Post by tekmac on Apr 25, 2006 20:17:28 GMT -5
In-water Recompression as an Emergency Field Treatment of Decompression Illness Richard L. Pyle and David A. Youngblood
Abstract In-Water Recompression (IWR) is defined as the practice of treating divers suffering from Decompression Sickness (DCS) by recompression underwater after the onset of DCS symptoms. The practice of IWR has been strongly discouraged by many authors, recompression chamber operators, and diving physicians. Much of the opposition to IWR is founded in the theoretical risks associated with placing a person suffering from DCS into the uncontrolled underwater environment. Evidence from available reports of attempted IWR indicates an overwhelming majority of cases in which the condition of DCS victims improved after attempted IWR.
At least three formal methods of IWR have been published. All of them prescribe breathing 100% oxygen for prolonged periods of time at a depth of 30 feet (9meters), supplied via a full face mask. Many factors must be considered when determining whether IWR should be implemented in response to the onset of DCS. The efficacy of IWR and the ideal methodology employed cannot be fully determined without more careful analysis of case histories.
Introduction There are many controversial topics within the emerging field of "technical" diving. This is not surprising, considering that technical diving activities are often high-risk in nature and extend beyond widely accepted "recreational" diving guidelines. Furthermore, many aspects of technical diving involve systems and procedures which have not yet been entirely validated by controlled experimentation or by extensive quantitative data. Seldom disputed, however, is the fact that many technical divers are conducting dives to depths well in excess of 130 feet for bottom times which result in extensive decompression obligations, and that these more extreme dive profiles result in an increased potential for suffering from Decompression Sickness (DCS).
Although technical diving involves sophisticated equipment and procedures designed to reduce the risk of sustaining DCS from these more extreme exposures, the risk nevertheless remains significant. Along with this increased potential for DCS comes an increased need for many "technical" divers to be aware of, and be prepared for, the appropriate implementation of emergency procedures in response to DCS. In the words of Michael Menduno (1993), "The solution for the technical community is to expect and plan for DCS and be prepared to deal with it". There is almost universal agreement on the practice of administering oxygen to divers exhibiting symptoms of DCS. This practice is strongly supported both by theoretical models of dissolved-gas physiology, and by empirical evidence from actual DCS cases. The answer to the question of how best to treat the afflicted diver beyond the administration of oxygen, however, is not as widely agreed upon.
Perhaps the most controversial topic in this area is that of In-Water Recompression (IWR); the practice of treating a diver suffering from DCS by placing them back underwater after the onset of DCS symptoms, using the pressure exerted by water at depth as a means of recompression. At one extreme of this controversy is conventional conviction: divers showing signs of DCS should never, under any circumstances, be placed back in the water. As pointed out by Gilliam and Von Maire (1992, p. 231), "Ask any hyperbaric expert or chamber supervisor their feelings on in-the-water recompression and you will get an almost universal recommendation against such a practice." Most diving instruction manuals condemn IWR, and the Divers Alert Network (DAN) Underwater Diving Accident & Oxygen First Aid Manual states in italicized print that "In-water recompression should never be attempted" (Divers Alert Network, 1992, p. 7).
On the other hand, IWR for treatment of DCS is a reality in many fields of diving professionals. Abalone divers in Australia (Edmonds, et al., 1991; Edmonds, 1993) and diving fishermen in Hawaii (Farm et al., 1986; Hayashi, 1989; Pyle, 1993) have relied on IWR for the treatment of DCS on repeated occasions. Many of these individuals walking around today might be dead or confined to a wheelchair had they not re-entered the water immediately after noticing symptoms of DCS. At the root of the controversy surrounding this topic is a clash between theory and practice.
IWR in Theory There are many important reasons why the practice of IWR has been so adamantly discouraged. The idea of placing a person who is suffering from a potentially debilitating disorder into the harsh and uncontrollable underwater environment appears to border on lunacy. Hazards on many levels are increased with immersion, and the possibility of worsening the afflicted diver's condition is substantial. The most often cited risk of attempted IWR is the danger of adding more nitrogen to already saturated tissues. Using air or Enriched Air Nitrox (EAN) as a breathing gas during attempted IWR may lead to an increased loading of dissolved nitrogen, causing a bad situation to become worse. Furthermore, the elevated inspired partial pressure of nitrogen while breathing such mixtures at depth leads to a reduced nitrogen gradient across alveolar membranes, slowing the rate at which dissolved nitrogen is eliminated from the blood (relative to breathing the same gas at the surface).
The underwater environment is not very conducive to the treatment of a diver suffering from DCS. Perhaps the most obvious concern is the risk of drowning. Depending on the severity of the DCS symptoms, the afflicted diver may not be able to keep a regulator securely in his or her mouth. Even if the diver is functioning nearly perfectly, the risk of drowning while underwater far exceeds the risk of drowning while resting in a boat. Another complicating factor is that communications are extremely limited underwater. Therefore, monitoring and evaluating the condition of the afflicted diver (while they are performing IWR) can be very difficult. In almost all cases, attempts at IWR will occur in water which is colder than body temperature. Successful IWR may require several hours of down-time, and even in tropical waters with full thermal diving suits, hypothermia is a major cause for concern.
