Hypotension During Extracorporeal Circulatory Support Indicated for Cardiogenic Shock

Cardiogenic shock is characterized by global tissue hypoperfusion following a decrease in cardiac output by impairing myocardial performance in the absence of hypovolemia. This life-threatening hypoperfusion quickly leads to multiple organs dysfunction with a high risk of cardiac arrest. The main cause is ischemic. The prognosis remains poor with mortality between 40 and 50% and depends on the speed of care by a specialized team. Early etiologic treatment is essential, but initial symptomatic management is based on catecholamines, mainly norepinephrine and dobutamine. The intra-aortic balloon pump showed no improvement in survival in large randomized studies. Refractory cardiogenic shock is defined by the inefficiency or intolerance of catecholamines and the indication of temporary circulatory support should be considered as soon as possible in the absence of contraindications (comorbidities, advanced age, therapeutic limitation). The veno-arterial extracorporeal membrane oxygenation (VA-ECMO or ECLS) is the preferred circulatory assistance in this indication because it provides an overall circulatory support up to 100% of the theoretical cardiac output, with oxygenation, and is quickly implanted peripherally (surgical or percutaneous cannulation of the femoral vein and the femoral artery). However, this extracorporeal circulation also has disadvantages by opposing a major afterload to the failing left ventricle and reducing or even abolishing the pulmonary circulation and blood flow in the heart chambers. In addition, the interaction with the artificial surfaces and the oxygenation membrane of the extracorporeal circuit contributes to the inflammatory response already initiated as a result of low cardiac output, tissue hypoperfusion, mesenteric ischemia and possibly myocardial infarction in case of acute coronary syndrome. This systemic inflammatory response syndrome (SIRS) is similar to sepsis and its main clinical presentation is a vascular dysfunction resulting in vasoplegia and capillary leak syndrome responsible for relative hypovolemia and interstitial inflation.

Since the flow provided by the centrifugal pump is continuous, the blood pressure under VA-ECMO presents low or no pulsatile waves and is better represented by the mean arterial pressure (MAP). The ideal targets of MAP under VA-ECMO are controversial but it is widely accepted that the MAP should not be less than 65mmHg as recommended in septic shock to maintain an acceptable perfusion pressure and should not exceed 95mmHg to limit afterload. Between these limits, the MAP must be individualized according to each situation (hypertensive patient for example). In France, Norepinephrine is the first-line drug to achieve this goal of MAP after correction of volemia, without dose limitation in the absence of currently validated alternative, while resistance mechanisms can be activated, and its efficiency may be limited in case of acidosis. Potential side effects are the occurrence of atrial or ventricular arrhythmias, tachycardia, pro-inflammatory cytokine release, immunosuppression, renal dysfunction.

Management of MAP and vasopressors under VA-ECMO is poorly described in the literature (5), although Norepinephrine is widely used in routine practice. In particular, the investigators do not know the frequency of use and Norepinephrine doses during ECMO-VA, as well as their prognostic involvement. Vasoplegia during VA-ECMO is defined by a Norepinephrine dose greater than 0.1µg/kg/min after a 500ml fluid challenge despite overall blood flow (ECMO + native heart) greater than 2l/min/m2 or allowing to achieve 65% of ScvO2.

This cohort study aims to describe the vasoplegia observed during VA-ECMO, the Norepinephrine treatment characteristics, complications and outcome. The primary end-point is the incidence of a composite criteria of major complications including death, acute kidney injury and arrythmias.