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In-water recompression
Abstract
Divers suspected of suffering decompression illness (DCI) in locations remote from a recompression chamber are sometimes treated with in-water recompression (IWR). There are no data that establish the benefits of IWR compared to conventional first aid with surface oxygen and transport to the nearest chamber. However, the theoretical benefit of IWR is that it can be initiated with a very short delay to recompression after onset of manifestations of DCI. Retrospective analyses of the effect on outcome of increasing delay generally do not capture this very short delay achievable with IWR. However, in military training and experimental diving, delay to recompression is typically less than two hours and more than 90% of cases have complete resolution of manifestations during the first treatment, often within minutes of recompression. A major risk of IWR is that of an oxygen convulsion resulting in drowning. As a result, typical IWR oxygen-breathing protocols use shallower maximum depths (9 metres' sea water (msw), 191 kPa) and are shorter (1-3 hours) than standard recompression protocols for the initial treatment of DCI (e.g., US Navy Treatment Tables 5 and 6). There has been no experimentation with initial treatment of DCI at pressures less than 285 kPa since the original development of these treatment tables, when no differences in outcomes were seen between maximum pressures of 203 kPa (10 msw) and 285 kPa (18 msw) or deeper. These data and case series suggest that recompression treatment comprising pressures and durations similar to IWR protocols can be effective. The risk of IWR is not justified for treatment of mild symptoms likely to resolve spontaneously or for divers so functionally compromised that they would not be safe in the water. However, IWR conducted by properly trained and equipped divers may be justified for manifestations that are life or limb threatening where timely recompression is unavailable.
... IWR breathing air has been used by indigenous divers, with a high reported success rate, although clinical details are scant [81]. There is anecdotal evidence that IWR using oxygen is more effective [82]; however, a major risk is an oxygen convulsion resulting in fatal drowning. IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. ...
... There is anecdotal evidence that IWR using oxygen is more effective [82]; however, a major risk is an oxygen convulsion resulting in fatal drowning. IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. Typical IWR oxygen-breathing protocols recommend depths no greater than 30 fsw (USN) or shallower [82]. ...
... IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. Typical IWR oxygen-breathing protocols recommend depths no greater than 30 fsw (USN) or shallower [82]. Recommendations include a requirement that the diver not use a regular scuba mouthpiece but rather a full face mask, surface-supplied helmet breathing ap-paratus or regulator retention strap ("gag strap") [84]. ...
Hyperbaric oxygen for decompression sickness: 2021 update Decompression sickness (DCS, “bends”) is caused by the formation of bubbles in tissues and/or blood when the sum of dissolved gas pressures exceeds ambient pressure (supersaturation). This may occur when ambient pressure is reduced during: ascent from a dive; rapid ascent to altitude in an unpressurized aircraft or hypobaric chamber; loss of cabin pressure in an aircraft [2]; and during space walks. In diving, compressed-gas breathing is usually necessary, although occasionally DCS has occurred after either repetitive or very deep breath-hold dives
... IWR breathing air has been used by indigenous divers, with a high reported success rate, although clinical details are scant [81]. There is anecdotal evidence that IWR using oxygen is more effective [82]; however, a major risk is an oxygen convulsion resulting in fatal drowning. IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. ...
... There is anecdotal evidence that IWR using oxygen is more effective [82]; however, a major risk is an oxygen convulsion resulting in fatal drowning. IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. Typical IWR oxygen-breathing protocols recommend depths no greater than 30 fsw (USN) or shallower [82]. ...
... IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. Typical IWR oxygen-breathing protocols recommend depths no greater than 30 fsw (USN) or shallower [82]. Recommendations include a requirement that the diver not use a regular scuba mouthpiece but rather a full face mask, surface-supplied helmet breathing ap-paratus or regulator retention strap ("gag strap") [84]. ...
Decompression sickness (DCS, "bends") is caused by formation of bubbles in tissues and/or blood when the sum of dissolved gas pressures exceeds ambient pressure (supersaturation). This may occur when ambient pressure is reduced during any of the following: ascent from a dive; depressurization of a hyperbaric chamber; rapid ascent to altitude in an unpressurised aircraft or hypobaric chamber; loss of cabin pressure in an aircraft [2] and during space walks.
