Keep calm and cannulate!

Author: Aidan Burrell
Reviewers: Josh Ihle, Chris Nickson

Everything ECMO 010

A 45-year-old lady with ARDS remains hypoxic despite mechanical ventilation, proning, and nitrous oxide. She has a central venous catheter (CVC) in the left femoral vein, and an arterial line in the right femoral artery.

You prepare her for VV ECMO cannulation.

Q1. Describe the equipment you require to perform VV ECMO cannulation.

ECMO cannulas are long, wide, wire reinforced cannulas. The venous cannulas (figure 1) can be single-stage or multi-stage. Single stage cannulas only have holes at the distal tip (figure 1, bottom cannula) whereas multi-stage cannulas have multiple access points along the cannula that are designed to reduce suck down (figure 1, top cannula). They come in a variety of diameters and 19-27 Fr gauges are typically used. Lengths also vary and are chosen to accommodate different configurations – shorter cannula for the neck (15-25cms) and longer cannula (55cm) for the femoral vessels.

Figure 1. Distal tips of venous ECMO cannulas. Single-stage (bottom) and multi-stage (top).

 

Arterial cannulas (figure 2) are shorter, narrower (typically 15-23Fr), and often have a luer lock to connect to the distal perfusion cannula during VA ECMO. The arterial cannula can be also used in VV ECMO for the internal jugular vein. If this is chosen, the luer lock must be carefully closed. This prevents air embolism if used as an access cannula and prevents bleeding if used as a return cannula.

Figure 2. Arterial ECMO cannulas (top two with red caps)

 

Dilators come in a range of brands, such as Biomedicus, Cook and Avalon (figure 3). Different dilators have different characteristics.

Figure 3. Dilators for ECMO cannulation (Biomedicus, Cook, and Avalon, from top to bottom)

 

Wires are very long (1.8m or 2.4m) and have J looped tips. There are soft wires and stiffer wires. The soft wires are safer in terms of minimising vascular injury, however, they are more easily bent by poor cannulation technique (figure 4). The stiff wires (i.e. Amplatz, figure 5) can make dilation much easier but come with a higher risk of inadvertent vascular injury despite having a flexible tip.

Figure 4. Soft wire (in right hand)

Figure 5. Amplatz stiff wire.

Q2. Where will you place the cannulas for VV ECMO? What are the advantages and disadvantages of the commonest two configurations?

 

At the Alfred ICU, a femoral-femoral configuration is usually preferred initially.

Advantages Disadvantages
Femoral – femoral Rapid access

Easier to place and secure

Easier to transport

Potentially less flow
Femoral – internal jugular vein (IJV) Potentially higher flow More recirculation

Securing IJV line is more complex

Q3. Should you re-wire the existing lines?

No (in an ideal world!)

The risk of infection by re-wiring a cannula is high. The venous CVC should be removed and a new clean puncture performed. A new radial arterial line should be placed and the femoral arterial line also removed (arterial line placement can often be delayed until after the ECMO cannulation is completed).

ECMO cannulas have high rates of infection as they are large and often remain in situ for weeks. Thus insertion of new, clean lines using sterile technique is preferred. If an ECMO cannula does become infected it may be difficult to resite them depending on the access points available. Finally, ECMO cannulation requires a nice clean entry point into the vessel – an existing line may enter the vessel via a tortuous route. This may have been OK with a CVC, but will tend to cause problems with the stiffer ECMO dilators and cannulas. There have even been cases of CVCs that have transected an artery during insertion – this can be a catastrophic discovery to make when attempting a ‘rewiring’ for ECMO cannula insertion…

Q4. Your colleague says he has done many CVCs and can cannulate just fine using the landmark technique. What is the role of Ultrasound (US) during cannulation?

Ultrasound is essential for percutaneous cannulation.

