Decompression Sickness Treatment & Management

Updated: Mar 05, 2019
  • Author: Stephen A Pulley, DO, MS, FACOEP; Chief Editor: Joe Alcock, MD, MS  more...
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Treatment

Prehospital Care

Extricate the patient from the water. Immobilize if trauma is suspected.

Generally, in-water recompression (IWR) is not believed to be a safe option. Problems with air supply, hypothermia, potential oxygen toxicity with seizure, dehydration, and the uncontrolled environment make it less than ideal and increase the risks of drowning. [141] However, in remote areas without reasonable-distance hyperbaric oxygen (HBO) chamber support, this may be the only option.

Studies exist of indigenous native fishermen divers. In Thailand, home to the diving Urak Lawoi fishermen, 72.1% exceed the no-decompression limits, yet medical treatment and HBO facilities are distant (10 h and 16 h, respectively). In this population, one third reported having experienced decompression sickness (DCS). [142, 143, 144] In Yucatan, Mexico, an alarming incidence of DCS is present. [145] There is a similar population in Vietnam. [146] The economic drive for valuable ocean species, coupled with the nature of their remote location, along with general education, conspire to create high rates of DCS. Education (see Prevention) and IWR have been shown to be appropriate first-aid measures. Much more research needs to be performed on the concept of IWR, as over half of the Urak Lawoi (not just one third) were classified as experiencing recurring nondisabling DCS and about one quarter as having disabling DCS. [142, 143, 144] A shorter IWR protocol is also in use in the remote Northern Pacific Clipperton Atoll in an attempt to address the above concerns. [141] IWR has been used successfully in the fishing population in Vietnam. Better outcomes were obtained when the recompression was done with oxygen instead of air. [146] IWR is probably not for the extremes in DCS. Mild type I DCS will probably improve with 100% oxygen and rehydration. Type II DCS with disabling signs would make IWR too risky. [147]

A consensus statement from Divers Alert Network (DAN) and the Undersea and Hyperbaric Medical Society (UHMS) addresses the concept of IWR. They recognize that many diving activities occur in remote areas that lack the resources for an HBO therapy and are distant from appropriate facilities. In the case of significant or progressive symptoms, IWR may be a reasonable emergent alternative to avoid delays, sometimes many hours, but with the need for specific training, equipment, and protocols. [33] The requirements are as follows:

  • Enough properly trained personnel that understand the protocol [141, 146, 147, 148] and principles, in addition to the risks: In addition to the patient, this would include a continuous dive buddy and a surface supervisor at a minimum.
  • Certification in the use of 100% oxygen for diving emergencies
  • Adequate thermal protection, enough 100% oxygen, a writing board for communication, and a means for maintaining a constant depth (no deeper than 30 ft [9 m]).
  • Either a full-facemask or a mouthpiece-retaining device: The concept here is that if the DCS diver were to have a seizure, due to oxygen toxicity or the DCS, or lose consciousness for another reason, he or she would still receive the oxygen without risk of aspiration while the dive buddy starts the ascent to the surface. Two available products are the Dräger or rEvo, safety mouthpieces with retaining head straps. [149] The former may not be in production anymore.
  • Restriction on the use of technical specialty gases: Only use 100% oxygen. [148]
  • Diving medicine specialist consultation: Seek out a diving medicine specialist as soon as is possible for consultation.

Administer 100% oxygen, intubate if necessary, and intravenously administer isotonic crystalloid (saline or lactated Ringer solution).

The use of first aid oxygen has proven so beneficial that the DAN has made a major effort to place oxygen at dive locations, in particular those that are remote with lengthy transport times to the nearest hyperbaric chambers and to ensure that people are trained in its use. A study of the use of first aid oxygen found that the median time to its use after surfacing was 4 hours and 2.2 hours after the onset of DCS symptoms. Forty-seven percent of victims received the oxygen. Complete relief of symptoms occurred in 14% of victims. Even more striking was that 51% of victims showed improvement. This was with the oxygen before HBO treatment. Even after a single HBO treatment, those that had received oxygen before the HBO dive, even if many hours earlier, had better outcomes. [150] The consensus statement from DAN/UHMS highlights the importance of 100% normobaric (not HBO) treatment by trained individuals as an important first aid measure. They also mention that if there is a limitation in supply (due to a prolonged transport), less than 100% can be used with the intent being to continue some oxygen therapy throughout the transport until reaching definitive medical care. [33]

Many divers dehydrate for a number of reasons delineated earlier in this article. Oral rehydration can be appropriate if not contraindicated. These fluids are ideally isotonic but can be regular drinking water. Carbonation, caffeine, and alcohol are to be avoided. If oral fluids are contraindicated, administer isotonic crystalloid intravenous fluids for rehydration until urinary output is 1-2 mL/kg/h. Avoid intravenous dextrose solutions. Rehydration improves circulation and perfusion. It also decreases postdive venous gas emboli formation. [33]

Aspirin is commonly considered and given in diving accidents for its antiplatelet activity if the patient is not bleeding or allergic. However, there are no current data to support this practice. [151] The nitrogen bubbles interact with platelets, leading to adhesion and activation, which is thought to contribute to microvenous obstruction and resultant ischemia in DCS; however, no studies or trials of the effect or benefit of aspirin on this process have been conducted. Giving aspirin could increase bleeding, especially in severe DCS. [152, 153, 154] Other drugs that have been used in DCS have insufficient clinical evidence. These include nitroglycerine, corticosteroids, lidocaine, and pentoxifylline. [33]

Thus far, there is no substantive data showing a benefit for other adjunctive treatments, such as recompression with helium/oxygen, and in the past, NSAIDs. [155] However, a benefit has been found for NSAID use in conjunction with HBO therapy. [33]

Perform cardiopulmonary resuscitation and advanced cardiac life support, if required, as well as needle decompression of the chest, or abdomen, if indicated.

