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

2. ECMO flow : cardiac output ratio

• Aim >60% to maintain systemic saturation; typical flows 3–6 L/min; drainage cannula caliber limits flow

3. Recirculation

• Return O₂-rich blood re-drained; patient SaO₂ low while pre-oxygenator SvO₂ rises (≥75%)
• Often from close cannula tips or position change

4. Native lung function

• Variable contribution depending on disease/recovery

5. 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

2. Order tests

• Chest X-ray
• Systemic patient blood gas
• Post-membrane blood gas

3. Increase RPMs to raise ECMO flow

• Aim flow >60% of cardiac output; measure CO by echo (LVOT diameter + VTI)

4. If flows do not rise

• Evaluate drainage insufficiency (hypovolemia, hemorrhage, pneumothorax, tamponade, ↑intra-abdominal pressure)
• Check mechanical issues (kink, clot, malposition, pump)

5. 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

6. 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

7. 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