The assessment of cardiac function in veno-venous extracorporeal membrane oxygenation: the emerging role of bedside echocardiography.

The management of patients with acute respiratory distress syndrome (ARDS) has deeply changed in recent years. While the ventilatory strategy was initially focused on the lung, now it also considers  pulmonary vascular injury and its effects on the right ventricle and on hemodynamics. This is mainly due to echocardiography, which allows intensivists to evaluate accurately, non invasively and at bedside right ventricular function (RV) at baseline and after adaptation of ventilatory settings. This “new” ventilatory approach was summarized as “what is good for the lung is good for the right ventricle” [1]  and, though not validated in randomized controlled trials, an RV protective approach was recently formalized  as a step-by-step approach to the ventilatory strategy, putting the pulmonary circulation and the right ventricle (and thus echocardiography) at the center of the decision-making process [1,2].

Veno-venous extracorporeal membrane oxygenation (VV-ECMO) is a well-established therapy in patients with ARDS unresponsive to conventional therapy and it is being increasingly used in these patients. However,  so far,  there is a paucity of data (mainly including case reports and observational studies) delineating the role of echocardiography in the management of adult patients supported by  VV ECMO [3].

To date, echocardiography is mainly used for selecting the type of ECMO (veno arterial vs veno-venous), monitoring cannulation and the early detection of complications [3] but its utilization show wide variations from center to center.

Nevertheless, latest scientific evidence highlights other potentials for the use of echocardiography in patients supported by VV ECMO. Firstly, the assessment and monitoring of cardiac (biventricular) function. Fagnoul D et. al [4] observed that RV and LV dysfunction occurred commonly in patients with H1N1 infection and that patients with RV dysfunction more frequently received inotropic agents and VV ECMO. In these patients, myocardial depression may be masked, and thus less easily identified, due to the decrease in left ventricle afterload related to peripheral vasodilation, and by tachycardia. Secondly, the identification of high cardiac output in patients supported by VV ECMO and refractory hypoxemia. Guerracino F et al. [5] observed that  the reduction of cardiac output (assessed by echocardiography) through short-acting Beta-blocker administration in selected patients with ARDS and refractory hypoxia despite ECMO support was associated with an increased in peripheral oxygenation.

Overall, data that can be obtained from the echocardiographic assessment in a patient supported by VV ECMO are numerous and many of these (i.e. assessment of LV and RV function, fluid responsiveness) can have an impact on therapy and  its adaptation to the changing conditions of this complex and vulnerable patients. In particular, echocardiography should be performed in all patients before VV-ECMO implantation with the aim to assess mainly LV and RV dimensions and functions and systolic pulmonary arterial pressure. Further serial echocardiographic examinations could provide information especially on adaptation of the RV ventricle to the VV-ECMO as well as on LV performance (systolic and diastolic function). For example, the development of RV dilatation and/or hypertrophy under VV ECMO support could indicate a more severe disease and probably the inefficiency of VV ECMO in the single patient. Survival and days on VV ECMO support could the first pragmatic endpoints for future investigations.

Since advanced echocardiography is spreading in our ICUs, it is probably time to merge echocardiography and VV ECMO in order to highlight its concrete advantages in the management of these patients as well as its limits.