Closed Loop Mechanical Ventilation and ECMO

Overview

Mechanical ventilation and ECMO are both technologies interacting on gas exchange. Nevertheless, besides a consensus paper, no evidence-based guidelines regarding protective lung ventilation on ECMO exist to date. Mechanical Ventilation with Intellivent-ASV, an algorithm driven, closed loop system, provides an opportunity to standardize ventilation on ECMO. We propose and validate lung protective ventilation with a closed loop ventilation mode in patients with ECMO.

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. The adaptive lung ventilation mode Intellivent-ASV+® has been shown to ventilate normal lungs, lungs with ARDS and COPD within the limits of safe ventilation recommended by the guidelines. Patients on Intellivent-ASV+® had tidal volumes (Vt) ≤ 8 ml/kg/BW, plateau pressure (Pplat) \< 30 cmH2O and a driving pressure \< 15 cmH2O. Compared to conventional ventilation, patients on Intellivent-ASV+® mode had higher PEEP and lower FiO2, suggesting better recruitment of the dependent part of the lung. Combining mechanical ventilation using the Intellivent-ASV+® mode and ECMO offers a unique opportunity of having a mechanical ventilator which automatically adapts to lung mechanics and the contribution of ECMO supporting gas exchange. The main objective of this research project is to propose and verify whether the ventilation mode Intellivent-ASV+® is capable to execute lung protective ventilation despite the presence of an ECMO altering gas exchange.

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