... IWR breathing air has been used by indigenous divers, with a high reported success rate, although clinical details are scant [81]. There is anecdotal evidence that IWR using oxygen is more effective [82]; however, a major risk is an oxygen convulsion resulting in fatal drowning. IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. ...
... There is anecdotal evidence that IWR using oxygen is more effective [82]; however, a major risk is an oxygen convulsion resulting in fatal drowning. IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. Typical IWR oxygen-breathing protocols recommend depths no greater than 30 fsw (USN) or shallower [82]. ...
... IWR using oxygen has been discussed in the literature [60,82,83] and is described in the U.S. Navy Diving Manual [58]. Typical IWR oxygen-breathing protocols recommend depths no greater than 30 fsw (USN) or shallower [82]. Recommendations include a requirement that the diver not use a regular scuba mouthpiece but rather a full face mask, surface-supplied helmet breathing ap-paratus or regulator retention strap ("gag strap") [84]. ...
Decompression sickness (DCS) is a clinical syndrome occurring usually within 24 hours of a reduction in ambient pressure. DCS occurs most commonly in divers ascending from a minimum depth of 20 feet (6 meters) of sea water, but can also occur during rapid decompression from sea level to altitude (typically > 17,000 feet / 5,200 meters). Manifestations are one or more of the following: most commonly, joint pain, hypesthesia, generalized fatigue or rash; less common but more serious, motor weakness, ataxia, pulmonary edema, shock and death. The cause of DCS is in situ bubble formation in tissues, causing mechanical disruption of tissue, occlusion of blood flow, platelet activation, endothelial dysfunction and capillary leakage. High inspired concentration of oxygen (O2) is recommended as first aid for all cases and can be definitive treatment for most altitude DCS. For most other cases, hyperbaric oxygen is recommended,most commonly 100% O2 breathing at 2.82 atmospheres absolute (U.S.Navy Treatment Table 6 or equivalent). Additional treatments (generally no more than one to two) are used for residual manifestations until clinical stability; some severe cases may require more treatments. Isotonic, glucose-free fluids are recommended for prevention and treatment of hypovolemia. An evidence-based review of adjunctive therapies is presented.
... 72 There is anecdotal evidence that IWR using oxygen is more effective. 73 However, a major risk is an oxygen convulsion resulting in fatal drowning. IWR using oxygen has been discussed in the literature 51,73-74 and is described in the U.S. Navy Diving Manual. ...
... 49 Typical IWR oxygen-breathing protocols recommend depths no greater than 30 fsw (USN) or shallower. 73 Recommendations include a requirement that the diver not use a regular scuba mouthpiece but rather a full face mask, surface-supplied helmet breathing apparatus or regulator retention strap ("gag strap"). 75 Other requirements include the need for a tender in the water and the symptomatic diver to be tethered. ...
... 75 Other requirements include the need for a tender in the water and the symptomatic diver to be tethered. 73 IWR is not recommended or may cause harm in the setting of isolated hearing loss, vertigo, respiratory distress, airway compromise, altered consciousness, extreme anxiety, hypothermia and hemodynamic instability. ...
... Divers with neurological symptoms suggesting AGE should be considered for recompression. A hyperbaric chamber may not be available, and as such in-water recompression has been used in the past (54,55). ...
Breath-hold divers, also known as freedivers, are at risk of specific injuries that are unique from those of surface swimmers and compressed air divers. Using peer-reviewed scientific research and expert opinion, we created a guide for medical providers managing breath-hold diving injuries in the field. Hypoxia induced by prolonged apnea and increased oxygen uptake can result in an impaired mental state that can manifest as involuntary movements or full loss of consciousness. Negative pressure barotrauma secondary to airspace collapse can lead to edema and/or hemorrhage. Positive pressure barotrauma secondary to overexpansion of airspaces can result in gas embolism or air entry into tissues and organs. Inert gas loading into tissues from prolonged deep dives or repetitive shallow dives with short surface intervals can lead to decompression sickness. Inert gas narcosis at depth is commonly described as an altered state similar to that experienced by compressed air divers. Asymptomatic cardiac arrhythmias are common during apnea, normally reversing shortly after normal ventilation resumes. The methods of glossopharyngeal breathing (insufflation and exsufflation) can add to the risk of pulmonary overinflation barotrauma or loss of consciousness from decreased cardiac preload. This guide also includes information for medical providers who are tasked with providing medical support at an organized breath-hold diving event with a list of suggested equipment to facilitate diagnosis and treatment outside of the hospital setting.