Do not put the patient into the Trendelenburg position. Placing the patient in a head-down posture used to be a standard treatment of diving injuries to prevent cerebral gas embolization. Avoid this practice. [33] The process actually increases intracranial pressure and exacerbates injury to the blood-brain barrier. [156] It also wastes time and complicates movement of the patient.

Transport to the nearest emergency department and hyperbaric facility, if feasible, and try to keep all diving gear with the diver. Diving gear may provide clues as to why the diver had trouble (eg, faulty air regulator, hose leak, carbon monoxide contamination of compressed air).

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Emergency Department Care

Administer 100% oxygen to wash nitrogen out of the lungs and set up an increased diffusion gradient to increase nitrogen offloading from the body.

Do not put the patient into the Trendelenburg position. Placing the patient in a head-down posture used to be a standard treatment of diving injuries to prevent cerebral gas embolization. Avoid this practice. [33] The process actually increases intracranial pressure and exacerbates injury to the blood-brain barrier. [156] It also wastes time and complicates movement of the patient.

Perform intubation and aggressive resuscitation including advanced cardiac and trauma life support. Be alert for the potential of tension pneumothorax and perform needle decompression followed by chest tube thoracostomy, if indicated. Also be aware of the potential for pneumoperitoneum from ruptured viscus. The air collection can be so great as to interfere with hemodynamics. Emergent needle decompression of the peritoneum is the corrective procedure.

Many divers dehydrate for a number of reasons delineated earlier in this article. Oral rehydration can be appropriate if not contraindicated. These fluids are ideally isotonic but can be regular drinking water. Carbonation, caffeine, and alcohol are to be avoided. If oral fluids are contraindicated, administer isotonic crystalloid intravenous fluids for rehydration until urinary output is 1-2 mL/kg/h. Avoid intravenous dextrose solutions. Rehydration improves circulation and perfusion. It also decreases postdive venous gas emboli formation. [33]

Aspirin is commonly considered and given in diving accidents for its antiplatelet activity if the patient is not bleeding, or allergic However, there are no current data to support this practice. [151] The nitrogen bubbles interact with platelets, leading to adhesion and activation, which is thought to contribute to microvenous obstruction and resultant ischemia in DCS; however, no studies or trials of the effect or benefit of aspirin on this process have been conducted. Giving aspirin could increase bleeding, especially in severe DCS. [152, 153, 154] Other drugs that have been used in DCS have insufficient clinical evidence. These include nitroglycerine, corticosteroids, lidocaine, and pentoxifylline. [33]

Treat the patient for nausea, vomiting, pain, and headache.

Contact the closest hyperbaric facility (or DAN for referral) to arrange transfer and try to keep all diving gear with the diver. The diving gear may provide clues as to why the diver had trouble (eg, faulty air regulator, hose leak, carbon monoxide contamination of the compressed air).

Patients with type I or mild type II DCS can dramatically improve and have complete symptom resolution. This improvement should not dissuade the practitioner from HBO referral or transfer, as relapses have occurred with worse outcomes.

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Consultations

Diving medicine and HBO specialists

Symptoms temporally related to diving should necessitate a consultation with a diving medicine or HBO specialist to determine if symptoms are related to diving and if HBO therapy is appropriate. Before contacting the specialist, ideally, complete a detailed neurological examination. However, this is not always possible if the patient is not with a physician. Also, detailed information about the dive and symptoms should be readily at hand for discussion. Those engaged in scuba diving should have the means (communication equipment) and the contact information for the regional diving medicine specialists and HBO centers, in addition to the DAN contact numbers. They should also know how to access the local emergency medical systems and should know their capabilities. Early involvement of a specialist in diving medicine can confirm, allay, or heighten concerns related to symptoms post diving. They can also direct emergency therapy and decrease time to definitive treatment. [33]

An increasing number of divers have significant medical issues. Many acquired them as they have aged. Surveys of health issues in divers found a group with significant health problems. Forty-nine percent had consulted a diving medicine specialist. Twenty-three percent modified their diving to decrease risk. [78, 157]

Divers Alert Network

Divers Alert Network is an excellent resource, especially if local support is not available. While their emergency contact numbers are below, visit their Web site at International DAN or IDAN for the full contact information. Use of this service is similar to use of a poison control center. DAN maintains a database of diving-related injuries and provides consultation services, including extent-of-injury assessment, recommendations for management, and referral to HBO therapy or local diving medicine specialists. Emergency contact 24 hours per day can be reached at the following numbers:

