Time-Varying Respiratory Elastance for Spontaneously Breathing Patients

Respiratory mechanics models can be used to optimise patient-specific mechanical ventilation (MV), but are limited to fully sedated MV patients who are not spontaneously breathing. This research presents a non-invasive model-based method to determine respiratory mechanics of spontaneously breathing MV patients. Patient-specific respiratory mechanics of 22 spontaneously breathing patients are described using a single compartment lung model with time-varying elastance (Edrs). The normalised Edrs trajectories and the area under the curves (AUCEdrs) are calculated using clinical data from 22 patients ventilated using pressure support (PS) and neurally adjusted ventilatory assist (NAVA). Edrs trajectories are also compared between ventilation modes. Edrs for PS ventilation were significantly higher compared to NAVA (p < 0.05). Edrs trajectories were more variable during NAVA than PS (p < 0.05). 20 of 22 patients had AUCEdrs > 25 cmH2Os/l. The AUCEdrs is a surrogate of elastance, and thus can be used as a respiratory failure severity indicator. This non-invasive model-based approach captures unique dynamic respiratory mechanics for spontaneously breathing patients during PS and NAVA. The model is fully general and is applicable to both fully controlled and partially assisted MV modes, with the resulting potential to standardise treatment for all MV patients.