METHODS: Ten mechanically ventilated ARDS patients from the Christchurch Hospital Intensive Care Unit were included in this study. Each patient underwent a stepwise PEEP recruitment manoeuvre. Airway pressure and flow data were recorded using a pneumotachometer. Patient-specific respiratory elastance (Ers ) and dynamic functional residual capacity (dFRC) at each PEEP level were calculated and compared. Optimal PEEP for each patient was identified by finding the minima of the PEEP-Ers profile.
RESULTS: Median Ers and dFRC over all patients and PEEP values were 32.2 cmH2O/l [interquartile range (IQR) 25.0-45.9] and 0.42 l [IQR 0.11-0.87]. These wide ranges reflect patient heterogeneity and variable response to PEEP. The level of PEEP associated with minimum Ers corresponds to a high change of functional residual capacity, representing the balance between recruitment and minimizing the risk of overdistension.
CONCLUSIONS: Monitoring patient-specific Ers can provide clinical insight to patient-specific condition and response to PEEP settings. The level of PEEP associated with minimum-Ers can be identified for each patient using a stepwise PEEP recruitment manoeuvre. This 'minimum elastance PEEP' may represent a patient-specific optimal setting during mechanical ventilation.
TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry: ACTRN12611001179921.
METHODS: An iterative airway pressure reconstruction (IPR) method is used to reconstruct asynchronous airway pressure waveforms to better match passive breathing airway waveforms using a single compartment model. The reconstructed pressure enables estimation of respiratory mechanics of airway pressure waveform essentially free from asynchrony. Reconstruction enables real-time breath-to-breath monitoring and quantification of the magnitude of the asynchrony (MAsyn).
RESULTS AND DISCUSSION: Over 100,000 breathing cycles from MV patients with known asynchronous breathing were analyzed. The IPR was able to reconstruct different types of asynchronous breathing. The resulting respiratory mechanics estimated using pressure reconstruction were more consistent with smaller interquartile range (IQR) compared to respiratory mechanics estimated using asynchronous pressure. Comparing reconstructed pressure with asynchronous pressure waveforms quantifies the magnitude of asynchronous breathing, which has a median value MAsyn for the entire dataset of 3.8%.
CONCLUSION: The iterative pressure reconstruction method is capable of identifying asynchronous breaths and improving respiratory mechanics estimation consistency compared to conventional model-based methods. It provides an opportunity to automate real-time quantification of asynchronous breathing frequency and magnitude that was previously limited to invasively method only.