Abstract
BACKGROUND: The end-tidal partial pressure of carbon dioxide (P(ET)CO(2)) can be used to estimate the arterial partial pressure of carbon dioxide (PaCO(2)) in patients who undergo mechanical ventilation via endotracheal intubation. However, no reliable method for measuring P(ET)CO(2) during noninvasive ventilation (NIV) has been established. The purpose of this study was to evaluate the correlation and agreement between PaCO(2) and P(ET)CO(2) measured by these two methods and to compare them in patients who underwent NIV after extubation. METHODS: This study was a randomized, open-label, crossover trial in a mixed intensive care unit. We included patients who were planned for NIV after extubation and for whom the difference between P(ET)CO(2) and PaCO(2) was ≤ 5 mmHg. We compared mainstream capnography using an inner cup via face mask (the novel method) with sidestream capnography (the previous method) during NIV. The relationships between PaCO(2) and P(ET)CO(2) were evaluated by computing the Pearson correlation coefficient, and the agreement between PaCO(2) and P(ET)CO(2) was estimated using the Bland-Altman method. RESULTS: From April 2020 to October 2021, 60 patients were included to the study. PaCO(2) and P(ET)CO(2) were well correlated in both methods (the novel methods: r = 0.92, P < 0.001; the previous method: r = 0.79, P < 0.001). Mean bias between PaCO(2) and P(ET)CO(2) measured using the novel method was 2.70 (95% confidence interval [CI], 2.15-3.26) mmHg with 95% limits of agreement (LoA) ranging from - 1.61 to 7.02 mmHg, similar to the result of measurement during SBT (mean bias, 2.51; 95% CI, 2.00-3.02; 95% LoA, - 1.45 to 6.47 mmHg). In contrast, measurement using the previous method demonstrated a larger difference (mean bias, 6.22; 95% CI, 5.22-7.23; 95% LoA, - 1.54 to 13.99 mmHg). CONCLUSION: The current study demonstrated that the novel P(ET)CO(2) measurement was superior to the previous method for PaCO(2) prediction. During NIV, the novel method may collect as sufficient exhalation sample as during intubation. Continuous P(ET)CO(2) measurement combined with peripheral oxygen saturation monitoring is expected to be useful for early recognition of respiratory failure among high-risk patients after extubation. Trial registration UMIN-CTR UMIN000039459. Registered February 11, 2020.