Abstract
ECMO can either provide total cardiopulmonary support (veno-arterial or VA-ECMO) or pulmonary support (veno-venous or VV-ECMO). The technique effectively enables the use of CPB in an ICU setting. In adult practice, ECMO was initially reserved for patients with severe respiratory failure secondary to ARDS. ECMO in adults fell out of favour, largely because of poor outcomes. In paediatric practice, where outcomes are generally better, ECMO has remained in routine use for over three decades. Recent H1N1 (‘swine flu’) epidemics have led to a re-examination of the role of ECMO in adults with respiratory failure and a re-emergence of VV-ECMO.
ECMO can either provide total cardiopulmonary support (veno-arterial or VA-ECMO) or pulmonary support (veno-venous or VV-ECMO). The technique effectively enables the use of CPB in an ICU setting. In adult practice, ECMO was initially reserved for patients with severe respiratory failure secondary to ARDS. ECMO in adults fell out of favour, largely because of poor outcomes. In paediatric practice, where outcomes are generally better, ECMO has remained in routine use for over three decades. Recent H1N1 (‘swine flu’) epidemics have led to a re-examination of the role of ECMO in adults with respiratory failure and a re-emergence of VV-ECMO.
The eighth Interagency Registry for Mechanical Circulatory Support (INTERMACS) annual report revealed that more than 20,000 patients from over 180 centres were included in their database. Disposable, durable extracorporeal versions of mechanical support technology are particularly suited to short- and medium-term ECMO. These devices are associated with significantly improved survival, fewer malfunctions, reduced bleeding during implantation and a reduced infection rate. These factors may explain the trend from VAD to ECMO therapy in patients requiring short-term, post-cardiotomy cardiopulmonary support.
Indications
The broad indications for instituting ECMO are shown in Box 29.1. A number of scoring systems have been developed to assist prediction of outcome following VA-ECMO, for example the Survival After Veno-arterial ECMO (SAVE) score developed jointly by the Extracorporeal Life Support Organization (ELSO) and the Alfred Hospital, Melbourne (save-score.com).
Box 29.1 Indications for ECMO
Acute MI
Dilated cardiomyopathy
Fulminant myocarditis
Post-cardiotomy low CO state
Persistent PHT (post pulmonary thromboendarterectomy)
Intractable ventricular arrhythmias
Perioperative cardiac arrest
Primary graft failure after heart transplantation
Fulminant respiratory failure
Contraindications
The decision to initiate ECMO is often difficult (Box 29.2). Not infrequently, the decision is clouded by emotion – the frustrated surgeon faced with intractable cardiac failure in an elderly patient at the end of long and complex surgery, or the intensivist managing a young mother with fulminant post-viral respiratory failure.
Box 29.2 Contraindications for ECMO
Severe AR
Aortic dissection
Contraindications to anticoagulation – e.g. intracerebral haemorrhage
Established multi-organ failure
Mechanical ventilation > 10 days
Equipment
A typical ECMO system comprises three principal components – a pump, an oxygenator and a heat exchanger – connected by polyvinyl chloride or silicone tubing to inflow and outflow cannulae (Figure 29.1). Unlike conventional CPB systems, ECMO systems are closed, have no venous reservoir or arterial line filter and can be operated at lower levels of anticoagulation.
Oxygenator
Three types of so-called ‘membrane lungs’ are used to oxygenate blood and remove CO2. The original silicone spiral coil oxygenators have been largely superseded by polymethylpentene oxygenators.
Cannulation
Cannulation for VA-ECMO may be either central or peripheral.
Central ECMO
Failure to wean from CPB is an indication for central VA-ECMO; with the (RA-to-aorta) CPB cannulae being used for up to 72 hours. If longer-term support is required, the patient will typically require VAD or peripheral ECMO support. Larger cannulae allow increased flow rates and maximum haemodynamic support. The main problems are bleeding and infection.
Peripheral ECMO
Peripheral VA-ECMO usually involves cannulation of a femoral or internal jugular vein and a femoral artery. Peripheral (femoro-jugular) cannulation is usually used for VV-ECMO. The availability of specialized cannulae (e.g. the Avalon Elite™ bicaval dual-lumen catheter) in a range of sizes (e.g. 16–31 Fr) has made peripheral cannulation a relatively straightforward bedside procedure. The distal (inlet) end is placed in the IVC, the proximal (inlet) is placed in the SVC and the outlet in the lower RA – typically under TOE and fluoroscopic guidance. Femoral arterial cannulation carries two significant risks.
1. The risk of distal limb ischaemia may be reduced by inserting a small antegrade perfusion line distal to the perfusion cannula.
2. Differential cyanosis (‘Harlequin syndrome’) occurs when deoxygenated blood that is ejected from the LV encounters oxygenated blood flowing from the femoral cannula. This may result in significantly reduced PaO2 in blood entering the head and right arm. The problem may only be resolved by proximal reinsertion of the arterial inflow cannula.
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