Bedside Contribution of Electrical Impedance Tomography to Setting Positive End-Expiratory Pressure for Extracorporeal Membrane Oxygenation-treated Patients with Severe Acute Respiratory Distress Syndrome

Abstract

Rationale: Optimal positive end-expiratory pressure (PEEP) is unknown in patients with severe acute respiratory distress syndrome (ARDS) on extracorporeal membrane oxygenation receiving mechanical ventilation with very low tidal volume.

Objectives: To evaluate the ability of electrical impedance tomography (EIT) to monitor a PEEP trial and to derive from EIT the best compromise PEEP in this setting.

Methods: A decremental PEEP trial (20-0 cm H₂O) in 5 cm H₂O steps was monitored by EIT, with lung images divided into four ventral-to-dorsal horizontal regions of interest. The EIT-based PEEP providing the best compromise between overdistention and collapsed zones was arbitrarily defined as the lowest pressure able to limit EIT-assessed collapse to less than or equal to 15% with the least overdistention. Driving pressure was maintained constant at 14 cm H₂O in pressure controlled mode.

Measurements and main results: Tidal volume, static compliance, tidal impedance variation, end-expiratory lung impedance, and their respective regional distributions were visualized at each PEEP level in 15 patients on extracorporeal membrane oxygenation. Low tidal volume (2.9-4 ml/kg ideal body weight) and poor compliance (12.1-18.7 ml/cm H₂O) were noted, with significantly higher tidal volume and compliance at PEEP₁₀ and PEEP₅ than PEEP₂₀. EIT-based best compromise PEEPs were 15, 10, and 5 cm H₂O for seven, six, and two patients, respectively, whereas PEEP₂₀ and PEEP₀ were never selected.

Conclusions: The broad variability in optimal PEEP observed in these patients with severe ARDS under extracorporeal membrane oxygenation reinforces the need for personalized titration of ventilation settings. EIT may be an interesting noninvasive bedside tool to provide real-time monitoring of the PEEP impact in these patients.

Keywords: acute respiratory distress syndrome; electrical impedance tomography; extracorporeal membrane oxygenation; mechanical ventilation; positive end-expiratory pressure.