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Oxygen v Carbon Dioxide

Newly diagnosed? Anticipatory planning Great meals Breathing issues    
Positioning the body Conserving energy Breath stacking Cough assist
PAP machines O2 for maintenance O2 for palliative care In summary


Breathing well is attacked by the progression of MND/ALS. Muscles are used to breathe, the lungs are really like a set of bellows. The action of the diaphragm contracting and dropping, and the intercostal muscles between the ribs contract pulling the ribcage upwards and outwards, is what causes the lungs to fill with air and to expel the air. This action pulls air into the lungs. Similarly the opposite then happens, the diaphragm relaxes and pushes upwards and the intercostal muscles relax bringing the ribcage inwards. This action forces air out of the lungs again. The lungs do not move of their own accord, it's the muscles that move the ribcage. The diaphragm does around 80% of the work in breathing.

These muscles are voluntary muscles and so are compromised in MND/ALS. There is an automatic response from the brain that tells you to breathe by measuring the levels of carbon dioxide (CO2) and oxygen (O2) in your blood. When CO2 rises and O2 drops, it is time to breathe out and the constant measuring in the brain tells your body whether you need to breathe more often or more deeply. This is why you keep breathing when you are asleep. Because the muscles involved are voluntary you can also make yourself breathe more deeply, more often, or more slowly.

This whole process is simple even while it is obviously complex. The body says I don't have enough O2 so I need to take some deep breaths to get more in. However as the nerves supplying the pathway from the brain to the diaphragm and intercostal muscles begin to die, the ability to breathe weakens. It is quite common to notice someone with the beginnings of this weakening are breathing more shallowly and are using their shoulders by raising them with each breath to attempt to expand the lungs more.

Some of the early signs that may indicate breathing is being compromised include:

  • Air hunger - often seen as gasping or laboured breathing, with and without physical activity
  • Fatigue - either a constant fatigue or becoming fatigued quickly on any exertion
  • Frequent yawning or sighing
  • Weakened cough
  • Waking up with a headache or fuzzy headed or confused feeling
  • Waking up frequently during the night, or insomnia (often compounded by a fear that the person will stop breathing if they fall asleep)
  • Difficulty in breathing when lying flat

The air hunger is caused by the brain telling the body that not enough O2 is being taken in. This causes the person to try and breathe more deeply. If the muscles are weakening it often results in laboured breathing as the person works hard to try and make weak muscles work harder.

The fatigue, yawning and headaches are caused by a build up of CO2 in the bloodstream. CO2 is a toxin, that's why we get rid of it when we breathe out, it's a waste product that results from many cellular activities. Normally our bodies constantly work by breathing to remove CO2 from our system.

Waking frequently is mostly a result of the natural process of breathing shallowly when asleep as normally our oxygen needs are low as we are not being active. However breathing shallow means we are not expelling CO2 well either and as it builds in our system the brain will wake us up to take some deep breaths. One of the issues that many people with MND/ALS then have is that they often fear they will simply stop breathing in their sleep. This is a valid fear as it is not uncommon for someone with MND/ALS to simply slip away during their sleep even when it was not expected that they were at end stage. So the brain waking the person to take some breaths can then mean they go into a cycle of fear and find it hard to fall back asleep again quickly. This means that person is not getting enough rest, let alone good quality rest, and so it is going to compound their fatigue.

When we lay down there are a few things that physically change for the diaphragm. Firstly there is a gravity change from this position and then there is a change in how the stomach and upper colon are putting pressure on the diaphragm. When the diaphragm begins to weaken one of the first things that you notice may be that it becomes difficult to breathe when lying down. This will of course then impact on waking frequently, and when the person does wake and finds it difficult to take a few good deep breaths they become more fearful.

In all the strategies available to help manage the symptoms of MND/ALS it is important to first understand that you will derive the best results, and for longer, if you start the strategies early. If you wait until your breathing is very poor, it is unlikely you will gave a good result from starting on a bi-level breathing support and even on invasive ventilation (if your country supports this procedure). This cannot be over-emphasised.

There are a few strategies that can be used to assist breathing. I am listing them in order of the time in progression that you would start the strategies. However they do not each replace the other, but usually more strategies are added to your regime.