  • DAN World[wide] Emergency Number: +1-919-684-9111 (accepts collect calls)
  • DAN America Emergencies: +1-919-684-9111 (accepts collect calls); nonemergency: +1-919-684-2948
  • DAN Brasil Emergencies: +1-919-684-9111 (accepts collect calls); in Brasil:  0800 684 9111
  • DAN Europe Emergencies: +39-06-4211-8685; nonemergency: +39-085-893-0333
  • DAN Southern Africa Emergencies: 0800-020-111 (within South Africa); +27-828-10-60-10 (outside South Africa, accepts collect calls); nonemergency: 0860-242-242 (within South Africa), +27-11-266-4900 (outside South Africa)
  • DAN Japan Emergencies: +81-3-3812-4999; nonemergency: +81-45-228-3066
  • DES Australia: 1-800-088-200 (toll free within Australia—English only); +61-8-8212-9242 (from outside Australia—English only)
  • DES New Zealand: 0800-4DES-111 (within New Zealand—English only)
  • Korean Hotline: 055-549-0912 (Korean and English)
  • China: +852-3611-7326

Note: Numbers do change from time to time. See https://www.diversalertnetwork.org/contact/international.asp for the latest list.

HBO treatment

Again, acute DCS is a purely clinical diagnosis that requires a fair amount of clinical suspicion. When the slightest suspicion or possibility is noted, timely transfer with 100% FIO 2 oxygen for HBO should be pursued. [34] Accessing consultation as discussed above is advised if any confusion or concerns are noted.

Patients with mild type I decompression sickness (DCS) probably do not require treatment other than breathing pure 100% FIO2 oxygen and hydration. However, as discussed with regard to inner-ear DCS (IEDCS) and cutis marmorata, there are newer theories that they are more serious and they should be considered for HBO therapy. Divers with type I DCS symptoms do, however, require observation for 24 hours, as symptoms may portend the onset of more serious problems requiring hyperbaric recompression. Consult a diving medicine or HBO specialist for all diving-related injuries. The only effective treatment for gas embolism is recompression; other treatments are merely for symptoms. [33]

Several types of hyperbaric chambers exist, ranging from small monoplace (single person) chambers to complex multiple place, multiple lockout chambers large enough for multiple patients and attendants. All chambers have the ability to maintain critical care monitoring and mechanical ventilation. A major difference with the size of chambers clinically is that some patients experience claustrophobia with the small monoplace chambers. Increased oxygen toxicity issues have been reported with the monoplace chambers because the entire environment is oxygenated, whereas, with the larger chambers, patients breathe the oxygen via mask, but the ambient environment is not supplementally oxygenated. In addition, the ability of attendants to be in with the patient allows for resuscitation or other intensive treatment in the sickest of patients. The number of hyperbaric chambers across the United States has increased rapidly as HBO therapy has extended to treat is many clinical entities ranging from wound care to multiple sclerosis. However, of 361 chambers contacted and interviewed nationwide, only 43 were judged to have the equipment and staff to treat high-acuity patients. This was thought to be an inadequate number for the United States. [158]

The basic theory behind HBO therapy is to repressurize the patient to simulate a depth where the bubbles from nitrogen or air are redissolved into the body tissues and fluids. Then, by breathing intermittently higher concentrations of oxygen, a larger diffusion gradient is established. The patient is taken slowly back to surface atmospheric pressure. This allows gases to diffuse gradually out of the lungs and body. The addition of helium to oxygen has been shown to yield an advantage over oxygen alone even in severe neurologic DCS or treatment-refractory DCS. [159, 160]

Treatment tables govern the exact combination of timing and depths. Developed primarily by the US Navy, there were some minor modifications by the US Air Force. Treatment Table 6 is most commonly used for initial treatment. Follow-up treatments followed Treatment Table 5. The US Navy introduced Treatment Table 9 in 1999 for follow-up treatment in incomplete resolution of DCS. Both Tables 6 and 5 start at a depth of 60 ft (18 m). In contrast, Table 9 starts at 45 ft (13.5 m). The advantage of Table 9 is that there is less risk of oxygen toxicity as the patients are breathing 100% oxygen. This decreases the risk to not only the patient, but the chamber attendant, if there is one. [161] However, more detail concerning the tables are beyond the scope of this article. While most improve with a single HBO treatment, 38.5% have relapses, half of those within 24 hours. Observation for 24 hours is strongly recommended after HBO treatment. [162] Another study reported complete resolution of symptoms in 49% with the first treatment and an additional 26.5% with additional treatments. However, 24.5% had long-term residual symptoms. [163] In Israel, 48% had complete recovery with HBO, while another 48% had partial recovery. Unfortunately, 4% did not respond to the therapy. [164] Yet, HBO effectiveness rates as high as 99% have been reported. [32] Of 103 patients (75% male), 53 (51%) had complete relief (with 28 only requiring one treatment), 45 (44%) had partial relief, and 5 (5%) had no relief of symptoms. [165]

Delay to treatment has long been felt to yield worse outcomes. Studies that are more recent conflict with that traditional thinking. In one study, a longer delay to treatment was related to incomplete recovery but the increased risk appeared negligible. [166] In another, delays in treatment of longer than 17 hours could not be correlated with increased number of HBO treatments or worse outcome in DCS. [167] Instead, the severity of the neurologic dysfunction and rapid onset of symptoms after surfacing were the main factors in predicting the severity of DCS and the resistance to treatment with worse outcomes. [32, 34, 166] In Israel, they specifically looked at delayed recompression defined as greater than 48 hours. They found no significant difference in outcome between early and delayed treatment groups. Complete recovery occurred in 78% versus 76%, respectively; partial recovery occurred in 15.6% versus 17.1%, respectively; and no improvement occurred in 6.2% versus 6.6%, respectively. [168]

Traditionally, the treatment protocols were staged, meaning that time would be spent at certain depths as the individual was "brought back to the surface." Recent studies suggest that a linear approach is more effective than the staged approach. Other variations on the tables are being researched to try to find shorter-term approaches. In addition, use of combination gases, such as Trimix, are being looked at in the same regard. Another mentioned adjunct to HBO includes negative-pressure breathing.