Exposure to cold also results in the constriction of peripheral circulatory vessels and decreased perfusion, reducing the efficiency of nitrogen elimination (Balldin, 1973; Vann, 1982). In addition to cold, other underwater environmental factors can decrease the efficacy of IWR. Strong currents often result in excessive exertion, which may exacerbate the DCS problems. (Although exercise can increase the efficiency of decompression by increasing circulation rates and/or warming the diver [Vann, 1982], it may also enhance the formation and growth of bubbles in a near- or post-DCS situation.) Depending on the geographic location, the possibility of complications resulting from certain kinds of marine life (such as jellyfish or sharks), cannot be ignored. Published methods of IWR prescribe breathing 100% oxygen at a depth of 30 feet (9 meters) for extended periods of time.
Such high oxygen partial pressures can lead to convulsions from acute oxygen toxicity, which can easily result in drowning. Another often overlooked disadvantage of immersion of a diver with neurological DCS symptoms is that detection of those symptoms by the diver may be hampered: the "weightless" nature of being underwater can make it difficult to assess the extent of impaired motor function, and direct contact of water on skin may affect the diver's ability to detect areas of numbness. Thus, an immersed diver may not be able to determine with certainty whether or not symptoms have disappeared, are improving, are remaining constant, or are getting worse. The factors described above are all very serious, very real concerns about the practice of IWR.
There are really only two main theoretical advantages to IWR. First and foremost, it allows for immediate recompression (reduction in size) of intravascular or other endogenous bubbles, when transport to recompression chamber facilities is delayed or when such facilities are simply unavailable. Bubbles formed as a result of DCS continue to grow for hours after their initial formation, and the risk of permanent damage to tissues increases both with bubble size and the duration of bubble-induced tissue hypoxia. Furthermore, Kunkle and Beckman (1983) illustrate that the time required for bubble resolution at a given overpressure increases logarithmically with the size of the bubble. Farm, et al. (1986, p. 8) suggest that "Immediate recompression within less than 5 minutes (i.e. when the bubbles are less than 100 micrometers in diameter) is...essential if rapid bubble dissolution is to be achieved" (italics added).
If bubble size can be immediately reduced through recompression, blood circulation may be restored and permanent tissue damage may be avoided, and the time required for bubble dissolution is substantially shortened. Kunkle and Beckman, in discussing the treatment of central nervous system (CNS) DCS, write: "Because irreversible injury to nerve tissue can occur within 10 min of the initial hypoxic insult, the necessity for immediate and aggressive treatment is obvious. Unfortunately, the time required to transport a victim to a recompression facility may be from 1 to 10 hours [Kizer, 1980].
The possibility of administering immediate recompression therapy at the accident site by returning the victim to the water must therefore be seriously considered." (p. 190) The second advantage applies only when 100% oxygen is breathed during IWR. The increased ambient pressure allows the victim to inspire elevated partial pressures of oxygen (above those which can be achieved at the surface). This has the therapeutic effect of saturating the blood and tissues with dissolved oxygen, enhancing oxygenation of hypoxic tissues around areas of restricted blood flow. There is also some evidence that immersion in and of itself might enhance the rate at which nitrogen is eliminated (Balldin and Lundgren, 1972); however, these effects are likely more than offset by the reduced elimination resulting from cold during most IWR attempts.
IWR in Practice Three different methods of IWR have been published. Edmonds et al., in their first edition of Diving and Subaquatic Medicine (1976), outlined a method of IWR using surface-supplied oxygen delivered via a full face mask to the diver at a depth of 9 meters (30 feet). According to this method, the prescribed time an treated diver spends at 9 meters varies from 30-90 min depending on the severity of the symptoms, and the ascent rate is set at a steady 1 meter per 12 min (~1 ft/4 min). This method of IWR was expanded and elaborated upon in the 2nd Edition (1981), and again in the 3rd Edition (1991); and has come to be known as the "Australian Method". It has also been outlined in other publications (Knight, 1984; 1987; Gilliam and von Maier, 1992; Gilliam, 1993; Edmonds, 1993), and is presented in Appendix A of this article. [NOTE: Appendices are not included on this web page].
The U.S. Navy Diving Manual (Volume 1, revision 1, 1985) briefly outlines a method of IWR to be used in an emergency situation when 100% oxygen rebreathers are available. Gilliam (1993, p. 208) proposed that this method could "easily be adapted to full facemask diving systems or surface supplied oxygen". It involves breathing 100% oxygen at a depth of 30 feet (9 meters) for 60 min in so-called "Type I" (pain only) cases or 90 min in "Type II" (neurological symptoms) cases, followed by an additional 60 min of oxygen each at 20 feet (6 meters) and 10 feet (3 meters). This method is outlined in Gilliam (1993), and in Appendix B of this article. [NOTE: Appendices are not included on this web page].
