 in the ensuing 5-min period and to real-time measurements. Ptcco2 was highly correlated with Paco2 (r=0.916; p<0.001), as determined by linear regression analysis. The mean difference between Paco2 and Ptcco2 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

Ptcco2 measurements provide a sensitive, continuous, and noninvasive method for monitoring alveolar ventilation in patients who are receiving short-term NPPV therapy. Drift correction of Ptcco2 measurements improves the accuracy of Ptcco2 monitoring compared to the “gold standard” Paco2 assessment. A lag time of approximately 2 min is present for reliable Ptcco2 values compared to Paco2 values. However, individual variance between Paco2 and Ptcco2 cannot be excluded. Trial registration: www.uniklinik-freiburg.de/zks/live/uklregister/Oeffentlich.html Identifier:UKF001271.

©2007 American College of Chest Physicians