Overview of Extracorporeal Membrane Oxygenation Weaning
Extracorporeal life support (ECLS), or extracorporeal membrane oxygenation (ECMO), acts like an artificial heart and lung machine. It’s used for patients whose heart and/or lungs are not functioning as they should. ECMO can be used for various medical conditions that need venovenous (VV) or venoarterial (VA) support. This machine either helps the patient recover or gives them time to receive a longer-term device or transplant.
The concept of ECMO has existed for a long time, but it’s only recently that healthcare professionals have genuinely mastered its use. Operating ECMO requires a large, well-coordinated team to perform various tasks, including inserting and removing the tubes that connect the patient to the machine, managing the machine, and dealing with any potential complications. This article will focus on the process of gradually reducing and eventually stopping a patient’s dependency on the ECMO machine, also known as weaning, for both adults and children.
Anatomy and Physiology of Extracorporeal Membrane Oxygenation Weaning
When talking about ECMO (Extracorporeal Membrane Oxygenation), the machine that acts like a lung and heart outside the body, it’s crucial to know the right way to place and remove the machine’s pieces, often called cannulas. The place where cannulas are put depends on what kind of support the patient needs. These cannulas go into the body either through a small puncture on the skin or a surgical incision on the vessels. When someone is having trouble breathing but their heart is fine, the doctor will use a method called venovenous cannulation. This involves placing two cannulas in either the neck or groin veins. One double-purpose cannula can be placed in a vein in the neck, which can both drain and reinfuse blood through the same cannula, which can help the patient move and require less sedation.
If the heart is not working as expected and can’t pump enough blood to the body, the venoarterial ECMO method will be used. This happens when a cannula is placed into the artery in the thigh and either in the vein in the neck or thigh. This method can also be done through a minor incision or in the aorta and the right atrium, the upper chamber of the heart, via a major surgical procedure.
Every living being, except a few bacteria types, needs oxygen to live. The ECMO machine acts like an artificial lung and heart to help the patient breathe and deliver oxygen to the body. Basically, the machine enriches the blood with oxygen and removes carbon dioxide. The blood with fresh oxygen goes back to the patient’s body through a tube near the heart or an artery. In ECMO, one must consider the patient’s blood flow and the flow of the ‘sweep’ gas through the machine carefully to manage oxygen and carbon dioxide levels in the patient’s body. The balance between the patient’s blood flow and the ‘sweep’ gas flow is crucial to keep the body’s normal workings.
When the person’s lungs can’t deliver enough oxygen to the blood, but the heart is functioning fine, the venovenous ECMO method can be used. In this method, the blood with less oxygen goes back to the ECMO machine and gets re-oxygenated. This oxygen-rich blood then goes back to the patient’s body through a tube near their heart. Filled with more oxygen, this blood mixes with the blood with less oxygen, increasing the oxygen concentration in the arteries. Then the heart pumps this oxygen-rich blood to the whole body. This makes maintaining the hemoglobin concentration essential, as most of the oxygen is carried by hemoglobin.
The aim of venovenous ECMO support is to allow the patient’s injured lung to rest and be exposed to lower lung volumes, peak end-expiratory pressures, and lower FiO2 support. Many considerations will have an impact on the ECMO circuit, including the size of the cannulas used.
Venoarterial ECMO oxygenation is very similar to venovenous ECMO, but the cannulas are positioned differently, with VA ECMO having an arterial catheter. We must closely watch the oxygenation of all extremities and the heart function. Other interventions may be necessary when these functions become impaired, such as the potential placement of a device to support the left chamber of the heart.
One of the most important points to note is removing carbon dioxide from the patient. This function is performed by the ECMO machine, replacing the normal function of human lungs. Carbon dioxide removal is an easier task compared to oxygenating the patient. Removal is possible through a low flow on the ECMO machine. CO2 removal becomes essential during a flare-up of the COPD respiratory disease, or when waiting for a lung transplant. The blood flow rate through the ECMO machine has minimal effect on CO2 removal. This can be done by the ‘sweep’ gas flow rate, which allows doctors to reduce patient’s breathing work. When it’s time for the patient to be disconnected from ECMO, you can titrate the sweep gas flow to see how well the lungs can ventilate. During VA ECMO, the lungs cannot be ventilated due to decreased heart function but still need some positive pressure to avoid complete collapse.
