Closed Loop Mechanical Ventilation Coupled to Extracorporeal Membrane Oxygenation Support in Therapy Refractory Acute Respiratory Distress Syndrome and Cardiogenic Shock

In critically ill patients admitted to the intensive care unit due to either acute respiratory failure or circulatory collapse, mechanical ventilation in combination with either extra-corporal lung assist (VV ECMO) or cardiac assist (VA ECMO) is increasingly used. Both mechanical ventilation and ECMO contribute to the control of gas exchange hence need to be adjusted accordingly.

As an assist device like a VV ECMO or a VA ECMO the control the gas exchange needs to be adjusted via sweep gas flow (ventilation), fraction of oxygen in the sweep gas (oxygenation, FsO2) and blood flow over the extracorporeal device. The combination of adaptive ventilation with ECMO is a novel concept allowing the control of oxygenation and ventilation by the adjustment of the ECMO device only.

Adaptive lung ventilation is a category of ventilation modes, which allow the control of oxygenation and ventilation with a closed loop. Using this type of ventilation modes one can control the gas exchange automatically. In terms of CO2-management they use a target minute volume to control end-tidal CO2 and adjust depending on the amount of spontaneously triggered breaths the respiratory rate and the inspiratory pressure support or solely the pressure support. In terms of O2-management according to the peripheral O2 saturation target the PEEP (lung recruitment) and the fraction of inspired oxygen (FiO2) will be set. Both of these controllers depend on an accurate measurement of either end-tidal CO2 and peripheral O2 saturation, respectively.

There exist two recommendations how to ventilate patients with ARDS on an ECMO. First and foremost, the general guidelines of the Extracorporeal Life Support Organization (ELSO) suggest for adults to target a FiO2 of less than 0.3 with a PEEP of 5 to 15 cmH2O and a plateau pressure of less than 25 cm H2O with a respiratory rate of 5 per minute. Whereas Richard et al. in their consensus conference report from 2014 suggest to minimize plateau pressure and PEEP not being specific in terms of numbers. Both guidelines have the goal of keeping the lung at rest concerning patients with ARDS. There are no specific suggestions on ventilation management in patients with heart failure on ECMO. Whether the lung has to be kept open (recruited and less prone to atelectrauma) or kept at rest (less prone to overdistension, either volu- or barotrauma) is at the moment unclear.

Concerning mechanical ventilation settings in patients with ARDS Serpa Neto and colleagues published in 2016 a meta-analysis of nine studies, which included around 550 patients receiving ECMO for refractory hypoxemia. They showed that in these patients driving pressure was associated with in-hospital survival (survivors had a driving pressure of 16.9 cmH2O and non-survivors of 19.4, p 0.004, adjusted HR 1.06 with a 95% CI of 1.03 - 1.10). This is consistent with the study of Amato et al where they showed a reduction of the multivariate relative risk of in-hospital mortality in patients with ARDS - without ECMO - with a driving pressure of less than 15 cmH2O.