DIR Explorers - View Single Post - In water re-compression

Mark Powell · May 10th, 2006, 01:46 PM

This may not be the official GUE line but the article below describes the standard view on IWR.

In Water Recompression
In water recompression (IWR) is a highly controversial subject. IWR involves treating a diver who is already showing signs or symptoms of suffering from the bends by re-descending and following a treatment profile in the water rather then in a recompression chamber. In most areas of the world the practice is completely counterproductive and has serious safety consequences.

The time involved in a recompression treatment is of the order of several hours. This introduces a number of logistic problems into the process. For all but the most tropical regions several hours of recompression in water will result in the casualty becoming extremely cold and even hypothermic. As well as the normal dangers from hypothermia the cold will also reduce the effectiveness of the treatment as the cold will slow the rate of off-gassing from the peripheral areas of the body.

Supplying enough gas for the casualty and support diver to spend several hours in the water is also a challenge. The procedure will need a large number of support divers and attendants to ensure that enough gas is available. Of course if the support divers were also involved in the dives then these repeat dives may also put them at risk from subsequent decompression sickness.

For the treatment to be effective the casualty needs to be breathing pure Oxygen. This is in order to ensure the maximum inert gas gradient which will give the fastest rate of off-gassing. Pure Oxygen will also help by saturating the blood and tissues dissolved Oxygen which will help to oxygenate the hypoxic areas caused by the bubbles in the capillary beds or tissues. Unless significant pre-planning for IWR has been carried out there may not be sufficient supplies of Oxygen to complete the treatment. Even if enough Oxygen is available the risk of central nervous system toxicity is extremely high. In a recompression chamber a patient may breathe Oxygen at a partial pressure of 2.8 Bar for extended periods of time. However it has been shown that the body can tolerate higher partial pressures of Oxygen whilst in a warm, comfortable recompression chamber then it can whilst immersed in water. For this reason the depth to which the casualty can be returned and hence the effectiveness of the recompression is reduced. If the casualty suffers a CNS toxicity hit whilst in a chamber then the treatment is simply suspended until the casualty recovers. A CNS hit underwater is much more serious and may result in drowning or other injuries.

Communications between the casualty and their support diver(s) as well as between the support divers and surface crew is very limited. In addition the facilities for additional treatment such as intravenous (IV) re-hydration are simply not possible underwater. If the casualty deteriorates whilst underwater then further treatment may be difficult. Identifying the extent and progression of symptoms whilst underwater is also difficult. Many of the tests used to detect decompression sickness, such as a 5 minute neurological exam, are difficult if not impossible to perform underwater. Balance cannot be tested, touch and sensation cannot be established and it will not be possible to estimate limb strength.

The location of the dive site is also a major variable. If a convenient sandy sea bed at 9m with no current is easily available then this is ideal but if the incident occurs on a live aboard and anchored over a deep wreck while the current is starting to turn then the conditions in the water; no convenient bottom and strong tides introduce a number of problems into the treatment procedure.

In the UK, US and many other popular diving locations the presence of excellent emergency services and easy access to recompression chambers, combined with the logistical problems associated with IWR make this procedure completely unnecessary. For these reasons almost all diving physicians, chamber operators and training agencies maintain that IWR recompression should not be attempted. DAN’s advice is clear "In-water recompression should never be attempted".

However if you are diving in very remote areas where the nearest recompression chamber is 24 or 48 hours away then IWR may be the only option. In situations such as these experienced divers will greatly extend their safety margin to try and ensure that they do not get into this position but despite the most cautious planning there is always the chance that an unearned decompression sickness hit will occur.

To deal with these extreme cases a number of IWR protocols have been developed. In Diving and Subaquatic Medicine by Edmonds and Pennefather a method for performing IWR, which has also become known as the Australian method, is described. This involves the diver re-descending to 9m while breathing pure Oxygen. They stay at this depth for 30 minutes in the case of a mild bend or 60 minutes for a severe bend. If symptoms persist then these times can be extended to 60 and 90 minutes respectively. The patient then ascends at the rate of 1 meter every 12 minutes. This results in a total treatment time of 126 to 156 minutes for a mild case and 156 to 186 minutes for a serious case.

