Case Scenario: Persistent hypoxemia despite VV ECMO
Presenter: Raj Ramanan Moderator: Ahmed Hegazy Discussion: A Systematic Approach to Hypoxemia on VV ECMO Interactive Poll: What are the initial steps you would take to treat hypoxemia on VV ECMO?
Case Scenario: Acute right ventricular dysfunction associated with ARDS: Which is best, VV or VA ECMO?
Presenter: Kumait Al Lawati Moderator: Hesham Faisal Discussion:
Effects of ARDS on right ventricular (RV) function VV ECMO effects on RV function Choice of ECMO modality in patients with RV failure Interactive Poll: Which ECMO choice would you go with, VV or VA?
Summary of the Webinar:
Talk 1 – Refractory Hypoxemia in Severe ARDS on VV ECMO
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Case: 56-year-old male, H1N1 influenza → severe ARDS.
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Initially on high-flow O₂ → intubated day 4.
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CT: bilateral GGOs, subsegmental PE (no RV strain).
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Developed MSSA bacteremia and later ESBL Klebsiella superinfection.
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Managed with proning, low tidal volume ventilation, deep sedation, paralysis.
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By day 7: PF ratio <80, plateau pressure 35, FiO₂ 100%, PEEP 16 → refractory hypoxemia → cannulated for VV ECMO.
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Key evidence reviewed:
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Mortality benefit: low tidal volume ventilation, prone positioning (PROSEVA).
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Not beneficial: recruitment maneuvers, HFOV, paralytics (ROSE trial negative).
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VV ECMO considered for PF ratio <80 >6–12 hrs despite optimal care.
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Relative contraindications discussed:
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E-cigarettes, mild alcohol use, subsegmental PE, treated bacteremia → not true contraindications.
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Persistent uncontrolled bacteremia would be concerning.
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Cannulation strategy:
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Tall 120-kg man → large vessel diameters → required 27 Fr drainage + 21 Fr return cannula to achieve adequate flows.
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Teaching point: always size cannulas to anatomy & flow needs.
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Complications:
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Necrotizing pneumonia, pulmonary hemorrhage, pneumothorax, renal failure.
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Despite advanced support (including dual ECMO circuits), patient died with multi-organ failure.
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Teaching highlights:
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Hypoxemia on VV ECMO results from:
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↓ Effective ECMO flow (drainage insufficiency, recirculation, insufficient pump flow).
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↑ Native cardiac output (fever, sepsis, agitation).
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Membrane lung dysfunction (gas failure, low FiO₂, excessive flow > rated capacity).
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↓ SvO₂ (low CO, anemia, fever).
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ECMO flow / cardiac output ratio must be >60% to maintain SaO₂ >90%.
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Beta-blockers ↑ SaO₂ but ↓ DO₂ → not useful.
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Adding a parallel circuit can augment flow when one oxygenator maxed out.
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Always treat cause of hypoxemia systematically with an algorithmic approach.
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Talk 2 – ARDS with RV Dysfunction & ECLS
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Background:
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ARDS increases pulmonary vascular resistance (PVR) via hypoxemia, hypercapnia, acidosis, high PEEP, and vascular leak.
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This leads to RV dilation, dysfunction, and failure.
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RV dysfunction complicates ~25% of ARDS; up to 50% of severe cases considered for ECMO.
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Mortality increases significantly when RV failure coexists with ARDS.
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Rescue therapies for RV dysfunction:
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Optimize preload (avoid over/underfilling).
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Reduce PVR (treat hypoxemia/hypercapnia, inhaled NO or prostacyclin, milrinone).
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Support systemic BP (vasopressors to optimize SVR/PVR ratio).
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Proning improves oxygenation and RV function.
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ECMO effects on RV:
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VV ECMO: corrects hypoxia, hypercapnia, acidosis → lowers PVR, reduces RV afterload.
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VA ECMO: bypasses RV → decompresses RV and supports circulation, but risks LV overload and Harlequin syndrome.
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Cannulation strategies & hybrid circuits:
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VV ECMO first-line in ARDS + RV dysfunction if no severe circulatory shock.
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VA ECMO indicated if severe shock coexists.
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Hybrid (V-AV) can avoid Harlequin syndrome by providing both systemic and pulmonary oxygenation.
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Correct labeling: drainage cannulas before the dash (V), return cannulas after (A or V).
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Case examples:
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Case 1: COVID ARDS + RV dysfunction → started on VV ECMO → improved, later discharged.
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Case 2: ARDS + RV failure + severe shock → started on VA ECMO, developed Harlequin → converted to hybrid V-AV ECMO.
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Key teaching points:
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Bad lungs + bad RV but preserved circulation → VV ECMO.
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Bad lungs + bad RV + shock → VA ECMO (or V-AV hybrid if risk of Harlequin).
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RVAD alone not useful in ARDS (doesn’t oxygenate).
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Hybrid configurations (VV-A, V-AV, etc.) useful in complex physiology.
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Adjuncts:
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Inhaled NO may improve oxygenation and reduce RV afterload short-term, though no mortality benefit.
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Inhaled prostacyclin (epoprostenol) sometimes used; effect mainly on PA pressures.
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Steroids not beneficial for viral ARDS with bacterial superinfection (risk of fungal infections).
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Overall Take-Home
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Talk 1: Hypoxemia on VV ECMO must be analyzed algorithmically → maintain ECMO flow/CO ratio >60%, avoid “futile” fixes.
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Talk 2: ARDS + RV dysfunction requires careful ECMO selection: VV for lungs, VA if shock, hybrid to avoid Harlequin.
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Both talks stress cannula strategy, flow optimization, and physiology-driven decision making as keys to outcomes.