Quantifying ventilator unloading in CPAP ventilation

• Published in: Computers in biology and medicine Vol. 142; p. 105225
• Main Authors: Guy, Ella F.S., Chase, J. Geoffrey, Knopp, Jennifer L., Shaw, Geoffrey M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01.03.2022; Elsevier Limited
• Subjects: Alveoli; Animals; Breathing; Continuous Positive Airway Pressure; CPAP; Diaphragm (Anatomy); Humans; Hypotheses; Internal Medicine; Lungs; Mechanical ventilation; Mechanics; Optimization; Other; Patient effort; Patients; PEEP; Pressure; Regression analysis; Respiration; Respiration, Artificial; Respiratory mechanics; Respiratory modelling; Respiratory system; Tidal Volume; Unloading; Ventilation; Ventilator unloading; Ventilators; Ventilators, Mechanical; Work of Breathing; NIMV; Ventilator unloading; CPAP; Respiratory modelling; PEEP; Work of breathing; Respiratory mechanics; WOB; Patient effort; Continuous Positive Airway Pressure; Work Of Breathing; Non-invasive Mechanical Ventilation; Positive End Expiratory Pressure
• ISSN: 0010-4825; 1879-0534; 1879-0534
• DOI: 10.1016/j.compbiomed.2022.105225

The intrinsic (muscular) patient effort driving inspiration in non-invasive ventilation modes, such as continuous positive airway pressure (CPAP) therapy, has not been identified from non-invasive data. Current CPAP settings are based on clinical judgment and assessment of symptoms of respiratory distress. Non-optimal settings, including too much positive end expiratory pressure (PEEP) can cause unintended lung injury and ventilator unloading, where patient effort drops and the CPAP device enables too much work being imposed on the injured lung. Currently, there is no non-invasive means of quantifying or identifying these effects. A novel model-based method of ascertaining intrinsic patient work of breathing (WOB) in CPAP is developed based on linear single compartment and 2nd order b-spline models previously used in invasive ventilation modes. Results are compared to current clinical indications, such as total Imposed WOB from the CPAP device and beak length, the latter of which is the clinical metric used to indicate alveolar overdistension. Intrinsic and Imposed WOB are compared. The hypothesis is that ventilator unloading can be assessed as a decrease in Intrinsic WOB relative to Imposed WOB, as PEEP and associated ventilator unloading rise. This hypothesis is tested using 14 subjects from a CPAP trial of several breathing rates at two PEEP levels. The ratio of Intrinsic to Imposed WOB, normalised per unit tidal volume, decreased with increasing PEEP (4–7 cm H2O), capturing the expected trend of ventilator unloading. Ventilator unloading was observed across all breathing rates. Beak length measurements showed no conclusive evidence of capturing overdistension at higher PEEP or ventilator unloading. Patient Intrinsic WOB in CPAP was non-invasively quantified using model-based methods, based on pressure and flow measurements. The ratio of Intrinsic to Imposed WOB per unit tidal volume clearly and consistently showed ventilator unloading across all patients and breathing rates, with Intrinsic WOB decreasing with increasing PEEP. This trend was not observed in the current clinical metric of beak length. Non-invasively quantifying Intrinsic WOB and ventilator unloading is the critical first step to objectively optimising clinical CPAP settings, patient care, and outcomes. •A model-based method of estimating patient inspiratory driving pressure in CPAP ventilation is presented.•The ratio of ventilator unloading is quantified in a pool of healthy subjects over different PEEP levels.•Identifies the concept of ventilator unloading as a potential clinical metric to inform the prescription of CPAP therapy.