ECMO
***ECMO does not “treat” any disease!!! It provides heart and lung bypass while you treat the underlying disease process***
***ECMO therefore serves as a “bridge” for 1) recovery 2) organ transplant 3) cardiac ventricular support devise or 4) decision***
Overview
Two Types:
1) Veno-Arterial (VA) ECMO -- cardiac and pulmonary support
2) Veno-Venous (VV) ECMO - pulmonary support
A overview of EMCO from ICU One Pager below.
Some of these elements are broken down into more detail on this page
General Terms
Drainage (Access) Cannula- Where the patient's blood is drained from the body and heads to the circuit. This is negative pressure
Return Cannula- Where the patient's blood is returned to the body, externally oxygenated
Flow- the flow of blood through the circuit and can be thought of as "cardiac output" in VA ECMO. This is a function of volume status, the diameter and length of the cannulas (Poiseuilles Equation, see "Cardiac" tab for more of this)
Generally, full ECMO support is considered 100-150 ml/kg/min for infants, ~ 90-100 ml/kg/min for pediatric patients, and ~ 70 ml/kg/min for adults
Sweep/Gas flow- The rate of oxygen flowing through the oxygenator measured in L/min
The higher your sweep, the more CO2 you will remove (see image below)
Pump
Centrifugal (see image below) - nonocclusive pump that moves blood forward by producing a constrained vortex within a polycarbonate structure
Has either "cones" or "impellers" in the inner workings of the pump to cause rotations and produced higher RPMs as compared to roller head pumps
Advantages - will not pump against resistance, less likely for tube rupture, preload dependent, less hemolysis
Disadvantages - increased prime volume, thrombus formation more likely, magnetic decoupling, allows for retrograde flow
Roller head (see image below) - historically used more in pediatrics, though now many programs transititoning to centrifugal pumps
Advantages- lower prime volume, constant flow rate, no retrograde flow
Disadvantages - hemolysis, because constant flow, can increase pressure and cause tubing rupture, an be occulsive, preload dependent, lower overall flow rates when compared to centrifugal pumps
Bladder - a reservoir at the lowest point of the ECMO circult that can trap air and has an access port. Also a nice way to gauge the volume status/pressure status of the circuit.When volume is low or negative pressure is too high, the bladder will collapse on itself.
Heater- maintains temperature of the blood outside the body --> will have temp stability for patient and difficult to determine if patient has an organic fever
Oxygenator - also known as the membrane lung; contains hollow fibers with countercurrent exchanges of water and oxygen in one direction and the patient's blood in another
SvO2 - measure of the venous blood saturation of oxygen PRIOR to circulating through the oxygenation
Normal ~ 70%; if higher, can indicate recirculation of deoxy and oxy blood in ecmo circuit or poor patient oxygen extraction; if lower, suggests higher patient oxygen demand/extraction and suggest patient needs more ECMO support
Pre-membrane pressure- positive pressure in the blood from the pump BEFORE the oxygenator
Post-membrane pressure - positive pressure in the blood after the oxygenator but BEFORE the patient
Physics of the Membrane Lung
https://www.elso.org/portals/0/files/pdf/elso_guidelines_for_adult_and_pediatric_membrane_oxygenation_circuits.pdfA nice overview of ECMO is here - from ELSO (Extracorporeal Life Support Organization)
ECMO Pump
Centrifugal Pump
Roller Head Pump
Types of Cannulas /Cannulation Strategies
Charts exists that determine the flow rates using Poiseuilles' Equation
Our ECMO Primers/Surgeons have these, please refer to RBC documentation for your patients
Example of one chart for VV ECMO below
Images of Different ECMO Cannulas
VA ECMO Cannulation strategies
Reperfusion Cannula
VV ECMO Cannulation Strategies
Anticoagulation
Need to prevent blood clotting while outside the body and in the circuit
Systemic anticoagulation for patient - risk for bleeding
Two main drugs
Heparin
Bolus and then continuous infusion
Measure heparin level/ACT
Bivalirudin
Continuous infusion
Measure INR
Important to monitor Hb, Plt, Coags, Fibrinogen levels and replace with blood products per desired goals in ECMO protocol
See "Heme/Onc" section for more information, especially relating to Thromboelastography (TEG)
Anticoagulation on ECMO is an evolving topic and in need of more research!
Complications/Troubleshooting
Summary form ICU One pager below
Common issues:
Patient Agitation
Hypovolemia
Anticoagulation vs Bleeding
Air Embolism
Circuit Thrombosis
Cannula Displacement
Cerebral Infarction
Recirculation - read more about this!
Weaning off ECMO
As with all things in the PICU, once started on ECMO the goal is to start to plan how to come off!
VV ECMO - turn down FiO2 and sweep on ECMO circuit, and increase ventilator support. Monitor patient's blood gases, respiratory effort, plateau pressures, tidal volumes
VA ECMO - do this with "clamp trails" aka stopping ECMO flow by clamping cannuals and seeing patient's innate hemodynamics.
Need to ensure medications, oxygen, heparin/bival are transferred from ECMO circuit to the patient during trails or else will not receive these medications
May start with 1 clamp tria a day and increase in frequency OR may do one and determine patients cardiac function has improved and proceed with decannulation from ECMO