How I approach membrane lung dysfunction in patients receiving ECMO
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EDITORIAL
How I approach membrane lung dysfunction in patients receiving ECMO Bishoy Zakhary1* , Leen Vercaemst2, Phillip Mason3, Marta V. Antonini4,5, Roberto Lorusso6 and Daniel Brodie7,8
Introduction With improvements in circuit technology and expanding supportive evidence, extracorporeal membrane oxygenation (ECMO) use has grown rapidly over the past decade [1]. Advances in pump and membrane lung (ML) design have led to simpler and more efficient circuits. Circuitrelated complications, however, remain frequent and associated with considerable morbidity [2]. Mechanisms of membrane lung dysfunction The ML is responsible for oxygen uptake and carbon dioxide removal. The non-biologic surface of the ML activates inflammatory and coagulation pathways with thrombus formation, fibrinolysis, and leukocyte activation [3–5] leading to ML dysfunction. Activation of coagulation and fibrinolysis can precipitate systemic coagulopathy or hemolysis, while clot deposition can obstruct blood flow [6, 7]. Additionally, moisture buildup in the gas phase and protein and cellular debris accumulation in the blood phase may contribute to shunt and dead-space physiology, respectively, impairing gas exchange [8, 9]. These three categories—hematologic abnormalities, mechanical obstruction, and inadequate gas exchange—prompt the majority of ML exchanges. Membrane lung monitoring Hematologic profile
Monitoring of hematologic variables, including coagulation and hemolysis labs, can help identify the development of an ECMO coagulopathy or hemolysis. *Correspondence: [email protected] 1 Division of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, OR, USA Full list of author information is available at the end of the article
Pressure monitoring
The pressure drop across the ML (ΔP) is measured as (Additional file 1: Supplemental Figure):
P = PPre − PPost where PPre = pre-ML pressure, PPost = post-ML pressure. As clot forms in the ML, increases in resistance (RML) are reflected as increases in ΔP. To correct for changes in blood flow rate (BFR), monitoring of ΔP normalized for BF rate (ΔP/BFR) more directly reflects RML. Membrane lung gas transfer
Applying the Fick principle across the ML, oxygen (O2) transfer may be calculated as:
V ′ O2 = BFR(CPost O2 −CPre O2 ) where V′O2 = O2 transfer across the ML (mL/min), BFR = blood flow rate (L/min), CxO2 = O2 content of (pre-/post-ML) blood (mL/L) for
Cx O2 = 13.4 · Hb · Sx O2 + 0.03 · Px O2 where Hb = hemoglobin (g/dL), SxO2 = O2 saturation of (pre-/post-ML) blood, PxO2 = O2 partial pressure of (pre-/post-ML) blood (mmHg). Measurement of V′O2 provides an objective measure of oxygen transfer and can confirm ML dysfunction, when clinically indicated.
Membrane lung dysfunction Prompt recognition of ML dysfunction is vital for safety, allowing for elective replacement in a controlled manner. On the other hand, replacement of an adequately functioning device—requiring temporary cessation of ECMO
© The Author(s) 2020. Open Access This article is
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