The third method, described in Farm et al. (1986), is a modification of the Australian Method which incorporates a 10-minute descent while breathing air to a depth 30 feet (9 meters) greater than the depth at which symptoms disappear, not to exceed a maximum depth of 165 feet (50 meters). Following this brief "air-spike", the diver then ascends at a decreasing rate of ascent back to 30 feet (9 meters), where 100% oxygen is breathed for a minimum of 1 hour and thereafter until either symptoms disappear, emergency transport arrives, or the oxygen supply is exhausted. This method of IWR, developed in response to the experiences of diving fishermen in Hawaii, has come to be known as the "Hawaiian Method". This method is described in Appendix C of this article. [NOTE: Appendices are not included on this web page].
All three of these methods share the requirement of large quantities of oxygen delivered to the diver via a full face mask at 30 feet (9 meters) for extended periods, a tender diver present to monitor the condition of the treated diver, and a heavily weighted drop-line to serve as a reference for depth. Also, some form of communication (either electronic or pencil and slate) must be maintained between the treated diver, the tending diver, and the surface support crew. Information on at least 535 cases of attempted IWR has been reported in publications. Summary data from the majority of these attempts are included in Farm et al. (1986), who present the results of their survey of diving fishermen in Hawaii.
Of the 527 cases of attempted IWR reported during the survey, 462 (87.7%) involved complete resolution of symptoms. In 51 cases (9.7%), the diver had improved to the point where residual symptoms were mild enough that no further treatment was sought, and symptoms disappeared entirely within a day or two. In only 14 cases (2.7%) did symptoms persist enough after IWR that the diver sought treatment at a recompression facility.
None of the divers reported that their symptoms had worsened after IWR. It is also interesting (and somewhat disturbing) to note that none of the divers included in this survey were aware of published methods of IWR (i.e. all were "winging it" - inventing the procedure for themselves as they went along), and all had used only air as a breathing gas. Edmonds et al. (1981) document two cases of successful IWR in which divers suffering from DCS in remote locations followed the Australian Method of IWR with apparently tremendous success (both are presented below as Case #8 and #9). Overlock (1989) described six cases of DCS involving divers using decompression computers. Of these, four involved attempted IWR, three of which were apparently successful (the results from the fourth case are unclear). Two of these cases are described as Case #1 and Case #4 below.
Hayashi (1989) reported two cases of attempted IWR, one of which involved the use of 100% oxygen, and the other, involving air as a breathing gas, was also described in Farm et al. (1986) and is described below as Case #2. At present, we are aware of about twenty additional cases of attempted IWR which have not previously been reported in literature. Of these, two resulted in the death of the attempting divers (both divers were together at the time - see Case #3 below), and one resulted in an apparent aggravation of the conditions (i.e. turning a sore shoulder into permanent quadriplegia - see Case #10 below).
Another case, for which we do not have details, involved a diver who apparently worsened his condition with IWR, but eventually recovered after proper treatment in a recompression chamber facility. In six other cases, the condition of the diver had remained constant or improved after attempted IWR, and further treatment in a recompression chamber was sought by most of them. In all of the remaining cases, the diver was asymptomatic after IWR, they sought no further treatment, and their symptoms did not return. Without doubt, many more attempts at IWR have occurred but have not been reported. Edmonds, et al. (1981, p. 175), in discussing the practice of the Australian Method of IWR, note that "Because of the nature of this treatment being applied in remote localities, many cases are not well documented.
Twenty five cases were well supervised before this technique increased suddenly in popularity, perhaps due to the success it had achieved, and perhaps due the marketing of the [proper] equipment..." Several professional divers have privately confided to one of us (RLP) that they have used IWR to treat themselves and companions on multiple occasions, and all have reported great success in their efforts. Some continue to teach the practice to their more advanced students (although the practice was once taught on a more regular basis, it has since fallen out of widely accepted instruction protocol).
