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On Sun, 29 May 1994 ddoolett@me*.ad*.ed*.au* wrote: > It is often > referred to as the Australian technique, this is not because we use it > alot but it was proposed, by Carl Edmonds I think, as useful in some > instances because we have very few RCCs servicing Australia and the > South Pacific and retrieval of a patient to a RCC is a problem. For The "Australian Method" is one of three published and relatively widely-known methods of IWR. It involves breathing O2 at 10m' depth for a period of time dependant upon the severity of the symptoms. Another method is the "Hawaiian Method", which is very similar but includes an "air-spike": a descent on air to a depth 30' (not to exceed 165') below the depth at which symptoms disappear for a period of 5 minutes (followed by long periods of O2 at 30'. The third mathod is the "U.S. Navy Method", which is a variation of the "Autralian Method". > I can not agree with Richard's suggestion of recompressing to 30 fsw > below relief of symtoms. I know that Hawaii is noted for its use of > deep recompression profiles in RCCs, and from a pragmatic point of > view, if this works do it. However there is no sound physiological > basis for deep recompression. Recompression for DCI has two aims, to > shrink bubbles and to provide HBO. To address the former, the volume > of a bubble is related to the cube of its radius and the area to the > square of its radius (I can never remember the formulas so check this > V=(4Pi/3)r^3 and A=(4Pi)r^2). So the effect of compression on bubble > radius and area diminishes with increasing pressure (cf. Boyle's law), > after the first couple bar of compression you aren't getting much value > in bubble shrinking. Next you want to breath HBO so that that you are > not putting any more inert gas back into your tissues or your bubbles. > HBO should also speed up the offgassing of inert gas from your tissues > and bubbles. If you try recompression therapy breathing an inert gas > you will be on-gassing in some tissues which will provide a inert gas > resevoir for further bubble growth during subsequent decompression. > Trying to recompress to below symptom relief will likely require > breathing other than pure O2. I should probably clarify my position a bit. The contorversy of IWR is basically a starck contrast between theory and practice. In theory, using air for IWR is a REALLY BAD idea (for the reasons David outlined above), and should never be recommended. In practice, it seems to have dramatically successful results a helluva lot more often than it exacerbates problems. David Youngblood & I discussed this at length in our review article of the subject (which, according to Bill Hamilton as of last week, will get published sometime this year). Breathing HBO is almost certainly the most important and effective response to DCI, but its use must be balanced with the risks of acute (CNS) oxygen toxicity problems. The value of a "spike" to greater depths on "diluted oxygen" (i.e., air, nitrox, etc.) is not clear and is under some amount of dispute. My recommendation to descend to 30' below the depth at which symptoms disappear was predicated upon the assumption that either: 1) oxygen is not available; or 2) symptoms arise deeper than, or during oxygen decompression. What I did not emphasize strongly enough in my original post is that this descent should not be exceedingly deep, and should be limited to no more than about 5 minutes in duration. In my experience, and in the experience of others I have spoken with, when DCI symptoms arise on the decompression line, they will usually disappear immediately upon descent, so horrendously deep "spike" are almost never an issue (provided recompression occurs very soon after the onset of symptoms). The obvious concern with this practice is the risk of additional nitrogen loading, which can (and, in fact has on rare occassions) turn a sore shoulder into permanent paralysis. > Let's not fool ourselves, IWR is a > quick and dirty solution to your problem, ideally you should be in a > RCC, so I would not try anythig too flash, I would stay shallow and > use pure O2, this will help and likely not exacerbate the DCI, > trying to recompress breathing an inert gas may make things worse. Total agreement here. > If you have no submersible O2 supply stay on the surface. In theory, I fully agree; however reality (i.e., practice) tends to suggest otherwise. In our review article, we strongly discourage the use of air or any other diluted oxygen for IWR; however we note that we cannot fully discount the practice in situations very remote from recompression chambers where NO oxygen is available. The question of whether to breathe O2 on the surface or air underwater is an extremely difficult one to answer and depends on too many variables. I would strongly recommend oxygen on the surface, but if I were the one who was bent, I would almost certainly opt to jump back in the water with an air tank. To avoid this dilema, the best solution is to always keep plenty of oxygen available in a way that it can be safely breathed underwater (i.e., full face mask, etc.). I think oxygen rebreather hold a lot of promise on this issue. Aloha, Rich
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