Ultrasound:

  1. Increases first pass success
  2. Helps with vessel selection (e.g. left versus right)
  3. Identifies potential problems with the site (e.g DVT, calcification)
  4. Enables sizing of cannulas
  5. Enables confirmation of wire in the vein or artery
  6. Enables insertion in the correct part of a vessel (e.g. avoid bifurcation of the common femoral artery into superficial femoral artery and profunda)
  7. Identifies complications (thrombus, haematoma, pseudo aneurysm)

There is no role for a blind multiple passes technique of cannulation. This leads to delays, haematoma (so-called “porcupine injuries”), and later places the patient at higher risk of infection.

The bleeding risk from multiple failed passes increases once the patient is established on ECMO, and therapeutic heparinisation is commenced. Therefore, ensuring the femoral vessel is punctured on the first attempt, below the inguinal ligament is important. A retroperitoneal haemorrhage can be difficult to diagnosis and often presents very late – the use of ultrasound is important to minimise this risk!

Q5. Describe the key steps that you will take to place the needle into the vessel using the US?

It is important to maximise your first pass success rate to prevent hematoma or vasospasm formation

  1. Under full sterile conditions, identify a straight part of vessel
  2. Find the most superficial part of the vessel (without moving too high or low relative to other anatomical structures, e.g. the inguinal ligament, or vessel bifurcation)
  3. Aim for a flat entry into the vessel where possible (angle approx. 25-30 degrees)
  4. Avoid thrombosed or calcified vessels
  5. Enter the middle of vessel to ensure a clean entry
  6. Once in the vessel, advance the needle within the lumen a few more millimetres under vision to ensure the tip is well within lumen and wire will pass freely – maintain an acute (“flat”) angle to the vessel minimises the risk of inadvertent puncture of the posterior wall (“back-walling”).
  7. Hold the needle steady as you remove the syringe to prevent inadvertent removal of the needle. This is best done with an ‘underhand’ grip on the needle so that your hand rests on the patient and allows you to continuously visualise the needle entry point at the skin.
  8. Feed the wire. Do not advance if there is resistance — stop! When using an Amplatz stiff wire, be very careful as the distal end as it approaches the heart to avoid a penetrating injury.
  9. Confirm the wire course at the femoral vessel by visualising with ultrasound near the point of entry.
  10. Ideally have another ultrasonographer available to confirm the distal end of the wire is advanced to the IVC-RA junction when inserting a venous return cannula at the femoral site.

Q6. You bend the wire on insertion (doh!) – how does this occur and how can you prevent this from happening?

The wire is most commonly bent or ‘kinked’ during dilation, especially when using soft wires and larger French stiff dilators.

Kinking occurs when the dilators are advanced ‘off axis’ in a direction that does not follow the path of the wire (figure 6 – the dotted lines represent the direction of force during dilation). The dilator then moves past the point the wire enters the vessel and kinks the wire. In figure 7, the dilator was advanced in the incorrect direction, at a different angle to the original needle cannulation, and then the wire became twisted like a corkscrew during the sequential dilation and rotation process.

Figure 6. Mechanism of wire kinking during dilatation

 

Figure 7. Yikes!

 

To help prevent this, the cannulator should be conscious of the trajectory of the needle and wire during insertion. Ensure dilators are advanced along the same path during subsequent dilatation.

Q7. The left femoral vein is 12mm. The right is 9mm. What size cannulas will you use?

The cannula size that fits inside a vessel can be estimated using this formula:

Vessel mm x3 = French gauge of cannula

In practice, other factors come into play as well:

  1. Size of the patient
  2. VA vs VV ECMO
    — in general, VA ECMO requires lower blood flows, while sick VV ECMO patients with high cardiac outputs often require very high ECMO blood flows and bigger cannulas
  3. Site of cannulation
  4. Access vs return
    — As most problems occur on the access side, such as access insufficiency, a large cannula is important, although a small return cannula diameter will also increase resistance on the circuit and reduce ECMO blood flow.

As a general rule of thumb, try to use as large cannulas as possible that can be safely and quickly inserted. In this patient, a 25Fr multistage access cannula and a 19 Fr return cannula were used.

Q8. Describe the dilation technique you will perform to insert the cannulas?

Dilation can be done with one or two person techniques, and is influenced by time and staff availability, and whether or not you are using stiff wires.