Evaluation of Case Histories In determining the relative value of IWR as a response to DCS, it is perhaps most useful to carefully examine case histories involving attempted IWR. DCS is, by nature, a very complex, dynamic, and unpredictable disorder, and evaluation of the role of IWR as a treatment in reported cases is often difficult. Assessing the success or failure of an attempt at IWR is obscured by the fact that a positive or negative change in the victim's condition may have little or nothing to do with the IWR treatment itself. Furthermore, even the determination of whether or not a DCS victim's condition was better or worse after attempted IWR is not always clear. For example, consider the following case, first reported by Overlock (1989):
Case #1. Fiji. Five minutes after surfacing from the fourth dive to moderate depth (75-120 feet) over a 24 hr period, a diver developed progressive arm and back weakness and pain. She returned to 60 feet for 3 min, then ascended (decompressed) over a 50-minute period (with stops at 30, 20, and 10 feet), breathing air. Tingling and pain resolved during the first 10 min of IWR. Three hours after completing IWR, she developed numbness in the right leg and foot, and reported "shocks" running down both legs, whereupon she was taken to a recompression chamber. After 3 successive U.S. Navy "Table 6" treatments, she still felt weakness and some decreased sensation. The effect of IWR on the recovery of this diver is unclear. Although the pain and weakness were resolved during IWR, more serious symptoms developed hours afterward. Perhaps numbness would never have developed had the diver been taken directly to a recompression chamber instead of re-entering the water, in which case she may have responded to treatment without residuals. On the other hand, had she not returned to the water, the initial symptoms may have progressed into paralysis during her evacuation to the chamber, and she might have ultimately suffered far more serious and debilitating residuals. Cases such as this do not contribute much insight into the efficacy of IWR. Other cases, however, provide stronger evidence suggesting that IWR has been of benefit. Consider the following case documented in Farm et al. (1986) and Hayashi (1989):
Case #2. Hawaii. "Four fisherman divers were working in pairs at a site about 165 to 180 feet deep. Each pair alternated diving and made two dives at the site. Both divers of the second pair rapidly developed signs and symptoms of severe CNS decompression sickness upon surfacing from their second dive. The boat pilot and the other diver decided to take both victims to the U.S. Navy recompression chamber and headed for the dock some 30 minutes away [the recompression chamber was an additional hour away from the dock]. During transport, one victim refused to go and elected to undergo in-water recompression, breathing air. He took two full scuba tanks, told the boat driver to come back and pick him up after transporting the other bends victim to the chamber, and rolled over the side of the boat down to a depth of 30 to 40 feet. The boat crew returned after 2 hours to pick him up. He was asymptomatic and apparently cured of the disease. The other diver died of severe decompression sickness in the Med-Evac helicopter en route to the recompression chamber." (Hayashi, 1989, p. 157) This is just one example of many which provide compelling evidence that IWR can, in some circumstances, result in dramatic relief of serious DCS symptoms. Ironically, had this incident occurred in an area where a recompression chamber was not an option, both divers would probably have opted for IWR, and the less fortunate victim might possibly have survived the ordeal. On the other hand, attempts at IWR under inappropriate circumstances can lead to tragedy, as is clearly evident from the following case:
Case #3. Sussex, England. Twelve experienced divers conducted an 18-minute dive on a wreck in about 215 feet. They surfaced following 38 minutes of air decompression, at which time two of the divers reported "incomplete decompression". These two divers obtained additional supplies of air and returned to the water in an apparent effort to treat DCS symptoms. They never returned to the boat, and their bodies were recovered two weeks later. The reason for their deaths remains a mystery. It is possible that they were suffering from neurological DCS symptoms, and drowned as a result of these symptoms. The tragedy of this case lies in the fact that they most likely would have survived had they not re-entered the water. The boat was equipped with 100% oxygen (surface-breathing) equipment, and the incident occurred in an area where emergency air-transport could have delivered the divers to a recompression chamber less than an hour after surfacing. The water temperature in this case was about 61-63° F (16-17° C), and the surface conditions were relatively rough (3-5 ft seas). Whether or not these divers perished as a direct result of DCS symptoms, they would, in all likelihood, have survived the incident had they not returned to the water. The main potential benefit of IWR lies in the ability to recompress the DCS victim immediately after the onset of DCS symptoms, before intravascular bubbles have a chance to grow or cause serious permanent damage. The apparent success of many reported attempts of IWR may be attributed to the immediacy of the recompression. In one case, reported by Overlock (1989), IWR began before the diver even reached the surface:
Case #4. Hawaii. After ascending from his second 10-minute dive to 190 feet, a diver followed the decompression `ceilings' suggested by his dive computer. As he was nearing the end of his computer's suggested decompression schedule, he suddenly noticed weakness and incoordination in both arms, and numbness in his right leg. He immediately descended to a depth of 80 feet where, after 3 min, the symptoms disappeared. After a total of 8 min at 80 feet, he slowly ascended over a period of 50 min to 15 feet (his companion supplied him with fresh air tanks). He remained at this depth until his decompression computer had "cleared". He felt tired after surfacing, but was otherwise asymptomatic. In many other cases, IWR was commenced within a few minutes after surfacing, usually resulting in the elimination or substantial reduction of symptoms. In cases where DCS results from gross omission of required decompression, divers may anticipate the probable consequences, and often return immediately to depth as soon as possible in an effort to complete the required decompression. Two such cases are presented here:
Case #5. Hawaii. While conducting a solo dive at a depth of 195 feet, a diver became entangled in lines and mesh bags. In his struggles to free himself, he extended his time at depth well beyond the intended 10 minutes, and squandered much of the air he had expected to use for decompression. Upon freeing himself, he immediately began his ascent, but was mortified to discover that the boat anchor had broken loose and was gone. Swimming down-current, he fortuitously saw the anchor dragging across the bottom, and quickly caught up with the anchor line at a depth of 60 feet. At this time, his decompression computer indicated a `ceiling' of 70 feet, and his pressure gauge showed that his scuba tank was nearly empty. He slowly ascended to the surface and quickly explained his predicament to his companion in the boat. While waiting for his companion to rig a regulator to a fresh tank of air, he began feeling symptoms of severe dizziness and had problems with his vision. Grasping the second tank under his arm, he allowed himself to sink back down, nearly losing consciousness. Upon reaching a depth of 80 feet, his clouded consciousness fully resolved, and he remained 10-15 ft below his computer's recommended `ceiling' during subsequent decompression. Although he eventually exited the water before his computer had "cleared", he did not experience any additional symptoms.
