Noninvasive and mainstream end-tidal carbon dioxide monitoring via nasal cannula is a unique and useful technique for diagnosing pulmonary hypertension in patients with heart failure

Abstract

Purpose: End-tidal carbon dioxide (ETCO2) monitoring is commonly used for intubated patients receiving mechanical ventilation in the fields of anesthesiology and critical care medicine. Noninvasive and mainstream ETCO2 monitoring has been long-awaited so as to expand its use to other clinical settings. The partial pressure of ETCO2 (PETCO2) depends on the pulmonary ventilation-perfusion (V/Q) relationship and cell metabolism, and in normal subjects, PETCO2 values of around 40 mmHg reflect normal alveolar PCO2. Heart failure (HF) is one of the suitable pathological conditions to apply ETCO2 monitoring and recently low PETCO2 has been reported to be a predictor of prognosis in patients with HF. In this study, we aimed to clarify the association between hemodynamic parameters and PETCO2 in patients with HF. Methods: Twenty-four consecutive patients who received both right heart catheterization (RHC) and ETCO2 monitoring were enrolled for analysis. We measured pulmonary capillary wedge pressure (PCWP), pulmonary arterial pressure (PAP), and right atrial pressure. Cardiac output was calculated using two approaches, thermodilution and the Fick method. The cardiac index, pulmonary vascular resistance index (PVRI) and trans-pulmonary gradient (TPG) were also calculated. Mixed venous oxygen saturation (SvO2) was obtained by analyzing pulmonary arterial blood gas. PETCO2 was simultaneously obtained during RHC using a newly developed mainstream ETCO2 monitoring technique that obtains noninvasive measurements via nasal cannula. Results: Study participants included 12 patients with dilated cardiomyopathy, 3 with hypertrophic cardiomyopathy, 7 with heart transplant, 1 with peripartum cardiomyopathy, and 1 with ischemic cardiomyopathy. In all cases, cardiomyopathy was complicated by New York Heart Association (NYHA) functional class II to IV HF, and heart transplant patients had NYHA functional class I to II symptoms. No patients had any lung disease complications. The average PETCO2 of all patients was 28±6 mmHg, and PETCO2 showed significant negative correlations with mean PAP, PCWP, PVRI and TPG respectively (r=0.78, p<0.0001; r=0.70, p<0.0001; r=0.75, p<0.0001; r=0.64, p=0.0006). Further, receiver operating characteristic analysis suggested that PETCO2 <27 mmHg was an appropriate cut-off value for diagnosing the presence of pulmonary hypertension (PH). Conclusions: This study demonstrates that PETCO2 measurement may be a simple and promising technique for determining the presence and severity of PH, a well-known predictive factor for poor prognosis in patients with HF.