ELSO Foundations Adult ECMO Flashcards
What are the components of an ECMO Circuit
Drainage Cannula
Pump Driver
Pump Console
Membrane Lung
Gas blender
Heat Exchanger
H20 Tubing
Return Cannula
Describe the features of a drainage cannula.
Long and multistage
Multiple holes both at the tip and along the length of the cannula
Describe the features of a return cannula.
Typically short and single stage
One hole at the tip of the cannula
What is the normal size for a return cannula in an adult?
17 to 19 French
What is the normal size for a drainage cannula in an adult?
21 and 25 French
Describe the Centrifugal Pump.
- Nonocclusive pump that propels blood using centrifugal forces
- When rotating the pump creates suction at the central hub
- Drives fluid to the periphery of the impeller
Describe the relationship of centrifugal pumps on preload and afterload.
Centrifugal pumps are preload dependent and afterload sensitive.
ECMO Pump
Explain Rotational Speed Concepts
- Blood is pumped forward at flow relative to resistance and rotational speed.
- While effective blood flow is dependent on the pump rotational speed, higher revolutions per minute, do not necessarily result in highter flow rates.
- Use the lowest RPM to achieve a certain flow
What is Cavitation?
While centrifugal pumps cannot generate very high positive pressures, they can generate significant and potentially unsafe **subatmospheric pressures of - 200 to - 300 mm Hg. **
This increases the risk of dissolved air being pulled out of the blood, a phenonmenon called “cavitation” that results in air bubbles comming out of the solution from the blood and causing cell damage.
Is it safe to clamp the ECMO Circuit?
It is safe to clamp the circuit with a running centrifugal pump
Centrifugal pumps cannot generate extreme positive pressure
Centrifugal pumps can generate unsafe negative pressures resulting in drainage insufficiency which can cause:
Cavitation
Hemolysis
Vessel wall damage
What is drainage insufficiency?
Extreme negative suction forces can cause blood vessels to collapse around the drainage cannula, potentially occluding drainage holes and damaging vessel intima.
What causes hemolysis on centrifugal pumps?
A clot or air is traped inside
The rotor is tilted
The revolutions per minute are high compared with the flow
Describe the membrane lung.
The membrane lung is an artificial lung responsible for oxygen uptake and carbon dioxide clearance.
It also modulates the temperature of the blood.
What are the the phases of the membrane lung
- Blood, gas, and water which are all physically separated.
- Blood from the drainage cannula enters the membrane lung and exits towards the return cannula.
- Gas from the blender enters and exits the membrane.
- Water from the heater enters and exits.
How does the membrane lung allow for gas exchange via diffusion according to pressure gradients?
Oxygen diffuses from the gas phase into the blood phase while carbon dioxide diffuses from the blood phase into the gas phase.
Describe polypropylene membranes.
Polypropylene membranes have a microporous design allowing for more efficient gas exchange but are prone to plasma leakage.
Describe Polymethylpentene (PMP) membranes
Polymethylpentene membranes have a nanoporous design with low risk for plasma leakage. They operate at low resistance and offer efficient gas exhange.
Modern membrane lungs primarily use PMP membranes.
What are the different types of membrane lung design.
Axial flow and transverse flow membrane lungs. Variations in design are associated with differences in priming volume, internal resistance, and working pressures.
What is the purpose of the blender in the ECMO circuit?
The blender provides fresh gas to the membrane lung, typically a mix of air and oxygen. This allows for the titration of FdO2, the device inlet oxygen fraction.
What are the three pressure regions in the ECMO circuit?
Drainage pressure
Pre-membrane lung pressure
Post-membrane lung pressure
Describe drainage pressure.
Drainage pressure is measured before the centrifugal pump inlet. The pressure is negative.
Describe Pre-membrane pressure.
Pre-membrane lung pressure is measured between the centrifugal pump outlet and near the membrane lung outlet. This pressure is positive.
Describe Post-membrane pressure.
