A pressure reconstruction method for spontaneous breathing effort monitoring
Introduction: Estimating respiratory mechanics of mechanically ventilated (MV) patients is unreliable when patients exhibit spontaneous breathing (SB) efforts on top of ventilator support. This reverse triggering effect  results in an M-wave shaped pressure wave. A model-based method to reconstruct the affected airway pressure curve is presented to enable estimation of the true underlying respiratory mechanics of these patients. Methods: Airway pressure and flow data from 72 breaths of a pneumonia patient were used for proof of concept. A pressure wave reconstruction method ‘fills’ parts of the missing area caused by SB efforts and reverse triggering by connecting the peak pressure and end inspiration slope (Figure 1). A time-varying elastance model  is then used to identify underlying respiratory elastance (AUCEdrs). The area of the unreconstructed M-wave has less pressure, resulting in a lower overall AUCEdrs without reconstruction. The missing area of the airway pressure or AUCEdrs is hypothesized to be a surrogate of patient-specific inspiratory to assess the strength of SB efforts. AUCEdrs and missing area A2 are compared with/without reconstruction. Results: Median AUCEdrs and breath-specific effort using reconstruction were 24.99[IQR:22.90-25.98] cmH2O/l and 3.64 [IQR:0.00-3.87] % versus AUCEdrs of 20.87[IQR:15.24-27.48] cmH2O/l for unreconstructed M-wave data, indicating significant patient and breath specific SB effort, and the expected higher elastance (p < 0.05). Conclusions: A simple reconstruction method enables the real-time measurements respiratory system properties of a SB patient and measure the surrogate of the SB effort, that latter of which has clinical useful in deciding whether to extubate or re-sedate the patient.