Why do People Need Extracorporeal Membrane Oxygenation Weaning
If a patient’s lungs have healed from their illness and are now thought to be capable of providing sufficient oxygen flow and proper breathing, they might be ready to stop (“wean” off) extracorporeal membrane oxygenation (ECMO). ECMO is a treatment that uses a pump to circulate blood through an artificial lung back into the patient’s bloodstream. Essentially this machine does the work of the patient’s lungs (and sometimes heart) so that their organs can rest or heal.
In other cases where the patient recovered from both heart and lung diseases, and their heart and lungs are now prepared for appropriate functioning, they could start the weaning process from veno-arterial ECMO (VA ECMO). VA ECMO is used when both the heart and lungs need time to rest or recover, it not only adds oxygen to the patient’s blood but also pumps blood back into their arteries.
When a Person Should Avoid Extracorporeal Membrane Oxygenation Weaning
The patient is still showing symptoms of heart and lung failure, which means that they are not yet ready to be taken off their medical support. Depending on the specific health issue they’re facing, the patient may need more time for their heart or lung condition to get better. In some cases, they might need a device to help their heart pump blood (a ventricular assist device) or even a heart or lung transplant.
Equipment used for Extracorporeal Membrane Oxygenation Weaning
An ECMO machine, which is a device that acts like an artificial heart and lungs for the body. This machine comes with an oxygenator (provides oxygen) and an artificial lung, along with all the necessary pipes, cannulas (tubes used to deliver or remove fluid), and devices for monitoring how the machine is working.
An intensive care unit is a specially staffed and equipped ward in the hospital for critically ill patients who require immediate and specialized care.
A fully functioning lab with a device to sample arterial blood gases is needed. Arterial blood gases are tests to monitor oxygen and carbon dioxide levels in the blood and ensure the lungs and kidneys are working correctly.
Transthoracic echocardiography and transesophageal echocardiography are two types of ultrasound techniques employed to take moving pictures of the heart. Transthoracic echocardiography is performed by moving an ultrasound device (transducer) along the chest or abdomen, while transesophageal echocardiography involves passing a specialized probe down the person’s throat into the esophagus (the pipe that connects the mouth to the stomach).
Who is needed to perform Extracorporeal Membrane Oxygenation Weaning?
Several types of specialized doctors and medical professionals work together to provide the best care for critically ill patients, such as those needing special heart and lung support or those recovering from major injuries. These teams include:
A Critical care doctor is an expert in caring for patients who are very ill or injured and need special attention. This doctor is also trained to use specialized medical technology that can help support or replace failing body functions until the patient can recover.
A Cardiothoracic, vascular, or trauma/acute care surgeon is a specially trained doctor who can perform surgeries on the heart and blood vessels, or surgeries needed after serious injuries.
The ECMO (Extracorporeal Membrane Oxygenation) coordinator and technicians are specially trained medical professionals who manage a life-saving machine that is used to support or replace the function of the heart and lungs when they fail.
There are also ICU (Intensive Care Unit) nurses who provide round-the-clock care to patients, helping with everything from monitoring vital signs to offering emotional support.
An ECHO (Echocardiogram) technician is a professional who uses ultrasound technology to create images of the heart to help diagnose and monitor conditions of the heart.
Respiratory therapists and physical therapists help patients with exercises to maintain or regain their muscle strength and breathing abilities. They often work closely with occupational therapists, who specialize in helping patients regain independence and skills needed for daily living activities.
All these professionals work together to give you the best care possible, coordinating their efforts to help you recover.
Preparing for Extracorporeal Membrane Oxygenation Weaning
Even when a patient is set to come off ECMO, which is a treatment that uses a pump to circulate blood through an artificial lung back into the bloodstream, it doesn’t automatically mean that they will fully recover. ECMO is used to support both heart and lung function, and it can be life-saving.
When patients are ready to potentially stop using ECMO, they should be in a stable condition – this means their blood flow and heart function should be steady and strong. If the patient still requires full support due to continued heart or lung failure, efforts to wean them off ECMO should not be taken. Patients who aren’t good candidates for coming off ECMO could be considered for treatments like a transplant or the installation of a device to assist their heart.
Patients should be checked daily using methods including physical examinations, blood tests, and heart scans. These checks allow doctors to determine if the patient is ready to wean off ECMO. Specific heart health indicators will be monitored such as heart enzymes, which should return to normal levels with successful treatment. Echocardiography, a type of heart scan, is crucial for checking whether the heart is recovering and if there are any new issues.