Post-membrane lung pressure is measured at the membrane lung outlet. This pressure is positive but lower compared to the pre-membrane lung pressure.
Describe the typical pressure change across the ECMO circuit.
Pressure in the drainage cannula and tubing is negative and becomes more negative the closer to the pump it is measured.
The most negative pressure is immediately pre-pump.
The most positive pressure is immediately post-pump.
The primary pressure drop occurs across the membrane lung due to resistance in the circuit.
Describe the delta P or pressure drop.
Delta P or pressure drop is the difference between the pre and post membrane lung pressures. This value can increase if the flow through the membrane lung is increased or if the resistance in the membrane lung increases.
Describe the purpose of the flowmeter within the ECMO circuit.
Centrifugal pumps are non-occlusive, circuit blood flow rate cannot be predicted from pump speed.
A flowmeter is required to determine the blood flow rate.
Flowmeters clamp onto circuit tubing and measure blood flow rate via ultrasonic transducers.
Describe the purpose of the Heater within the ECMO circuit.
Since a portion. of the patient’s blood is extracorporeal, there is a risk of hypothermia. Typically, heater exchange fibers are integrated with the membrane lung that circulate heated water.
Describe the purpose of tubing clamps.
Tubing clamps are considered integral components of an ECMO emergency kit. Clamps may be applied to circuit tubing to stop circuit blood flow.
Clamps can be used routinely during priming or emergently during an ECMO emergency.
What information do you need to collect to choose the right cannula diameter?
Size of patient
Vessel size and condition
Level of desired support
What are some potential risks of selecting an inappropirate cannula diameter?
Undersized cannulas may result in drainage insufficiency and inadequate patient support.
Undersized cannulas will decrease working pressures and result in lower pump revolutions per minute.
Oversized cannulas can result in distal artery ischemia or venous congestion.
What working principles are characteristic of a centrifugal pump?
Flow is impacted by both preload and afterload.
Inability to generate excessive positive pressures.
Ability to generate damaging negative pressures.
Ability to pump microair.
What functions does the membrane lung perform?
Oxygen uptake
Carbon dioxide clearance
A thrombus formation in the membrane lung will cause which pressure to rise?
Pre-membrane lung pressure
What is the significance about a pressure drop across the membrane lung?
It can provide information about clot formation inside the membrane lung.
Why do we need to measure circuit blood flow during ECMO?
Pump speed does not give information about actual blood flow.
What is open cannulation?
Refers to cannulation of peripheral vessels after surgical exposure. This strategy is primarily used for VA ECMO.
What is Central Cannulation?
For patients with postcardiotomy shock, central cannulation is typically used, switching the patient from cardiopulmonary bypass to ECMO with the right atrium and ascending aorta being directly cannulated.
Describe percutaneous cannulation?
Pecutaneous cannulation, with use of imaging, via Seldinger technique is used in the vast majority of Adult VV and VA ECMO.
Describe the steps for percutaneous cannulation.
Preparation
Vascular access
guidewire insertion
serial dilation
cannula insertion
Describe Cannula tip placement confirmation.
Can be confirmed by using ultrasound or x-ray.
Describe how the cannula is connected and secured.
Cannulas are connected to the ECMO circuit using wet to wet technique.
Cannula should be secured with 3 sutures.
The cannula should be properly dressed.
What are the different configurations of VV ECMO?
VV ECMO can be either dual site or single site with a dual lumen cannula.
Femoro-Femoral Cannulation
VV ECMO
Femoro-femoral cannulation is a common cannulation. The drainage cannula is typically placed with its tip in the intrahepatic IVC. The return cannula is typically placed with its tip in the right atrium.
Femoro-Jugular Cannulation
VV ECMO
The drainage cannula is placed with its tip in the intrahepatic IVC. The return cannula tip is placed in the SVC or right atrium.
Dual-Lumen Cannula
VV ECMO
The dual lumen cannula drains blood from the SVC and IVC. It then returns blood to the RA with a jet directed across the tricuspid valve.
