Principles and Initial Goals

  • Use VV ECMO to allow ultra-protective ventilation (3 mL/kg tidal volume; “10/10/10”: RR 10, PEEP 10, driving pressure 10)
  • Treat hypoxia by troubleshooting VV ECMO rather than increasing ventilator FiO₂ or driving pressures

CO₂ Removal vs Oxygenation

  • CO₂ removal
    1. Start sweep gas flow ≈2 L/min
    2. Minor sweep changes→large PaCO₂ changes
    3. Avoid rapid CO₂ drops to prevent cerebral vasoconstriction and neurologic injury
  • Oxygenation
    1. Requires higher pump flows (≈50–100 mL/kg/min)
    2. Set FdO₂ to 1.0 initially

Oxygen Targets

  • SaO₂: typical 80–90%
  • PaO₂: 61–100 mmHg; avoid hypoxia and hyperoxia

Five Determinants of Oxygenation (“Famous Five”)

  1. FdO₂ and membrane oxygenator efficiency
  • Post-membrane PaO₂ should be >200 mmHg
  • Rising ΔP (pre- vs post-oxygenator) suggests failure
  1. ECMO flow : cardiac output ratio
  • Aim >60% to maintain systemic saturation; typical flows 3–6 L/min; drainage cannula caliber limits flow
  1. Recirculation
  • Return O₂-rich blood re-drained; patient SaO₂ low while pre-oxygenator SvO₂ rises (≥75%)
  • Often from close cannula tips or position change
  1. Native lung function
  • Variable contribution depending on disease/recovery

 

  1. Tissue oxygen extraction (SvO₂)
  • High metabolic rate lowers SvO₂ and systemic oxygenation

Causes of Hypoxia on VV ECMO

  • Inadequate FdO₂ or oxygenator failure (low post-membrane PaO₂, rising ΔP)
  • Low ECMO flow relative to cardiac output (<60%)
  • Excessive recirculation
  • High oxygen consumption/low SvO₂
  • Severely impaired lung function

Stepwise Management Algorithm

  1. Immediate checks
  • Confirm oxygen tubing to blender; FdO₂ = 1.0; no kinks/clots; stable pump flows
  1. Order tests
  • Chest X-ray
  • Systemic patient blood gas
  • Post-membrane blood gas
  1. Increase RPMs to raise ECMO flow
  • Aim flow >60% of cardiac output; measure CO by echo (LVOT diameter + VTI)
  1. If flows do not rise
  • Evaluate drainage insufficiency (hypovolemia, hemorrhage, pneumothorax, tamponade, ↑intra-abdominal pressure)
  • Check mechanical issues (kink, clot, malposition, pump)
  1. If flows rise but SaO₂ remains low
  • Suspect recirculation; reduce flow slightly; verify cannula tip separation 10–15 cm (return in RA, drainage in intrahepatic IVC); consider double-lumen cannula
  1. If SvO₂ low/high demand
  • Treat fever/infection; control agitation/shivering; consider sedation/paralysis or mild hypothermia; optimize hemoglobin; rarely add second oxygenator; if cardiac failure, convert to VA or VAV
  1. If lungs severely impaired
  • Modest ventilator increases while maintaining protection (e.g., FiO₂ 40→50%, careful PEEP)
  • Selective recruitment (avoid periodic routine maneuvers)
  • Consider inhaled nitric oxide
  • Consider proning with precautions
  • Consider bronchoscopy to clear airways

Oxygenator Failure: Recognition and Action

  • Signs: falling post-membrane PaO₂ (<200 mmHg), rising ΔP, visual clot
  • Action: prepare primed replacement; clamp–cut–replace–reconnect–unclamp rapidly; support ventilation/hemodynamics during exchange

Conclusion

  • Always think A-B-C: Assess the patient, the ECMO circuit, and their interaction
  • Use the five determinants to diagnose cause of hypoxia and apply the stepwise algorithm while preserving lung protection

 

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