Hi large-diver,
Here's a long piece on in water recompression I did for the Sep '00 "Undercurrent":
"In-Water Recompression (IWR)
Youve sustained DCS in a remote location, many hours by air from the nearest hyperbaric chamber. The air ambulance cannot fly due to weather, and even if it could its uncertain if the chamber is fully operational. What to do? Some divers, especially those of a technical inclination, might respond, How about in-water recompression?
Not to be confused with the technique of re-entering the water to complete a missed deco obligation, IWR uses the pressure of water itself coupled with breathing high concentrations of O2 immediately following the first signs or symptoms of DCS.
The 4 primary techniques for IWR are commonly referred to as the Australian, U.S. Navy, Hawaiian, & Pyle methods. While each method differs somewhat & requires its own equipment, all methods require personnel knowledgeable in IWR, skilled tenders & adequate supplies of pure O2 or other gas.
All are precluded if the diver is unconscious, in shock or shows paralysis, vertigo or respiratory distress, or is seemingly unable to complete the procedure due to factors such as fear or possible hypothermia. Additionally, all variants direct that appropriate emergency transport be requested immediately and that medical attention be received as soon as possible even in those cases of IWR which appear completely successful.
Generally, mixes with higher concentrations of O2 are preferred over those with lower ones given their higher potential for off-gassing nitrogen, although any concentration above normoxic is superior to compressed air. One hundred percent O2 is recommend by all variants of IWR, although since the risk of O2 induced convulsions increases with increasing PO2 at least one expert has opined that 80% my be more appropriate. Whatever mix is used, it is best inspired via a full-face mask if possible. Not only does this help to insure that gas is available during a possible seizure, but the positive pressure aspect of most full-face masks promotes maximal O2 delivery, and their design may even bestow some thermal benefits. It is a decided plus if the mask has an integrated communications system.
IWR was possibly first applied to bent sponge divers off Key West by Doc Axle Buckmeister back in the late 1800s. More formalized forms have long been practiced by Hawaiian diving fishermen and Australian pearl & abalone divers. Veteran technical diving expert Bret Gilliam has knowledgeably written on the topic. It has been most recently & vigorously championed by Richard Pyle, a diver-academic currently working in the ichthyology collection at Bishop Museum in Honolulu & completing a Ph.D. in the Department of Zoology at the University of Hawaii. Another solid supporter is Dr. Ann Kristovich, Women Divers Hall of Fame member & co-leader of The Proyecto De Buceo Espeleologico Mexico Y America Central. She holds that if travel time to a recompression chamber would take longer than 30 minutes, the time frame of the Hawaiian Method of IWR discussed below, then IWR is recommended.
Not surprisingly, major recreational dive training agencies are very circumspect regarding IRW. PADI Educational Consultant Leroy Wickham told me that IWR is not taught in any of their programs, nor would the procedure be recommended except under extraordinary circumstances and then only by qualified & properly equipped personnel. Several technical agencies, IANTD & TDI among them, briefly touch on IWR as part of their curriculum for trimix classes, and the entire procedure for the Australian variant is published in IANTDs Technical Diver Encyclopedia. In a phone conversation, the encyclopedias author and IANTD founder Tom Mount reported that IANTD does not yet teach IWR because of its lack of broad acceptance. He includes a caveat that IWR is only to be done by qualified & properly equipped individuals in remote areas where a chamber is not readily available. When pressed for an example of such a location, he named Bikini, where chamber treatment could be 36 hours away. Fascinatingly, he mentioned performing the technique on about 15 divers over the years, including his wife during a trip a Roatan before a chamber was available there. His reported success rate is a startling 100%.
Dive medicine organizations express a similar prudence, indicating that such factors as fatigue, cold, panic, seasickness or an exhausted gas supply can result in incomplete treatment and a worsening of the DCS due to additional nitrogen on-loading. Not to be overlooked are such things as possible 02 induced convulsions, hypothermia, risk to tending divers, and the list goes on. Joel Dovenbarger, RN, Vice President of Medical Services at DAN, told me IWR should only be considered in those unique remote areas of the world where conventional & proven methods are not available, and where there are the requisite trained personnel & logistical support. Overseas, the recommendation of the 1996 Second European Consensus Conference on the Treatment of Recreational Diving Decompression Accidents was that in water recompression should never be performed as the initial recompression.
Despite warnings from various agencies, the sobering reality is that in Type II hits with serious vascular obstruction, irreversible tissue damage to brain can occur after about 7 minutes, to spinal cord after about 15 minutes & to lung after about 10-20 minutes. In addition, research has consistently shown that the sooner DCS of any nature is treated, the more salubrious the outcome.