A dual lumen cannula can also be placed in the RA and return blood to the pulmonary artery.
Femoro-Femoral Cannulation
VA ECMO
The drainage cannula is placed in the femoral vein with the tip near the right atrium. The return cannula is placed in the femoral artery with the tip positioned in the iliac artery or distal aorta.
Femoro-Femoral Limitations
VA ECMO
- Artery cannulation is dependent on vessel anatomy and can be challenging with atherosclerotic disease or small vessels
- Risk of lower extremity ischemia. Use of distal perfusion cannula may mitigate this
Internal Jugular - Axilary
VA ECMO
Another option is for a graft to be sewn on to the right axilary or subclavian artery. This is useful when femoral artery cannulation is not suitable.
It also allows for greater mobility while the patient is waiting recovery.
What is Central Cannulation?
Placement of the drainage cannula into the right atrium and the return cannula in to the aorta.
Central Cannulation Limitations
Higher bleeding and infection rates
Returns to the OR for chest washouts
List 3 forms of ECMO cannulation techniques.
Percutaneous Cannulation
Hybrid Cannulation
Open Cannulation
List 3 common configurations for VV ECMO support.
A 50-year-old female arrives to the ICU after initiation of VA ECMO via the right femoral vein and the left femoral artery in the cath lab for post-STEMI cardiogenic shock. The DP and PT pulses are absent on the left lower extremity. What is the next best step in management?
Place a distal perfusion catheter in the left femoral arter.
What is the an advantage of central VA ECMO?
Antegrade flow has an advantage of central VA ECMO. It is typically instituted for postcardiotomy shock syndrome when the patient already has an open chest in the operating room.
Describe Oxygen Content
Oxygen content refers to the amount of oxygen in the blood. This can be for the arterial side (CaO2) or the venous side (CVO2).
Describe Oxygen Delivery and uptake.
Oxygen delivery is the cardiac output multiplied by the Content of arterial oxygen. Oxygen uptake is the amount of oxygen consumed by the peripheral tissues.
What are the four factors that determine oxygen uptake in the membrane lung?
The membrane lung design, specifically the gas transfer properties, the venous blood partial pressure of oxygen, the fraction of oxygen in the sweep gas or the FD02 and the blood flow rate.
What 3 factors determine carbon dioxide removal in the membrane.
How does membrane lung design have an impact on carbon dioxide clearance?
Membrane surface area and membrane thickness are important determinants of gas transfer. Specifically smaller and thicker membranes reduce gas transfer.
How does Sweep Gas Flow Rate affect carbon dioxide clearance?
Higher gas flow rates are associated with higher CO2 clearance rates.
Changes in sweep gas flow rates have little impact on PO2 levels.
Are there hemodynamic changes associated with VV ECMO?
Blood is drained from the venous circulation into the ECMO circuit and then returned back into the venous circulation. Blood that is captured by the ECMO circuit does not bypass the heart and lungs. As such VV ECMO has no direct effect on hemodynamics.
How does VV ECMO assist patients with RV dysfunction in ARDS?
Some patients may have elevated pulmonary pressures due to hypoxemia, respiratory acidosis and high mean pulmonary pressures.
VV ECMO can indirectly improve RV function by improving oxygenation, acidosis and decreasing airway pressures by application of lung rest settings. This can reduce RV afterload and improve RV function.
What is the affect on venous oxygen saturation on VV ECMO?
It will improve arterial oxygen saturation and also central venous oxygen saturation.
Are there any changes to the Arterial line on VV ECMO?
On VV ECMO there is no change to mean arterial pressure or the arterial pressure waveform. Arterial saturation is increased an is used to titrate ECMO support.
How does VV ECMO affect the End-Tidal CO2?
End-Tidal CO2 is typically reduced once on VV ECMO. This is due to the extracorporeal clearance and reduced ventilator settings.
What are the hemodynamic effects of VA ECMO?
