Model-based PEEP optimisation in mechanical ventilation

Abstract

BackgroundAcute Respiratory Distress Syndrome (ARDS) patients require mechanical ventilation (MV) for breathing support. Patient-specific PEEP is encouraged for treating different patients but there is no well established method in optimal PEEP selection.MethodsA study of 10 patients diagnosed with ALI/ARDS whom underwent recruitment manoeuvre is carried out. Airway pressure and flow data are used to identify patient-specific constant lung elastance (Elung) and time-variant dynamic lung elastance (Edrs) at each PEEP level (increments of 5cmH2O), for a single compartment linear lung model using integral-based methods. Optimal PEEP is estimated using Elung versus PEEP, Edrs-Pressure curve and Edrs Area at minimum elastance (maximum compliance) and the inflection of the curves (diminishing return). Results are compared to clinically selected PEEP values. The trials and use of the data were approved by the New Zealand South Island Regional Ethics Committee.ResultsMedian absolute percentage fitting error to the data when estimating time-variant Edrs is 0.9% (IQR = 0.5-2.4) and 5.6% [IQR: 1.8-11.3] when estimating constant Elung. Both Elung and Edrs decrease with PEEP to a minimum, before rising, and indicating potential over-inflation. Median Edrs over all patients across all PEEP values was 32.2 cmH2O/l [IQR: 26.1-46.6], reflecting the heterogeneity of ALI/ARDS patients, and their response to PEEP, that complicates standard approaches to PEEP selection. All Edrs-Pressure curves have a clear inflection point before minimum Edrs, making PEEP selection straightforward. Model-based selected PEEP using the proposed metrics were higher than clinically selected values in 7/10 cases.ConclusionContinuous monitoring of the patient-specific Elung and Edrs and minimally invasive PEEP titration provide a unique, patient-specific and physiologically relevant metric to optimize PEEP selection with minimal disruption of MV therapy.

Visualisation of Time-Variant Respiratory System Elastance in ARDS Models

“…It was found that E drs during increasing PEEP is significantly different to E drs during decreasing PEEP (p<0.005). Thus, this case shows the typical finding where PEEP should be titrated after the lung has been recruited [3][4][5]7]. However, a local minimum E drs was also found at 10 mbar during increasing PEEP titration, suggesting similar optimal PEEP settings.…”

“…It was found that global minimal elastance PEEP occurs at 10 mbar. During a PEEP increase, E drs decreases as recruitment of new lung volume outweighs lung stretching [7]. It was found that E drs during increasing PEEP is significantly different to E drs during decreasing PEEP (p<0.005).…”

“…E rs and R rs can be determined using multivariate regression or the integralbased method [7]. If R rs is assumed constant throughout a breath [3,4,7], E drs can be re-estimated using Equation (2) after R rs is estimated using Equation (1). (2) Patient-specific E drs is only analysed during the inspiration portion of the breathing cycle.…”

“…Dynamic respiratory system elastance (E drs ) is a breathspecific time-varying elastance [6,7]. This dynamic parameter within a single breath provides unique insight into a patient's breathing pattern, revealing lung recruitment and overdistension.…”

“…This dynamic parameter within a single breath provides unique insight into a patient's breathing pattern, revealing lung recruitment and overdistension. In addition, identifying minimum E drs also reveals the potential to titrate optimal patient-specific positive end-expiratory pressure (PEEP) to maximise recruitment without inducing lung injury [7]. This work presents a novel method in visualising E drs .…”