... This approach remains controversial because of potential hazards such as hypothermia and an underwater seizure due to oxygen toxicity. However, published evidence of the efficacy of short, shallow recompression (at approximately 10 m), administered very early, 73 and experience from the 2018 Thailand cave rescue, showing that careful management and use of a full-face mask can protect the airway if a diver becomes unconscious, 74 have provided the basis for qualified endorsement of in-water recompression with the use of oxygen by divers with appropriate equipment and training. 64 In consideration of the natural history of mild decompression sickness, 75 a consensus has developed that some mild cases can be adequately treated with the use of surface oxygen and fluids, without recompression, particularly if evacuation for recompression is impractical or dangerous (Fig. 1). ...
Decompression sickness, in which bubbles formed from dis-olved gas (usually nitrogen) cause tissue and vascular injury after a reducion in environmental pressure, may occur in diving, aviation, and spaceflight. Arterial gas embolism, in which bubbles introduced into the arterial circulation cause multifocal ischemia, may occur after diving-related, iatrogenic, or accidental pulmonary barotrauma or by direct iatrogenic introduction of gas into the vasculature. Because it may be difficult to clinically differentiate decompression sickness from arterial gas embolism in divers and the treatment protocols for the two disorders are the same, the term “decompression illness” is sometimes used to indicate the presence of decompression sickness, arterial gas embolism, or both, but the separate terms are used here. Divers with nonspecific symptoms may present to clinicians who have received no specific training during medical school or residency in dealing with these disorders, which can pose challenges in the differential diagnosis and choice of appropriate treatment.
Guidelines for the pre-hospital management of decompression illness (DCI) had not been formally revised since the 2004 Divers Alert Network/Undersea and Hyperbaric Medical Society workshop held in Sydney, entitled "Management of mild or marginal decompression illness in remote locations". A contemporary review was initiated by the Diver's Alert Network and undertaken by a multinational committee with members from Australasia, the USA and Europe. The process began with literature reviews by designated committee members on: the diagnosis of DCI; first aid strategies for DCI; remote triage of possible DCI victims by diving medicine experts; evacuation of DCI victims; effect of delay to recompression in DCI; pitfalls in management when DCI victims present at hospitals without diving medicine expertise and in-water recompression. This was followed by presentation of those reviews at a dedicated workshop at the 2017 UHMS Annual Meeting, discussion by registrants at that workshop and finally several committee meetings to formulate statements addressing points considered of prime importance to the management of DCI in the field. The committee placed particular emphasis on resolving controversies around the definition of "mild DCI" arising over 12 years of practical application of the 2004 workshop's findings, and on the controversial issue of in-water recompression. The guideline statements are promulgated in this paper. The full workshop proceedings are in preparation for publication.
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.
This first-ever validation trial of a probabilistic decompression algorithm was conducted from 1991-92. A real time computer algorithm updated subjects' optimal decompression schedule within a numerical specification of the acceptable risk of decompression sickness (DCS). Long dives (majority over 6 hours) were chosen for testing because of operational needs and under-representation in the calibration data set: long repetitive air dives and multi-level dives - with air throughout, or with 0.7 ATA O2 during shallow transits or during the final decompression. Non-acclimatized divers wearing wet suits were immersed, chilled, and performed moderate exercise on the bottom but rested during decompression. A total of 730 dives resulted in 36 DCS cases, and another 20 cases with marginal symptoms. A subset (158 dives) were performed with the Combat Swimmer Multi-level Dive procedure, demonstrating greater safety when shallow transits were taken at 15 than at 30 feet of seawater. Overall the model was a predictive success: on none of the profiles were observed DCS incidence outside statistical uncertainty, and optimal model parameters were not greatly changed by the addition of the trial data. The real time algorithm is reliable enough for general Navy use.