An interesting area of research relates to the use of intravenous perfluorocarbon (PFC) emulsions. [169, 170] PFCs are synthetic liquids made up of carbon and fluorine that has the ability to dissolve significant amounts of gases especially oxygen. As they are hydrophobic, they have to be emulsified in order to use them intravenously in water based organism such as humans. This is being studied as a temporary blood substitute in numerous clinical settings. [171] It is being studied in the setting of the treatment of DCS in conjunction with HBO therapy.

One such PFC, trade name Oxycyte, provides protection and improves outcomes in spinal DCS at 5 mL/kg IV. Improved oxygenation is the presumed mechanism. [172, 173, 174] PFCs appear to decrease DCS symptoms through a combination of decreasing bubble formation, hemodynamic protection against gas embolism, enhanced oxygen delivery to tissues, and increased pulmonary nitrogen washout (this last effect is hypothesized but not shown). [175, 176] There was concern for decreased platelet counts as both decompression and PFCs appeared to cause that decrease. Oxycyte PFC was not found to affect platelets or clotting or bleeding. [177] The positive effects of PFCs are further enhanced by oxygen prebreathing (before HBO treatment) with increased oxygen delivery. [178] A swine study found no benefit, but also no harm, in using HBO treatment. [179]

With early recognition and treatment, more than 75% of patients improve. Even with significant delays in recognition and treatment, positive results are obtained. [180, 181] Studies of the Miskito Indians of Central America highlight this. They are diving seafood harvesters who dive repeatedly without consideration for diving tables or profiles. They have a high prevalence of the bends and neurologic DCS that affects the thoracolumbar spine in particular. Despite very high rates of DCS, and sometimes days delays in HBO treatment (if sought at all), HBO treatment yields positive results, with 30% regaining strength and many more ambulating. However, HBO treatment is usually only sought for significant neurologic symptoms, while painful DCS, such as the bends, is usually treated with only analgesia. [182, 183]

Differentiating inner ear barotrauma or dysbarism from inner ear labyrinthine or alternobaric vertigo is difficult. The difference is that dysbarism responds well to treatment, and inner ear DCS is less responsive and is associated with a higher frequency of permanent damage. Patients with inner ear DCS may be asymptomatic after treatment yet still have vestibular problems at detailed testing. Therefore, consider both conditions in the differential diagnosis, and treat the patient for both. One recommendation is to perform immediate tympanocentesis and then to follow with HBO therapy. IEDCS is less responsive to HBO treatment than is DCS affecting other sites. Incomplete recovery has been reported in 68% of those receiving HBO therapy. [46] HBO typically results in significant improvement in severe neurologic DCS if it is identified early and the patient is rapidly transported to an HBO facility.

Rapid treatment is also crucial in the face of arterial gas embolization (AGE). Those with AGE who reach recompression within 5 minutes have a death rate of only 5%. This rapid treatment also results in little morbidity. However, when AGE recompression delays 5 hours, the mortality rate approaches 10%. More than 50% of the survivors experience residual signs.

Transfer to a hyperbaric facility is strongly advised. An important issue is timely transport of the patient to the closest hyperbaric facility. Frequently, this is accomplished by land transport, although air transportation is occasionally required. The effort is to minimize the transport time. Helicopter transport requires the pilot to maintain an altitude of less than 500 ft (152 m) above the departure point (which could be more than 500 ft [152 m] above sea level depending on the dive location). [33, 184] This can be difficult when there are mountains to traverse in flight. In this situation, explore options other than rotary-wing transportation to the closest chamber. Another potential issue is bubble creation due to the vibration of the helicopter. [185] Fixed-wing transport should be limited to aircraft that can maintain cabin pressure at normal surface pressure of 1 atm (eg, Lear Jet, Cessna Citation, and military C-130 Hercules).

Those involved in diving activities, especially in remote areas, should arrive with a plan, including contact information, for evacuation if it were to become necessary. These types of evacuations, if there are no local HBO facilities, can be excessively expensive. Thus, part of the planning could be a consideration of commercial insurance.