Abstract In-Water Recompression (IWR) is defined as the practice of treating divers suffering from Decompression Sickness (DCS) by recompression underwater after the onset of DCS symptoms. The practice of IWR has been strongly discouraged by many authors, recompression chamber operators, and diving physicians. Much of the opposition to IWR is founded in the theoretical risks associated with placing a person suffering from DCS into the uncontrolled underwater environment. Evidence from available reports of attempted IWR indicates an overwhelming majority of cases in which the condition of DCS victims improved after attempted IWR.
At least three formal methods of IWR have been published. All of them prescribe breathing 100% oxygen for prolonged periods of time at a depth of 30 feet (9meters), supplied via a full face mask. Many factors must be considered when determining whether IWR should be implemented in response to the onset of DCS. The efficacy of IWR and the ideal methodology employed cannot be fully determined without more careful analysis of case histories.
Introduction There are many controversial topics within the emerging field of "technical" diving. This is not surprising, considering that technical diving activities are often high-risk in nature and extend beyond widely accepted "recreational" diving guidelines. Furthermore, many aspects of technical diving involve systems and procedures which have not yet been entirely validated by controlled experimentation or by extensive quantitative data. Seldom disputed, however, is the fact that many technical divers are conducting dives to depths well in excess of 130 feet for bottom times which result in extensive decompression obligations, and that these more extreme dive profiles result in an increased potential for suffering from Decompression Sickness (DCS).
Although technical diving involves sophisticated equipment and procedures designed to reduce the risk of sustaining DCS from these more extreme exposures, the risk nevertheless remains significant. Along with this increased potential for DCS comes an increased need for many "technical" divers to be aware of, and be prepared for, the appropriate implementation of emergency procedures in response to DCS. In the words of Michael Menduno (1993), "The solution for the technical community is to expect and plan for DCS and be prepared to deal with it". There is almost universal agreement on the practice of administering oxygen to divers exhibiting symptoms of DCS. This practice is strongly supported both by theoretical models of dissolved-gas physiology, and by empirical evidence from actual DCS cases. The answer to the question of how best to treat the afflicted diver beyond the administration of oxygen, however, is not as widely agreed upon.
Perhaps the most controversial topic in this area is that of In-Water Recompression (IWR); the practice of treating a diver suffering from DCS by placing them back underwater after the onset of DCS symptoms, using the pressure exerted by water at depth as a means of recompression. At one extreme of this controversy is conventional conviction: divers showing signs of DCS should never, under any circumstances, be placed back in the water. As pointed out by Gilliam and Von Maire (1992, p. 231), "Ask any hyperbaric expert or chamber supervisor their feelings on in-the-water recompression and you will get an almost universal recommendation against such a practice." Most diving instruction manuals condemn IWR, and the Divers Alert Network (DAN) Underwater Diving Accident & Oxygen First Aid Manual states in italicized print that "In-water recompression should never be attempted" (Divers Alert Network, 1992, p. 7).
On the other hand, IWR for treatment of DCS is a reality in many fields of diving professionals. Abalone divers in Australia (Edmonds, et al., 1991; Edmonds, 1993) and diving fishermen in Hawaii (Farm et al., 1986; Hayashi, 1989; Pyle, 1993) have relied on IWR for the treatment of DCS on repeated occasions. Many of these individuals walking around today might be dead or confined to a wheelchair had they not re-entered the water immediately after noticing symptoms of DCS. At the root of the controversy surrounding this topic is a clash between theory and practice.
IWR in Theory There are many important reasons why the practice of IWR has been so adamantly discouraged. The idea of placing a person who is suffering from a potentially debilitating disorder into the harsh and uncontrollable underwater environment appears to border on lunacy. Hazards on many levels are increased with immersion, and the possibility of worsening the afflicted diver's condition is substantial. The most often cited risk of attempted IWR is the danger of adding more nitrogen to already saturated tissues. Using air or Enriched Air Nitrox (EAN) as a breathing gas during attempted IWR may lead to an increased loading of dissolved nitrogen, causing a bad situation to become worse. Furthermore, the elevated inspired partial pressure of nitrogen while breathing such mixtures at depth leads to a reduced nitrogen gradient across alveolar membranes, slowing the rate at which dissolved nitrogen is eliminated from the blood (relative to breathing the same gas at the surface).
The underwater environment is not very conducive to the treatment of a diver suffering from DCS. Perhaps the most obvious concern is the risk of drowning. Depending on the severity of the DCS symptoms, the afflicted diver may not be able to keep a regulator securely in his or her mouth. Even if the diver is functioning nearly perfectly, the risk of drowning while underwater far exceeds the risk of drowning while resting in a boat. Another complicating factor is that communications are extremely limited underwater. Therefore, monitoring and evaluating the condition of the afflicted diver (while they are performing IWR) can be very difficult. In almost all cases, attempts at IWR will occur in water which is colder than body temperature. Successful IWR may require several hours of down-time, and even in tropical waters with full thermal diving suits, hypothermia is a major cause for concern.
