Oxygen therapy for first responders – July 2015
There was a time in pre-hospital practice where the administration of oxygen therapy was considered so routine that it was simply part of early management. The responders entered the room, introduced themselves, asked how they could help, pulled out the blood pressure cuff and applied an oxygen mask. The ‘good gas’ it was referred to could do no harm. There was also a psychological element whereby the patient felt that something was being done to help them as the mask was slid over their head.
Clinical need for oxygen was understood back in the 18th century though did not achieve medical application until the 20th. Early application involved tents with oxygen supplied as well as early versions of masks.
At the other end, oxygen supply for medical use was a problem. Two main options were followed that exist today. The oxygen cylinder containing compressed gas is one. The oxygen concentrator device capable of drawing in room oxygen for use is the other. Oxygen cylinders are in common medical use and sometimes patients have them. In contrast, concentrators are commonly provided to patients who require oxygen support out of hospital. The COPD patient is the most typically encountered example of this. Cylinders can have a flow meter attached and allow high flow rates. In contrast, concentrators typically only allow smaller flow rates aimed to support nasal cannula.
Oxygen is essential for life. It forms half of the energy equation that maintains cell life and the activities within: O2 + Sugar = energy + CO2. Without oxygen supply to the cells, metabolism can fail as the energy equation fails to function properly.
The cells normally take oxygen from the available air. Air contains around 21% oxygen. At high altitude it is still 21% only there is a whole lot less air overall. So 21% of not much is not much. The percentage can change in some specific situations, usually by being less. This is encountered where something else uses up the oxygen first such as in drains or confined spaces where organic plants or chemical reactions burn up the oxygen. It is also encountered where some other gas fills the air and displaces the oxygen out. This can include exhaust from a running engine or other gas leaking into the atmosphere. If another gas moves in, the 21% oxygen will have to reduce as it is pushed out.
In contrast, excess oxygen is rare and most likely when oxygen is administered artificially. In the short term this does not usually have any adverse effect. If oxygen is administered at high levels for a longer period of time it can have adverse effects on newborns and some adults. This isn’t usually a problem for pre-hospital responders.
Oxygen is drawn into the body through the respiratory system and via the lungs. On inspiration, the alveoli fill with air. The oxygen diffuses across the very thin alveoli walls and dissolves into the blood in the capillaries flowing past. Almost all the oxygen attaches to haemoglobin where it flows in the blood to the cells. At this point it can be released again and enter the cells for use. In return, the waste carbon dioxide escapes from the cells and is taken back in the blood to the lungs where it crosses into the alveoli to be exhaled out. The key elements needed are a functioning respiratory system to draw gas in and out of the lungs, effective circulation to move the blood between the lungs and cells and back and enough haemoglobin in the blood to carry the oxygen.
Two critical issues must be considered in this process. The first is those situations where not enough oxygen is available to the patient. The respiratory system is normally able to draw in more than enough oxygen for needs. Even in vigorous exercise more can be brought in by increasing breathing effort. At some point the demand for oxygen can exceed the ability to provide it to the cells. This could be because of respiratory disease or other illness such as infection. Additional oxygen therapy can be provided to make up the shortfall.
Where there is a need for extra oxygen, oxygen therapy can provide it. There are multiple ways to do this. These include nasal cannula, simple oxygen masks and non re-breathing masks.
Nasal cannulae are commonly found being used by patients in their home attached to an oxygen concentrator. The common recipient is the patient with COPD or other chronic lung disease such as from cancer or asbestosis. This patient has chronic difficulty drawing sufficient air into the lungs forcing them to live getting not enough. To enable even small exertion, extra oxygen might be needed. The nasal cannula has the advantage of being able to deliver a small increase in oxygen and so not make too dramatic a change to oxygen supply. It also sits relatively comfortably in the patient’s nose and to be able to speak and eat freely. One limitation with their use is when the nose is blocked from infection or injury.
These are generally supplied with less than six litres per minute of oxygen. Any more than this and the cannula can be very irritating and dry the nose. This of course means the increase in oxygen given to the patient is small at between 24 to 40%. The more oxygen flow, the higher the percent.
A simple oxygen mask can deliver more oxygen than a nasal cannula. The mask sitting over the nose and mouth forms a small catchment where oxygen fills before being inhaled. The more oxygen supplied to the mask, the greater the percent of oxygen available. Masks typically require 5 – 10 litres per minute providing 35 – 50% oxygen. This makes them useful when a nasal cannula isn’t able to provide enough oxygen.
Simple oxygen masks have limitations. Some patients do not like having a mask over their face because of a claustrophobic feeling. It is important to ensure a minimum of five litres per minute oxygen flows into the mask. If there is not, the patient’s exhaled breath can build up in the mask forcing the patient to rebreathe their own carbon dioxide. There are small holes in the mask to ensure that exhaled breath can escape.
In some cases the oxygen supplied to the patient will still not be enough. This includes patients with acute severe respiratory disease such as pneumonia, pulmonary oedema or chest trauma. In such cases the amount of oxygen reaching the blood and cells may be very inadequate and not improved enough with a simple oxygen mask. Where this happens a means to deliver even more oxygen is needed. The non re-breather mask is one way.
These masks resemble simple face masks in that they look and fit the face in the same way. The most notable difference though is that they have a large plastic bag attached that sits at the bottom of the mask. Oxygen not only flows into the facemask, it also fills the bag. This creates a reservoir increasing the amount of oxygen that is being inhaled. To fill this reservoir the non re-breather mask should be attached to ten or more litres of oxygen per minute. When this occurs between 60 to 80% oxygen can be provided to the patient.