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Prevention

Key to preventing decompression sickness (DCS) is exercising conservatism in the diving profile and always putting safety first. Education is key in this regard. In Vietnam, severe DCS in fishermen divers was decreased by 75%, and mortality also dropped, after a concerted educational effort. [146] This is important as there are real human and economic costs regarding DCS in fishermen divers. During a 3-year period in Yucatan, Mexico, 282 divers received treatment for DCS. The total societal economic impact was $1.6 million (US). [186] Even with education and a conservative approach, DCS can still occur. The total amount of saturated nitrogen at one time was thought to be the primary determinant of an individual's risk of developing DCS. Thus, the diving tables reflected close attention to the time spent at depths and surface intervals for repetitive dives. Further research and thought suggests that the rate of ascent from depths may be a more critical factor. [109, 110]

Early diving instruction recommended a rate of ascent no faster than 60 ft (18 m) per minute. The more recent recommendation was to ascend no faster than 30 ft (10 m) per minute and to make a 3- to 5-minute safety stop at 15-20 ft (4.6-6 m). [187, 188] Therefore, the time of ascent was increased for a 60-ft dive from 1 minute to a maximum of 7 minutes.

Doppler bubble research has revealed that the release of bubbles from tissues is a critical factor in the development of DCS. The tissues that appear to saturate the fastest are in the spinal cord, with maximum saturation occurring in as few as 12 minutes. Desaturation, or off gassing, is much slower. Thus, even a no-decompression dive at 60 ft (20 m) for 20 minutes maximally saturates spinal tissues. As mentioned earlier, spinal cord is tissue most commonly affected in type II DCS.

Even the slower 7-minute ascent to reach the surface from a 60-ft (20 m) dive still leaves a sizable amount of dissolved nitrogen in the faster-saturating spinal tissues. The remaining nitrogen can then bubble even on this slower ascent.

According to DAN, data from a European study revealed that increasing this ascent time to 18 minutes eliminated the dangerous bubbles. Therefore, one would need one or more additional stops at deeper level(s) to lengthen ascent time adequately and thus protect against DCS. Research has shown that a safety stop of 2.5-5 minutes at 50 ft (15 m) in addition to another stop at 20 ft (6 m) for 3-5 minutes decreases venous bubble formation at least for a no-decompression dive of 82 ft (25 m). The supposition here is that this can decrease the risk of DCS. [188] Obviously, this requires that more of the air reserve is allotted for the ascent. In addition, premeasured, weighted ropes attached to the diving platform for the set safety stops can help maintain the desired depth and prevent drifting away from the surface vessel. Adding scuba tanks at each safety level is prudent in case diver air supplies reach a critical level.

Breathing 100% fraction of inspired oxygen (FIO2) oxygen during the decompression stops may help prevent DCS. [189] One should consider the partial pressure of oxygen at the decompression stop depth to prevent toxicity. Being active during the decompression stops may also decrease the likelihood of bubble formation. [190, 191, 192]

Close attention to adequate hydration before and immediately after a dive may also have protective effects. See Pathophysiology for discussion of the mechanism. In an individual with normally functioning kidneys, the frequency of urination and the concentration color of the urine are easy indicators of whether sufficient fluids are being taken in. A long time between urinating and a deep color are signs of inadequate intake. Note that these fluids should not be caffeinated and should be alcohol free.

The culture of diving, at least in military naval diving, may have some impact on prevention of diving accidents. The two most common causes of naval diving accidents, or near misses, were leadership failures and decreased situational awareness. These came into play when the overall risk was underestimated and the time was not closely monitored. In addition, the need for junior divers to ask questions was rebuffed by the posture of the senior divers not being interested in providing answers. [193] While this was found in the US Navy, correlations could be considered in the average dive situation, namely daily dive charters. A lack of leadership, in the form of a dive master, and the generally isolated situation of a number of divers not knowing each other, could lead to the same overall environment.

When an air bubble expands within a normally air-containing structure such as ears, sinuses, lungs, and GI system, a problem emerges. Another issue is when nitrogen that is saturated in tissues and blood expands with decreasing pressure. Normally, it returns to the lungs and is exhaled. It does not have any other ready exit to the outside. When the bubbles occur, they cannot be exhaled from the lungs.  They can interfere with blood flow directly causing ischemia, or their expansion in tissues causes dysfunction of those tissues. If in a sensory nerve‒containing area, such as the synovium of the joints, they can cause pain. This causes DCS. However, another mechanism is also at work. That is the interaction between the bubbles and the normal blood clotting system. The interface causes clot formation and inflammation, which further increases ischemia and dysfunction.

To this point, the major way to avoid this bubbling has been through conservative diving using tables or computers based on the experiences of fit military divers. By staying within the table parameters, it was hoped that excessive tissue nitrogen saturation could be avoided so that it would not come out of solution as bubbles on ascent. Computer models are being validated that may lead to more accurate determination of these tables. [194] The next step in the process to avoid DCS was to ascend slowly. The recommended ascent rate has decreased steadily, as mentioned above, to the point where the recommendation is to stop ascent at decompression stops to allow the exhalation of nitrogen gas, rather than it bubbling in the blood.

Despite these measures, individuals with similar body types and diving the same profiles resulted in some getting DCS and others not. The hope is that further research will decrease the risk and incidence of DCS.

Predive

The gas nuclei and nitrogen interface appear to be key in better prevention strategies regarding DCS. In particular, the protection appears to relate to the interplay of nitric oxide and nitric oxide synthase. A progression of studies from rats to trained, fit, military divers and now in experienced recreational divers is showing that inhibiting nitric oxide synthase increases the number and sizes of bubbles. Administration of a nitric oxide donor decreases the number and size of bubbles. [195] This effect occurred with a long-acting agent at 20 hours and 30 minutes before the dive.

