Editing In-water recompression (section)

== Background ==
{{Main|Decompression sickness}}
{{Further|Hyperbaric medicine|Hyperbaric treatment schedules}}
Decompression sickness (DCS) is a medical condition caused by dissolved gases emerging from [[Solution (chemistry)|solution]] as bubbles inside the body tissues during [[Decompression (physics)|decompression]]. DCS most commonly occurs during or soon after a [[Decompression (diving)|decompression]] ascent from [[underwater diving]] DCS and [[Air embolism|arterial gas embolism]] are collectively referred to as [[decompression illness]]. Since bubbles can form in, or migrate to, any part of the body, DCS can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. Individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all. The severity of symptoms varies from barely noticeable to rapidly fatal.<ref name="Walker and Murphy-Lavoie" />

The risk of DCS caused by diving can be managed through proper [[Decompression practice|decompression procedures]], and contracting the condition has become uncommon. Its potential severity has driven much research to prevent it, and divers almost universally use [[dive tables]] or [[dive computers]] to limit their exposure, to monitor their ascent speed, and to ensure theoretically adequate decompression stops. If DCS is suspected, it is treated by [[hyperbaric oxygen therapy]] in a [[recompression chamber]]. Where a chamber is not accessible within a reasonable time frame, In-water recompression mat be indicated for a narrow range of presentations, if there are suitably skilled personnel and appropriate equipment available on site. Diagnosis is confirmed by a positive response to the treatment. Early treatment results in a significantly higher chance of successful recovery.<ref name="Doolette and Mitchell 2018" /><ref name="Walker and Murphy-Lavoie" />

Treatment of DCS utilizing the US Navy Treatment Table 6 with oxygen at 18m or an equivalent alternative is a widely recognised [[standard of care]].<ref name="Moon 2000" /><ref name="Berghage et al 1978" /><ref name=usn /><ref name="Yarbrough 1939" /> Ideally, treatment should take place in a chamber where there is no risk of drowning or hypothermia, and other medical problems can be managed conveniently. Significant delay to treatment, difficult transport, and facilities with limited experience may lead to consideration of on site treatment.<ref name="Brubakk 2000" /> Surface [[Oxygen first aid|oxygen for first aid]] has been proven to improve the efficacy of recompression and decreased the number of recompression treatments required when administered within four hours post dive.<ref name=Longphre /> IWR to 9&nbsp;m breathing oxygen is one option that has shown success over the years<ref name=Pyle/><ref name="Pyle 1997" /><ref name=farm /> IWR is not without risk and should be undertaken with certain precautions.<ref name=uhms/><ref name=Pyle/><ref name="Knight 1984" /><ref name=edmonds1979 /> IWR would only be suitable for an organised and disciplined group of divers with suitable equipment and practical training in the procedure.<ref name=uhms/><ref name=Pyle/><ref name="Doolette and Mitchell 2018" /><ref name="Walker and Murphy-Lavoie" />

The principle behind IWR treatment is the same as that behind the treatment of DCS in a recompression chamber:<ref name=uhms/><ref name=Pyle/> an increase in ambient pressure will reduce the volume of the bubbles allowing better blood transport downstream of the bubbles. If the casualty can breathe pure [[oxygen]] further improvements will occur because the increase in the proportion of oxygen in the blood may keep previously oxygen-starved tissues alive and the [[oxygen window]] will accelerate the removal of inert gases from the bubbles making the bubbles smaller. The unacceptable risks of oxygen toxicity convulsions can be reduced by recompressing to lower pressures and for shorter durations than otherwise preferred.<ref name="Doolette and Mitchell 2018" />

Experimental work on verification of decompression tables by the US Navy Experimental Diving Unit with outcomes of symptomatic decompression sickness treated divers displaying symptoms by immediate recompression on oxygen, with 100% resolution of symptoms, and almost all cases resolved during the first treatment on Table 6, most of them during repressurisation or within the first 10 minutes at treatment depth. During the experimental work of developing the standard US Navy treatment tables 5 and 6, some experimentation was done with shorter treatment to shallower depths before standardising on 60 fsw (18 msw). This included immediate recompression on oxygen to 33 fsw (10 msw) for 30 minutes, which provided complete resolution in the majority of cases, but was not as effective as the full Table 6. Compression to 60 fsw (18 msw) would follow if symptoms did not resolve during initial treatment at 33 fsw. This previously unpublished data indicates that immediate recompression on oxygen to shallower depths for shorter periods does positively affect the probable long term outcome of decompression sickness, and compares favourably with outcomes for delayed hyperbaric treatment, and has been used as supporting evidence for new (2022) recommendations on in-water recompression. Outcomes for in-water recompression on other gas mixtures are mostly anecdotal and unsuitable for informing medical policy.(Mitchell et al. Sept 2022 in press)<ref name="Mitchell 2022" /><ref name="Doolette and Mitchell 2018" />

The use of in-water oxygen at 6 meters has been shown to reduce bubble loads in divers compared to divers breathing oxygen on the surface.<ref name="Blatteau and Pontier 2009" />