Veno-Venous ECMO

Temporary mechanical support for severe respiratory failure with preserved cardiac function, used as:

Indications

In suitable patients, consider initiating support with:

  • Severe respiratory failure at safe ventilation settings
    Indicated by:
    • SpO2 <88%
    • pH <7.2
  • Despite optimal:
    • Cardiac support
      Use of inotropes to optimise DO2.
    • Trial of high PEEP (18-22cmH2O) and recruitment manoeuvre
      If haemodynamically safe.
    • Trial of pulmonary vasodilator
      iNO for 2-12 hours; depending on patient trajectory.

The EOLIA trial had the following thresholds:

  • P/F <50 for 3 hours
  • P/F <80 for 6 hours
  • pH <7.25 with PaCO2 >60mmHg for 6 hours, despite ventilator optimisation

Concepts

Key concepts include:

  • Recirculation
  • Weaning

Recirculation

Recirculation describes blood that undergoes gas exchange and is returned via the venous return cannula, but then removed via the access cannula without passing through the lungs and participating in DO2. Recirculation:

  • Introduces significant inefficiencies in VV ECMO
  • Is not completely avoidable, but can be minimised
  • Is clinicially significant with a pre-oxygenator saturation of >80%
  • More profound with:
    • High ECMO flow rates
    • Low CO
  • Reduces colour differential between access and return cannula

Weaning

Weaning involves assessing patient suitability for and removing from ECMO support. Weaning:

VV ECMO weaning is much simpler than VA weaning because the patient can be managed completely off support indefintely, whilst maintaining circuit flows and minimising risk of clot.

  • Can be considered when ECMO flows are <3L/min and lung recovery is occurring
  • FGF is turned off (so there is no gas in the oxygenator) and ECMO circuit flows continue
    The patient is functionally off ECMO support as venous blood is being recirculated, but clot risk is minimised.

Configurations

Include:

  • Femoro-femoral
    Access in one femoral vein and return in the other.
    • Technically easy to establish
    • Easy to secure
    • Easy to transport
    • Access insufficiency more common
    • Recirculation more common
  • Femoro-jugular
    Access in one femoral vein and return in the right IJV vein.
    • Positioning of right IJV cannula can be difficult
      Often small adjustments can affect recirculation percentage.
    • Securing more difficult
    • Risk of decannulation
  • High-flow
    Access in one femoral vein and right IJV, return in the other femoral vein.
    • Significantly ↓ access insufficiency
    • Requires multiple cannulations
  • Dual-lumen
    Single right IJV cannula that provides access and return.
    • Single cannulation
    • Positioning difficult
    • Nursing care difficult
    • Access insufficeincy very common

Complications

Key complications include:

  • Pneumothorax

Pneumothorax

Whilst not a complication of ECMO, they occur commonly in patients on VV ECMO support. Key differences in management:

  • Avoid pleural drainage if possible
    • Significant iatrogenic harm of intercostal catheters in patients on VV ECMO
  • Manage with:
    • ↑ ECMO support
    • ↓ Ventilation or ceased ventilation

Key Studies

  • CESAR (2009)
    • Britons aged 18-65 with potentially reversible severe respiratory failure without contraindications to heparin or Pip >30
      • Multi-centre (92 tertiary, 11 conventional, 1 ECMO, assessor-blinded RCT
      • 80% power to detect 18% ↓ ARR in death or severe disability from control group of 73%
    • Transfer to ECMO centre vs. conventional ventilation
      • Transfer ECMO centre for consideration of ECMO
        • Standardised low-volume, low-pressure ventilation in majority
        • If no response to ventilation in 12 hours, then VV ECMO initiated (68/85, 75%)
          • Percutaneous cannulation
          • Roller pumps
          • PMP oxygenators
      • Conventional ventilation
        • Unprotocolised PCV or HFOV
    • Significant ↑ in survival without severe disability in ECMO group (63% vs. 47%, RR 0.69 (CI 0.05 - 0.97))
    • Secondary outcomes: ECMO group had significantly:
      • ↓ Proning (36%. vs 42%)
      • ↑ Steroids (84% vs. 64%)
      • ↑ MARS (17% vs. 0%)
      • ICU and hospital length of stay
    • Significant ↑ in survival with transfer to an ECMO centre, even if you didn’t get ECMO, compared to management in a non-ECMO centre
    • No protocolised ventilation in conventional group
    • Significant loss to follow up

CESAR was not so much a study of ECMO, as to whether transfer to an ECMO centre results in better management of respiratory failure.

  • EOLIA (2018)
    • 249 non-pregnant Europeans with ARDS with severe hypoxia despite adjunctive therapies and no ECMO contraindications
      Severe hypoxia including
      • P/F <50mmHg for 3 hours
      • P/F <80mmHg for 6 hours
      • pH <7.25 with PaC2 >60mmHg for >6 hours with lung protective ventilation
    • Prospective, multicenter, industry-supported RCT
    • 331 patients powers for 20% ARR in ECMO group, assuming 60% control mortality
    • VV ECMO vs. standard care
      • ECMO group
        • Percutaneous femoral/jugular configuration
        • FiO2 and pump flow adjusted for SpO2 >90%
        • Sweep adjusted for PaCO2 <45mmHg
      • Standard care
        • Lung protective ventilation
        • Encouraged:
          • NMBA
          • Proning
          • Recruitment
        • Inhaled pulmonary vasodilators permitted if above ineffective
        • Crossover to VV ECMO if SpO2 <80% despite the above
          28% crossed over.
    • Stopped early for futility
      Underpowered due to early stoppage and lower than expected control mortality.
    • No difference in mortality at day 60 (35% vs. 46%, RR 0.76 (CI 0.55-1.04)))
      This is clouded by the high proportion of control patients crossing over to receive ECMO.
      • If none of them got ECMO and as few as 30% survived, there would be a significant mortality benefit from ECMO
    • Secondary outcomes showed the ECMO group had:
      • ↓ “Treatment failure” (RR 0.62, CI 0.47-0.82)
        Death or crossover to ECMO.
      • ↓ RRT
      • ↑ Thrombocytopenia
      • ↑ Bleeding
    • Slow (6 years) recruitment

References

  1. Combes A, Hajage D, Capellier G, et al. Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome. New England Journal of Medicine. 2018;378(21):1965-1975. doi:10.1056/NEJMoa1800385
  2. Peek GJ, Mugford M, Tiruvoipati R, et al. Efficacy and economic assessment of conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure (CESAR): a multicentre randomised controlled trial. The Lancet. 2009;374(9698):1351-1363. doi:10.1016/S0140-6736(09)61069-2