Exposure to cold also results in the constriction of peripheral circulatory vessels and decreased perfusion, reducing the efficiency of nitrogen elimination (Balldin, 1973; Vann, 1982). In addition to cold, other underwater environmental factors can decrease the efficacy of IWR. Strong currents often result in excessive exertion, which may exacerbate the DCS problems. (Although exercise can increase the efficiency of decompression by increasing circulation rates and/or warming the diver [Vann, 1982], it may also enhance the formation and growth of bubbles in a near- or post-DCS situation.) Depending on the geographic location, the possibility of complications resulting from certain kinds of marine life (such as jellyfish or sharks), cannot be ignored. Published methods of IWR prescribe breathing 100% oxygen at a depth of 30 feet (9 meters) for extended periods of time.
Such high oxygen partial pressures can lead to convulsions from acute oxygen toxicity, which can easily result in drowning. Another often overlooked disadvantage of immersion of a diver with neurological DCS symptoms is that detection of those symptoms by the diver may be hampered: the "weightless" nature of being underwater can make it difficult to assess the extent of impaired motor function, and direct contact of water on skin may affect the diver's ability to detect areas of numbness. Thus, an immersed diver may not be able to determine with certainty whether or not symptoms have disappeared, are improving, are remaining constant, or are getting worse. The factors described above are all very serious, very real concerns about the practice of IWR.
There are really only two main theoretical advantages to IWR. First and foremost, it allows for immediate recompression (reduction in size) of intravascular or other endogenous bubbles, when transport to recompression chamber facilities is delayed or when such facilities are simply unavailable. Bubbles formed as a result of DCS continue to grow for hours after their initial formation, and the risk of permanent damage to tissues increases both with bubble size and the duration of bubble-induced tissue hypoxia. Furthermore, Kunkle and Beckman (1983) illustrate that the time required for bubble resolution at a given overpressure increases logarithmically with the size of the bubble. Farm, et al. (1986, p. 8) suggest that "Immediate recompression within less than 5 minutes (i.e. when the bubbles are less than 100 micrometers in diameter) is...essential if rapid bubble dissolution is to be achieved" (italics added).
If bubble size can be immediately reduced through recompression, blood circulation may be restored and permanent tissue damage may be avoided, and the time required for bubble dissolution is substantially shortened. Kunkle and Beckman, in discussing the treatment of central nervous system (CNS) DCS, write: "Because irreversible injury to nerve tissue can occur within 10 min of the initial hypoxic insult, the necessity for immediate and aggressive treatment is obvious. Unfortunately, the time required to transport a victim to a recompression facility may be from 1 to 10 hours [Kizer, 1980].
The possibility of administering immediate recompression therapy at the accident site by returning the victim to the water must therefore be seriously considered." (p. 190) The second advantage applies only when 100% oxygen is breathed during IWR. The increased ambient pressure allows the victim to inspire elevated partial pressures of oxygen (above those which can be achieved at the surface). This has the therapeutic effect of saturating the blood and tissues with dissolved oxygen, enhancing oxygenation of hypoxic tissues around areas of restricted blood flow. There is also some evidence that immersion in and of itself might enhance the rate at which nitrogen is eliminated (Balldin and Lundgren, 1972); however, these effects are likely more than offset by the reduced elimination resulting from cold during most IWR attempts.
IWR in Practice Three different methods of IWR have been published. Edmonds et al., in their first edition of Diving and Subaquatic Medicine (1976), outlined a method of IWR using surface-supplied oxygen delivered via a full face mask to the diver at a depth of 9 meters (30 feet). According to this method, the prescribed time an treated diver spends at 9 meters varies from 30-90 min depending on the severity of the symptoms, and the ascent rate is set at a steady 1 meter per 12 min (~1 ft/4 min). This method of IWR was expanded and elaborated upon in the 2nd Edition (1981), and again in the 3rd Edition (1991); and has come to be known as the "Australian Method". It has also been outlined in other publications (Knight, 1984; 1987; Gilliam and von Maier, 1992; Gilliam, 1993; Edmonds, 1993), and is presented in Appendix A of this article. [NOTE: Appendices are not included on this web page].
The U.S. Navy Diving Manual (Volume 1, revision 1, 1985) briefly outlines a method of IWR to be used in an emergency situation when 100% oxygen rebreathers are available. Gilliam (1993, p. 208) proposed that this method could "easily be adapted to full facemask diving systems or surface supplied oxygen". It involves breathing 100% oxygen at a depth of 30 feet (9 meters) for 60 min in so-called "Type I" (pain only) cases or 90 min in "Type II" (neurological symptoms) cases, followed by an additional 60 min of oxygen each at 20 feet (6 meters) and 10 feet (3 meters). This method is outlined in Gilliam (1993), and in Appendix B of this article. [NOTE: Appendices are not included on this web page].
