Types of ECMO and Indication
The two main subtypes of ECMO, VV-ECMO and VA-ECMO, differ in the
configurations of their circuit which allows for them to carry out
different functions and enables them to be utilised for respiratory
support, cardiac support, or both1,2.
VV-ECMO involves venous cannulation alone- either single dual-lumen
cannulation via the right jugular vein to enable removal of blood from
the vena cava or right atrium by a pump device for oxygenation via an
extracorporeal membrane oxygenator before it is returned to the right
atrium, or double cannulation where blood is removed from the inferior
vena cava (IVC) vein through cannulation of the right common femoral
vein and infused into the right atrium via cannulation of the right
internal jugular or vice versa though the former is more commonly used
in modern practice (Figure 1)14. This configuration
allows for gas exchange to occur but does not provide circulatory
support, meaning VV-ECMO is only indicated for isolated respiratory
failure and the patient must be haemodynamically stable. By contrast,
VA-ECMO involves both arterial and venous cannulation, enabling removal
of blood from the right atrium or IVC before it is returned to the
arterial system via a peripheral cannula i.e. peripheral VA-ECMO
(through the femoral, axillary or carotid artery) or a central cannula
i.e. central VA-ECMO via the ascending aorta (Figure
2)15. The setup of the VA-ECMO circuit enables it to
carry out gas exchange along with providing circulatory support thus it
is indicated for isolated cardiac failure along with combined
cardiopulmonary failure. The key differences between the two types of
ECMO are summarised in Table 1.
Indications for ECMO are broadly divided according to cardiac support,
respiratory support or a combination of both in the case of
cardiopulmonary failure1. VA-EMCO is indicated for
cardiac failure where there is a low cardiac output (defined as a
cardiac index less than 2L/min/m2) and hypotension
(defined as a systolic blood pressure of less than 90mmHg) refractory to
adequate intravascular volume, high-dose inotropic support and IABP
support16-18. Both VV- and VA-ECMO are indicated for
acute respiratory failure as rescue therapy to provide gas exchange
until the lungs recover or as a bridge to lung
transplantation19-21. The main absolute
contraindications to ECMO are pre-existing pathologies that make
recovery unlikely such as disseminated malignancy and severe
neurological injury, or unsuitability for destination therapy. Specific
cardiac and respiratory indications, absolute and relative
contraindications to for ECMO are summarised in Table 2.