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This is a simple strategy but incredibly important. Keeping the person in a semi-upright position will reduce pressure on the diaphragm. If bulbar issues are also present, laying down often can give rise to gagging and choking as dealing with saliva pooling in the mouth on top of reduced breathing ability become a very dangerous combination.

Positioning may require a high backed chair at all times as the neck may need some support. Electric recliner chairs are perfect as they allow many levels of positioning and are comfortable. Adding a riser function will assist in getting the person in and out of the chair safely and with less strain on leg muscles that may be weakening.

Power wheelchairs (PWC) have head rests and if you choose one that has a tilt-in-space function, they are comfortable to sleep in by reclining enough to sleep but remaining upright for best breathing.

Hospital beds are normally needed at some stage in progression as they allow both the head and leg areas to be raised to provide good positioning for breathing and comfort as well. Split beds are available with the ability to raise the head of one side at a time. Many people like these, but if progression is rapid you may need to swap to a hospital bed quite quickly and this could be costly.

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Conserving energy

This is truly an important strategy. It can be difficult to get this across to someone who has previously been a very physically active person. Not only does the person miss physical activity, but many people feel they are less of a person if they are not able to do all the things they used to do or want to do.

Even though there are different opinions on how much is too much exercise, it is agreed by all research that over-using your muscles when the nerves supplying them are dying, will hasten progression. This is important to think about when the breathing is declining. The breathing ability is declining because the muscles needed for breathing are weakening and dying too. Pushing yourself physically will cause more need for oxygen and therefore you will have to breath harder to provide this. If the breathing is becoming weak, then the diaphragm is being pushed even harder again. The more strain being put on the diaphragm to work so hard, the faster the diaphragm could weaken and atrophy.

It's such a hard concept to grasp. In everything else in life we have been taught that in order to build muscles up you need to use them more. In MND/ALS it is the exact opposite. It is hard to grasp that you are going to lose the muscles completely, and yet if you push them too hard you are going to lose them faster.

Energy can be conserved in many ways, and you should try to use your energy to have the most enjoyment you can instead of in struggling with things that are really too hard. You can help the person you care for by making a list of all the activities that happen in a typical day and see if you can work out what things can be done by someone else, what may require a little help, and how you can space things out. For example if dressing is difficult and takes more than 15 minutes. A strategy may be that someone else gets out the clothes and lays them out. Sit down to get dressed. Let someone else do your shoe laces. This simple change in one activity may turn a 15 minute activity that takes a lot of energy into a 5 minute activity that leaves energy to eat breakfast.

When you look at spacing out activities, you may also combine activities to reduce the amount of walking through the day. For example: walk to the bathroom, sit on a chair to dress, then do teeth, hair and any morning routines still sitting on that chair, use the loo.

Here is an example of how much energy can be consumed when my husband tried to do everything himself. He would take around 20 minutes to get dressed of a morning and often he would fall over as he refused to sit and dress. By the time he came to the kitchen he was irritated and fatigued. He would make a coffee and manage only half the cup, and with the walking involved this would take 30 minutes. It would take at least 30 minutes to make and eat his breakfast. It would take 15 minutes to walk to the toilet and back. So he would rise at 6am, and just to get dressed, eat and go to the loo would take him more than 2 hours of his morning and by 8am he was exhausted. Whatever he had thought the previous day he might achieve would already be slipping away from him, as he would wonder how he was going to find the energy for the next trip to the toilet. He would need to sit for a couple of hours before he was capable of anything more.

When he first accept help dressing he could not believe that it took me less than 2 minutes to put a set of clothes on him, and it took him almost no energy to comply with my help.

A better morning routine would have been to have assistance dressing then sit to have a coffee given to him. Use a urinal if needed before or after breakfast. Allow breakfast to be made and brought to him. Allow half an hour for breakfast to go down, then take a short walk outside to sit in the garden with me. This would have then given us some nice time together, allowed all the morning wake up activities to happen fairly quickly and pleasantly, and give him at least a half hour after that to think about what he might be able to do with his day and some energy to give it a go.

Breathing exercises

People who do a technique called breath stacking, particularly early on report they feel more energy and feel their breathing is easier. This will not slow progression, but while it can be done may help by keeping the lungs clear. A true issue with not being able to breath deeply is that the lungs are more prone to infection as fluids can pool in the lower lungs if they are not being used.

