Transcutaneous PCO2 monitoring during initiation of noninvasive ventilation.
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.


BACKGROUND
www.uniklinik-freiburg.de/zks/live/uklregister/Oeffentlich.html Identifier:UKF001271.
Storre
Jan H
JH
Department of Pneumology, University Hospital Freiburg, Killianstrasse 5, D-79106 Freiburg, Germany.
Steurer
Boris
B
Kabitz
Hans-Joachim
HJ
Dreher
Michael
M
Windisch
Wolfram
W
D000368:Aged; D000704:Analysis of Variance; D001785:Blood Gas Monitoring, Transcutaneous / Q000379:methods*; D002245:Carbon Dioxide / Q000097:blood*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000628:therapy*; D008297:Male; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000378:metabolism
D002245:Carbon Dioxide