Time-Varying Respiratory System Elastance: A Physiological Model for Patients Who Are Spontaneously Breathing

Abstract

BackgroundRespiratory mechanics models can aid in optimising patient-specific mechanical ventilation (MV), but the applications are limited to fully sedated MV patients who have little or no spontaneously breathing efforts. This research presents a time-varying elastance (Edrs) model that can be used in spontaneously breathing patients to determine their respiratory mechanics.MethodsA time-varying respiratory elastance model is developed with a negative elastic component (Edemand), to describe the driving pressure generated during a patient initiated breathing cycle. Data from 22 patients who are partially mechanically ventilated using Pressure Support (PS) and Neurally Adjusted Ventilatory Assist (NAVA) are used to investigate the physiology relevance of the time-varying elastance model and its clinical potential. Edrs of every breathing cycle for each patient at different ventilation modes are presented for comparison.ResultsAt the start of every breathing cycle initiated by patient, Edrs is < 0. This negativity is attributed from the Edemand due to a positive lung volume intake at through negative pressure in the lung compartment. The mapping of Edrs trajectories was able to give unique information to patients’ breathing variability under different ventilation modes. The area under the curve of Edrs (AUCEdrs) for most patients is > 25 cmH2Os/l and thus can be used as an acute respiratory distress syndrome (ARDS) severity indicator.ConclusionThe Edrs model captures unique dynamic respiratory mechanics for spontaneously breathing patients with respiratory failure. The model is fully general and is applicable to both fully controlled and partially assisted MV modes.

Noninvasive Estimation of Respiratory Mechanics in Spontaneously Breathing Ventilated Patients: A Constrained Optimization Approach.

“…Chiew et al [20] have developed a method that provides estimation of a time-varying elastance parameter in spontaneously breathing patients, without requiring any specific maneuver. However, the elastance parameter estimated by this method includes the confounding effects of the respiratory muscles pressure exerted by the patient.…”

Model-based PEEP titration versus standard practice in mechanical ventilation: a randomised controlled trial

“…The CURE RCT implements a protocolised staircase PEEP recruitment manoeuvre together with novel computer software to calculate respiratory system elastance in real time. The computer software, CURE Soft [25], uses a single compartment lung model [39] together with other model-based approach [24,40] to aid clinicians during PEEP selection. This process potentially reduces selected PEEP variability and provides more consistent clinical guidance.…”

Respiratory mechanics assessment for reverse-triggered breathing cycles using pressure reconstruction

“…The reverse-triggering or patient effort creates anomalies in the patient airway pressure waveform, resulting in potential mis-identification of underlying respiratory mechanics if using simple models [6,9]. Specifically, patient effort reduces the net airway pressure for a given volume and leads to a lower calculated respiratory elastance due to the effective negative elastance component resulting from the patient's inspiratory effort [10]. Hence, the identified parameters do not represent the true underlying mechanics, as the patient-specific, variable inspiratory effort input was not accounted for in the model.…”

“…These 'unaffected' pressure waveforms can be used to estimate the patient-specific underlying respiratory mechanics in real-time, which can be used to guide MV therapy [10,13,14].…”