This is a brief overview of the process of taking over the job of somebody's circulatory system. ECMO has made a few appearances in the past papers:
Indications for ECMO
In order to qualify for this level of critical care, one must be special in the following ways:
- The condition must be reversible; OR the patient qualifies for a heart/lung transplant
- The conventional management strategies have failed.
The following situations call for ECMO:
- Cardiac arrest (in certain settings)
- Failure to wean from cardiopulmonary bypass
- Cardiogenic shock
- Hypoxic respiratory failure
- Hypercapneic respiratory failure
Contraindications for ECMO
- Contraindications to anticoagulation: recent surgery, uncontrolled bleeding, intracranial haemorrhage
- Irreversible condition
- Contraindications for heart/lung transplant
Caveats to ECMO
Before subjecting a patient to such a perversely unnatural therapy, one ought to satisfy onself that every "conventional" strategy has failed. These include:
- Recruitment manoeuvres
- prone positioning
- NO/inhaled prostacyclin
- Fluid resuscitation and decreased PEEP to improve V/Q matching
Basic physics of ECMO
- Oxygenation is controlled by the blood flow rate
- CO2 removal is controlled by the countercurrent flow of fresh gas
Veno-venous vs veno-arterial ECMO
Each has advantages and disadvantages.
- VA ECMO has the advantage of providing complete cardiorespiratory support, and is therefore applicable in patients with very poor cardiac function (LVEF less than 25%)
- VA ECMO has the disadvantage of large-bore arterial puncture, which is a major problem. VV ECMO has less vascular access issues, but is only indicated for patients with good myocardial function.
- The college answer to Question 23 from the first paper of 2014 mentions animal studies which demonstrated an improved outcome from pulmonary sepsis with preserved pulmonary blood flow in VV ECMO.
Anticoagulation during ECMO
- Heparin is the poison of choice
- ACT (Activated Clotting Time) is the chosen method for measuring the anticoagulation
- ACT target is 180-210 seconds
Major complications of ECMO
- Vascular access complications
- Limb ischaemia (with VA ECMO)
- LV distension and pulmonary haemorrhage (with VA ECMO)
- Cardiac chamber thrombosis (with VA ECMO)
- Bleeding complications (in as many as 30-40%)
- Systemic thromboembolism through the circuit
Weaning off ECMO
- VV ECMO:
- Gas sweep is turned off. No fresh gas passes through the oxygenator. The patient's lung function can thus be isolated, and observed. If it passes muster, the pump is turned off and the blood returned.
- The drainage and infusion lines are temporarily clamped, to observe what the patient does with his own circulation.