The key principle is to sequentially dilate up the skin and tissues without causing tissue trauma. It is important to push the dilator along the direction of the wire (see question 6). Push the dilator in straight until there is resistance and then twist in one direction whilst maintaining forward pressure and torque, which will apply tension on the subcutaneous connective tissue fibres. When you withdraw the dilator, this loosens or tears the underlying connective tissue fibres making the next pass a little easier. Repeat the process, each time advancing the dilator further before twisting. Several ‘advance and twist’ attempts may be required with each dilator, be patient!

“It is like medical school, you go in straight and come out twisted!”
— Vin Pellegrino on sequential dilation for ECMO cannulation

If using a two person technique, the second person can jiggle (or “rack”) the wire in and out of the dilator to feel for “play” (free movement) and “hold up” (resistance to free movement). “Hold up” is the earliest signal that the wire is being bent or kinked when the dilator is moving NOT in line with the wire. If the second person feels any increase in resistance when jiggling the wire the cannulator must stop dilating and adjust the angle of dilator until the wire freely passes through the dilator again.

Q9. You are having difficulty passing the cannulas through the right skin. Do you cut the skin?

No (in an ideal world!)

This varies between centres – some do not cut the skin at all, while others routinely perform open incisions (particularly when done by surgical teams). In our centre’s experience is that meticulous sequential dilation usually allows the skin to stretch to accommodate the

Our centre’s experience is that meticulous sequential dilation usually allows the skin to stretch to accommodate the cannulas, while keeping a tight fit to prevent bleeding and haematoma formation. It is also often faster. The advantage of the open cannulation technique is it can give excellent visualisation and confirmation of the vessels and may decrease vessel wall damage.

Q10. Describe how you will advance the cannula into the patient.

Even after dilation, the lip between the obturator and cannula can get caught at the skin or at the point where the cannula enters the vessel. Twisting (rotating) the cannula upon reaching these points often helps the cannula pass more smoothly.

The cannula should be advanced until all the side holes are beneath the skin and within the vessel. At this point the obturator within the cannula is pulled back to the specified marking before advancing the cannula any further. This is important so that the leading tip of the cannula is the soft plastic at the end of the cannula, not the firm, sharp obturator which can lead to serious or fatal perforations of the right atrium.

The obturator does not need to be pulled back when advancing the shorter arterial cannula at the femoral site for VA ECMO.

Q11. You observe that during femoral-femoral cannulation, both cannulas are in the IVC. Describe how will you position them for VV ECMO?

The IVC is almost always able to accommodate both the access and return cannulas. The access cannula needs to be in more proximal IVC (ie closer to the skin), while the return needs to be distal – usually in the right atrium. In general, a separation of ≥10cm between the distal holes of the access and the return cannulas is needed to prevent recirculation.

We use ultrasound to guide their positioning, usually via a transthoracic subcostal view of the IVC, or a bicaval view during transoesophageal echocardiography (TOE).

Other methods include using an imaging intensifier in radiology or the cath lab, or by measuring the cannula depth at the skin (followed usually by an abdominal or chest X-ray).

Note the last 4cm of the Biomedius single stage cannula tip is plastic – this cannot be seen on X-ray and may appear much lower than it really is. This plastic tip can only be seen with good quality US imaging (e.g. TOE).

Q12. What is the role of the Avalon cannula? What are the pros and cons in this case?

The Avalon cannula combines both access and return cannulas into a single cannula. They are usually larger cannulas (up to 31 Fr), and are typically sited via the internal jugular vein in the neck.

Advantages include the need for only a single puncture and they may be better tolerated enabling mobilisation and rehabilitation.

Disadvantages are that they can be more challenging to position correctly and blood flows may be lower than other dual cannula techniques. Careful positioning is paramount as the returning jet of blood must be directed through the tricuspid valve. Any malposition will lead to recirculation.

