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 .