This study was designed to examine the influence of short delay to recompression and other risk factors associated with the development of severe neurological decompression sickness (DCS) in military divers.
Fifty-nine divers with DCS treated in less than 6 hours from onset of symptoms to hyperbaric recompression were included retrospectively. Diving parameters, symptom latency and recompression delay were analysed. Clinical symptoms were evaluated for both the acute event and one month later.
Median delay to hyperbaric treatment was 35 min (2-350 min). Resolution was incomplete after one month in 25.4 % of divers with DCS. Multivariate analysis demonstrated that severe symptoms, classified as sensory and motor deficits or the presence of bladder dysfunction, were predictors of poor recovery with adjusted odds ratios (OR) of 4.1 (1.12 to 14.92) and 9.99 (1.5 to 66.34) respectively. There was a relationship between a longer delay to treatment and incomplete recovery, but the increased risk appeared negligible with an adjusted OR of 1.01 (1-1.02).
Our results suggest that neurological severity upon occurrence is the main independent risk factor associated with a poor outcome in military divers with DCS. Clinical recovery was not dramatically improved in this series when recompression treatment was performed promptly.
Rebreathers are routinely used by military divers, which lead to specific diving injuries. At present, there are no published epidemiologic data in this field of study.
Diving disorders with rebreathers used in the French army were retrospectively analyzed since 1979 using military and medical reports.
One hundred and fifty-three accidents have been reported, with an estimated incidence rate of 1 event per 3,500 to 4,000 dives. Gas toxicities were the main disorders (68%). Loss of consciousness was present in 54 cases, but only 3 lethal drowning were recorded. Decompression sicknesses (13%) were exclusively observed using 30 and 40% nitrox mixtures for depth greater than 35 msw. Eleven cases of immersion pulmonary edema were also noted.
Gas toxicities are frequently encountered by French military divers using rebreathers, but the very low incidence of fatalities over 30 years can be explained by the strict application of safety diving procedures.
This study aims to determine the potential risk factors associated with the development of severe diving-related spinal cord decompression sickness (DCS).
Two hundred and seventy nine injured recreational divers (42 ± 12 years; 53 women) presenting symptoms of spinal cord DCS were retrospectively included from seven hyperbaric centers in France and Belgium. Diving information, symptom latency after surfacing, time interval between symptom onset and hyperbaric treatment were studied. The initial severity of spinal cord DCS was rated with the Boussuges severity score, and the presence of sequelae was evaluated at 1 month. Initial recompression treatment at 2.8 ATA with 100% oxygen breathing or deeper recompression up to 4 or 6 ATA with nitrogen or helium-oxygen breathing mixture were also recorded.
Twenty six percent of DCS had incomplete resolution after 1 month. Multivariate analysis revealed several independent factors associated with a bad recovery: age ≥ 42 [OR 1.04 (1-1.07)], depth ≥ 39 m [OR 1.04 (1-1.07)], bladder dysfunction [OR 3.8 (1.3-11.15)], persistence or worsening of clinical symptoms before recompression [OR 2.07 (1.23-3.48)], and a Boussuges severity score >7 [OR 1.16 (1.03-1.31)]. However, the time to recompression and the choice of initial hyperbaric procedure did not significantly influence recovery after statistical adjustment.
Clinical symptoms of spinal cord DCS and their initial course before admission to the hyperbaric center should be considered as major prognostic factors in recovery. A new severity score is proposed to optimize the initial clinical evaluation for spinal cord DCS.
It is unknown if the benefits of rapid treatment always outweigh the risks of emergency evacuation for recreational divers. To investigate current triage practice, we reviewed a three-year consecutive series of evacuations and analyzed the relationship of evacuation completion time (EvCT) to outcome in the decompression illness (DCI) cases.
Checkbox-keyword searches of calls to Divers Alert Network (DAN) between 4/06 and 2/09 identified cases for review.
Of 24,275 calls, 107 were evacuations. Median EvCT, (defined as time from injury to arrival at treatment facility) was 20 hours (mean +/- SD, 27.3 +/- 27.2). Indications were: DCI 56% (60), medical illness 28% (30) or trauma 16% (17). Twenty-five percent of medically indicated evacuations were for pre-existing conditions. One-third of all DCI air evacuations (17 of 51) were for mild cases (pain or tingling only). EvCT and presentation severity were not significant predictors of DCI outcome; however, early data (< 6 hours) was sparse.
