C105-15 Non-invasive Assessment of Inspiratory Effort in Patients Undergoing Non-invasive Ventilation: The Inspire Study

Abstract Rationale Monitoring of patient inspiratory effort during noninvasive ventilation (NIV) may help to optimize ventilator settings and prevent deleterious consequences of excessive load (1, 2). Esophageal manometry remains the reference method to assess the pressure generated by the inspiratory muscles (Pmus), yet its invasiveness limits routine application. In intubated patients, a brief end-expiratory occlusion maneuver allows measurement of the decrease of airway occlusion pressure (Pocc), which provides a noninvasive estimate of Pmus (3). However, whether this approach is valid in patients receiving NIV, remains unexplored. Method In this multicenter physiological study (NCT06344234), hypoxemic patients during post-extubation NIV through an oronasal interface and high-performance ICU ventilators were monitored with esophageal manometry. Before extubation, occlusion maneuvers were performed during passive ventilation, to verify the correct positioning of the esophageal balloon (4) and to calculate chest-wall elastance (5). During NIV, three brief end-expiratory occlusions in each patient were performed to measure Pocc. Gas flow and airways and esophageal pressure signals were continuously recorded and stored for offline analysis. Pmus was measured by subtracting chest-wall recoil from esophageal pressure (5). In a derivation cohort the Pocc/Pmus ratio was used to calculate a conversion constant (K), which was then applied to calculate the estimated Pmus from Pocc (PMUSestimated = Pocc*K) in an internal derivation cohort. Agreement between measured and estimated Pmus was assessed. Results Data from 40 patients were analyzed. Ten patients (30 measurements) formed the derivation cohort, yielding a mean conversion constant (K) of -0.84 (95% CI to -0.90 to -0.78). The validation cohort included 30 patients (90 measurements). In the validation cohort, PMUSestimated and esophageal-derived Pmus measured during non-occluded breathing (PMUSmeasured) showed a strong linear relationship (R² = 0.88) (Figure 1, panel A). Bland-Altman analysis revealed a bias of -0.31 cmH2O (95% CI -0.59 to -0.02), with limits of agreement ranging from -2.91 to + 2.30 cmH2O (Figure 1, panel B). Conclusion In this preliminary analysis, in patients receiving post-extubation NIV, Pmus estimated from Pocc demonstrated a strong correlation and acceptable agreement with Pmus measured during non-occluded breathing. These findings suggest that Pocc may serve as a noninvasive surrogate of Pmus at the bedside during NIV. These data require confirmation upon completion of the adequate study sample size. Bibliography 1.Grieco DL et al. Minerva Anestesiol 2019;85:1014-1023.2.Yoshida T, et al. Curr Opin Crit Care 2020;26:59-65.3.Bertoni M, et al. Crit Care 2019;23:.4.Baydur A, et al. Am Rev Respir Dis 1982;126:788-791.5.Henderson WR, et al. Am J Respir Crit Care Med 2017;196:822-833. This abstract is funded by: None