Figure 8. Avalon ECMO cannula. From: Lazar DA, et al. (2012) Journal of Pediatric Surgery 47(2):430-4 (Click image for source)

 

References and Links

  • Pellegrino V, Ihle J, Hilton A, Murphy D. Guideline for Cannulation for Peripheral ECMO. Alfred ICU, 2012

If you want to learn ECMO cannulation come to the Alfred ICU ECMO Cannulation course. It is held twice yearly — details are available at the Alfred ICU Courses website.

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CICM Second Part Exam Practice SAQs 12042017

As prepared by Chris Nickson, here are the practice written questions from this week’s CICM Second Part exam practice session at The Alfred ICU, with recommended reading from Lifeinthefastlane.com’s Critical Care Compendium and other FOAM sources:

Q1.

You note that a 50 year-old man in the emergency department with severe pneumonia has trismus. He requires intubation and mechanical ventilation for type I respiratory failure.

  1. List the important causes of trismus (30%)
  2. Describe how you clinically assess the severity of trismus (20%)
  3. Discuss the implications of trismus for airway management and the options available (50%)

Learn more here:

Trismus and Restricted Mouth Opening

Q2. (from CICM Second Part Exam 2016.2)

You are asked to head a working party to establish a Rapid Response System (RRS) in your hospital.

Outline the steps you will take to do this.

Learn more here:

Rapid Response Systems

Q3.

A 45-year-old man required urgent intubation at a MET call for rapid deterioration resulting in severe hypoxia. He had been admitted to hospital two days previously with bilateral infiltrates on his chest x-ray. You are told that his sputum PCR is positive for Pneumocystis jirovecii.

Outline the key issues and your approach to the assessment and management of this patient.

Learn more here:

Pneumocystis pneumonia


You can access all the previous practice questions since 2014 here:
https://docs.google.com/document/d/1_Ta8IvVaVtc5Il7-kJwj6qKGu54OmifJGRUWCXud8dY/edit
See this link on INTENSIVE for exam resources:
http://intensiveblog.com/resources/#3

The post CICM Second Part Exam Practice SAQs 12042017 appeared first on INTENSIVE.

Differential hypoxia in reverse?!

Author: Arne Diehl
Reviewers: Chris Nickson, Aidan Burrell

Everything ECMO 009

A 41-year-old man is on a prolonged VA ECMO run after a large anterior STEMI. He had a reconfiguration of the ECMO circuit to a jugular venous access cannula and a surgically created return graft onto his right subclavian artery. Since then he has been extubated (2 days ago) and has now developed hypoxia.

You assess him carefully and note that pulse oximetry on the right upper limb indicates an oxygen saturation of 83%, while on the left it is 94%. Lung fields are clear on his chest x-ray.

Q1. Is this differential hypoxia?

No…!

Differential hypoxia (aka Harlequin Syndrome or ‘North-South’ phenomenon) is discussed in Everything ECMO 007. Briefly, this occurs in patients on peripheral VA ECMO with the combination of improved cardiac function and poor pulmonary gas exchange.

In this scenario, there is a difference between the oxygen saturations of the right and left upper limbs, but there is no co-existing pulmonary dysfunction.

Oxygenated blood from the ECMO circuit is returned to the patient via the subclavian artery graft so that the right upper limb is entirely supplied by blood from the ECMO circuit.

This is illustrated below, the chest x-ray shows the external return cannula with the surgical graft outlined onto the subclavian artery. Blood flow is anterograde into the right upper limb and is retrograde into the aorta. The jugular access cannula is seen with its tip just in the right atrium.

Click image to enlarge

Q2. What is the likely cause?

In a VA ECMO patient with a subclavian artery return cannula, the most likely cause of this ‘pseudo-differential hypoxia’ is oxygenator failure.

Paradoxically, this mimics the differential hypoxia that can occur in a VA ECMO patient with a femoral artery return cannula who has pulmonary dysfunction and cardiac recovery. That is, there is hypoxia in the right arm, and normal/high oxygen to the left hand and lower parts of the body.

A second possibility includes ischaemia of the upper limb through obstruction of the limb component of the graft.

Q3. How can you confirm your suspicion?

Check for:

  1. Loss of colour differential pre and post oxygenator
  2. Low PO2 on a post-oxygenator blood gas
  3. Confirm there is adequate blood flow into the right upper limb using arterial doppler.

