Commencement of weaning
Weaning VV ECMO is achieved by progressively reducing the Fresh Gas Flow to the oxygenator whereas blood flow does not need to be altered.
In parallel, weaning of fresh gas flow and maximising is discouraged, it is rather advisable to “rest” the lung until ready to increase the power of ventilation. Intermittently lung compliance can be measured as a marker of lung improvement. Subsequently, an increase in lung ventilation is required to ensure adequate CO2 clearance when that is considered safe.
In normal circumstances there is no requirement to wean the blender FiO2 as part of the weaning process (but may be used to assess or regulate ventilation and oxygenation fairly independently).
It is usual to observe the patient to be stable for 4-24 hours with the Fresh Gas Flow to the ECMO circuit at 0 L/min. The time period is at the discretion of the treating Intensivist.
The tubing does not need to be disconnected from the oxygenator, this will not stop room air circulation through the oxygenator. Echocardiography is not required unless there is concern about right heart failure which would primarily raise suspicion of insufficiently resolved lung pathology, prior pulmonary hypertension or venous thromboembolism as a complication of the ECMO run.
Overall it has to be emphasised not to rush the weaning from VV ECMO. The lung pathology requires time to resolve and unless there is a substantial resolution of the initial injury and improvement in the ventilatory parameters such as lung compliance weaning may be harmful. It is also worth noting that the philosophy around lung ventilation, adjunct therapies including proning whilst the patient is on ECMO is managed vastly differently around the world. More formal and advanced weaning protocols are desirable in the future including the management of patient respiratory drive.
It is useful to remember that an average VV ECMO run approaches 2 weeks with outliers not uncommonly a multiple of this time period. Fulminant aspiration pneumonitis or obstructive respiratory diseases maybe weanable in a fraction of this time period.
Criteria for decannulation
- Prolonged period with no fresh gas flow 4-24 hours
- No need to reduce ECMO blood flow below 2.5 L/min
- Safe lung ventilation with lower levels of support that allow a buffer to increase oxygenation as well as ventilation as required once separated from ECMO
- Absence of increased work of breathing clinically and no suspected increase in transpulmonary pressure
- Radiological clearance of initial pathology on CXR
Consensus should be sought with the ECMO consultant about the timing of decannulation and evaluation of the risks and benefits in borderline cases.
Once the decision is made for decannulation from VV ECMO, an appropriate time should be reserved to perform this in ICU for percutaneously placed cannulae. Surgically placed cannulae are to be removed by the surgical team. Two staff members are required to apply pressure at each side for at least 20 min or longer if haemostasis is not achieved.
A plan for further ECLS or limitations should be discussed and documented prior to decannulation .
Venous cannula removal
- Heparin should be ceased for at least 2 hours prior
- Check platelet count and coagulation parameters and replace as indicated
- Ensure valid crossmatch
- Small sterile setup with sterile gauze (sterile gloves only, sterile gown not required)
- Patient in a horizontal position
- Analgesia as required, in awake patients atropine at the bedside in case or pronounced vasovagal response
- Remove dressings and clean field with betadine
- Clamp all access and return lines and remove cannula – ensure pressure is applied above vessel entry point generally 1-3 cm proximal to skin puncture site
- As mentioned pressure is applied for at least 20 min
- Skin closure with nylon suture
The circuit should be disposed of in a biohazard bag/bin with cytotoxic precautions where appropriate. Re-usable (metal) ECMO Clamps MUST not be discarded.
Returning blood held within the ECMO circuit to the patient prior to cannula removal carries an additional risk of air and thrombus entering the patient’s circulation and volume overload. It should only be performed if there is a clinical imperative to conserve blood (e.g. Jehovah’s Witness patient) and warrants prior discussion with the ECMO consultant.
Post decannulation care
The patient must remain supine and still (avoid coughing) for approximately 4 hours post cannula removal and the site monitored for re-bleeding.
Failure to wean
VV ECMO runs are commonly prolonged and can far exceed the average of 2 weeks. Mortality in VV ECMO stems from the underlying disease, associated sepsis, ICU and/or ECMO related complications during a prolonged run. Failure to wean otherwise is exceptionally rare unless end-stage lung disease was unrecognised or bridge to transplantation was the indication for ECMO. Failure to wean should therefore not be concluded prematurely. However, a prolonged run in the setting of complex systemic disease and/or new progressive lung disease with failure to wean may require a multidisciplinary reassessment of the goals of care. See also end of life care.