Hyperbaric treatment schedules
The risks of in-water recompression include maintaining gas supplies for multiple divers and people able to care for a sick patient in the water for an extended period of time.
[1][2] Recompression of diving casualties presenting symptoms of decompression sickness has been the treatment of choice since the late 1800s.
[3] During the building of the Brooklyn Bridge, workers with decompression sickness were recompressed in an iron chamber built for this purpose.
This changed when the first standard table for recompression treatment with air was published in the US Navy Diving Manual in 1924.
[3] Field results showed that the 1944 oxygen treatment table was not yet satisfactory, so a series of tests were conducted by staff from the Navy Medical Research Institute and the Navy Experimental Diving Unit using human subjects to verify and modify the treatment tables.
The type of chamber which can be used depends on the maximum pressure required for the schedule, and what gases are used for treatment.
[6] Outside of the diving industry, most chambers are intended for a single occupant, and not all of them are fitted with built-in breathing systems (BIBS).
Some schedules have been developed specifically for hyperbaric oxygen treatment in monoplace chambers, and some hyperbaric treatment schedules nominally intended for chambers with BIBS have been shown to be acceptable for use without air breaks if the preferred facilities are not available.
Originally therapeutic recompression was done using air as the only breathing gas, and this is reflected in several of the tables detailed below.
At greater pressures, treatment gas mixtures using Nitrogen or Helium as a diluent to limit partial pressure of oxygen to 3 ata (3 bar) or less are preferred to air as they are more effective both at elimination of inert gases and oxygenating injured tissues in comparison with air.
If the oxygen fraction rises above this limit the chamber must be ventilated with air to bring the concentration to an acceptable level.
BIBS masks provide gas on demand (inhalation), much like a diving regulator, and use a similar system to control outflow to the normobaric environment.
The BIBS system is normally used with medical oxygen, but can be connected to other breathing gases as required.
As a general rule, more recent tables from the same source have a greater success rate than the superseded schedules.
[16] Table 1A is included in the US Navy Diving Manual Revision 6 and is authorized for use as a last resort when oxygen is not available.
[16] Table 2A is included in the US Navy Diving Manual Revision 6 and is authorized for use as a last resort when oxygen is not available.
[16] Table 3 is included in the US Navy Diving Manual Revision 6 and is authorized for use as a last resort when oxygen is not available.
[17] Use: Treatment of pain-only decompression sickness when oxygen can be used and symptoms are not relieved within 10 minutes at 60 fsw (18 msw).
[24] Use: Treatment of vestibular and general neurological decompression sickness when signs of oxygen toxicity are present.
[24] Use: Treatment of light forms of decompression sickness when the symptoms are completely resolved when reaching a pressure of 29 msw (96 fsw).
[25] Use: Treatment of light forms of decompression sickness when the symptoms are completely resolved when reaching a pressure of 49 msw (160 fsw), or if there is a relapse after use of Regimen I.
[18] Indication: In-water recompression (IWR) or underwater oxygen treatment is the emergency treatment of decompression sickness (DCS) by sending the diver back underwater to allow the gas bubbles in the tissues, which are causing the symptoms, to resolve.
It is a risky procedure that should only ever be used when the time to travel to the nearest recompression chamber is too long to save the victim's life.
[1][2] The risk of the procedure comes from the fact that a diver with DCS is seriously ill and may become paralysed, unconscious or stop breathing whilst under water.
Each of these methods have several commonalities including the use of a full face mask, a tender to supervise the diver during treatment, a weighted recompression line and a means of communication.
The history of the three older methods for providing oxygen at 9 m (30 fsw) was described in great detail by Drs.
[2] The fourth method for providing oxygen at 7.5 m (25 fsw) was described by Pyle at the 48th Annual UHMS Workshop on In-water Recompression in 1999.
For the Clipperton IWR table, oxygen is then breathed the entire portion of the treatment without any air breaks.
For the Clipperton(a) IWR table, descent is made to the initial treatment depth maintaining a partial pressure of 1.4 ATA.
[20][3] Although in-water recompression is regarded as risky, and to be avoided, there is increasing evidence that technical divers who surface and demonstrate mild DCS symptoms may often get back into the water and breathe pure oxygen at a depth 20 feet (6.1 meters) for a period of time to seek to alleviate the symptoms.