Leaving aside the practical arguments for and agency positions on IWR, there is a strong theoretical basis to speculate that the procedure could be beneficial if applied correctly. Expected would be a reduction in bubble growth due to both increased pressure and the washout of nitrogen by high blood levels of O2. Additionally, the increased PO2 from breathing pure oxygen could mitigate tissue hypoxia secondary to gas embolization.
Clearly the proper place for IWR lies within the field of technical diving due to both the training received and gases used. This seems appropriate, as technical divers are probably the most likely to get DCS, and the most likely to get bent in venues inconvenient to medical care & hyperbaric facilities.
The following discussion of each technique are simplified, but convey their essences.
Australian
The most popular to date, the Australian procedure mandates continuous breathing of 100% oxygen at a depth of 30for 30 minutes for mild symptoms up to 90 minutes for severe ones. As a rule of thumb, it seems prudent to remain at the target depth for as close to the maximum time as diver & environmental conditions allow. Ascent rate is not to exceed 1per 4 minutes, and inspiration of pure O2 is to continue for 1 hour periods interrupted with 1 hour breaks for a period of 12 continuous hours.
Hawaiian
Reasoning that increased atmospheres provide increased reduction in bubble size, the Hawaiian method directs a spike on air to 30 deeper than the depth at which symptoms resolve, but not more than 165, for 10 minutes. The diver then ascends to 30 and breathes surface supplied oxygen for prolonged periods. Any O2 still on board after surfacing is to be finished. It remains uncertain whether the increased NO2 uptake occasioned by the air spike is offset by the increased pressure effect, and this may well be one reason it is not recommended by as many proponents as the Australian method. The additional depth involved also has obvious drawbacks. In the absence of equipment necessary for surface supplied O2, the procedure easily can be adapted for execution with full-face mask or standard scuba gear.
US Navy
The least often recommended of the established techniques is the US Navys. Most likely because it requires substantial amounts of pure O2, and recommends use of a 100% O2 rebreather. It directs descent to 30 for 30 minutes for Type I DCS & 90 minutes for Type II, followed by an ascent completed in two 60 minute segments, one at 20 and a second 10. Pure oxygen is to be inspired continuously for 3 hours after surfacing. The technique could readily be adapted for full-face mask or surface supplied approaches. The Navy method is recommended in situations where a hyperbaric facility is more than 12 hours away.
Pyle
The newest & most complex, the Pyle method allows for use of surface, mounted cylinder or rebreather supplied pure or diluted oxygen mixtures. At the first indication of DCS, 100% oxygen is administered at the surface for 10 minutes, during which the progression of symptoms is assessed, and logistical & environmental conditions evaluated. If IWR appears appropriate after this appraisal, the diver & a tender are lowered to a depth of 25 breathing 100% oxygen for 10 minutes. If symptoms are resolving after 10 minutes of IWR, depth is maintained and pure O2 continued for 90 minutes, interspersed with 5 minute periods breathing air or EAN every 20 minutes. Should symptoms persist or progress after the initial 10 minutes at 25 ft, breathing gas is changed to air or EAN and a potentially complicated series of descents at 25 foot increments, not to exceed 125, are conducted.
So, how effective is IWR? Although research data to date lacks scientific rigor, and is scattered & cuts across a hodge-podge of divers, variants & gases, a meta-analysis does suggest the procedure is efficacious. An overwhelming majority of bent divers appear to come out of IWR either asymptomatic or improved, with only a only tiny fraction being worsened or having an ambiguous result. This tentative finding is especially provocative given that much of the reported IWR was done using compressed air rather than recommended 100% O2.
While IWR obviously requires much further study & adjustment, it has a promising future under the unique set of circumstances for which it is designed."
The actual Australian protocol is:
Equipment
The following equipment is essential before attempting this form of treatment:
1. Full face mask with demand valve and surface supply system or helmet with free flow.
2. Adequate supply of 100% oxygen for patient, and air for attendant, typically about 200 cf per treatment.
3. Shot with at least 10 metres of rope (a seat or harness may be rigged to the shot).
4. Some form of communication system between patient, attendant and surface, preferably voice communications.
Method
1. The patient is lowered on the shot rope to 9 metres (30 fsw), breathing 100% oxygen.
2. Ascent is commenced after 30 minutes in mild cases, or 60 minutes in sever cases, if improvement has occurred. These times may be extended to 60 minutes and 90 minutes respectively if there is no improvement.
3. Ascent is at the rate of 1 metre every 12 minutes. Staging may be applied where applicable.
4. If symptoms recur remain at depth a further 30 minutes before continuing ascent.
5. If oxygen supply is exhausted, return to the surface, rather than breathe air.
6. After surfacing the patient should be given one hour on oxygen, one hour off, for a further 12 hours."
Had enough yet?
DocVikingo
