B78-08 Transcutaneous Carbon Dioxide Trajectory During Noninvasive Ventilation Titration

Abstract Rationale COPD patients with chronic hypercapnic respiratory failure may benefit from high intensity noninvasive ventilation (NIV) which aims to reduce arterial PaCO2. We previously reported our experience with protocolized outpatient titration of NIV settings to high intensity ventilation with transcutaneous CO2 (TcCO2) monitoring over 90 minutes. We hypothesized that TcCO2 stabilized within 15 minutes of a change in NIV settings. Methods Patients with chronic hypercapnic respiratory failure attributed primarily to COPD underwent protocolized NIV titration as outpatient. Titration protocol allowed stepwise adjustment of inspiratory pressure, inspiratory time, cycling threshold and backup rate using bilevel S/T mode with the goal of reducing TcCO2. Each stepwise adjustment was made following 15 minutes of ventilation on the prior setting. TcCO2 was recorded every 3 minutes. To assess group-level changes in TcCO2 following NIV titration, a linear mixed-effects model was fit including time as a categorical fixed effect and random intercepts for patient and snippet nested within patient to account for repeated measurements. Post-hoc pairwise comparisons of estimated marginal means were obtained using Tukey adjustment for multiple testing. Results 15 patients (9 female) underwent titration. The average age(±SD) was 68.9(6.9) years old. Patients had severe COPD with mean FEV1 26.2(3.9)% predicted and chronic ventilatory failure with mean PaCO2 58.9(7.9) mmHg and TcCO2 60.9(8.1) at baseline. We reviewed 62 episodes (15-minute snippets) of TcCO2 trajectories following NIV setting change. Percent change in TcCO2 (median Q1, Q3) was -0.56 (-2.86, 0.00) during the first 3 minutes of setting change and 0.00 (-1.49, 0.35) during the second 3 minutes of setting change, remaining stable afterwards. Estimated marginal means decreased from 58.9 mmHg at baseline to 57.7 mmHg at 3 minutes and 57.4 mmHg thereafter. Pairwise Tukey comparisons showed that all post-titration timepoints differed significantly from baseline (all p 0.001), while no differences were observed among 3, 6, 9, 12, and 15 minutes (all p 0.7). High variability in coefficient of variation (5%) was not observed in any of the snippets after 6 minutes of NIV setting change. Conclusions Among a group of COPD patients with stable hypercapnic respiratory failure presenting to an outpatient clinic, noninvasive ventilator setting changes resulted in a relatively stable and lower transcutaneous CO2 measurement within 3-6 minutes. This abstract is funded by: None