Total Respiratory Extracorporeal Support

Total respiratory extracorporeal support refers to ECMO application in the most severe acute respiratory failure patients with hypoxaemia refractory to lung- protective ventilation and adjunctive therapies like inhaled nitric oxide, prone positioning and recruitment manoeuvres. The aim is to provide viable oxygenation when the natural lung becomes unable to provide it and prevent the mechanical ventilation-associated lung damage. Therefore, total extracorporeal respiratory support is viewed as a rescue therapy for severely hypoxaemic ARDS patients.

The reason to institute ECMO in severe ARDS is to break the “vicious cycle” of tissue hypoxia (Fig. 7.3) [64]. Refractory hypoxaemia leads in the most severe cases to tissue hypoxia; in this setting the weapons that conventional mechanical ventilation uses to relieve hypoxaemia are the increase of FiO₂ up to 1 and the increase of mean airway pressure (PEEP, I:E ratio manipulation, plateau, recruitment manoeuvres). The increase in intrathoracic pressures leads in turn to haemodynamic compromise defacing, in the most severe cases, the effects of the relief of hypoxaemia on tissue hypoxia. In this setting, institution of high-flow total ECMO support can provide viable delivery of oxygen to the tissues also when gas exchange through the natural lung is completely abolished.

Indeed, high-flow ECMO provides also total CO₂ removal, abolishing the need of tidal ventilation of the natural lung to remove CO₂. During ECMO the natural lungs can be maintained “at rest” avoiding high plateau pressures and high minute ventilation requirements that stretch the low-compliance “baby lungs” of severe ARDS leading to barotrauma, volutrauma and biotrauma and breaking therefore the vicious cycle of ventilator-associated lung injury (VALI or VILI) and the final dismal result of multiple organ failures (MOFs) leading to death [65].