More recently, a short-acting nitric oxide donor, the common sublingual medication nitroglycerin (0.4 mg), administered 30 minutes prior to a dive, was found to provide this same level of protection by decreasing bubble formation. [196] Because it is arginine and oxygen that are converted by nitric oxide synthetase to nitric oxide, one might surmise that taking the common L-arginine amino acid would help drive the equation to nitric oxide. Caution is advised as this has not been studied in this realm. In relation to erectile dysfunction, nitric oxide plays a role in erection. Apparently, significant improvement has not been found and it is hypothesized that some other mechanism prevents it. [171]

Toxic effects of oxygen under pressure have also been studied. Oxidation and free radicals may also be important instigating factors. It causes vasoconstriction, which causes ischemia, activation of the inflammation cascade, and subsequent damage to the vascular endothelium. Antioxidants, maintaining normal hemostasis, and preventing inflammatory responses may help stop the DCS process from starting. [197] After a DCS neurologic injury, many (about 30%) have incomplete recovery despite appropriate management. Inflammatory changes are believed to be at least part of the reason. There has been study of several substances in this realm, and preliminary data suggest that they may be useful. Fluoxetine, a common antidepressant medication in the serotonin-specific reuptake inhibitor (SSRI) class, has been found to decrease the incidence of DCS and improve motor function recovery by the limiting the inflammatory process. [198] It is thought to be safe in diving, as well as protective against DCS. [199] Based on rat models, it decreases inflammation through cytokine interleukin 10 suppression. [200] Ascorbic acid 2 g daily for 6 days before a dive decreased neutrophil activation and microparticle generation. [15] Simvastatin has been found to decrease the incidence of DCS in a rat population through its anti-inflammatory properties. [201] Again, the reader is cautioned about taking any substance with the end goal of decreasing DCS until more advanced studies are completed and the individual has discussed their use with a physician well versed in diving medicine.

Another significant event has been the discovery of the positive benefit of a period of aerobic exercise at around 80% of maximal oxygen uptake in humans and 85-90% in rats. [202] The timing of this exercise appears to be key. A period of exercise of 90 minutes in rats and 40 minutes in humans timed at 20 hours and 24 hours before the dive, was found to have significant long-lasting effects on the number and size of nitrogen bubble formation. [202, 203, 204, 205] When the same exercise is completed at 2 hours and 30 minutes prior to the dive, the results are less clear. In some groups, a benefit was noted; in others, no benefit was noted. [206, 207] The exercise at 24 or 2 hours predive appears to affect bubble formation as it has no effect on enhancing nitrogen washout. [208] It also did not decrease the median number of circulating venous gas emboli. [209]

In one study, there was demonstration that the positive effect of the exercise the day before was eliminated by a second period of exercise prior to the dive. It is not the overall level of fitness, but rather the timing of the exercise that provided the protection. This level of protection appears to be similar to that offered by the nitric oxide donor. [210, 211] The next step is to see exactly what biochemical effects the exercise causes. Nitric oxide appears to be the protective agent in the predive exercise. [64]

Regular exercise, physical conditioning, and diving also appear to have a protective effect against bubble formation and DCS. [212] In addition, a single HBO treatment 18 hours before a dive protected swine from DCS, possibly through induction of heat shock proteins. [213]

So, the question is what should the average diver do, or not do, based on the research?

As with anything in medicine, broad recommendations can only be reached after a sufficient number of large studies show benefit. This level of evidence has not yet been reached in the diving literature. Specific medical recommendations cannot be made because the knowledge has to be applied with consideration of the individual. Consultation with a physician experienced and knowledgeable in diving medicine is strongly advised.

Clearly, the benefit of aerobic exercise the day prior to a dive is evident. For the many recreational divers who are relatively sedentary as they fly long distances to remote areas and then start diving soon after arrival, this may have important consequences.

As with any physical activity, including scuba diving, the person must be physically fit before engaging in a stressful activity. This means being aerobically and strength conditioned. This should be completed in consultation with a physician, in particular one with experience with the recreational activity.

Only take medications on the recommendation of a physician who is familiar with the patient and the patient’s health history and only after consideration of the risks and benefits of the medication. In this specialized, off-label use, a specialist in diving medicine should be the consultant. Nitroglycerin is mentioned above. Nitroglycerin has many adverse effects, such as dilation of blood vessels, lowering of blood pressure, and headaches. Others also mentioned are L-arginine, fluoxetine, ascorbic acid, and simvastatin, with the same caution advised for all.

A period of prebreathing normobaric (regular oxygen bottle) 100% FIO2 oxygen for 30 minutes was found to decrease venous bubble formation for the subsequent dive and repetitive dives afterwards with no further prebreathing. [152, 214] In swine models, prebreathing oxygen at depth for as little as 5 minutes before rapid decompression helped prevent type II DCS. When breathed for 15 or 45 minutes, it decreased type I DCS symptoms. [215] It also was found in swine models to decrease venous ischemia and osteonecrosis from DCS. [216] In a rat model, oxygen prebreathing was not found to decrease DCS, but was found to decrease inflammatory reactions, and protein infiltration, in lung tissue. [217] As with the statement about nitroglycerin above, oxygen is a medical gas and its use needs to prescribed by a physician. In addition, if oxygen were to be used at depth, the toxic effects of partial pressures of oxygen must be considered.

