Strategies for Managing Hepatopulmonary Shunting
Hepatopulmonary shunting is a significant concern for practitioners of interventional oncology, as excessive shunting can result in complications such as radiation pneumonitis. There are a variety of strategies for managing these shunts in patients who hope to be treated with radioembolization. In this Q&A with Interventional Oncology 360, Brian Schiro, MD, discusses his preferred approaches to managing shunting. Dr Schiro is an interventional radiologist at Miami Cardiac & Vascular Institute in Florida, and he has collaborated on the development of the program for the Symposium on Clinical Interventional Oncology, which takes place from February 3-4, 2018 in Hollywood, Florida.
What are some ways of managing hepatopulmonary shunting?
We look for hepatopulmonary shunts particularly when we do a radioembolization planning procedure. In particular, we look for the amount of radioactive material that passes through blood vessels from the liver (that is, from the hepatic arteries through the hepatic veins) and into the lungs. The traditional thinking is that patients with a significant amount of shunting are not candidates for radioembolization. If the lung shunt fraction is about 20% or more, then that’s often thought of as a contraindication for radioembolization procedures.
There are a several ways to manage this dilemma. The first is dose reduction. This means that we indiscriminately decrease the Y-90 dose so that the amount of activity that goes to the lungs is actually reduced.
However, I think that approach is not the optimal way to treat these patients. Rather than decreasing the prescribed dose, we should increase the dose so that a higher dose reaches the target tissue in the liver. We want to have enough of a radiation dose to effectively kill the target tissue in the liver without damaging the lungs.
It’s true that the lung will then receive a higher dose of radiation, but our objective is to prevent the lungs from getting more than a 30 Gy dose of Y90 at a single session. Thus, we can safely increase the dose of Y90 to the liver, provided that we ensure that the dose to the lung remains below 30 Gy.
You mentioned that many people sometimes don’t dose the way that you advise. Is there a reason for that kind of division in the field?
This was the traditional way of thinking that’s still observed by many practitioners. I think more interventional oncologists are coming around to the idea of providing the appropriate, effective dose to the tumor in the liver, as long as the dose to the lung is less than 30 Gy.
What are some other ways to manage hepatopulmonary shunts?
One way is to perform another procedure in order to decrease the lung shunt fraction, such as providing bland embolization or even chemoembolization to the liver tissues. Many times, that approach does decrease the amount of shunting that patients experience. There have also been some suggestions to use low-dose radioembolization—that is, providing the low-dose radioembolization first to the patient and then repeating the mapping procedure to see if the lung shunt fraction has significantly decreased.
A second way of managing the shunt is to insert occlusion balloons into the hepatic veins. By occluding venous outflow, the amount of blood passing through the shunt decreases. There have been some variable reports of this management achieving the goal, and we have also had varying success in our practice.
Another approach is embolization of variceal branches. If there are varices that are shunting from the hepatic arteries and extending outside of the liver, we can embolize those branch vessels in order to decrease flow into the systemic circulation. We see that sometimes in patients who have recanalized paraumbilical veins.
A study by a group from Stanford looked at 80 patients, tried some of these various techniques, and was actually successful in decreasing the lung shunts by about 40%. There certainly is some variability in performing these techniques in order to decrease the lung shunt. However, by doing all this, we gain the ability to safely proceed with radioembolization and give the patients the optimal treatment.
When performing mapping or any of the techniques you described, are there any common mistakes that you would advise colleagues to watch out for?
When performing bland or chemoembolization to decrease lung shunt, it is important to keep in mind that doing so may limit blood flow to the tumor on subsequent angiogram. This may limit the ability to proceed with Y90 at a later date. When placing occlusion balloons in the hepatic veins, intrahepatic shunting is commonly seen. Thus, it is important to occlude all 3 hepatic veins if infusing MAA into only the right lobe, for instance.
I think the most important point to keep in mind is that if one of these techniques doesn’t work, we still have the option of another of these methods as alternatives to achieve the same goal.
What are some best practices to remember when managing hepatopulmonary shunting?
For bland or chemoembolization to decrease shunting, use small particles so as not to occlude larger vessels. If low-dose radioembolization is used, be sure that the cumulative dose to the lungs does not exceed 50 Gy with all treatments. This is the lifetime limit to prevent radiation pneumonitis. When placing occlusion balloons, a jugular approach is preferred, and multiple accesses can be used to place balloons. Sometimes the shunt may visibly decrease on angiography but does not diminish significantly on MAA administration. It’s important to adopt and try all these approaches, and all these techniques should be incorporated into your practice. If one way doesn’t work, there is another option available.
How do patients respond after learning they have a hepatopulmonary shunt. Is this conversation hard to manage?
It’s important to have the discussion ahead of time. Whenever patients are evaluated for hepatopulmonary shunts, they’re here for the mapping procedure with the hope that they’re going to be a candidate for radioembolization. In our practice, we tell patients ahead of time that we may have to do other procedures in order to allow them to become appropriate candidates for radioembolization if there is a significant hepatopulmonary shunt.
Patients are generally understanding if you temper expectations, explain that some additional procedures may be required in order to make them candidates for radioembolization, and also explain that we’re doing everything we can to give them the best treatment available.
What is the most important take-away on this topic?
Just because a patient has what we consider significant hepatopulmonary shunting, it does not mean that he or she should be excluded from a treatment that’s going to be life-saving or life-extending.