End-tidal carbon dioxide monitoring using a naso-buccal sensor is not appropriate to monitor capnia during non-invasive ventilation

BACKGROUND: In acute respiratory failure, arterial blood gas analysis (ABG) is used to diagnose hypercapnia. Once non-invasive ventilation (NIV) is initiated, ABG should at least be repeated within 1 h to assess PaCO(2) response to treatment in order to help detect NIV failure. The main aim of this study was to assess whether measuring end-tidal CO(2) (EtCO(2)) with a dedicated naso-buccal sensor during NIV could predict PaCO(2) variation and/or PaCO(2) absolute values. The additional aim was to assess whether active or passive prolonged expiratory maneuvers could improve the agreement between expiratory CO(2) and PaCO(2). METHODS: This is a prospective study in adult patients suffering from acute hypercapnic respiratory failure (PaCO(2) ≥ 45 mmHg) treated with NIV. EtCO(2) and expiratory CO(2) values during active and passive expiratory maneuvers were measured using a dedicated naso-buccal sensor and compared to concomitant PaCO(2) values. The agreement between two consecutive values of EtCO(2) (delta EtCO(2)) and two consecutive values of PaCO(2) (delta PaCO(2)) and between PaCO(2) and concomitant expiratory CO(2) values was assessed using the Bland and Altman method adjusted for the effects of repeated measurements. RESULTS: Fifty-four datasets from a population of 11 patients (8 COPD and 3 non-COPD patients), were included in the analysis. PaCO(2) values ranged from 39 to 80 mmHg, and EtCO(2) from 12 to 68 mmHg. In the observed agreement between delta EtCO(2) and deltaPaCO(2), bias was −0.3 mmHg, and limits of agreement were −17.8 and 17.2 mmHg. In agreement between PaCO(2) and EtCO(2), bias was 14.7 mmHg, and limits of agreement were −6.6 and 36.1 mmHg. Adding active and passive expiration maneuvers did not improve PaCO(2) prediction. CONCLUSIONS: During NIV delivered for acute hypercapnic respiratory failure, measuring EtCO(2) using a dedicating naso-buccal sensor was inaccurate to predict both PaCO(2) and PaCO(2) variations over time. Active and passive expiration maneuvers did not improve PaCO(2) prediction. TRIAL REGISTRATION: ClinicalTrials.gov: NCT01489150.