First, the usual disclaimer. This document is not a guide for the layman who fancies doing some good with the oxygen cylinder off his gas axe, and in particular does not cover essential details like airway management. It is written by someone who is not trained to give medical advice, as a training exercise for the Laingholm Volunteer Fire Brigade's first response unit. It is only on the web because it amuses the author to put it there. If you want real medical advice, go to a real doctor.
A clear, odourless gas, boiling at -193oC, making up 21% of the atmosphere and without which life on Earth would not be possible. More to the point, without which human life is not possible. Unlike insects, we're picky. It has to get from the outside of us to the inside, and then get passed around the body. Any interruption in this journey usually results in an emergency call to the ambulance comms centre.
While pretty much non-toxic, oxygen is not without its dangers. Oxygen cylinders contain a compressed gas at 2,200psi (15 MegaPascals for pump operators), and so deserve treating with a certain respect. If you drop an oxygen cylinder on yourself or the patient, it hurts. If the neck of the cylinder breaks off, it'll blast itself through a wall like an anti-tank rocket. A badly-fitting regulator can fly off with sufficient force to decapitate someone. If the cylinder is put in a fire, it will explode violently as oxygen cylinders have no pressure relief valve. All this and we haven't even got to the contents yet!
There are two things that oxygen really doesn't get on with. Things that are burning, and things that will burn if given a little encouragement. Oxygen should not be used anywhere near flames, smouldering ashes, cigarettes or other handy sources of ignition. If you put a smouldering thing in oxygen, it ceases to be a smouldering thing and becomes a rapidly burning thing. This includes patients who have been dragged out of the smoke, and nobody has noticed that their clothing is still smouldering. Very embarrassing.
Where things get really devastating though are where you combine oxygen with any form of hydrocarbon. Grease, oil, WD40, CRC, tape adhesives, alcohol - all wonderfully flammable things. If any of these substances find themselves in the workings of an oxygen cylinder valve or regulator, the resulting combination is technically called "a bomb". The detonator is the handle of the oxygen cylinder valve. Just turn it on, and pure oxygen rushes out of the cylinder with a pressure equivalent to the compression stroke on a diesel engine. The pressure first disperses and then compresses the hydrocarbon, but unlike an engine which runs on 21% oxygen, this is the pure stuff. The force created by even a tiny smear of WD40 going off has to be seen to be believed.
It's wonderful stuff, just be careful with it.
Generally, we tend to give it to most patients that we encounter unless we know that there is no danger of the patient going into shock or having restricted blood flow to vital parts of their body. Even something such as a dislocation gets oxygen as part of the pain relief, Entonox being 50% oxygen and 50% nitrous oxide.
Patients with suspected restricted circulation benefit from additional oxygen because it allows what little blood can get through to perfuse the tissues with oxygen more efficiently. This is equally true in myocardial infarctions, CVAs, or even a damaged limb. Equally, patients who have lost blood benefit for exactly the same reason: What blood gets around can do its job better.
Patients with reduced lung function have a different class of problem. Their lungs - whether from physical damage to the chest, asthma, smoke damage, or some injury resulting in a lower lung capacity - may not be able to get enough air through the system to fully oxygenate their blood. Raising the percentage of oxygen reduces the volume their lungs need to shift, reducing stress on the patient.
People suffering from carbon monoxide poisoning also benefit from oxygen, but unfortunately the blood is permanently damaged by the poisonous gas. The patient must be taken away from the source of the carbon monoxide before resuscitation is attempted.
Newborn babies who have perhaps not fully developed their lungs and not yet gone a nice shade of pink also benefit from oxygen. As we don't carry super-small oxygen masks and a paediatric resuscitator may be a little over the top, holding the oxygen tube near (not in!) the infant's airway may be useful.
There is one class of patient that may unhelpfully stop breathing when oxygen is administered. Sufferers of a Chronic Obstructive Airway Disease (COAD or COPD in the US) sometimes end up with their body using oxygen levels to stimulate breathing rather than the CO2 levels that are normally relied on. This is called hypoxic drive. If you flush them with oxygen for a long period, their body thinks it is full of oxygen and the breathing reflex stops. However, this is unlikely to happen in short-term emergency care and we never leave patients on oxygen unmonitored anyway, do we? In short, their need for oxygen outweighs the disadvantages.
Well, first you have to turn it on. You'll figure that bit out pretty quickly if you forget because the hissing noise will be absent. The handy key or T-bar on our equipment is tied on to the regulator. If the key is missing, say so and hope someone has folding pliers or knows where it is. If the patient is of a nervous disposition, tell them when you're turning it on as the regulator can make quite a >Whup!< It is also a good idea to tell the patient what you are doing and why you are doing it, even if they appear unconscious.
Fitting the right size of mask to the patient is also important, whatever implement you are using. Sometimes you have to improvise or use the bag mask resuscitator. Sometimes you just have to admit you stuck a mask three sizes too big on a patient four sizes too small. No problem. Get the right one ready and swap them at the earliest convenience.
