- 19 Apr 2022
- 15 min 57
- 19 Apr 2022
- 15 min 57
When and for whom should home oxygen therapy be prescribed, and what is the evidence behind it? David Liew chats with respiratory physician Christine McDonald. Read the full article in Australian Prescriber.
Oxygen is a treatment for hypoxaemia, not necessarily a treatment for breathlessness.
[Music] Welcome to the Australian Prescriber Podcast. Australian Prescriber, independent, peer-reviewed and free.
Home oxygen therapy. Potentially lifesaving in some, but also potentially futile in others. It's far from logistically straightforward, and it's confusing to many outside the field. But with a bit of guidance and space, we can learn to navigate.
I'm David Liew, your host for today, and I'm here with an expert to guide us through this space, Professor Christine McDonald, the director of respiratory and sleep medicine at Austin Health and Professor at the University of Melbourne. She has written an article in Australian Prescriber on home oxygen therapy, which will help us to navigate this. Christine, welcome to the program.
Thanks very much, David. Lovely to be here.
Thank you for being here. So tell me, Christine, why should we be using home oxygen therapy? What can we expect from it? Sometimes it feels like people expect the world from it, possibly too much for it.
I think that's absolutely right, David. We certainly have some strong backing for people who have severe hypoxic respiratory failure, secondary to COPD. Those trials were done in the '80s, and there was one done in the UK, one done in the US, and the results of those trials were very similar. That is, in the UK, it was oxygen versus no oxygen or air, and in the US study, there was oxygen all day or as many hours as you could in the day, which worked out about 17 or 18 hours versus just nocturnal oxygen therapy.
There were similar findings in both the studies so there was a mortality benefit from oxygen versus no oxygen and, although it was a different study, there was a greater mortality benefit in the oxygen for 17+ hours versus nocturnal oxygen in the US group. So mortality is a very hard end point in respiratory medicine.
We have a lot of softer end points. In the US study, patients didn't receive placebo. They didn't in the UK, either. We tend to do studies now with placebo air because there may well be a placebo benefit from having something running into your nostrils.
Oh, really? How does that work?
Well, we don't know how that works, but certainly with our palliative oxygen study because a lot of people think breathless, you must need oxygen therapy. But, in fact, oxygen is a treatment for hypoxaemia, not necessarily a treatment for breathlessness.
I mean, that's such an important point. Many of us know that breathlessness, dyspnoea can be symptomatically managed by a number of different measures, breathing techniques and positions and changing activity with energy conservation, fans blowing on the face and other distraction techniques and even sometimes opioids. But I guess there's a temptation to think about oxygen therapy to manage the symptoms of breathlessness, isn't there?
In lab studies, which we've done ourselves looking at six-minute-walk tests and exercise capacity and dyspnoea scores, we can show small benefits in patients who were given oxygen versus air in a double-blind randomised way. And others have studied this as well, looking at n=1 studies, for example. The Canadians have looked at that. However, when we've done studies in the field with sending patients home with oxygen, if they desaturate and we see that there's some improvement perhaps in their six-minute-walk test with oxygen compared with air, they use it very little, generally not more than about 40 minutes a day in the studies that we've done. So the idea that we are going to improve their lives significantly is not proven, I would say.
On the other hand, we did a study looking at patient's attitudes to oxygen therapy, which was published just earlier this year. These were patients, many of whom had home oxygen, and they all almost uniformly believed that it did help them. These were people who had oximeters at home. We looked at what they did when their oxygen level fell, and we hadn't recommended that they used the oximeters, but there was a range of sometimes concerning things that people did, such as taking an opiate if their oxygen saturation was low, and other sorts of things. So there is a lot of misinformation about oxygen therapy amongst users, as well as amongst prescribers.
Fascinating. Just so we can understand the basics, let's talk a little bit about the different indications for home oxygen therapy with the different types of therapy. I guess there's long-term continuous oxygen therapy, as well as ambulatory, and then there are a whole lot of other different places where oxygen is used, isn't it?
The long-term continuous is really the easy one because we have the benefit of those old studies, but good studies, demonstrating a mortality benefit. So perhaps it's not necessarily suitable for every patient who is hypoxaemic. If people are cognitively impaired or suffering from dementia etc., we have to look at whether or not the benefit in mortality terms outweighs the downside, I guess, of tripping over oxygen tubing, or smoking and causing fire or causing injury to the patient. But long-term oxygen therapy has been shown to improve mortality so we do assess patients in a stable state to determine whether they fulfill criteria. Those criteria are mentioned in this piece so significant hypoxaemia and preferably in a stable state.