The third method, described in Farm et al. (1986), is a modification of the Australian Method which incorporates a 10-minute descent while breathing air to a depth 30 feet (9 meters) greater than the depth at which symptoms disappear, not to exceed a maximum depth of 165 feet (50 meters). Following this brief "air-spike", the diver then ascends at a decreasing rate of ascent back to 30 feet (9 meters), where 100% oxygen is breathed for a minimum of 1 hour and thereafter until either symptoms disappear, emergency transport arrives, or the oxygen supply is exhausted. This method of IWR, developed in response to the experiences of diving fishermen in Hawaii, has come to be known as the "Hawaiian Method". This method is described in Appendix C of this article. [NOTE: Appendices are not included on this web page].
All three of these methods share the requirement of large quantities of oxygen delivered to the diver via a full face mask at 30 feet (9 meters) for extended periods, a tender diver present to monitor the condition of the treated diver, and a heavily weighted drop-line to serve as a reference for depth. Also, some form of communication (either electronic or pencil and slate) must be maintained between the treated diver, the tending diver, and the surface support crew. Information on at least 535 cases of attempted IWR has been reported in publications. Summary data from the majority of these attempts are included in Farm et al. (1986), who present the results of their survey of diving fishermen in Hawaii.
Of the 527 cases of attempted IWR reported during the survey, 462 (87.7%) involved complete resolution of symptoms. In 51 cases (9.7%), the diver had improved to the point where residual symptoms were mild enough that no further treatment was sought, and symptoms disappeared entirely within a day or two. In only 14 cases (2.7%) did symptoms persist enough after IWR that the diver sought treatment at a recompression facility.
None of the divers reported that their symptoms had worsened after IWR. It is also interesting (and somewhat disturbing) to note that none of the divers included in this survey were aware of published methods of IWR (i.e. all were "winging it" - inventing the procedure for themselves as they went along), and all had used only air as a breathing gas. Edmonds et al. (1981) document two cases of successful IWR in which divers suffering from DCS in remote locations followed the Australian Method of IWR with apparently tremendous success (both are presented below as Case #8 and #9). Overlock (1989) described six cases of DCS involving divers using decompression computers. Of these, four involved attempted IWR, three of which were apparently successful (the results from the fourth case are unclear). Two of these cases are described as Case #1 and Case #4 below.
Hayashi (1989) reported two cases of attempted IWR, one of which involved the use of 100% oxygen, and the other, involving air as a breathing gas, was also described in Farm et al. (1986) and is described below as Case #2. At present, we are aware of about twenty additional cases of attempted IWR which have not previously been reported in literature. Of these, two resulted in the death of the attempting divers (both divers were together at the time - see Case #3 below), and one resulted in an apparent aggravation of the conditions (i.e. turning a sore shoulder into permanent quadriplegia - see Case #10 below).
Another case, for which we do not have details, involved a diver who apparently worsened his condition with IWR, but eventually recovered after proper treatment in a recompression chamber facility. In six other cases, the condition of the diver had remained constant or improved after attempted IWR, and further treatment in a recompression chamber was sought by most of them. In all of the remaining cases, the diver was asymptomatic after IWR, they sought no further treatment, and their symptoms did not return. Without doubt, many more attempts at IWR have occurred but have not been reported. Edmonds, et al. (1981, p. 175), in discussing the practice of the Australian Method of IWR, note that "Because of the nature of this treatment being applied in remote localities, many cases are not well documented.
Twenty five cases were well supervised before this technique increased suddenly in popularity, perhaps due to the success it had achieved, and perhaps due the marketing of the [proper] equipment..." Several professional divers have privately confided to one of us (RLP) that they have used IWR to treat themselves and companions on multiple occasions, and all have reported great success in their efforts. Some continue to teach the practice to their more advanced students (although the practice was once taught on a more regular basis, it has since fallen out of widely accepted instruction protocol).