On checking these you note that there is no appreciable colour differential between the access and return limbs of the ECMO circuit. 

The post-oxygenator gas shows:

pH       7.56
pCO2   28 mmHg
pO2     39 mmHg
SO2     76%
HCO3   24 mmol/L

Q4. Given the findings in Q3, what do you need to do next?

Check the oxygenator

  1. Confirm oxygen flow to the oxygenator:
    1. Ensure that the cap on the oxygen inlet where oxygen tubing is connected was removed prior to connection
    2. Feel the fresh gas flow at the inlet to the oxygenator with your hand
    3. Check that oxygen tubing is securely connected
    4. Check that the oxygen blender is set to 100% oxygen
    5. Set the fresh gas flow of oxygen (aka “sweep gas”) at a minimum flow rate of 2 L/min
  2. Check for clotting:
    1. Visually inspect for increased clot in the oxygenator using a torch
    2. Check for rising D-dimer (suggests clotting) and plasma free haemoglobin (suggests haemolysis)
  3. Check the transmembrane pressure:
    1. This should be <10 mmHg/L of ECMO flow (and is normally around 5 mmHg/L)
    2. A TMP >40-50mmHg at any time is highly suspicious for oxygenator thrombosis

The only abnormality you find on these checks is that the transmembrane pressure is 32 mmHg, which is mildly elevated given the low ECMO circuit blood flow of 2L.

Q5. What is the next step and why?

A timely circuit change is indicated, as the oxygenator has failed.

Although there is no evidence of an oxygenator thrombus, oxygenator failure is a recognised phenomenon after 2-3 weeks of circuit life and is characterised by a gradually decreasing post oxygenator pO2.

Theoretically, you could change the oxygenator in isolation, however, this is a slow, laborious task and the oxygenator is only available commercially with an entire circuit. In addition, biological material adherent to the circuit, which is a potential trigger for inflammatory and thrombotic cascades, is also removed by changing the circuit.

Two days after correcting the problem you are asked to review the same patient for hypoxia once again. This time the left upper limb arterial O2 saturation is 86% compared with 100% on the right upper limb.

A chest X-ray was performed:

Click image to enlarge

Q6. What is the explanation for the difference in arterial O2 saturations between the left and right upper limbs?

This is “true” differential hypoxia in a subclavian return configuration, we like to call this ‘reverse differential hypoxia’.

The chest x-ray demonstrates bilateral alveolar opacities consistent with pulmonary oedema, which impairs oxygenation of blood in the native circulation.

Compared with the first scenario two days previously, the oxygen differential between upper limbs has reversed resulting in lower arterial oxygen saturations in the left upper limb. This has occurred because poorly oxygenated blood that has passed through the pulmonary circulation and ejected from the heart mixes with highly oxygenated blood from the ECMO circuit which enters the aorta from the right subclavian artery.

Thus, in this VA ECMO configuration, pulse oximetry on the right upper limb monitors circuit function and pulse oximetry on the left upper limb monitors his respiratory function.

The hypoxia in the left upper limb can be corrected by treating the pulmonary oedema (e.g. increasing FiO2, positive pressure ventilation with PEEP, fluid removal and optimising cardiac function).

Low arterial oxygen saturations in the right upper limb compared to the left is usually characteristic for differential hypoxia in peripheral femoro-femoral VA ECMO. However, in a configuration where the return line connects to the right subclavian artery, arterial desaturation in the right upper limb indicates a failure of ECMO oxygenation rather than pulmonary dysfunction. Beware of ‘pseudo-differential hypoxia’!

Observing for a colour differential between blood in the access and return limbs of the ECMO circuit is is a vital clue in the absence of routine post oxygenator oximetry and should be part of the rapid visual assessment of ECMO patients. Watch out!

Click image to enlarge

Dark red blood flows from the patient toward the oxygenator in the access limb of the ECMO circuit, whereas bright red blood – if the oxygenator is working! – leaves the oxygenator and is pumped toward the patient via the return limb of the ECMO circuit.