A study conducted on Sprague-Dawley rats using 79% helium/21% oxygen predive (helium preconditioning) also showed a benefit. There was a decrease in DCS incidence, delay in onset of DCS, decreased decompression-related neurological issues, and decreased depression of platelet counts. Administration of the helium-oxygen mixture was for 5 minutes, followed by 5 minutes on room air, then repeated for a total of 3 cycles over 30 minutes. [218]

In addition, a 30-minute predive sauna session at 65ºC (149ºF) was shown to decrease venous bubble formation, although the mechanism was not known. [219] Nowadays, the mechanism is being demystified. A heat stress of 45ºC/113ºF for 1 hour decreased nitric oxide synthetase activity. It potentiates heat stress protein (HSP)70 and decreased HSP90. Glutathione (GSH) activity was found inversely related to the nitric oxide synthetase activity. [220] The protective effects of HSP70 are believed to be related to the antioxidation and antiapoptosis. [221] It showed an effect on decreasing vascular gas emboli, along with decreasing vascular dysfunction as measured through “flow-mediated dilation.” Vibration decreased the emboli, [222] and dark chocolate only decreased the “flow-mediated dilation.” [223]

In contrast to this, being warm during the bottom portion of a dive actually increases nitrogen uptake, whereas being cool during that phase of the dive decreases uptake. On ascent, the reverse is true. Being warm on ascent increases off gassing of nitrogen, while being cool delays this process. In this modern age of dry suits and suit warmers, one might be tempted to manipulate the temperature to be cool on descent and at the bottom and warm on the ascent. One is cautioned against doing this, as being too cool at the bottom can inhibit overall functioning and being too warm on ascent can promote localized gas bubbling. [101, 102]

What to do after the dive is less clear and needs more investigation in less-fit populations. Although the research appears promising that exercise after diving does not have an adverse effect and that some benefit may exist, the research is insufficient to recommend any changes.

Postdive activity and exercise are controversial. Intense activity after a dive was believed to promote bubble formation. In small studies on trained, fit, military divers, a positive benefit has been found for mild exercise, at 30% of maximal oxygen uptake, during the 3-minute decompression stop on ascent. Other studies incorporating similar aerobic exercise, at 80% of maximal oxygen uptake, starting at 30 minutes and 40 minutes post dive, have failed to demonstrate any adverse effects on trained, fit, military divers. [192] Postdive exercise is believed to dilate intrapulmonary arteriovenous anastomoses. This allows for a mechanism of right-to-left shunt and thus arterialization of the venous gas emboli (bubbles). As a result, the incidence of DCS increases. [224]

A puzzling situation is when an individual experiences DCS when all facets of the dive appeared normal and highly conservative. This prompted a search for other possible influencing etiologies. The identification of the injured diver’s thrombotic state is a possible explanation.

A high percentage of the unexplained DCS injured divers were found to have moderate increases in total plasma homocysteine, a substance found to be implicated in the formation of atherosclerosis (hardening of the arteries), and deficiencies in folate and vitamin B-12, common nutritional substances. [225, 226] These three chemicals are easily screened for with common laboratory testing. Correction of folate and B-12 deficiencies are easily treated with vitamin supplementation. Studies suggest that the homocysteine level increase can be treated favorably with folate and vitamin B-6 supplements. Again, this should be under the advice of a physician.

Current research is aiming at fine-tuning the prevention of DCS. Transcranial, precordial, and subclavian vein Doppler examination, along with echocardiography and regular ultrasonographic imaging, have been used to detect the presence of bubbles in the vascular system of the volunteers being studied. [182, 227, 228, 229] At the same time, various HBO decompression models are being evaluated using the same studies. [230, 231] As the database expands across the full spectrum of divers (not just young, healthy divers), the tables and recommended dive profiles continue to improve. However, since people respond differently to DCS, a universal profile is unlikely to be established. For this reason, all divers should fully understand their dive profiles (especially if generated by computer) and should always be conservative and allow plenty of room for individual variation and error.

Future trends are promising. Efforts are underway to identify specific biomarkers for DCS. [232] S-100B is a sensitive biomarker being studied in brain injury in general and neurologic DCS specifically. [233] Serum procalcitonin has been suggested as a potential decompression stress biomarker. Endothelial damage is theorized to increase permeability and inflammatory cytokines, leading to the elevated levels. [234] D-dimer is a biomarker for activation of coagulation. In combination with a severity score, it improved judging of the severity in neurological DCS. [235] Lactate dehydrogenase (LDH) is a marker of cell injury that has been used in decompression research. [236]

Increased hematocrit correlates with hydration status after diving. The importance of adequate hydration has already been discussed as a risk factor in DCS. Platelet count decreases can correlate with increased platelet aggregation. This is one of the contributing causes of DCS.

Studies have identified a medication class with an adverse effect. Sildenafil, a phosphodiesterase-5 blocker, was found to promote the onset and severity of neurological DCS. [21] It is a potent smooth muscle relaxation vasodilator that is used in erectile dysfunction. Several medications are available in this class. Of note is that there are pulmonary hypertension medications also in this same class. Many divers engage in diving while on vacation, when sexual activity may increase. Many of these medications are available without a prescription in other countries. Thus, divers must be aware of the potential for this class to worsen DCS and avoid their use before diving. The half-lives of these medications range from 4 hours for sildenafil and vardenafil to 17.5 hours for tadalafil. [237] Clearance of a medication from the body requires 4-5 half-lives. Thus, the time to clear sildenafil and vardenafil would be 16-20 hours and for tadalafil it would be 70-87.5 hours, about half of a one-week vacation. Numerous common medications can prolong the effects of these medications. A diver prescribed one of these medications should discuss their use with the prescribing physician and consider consultation with a diving medicine specialist.

