Letters to the Editor
We thank Lim for his interest and comments on our review article that was recently published in ASAIO Journal.1,2 We agree that extracorporeal life support (ECLS) recommendations must be made on a sound understanding of physiological principles, which explains our deliberate dedication of an entire section to clinical applied physiology. Lim clearly illustrated the physiological basis to the two values, that is, a pre-oxygenator saturation of >80% indicating a possibility of recirculation, and an ECLS flow of at least 60% of the cardiac output in our proposed algorithms to troubleshoot hypoxemia in venovenous ECLS. Although these conclusions could be derived from the equations on the determinants of pulmonary artery oxygen saturation in our review, we concur that substituting variables with actual numbers—as what Lim has elegantly demonstrated—would provide more clarity to readers. We have also acknowledged Lim’s comments and improved our original figure to highlight the concept of shunt flow, which is the blood flow (as a fraction of the cardiac output) that bypasses the ECLS circuit and therefore does not get oxygenated (see Figure, Supplemental Digital Content, http://links.lww.com/ASAIO/A279). Finally, values notwithstanding, in the absence of validated measurement tools in ECLS for variables such as recirculation flow, cardiac output, and mixed venous oxygen saturation, a thorough understanding of the physiological basis of ECLS cannot be overemphasized.
Chee Kiang Tay, MBBS
Department of Respiratory and Critical Care Medicine
Singapore General Hospital
Yang Hyun Cho, MD
Department of Thoracic & Cardiovascular Surgery
Samsung Medical Center
Seoul, South Korea
1. Sern L. The physiological basis for venovenous extracorporeal membrane oxygenation management. ASAIO J 201865: e25.
2. Tay CK, Sung K, Cho YH. Clinical pearls in venovenous extracorporeal life support for adult respiratory failure. ASAIO J 2018.64: 1–9.