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Am I right in thinking that treatment for DCS is on the NHS or do some Chambers bill the diver afterwards?
If you are treated for decompression sickness in the UK then that is done on the NHS. It is considered an "emergency treatment" and so is fully funded by our hard earned taxes.
Some chambers are within the grounds of NHS hospitals and some are located at privately owned hospitals or buildings, but it doesn't matter where they are as the treatments are payed for by the Health Authority that sits over the area your GP works in.
Where problems arise is if a diver is not registered to a GP, but this is unlikely if you are born and live in the UK as you probably have been for your childhood shots.
But if you are say an expat working in the UK and haven't registered to a local GP then there may be a problem. The rules are that anyone working in the UK is entitled to register on the NHS once they have worked for 6 months over here, so cover yourself with insurance if you still have time left to do.
Effectively no chamber should ever bill a patient in the UK, so don't worry about cost when it comes to DCS.
Are there any tests for decompression illness?
Hot off the press, there were some interesting developments on this, the holy grail of diving medicine, at a recent meeting of the UHMS in Utah. Papers were presented on the ability of doppler ultrasound and transthoracic echocardiography (both basically refinements of the gel-on-tummy baby scan) to pick up microbubbles. The bottom line is that although both can detect the little bleeders (microbubbles, not babies), some are too small for the current top-end devices to pick up, and the idea of a test has to be exclude DCI with as near to 100% certainty as possible. A non-invasive optical method has been developed which has higher resolution, so this has potential, but as yet is still some way off the affordable market. So progress is being made, but for the time being at least, we will have to put our faith in good old fashioned clinical acumen. Which is no bad thing. Iíd hate to be replaced by a machine.
I have a recompression treatment question. Do you use different recompression tables when treating a diver with DCI, depending on what depth they got symptoms, or which gas they have been using? If someone has been diving on a rebreather or trimix, does that change things?
Basically, the answer is no. Diving physicians select from a range of treatment tables, but the choice is rarely influenced by depth or gas mix; more by the clinical picture and severity of the symptoms. There are several different sets of tables in use, some developed by the military, some by commercial or sport diving organisations, and they do vary depending on which particular gas bubble model they are based on. The primary purposes of recompression, though, are threefold:
- to compress gas bubbles to relieve local pressure and restart blood flow
- to allow enough time for bubbles to redissolve and be breathed out
- to increase blood oxygen content and oxygen delivery to damaged tissues
Success in achieving these 3 aims is largely independent of the depth and gas mix used in the accident. Over the years countless divers have been guinea pigs to the fine tuning of the commonly used tables, and the protocols that have evolved are tried and tested in all sorts of diving accident situations. Some macabre research has been performed recently on rats (unlucky creatures) Ė they were exposed to trimix in a hyperbaric chamber, decompressed rapidly to induce DCI, then treated with either oxygen or Heliox (50% helium and 50% oxygen). The control group (the REALLY unlucky ones) were not treated at all. 40% of the control rats died; none of the treated ones did, and the rate of recovery was the same whether they were treated with oxygen or Heliox. So in this model thereís no advantage to using Heliox to treat trimix DCI over good old oxygen.
Sometimes, when DCI symptoms are very severe or not responding to the usual tables, deeper ones are used, and in these cases we often use Heliox. This is because 100% oxygen at the depth of these tables can become toxic, so a 50% oxygen and 50% helium mix is used. Theoretically, diving on a closed-circuit rebreather where the pO2 is kept constant reduces the amount of nitrogen absorbed, thus lessening DCI risk, but treatment-wise the tables would be exactly the same. Itís a complex subject, as youíd imagine, but I hope that gives you a flavour.
I've read that diving mammals such as whales have large amounts of body fat, which I suppose is there to keep them warm. So why don't they get the bends? Isn't fat partly to blame for decompression sickness?
This is a proper brain teaser that has taxed marine biologists for many years. Theories of heightened DCS risk in obese humans doesnít apply here, as diving mammals have quite different physiological mechanisms to deal with it. The fattest whale is thought to be the Pacific right whale (Eubalaena japonica), which can weigh 100 tons, 40% of which is fat. The blubber layer on a right whale can be up to 6 feet thick, and their high body fat percentage means they don't sink when they die (which is why they were the "right" whale to kill). Most of the oxygen a whale requires for a dive is stored in blood and muscle, with only 9% in their lungs (compared with 34% in human lungs).
There are several explanations as to why whales donít get bent. Firstly, they are diving with a single breath (albeit a very big one), so they are not taking on more compressed gas at depth, as SCUBA divers do. To some extent this is why freedivers donít get narced or bent as well, despite diving to depths far in excess of what is theoretically possible. Secondly, the ribs of whales are flexible and mobile, and collapse inwards with pressure, thereby compressing the lungs and forcing the air into areas where absorption does not occur (mainly the upper airways). Thirdly, this lung compression reduces blood flow to the lungs. The net result is that nitrogen absorption into the blood is minimal, and hence the risk of DCS negligible.
People always say that you should ask a question even if it seems stupid, because a lot of people probably want to know the answer but are too embarrassed to admit it. So here goes my stupid question: how does oxygen work as a treatment in DCS? We're all taught to use it as part of basic first aid for an injured diver but why is it given?
Like all stupid questions, itís actually a very good one. If we take the example of an injured diver bobbing up to the surface, they could be suffering from any number of problems, aside from DCS Ė heart attack, stroke, gas embolism, saltwater aspiration, barotraumaÖ luckily oxygen is good for what ails you in all of these situations, so you canít go wrong by administering 100% at high flow as soon as possible. The reason is simple: the end result of all of these diverse processes is hypoxia (a low oxygen level) and 100% oxygen will go some way towards correcting it. DCS is a specific bubble-related diving injury, and oxygen in this situation has additional benefits, aside from correcting hypoxia. The speed of nitrogen off-gassing is dependent on the gradient between the saturated tissues and the gas we are breathing. If we breathe 100% oxygen (ie. a gas with no nitrogen in it), then this gradient is maximised and nitrogen will be flushed out more quickly. In this way we can stop bubbles forming, or reduce the size of those already formed. Also, oxygen dissolved in the blood plasma can circumvent any areas where circulation is blocked due to bubbles, and revitalise oxygen-starved tissue to prevent it from dying. So although recompression is the mainstay of DCS treatment, doing it with oxygen improves results and accelerates the recovery massively.