The non re-breather oxygen mask should be reserved for the critically ill patient who is still breathing but with severe breathing difficulty interfering with oxygen supply to the cells.
A number of key features are relied on to assess the patient who may need some form of oxygen therapy. The level of respiratory distress is an important clue. This must be distinguished from the patient who is complaining of feeling breathless. This feeling, known as shortness of breath, is what the patient complains of. It does not mean that the patient is actually in respiratory distress. They may be and this has to be determined in examination using a respiratory status assessment. Oxygen therapy does not help fix the feeling of breathlessness.
The other key assessment is consciousness. Once respiratory failure stops sufficient oxygen reaching the blood and carbon dioxide removed, consciousness may become reduced. Altered consciousness is a bad sign in any patient with respiratory failure and must be managed. Oxygen therapy with a non re-breather mask may help but in some cases assisted ventilation may also be needed.
This is the second critical issue where the patient is not receiving enough oxygen because they are simply not breathing sufficiently. If a patient is not breathing adequately then not only will not enough oxygen be delivered to the cells, but waste carbon dioxide will also not be removed. In such cases oxygen delivery alone will not correct the problem. The patient will also need some assisted ventilation using a bag/valve/mask ventilator device. This patient is not just in respiratory difficulty where they need even a non re-breather mask. This patient is either not or hardly breathing at all. One of the most noticeable features is the patient isn’t breathing enough to keep their brain functioning and to stay fully awake.
A third key assessment is pulse oximetry. This is not always available to first responders. Pulse oximetry uses an infrared light to measure the amount of oxygen circulating in the blood attached to haemoglobin. It is simple and effective. To provide a reading a painless probe is simply attached to the finger or sometimes a toe or ear. In all cases it is over a body part where blood runs close to the surface allowing analysis. Despite its ease, there are limitations to how they work. These must be understood before the readings can be relied on for patient management.
Once pulse oximetry is understood though, oxygen is commonly now only administered when the device proves the patient is actually in need of oxygen. Patients not in need of oxygen, even if they are very sick, will not benefit from the extra oxygen. In some cases, particularly heart attack or stroke, oxygen delivery can even make the problem worse.
Oxygen is a very reactive substance. It is very capable of reacting with many other substances to form new ones. Rust, for example, is iron reacting with oxygen. Inside the cells of the body, oxygen also forms a lot of reactions. Many are useful but sometimes the products are unhelpful to the body. These are referred to as ‘free radicals’. Normally the body can clear these away quickly before they do any harm. If there are a lot of them in the cells the body may have trouble getting rid of them all. This is sometimes the case where extra oxygen is being administered.
A second problem is that oxygen and carbon dioxide both cause blood vessels to narrow (constrict) or dilate (widen). This is to ensure that if there is too much or not enough of either in the blood, the body can change the amount of blood getting through to help temporarily return things to normal.
Understanding this provides a new understanding with oxygen administration. Oxygen is best administered only when there is not enough already in the blood and the therapy will return the levels back to normal and not into excess. The only way for pre-hospital responders to know if oxygen is needed is using pulse oximetry.
For those who do not have pulse oximetry, the only choice is to administer oxygen therapy until such a device becomes available. Typically paramedics carry these and can make the assessment as to whether the oxygen therapy should be continued.
There are two specific medical problems that warrant discussion in regard to oxygen therapy: COPD and asthma.
COPD is a respiratory problem that progresses over years. There are two main problems that fit into the COPD heading: chronic bronchitis and emphysema. These are quite different but can lead to some common problems. One of these is the movement of oxygen into the blood from the alveoli and carbon dioxide back out are both interfered with. The result is that the patient adjusts to having the wrong levels of both. They become unable to live a normal life being unable to exercise and experiencing difficulty breathing much of the time.
Many people with COPD have oxygen for home use as discussed earlier. Frequently this will be an oxygen concentrator. Pre-hospital responders will have to be careful how much extra oxygen they administer to these patients as their ‘normal’ might be very abnormal compared to anyone else. In the short term, if there is no pulse oximetry available, oxygen therapy should be administered where the patient is having more trouble breathing than normal. As soon as pulse oximetry arrives, the oxygen therapy may be changed substantially to better target the different levels of oxygen frequently seen in COPD patients.
The asthma patient is also a bit different. This patient suffers from narrowing of the smallest airways, the bronchioles. Respiratory muscles help draw air in but there is little help to breathe out again. As such air can be pulled in and trapped in the alveoli. The main treatment is to administer bronchodilators such as salbutamol to open up the bronchioles again. This is often done using a nebuliser mask with oxygen running through it to help mist the drug for inhaling. To make a nebuliser mask work in this way at least 8 litres per minute of oxygen is needed. These masks have very large holes in them to allow exhaled air and excess drug to escape. This also means that the amount of oxygen that is provided to the patient will be less than 50%.
With air being trapped in the alveoli, oxygen can still pass across into the blood. However because the air is not being properly exhaled again, carbon dioxide builds up in the blood. Eventually this can build up and affect brain function. Asthmatic patients who become unresponsive should have the nebuliser taken from their face and replaced with higher concentration oxygen therapy or even have their ventilation assisted by using a bag/valve/mask.
Oxygen therapy has now become a specific treatment aimed at treating a recognised problem. It is no longer simply give to every patient without thought. Today’s paramedic will manage far more patients with no oxygen therapy at all. However for the small number of sick patients who are not receiving enough oxygen, oxygen therapy may prove the critical difference.
Jeff Kenneally www.prehemt.com