More data are needed assess the benefits of faster evacuations. However, in real-world scenarios with EvCTs in the 20-hour range, time did not influence outcome. Risk-benefit analysis of emergency transport is advised, especially for mild cases of DCI with a low probability of symptom progression.
Diving conditions, dive profiles, vascular bubbles, and symptoms of decompression sickness (DCS) in a group of Galapagos commercial divers are described. They harvest sea cucumbers from small boats with surface supplied air (hookah). Dive profiles for 12 divers were recorded using dive loggers, and bubble formation was measured in the pulmonary artery. DCS symptoms were assessed by interview. A total of 380 immersions were recorded over a nine day period. The divers did on average 6.3 immersions per day, in a yo-yo pattern. Mean overall depth was 34.5 FSW. Maximum recorded depth was 107 FSW. Average bottom time per day per diver was 175 minutes. 82 % of all ascents exceeded the recommended maximum ascent rate of 30 FSW/ min. High bubble grades were observed on six occasions, but the test was unreliable. Muscle and joint pain was reported on five occasions, in three different divers. Symptoms were typically managed by analgesics, in-water recompression or not at all. The divers were extremely reluctant to seek professional help for DCS symptoms, mostly due to the high costs of treatment. We conclude that the fishermen dive beyond standard no-decompression limits, and that DCS symptoms are common.
Re-circulating underwater breathing apparatus (rebreathers) have become increasingly popular amongst sport divers. In comparison to open-circuit scuba, rebreathers are complex life support equipment that incorporates many inherent failure modes and potential for human error. This individually or in combination can lead to an inappropriate breathing gas. Analysis of rebreather diving incidents suggests that inappropriate breathing gas is the most prevalent disabling agent. This can result in spontaneous loss of consciousness (LoC), water aspiration and drowning. Protecting the airway by maintaining the diver/ rebreather oral interface may delay water aspiration following LoC underwater; the possibility of a successful rescue is, thus, increased. One means of protecting the airway following LoC underwater is the use of a full-face mask (FFM). However, such masks are complex and expensive; therefore, they have not been widely adopted by the sport diving community. An alternative to the FFM used extensively throughout the global military diving community is the mouthpiece retaining strap (MRS). A recent study documented 54 LoC events in military rebreather diving with only three consequent drownings; all divers were reported to be using a MRS. Even allowing for the concomitant use of a tethered diving partner system in most cases, the low number of fatalities in this large series is circumstantially supportive of the efficacy of the MRS. Despite drowning featuring as a final common pathway in the vast majority of rebreather fatalities, the MRS has not been widely adopted by the sport rebreather diving community. © 2016, South Pacific Underwater Medicine Society. All rights reserved.
Pearl diving in Australian waters began towards the end of 19th Century. Over the years the current mode of diving has evolved.1 This paper traces the modifications to diving from drifting vessels (drift diving) which have led to the current practise in pearl diving in Broome.
Pearl divers are a unique diving group. It remains a fairly hazardous occupation, but much less so than in the past. A survey covering four seasons (1988-91) of pearl diving has been conducted. In 1991 decompression sickness (DCS) was the dominant medical disorder (45%), followed by ear problems in 15%, salt water aspiration in 10% and others less than 10% each. The decompression profiles are discussed in relation to the DCS incidence. Decompression and treatment experience with oxygen is described, and the relevance of this to diving physiology is noted.
The initial observations in the 19th century of DCS in compressed air workers and divers revealed a disease that could cause severe neurological injury and death, but would often surprisingly resolve spontaneously. The standard of care for this illness today includes recompression with oxygen. For diving injuries occurring in scuba divers or air crew there are presently no convincing data indicating the superiority of any table compared with USN Table 6 or its equivalent. Recompression is a highly effective treatment in most cases if applied shortly after the onset of symptoms. Therefore there is (fortunately) opportunity to monitor the natural course of this illness. However, in keeping with the 19th century experience, it is frequently observed that, when severe instances of DCI do not respond to recompression therapy, the prognosis several weeks or months later is often good. Unlike traumatic spinal cord injury, in which improvements are usually small, the cord is often tolerant to injury of similar severity due to gas bubbles. The obvious combinations of treatment pressure, time and breathing gas composition have been examined, at least anecdotally. Further advances in the treatment of decompression illness are unlikely to occur through new table development, but rather mechanisms by which more prompt recompression can be administered and new adjunctive resuscitative measures.
