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 (p_tcCO₂) versus arterial (p_aCO₂) 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. p_tcCO₂ was monitored for 12 hours (Radiometer TOSCA TCM4) and compared to measures of p_aCO₂ from samples taken from the arterial lines. Non-invasive pH_tc was calculated from p_tcCO₂. 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 p_aCO₂ and p_tcCO₂ was -0.31 (95% CI 0.98) kPa, R² = 0.79 (p < 0.0001). p_tcCO₂ followed the same time trend as p_aCO₂. 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.

Conclusion This pilot study demonstrates the potential for using transcutaneous pCO₂ monitoring to calculate pH and guide therapy, in the acute care setting. p_tcCO₂ shows promise in replacing arterial blood gases, in acute hypercapnic respiratory failure.

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Abstract P173 Figure 1.