Reduction in right ventricular preload.
Increased left ventricular afterload due to retrograde blood flow up the aorta.
What happens when there is a mistmatch of venous return to the drainage cannula?
The pre-pump side of the circuit is under negative pressure and the post-pump side of the circuit is under positive pressure.
The pump is preload dependent. For increasing pressure drops along the drainage cannula a higher venous return into the cannula is required.
Collapse of the vasculature around the cannula can occur causing drainage insufficiency.
What circuit factors cause drainage insufficiency?
Excessive pump speed
Inadequate cannula size
Malpositioned or occluded cannula
What patient factors can cause drainage insufficiency?
How do you diagnose drainage insufficiency?
How is drainage insufficiency managed?
Reduce pump speed until blood flow is stable
Look for causes of drainage insufficiency
Consider fluid bolus and overall volume status
Consider adding an additinal drainage cannula
What is “Return Obstruction”?
Resistance to blood flow in the ECMO circuit distal to the pump.
What are some examples of “Extraluminal Obstruction”?
What are some patient complications that can increase return obstruction?
Tension pneumonthorax (usuallly VV ECMO)
Hypertension (VA ECMO)
Aortic Dissection (VA ECMO)
How do you diagnose return obstruction?
Increasing pre and post membrane lung pressures while the pressure drop remains unchanged across the membrane lung.
Blood flow decreases in a partial obstruction or stops with a complete obstruction.
What is the point below which tissue hypoxia occurs?
Carbon dioxide removal on ECMO is a function of which of the following?
VV ECMO may improve RV function by:
Right ventricular failure in ARDS can be caused by which of the following?
What is the hemodynamic effect of VA ECMO on the right ventricle?
What is the hemodynamic effect of VA ECMO on the left ventricle?
Which of the following could determine return obstruction on veno-venous ECMO support with femoro-jugular cannulation?
Which of the following are causes of extraluminal return cannula obstruction?
What are the two classifications of respiratory failure?
Hypoxemic Respiratory Failure
Hypercapnic Respiratory Failure
Ventilator-Induced Lung Injury
Inflammatory mediators can be released from the lung as a result of biotrauma which can have a downstream affect on other organs.
Rationale for VV ECMO
What are the indications for VV ECMO?
Hypoxemic or Hypercapnic respiratory failure that has not responded to conventional therapy.
Post cannulation x-ray
Post cannulation chest x-ray should be taken to confirm cannulation positions.
Once the patient is on VV ECMO what are the treatment goals?
How is sweep gas titrated?
Titrated to maintain a pH of 7.35 - 7.45
What is ultra protective lung ventilation?
How is recirculation managed?
What should be included in the Pre-initiation ECMO Checklist.
Titrate ECMO support after initiation.
Once ECMO circuit is running the support should be titrated to patient needs. ECMO blood flow should be titrated to mean arterial pressure and organ perfusion. Sweep gas flow should be titrated to PCO2 and pH.
VA blood flow titration
Blood flow should be titrated to markers of perfusion.
Invasive management of Left Ventricular dysfunction
Why would a patient on VA ECMO be also on a IABP?
IABP during deflation lowers left ventricular afterload and encourages aortic valve opening.
Why would a patient on VA ECMO also be on an impella?
An axial flow LVAD directlly drains blood from the left ventricle into the proximal aorta.
Dual Circulation
Diagnosis
Diagnosis made by comparing the right upper extremity pulse oximetry to the lower extremity pulse oximetry.
Arterial line placement on VA ECMO
All patients on VA ECMO should have and arterial line and pulse oximeter monitored on the right upper extremity. This way you can assess dual circulation or differential oxygenation.
Dual Circulation
Definition
On peripheral VA ECMO the native lung and artificial lung can supply different regions of the body, with the native lungs supplying the upper portion and the ECMO circuit supplying the lower portion. As such these circulatory beds may have different oxygen and carbon dioxide tensions - a phenomenon termed “differential oxygenation and differential carbon dioxide removal”.
