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

  • Case: 56-year-old male, H1N1 influenza → severe ARDS.

    • Initially on high-flow O₂ → intubated day 4.

    • CT: bilateral GGOs, subsegmental PE (no RV strain).

    • Developed MSSA bacteremia and later ESBL Klebsiella superinfection.

    • Managed with proning, low tidal volume ventilation, deep sedation, paralysis.

    • By day 7: PF ratio <80, plateau pressure 35, FiO₂ 100%, PEEP 16 → refractory hypoxemia → cannulated for VV ECMO.

  • Key evidence reviewed:

    • Mortality benefit: low tidal volume ventilation, prone positioning (PROSEVA).

    • Not beneficial: recruitment maneuvers, HFOV, paralytics (ROSE trial negative).

    • VV ECMO considered for PF ratio <80 >6–12 hrs despite optimal care.

  • Relative contraindications discussed:

    • E-cigarettes, mild alcohol use, subsegmental PE, treated bacteremia → not true contraindications.

    • Persistent uncontrolled bacteremia would be concerning.

  • Cannulation strategy:

    • Tall 120-kg man → large vessel diameters → required 27 Fr drainage + 21 Fr return cannula to achieve adequate flows.

    • Teaching point: always size cannulas to anatomy & flow needs.

  • Complications:

    • Necrotizing pneumonia, pulmonary hemorrhage, pneumothorax, renal failure.

    • Despite advanced support (including dual ECMO circuits), patient died with multi-organ failure.

  • Teaching highlights:

    • Hypoxemia on VV ECMO results from:

      1. ↓ Effective ECMO flow (drainage insufficiency, recirculation, insufficient pump flow).

      2. ↑ Native cardiac output (fever, sepsis, agitation).

      3. Membrane lung dysfunction (gas failure, low FiO₂, excessive flow > rated capacity).

      4. ↓ SvO₂ (low CO, anemia, fever).

    • ECMO flow / cardiac output ratio must be >60% to maintain SaO₂ >90%.

    • Beta-blockers ↑ SaO₂ but ↓ DO₂ → not useful.

    • Adding a parallel circuit can augment flow when one oxygenator maxed out.

    • Always treat cause of hypoxemia systematically with an algorithmic approach.

Talk 2 – ARDS with RV Dysfunction & ECLS

  • Background:

    • ARDS increases pulmonary vascular resistance (PVR) via hypoxemia, hypercapnia, acidosis, high PEEP, and vascular leak.

    • This leads to RV dilation, dysfunction, and failure.

    • RV dysfunction complicates ~25% of ARDS; up to 50% of severe cases considered for ECMO.

    • Mortality increases significantly when RV failure coexists with ARDS.

  • Rescue therapies for RV dysfunction:

    • Optimize preload (avoid over/underfilling).

    • Reduce PVR (treat hypoxemia/hypercapnia, inhaled NO or prostacyclin, milrinone).

    • Support systemic BP (vasopressors to optimize SVR/PVR ratio).

    • Proning improves oxygenation and RV function.

  • ECMO effects on RV:

    • VV ECMO: corrects hypoxia, hypercapnia, acidosis → lowers PVR, reduces RV afterload.

    • VA ECMO: bypasses RV → decompresses RV and supports circulation, but risks LV overload and Harlequin syndrome.

  • Cannulation strategies & hybrid circuits:

    • VV ECMO first-line in ARDS + RV dysfunction if no severe circulatory shock.

    • VA ECMO indicated if severe shock coexists.

    • Hybrid (V-AV) can avoid Harlequin syndrome by providing both systemic and pulmonary oxygenation.

    • Correct labeling: drainage cannulas before the dash (V), return cannulas after (A or V).

  • Case examples:

    • Case 1: COVID ARDS + RV dysfunction → started on VV ECMO → improved, later discharged.

    • Case 2: ARDS + RV failure + severe shock → started on VA ECMO, developed Harlequin → converted to hybrid V-AV ECMO.

  • Key teaching points:

    • Bad lungs + bad RV but preserved circulation → VV ECMO.

    • Bad lungs + bad RV + shock → VA ECMO (or V-AV hybrid if risk of Harlequin).

    • RVAD alone not useful in ARDS (doesn’t oxygenate).

    • Hybrid configurations (VV-A, V-AV, etc.) useful in complex physiology.

  • Adjuncts:

    • Inhaled NO may improve oxygenation and reduce RV afterload short-term, though no mortality benefit.

    • Inhaled prostacyclin (epoprostenol) sometimes used; effect mainly on PA pressures.

    • Steroids not beneficial for viral ARDS with bacterial superinfection (risk of fungal infections).

Overall Take-Home

  • Talk 1: Hypoxemia on VV ECMO must be analyzed algorithmically → maintain ECMO flow/CO ratio >60%, avoid “futile” fixes.

  • Talk 2: ARDS + RV dysfunction requires careful ECMO selection: VV for lungs, VA if shock, hybrid to avoid Harlequin.

  • Both talks stress cannula strategy, flow optimization, and physiology-driven decision making as keys to outcomes.

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