Extracorporeal Membrane Oxygenation (ECMO)

• In cardiology, the main indications for ECMO include cardiac arrest, cardiogenic shock, post-cardiotomy shock, refractory ventricular tachycardia, and acute management of complications of invasive procedures.¹
• ECMO provides continuous blood flow. Any pulsatility, if present, is created by the residual function of the LV. In severe cases of cardiogenic shock or in the presence of cardiac tamponade, Korotkoff sounds may be absent and only mean blood pressure can be measured, necessitating use of an arterial line. As cardiac function improves, pulsatility on the arterial tracing is increasingly pronounced and may be a sign of recovery.

VA-ECMO

• “VA” means that the blood is taken from a vein and returned to an artery
• Acts as a machine that acts like a “heart and lung bypass” system for people whose hearts or lungs aren’t working well enough on their own.
• How it works:
  • Deoxygenated blood is taken out of the body : A tube (catheter) is placed in a large vein(s), usually femoral vein(?), to pull out blood that isn’t getting enough oxygen.
  • Oxygenation of blood : The oxygenator adds oxygen to the blood and removes carbon dioxide (like your lungs normally would). It also pumps the blood back into the body with extra force (like your heart normally would).
    • As the blood transits through the membrane oxygenator, hemoglobin becomes fully saturated with oxygen and carbon dioxide (CO2) is removed. The degree of oxygenation is determined by the flow rate and fraction of inspired oxygen. The membrane oxygenator can provide up to full oxygen saturation. Even in the state of pulmonary edema or massive pulmonary embolism, oxygen saturation is normal.¹
  • Blood is returned to the body : Another tube (reinfusion cannula) sends the oxygen-rich blood back into an artery (typically femoral artery) so it can circulate through the body.
    • Blood from the femoral artery flows retrograde up the aorta and meets the native heart’s forward flow (antegrade flow) at some point in the aorta
  • 

Device	VA-ECMO	IABP	Tandem Heart	Impella (2.5; CP; 5; RP)
Flow, l/min	4–6	0.5–1	4–6	2.5–5
Duration of support, FDA approved	6 h (limited by oxygenator durability)	9 days	21 days	4 days (2.5, CP), 6 days (5) 14 days (RP)
Ventricles supported	LV and RV	LV	LV or RV	LV or RV
Cannula size, F	Inflow 18–21 Outflow 15–22	7–9	Inflow 21 Outflow 15–17	12–21
Additional requirements	Potential need for LV venting, possible cutdown		Transseptal puncture	Surgical cutdown for Impella 5
Advantages	Highest cardiac output Complete cardiopulmonary support (including oxygenation and CO2 removal)	Easy to place Good safety profile Fewer side effects, especially vascular	Highest cardiac output, comparable with VA-ECMO, and no LV distension	Multiple devices to choose from
Disadvantages	Requires more resources and support staff than other devices Retrograde blood flow with worsening of afterload (LV distension) Vascular complications Thrombocytopenia	Limited hemodynamic support Contraindicated in severe aortic regurgitation	Need tertiary or quaternary specialized care center Necessitates atrial transseptal puncture with its potential complications Vascular complications Retrograde blood flow	More invasive and complex to implant than the IABP Unstable position Frequent hemolysis Vascular complications
Table source: Table 1 in 1

Venting or Decompressing the LV

You’ll often seen ↑ LV afterload and LVEDP in patients on VA-ECMO. Further, in patients with significantly reduced ejection fractions at baseline, VA-ECMO may cause an increase in wall stress and oxygen demand, which impedes myocardial recovery and may precipitate progressive pulmonary edema and acute lung injury (LV distension or “ECMO lung”) and worsen outcomes.¹ Treatment of anticipated or observed increases in LV systolic and end-diastolic pressure includes venting or decompressing the LV. Multiple strategies to reduce pulmonary congestion during VA-ECMO support have been used:¹

1. Increase in forward flow by introducing inotropes or devices such as Impella (so-called EC-pella) or IABP
2. Decrease in LV afterload by placement of an IABP.
3. Mechanical decompression of the LV by shunting the blood to the right side via atrial septostomy or removal of LV volume via placement of Impella, transseptal cannulation of the LV or left atrium (LA), or direct surgical LV apical drainage.
4. Removal of fluid from intravascular space using diuretic agents, ultrafiltration, or hemodialysis.
5. Reduction in ECMO speed and consequently ECMO flow (which may not be well tolerated).

Footnotes

1. Guglin, M., Zucker, M. J., Bazan, V. M., Bozkurt, B., El Banayosy, A., Estep, J. D., Gurley, J., Nelson, K., Malyala, R., Panjrath, G. S., Zwischenberger, J. B., & Pinney, S. P. (2019). Venoarterial ecmo for adults. Journal of the American College of Cardiology, 73(6), 698–716. https://doi.org/10.1016/j.jacc.2018.11.038 ↩ ↩² ↩³ ↩⁴ ↩⁵