What is the goal of sedation while on ECMO?
What are the benefits of awake ECMO?
What patient characteristics should be considered for physiotherapy while a patient is on ECMO?
Why do patients on ECMO need to be anticoagulated?
Patients on ECMO have a tendency to clot. This is due to the procoagulant and inflammatory effects of the ECMO circuit.
When blood comes into contact with the foreign surface of the circuit, there is associated protein adsorption, platelet adhesion and activation, and subsequent fibrin and thrombus formation.
ECMO Circuit
Inflammatory Response
The artifical surface activates several inflammatory mediators including the complement, kinin and coagulation systems. These lead to systemic inflammation and thrombus formation.
What are the two interventions aimed at reducing the procoagulant and inflammatory effects of the ECMO circuit?
Use circuits with biocompatible surfaces and provide systemic anticoagulation.
Ideal Anticoagulant while on ECMO
Heparin while on ECMO
Heparin binds inactive antithrombin. This leads to conformation change in antithrombin, allowing it to bind to thrombin, inactivating it, and to factor Xa, which reduces the conversion of prothrombin to thrombin.
The net effect is reduced cleavage of fibrinogen to fibrin and effective anticoagulation.
Antithrombin is a naturally occuring glycoprotein anticoagulant present in plasma.
Direct Thrombin Inhibitor while on ECMO
The direct thrombin inhibitors bind to thrombin directly and inactivate it.
Monitoring Anticoagulation on ECMO
Activated clotting time measures the time for whole blood to clot on exposure to an activator.
aPTT assay is a plasma-based test that uses and activator, calcium, and phospholipids to measure the time to fibrin formation.
The anti-Xa assay is a measure of heparin activity. It is based on the ability of heparin to catalyze antithrombins inhibition of factor Xa.
Anticoagulation Choice on ECMO
Both heparin and direct thrombin inhibitors have short half lives. Heparin has the availabiity of a reversal agent.
Heparin MDSO
ECMO
Mechanical Ventilation MDSO
ECMO
Norepinephrine MDSO
ECMO
Vasopressin MDSO
ECMO
Epinephrine MDSO
ECMO
Phenylephrine MDSO
ECMO
Dobutamine MDSO
ECMO
Milrinone MDSO
ECMO
Fluid Administration MDSO
ECMO
Red Blood Cell MDSO
ECMO
Hydromorphone MDSO
ECMO
Propofol MDSO
ECMO
Cisatracurium MDSO
ECMO
Rocuronium MDSO
ECMO
Acute Kidney Injury
ECMO
Kidney injury and the need for renal replacement therapy are common while patients are on ECMO. Incident rates range from 30 - 78% acute kidney injury and 47 - 60% renal replacement therapy.
Etiology of Kidney Injury
ECMO
Renal Replacement Therapy Options while on ECMO
Dialyze or provide hemofiltration through a dedicated hemodialysis catheter or to dialyze or provide hemofiltration via the circuit.
Renal Replacement Therapy
Dedicated hemodialysis catheter
Requires placement of a catheter as a point of access.
Renal Replacement Therapy
Safe Zone ECMO Circuit
Connections should be made in the safe zone, defined as the circuit tubing between the pump and the membrane lung. The reason this is the safe zone is because it avoids accessing the circuit pre-pump, thereby minimizing the risk of air embolus, and returns blood pre-oxygenator, allowing the membrane lung to filter out air or clots.
Explain the following sample configuration for Renal Replacement Therapy
Both the access and the return lines for RRT are in the safe zone of the ECMO circuit - post-pump and pre-oxygenator.
