Feasibility of titrating PEEP to minimum elastance for mechanically ventilated patients

Abstract

Background: Selecting positive end-expiratory pressure (PEEP) during mechanical ventilation is important, as it can influence disease progression and outcome of acute respiratory distress syndrome (ARDS) patients. However, there are no well-established methods for optimizing PEEP selection due to the heterogeneity of ARDS. This research investigates the viability of titrating PEEP to minimum elastance for mechanically ventilated ARDS patients.

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 (E_rs ) 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-E_rs profile.

Results: Median E_rs 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 E_rs corresponds to a high change of functional residual capacity, representing the balance between recruitment and minimizing the risk of overdistension.

Conclusions: Monitoring patient-specific E_rs can provide clinical insight to patient-specific condition and response to PEEP settings. The level of PEEP associated with minimum-E_rs 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.

Keywords: ARDS; Dynamic functional residual capacity; Mechanical ventilation; PEEP; Respiratory elastance.

Figure 1

Cohort respiratory data plotted against positive end-expiratory pressure (PEEP) level. The top panel shows the distribution of patient-specific elastance (E_rs) across the 10 patients at each PEEP level. The middle panel shows peak inspiratory pressure (PIP) and the bottom plot dynamic functional residual capacity (dFRC). Red cross outliers: the outliers in E_rs are mainly from patient 5. PEEP levels were classified by rounding to the nearest 5 cmH₂O.

Figure 2

Respiratory mechanics as a function of positive end-expiratory pressure (PEEP). Top left panel, patient 2; top right panel, patient 6; bottom left panel, patient 8; bottom right panel, patient 10. PEEP derived from minimum-E_rs and inflection-E_rs method are as indicated. The dashed line is the range for inflection-E_rs. The dynamic functional residual capacity (dFRC) is also indicated.

Figure 3

Pearson’s correlation. (Left) Elastance-work of breathing (E_rs-WOB), R = 0.62. (Right) Elastance-dynamic functional residual capacity (E_rs-dFRC), R = −0.62.

Figure 4

Positive end-expiratory pressure (PEEP) selection comparison. Comparison between clinical selection, minimum-E_rs and inflection-E_rs.

Figure 5

Ventilation with no perfusion. This condition is due to insufficient blood flow into the ‘newly opened’ alveoli capillaries. A darker colour shows better perfusion (red) and/or better distribution (blue) of air.