Weaning from ECMO:
We currently do not have exact criteria to tell us when a patient does not need the support from an ECMO circuit. Decisions around weaning are based more on the individual patient and clinical judgment than they are on numerical quantities. There are guidelines provided by ELSO that can be interpreted in the context of each patient that can help to determine whether they are ready for liberation from an ECMO circuit.
As discussed in the section "Daily Care of the ECMO Patient", every day the patient should be evaluated and put on the minimum support that they require from the ECMO circuit. Weaning is a part of everyday ECMO care.
Liberation from V-V ECMO
In general, a trial off V-V ECMO is reasonable in patients when:
- The native lungs are providing ≥ 70-80% of oxygenation.
- Pulmonary compliance and airway resistance allow for ventilation at reasonable pressures.
- The FiO2 provided by the ventilator is ≤ 50-60%.
- The PaCO2 can be maintained at a near-normal level within the range of acceptable ventilator settings,
When a patient seems ready for a trial off V-V ECMO, the circuit settings are adjusted to trial the patient without support (analogous to a spontaneous breathing trial):
- Usually when a patient is thought to be ready, the following steps happen:
- The sweep gas flow to the oxygenator is reduced to zero.
- The patient is observed for signs of respiratory distress.
- The tidal volumes, minute ventilation and respiratory rate are measured on the ventilator.
- The patient's vital signs are monitored.
- Serial blood gases are taken to monitor the gas exchange of the native lungs.
- Remember in V-V ECMO the pump is providing no circulatory support, so the flow does not need to be reduced as part of the trial off V-V ECMO (however it can be reduced).
- Typically patients are trialled "off sweep" for a period of 24 hours before a decision is made to decannulate.
Liberation from V-A ECMO
Liberation from V-A ECMO is more complicated than from V-V ECMO, because the circuit is providing both cardiac and respiratory support. There are no strict criteria for liberation from V-A ECMO, but in general before trying to wean patients the following criteria are reasonable to try and meet:
- The cause of cardiogenic shock should be resolved.
- A minimum of 24-48 hours on V-A ECMO before trying to wean.
- MAP > 70 mmHg.
- Low doses of vasopressors and inotropes.
- Oxygen saturation > 95%.
- Central venous saturation > 70%.
- Resolving pulmonary edema.
- LVEF >25-30%.
- Normal right ventricular function.
- Blood lactate level low and not increasing.
- Aortic valve velocity time integral > 12 cm.
- Mitral annulus peak systolic velocity > 6 cm.
- Pulse pressure > 30 mmHg.
The steps involved in weaning from V-A ECMO vary with each individual patient, but in general the approach is done with echocardiography:
- A TTE or TEE is used to obtain several views of the patient's heart.
- The flow is decreased stepwise down to around 1.0 L/min.
- The ventilator settings are adjusted to account for the increase in pulmonary blood flow.
- The patient is continuously monitored for signs of inadequate cardiac output:
- Rise in filling pressures
- Elevation of blood lactate
- Hypoxemia
- High inotrope and/or vasopressor requirements
- Decreased central venous saturation
- Echocardiographic signs of right or left ventricular dysfunction
- It is important that the heparin infusion continue throughout this process as reducing the flows produces a more thrombophilic environment.
- The cannulas are then clamped, and can be left in for up to 24 hours (with heparin flushes periodically).
- If the patient tolerates a trial off ECMO, then they may proceed to decannulation.
- If at any point the patient shows signs of inadequate cardiac output, the ECMO flows are increased until perfusion is restored.
Next page: Weaning from ECMO: Decannulation