Medscape Orthopaedics & Sports Medicine eJournal 1(5), 1997. © 1997 Medscape Portals, Inc
DCS, AGE, and all of their presentations are grouped together under the heading "decompression illness" (DCI). Treatment consists of recompression in a chamber using air or a combination of helium-oxygen. Bubbles may form in blood vessels, where they may cause ischemia and infarct, and in tissues, where they may initiate an inflammatory response. Inflammatory changes can lead to extravasation into the tissues, further compromising the circulation and resulting in edema.
Hyperbaric exposures (situations where there are elevated pressures) can occur during construction and tunneling projects, in hyperbaric oxygen treatment facilities and in aviation. (The airman is subject to the same problem as divers, except that the situation is reversed--bubbles form on ascent, due to a decrease in pressure and supersaturation. Returning to the ground increases pressure and is analogous to recompression. However, DCS symptoms may occur after returning to the ground and sometimes require additional recompression.)
Recreational scuba diving is the most common type of hyperbaric exposure, especially since the explosive growth of sports scuba (self-contained underwater breathing apparatus) diving in the past decade. Hyperbaric oxygen (HBO) treatment is gaining popularity as the definitive therapy for a growing number of disorders, including decompression sickness, AGE, CO poisoning, clostridial infections, crush injuries, diabetic leg ulcers, skin graft failures, refractory osteomyelitis, thermal burns, necrotizing soft tissue infections, and osteoradionecrosis.
It is incumbent on physicians to be fully conversant with the diagnosis and treatment of decompression illness, especially because the hyperbaric chamber is now widely recognized as effective in reversing the sometimes-deadly changes that take place with DCI.
Some people provide aspirin, 600 mg, for its anti-platelet effects; this modality is debatable because of the possibility of associated spinal cord hemorrhage. Lidocaine has been shown to be protective in animal models but has not been studied adequately in humans.
Transportation. Ascending to an altitude greater than 1000 feet should be avoided. Sea level aircraft that are acceptable for transportation include the military C9, the Cessna Citation and the Lear Jet. Commercial aircraft fly at 5000 to 8000 feet cabin pressure. The "ABCs" initiated at the dive site should be continued while in transport.
Treatment in the chamber. The treatment of choice for decompression illness, whether DCS or AGE, is recompression in a multiplace, hands-on chamber. It should have the capability of locking personnel and equipment in or out with trained attendants available for critical care monitoring.
Multiplace chambers. These units (Fig. 1) can accommodate between 2 to 18 patients, depending upon configuration and size. They incorporate a minimum pressure capability of 6 atmospheres absolute. Patients are accompanied by hyperbaric staff members, who may enter and exit the chamber during therapy via an adjacent access lock or compartment. The multiplace chamber is compressed on air and patients are provided with oxygen via an individualized internal delivery system. A dedicated compressor package and high volume receivers provide the chamber's air supply.
Advantages include constant patient attendance and evaluation (particularly useful in treating evolving diseases such as decompression sickness), and multiple patients treated per session; disadvantages include high capitalization and staffing costs, large space requirements and risk of decompression sickness in the attending staff.
Figure 1. Multiplace chambers accommodate between 2-18 patients, depending upon configuration and size. They have a pressure capability of 6 atmospheres absolute. Reprinted from Hyperbaric Medicine, Brooks Airforce Base.
The multiplace chamber is not always possible, however, and the monoplace chamber is sometimes the only alternative. Hart and coworkers, as well as Kindwall and colleagues have developed protocols with the monoplace chamber, utilizing Navy Treatment Table 6 (Table I) which can be used with air breaks.
Monoplace chambers. These units (Fig. 2), first introduced in the 1960s are designed for single occupancy. They are constructed of acrylic, have a pressure capability of 3 atmospheres absolute and are compressed with 100% oxygen. Recent technical innovations have allowed critically-ill patients to undergo therapy in the monoplace chamber. The high flow oxygen requirement is supplied via the hospital's existing liquid oxygen system.
Figure 2. Recent technical innovations have allowed critically-ill patients to undergo therapy in the monoplace chamber. Monoplace chambers are designed for single occupancy. They have a pressure capability of 3 atmospheres absolute and are compressed with 100% oxygen. Reprinted from Hyperbaric Chambers Systems & Management.
Treatment goals in all instances are to reduce bubble size and surface area while providing hyperbaric oxygenation (HBO). HBO reduces edema, blocks WBC adherence, protects and preserves the microcirculation, corrects hypoxia (100% oxygen under pressure produces 7 volume % in the plasma), blocks reperfusion injury, and facilitates the removal of dissolved gas from the lungs through perfusion.
Outcome. The most recent DAN (Divers Alert Network) report (1994 data) suggests that complete resolution of symptoms occurred in only 56% of cases while 28% of divers had neurologic sequelae and 17% continued to experience pain. Travel after treatment of DCS should be delayed for at least 48 hours; 72 hours for arterial gas embolism. Recurrence of symptoms has occurred with flying more than one week after the initial event. Diving should not be resumed if there is any residual neurological damage.
60† 20 O2§ 0:20‡ 60 5 Air 0:25 60 20 O2 0:45 60 5 Air 0:50 60 20 O2 1:10 60 5 Air 1:15 60 to 30 30 O2 1:45 30 15 Air 2:00 30 60 O2 3:00 30 15 Air 3:15 30 60 O2 4:15 30 to 0 30 O2 4:45
* Treatment of Type II or Type I decompression sickness when symptoms are not relieved within 10 minutes at 60 feet. † Descent rate--25 ft/min. Ascent rate--1 ft/min. Do not compensate for slower ascent rates. Compensate for faster rates by halting the ascent. ‡ Time at 60 feet begins on arrival at 60 feet. § If oxygen must be interrupted because of adverse reaction, allow 15 minutes after the reaction has entirely subsided and resume schedule at point of interruption. ¥ Caregiver breathes air throughout unless he has had a hyperbaric exposure within the past 12 hours, in which case he breathes oxygen at 30 feet. ¶ Extensions to Table 6: Table 6 can be lengthened up to 2 additional 25 minute oxygen breathing periods at 60 feet (20 minutes on oxygen and 5 minutes on air) or up to 2 additional 75 minute oxygen breathing periods at 30 feet (15 minutes on air and 60 minutes on oxygen) or both. If Table 6 is extended only once at either 60 or 30 feet, the tender breathes oxygen during the ascent from 30 feet to the surface. If more than one extension is done, the caregiver begins oxygen breathing for the last hour at 30 feet during ascent to the surface. Adapted from the US Navy Diving Manual.
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