To the Editor

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We read with interest the recent article by Gutsche et al1 regarding veno-venous (VV) extracorporeal membrane oxygenation (ECMO) in hemodynamically unstable patients. It certainly adds to the discussion about which patients are likely to be supported by and benefit from such an invasive intervention. The authors focus on the importance of evaluating cardiac function before determining whether VV or veno-arterial ECMO is appropriate. However, they do not report on the cardiac function of any of the patients in the study other than saying simply that patients with severe ventricular dysfunction were excluded from consideration. This is relevant, as the reduction in vasopressor need may differ based on the underlying cause of hypotension. As discussed in the accompanying editorial, the shock present at the time of cannulation may be due to right ventricular (RV) dysfunction, septic shock, or both.2 In patients with significant RV dysfunction, support with VV ECMO may improve cardiac output through multiple beneficial effects on pulmonary vascular resistance and thus decrease vasopressor or inotrope requirements.3 As the authors converted all infusions to norepinephrine equivalents, it is impossible to know if the reduction in dosage correlated more with vasopressors, inotropes, or differential effects on pulmonary vascular resistance. It would be of interest to note whether there was any pattern in reduction specific to inotropes that would suggest improvement in ventricular function. This additional information might help inform the crucial question posed by the authors in their discussion—the minimum RV function which is safely supported with VV ECMO alone.
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