Depth (Metres) - Elapsed Time (minutes) Mild - Elapsed Time(minutes) Serious

9 30-60 60-90

8 42-72 72-102

7 54-84 84-114

6 66-96 96-126
5 78-108 108-138
4 90-120 120-150
3 102-132 132-162
2 114-144 144-174
1 126-156 156-186

Table 11: Australian In Water Recompression Table

It is recommended that, to carry out this treatment, a shotline with at least 10m of line is rigged and if possible a seat or harness is used to attaché the casualty to the shotline. Furthermore the casualty should be wearing a full face mask in case of Oxygen toxicity. If insufficient Oxygen is available to complete the treatment then the casualty should be returned to the surface rather than continue the treatment on air. After surfacing this procedure specifies that the casualty should breathe pure Oxygen on a one hour on, one hour off basis, for a further 12 hours.

The US Navy Diving Manual also includes a procedure for conducting IWR. Although designed for use with an Oxygen rebreather it can also be used with an open circuit or surface supply source of pure Oxygen. This procedure involves the casualty descending to 9m whilst breathing pure Oxygen. The casualty then remains at 9m for 60 minutes for mild symptoms and 90 minutes for serious symptoms. The casualty then ascends to 6m and spends a further 60 minutes at this depth followed by another 60 minutes at 3m. This results in a treatment time of 180 minutes for a mild bend and 210 minutes for a serious bend.

Depth (Metres) - Elapsed Time (minutes) Mild - Elapsed Time(minutes) Serious

9 60 90

6 120 150

3 180 210

Table 12: US Navy In Water Recompression Table

After surfacing the US Navy treatment specifies that the casualty should breathe Oxygen on the surface for an additional 3 hours.

It is clear that IWR recompression is a process that can only be carried out after considerable pre-planning and preparation. The provision of sufficient supplies of Oxygen together with a full face mask delivery system is not something that will be available for an ad-hoc treatment. As such IWR can only be considered a last resort treatment in situations where evacuation to a recompression chamber is not an option.

