**9.5 Disadvantages of ECMO in cardiogenic shock**

1.Left ventricular (LV) distension: ECMO drains the blood from the right atrial, but, has no direct effect on the left side of the heart. Due to the absence of reservoir, smaller size of venous cannula, significantly amount of blood escapes the venous drainage and reaches the left heart. Further, blood returning to the left atrium vis. Thebesian veins, bronchial veins draining into the pulmonary veins, and blood returning to the LV due to aortic regurgitation also reach the left ventricle. Further, ECMO increases LV afterload by retrogradely flowing the blood into the ascending aorta. The heart with severely reduced contractility is unable to overcome this afterload, and the aortic valve remains closed. These patients are at risk of left ventricular distention, left atrial hypertension, and pulmonary edema [119].

2.Complications: Due to the large size of arterial and venous cannula, patients are at risk of vascular injury and injury to the heart. A meta-analysis reported 40.8% incidence of bleeding, 30.4% incidence of infection, 5.8% incidence of stroke, and 4.7% incidence of lower limb amputation [60]. The cannulation site is the most common site for bleeding [109, 120]. In a Japanese study, use of smaller cannula in small caliber vessels was associated with reduced risk of bleeding without compromising the outcome [121]. A meta-analysis of 22 cohort studies also found that distal perfusion cannulas reduced the limb ischemia by 15.7% [122]. Another devastating complication of ECMO is intracranial hemorrhage as patients on VA-ECMO are anticoagulated with heparin or bivalirudin. In a large study of adult patients with intracranial bleeds after ECMO, low platelets were independently associated with an increased risk of bleeding [123]. The risk of inter-cranial bleeding increased significantly at platelet counts below 50,000/cc. Therefore, it is recommended to maintain the platelet counts ≥100,000/cc while a patient is on ECMO [124].

The outcome of ECMO can be improved by using smaller cannula in small vessels, more liberal use of LV venting, routine use of distal limp perfusion cannula, and maintaining adequate platelet counts. SAVE and ENCOURAGE score systems, which are used in pre-ECMO patient variables to predict outcomes, may help in better patient selection for this risky but life-saving intervention [125].