Evaluation of Case Histories In determining the relative value of IWR as a response to DCS, it is perhaps most useful to carefully examine case histories involving attempted IWR. DCS is, by nature, a very complex, dynamic, and unpredictable disorder, and evaluation of the role of IWR as a treatment in reported cases is often difficult. Assessing the success or failure of an attempt at IWR is obscured by the fact that a positive or negative change in the victim's condition may have little or nothing to do with the IWR treatment itself. Furthermore, even the determination of whether or not a DCS victim's condition was better or worse after attempted IWR is not always clear. For example, consider the following case, first reported by Overlock (1989):
Case #1. Fiji. Five minutes after surfacing from the fourth dive to moderate depth (75-120 feet) over a 24 hr period, a diver developed progressive arm and back weakness and pain. She returned to 60 feet for 3 min, then ascended (decompressed) over a 50-minute period (with stops at 30, 20, and 10 feet), breathing air. Tingling and pain resolved during the first 10 min of IWR. Three hours after completing IWR, she developed numbness in the right leg and foot, and reported "shocks" running down both legs, whereupon she was taken to a recompression chamber. After 3 successive U.S. Navy "Table 6" treatments, she still felt weakness and some decreased sensation. The effect of IWR on the recovery of this diver is unclear. Although the pain and weakness were resolved during IWR, more serious symptoms developed hours afterward. Perhaps numbness would never have developed had the diver been taken directly to a recompression chamber instead of re-entering the water, in which case she may have responded to treatment without residuals. On the other hand, had she not returned to the water, the initial symptoms may have progressed into paralysis during her evacuation to the chamber, and she might have ultimately suffered far more serious and debilitating residuals. Cases such as this do not contribute much insight into the efficacy of IWR. Other cases, however, provide stronger evidence suggesting that IWR has been of benefit. Consider the following case documented in Farm et al. (1986) and Hayashi (1989):
Case #2. Hawaii. "Four fisherman divers were working in pairs at a site about 165 to 180 feet deep. Each pair alternated diving and made two dives at the site. Both divers of the second pair rapidly developed signs and symptoms of severe CNS decompression sickness upon surfacing from their second dive. The boat pilot and the other diver decided to take both victims to the U.S. Navy recompression chamber and headed for the dock some 30 minutes away [the recompression chamber was an additional hour away from the dock]. During transport, one victim refused to go and elected to undergo in-water recompression, breathing air. He took two full scuba tanks, told the boat driver to come back and pick him up after transporting the other bends victim to the chamber, and rolled over the side of the boat down to a depth of 30 to 40 feet. The boat crew returned after 2 hours to pick him up. He was asymptomatic and apparently cured of the disease. The other diver died of severe decompression sickness in the Med-Evac helicopter en route to the recompression chamber." (Hayashi, 1989, p. 157) This is just one example of many which provide compelling evidence that IWR can, in some circumstances, result in dramatic relief of serious DCS symptoms. Ironically, had this incident occurred in an area where a recompression chamber was not an option, both divers would probably have opted for IWR, and the less fortunate victim might possibly have survived the ordeal. On the other hand, attempts at IWR under inappropriate circumstances can lead to tragedy, as is clearly evident from the following case:
Case #3. Sussex, England. Twelve experienced divers conducted an 18-minute dive on a wreck in about 215 feet. They surfaced following 38 minutes of air decompression, at which time two of the divers reported "incomplete decompression". These two divers obtained additional supplies of air and returned to the water in an apparent effort to treat DCS symptoms. They never returned to the boat, and their bodies were recovered two weeks later. The reason for their deaths remains a mystery. It is possible that they were suffering from neurological DCS symptoms, and drowned as a result of these symptoms. The tragedy of this case lies in the fact that they most likely would have survived had they not re-entered the water. The boat was equipped with 100% oxygen (surface-breathing) equipment, and the incident occurred in an area where emergency air-transport could have delivered the divers to a recompression chamber less than an hour after surfacing. The water temperature in this case was about 61-63° F (16-17° C), and the surface conditions were relatively rough (3-5 ft seas). Whether or not these divers perished as a direct result of DCS symptoms, they would, in all likelihood, have survived the incident had they not returned to the water. The main potential benefit of IWR lies in the ability to recompress the DCS victim immediately after the onset of DCS symptoms, before intravascular bubbles have a chance to grow or cause serious permanent damage. The apparent success of many reported attempts of IWR may be attributed to the immediacy of the recompression. In one case, reported by Overlock (1989), IWR began before the diver even reached the surface:
Case #4. Hawaii. After ascending from his second 10-minute dive to 190 feet, a diver followed the decompression `ceilings' suggested by his dive computer. As he was nearing the end of his computer's suggested decompression schedule, he suddenly noticed weakness and incoordination in both arms, and numbness in his right leg. He immediately descended to a depth of 80 feet where, after 3 min, the symptoms disappeared. After a total of 8 min at 80 feet, he slowly ascended over a period of 50 min to 15 feet (his companion supplied him with fresh air tanks). He remained at this depth until his decompression computer had "cleared". He felt tired after surfacing, but was otherwise asymptomatic. In many other cases, IWR was commenced within a few minutes after surfacing, usually resulting in the elimination or substantial reduction of symptoms. In cases where DCS results from gross omission of required decompression, divers may anticipate the probable consequences, and often return immediately to depth as soon as possible in an effort to complete the required decompression. Two such cases are presented here:
Case #5. Hawaii. While conducting a solo dive at a depth of 195 feet, a diver became entangled in lines and mesh bags. In his struggles to free himself, he extended his time at depth well beyond the intended 10 minutes, and squandered much of the air he had expected to use for decompression. Upon freeing himself, he immediately began his ascent, but was mortified to discover that the boat anchor had broken loose and was gone. Swimming down-current, he fortuitously saw the anchor dragging across the bottom, and quickly caught up with the anchor line at a depth of 60 feet. At this time, his decompression computer indicated a `ceiling' of 70 feet, and his pressure gauge showed that his scuba tank was nearly empty. He slowly ascended to the surface and quickly explained his predicament to his companion in the boat. While waiting for his companion to rig a regulator to a fresh tank of air, he began feeling symptoms of severe dizziness and had problems with his vision. Grasping the second tank under his arm, he allowed himself to sink back down, nearly losing consciousness. Upon reaching a depth of 80 feet, his clouded consciousness fully resolved, and he remained 10-15 ft below his computer's recommended `ceiling' during subsequent decompression. Although he eventually exited the water before his computer had "cleared", he did not experience any additional symptoms.