Finally, patients with a subclavian return configuration can still get “true” differential hypoxia from pulmonary dysfunction, however it will manifest as ‘reverse differential hypoxia’. Watch out for that too!

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CICM Second Part Exam Practice SAQs 22032017

As prepared by Chris Nickson, here are the practice written questions from this week’s CICM Second Part exam practice session at The Alfred ICU, with recommended reading from Lifeinthefastlane.com’s Critical Care Compendium and other FOAM sources:

Q1.

Critically evaluate the use of chloride-rich crystalloid solutions (e.g. normal saline) for fluid therapy in the critically ill.

Learn more here:

Chloride in Critical Illness

Q2. 

Regarding infectious endocarditis:

  1. List 8 findings on physical examination (20%)
  2. Discuss the role of echocardiography in making the diagnosis (40%)
  3. Outline the specific therapies required for successful treatment (40%)

Learn more here:

Infective Endocarditis

Infective Endocarditis Echocardiography

Q3.

You have been referred a patient from the emergency department. He is a 35-year-old man who has presented unconscious (GCS 3) with fixed dilated pupils after drinking ‘homemade moonshine’ the previous day.

His initial arterial blood gas (FiO2 0.3) shows:

pH             6.8
PaCO2        40 mmHg
PaO2          80 mmHg
HCO3           6 mmol/L
Na             138 mmol/L
K                5.5 mmol/L
Cl              105 mmol/L
Glucose       12 mmol/L
Lactate          7 mmol/L

He has been intubated and is haemodynamically stable (HR 90/min, BP 110/70 mmHg, no vasopressors).

Outline your management over the first 24 hours.

Learn more here:

Methanol Toxicity


You can access all the previous practice questions since 2014 here:
https://docs.google.com/document/d/1_Ta8IvVaVtc5Il7-kJwj6qKGu54OmifJGRUWCXud8dY/edit
See this link on INTENSIVE for exam resources:
http://intensiveblog.com/resources/#3

The post CICM Second Part Exam Practice SAQs 22032017 appeared first on INTENSIVE.

Weaning from VA ECMO

Author: James Day
Reviewers: Aidan Burrell, Chris Nickson

Everything ECMO 008

A 54-year-old man developed acute pulmonary oedema and cardiogenic shock after an anterior STEMI. He was cannulated and started on VA ECMO after revascularisation in the cath lab. He is now five days post cannulation and was extubated 2 days ago.

Q1. How can you determine if he is ready to be weaned from VA ECMO?

Check for the following:

  1. Aetiology of cardiac failure is compatible with myocardial recovery
  2. Requires minimal ECMO support (flows ≤2-3L/min)
  3. Pulsatile arterial waveform present for >24h
  4. MAP> 60 mmHg in the absence of “high-dose” inopressors
  5. Major metabolic disturbances have resolved
  6. Lung function is not severely impaired

Q2. How do you perform a weaning trial?

This is what is required:

  • About 1 hour of time
  • Echocardiographer (either TTE or TOE depending on views)
  • IV heparin bolus (if not anticoagulated or coagulopathic)
  • A weaning proforma
  • Support person (to manage patient and ECMO console)

If the patient does not have a coagulopathy then a small bolus of IV heparin (e.g. 2,500 units; though the dose used varies depending on individual circumstances) should be given to prevent clotting at low circuit blood flows. A baseline transthoracic echo should be performed. One person will need to reduce the flows and watch the patient whilst the other concentrates on the echo.

Many variables can be measured, but the following variables should be measured using echocardiography at a minimum:

  • Aortic VTI
  • TDSa mitral annulus
  • LVEF
  • TAPSE

The ECMO flow is dropped in 0.5l/min increments for five minutes at a time. The flows are reduced to 1-1.5L/min but no less. The above variables are measured at each increment.

The following haemodynamic variables are observed and recorded at each increment as well:

  • MAP
  • HR
  • CVP
  • PAP (if pulmonary arterial catheter is present)
  • SpO2

The level of vasopressor and inotropic support are also recorded at each increment.