When preparing to take a patient off ECMO, certain signs can suggest that it may be difficult. They include abnormal heart functionality, failure of the heart’s left or right ventricles, unusual heart wall movement, fluid around the heart, low blood volume, or high blood pressure in the lungs’ arteries. For a smooth transition off ECMO, patients’ hearts should be able to pump a good amount of blood, specifically, more than 25-30% of the blood in the ventricle each heartbeat, and they should demonstrate other normal measurements while on minimal ECMO support.
How is Extracorporeal Membrane Oxygenation Weaning performed
Coming off Extracorporeal Membrane Oxygenation, or ECMO, treatment is a challenging process. Each patient’s situation is unique, so there’s no one-size-fits-all way to do it.
In the VA ECMO weaning process, the initial condition that caused severe shock across the body should be addressed before starting. The first steps of weaning include ensuring the patient is stable and performing health checks such as normal oxygen levels, normal breathing, good heart function, and so on.
The weaning process is initiated by reducing the flow in the ECMO machine. The patient may need certain drugs to regulate heart function and may have additional devices in place to support heart performance. The gradual reduction in flow requires careful monitoring, as a decrease can increase demand on the heart. If anytime the patient appears to struggle, they will be returned to the full ECMO support and monitored until their heart regains strength.
It’s essential to regularly monitor the patient’s lung function too. As the blood flow increases, the settings of the machines assisting in breathing (ventilators) might need adjustments. We recommend reducing the flow rates in small increments while watching out for any signs of clotting in the ECMO tubes.
Each reduction should be maintained for at least 60 minutes to assess its effects on the patient. If the patient starts showing signs of inadequate blood flow or other problems, they are returned back to full ECMO support.
If the patient is stable and has a sufficient heart function after weaning, they can be taken off ECMO. The tubes are carefully removed, and the patient is monitored continuously to ensure all their body functions remain healthy post-ECMO. After being weaned off, it’s not unusual for patients to have signs of inflammation, requiring a temporary increase in their heart-supporting medication.
In the process of weaning from VV ECMO, the patient’s lung function must be recovered fully. Before even attempting to wean them off, their lungs need to be working well with only minimal ECMO support. As their lungs improve, the ECMO support can be gradually decreased.
The process of weaning a patient from VV ECMO involves decreasing the gas flow while observing the patient’s response. However, it’s crucial to avoid exposing the healing lungs to excessive oxygen. Also, the ventilator settings must be adjusted according to the patient’s need and comfort during the weaning process. Blood oxygen levels should regularly be checked, and any adjustments should be made based on the findings. If there are any signs of struggle, the patient is promptly put back on full ECMO support.
Possible Complications of Extracorporeal Membrane Oxygenation Weaning
Although patients who don’t seem ready to be weaned from certain medical treatments, like a ventilator, or who seem to respond well at first can face difficulties. Some potential complications can include:
* Bleeding — when excess blood leaks from the body.
* Ischemia to limbs — this is decreased blood flow to the arms or legs, which could cause pain or problems moving.
* End organ hypoperfusion — a medical term meaning that there isn’t enough blood flow to an organ. This could cause that organ to not work as well as it should.
* Neurological complications — issues related to the brain, spinal cord, or nerves.
* Infections — when harmful germs enter the body and cause illness.
What Else Should I Know About Extracorporeal Membrane Oxygenation Weaning?
Extracorporeal membrane oxygenation (ECMO) is a treatment that uses a pump to circulate blood through an artificial lung back into the bloodstream. It’s often used for people with severe heart or lung conditions. When recovering from ECMO, doctors look at several factors to determine if a patient may start to live without the support of this machine, often referred to as weaning.
Signs that point towards successful weaning include:
- Normal levels of lactic acid in blood tests. Lactic acid levels can indicate how well your body is using oxygen.
- Echocardiographic (a type of ultrasound) evidence showing the heart’s ability to pump effectively has been fully restored.
- Certain signs of good blood flow and heart function, such as the aortic velocity-time interval and other specific measurements, are detected at lower ECMO support settings.
- A larger pulse pressure (the difference between the systolic and diastolic blood pressure) might mean a greater chance of successful weaning.
- No signs of the heart being overstretched and filled with too much blood, which can be a signal of heart failure.
Unfortunately, some factors predict a higher chance of death in weaned patients. These include being over 60 years old, long-term ECMO use with associated complications, a low pH with high lactate levels (indicating the body is overly acidic), and a high sequential organ failure assessment score, which indicates the severity of a person’s illness.
If it appears that weaning off ECMO will not be successful, doctors need to start discussing other support options. This might include long-term ECMO support, using a device to aid the heart’s function, or even considering a potential transplant.
