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 [1] 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 [2] was then used to identify underlying respiratory elastance (AUCE _drs ). The area of the unreconstructed M-wave has less pressure, resulting in a lower overall AUCE _drs without reconstruction. The missing area of the airway pressure or AUCE _drs is hypothesized to be a surrogate of patient-specific inspiratory to assess the strength of SB efforts. AUCE _drs and missing area A₂ are compared with/without reconstruction.

Figure 1

E _drs for M-wave and reconstructed airway pressure at PEEP = 15 cmH ₂ O.

Results

Median AUCE _drs and breath-specific effort using reconstruction were 24.99 (IQR: 22.90 to 25.98) cmH₂O/l and 3.64 (IQR: 0.00 to 3.87)% versus AUCE _drs of 20.87 (IQR: 15.24 to 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).

Conclusion

A simple reconstruction method enables the real-time measurement of respiratory system properties of a SB patient and measures the surrogate of the SB effort, that latter of which has clinical use in deciding whether to extubate or re-sedate the patient.