One study found a patent foramen ovale (PFO) or atrial septal defect (ASD) in 56% of those with DCS. [238] Closure of documented right-to-left shunt appears to prevent both symptomatic DCS and asymptomatic brain ischemia. [83, 239, 238] However, routine screening of all divers is not recommended. Also controversial is prophylactic transcatheter closure of a PFO without documented DCS. As mentioned earlier, only large PFOs appear to greatly increase the risk in diving. The complication rate for this procedure is about 1%, which is much greater than the incidence of developing serious neurologic DCS. A proper medical approach to everything is to balance risk versus benefit. In this case, the weight appears to angle more towards risk. A better approach is to screen those divers who have developed DCS of the cerebral, spinal, inner ear, and cutaneous types. Also for consideration would be divers with a history of migraine with aura and ischemic strokes (especially if younger). The screening study is agitated saline echocardiography under strict protocol, with meticulous technique and provocative maneuvers. [240, 241, 242] Those individuals found to have a PFO should then consult closely with a diving medicine specialist. It may be that using the strategies mentioned in this article in a very conservative manner is a better approach to mitigate risk than would be a recommendation for a surgical procedure. If the later procedure is chosen, the patient must be rescreened to ensure that the closure was complete. [68, 243, 244]

Delaying significant changes in altitude and resultant decreases in barometric pressure for 24 hours after the last dive had been a recommended strategy. This could include flying or ascending a mountain. Consensus guidelines from DAN in 2002 apply to jetliner cabin altitudes of 2,000-8,000 ft (610-2,438 m). Below 2,000 ft (610 m), the pressure change was thought to be inconsequential. Most commercial airlines pressurize to 8,000 ft (2,438 m). One should avoid flying within 12 hours of a single no-decompression dive. This extends to 18 hours for multiple dives either per day or over several days. There is no consensus if a dive involves decompressions stops. Obviously, it should be much more than 18 hours. If the individual develops DCS, except for travel to receive treatment (see earlier), measure the delay to flying in multiples of days. [245] However, in one study using inflight transthoracic echocardiography, 8 (14%) of 56 study participants who followed the 24-hour recommendation still had bubbles during the return flight. Therefore, a longer interval between the last dive and flying (eg, 36 h) may be more appropriate. [90]

Finally, to add to the mix of influencing factors, diet can have an adverse effect on the risk of developing DCS. Previously mentioned were specific nutritional deficiencies, including folate and vitamin B-12. Hydration status is also important. Additionally, meals high in cholesterol and triglycerides have been identified as increasing the risk for DCS. [99]

A summary of protective strategies is as follows:

  • Good aerobic conditioning through regular cardiovascular exercise
  • Exercise 24 or 2 hours prior to diving
  • Hot environmental exposure prior to diving
  • Ensure good hydration before and after the dive
  • Prebreathing 100% FIO 2 oxygen predive
  • Prebreathing sessions of 79% helium-21% oxygen
  • Using Nitrox (higher percentage of oxygen, lower nitrogen) with a maximum depth limit depending upon the exact mixture [89, 246]
  • Regular diving has a protective acclimatization effect
  • A slow ascent with more than one safety/decompression stop, with (1) breathing oxygen during decompression stops and (2) being active (but not excessive exercise) during decompression stops
  • Allow for a period of 24-36 hours after the last dive prior to flying or high-altitude ascent
  • Avoid high-fat meals prior to diving
  • Avoid alcohol the evening before, or day of, diving
  • Normal body temperature (not chilled or hyperthermic) post-diving [89]

Consider the following recommendations when there is a history of DCS:

  • The decision to continue diving must be made in consultation with a diving medicine specialist
  • If prior DCS is noted, with or without a right-to-left shunt, adopting a highly conservative dive profile greatly decreases the risk or DCS recurrence [239, 247]
  • To prevent recurrent DCS, the use of oxygen-enriched breathing mixtures may help [239] ; caution is advised related to oxygen partial pressures at depth and the potential for oxygen toxicity
  • Consider the protocols in the commercial and military disciplines related to return to diving after suffering from DCS; there are no similar recommendations for the recreational population, [248] so it is very important that those effected consult with a diving medicine specialist; especially important is full understanding of the risks and strategies to avoid recurrence.

Although there is mention of specific medications, individual recommendations cannot be made. Any medication taken related to diving should be done in consultation with a diving medicine specialist.

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Long-Term Monitoring

Do not discharge a patient with decompression sickness (DCS) from the emergency department to outpatient care. Patients can dramatically improve or have complete resolution in type I or mild type II DCS with just oxygen and rehydration. However, this improvement should not dissuade the practitioner from diving medicine or HBO specialist consultation, and referral or transfer for HBO therapy. Observe these patients for 24 hours as relapses have occurred with worse outcomes. Therefore, referral to a hyperbaric facility is strongly advised.

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