How best to set the ventilator on extracorporeal membrane lung oxygenation

Extracorporeal respiratory support in patients with acute respiratory distress syndrome is applied either as rescue maneuver for life-threatening hypoxemia or as a tool to reduce the harm of mechanical ventilation. Depending on the blood and gas flow, extracorporeal support may completely substitute the natural lung as a gas exchanger (high-flow venovenous bypass) or reduce the need for mechanical ventilation, enabling the removal of a fraction of the metabolically produced CO2.

Recent studies provide a description on how mechanical ventilation is normally applied in combination with extracorporeal support in acute respiratory distress syndrome. The data show a general trend: a variable decrease of fraction of inspired oxygen (0.9 to 0.7 or 0.4), a consistent decrease in tidal volume (by 2 ml/kg), no change in positive end-expiratory pressure (maintained around 12-13 cmH2O) and a moderate decrease in the respiratory rate (22 to 15 bpm). These ventilatory settings are applied in whatever extracorporeal membrane lung oxygenation modality (venovenous versus venoarterial) and independent from the extent of extracorporeal support (partial or total substitution of gas exchange).

Mechanical ventilation and extracorporeal support are marginally integrated. The best environment for lung healing - complete lung collapse or protective ventilation strategy or fully open and immobile lung (all three conditions feasible with extracorporeal support) - remains to be defined.