title: What is the potential role of transcutaneous carbon dioxide in guiding acute noninvasive ventilation?
abstract: BACKGROUND
  Transcutaneous carbon dioxide (PtcCO2 ) monitoring is rarely used in the acute hospital setting, where serial samples of arterial blood are instead taken to measure carbon dioxide tension (PaCO2 ). In this pilot observational study, we assessed the potential of PtcCO2 monitoring to calculate pH and guide management of acute noninvasive ventilation (NIV).
  
  
  METHODS
  Ten subjects with acute hypercapnic respiratory failure were recruited. All had arterial lines placed to guide acute NIV. PtcCO2 was monitored for 12 h (TOSCA TCM4) and compared with PaCO2 . Noninvasive transcutaneous pH was determined from PtcCO2 and calculated bicarbonate and then compared with true arterial pH. Agreements between PCO2 and pH methods were assessed using Bland-Altman analysis of limits of agreement and Pearson correlation coefficients. Hypothetical adjustments to acute NIV settings were based on transcutaneous data alone and evaluated in comparison with true management. Pain scores for each method were compared using the Wilcoxon signed-rank test.
  
  
  RESULTS
  PCO2 time trends were concordant. Mean PCO2 bias was -2.33 (95% limits of agreement of -9.60 to 5.03) mm Hg, and r = 0.89 (P < .001). Mean pH bias was 0.012 (95% limits of agreement of -0.070 to 0.094), and r = 0.84 (P < .001). Hypothetical clinical decisions based on transcutaneous data alone matched true management on 85% of 34 occasions. Initiation of transcutaneous monitoring was less painful than the arterial equivalent (P = .008).
  
  
  CONCLUSIONS
  This pilot study demonstrates that PtcCO2 monitoring provides a continuous and reliable trend and also allows pH prediction. This patient-friendly approach is a promising alternative to repeated arterial blood gas sampling in patients requiring NIV for acute hypercapnic respiratory failure.
authors.affiliation: The University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom. james@vanoppen.org.uk.
authors.forename: James D
authors.initials: JD
authors.lastname: van Oppen
authors.affiliation: Department of Respiratory Medicine, Nottingham University Hospitals NHS Trust, Nottingham, United Kingdom.
authors.forename: Priya S
authors.initials: PS
authors.lastname: Daniel
authors.affiliation: Department of Respiratory Medicine, Nottingham University Hospitals NHS Trust, Nottingham, United Kingdom.
authors.forename: Milind P
authors.initials: MP
authors.lastname: Sovani
mesh_terms: D000368:Aged; D001785:Blood Gas Monitoring, Transcutaneous / Q000379:methods*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods*; D063087:Noninvasive Ventilation / Q000379:methods*; D010147:Pain Measurement; D010865:Pilot Projects; D015203:Reproducibility of Results; D012131:Respiratory Insufficiency / Q000097:blood* / Q000628:therapy
keywords: NIV; acute hypercapnic respiratory failure; noninvasive ventilation; transcutaneous carbon dioxide; type 2 respiratory failure