Many fisherman divers in Vietnam suffer from decompression sickness (DCS) causing joint pain, severe neurological deficit or even death. The objective of this pilot study was to evaluate the effectiveness of a training programme to prevent DCS and also treat DCS using the method of in-water recompression (IWR).
63 divers were interviewed and trained over a period of 3 years from 2009. Fifty one per cent of all trained divers were reinterviewed in 2011-2012 to collect mortality and morbidity data as well as information on changes in diving practices.
Since 2009, most fisherman divers have changed their practices by reducing bottom time or depth. Mortality was reduced and the incidence of severe neurological DCS decreased by 75%. Twenty four cases of DCS were treated by IWR. Ten cases of joint pain were treated with IWR using air, affording immediate relief in all cases. Out of 10 cases of neurological DCS, 4/4 recovered completely after IWR with oxygen whereas only 2/6 subjects recovered immediately after IWR with air. In addition, 3/4 further cases of DCS treated with IWR using oxygen immediately recovered.
Our results suggest that IWR is effective for severe neurological DCS in remote fishing communities, especially with oxygen.
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Chapter 185. Human Papillomavirus Infections.
The treatment of divers for decompression illness (DCI) in Auckland, New Zealand, has not been described since 1996, and subsequent trends in patient numbers and demographics are unmeasured.
This was a retrospective audit of DCI cases requiring recompression in Auckland between 01 January 1996 and 31 December 2012. Data describing patient demographics, dive characteristics, presentation of DCI and outcomes were extracted from case notes and facility databases. Trends in annual case numbers were evaluated using Spearman's correlation coefficients (ρ) and compared with trends in entry-level diver certifications. Trends in patient demographics and delay between diving and recompression were evaluated using regression analyses.
There were 520 DCI cases. Annual caseload decreased over the study period (ρ = 0.813, P < 0.0001) as did entry level diving certifications in New Zealand (ρ = 0.962, P < 0.0001). Mean diver age was 33.6 (95% confidence limits (CI) 32.7 to 34.5) years and age increased (P < 0.0001) over the study period. Median (range) delay to recompression was 2.06 (95% CI 0.02 to 23.6) days, and delay declined over the study period (P = 0.005).
Numbers of DCI cases recompressed in Auckland have declined significantly over the last 17 years. The most plausible explanation is declining diving activity but improvements in diving safety cannot be excluded. The delay between diving and recompression has reduced.
Technical divers use gases other than air and advanced equipment configurations to conduct dives that are deeper and/or longer than typical recreational air dives. The use of oxygen-nitrogen (nitrox) mixes with oxygen fractions higher than air results in longer no-decompression limits for shallow diving, and faster decompression from deeper dives. For depths beyond the air-diving range, technical divers mix helium, a light non-narcotic gas, with nitrogen and oxygen to produce 'trimix'. These blends are tailored to the depth of intended use with a fraction of oxygen calculated to produce an inspired oxygen partial pressure unlikely to cause cerebral oxygen toxicity and a nitrogen fraction calculated to produce a tolerable degree of nitrogen narcosis. A typical deep technical dive will involve the use of trimix at the target depth with changes to gases containing more oxygen and less inert gas during the decompression. Open-circuit scuba may be used to carry and utilise such gases, but this is very wasteful of expensive helium. There is increasing use of closed-circuit 'rebreather' devices. These recycle expired gas and potentially limit gas consumption to a small amount of inert gas to maintain the volume of the breathing circuit during descent and the amount of oxygen metabolised by the diver. This paper reviews the basic approach to planning and execution of dives using these methods to better inform physicians of the physical demands and risks.
