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[ Home ](https://mdster.com) 2. [ Blog ](https://mdster.com/blog) 3. [ Medical Education ](https://mdster.com/blog?category=medical-education) 4. ECMO Basics in ARDS: VV vs VA, Anticoagulation, and OR Pearls [ Medical Education ](https://mdster.com/blog?category=medical-education) ECMO Basics in ARDS: VV vs VA, Anticoagulation, and OR Pearls =============================================================== An exam-focused review for anesthesiology trainees on ECMO physiology, mode selection, bleeding risk, and perioperative thinking in refractory hypoxemia. [ MDster Editorial Team ](https://mdster.com/about) · Mar 26, 2026 · 1 min read · 172 [ Reviewed by Dr. Ali Ragab, MBBCH, MSc, MCAI ](https://mdster.com/medical-reviewers/dr-ali-ragab) [Editorial Policy](https://mdster.com/editorial-policy) | [Corrections Policy](https://mdster.com/corrections) [ Anesthesiology ](https://mdster.com/blog?tag=anesthesiology) [ Anesthesiology Boards ](https://mdster.com/blog?tag=anesthesiology-boards) [ Critical Care ](https://mdster.com/blog?tag=critical-care) [ ECMO ](https://mdster.com/blog?tag=ecmo) [ ARDS ](https://mdster.com/blog?tag=ards) [ Mechanical Ventilation ](https://mdster.com/blog?tag=mechanical-ventilation) ![ECMO Basics in ARDS: VV vs VA, Anticoagulation, and OR Pearls](https://mdster.com/storage/blog/01KMSZCJV9XHSM73AR9XCG4TA5.jpg) Share this article Share this post On this page 1. [ Start with the physiology, not the machine ](#start-with-the-physiology-not-the-machine) 2. [ VV vs VA ECMO: choose by failed organ ](#vv-vs-va-ecmo-choose-by-failed-organ) 3. [ Anticoagulation: the bleeding-thrombosis knife edge ](#anticoagulation-the-bleeding-thrombosis-knife-edge) 4. [ Clinical Correlations ](#clinical-correlations) 5. [ Key Takeaways ](#key-takeaways) 6. [ Conclusion ](#conclusion) 7. [ References ](#references-heading) On this page 1. [ Start with the physiology, not the machine ](#start-with-the-physiology-not-the-machine) 2. [ VV vs VA ECMO: choose by failed organ ](#vv-vs-va-ecmo-choose-by-failed-organ) 3. [ Anticoagulation: the bleeding-thrombosis knife edge ](#anticoagulation-the-bleeding-thrombosis-knife-edge) 4. [ Clinical Correlations ](#clinical-correlations) 5. [ Key Takeaways ](#key-takeaways) 6. [ Conclusion ](#conclusion) 7. [ References ](#references-heading) A patient with influenza ARDS is proned, paralyzed, on FiO2 1.0 and high PEEP, and still saturating in the low 80s. That is the moment boards love and ICUs fear: do you keep turning the ventilator, or do you move to ECMO? ECMO is not a treatment for ARDS. It is a way to keep the patient alive while you stop injuring the lung. As of March 2026, ATS still suggests **VV ECMO** in selected severe ARDS, and current ELSO guidance recommends considering it for severe reversible respiratory failure after optimal conventional management, including prone positioning, when **PaO2/FiO2 <80 mm Hg** or when severe hypercapnia persists with **pH <7.25 and PaCO2 ≥60 mm Hg**. [\[1\]](#cite-1 "Reference [1]") Start with the physiology, not the machine ------------------------------------------ Think circuit, not magic. Blood is drained from the venous side, pumped through a membrane oxygenator, and returned to the patient. On **VV ECMO**, blood flow is the major lever for oxygen delivery, while **sweep gas** is the main lever for CO2 clearance. That is a favorite exam distinction: if the PaCO2 is high on ECMO, first think about sweep, not ventilator rate. Once VV ECMO is running, the goal is **lung rest**. ELSO describes typical rest settings with low FiO2, low RR, **plateau pressure ≤25 cm H2O**, and **PEEP ≥10 cm H2O** to reduce VILI rather than chase a perfect saturation. [\[2\]](#cite-2 "Reference [2]") VV vs VA ECMO: choose by failed organ ------------------------------------- Choose the mode by asking which organ is failing. **VV ECMO** supports gas exchange only. It provides **no direct hemodynamic support**, and increasing VV flow will not fix hypotension. **VA ECMO** returns oxygenated blood to the arterial system, so it supports both circulation and gas exchange; that is why it belongs in **cardiogenic shock**, severe biventricular failure, or arrest physiology, not isolated ARDS. [\[2\]](#cite-2 "Reference [2]") QuestionVV ECMOVA ECMOPrimary jobGas exchangeGas exchange + circulatory supportClassic patientSevere ARDS with refractory hypoxemia or hypercapniaCardiogenic shock with or without respiratory failureHemodynamic effectNo direct BP supportImproves perfusion but can increase LV afterloadCommon exam trapEscalating ventilator settings instead of ECMO settingsMissing differential hypoxemia or limb ischemia Use that table as the board-style shortcut. [\[2\]](#cite-2 "Reference [2]") The highest-yield pitfall is overcalling VA ECMO in ARDS. A severely hypoxemic patient may show RV strain and elevated pulmonary pressures, but ELSO explicitly warns that hypoxemia and hypercarbia can create RV dysfunction that often improves once VV ECMO corrects gas exchange and lets you reduce intrathoracic pressure. If the primary problem is lungs, think **VV first**. [\[2\]](#cite-2 "Reference [2]") Anticoagulation: the bleeding-thrombosis knife edge --------------------------------------------------- ECMO is a constant tug-of-war between hemorrhage and clot because blood is circulating through a foreign surface while the patient is critically ill. **Unfractionated heparin** remains the default anticoagulant in most adult ECMO programs. ELSO's anticoagulation guideline notes that **bivalirudin** and **argatroban** are increasingly used when HIT is suspected or heparin response is unreliable. Monitoring is imperfect: **ACT** is fast but nonspecific, **aPTT** is familiar but incomplete, and viscoelastic testing can add useful context when the lab number and the patient do not match. [\[3\]](#cite-3 "Reference [3]") For exams, remember the complication pattern, not just the infusion. Expect **cannulation-site bleeding**, surgical bleeding, GI or pulmonary bleeding, and the feared catastrophe of **intracranial hemorrhage**. Also expect the opposite problem: circuit clot, oxygenator failure, embolic events, and cannula thrombosis if anticoagulation is inadequate. UFH adds the possibility of **HIT**. VA ECMO adds vascular complications such as **limb ischemia**, LV afterload increase, and mode-specific neurologic risk. The practical lesson is simple: do not treat the ACT alone. Reassess hemoglobin, platelets, fibrinogen, hemolysis markers, circuit inspection, and the actual clinical bleeding or thrombosis. [\[3\]](#cite-3 "Reference [3]") > **Clinical Pearl:** On VV ECMO, tolerate an SpO2 that looks mediocre if oxygen delivery and tissue perfusion are acceptable. The classic resident mistake is turning the ventilator back into a lung-injury machine to chase 100%. [\[4\]](#cite-4 "Reference [4]") Clinical Correlations --------------------- For anesthesiologists, the perioperative issue is not memorizing the pump. It is preventing physiology from unraveling during induction, transport, positioning, and procedures. Before any trip to the OR, know the **cannulation configuration**, blood flow, sweep, delivered oxygen fraction, and recent imaging of cannula position. The current ELSO rehabilitation guideline makes the same point even for mobilization: review cannula sites, circuit settings, and the risk of kinking or migration before moving the patient. [\[5\]](#cite-5 "Reference [5]") Induction is the danger zone. In severe cardiopulmonary failure, positive-pressure ventilation can reduce venous return, hypoxemia and hypercarbia can sharply increase pulmonary vascular resistance, and anesthetic induction can drop SVR and myocardial performance. The recent ISHLT perioperative ECLS consensus therefore recommends considering **preinduction ECLS** in patients at high risk of collapse. Even outside lung transplantation, the teaching generalizes: if you think induction may be the last straw, secure the support strategy before you give the anesthetic. [\[6\]](#cite-6 "Reference [6]") Monitoring changes with the mode. On VV ECMO, circuit flow does not rescue blood pressure. On **peripheral VA ECMO**, right radial monitoring is high yield because **differential hypoxemia** can leave the brain and coronaries perfused by