Breath stacking can be done alone early on, or with the help of an ambu bag or cough assist machine. Not all countries have the cough assist available.

Basically it is a matter of forcing the lungs to fill with air by taking a deep breath, holding for a second then taking a further breath, holding for a second and taking a third breath and holding for 3 -5 seconds. You use the ambu bag or cough assist to get the second and third breaths in.

This technique does not make you push your weakening muscles, but does force more air into the lower parts of the lungs and expand the chest cavity. Repeat the breath stacking up to 5 times in a session. Repeat the sessions several times each day.

If a point is reached where this exercise is uncomfortable or does not make you feel better, it is time to stop.

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Cough Assist

This machine is designed to assist in coughing, just as the name suggests. Along with the weakening of the breathing muscles is the weakening of the cough. Coughing is an important physical function designed to remove excess moisture and any foreign particles from the lungs and upper airways. Any time the person affected with MND/ALS has any feeling of a need to cough the machine can be used to clear the airways effectively. Pneumonia is one of the leading secondary causes of death in someone with MND/ALS. Often the pneumonia is caused by aspirating some particle of food or fluids when the swallowing has become difficult, however it can be caused by shallow breathing and inability to cough that has caused fluid pooling in the lower lungs.

Here is a cough assist machine being used.

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Positive airway pressure machines

Most people call these machines a Bipap but this is a brand and today there are many brands of this kind of machine.

Starting early with one of these machines has been shown to greatly increase the quality of life for the person with MND/ALS and it is likely to also extend their life. There are no certainties with life expectancy and MND/ALS, so we can only say like to extend life as many other factors of the disease may still see a person using a pap machine lose their life early.

It is certain that anyone who is able to breathe well is going to have quality of life benefits as they get enough O2 and remove CO2 effectively.

These machines provide two levels of pressure as they assist the person to breathe - a higher level to inhale and a lower level to exhale. The machine senses when the user takes a breath and delivers the pressure. There are a range of settings so that the machine will function according to the persons needs, and these settings will be changed over time as the disease progresses.

It may be used with a full-face mask, nasal mask or nasal pillows. Some people find they use different masks in the day compared to at night. Mask types may need to be revised as the disease progresses also.

This machine should not be confused for a Cpap (continuous pressure) which is used for obstructive sleep apnoea. If the person was using a Cpap before being diagnosed with MND/ALS they should not believe they can just continue using this. The problem with the Cpap is that it will deliver O2 but will not assist in the removal of CO2. The issues behind CO2 build up are discussed further down this page.

Invasive ventilation

A tracheostomy and ventilation machine will continue to breath for a person but will not stop progression of MND/ALS throughout the person's body. It will not keep them alive indefinitely and will require round the clock care. Not all countries provide this as an option to people with MND/ALS. In the US, less than 10% of people with MND/ALS elect to attempt ventilation. Not all who do choose it are successful in adjusting to it.

If you think you would want to explore this option it is very important that the entire family are involved in discussions with your neurologist and pulmonologist so that you can make a fully informed decision.

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Oxygen as a maintenance strategy

As breathing declines many people, including health professionals who are not very familiar with MND/ALS may suggest giving oxygen. This is often because it is very easy to check O2 levels in the blood with simple devices that you clip onto a finger. One of the issues we have is that O2 levels will remain at a good level until CO2 levels become quite high. So checking on O2 does not tell you enough about what is happening with the breathing efficiency. By the time O2 levels are dropping, CO2 levels may have become critical. If O2 were noticed to be showing a bit low, in any other disease the strategy would be to start giving O2.

With MND/ALS this can be a dangerous strategy and hasten death.

Getting enough O2 is not really the problem with MND/ALS, though it would be with lung disease. The problem is that the muscles are weakening and so the person is not breathing deeply enough to take in enough O2. But this is only one side of the problem. Remember that if they are not breathing in deeply enough, they are also not breathing out well enough to expel CO2 efficiently.

If O2 is given, it tricks the body into believing it is breathing well enough and the danger is that the breathing remains at the same level, or worse it becomes more shallow as it takes no real effort to get O2 in now. The body also learns to adjust, which normally would be a good thing. If CO2 levels remain high for a period of time the body adjusts by accepting that this is now normal. So the body stops trying to encourage you to breathe more deeply which would be the normal response to a high CO2 level. If O2 is being given, it compounds this further by tricking the body into believing everything is normal enough and that breathing is proceeding well enough.