I would say that a lot of patients get sent home on oxygen after acute exacerbation of whatever their condition might be, but 30 to 50% of those people reviewed at six to eight weeks actually won't fulfill criteria for home oxygen and don't need it, and I think that's an important thing to tell patients.
Unfortunately, some people say, "You don't actually meet the criteria now," but I think it's really important to say, "Look, isn't that great? Your oxygen level was low in the hospital, but you've improved clinically. Now your oxygen's much better and you don't actually need to have that long-term continuous oxygen therapy."
Not everyone who's on home oxygen therapy is on continuous therapy.
So what's the difference between the two?
There's a bit of a debate about ambulatory oxygen and who should receive that, and there's differences in the different guidelines.
The UK guidelines are quite specific about not giving portable oxygen to people unless they are very active. And we, in our previous guidelines, and we'll be revising those soon, we recommended that for people who need or fulfill criteria for long-term continuous oxygen, and if they're wanting to be active and to use oxygen for as many hours in the day as possible, they would receive portable oxygen therapy, either via a cylinder or via a portable concentrator.
There is some evidence that patients may improve their exercise tolerance, as I was mentioning before, if they desaturate. Here we get into: has the patient got COPD, has the patient got interstitial lung disease, or what is the underlying mechanism for their hypoxaemia, and their breathlessness? So some patients will desaturate significantly when they do a six-minute-walk test and may show an improvement with oxygen therapy.
There's debate about how much improvement they need to have shown before they receive the cylinders or the portable oxygen concentrator and, again, a lot of patients choose not to use those cylinders or concentrators. So I think it's education that's really important when people are going on to home oxygen, and many people don't receive the education that they should.
Maybe let's talk a little bit about that process so we can understand, so we can keep on educating our patients. Let's start with the devices that there are. Which device should we be using, and how do you decide?
For the long-term continuous oxygen, a concentrator is the ideal thing. That's a concentrator that's electrically driven, and it concentrates the oxygen out of the air so it removes nitrogen via a filter mechanism. That's the most appropriate therapy for people who are on it continuously, nocturnally. They may also receive some portable cylinders if they find it beneficial to enable them to be more active.
The portable cylinders are the older means of providing portable oxygen. The portable oxygen concentrators are somewhat more expensive, but also probably easier to manage, and so a number of patients will be using those while some are still using the cylinders. Again, that depends on what other conditions they may have, whether they're using a walking frame etc., and that needs to be tailored to the patient and discussed with the patient before they receive it.
Okay. Maybe just to talk through the process as it happens in real life once you've identified a potentially suitable candidate for home oxygen therapy, what kind of assessment are you doing throughout that to get to the point where we start to enact the logistics of making it happen?
A lot of patients are picked up in terms of their hypoxaemia, when they have an exacerbation of their condition. I guess I should just say that, remember, we're basing all our recommendations on studies that were done a long time ago in patients who probably didn't have the significant comorbidities. In fact, they were excluded, and they were patients with COPD.
In guidelines, we've extended it to all hypoxaemia due to all respiratory conditions, and we're trying to look at patients with interstitial lung disease right now with an NHMRC-funded trial. So many patients go on to interim oxygen, we would call it, because they're discharged still with significant hypoxaemia. Not because there's any evidence for the short-term use of it in that situation, but because people get very hung up on the SpO2 in hospital, more so perhaps when they're out of hospital.
So they'll often go home, they'll be assessed by our oxygen therapist here at the Austin. Obviously, this is different in different parts of Australia, and a lot of patients live further away and may need to be assessed at a local centre because we do require arterial blood gases to confirm their hypoxaemia. Pulse oximetry is a bit variable and there are all sorts of issues that may affect it. So we do recommend that the patient sort of be stable, at rest for 10, 15 minutes before the arterial blood gases are done, in order to determine whether or not resting hypoxaemia exists.
I guess it's also a matter of making sure that some of the other comorbidities are stable, and we're talking about non-smokers as well still, aren't we?
