Background Transcutaneous carbon dioxide monitoring is rarely used in the acute hospital setting, where samples of arterial blood are used to measure pCO2. This is a pilot observational study to assess the role of transcutaneous (ptcCO2) versus arterial (paCO2) monitoring during acute NIV, both to calculate pH and to guide therapy.
Methods Ten patients with acute hypercapnic respiratory failure were recruited. All had arterial lines placed for guiding acute NIV therapy. ptcCO2 was monitored for 12 hours (Radiometer TOSCA TCM4) and compared to measures of paCO2 from samples taken from the arterial lines. Non-invasive pHtc was calculated from ptcCO2. Agreements between pCO2 and pH methods were assessed using Bland-Altman analysis and regression. The potential for guiding acute NIV therapy based on transcutaneous data was assessed and pain scores for each method were compared using the Wilcoxon signed rank test.
Results Mean bias between paCO2 and ptcCO2 was -0.31 (95% CI 0.98) kPa, R2 = 0.79 (p < 0.0001). ptcCO2 followed the same time trend as paCO2. Mean pH bias was not statistically significant at 0.006 (95% CI 0.116), R2 = 0.64 (p < 0.0001). If based on transcutaneous data only, clinical decisions would have been unchanged in nine out of ten patients. Transcutaneous readings were also less painful (p < 0.001) and preferred by patients.