May 10th, 2006, 01:46 PM	#8 (permalink)
Mark Powell(Offline) New Member Join Date: Jan 2006 Location: Guildford Posts: 49	This may not be the official GUE line but the article below describes the standard view on IWR. In Water Recompression In water recompression (IWR) is a highly controversial subject. IWR involves treating a diver who is already showing signs or symptoms of suffering from the bends by re-descending and following a treatment profile in the water rather then in a recompression chamber. In most areas of the world the practice is completely counterproductive and has serious safety consequences. The time involved in a recompression treatment is of the order of several hours. This introduces a number of logistic problems into the process. For all but the most tropical regions several hours of recompression in water will result in the casualty becoming extremely cold and even hypothermic. As well as the normal dangers from hypothermia the cold will also reduce the effectiveness of the treatment as the cold will slow the rate of off-gassing from the peripheral areas of the body. Supplying enough gas for the casualty and support diver to spend several hours in the water is also a challenge. The procedure will need a large number of support divers and attendants to ensure that enough gas is available. Of course if the support divers were also involved in the dives then these repeat dives may also put them at risk from subsequent decompression sickness. For the treatment to be effective the casualty needs to be breathing pure Oxygen. This is in order to ensure the maximum inert gas gradient which will give the fastest rate of off-gassing. Pure Oxygen will also help by saturating the blood and tissues dissolved Oxygen which will help to oxygenate the hypoxic areas caused by the bubbles in the capillary beds or tissues. Unless significant pre-planning for IWR has been carried out there may not be sufficient supplies of Oxygen to complete the treatment. Even if enough Oxygen is available the risk of central nervous system toxicity is extremely high. In a recompression chamber a patient may breathe Oxygen at a partial pressure of 2.8 Bar for extended periods of time. However it has been shown that the body can tolerate higher partial pressures of Oxygen whilst in a warm, comfortable recompression chamber then it can whilst immersed in water. For this reason the depth to which the casualty can be returned and hence the effectiveness of the recompression is reduced. If the casualty suffers a CNS toxicity hit whilst in a chamber then the treatment is simply suspended until the casualty recovers. A CNS hit underwater is much more serious and may result in drowning or other injuries. Communications between the casualty and their support diver(s) as well as between the support divers and surface crew is very limited. In addition the facilities for additional treatment such as intravenous (IV) re-hydration are simply not possible underwater. If the casualty deteriorates whilst underwater then further treatment may be difficult. Identifying the extent and progression of symptoms whilst underwater is also difficult. Many of the tests used to detect decompression sickness, such as a 5 minute neurological exam, are difficult if not impossible to perform underwater. Balance cannot be tested, touch and sensation cannot be established and it will not be possible to estimate limb strength. The location of the dive site is also a major variable. If a convenient sandy sea bed at 9m with no current is easily available then this is ideal but if the incident occurs on a live aboard and anchored over a deep wreck while the current is starting to turn then the conditions in the water; no convenient bottom and strong tides introduce a number of problems into the treatment procedure. In the UK, US and many other popular diving locations the presence of excellent emergency services and easy access to recompression chambers, combined with the logistical problems associated with IWR make this procedure completely unnecessary. For these reasons almost all diving physicians, chamber operators and training agencies maintain that IWR recompression should not be attempted. DAN’s advice is clear "In-water recompression should never be attempted". However if you are diving in very remote areas where the nearest recompression chamber is 24 or 48 hours away then IWR may be the only option. In situations such as these experienced divers will greatly extend their safety margin to try and ensure that they do not get into this position but despite the most cautious planning there is always the chance that an unearned decompression sickness hit will occur. To deal with these extreme cases a number of IWR protocols have been developed. In Diving and Subaquatic Medicine by Edmonds and Pennefather a method for performing IWR, which has also become known as the Australian method, is described. This involves the diver re-descending to 9m while breathing pure Oxygen. They stay at this depth for 30 minutes in the case of a mild bend or 60 minutes for a severe bend. If symptoms persist then these times can be extended to 60 and 90 minutes respectively. The patient then ascends at the rate of 1 meter every 12 minutes. This results in a total treatment time of 126 to 156 minutes for a mild case and 156 to 186 minutes for a serious case. Depth (Metres) - Elapsed Time (minutes) Mild - Elapsed Time(minutes) Serious 9 30-60 60-90 8 42-72 72-102 7 54-84 84-114 6 66-96 96-126 5 78-108 108-138 4 90-120 120-150 3 102-132 132-162 2 114-144 144-174 1 126-156 156-186 Table 11: Australian In Water Recompression Table It is recommended that, to carry out this treatment, a shotline with at least 10m of line is rigged and if possible a seat or harness is used to attaché the casualty to the shotline. Furthermore the casualty should be wearing a full face mask in case of Oxygen toxicity. If insufficient Oxygen is available to complete the treatment then the casualty should be returned to the surface rather than continue the treatment on air. After surfacing this procedure specifies that the casualty should breathe pure Oxygen on a one hour on, one hour off basis, for a further 12 hours. The US Navy Diving Manual also includes a procedure for conducting IWR. Although designed for use with an Oxygen rebreather it can also be used with an open circuit or surface supply source of pure Oxygen. This procedure involves the casualty descending to 9m whilst breathing pure Oxygen. The casualty then remains at 9m for 60 minutes for mild symptoms and 90 minutes for serious symptoms. The casualty then ascends to 6m and spends a further 60 minutes at this depth followed by another 60 minutes at 3m. This results in a treatment time of 180 minutes for a mild bend and 210 minutes for a serious bend. Depth (Metres) - Elapsed Time (minutes) Mild - Elapsed Time(minutes) Serious 9 60 90 6 120 150 3 180 210 Table 12: US Navy In Water Recompression Table After surfacing the US Navy treatment specifies that the casualty should breathe Oxygen on the surface for an additional 3 hours. It is clear that IWR recompression is a process that can only be carried out after considerable pre-planning and preparation. The provision of sufficient supplies of Oxygen together with a full face mask delivery system is not something that will be available for an ad-hoc treatment. As such IWR can only be considered a last resort treatment in situations where evacuation to a recompression chamber is not an option. __________________ Mark Powell Dive-Tech: Technical Diver Training http://www.dive-tech.co.uk Visit the online technical diving shop: Analox, Fourth Element, Halcyon and Apeks