The Diving Committee of the Undersea and Hyperbaric Medical Society has reviewed available evidence in relation to the medical aspects of rescuing a submerged unresponsive compressed-gas diver. The rescue process has been subdivided into three phases, and relevant questions have been addressed as follows. Phase 1, preparation for ascent: If the regulator is out of the mouth, should it be replaced? If the diver is in the tonic or clonic phase of a seizure, should the ascent be delayed until the clonic phase has subsided? Are there any special considerations for rescuing rebreather divers? Phase 2, retrieval to the surface: What is a "safe" ascent rate? If the rescuer has a decompression obligation, should they take the victim to the surface? If the regulator is in the mouth and the victim is breathing, does this change the ascent procedures? If the regulator is in the mouth, the victim is breathing, and the victim has a decompression obligation, does this change the ascent procedures? Is it necessary to hold the victim's head in a particular position? Is it necessary to press on the victim's chest to ensure exhalation? Are there any special considerations for rescuing rebreather divers? Phase 3, procedure at the surface: Is it possible to make an assessment of breathing in the water? Can effective rescue breaths be delivered in the water? What is the likelihood of persistent circulation after respiratory arrest? Does the recent advocacy for "compression-only resuscitation" suggest that rescue breaths should not be administered to a non-breathing diver? What rules should guide the relative priority of in-water rescue breaths over accessing surface support where definitive CPR can be started? A "best practice" decision tree for submerged diver rescue has been proposed.
The purpose of this report is to provide access to experimental laboratory data involving human decompression exposure that have not been published and thus are not presently available for analysis by Navy and other researchers. As such, this is only a report of the date, not a write-up of the experiment. This project was designed to evaluate the decompression sickness risk in no-decompression dives breathing air, heliox, and nitrox mixtures.
In a review of the most recent 50 consecutive cases of acute decompression sickness in US Navy divers undergoing training at the Naval School, Diving and Salvage, in no instance was recompression following the initial treatment necessary, nor was there any permanent morbidity post-treatment. Factors common to this series are 1) strict physical screening and conditioning; 2) physician and diver awareness of the signs and symptoms of decompression sickness; 3) short surface interval between symptom onset and recompression; 4) aggressive diagnostic and therapeutic use of hyperbaric oxygenation, and 5) judicious use of adjunctive measures such as intravenous fluid and dexamethasone (Decadron). In the ideal management, the physician sees the patient shortly after symptom appears. As soon as central nervous system involvement appears, 100% oxygen by mask is administered and the patient is recompressed supine to 60 feet of sea water.
The effectiveness of the U.S. Navy (USN) Diving Manual treatment algorithm in treating pain-only decompression sickness (DCS) was analyzed. Treatment logs from the Naval Diving and Salvage Training Center and the Navy Experimental Diving Unit during the decade 1976-1986 were examined. Two hundred and ninety-two cases diagnosed initially as pain-only DCS were identified. Using the treatment algorithm, 208 cases were completed on USN Treatment Table 5 (TT-5), and 84 cases completed on USN Treatment Table 6 (TT-6). Recurrence of symptoms was 4.3% after TT-5, and 3.6% following TT-6. Difference in rate of recurrence was not statistically significant between treatment tables. Overall, the success rate for following the USN treatment algorithm was 95.9%. These data support the use of the shorter TT-5 in accordance with the Navy treatment algorithm.
Twenty years of treatment records were searched for cases of serious decompression sickness (DCS). Spinal cord DCS was the most common presentation. The efficacy of various treatment tables were compared. Oxygen tables were found to be as effective as long air tables in treating cases presenting within 12 h of the onset of symptoms and were superior for cases presenting later. Using RN 61 (USN 5) to treat serious decompression sickness resulted in a high post-treatment relapse rate. Other inappropriate practices such as in-water air treatment and nontreatment of spontaneously recovering cases resulted in a high incidence of deterioration or relapse.