We are. In Australia, we are, yes. So our guidelines do recommend that the patient is non-smoker. In some parts of the world that is not the case, but we've certainly seen a number of accidents and injuries over the years from people who continue to smoke, and we know it's a very addictive problem. We actually ask patients to sign a form saying that they're not going to be smoking, and certainly that there shouldn't be any household smokers around them whilst they're using their oxygen.
Okay. So then what needs to happen between there to the point where patients get oxygen into their nostrils?
If they fulfill these criteria, which may include a six-minute-walk test to assess whether or not they desaturate and whether they may benefit and can walk further with oxygen, they'll receive a home oxygen concentrator plus perhaps a couple of cylinders. They receive instruction from our home oxygen therapist, and the oxygen is delivered to them when they go home.
There's advice given by the provider of the oxygen, and this varies from state to state in terms of how much portable oxygen is available or how much is not, which is why I've given the information in the paper that I've produced to help people know where to go for advice about what criteria are used in various states.
Wonderful. And what happens for patients who might be identified in the community in primary care or by clinicians outside of the hospital? What's the pathway to get those patients in to see an oxygen therapist?
Arterial blood gases are really the standard, and if a person is sort of living a distance from a large centre, that may be tricky. So they may need to attend that large centre to enable them to have an arterial blood gas taken because it needs to be measured quite quickly.
But when would we think that a patient might require oxygen? Obviously, an oximeter is an easy-to-use device, which is available, I'm sure, in most general practices. So if a patient is continually hypoxaemic on measuring their SpO2, so SpO2 of 90 or less with severe lung disease, then I would be automatically suggesting that they be assessed for home oxygen therapy at their local pathology provider.
Well, I know that COVID has thrown a lot of different things in this country over the last two years, but I can imagine that it must have been particularly complicated, especially with the complication of having COVID and post-COVID patients potentially on oxygen as well. How has this changed the world of home oxygen therapy?
Many patients do require oxygen when they're in hospital as you know, David, but in fact many do not require it on discharge. So we're thinking about the most severe end of the spectrum, those patients who've had ventilation in intensive care and developed an ARDS-type syndrome. Those patients may have a long hospital stay and indeed may develop some pulmonary fibrosis as a consequence of their illness and may persistently remain hypoxaemic.
We have not been in that situation in Australia, fortunately, and we do have our high dependency unit here in the respiratory ward. So we have patients weaning off ventilation and some of those patients may require interim oxygen. But when we review them a couple of months down the track, it's a reversible condition in most cases, we've found, and they don't require it long term.
What about patients who've been on home oxygen therapy from before COVID or who've had reasons to go on it during the pandemic unrelated to COVID? These patients already have a pretty scary life to start with at the moment during the pandemic, they've got an existential threat to them. How has home oxygen therapy become complicated during COVID?
I think it's become complicated for the providers, really, and for the assessors. Because of the lockdowns, patients, of course, have been shielding at home and particularly our respiratory patients. We've been encouraging them to get vaccinated and to wear masks and many of them don't go out very much. We encourage them to go out and exercise because that's an important part of maintenance of health with chronic lung disease.
For the patients themselves, if they're on home oxygen already, it won't change anything. But for those patients who we might be wanting to assist, there have been difficulties in just getting appointments for them. So we've got a significant waiting list, which is not what we like, for patients to be reviewed following commencement of their home oxygen.
I guess the future for home oxygen therapy also is one which is filled with more people looking for different indications for home oxygen therapy. How do you think that's likely to proceed in the future?
I think what we need to do in the future is to pin down really who benefits from oxygen therapy. Hypoxaemic respiratory failure clearly requires home oxygen therapy. For some of these other indications we don't have strong evidence.
I guess it's fair to say that home oxygen in appropriate individuals may lengthen life, but there is a downside to it and, in future, I'd love it if there were more sort of patient-friendly interfaces that could be developed so that our patients really can get about with their oxygen therapy and not be tripping over tubing or feeling embarrassed about using these cumbersome devices.
So that's what I would like to see, better patient interface and also better evidence for all the other conditions besides COPD, for which the studies haven't been done.
Well, here's hoping for progress on both of those. Professor Christine McDonald, thank you very much for joining us in the program today.
Thanks very much, David.
There are no disclosed conflicts of interest from either Professor McDonald or myself. The views of the guests and the hosts on the podcast are their own and may not represent Australian Prescriber or NPS MedicineWise. I'm David Liew. Stay safe and thanks for joining us today.