If the patient can't breathe at all, or can't breathe enough, we use the bag mask resuscitator. Oxygen tube plugs onto the little spigot on the end with the bag on. Crank up oxygen to full until the bag puffs up, turn it back down to about 15l/min. and carry on bag masking.
To get the most oxygen into a conscious patient, the nonrebreathing mask is recommended. This is the mask with the bag underneath it and the two rubber valves on the side. It gives 90-100% oxygen and needs a flow rate of up to 15l/min depending on the patient. You must fully inflate the bag before fitting the device to the patient, and ensure that the bag refills between breaths. If the patient lapses in an out of consciousness, use the bag mask resuscitator.
Partial rebreather masks look much the same as nonrebreathing ones, but if you look closely the main valve is different and there aren't any rubber bits on the sides. These give about 35-60% oxygen and run at between 6l/min. and 10l/min., so your oxygen goes further. Again, inflate the bag before use.
What we usually use is the bog standard simple face mask. This has no fancy add-ons and can give up to 60% oxygen if you crank the flow right up. We usually run them at 8l/min. but patients may require anywhere between 6 and 10. As with all masks, the minimum flow rate is 6l/min. Below that, exhaled CO2 builds up in the mask with unhelpful results.
Nasal cannula are those tubes beloved of TV medical shows that pass into the patient's nostrils. While very conveniently allowing cameras to film actor's faces, they do not provide much in the way of improved oxygen supply - a meagre 24-44%. But some patients are awkward and will not tolerate the use of an oxygen mask, particularly if they are suffering from a lack of oxygen as this can cause mental disturbances. Some patients may have facial injuries which make the use of a face mask impractical, or vomit continuously. While not efficient, a nasal cannula hanging around their ears delivering oxygen at up to 6l/min. is better than nothing.
The nasal cannula is also handy for making sure a patient on Entonox keeps their oxygen levels up. Particularly with prolonged entrapment, you find that the patient may miss out on oxygen when they pass out and the mask falls off. A nasal cannula can be fitted underneath an Entonox mask, so they continue to get some additional oxygen.
One neat trick concerns full-face crash helmets. They may prevent a mask being applied, but until removal of the helmet can be arranged, it is possible to pull the mask off the end of the oxygen tubing and poke oxygen directly into the interior of the helmet.
Humidity is not generally an issue with oxygen in short-term emergency care. If the oxygen is going to be on for an hour or more, the patient will certainly feel better if the oxygen is put through a humidifier. But we don stock 'em, don't use 'em and to be quite honest probably don't want to carry 'em around and care for 'em.
Very occasionally you may find a patient who does not breathe through the mouth or nose in the traditional manner, but instead breathes through the neck. With luck, you will find that the end of the bag mask resuscitator fits the attachment in the air hole. If not, apply a small, soft mask over the hole for the best seal you can get, block nose and mouth (theirs, you idiot), and puff away. You may need to suction the hole. If you're first on scene and don't have a bag mask, welcome to the delights of mouth-to-trachaeostomy ventilation!
Panic not. You've been watching the regulator gauge, lowered the flow to the practical minimum and have called in a new bottle, right? A changeover is something that you don't want to rush - see concerns on safety above. Take the protective "condom" cover off the top of a new bottle in advance, and crack off some oxygen to blast any crud out of the valve - not good to have it in the regulator. Also a good idea to forewarn patients and colleagues unless you particularly want them to jump six foot in the air (not recommended for cardiac cases).
Take mask off patient and turn off the old bottle at the main valve. When the flow ceases, undo the regulator taking care to watch the bodock washer to make sure it does not sneak off. Put regulator on the new bottle, tighten down and turn on the main valve.
Now at this point you will very occasionally get a very loud noise and oxygen hosing all over the place. Turn the main valve off, remove the regulator, adjust the bodock washer and try again. If nothing improves, turn it off, reverse the bodock washer and try once more. If that fails you need a brand new washer or a new oxygen kit.
Well, not all of it. Patients get very distressed if you cut off their oxygen supply. However weaning them back onto atmospheric oxygen is a simple task. Just remove the mask from the patient, turn off the regulator and then shut the bottle's main valve off. If you're feeling tidy and want the regulator to last longer, drain it and turn the flow control off again.
For some awkward problems such as carbon monoxide poisoning and some skin problems, the ultimate oxygen therapy is required. We won't get to do this though as you need a very expensive bit of equipment called a hyperbaric chamber. You put the patient in, load it with pure oxygen, and then increase the pressure to the point where adequate oxygen to sustain life will actually dissolve in the body fluids without the help of blood cells. Michael Jackson swears by it.
"Mars
is essentially in the same orbit... somewhat the same distance from
the
Sun,
which is very important. We have seen pictures where there are
canals,
we
believe, and water. If there is water, that means there is oxygen. If
oxygen, that means we
can breathe."
-Vice
President Dan Quayle, oh dear, oh dear.
Vik Olliver, 26 Feb 2002 vik@asi.org
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