Central nervous system oxygen toxicity is currently the limiting factor in underwater swimming/diving operations using closed-circuit oxygen equipment. A dive series was conducted at the Navy Experimental Diving Unit in Panama City, FL, to determine whether these limits can be safely extended and also to evaluate the feasibility of making excursions to increased depth after a previous transit at a shallower depth for various lengths of time. A total of 465 man-dives were conducted on 14 different experimental profiles. In all, 33 episodes of oxygen toxicity were encountered, including 2 convulsions. Symptoms were classified as probable, definite, or convulsion. Findings were as follows: symptom classification is a useful tool in evaluating symptoms of oxygen toxicity; safe exposure limits should generally be adjusted only as a result of definite symptoms or convulsions; the following single-depth dive limits are proposed: 20 fsw (6.1 msw)--240 min, 25 fsw (7.6 msw)--240 min, 30 fsw (9.1 msw)--80 min, 35 fsw (10.7 msw)--25 min, 40 fsw (12.2 msw)--15 min, 50 fsw (15.2 msw)--10 min; a pre-exposure of up to 4 h at 20 fsw causes only a slight increase in the probability of an oxygen toxicity symptom on subsequent downward excursions; a pre-exposure depth of 25 fsw will have a more adverse effect on subsequent excursions than will 20 fsw; a return to 20 fsw for periods of 95-110 min seems to provide an adequate recovery period from an earlier excursion and enables a second excursion to be taken without additional hazard; nausea was the most commonly noted symptom of oxygen toxicity, followed by muscle twitching and dizziness; dives on which oxygen toxicity episodes were noted had a more rapid rate of core temperature cooling than dives without toxicity episodes; several divers who had passed the U.S. Navy Oxygen Tolerance Test were observed to be reproducibly more susceptible to oxygen toxicity than the other experimental divers.
The Urak Lawoi, part of the Sea Gypsies of Thailand, have been diving using surface-supplied compressed air for more than 30 years. Their dive sites range from one hour to several days from their villages. Similar to other indigenous fisherman divers, the Urak Lawoi suffer from a high incidence of decompression illness. Their methods of in-water recompression were investigated.
In December 1998, available divers in two Urak Lawoi villages were asked if they had ever been treated using in-water recompression following decompression illness. If the divers responded positively, a questionnaire-based interview was carried out. Divers were asked to recall the cause of the accident, their diving patterns of the day, the parts of the body affected, the depths and times of in-water recompression and whether the problems were resolved as a direct result of this action.
Eleven divers, aged 19-52, were interviewed. Causal factors listed by the divers included diving pattern 55% (6/11), rapid ascent 27% (3/11), and equipment failure 18% (2/11). Divers were recompressed in water using surface-supplied compressed air. The time between surfacing from the accident-related dive and being put back in the water ranged from immediately to 60 minutes. Depth and duration of in-water recompression ranged from 4 to 30 meters and 5 to 120 minutes. Outcomes reported by the divers were: improved or resolved at depth with no return of symptoms at surface in 64% (7/11), improved or resolved at depth with a return of symptoms at surface in 18 (2/11), and not resolved at depth in 18% (2/11).
Health-care workers in the villages may be able to provide basic first aid but, for some villages, a medical doctor may be as much as 10 hours away and a recompression facility as far as 16 hours in good weathier. In-water recompression has, within the diving population, proved to be an appropriate first-aid measure for decompression illness. A future project activity will develop consensus guidelines for determining under what circumstances in-water recompression using surface-supplied air should be carried out and identify appropriate methods that the Urak Lawoi can apply.
Most cases of decompression sickness (DCS) in the U.S. are treated with hyperbaric oxygen using U.S. Navy Treatment Tables 5 and 6, although detailed analysis shows that those tables were based on limited data. We reviewed the development of these protocols and offer an alternative treatment table more suitable for monoplace chambers that has proven effective in the treatment of DCS in patients presenting to our facility.
We reviewed the outcomes for 140 cases of DCS in civilian divers treated with the shorter tables at our facility from January 1983 through December 2002.
Onset of symptoms averaged 9.3 h after surfacing. At presentation, 44% of the patients demonstrated mental aberration. The average delay from onset of symptoms to treatment was 93.5 h; median delay was 48 h. Complete recovery in the total group of 140 patients was 87%. When 30 patients with low probability of DCS were excluded, the recovery rate was 98%. All patients with cerebral symptoms recovered. Patients with the highest severity scores showed a high rate of complete recovery (97.5%).
Short oxygen treatment tables as originally described by Hart are effective in the treatment of DCS, even with long delays to definitive recompression that often occur among civilian divers presenting to a major Divers Alert Network referral center.
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