What is ECMO?
Extracorporeal Membrane Oxygenation (ECMO) is a form of partial cardiopulmonary bypass used for long-term support of respiratory and/or cardiac function. This means that an artificial lung (the membrane) oxygenates the blood outside the body (extra- corporeal). The ECMO machine is very similar to the heart-lung machines used to keep patients alive during open-heart surgery. There has been a growing interest in the use of ECMO for patients with severe respiratory failure especially in the UK following the HIN1 epidemic in 2009. In the UK, six centres registered with the Extracorporeal Life Support Organisation (ELSO) provide an ECMO service.
ECMO is primarily indicated for patients with such severe ventilation and/or oxygenation problems that they are unlikely to survive conventional mechanical ventilation. Examples of such patients would include those with the adult respiratory distress syndrome (ARDS) without major non-pulmonary organ failure who are failing mechanical ventilation or who are suffering from major barotrauma that makes adequate ventilation impossible. With conventional ventilator care, the ventilator is adjusted to make up for the patient’s reduced or absent lung function. Increasing the amount of oxygen blown into the lungs by the ventilator and increasing the pressure at which it is delivered do this. This forces more oxygen into the blood. Unfortunately, we now know that high- pressure ventilation with large amounts of oxygen can actually cause further injury to the lungs and can prevent them from recovering. The main advantage of ECMO is that the pressure and oxygen concentration used to ventilate the lungs can be greatly reduced to safe levels. We call this gentle ventilation “lung rest”, and we believe that it may give the lungs a chance to heal and recover.
ECMO currently comes in two varieties: Venovenous (VV) and Venoarterial (VA). VV ECMO takes blood from a large vein and returns oxygenated blood back to a large vein. VV ECMO does not support the circulation. VA ECMO takes deoxygenated blood from a central vein or the right atrium, pumps it past the oxygenator, and then returns the oxygenated blood, under pressure, to the arterial side of the circulation (typically to the aorta). This form of ECMO partially supports the cardiac output as the flow through the ECMO circuit is in addition to the normal cardiac output. VA ECMO helps support the cardiac output and delivers higher levels of oxygenation support than does VV ECMO. VA ECMO carries a higher risk of systemic emboli than does VV. In all forms of ECMO, CO2 removal is more efficient than O2 addition because of the solubility and diffusion properties of CO2 relative to O2. In fact, CO2 normally has to be added to ECMO circuits to offset this efficiency at CO2 removal. The flow through the ECMO circuit is typically on the order of 100 mL/kg/minute. This would be from 25-75% of the cardiac output. This high flow requires the placement of large catheters into the circulation.
As mentioned previously, usual ECMO criteria include patients with a severe reversible process that would result in a very high-predicted mortality with conventional ventilatory support. Indications include:
- Hypoxemic respiratory failure with a ratio of arterial oxygen tension to fraction of inspired oxygen (PaO2/FiO2) of <100 mmHg despite optimization of the ventilator settings, including the tidal volume, positive end-expiratory pressure (PEEP), and inspiratory to expiratory (I: E) ratio
- Hypercapnic respiratory failure with an arterial pH less than 7.20
- Refractory cardiogenic shock
- Cardiac arrest
- Failure to wean from cardiopulmonary bypass after cardiac surgery
- As a bridge to either cardiac transplantation or placement of a ventricular assist device.
ECMO complications are those associated with cannulation (pneumothorax, vascular disruptions, bleeding, infection, emboli), those associated with systemic anticoagulation (GI bleeding, intracranial bleeding etc.), and exsanguination resulting from circuit disruptions. These potential complications require that a trained ECMO technician be present at the bedside 24 hours per day in addition to the patient’s usual nursing presence.
ECMO can be used in adult patients with ARDS or cardiogenic shock who failed to respond to conventional therapy. Although the evidence in favour of ECMO for ARDS treatment is not strong enough to make a general recommendation, it should be considered when other therapies fail.
Location: Prime Hospital Conference Room
Time: 10:00 – 12:00
|ECMO workshop seats have been fully booked|