Q3. What is a successful weaning study?

As ECMO flows are dropped, there is increased venous return to the right heart, which when the heart is adequately recovered, will translate into an increase in left ventricular performance. This should offset any deleterious effects of a reduction in ECMO flows. A successful weaning study therefore will have

  • No significant deterioration in the haemodynamic variables
  • Improvements in cardiac function as assessed by echocardiography

Q4. Are there specific values that predict weaning success?

Several studies have looked at specific values1-3. The measurements below are predictive of success on decannulation:

  • Aortic VTI (>10cm)
  • TDSa mitral annulus (>6cms-1)
  • LVEF (>20-25%)

In practice no single number is entirely predictive, rather, a combination of factors which include echocardiographic values, hemodynamic and patient factors are all taken into account in the decision.

At  an ECMO circuit blood flow of 1 L/min the MAP drops to 40 mmHg and the CVP rises to 20 mmHg. The oxygen saturations also drop to 80%. As a result you decide to abandon the weaning study.

Q5. What should you do now?


Turn the ECMO circuit blood flow setting back up to where it was prior to the weaning study and reduce the ventilator support back to where it was pre-study.

Wait 48 hours before attempting another weaning study.

Two days later, another weaning study is performed. This time there is no instability in the haemodynamic variables and the echocardiogram shows an improvement in left ventricle performance on lowering the ECMO blood flows.

Q6. What should you do now?

The patient should be decannulated as soon as is feasible. Femoral arterial cannulae (whether inserted percutaneously or open) and femoral venous cannulae inserted via surgical cut down approach are usually removed in the operating theatre by the vascular or cardiothoracic surgical teams.

In the meantime, the ECMO blood flow can be reduced to ~2.5 L/min pending this. The ventilator should be optimised and the patient should be observed for any signs of differential hypoxia due to secondary respiratory dysfunction given that cardiac function has recovered (see Everything ECMO 007). A low dose inotrope may be restarted prior to decannulation (if not on any) in case cardiac output is still inadequate post decannulation. If there is significant pulmonary dysfunction the patient may need to be transitioned from VA ECMO to VV ECMO.

Q7. What if the patient had failed the weaning study again?

As the number of days on VA ECMO increases the risk of complications increases. It may be that the underlying pathology leading to cardiac failure may not recover and the patient may need to be considered for longer term mechanical support such as a ventricular assist device (VAD).

If the patient is not a candidate for a VAD then the decision may be to withdraw care on ECMO or decannulate with the understanding that the patient would not be a candidate for further ECMO if deteriorates despite medical optimization.

These decisions typically involve in-depth discussions between the intensive care, cardiology and allied health teams and the patient/surrogate to reach a consensus. The timing of the decision to withdraw ECMO support depends on many factors, and further weaning studies may be attempted if further optimisation is possible or there is still some potential for cardiac recovery.

 


The Alfred ICU approach to weaning VA ECMO was discussed on the EDECMO podcast in an interview with Deirdre Murphy (Former Deputy Director at the Alfred ICU)4.

 

References and Links

  1. Aissaoui N, El-Banayosy A, Combes A. How to wean a patient from veno-arterial extracorporeal membrane oxygenation. Intensive Care Med (2015) 41:902-905. [pubmed]
  2. Aissaoui N, Luyt CE, Leprince P, Trouillet JL, Leger P, Pavie A, Diebold B, Chastre J, Combes A. Predictors of successful extracorporeal membrane oxygenation (ECMO) weaning after assistance for refractory cardiogenic shock. Intensive Care Med (2011) 37:1738–1745 [pubmed]
  3. Pappalardo F et al. Timing and strategy for weaning from venoarterial ECMO are complex issues. Journal of Cardiothoracic and Vascular Anesthesia (2015) 29:906-911. [pubmed]
  4. EDECMO 24 – Weaning VA-ECMO, with Deirdre Murphy [Internet]. ED ECMO. 2017 [cited 16 March 2017]. Available from: http://edecmo.org/edecmo-24-weaning-va-ecmo-with-deirdre-murphy/

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