poorly oxygenated native output while the lower body looks fine. If the right hand saturation or right radial gas looks bad, think **Harlequin syndrome**, not just worsening lung disease. [\[2\]](#cite-2 "Reference [2]") Surgery on ECMO is fundamentally a hemostasis problem layered onto a respiratory or circulatory problem. Expect more bleeding than the field initially suggests because ECMO patients develop platelet dysfunction, factor consumption, loss of large von Willebrand multimers, and systemic anticoagulation. Coordinate anticoagulation timing with the ECMO team, use point-of-care coagulation when available, and have a transfusion strategy before incision. [\[7\]](#cite-7 "Reference [7]") Key Takeaways ------------- - **ECMO is rescue support, not ARDS therapy.** Use it after optimized conventional care, including prone positioning, when gas exchange remains dangerous. [\[1\]](#cite-1 "Reference [1]") - On **VV ECMO**, **blood flow mainly affects oxygen delivery** and **sweep gas mainly affects CO2 clearance**. [\[2\]](#cite-2 "Reference [2]") - Choose **VV** for isolated respiratory failure; choose **VA** when true circulatory support is required. [\[2\]](#cite-2 "Reference [2]") - **RV strain in severe ARDS does not automatically mean VA ECMO.** Correct gas exchange first and reassess the physiology. [\[2\]](#cite-2 "Reference [2]") - Anticoagulation management is a balance between **hemorrhage and circuit thrombosis**; treat the patient and the circuit, not the ACT alone. [\[3\]](#cite-3 "Reference [3]") - In the OR, know the cannulas, monitor the **right arm on VA ECMO**, and anticipate induction-related collapse and bleeding. [\[6\]](#cite-6 "Reference [6]") Conclusion ---------- At exam level, ECMO becomes manageable once you stop thinking of it as a heroic black box. Ask three questions: **what organ am I supporting, what variable do I need to change, and what complication will kill this patient first?** In refractory ARDS, that mindset usually leads you to VV ECMO, lung-rest ventilation, disciplined anticoagulation, and safer anesthetic planning. [\[2\]](#cite-2 "Reference [2]") References (9) ------------------ 1. 1. [ pubmed.ncbi.nlm.nih.gov/38032683 ](https://pubmed.ncbi.nlm.nih.gov/38032683/) [↩](#cite-ref-1-1 "Back to text") 2. 2. [ Tonna JE, et al. Management of Adult Patients Supported with Venovenous Extracorporeal Membrane Oxygenation (VV ECMO): Guideline from the Extracorporeal Life Support Organization. ASAIO J. 2021. ](https://www.elso.org/Portals/0/files/pdf/Management_of_Adult_Patients_Supported_with.1.pdf) [↩](#cite-ref-2-1 "Back to text") 3. 3. [ McMichael ABV, et al. 2021 ELSO Adult and Pediatric Anticoagulation Guidelines. ASAIO J. 2022. ](https://www.elso.org/Portals/0/files/pdf/2021_ELSO_Adult_and_Pediatric_Anticoagulation.1.pdf) [↩](#cite-ref-3-1 "Back to text") 4. 4. [ pmc.ncbi.nlm.nih.gov/articles/PMC8315725 ](https://pmc.ncbi.nlm.nih.gov/articles/PMC8315725/) [↩](#cite-ref-4-1 "Back to text") 5. 5. [ www.elso.org/Portals/0/files/guideline/EarlyRehaborMobilizationofAdultECMOPatients.pdf ](https://www.elso.org/Portals/0/files/guideline/EarlyRehaborMobilizationofAdultECMOPatients.pdf) [↩](#cite-ref-5-1 "Back to text") 6. 6. [ Martin A, et al. ISHLT consensus statement on the perioperative use of ECLS in lung transplantation: Part II: Intraoperative considerations. J Heart Lung Transplant. 2024. ](https://www.ishlt.org/docs/default-source/standards-guidelines/2024_consensusdocument_perioperativeuseofecls_intraoperativeconsiderations.pdf?sfvrsn=d968c647_1) [↩](#cite-ref-6-1 "Back to text") 7. 7. [ Lorusso R, et al. ELSO Interim Guidelines for Venoarterial Extracorporeal Membrane Oxygenation in Adult Cardiac Patients. ASAIO J. 2021. ](https://www.elso.org/Portals/0/files/pdf/ELSO_Interim_Guidelines_for_Venoarterial.2.pdf) [↩](#cite-ref-7-1 "Back to text") 8. 8. [ Fan E, et al. An Update on Management of Adult Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2024. ](https://pmc.ncbi.nlm.nih.gov/articles/PMC10870893/) 9. 9. [ Tschernko E, et al. The role of extracorporeal membrane oxygenation in thoracic anesthesia. 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