ECMO Transport
Interhospital Transport
ECMO Classifications
List Medical Complications of ECMO
List Mechanical Complications of ECMO
List potential Neurological Complications while on ECMO
Risk of Bleeding
ECMO
Incidence of Bleeding while on ECMO
Risk of Thrombosis
ECMO
Incidence of Thrombosis
ECMO
Incidence of Limb Ischemia
ECMO
Pump Failure
Definition
ECMO
Pump failure refers to the inability of the pump to generate and maintain a circuit blood flow. This typically presents as an abrupt cessation of blood flow in the ECMO circuit with a subsequent loss of ECMO support.
Pump Failure
Etiology
ECMO
Pump failure can occur at the level of the console, driver or pump head.
What can cause the console or driver to fail?
Loss of power or electronic malfnction leading to loss of blood flow. If the pump head is not well seated within the driver or not coupled with the magnet, pump operation is compromised.
What can cause the Pump head to fail?
The pump head can fail if there is pump head thrombosis or air embolism leading to loss of blood flow.
The latter of these is termed pump head airlock.
Pump Failure
Diagnosis
ECMO
The presentation of pump failure is dramatic as an abrupt cessation of blood flow leads to loss of ECMO support. As such, patients may present with acute cardiopulmonary failure and eventually cardiac arrest.
Flow sensor failure
ECMO
The flow sensor can fail such that the pump functions appropriately but circuit blood flow is not properly monitored.
The flow sensor should be replaced.
Pump Failure
Management
Isolate patient from ECMO circuit
Clamp the ECMO circuit by clamping the return tubing.
Use hand-crank allows for resumption of ECMO support while addressing the cause of pump failure.
The return clamp must be removed prior to proceeding with the hand crank.
Membrane Lung Dysfunction
ECMO
As a foreign body with a high surface area, the membrane lung can activate blood inflammatory and coagulation pathways. The membrane lung can be a site for fibrin and clot deposition which can result in dysfunction.
Membrane Lung Dysfunction
Diagnosis
Serial monitoring of the hematologic profile can identify systemic coagulopathy or hemolysis.
The pressure drop across the membrane lung can be trended to identify internal resistance and obstruction to blood flow.
Comparing pre and post membrane lung blood gases can allow quantification of oxygen uptake and carbon dioxide clearance and identify impaired gas exchange efficiency.
Explain pressure drop across the membrane lung.
The pressure drop across the membrane lung is the difference between the pre- and post-membrane lung pressures. Subsequently, the internal resistance of the membrane lung is calculated as the pressure drop divided by the circuit blood flow rate.
An increase in resistance, or the need for higher pump speed to maintain a stable flood flow rate, is suggestive of increasing membrane lung clot burden.
How do you assess lung membrane gas efficiency and identify a failing membrane lung?
A maximal VO2 less than 100 - 150 ml/min despite maximal effective blood flow rate and fraction of delivered oxygen of 1.0 suggests a failing membrane.
Persistently elevated CO2 with a clearance between pre and post membrane lung of less than 10 mmHg despite maximal sweep gas flow rate suggest a failing membrane.
Air Embolism
Definition
ECMO
Refers to the presence of air within the ECMO circuit. It can be caused by small or large bubbles.
How can Air enter the ECMO Circuit?
Entrainment through improper connection of the circuit. Cavitation when dissovled gas is exposed to very negative pressure which creates micro air-bubbles in the blood.
Prevention of Air Embolism
ECMO
Proper circuit priming and connection. Circuit connections should be made as a wet connection or underwater.
All central line lumens need to be properly protected with needleless connection hubs during ECMO support.
Air Embolism Management ECMO
Clamp the return tubing close to the patient. At this point the circuit will need to be de-aired. Once de-aired and the source of air is identified ECMO support can be resumed.
What are the four indications for coming off ECMO Emergently?
Describe the process of coming off ECMO support Emergently.
Place a clamp on the return tubing. Call Transport Physician and identify and troubleshoot cause.
What are the characteristics of the HLS Module on Cardiohelp?
The HLS module integrates a gas exchanger, heat exchanger and centrifugal pump.
It is available in two versions for a blood flow of up to 5.0 l/min or a blood flow of up to 7.0 l/min.
