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Abstract

Introduction: We propose a novel mathematical method that can provide continuous and accurate lung mechanic measurements of respiratory system compliance (Crs), resistance (Rrs), and plateau pressure (Pplt) without flow interruption VC+. Hypothesis: We hypothesized that a real time calculation of the expiratory time constant during passive deflation of the lung can be used for accurate and continuous calculation of Pplt, Rrs, and Crs without the need of flow pattern modification or interruption. Methods: 32 ICU patients with heterogeneous respiratory failure requiring mechanical ventilation on VC+ mode were studied following IRB approved protocol. All patients were sedated between a Riker score of 2 and 3. PPlt, Rrs, and Crs were determined using the traditional method by introducing an EIP with a constant inhalation flow in a volume controlled breath. Inspiratory flow on VC was adjusted by matching it with the Ti of the VC+ breath. Pplt, Rrs, and Crs were determined using the proposed expiratory time constant method on breaths with identical tidal volumes and peak inspiratory flow rates. The Pplt, Crs, and Rrs from the two methods were compared using Bland-Altman plot. Results: The proposed method was able to predict the Pplt, Crs, and Rrs values as well as the traditional method with correlation coefficients (r2) of 0.98, 0.97, and 0.88, respectively. The Bland-Altman analysis found a bias in prediction of 0.6 cmH2O, -0.003 L/cmH2O, and -0.6 cmH2O/L/s, respectively for Pplt, Crs, and Rrs. Average breathing frequency while on PRVC was 16 +/- 5, Fio2 0.45 +/- 12, tidal volume 6 to 10 ml/kg ideal body weight, peak inspiratory pressure 29 +/- 8 cmH2O, PEEP 8 +/- 4 cmH2O. Conclusions: We demonstrated that the expiratory time constant can be used to calculate pulmonary mechanics accurately and continuously. Real time measurement of pulmonary mechanics may allow clinicians to better address underlying pulmonary pathophysiology resulting in improved patient care.