This means that as the person is actually becoming poisoned by the CO2, they are continuing to breathe less deeply, partly because of muscle weakening, but also because the body believes it is fine. The person will be sleeping a lot, appear confused or dazed, have headaches and be very slow to react to stimulation. The provision of O2 without any strategies to increase breathing pressure may well cause respiratory depression and early death.

One thing we have to remember is that this is a common way for people with MND/ALS to pass away. Eventually the breathing will be compromised to a point where it cannot sustain life. Some people elect to refuse assistance by devices or machines to assist breathing and let the disease take its course. This is a valid choice they may make. However, if the person would like to have assistance in breathing as well as possible for as long as this will help them, and increase their quality of life by breathing more deeply and expelling CO2, then they need to use a PAP machine as early as possible. Very often this may be used only for periods of time during the day, or maybe only when sleeping. As the breathing declines the person may move to using the machine all the time.

The above information is purely about supplying O2 without any PAP machine or invasive ventilation.

Some professionals believe that anything up to 2 litres of O2 is considered a very low dosage rate and is no problem. This is not quite true if it is instigated as a long term strategy for a person who is experiencing failure of the breathing muscles.

O2 may however be administered inline with a PAP machine or mechanical ventilation if O2 levels cannot be maintained and there are regular tests done for arterial CO2 levels. The machine will be adjusted to ensure that it assists a good exhalation. Please note there is a large difference between supplementing O2 inline with a PAP machine and simply giving O2 alone.

An important consideration that should be taken into account is that there can be other issues arising from the reduced breathing capacity that need attention before pumping in O2. With reduced muscle function fluids and mucous can build up in the lower lungs and this will reduce the capacity of the lungs and the ability to efficiently eliminate CO2 and take up O2. This is where the cough assist machine and breath stacking become an important strategy for maintaining clear lungs and improving the ability to take deep breaths.

Oxygen for lung disease

Pneumonia is the most common lung disease that is experienced as a secondary condition as a result of either poor breathing ability or aspiration. It is common to administer small amounts of O2 during the treatment of pneumonia but it is best administered inline with a PAP machine if the person is using one. It is only used for a short period of time, say a couple of days, to assist in healing of the infection. Again in this situation if high levels of O2 are administered alone there is a high risk of depressing the breathing completely causing death. 2 - 3 litres of O2 in this situation are beneficial, but CO2 levels must be monitored closely.

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Oxygen as a Palliative strategy

When the person with MND/ALS is heading to respiratory failure and the end of life is recognised as approaching, there is a definite palliative benefit that may be gained by supplying O2. If the person is in distress and experiencing air hunger, the purpose of palliative care is to provide comfort. O2 will give them comfort by eliminating the air hunger, even though it is very possible it will hasten the cessation of breathing.

At any point when breathing is declining and laboured, and causing any anxiety or distress, morphine or similar class of drugs and anti-anxiety medications are very useful. In high doses these medications can have the side effect of depressing breathing. However in low doses they have the opposite effect, by lowering anxiety and relaxing the body, they usually increase the ability to breathe.

As progression continues towards end of life, again the objective of palliative care is to provide comfort and so increasing any O2 therapies and medications should not be feared. It is better to give a dignified, pain and fear free death, than to leave someone suffering, in distress and labouring to breathe.


There is a large volume of information on this page, so in summary the most effective ways to assist a person with MND/ALS with decline in breathing function is to:

  • use positioning to put the least pressure on the diaphragm as possible
  • conserve energy wherever possible so you can do the things you enjoy most
  • practice breathing exercises as long as possible
  • use a cough assist to keep your lungs clear
  • use a PAP machine as soon as breathing declines are detected
  • avoid the use of O2 alone as a long term maintenance strategy

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IMPORTANT: keep away from people who have any kind of cold or flu as an infection can become serious and even deadly
This website has been designed to support CALS - people who are caring for someone with MND/ ALS.
Katrina Jeffery cared for her husband Chris through MND/ALS with FTD and provides these supports from first hand experience.
Copyright 2015. All resources that have been used or quoted provide direct links to the source.