Preparation for Board Examination
Decompression Accidents: Management

Compiled and maintained
by Ernest S Campbell,MD

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Early Treatment

• Recognition *Symptoms usually appear 15 minutes to 12 hours after surfacing*

• Blotchy rash
• Paralysis or weakness
• Coughing spasms
• Staggering or instability
• Unconsciousness

• Tired feeling
• Itching
• Pain, arms, legs or trunk
• Dizziness
• Numbness, tingling or paralysis
• Chest compression or shortness of breath

• Immediate oxygen breathing, continue even if person improves markedly
• Stabilize patient the same way as for Air Embolism
• Urgent recompression after stabilization in trauma facility
• Early recompression treatment for all forms of decompression sickness

Medical Management of DCS and AGE

• Provide 100% oxygen through a tight-fitting mask. This helpsto off-gas inert gases. The oxygen will wash nitrogen out of the lungsand set up an increased diffusion gradient to increase nitrogen off-loadingfrom the body. Resuscitation equipment should be available on all diveboats and in all dive facilities. Divers should refuse to dive if thisequipment is not readily available.
• Give copious fluids as needed to maintain good urinary output.Fluids should be administered at a rate greater than 0.5ml/kg/hr--usually1 L qhr or 1 L q4hr, titrated against the hematocrit, which should be maintainedat less than 50%. The hemoconcentration associated with decompression sicknessis the result of increased vascular permeability mediated by endothelialdamage and kinin release. The fluids can be given orally if the diver isconscious--if not, give fluids by intravenous, if available. Avoid usinghypotonic fluids, such as D5W, using 0.9% saline instead. Insert a urinarycatheter if there is spinal cord DCS.
• Intubation, aggressive resuscitation and chest tube thoracostomyshould be performed, if indicated.
• Give steroids if there is neurological DCS; dexamethasone10 to 20 mg IV initially, followed by 4 mg every 6 hours; diazepam (5 to10 mg) controls the dizziness, instability and visual disturbances associatedwith labyrinthine (vestibular) damage to the inner ear.
• Seizure activity is treated with a loading dose of Dilantin.Seizures result from damage incurred from cerebral bubbles formed fromDCS or air embolism (resulting from pulmonary barotrauma); they can alsoresult from oxygen toxicity associated with the treatment schedule. Dilantin(phenytoin) is given IV at 50 mg/min for 10 minutes for the first 500 mgand then 100 mg every 30 minutes thereafter. Blood levels of Dilantinshould be monitored to maintain a therapeutic concentration of 10 to 20mcg/mL. Levels over 25 mcg/mL are toxic.
• Some people provide aspirin, 600 mg, for its anti-plateleteffects; this modality is debatable because of the possibility of associatedspinal cord hemorrhage. Lidocaine has been shown to be protective in animalmodels but has not been studied adequately in humans. Standard cardiacdoses could be used as a guide.

Attempting to treat the diver by returning him/her tothe water, (known as in-water recompression), is hazardous not only tothe diver, but to the caregivers who have to be re-subjected to pressure.This should not be attempted unless special arrangements have been madeto do so. For example, in Australia, because of the great distances andtime lags involved in reaching a recompression chamber, dive operatorshave a system of surplus air and oxygen tanks ready for in-water recompression.

See Edmonds 'In-WaterRecompression',
Otherlinks

Transportation. Ascending to an altitude greaterthan 1000 feet should be avoided. Sea level aircraft that are acceptablefor transportation include the military C9, the Cessna Citation and theLear 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. Thetreatment of choice for decompression illness, whether DCS or AGE, is recompressionin a multiplace, hands-on chamber. It should have the capability of lockingpersonnel and equipment in or out with trained attendants available forcritical care monitoring.

Multiplace chambers. These units (Fig. 1) can accommodatebetween 2 to 18 patients, depending upon configuration and size. They incorporatea minimum pressure capability of 6 atmospheres absolute. Patients are accompaniedby hyperbaric staff members, who may enter and exit the chamber duringtherapy via an adjacent access lock or compartment. The multiplace chamberis compressed on air and patients are provided with oxygen via an individualizedinternal delivery system. A dedicated compressor package and high volumereceivers provide the chamber's air supply.

Advantages include constant patient attendance and evaluation(particularly useful in treating evolving diseases such as decompressionsickness), and multiple patients treated per session; disadvantages includehigh capitalization and staffing costs, large space requirements and riskof decompression sickness in the attending staff.

Duoplace chambers include the Reneau (Proteus) and theSigma II with pressurization capabilities to 6 ATA and 3 ATA respectively.The chambers are compressed with air, and the patient breathes oxygen byan individualized internal delivery system. Advantages include constantpatient attendance, with access limited to the head and neck; disadvantagesinclude relatively high capitalization cost for single patient treatmentsand risk of decompression sickness in the attending staff.

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 monoplacechamber, utilizing Navy Treatment Table 6  which can be used withair breaks.

Monoplace chambers. These units, first introducedin the 1960s are designed for single occupancy. They are constructed ofacrylic, have a pressure capability of 3 atmospheres absolute and are compressedwith 100% oxygen. Recent technical innovations have allowed critically-illpatients to undergo therapy in the monoplace chamber. The high flow oxygenrequirement is supplied via the hospital's existing liquid oxygen system.

Advantages of this chamber include that it provides themost cost efficient delivery of hyperbaric oxygen (capitalization and operatingcosts), and that it presents essentially no risk of decompression sicknessto the attending staff. Disadvantages include relative patient isolationand increased fire hazard.

Treatment goals in all instances are to reduce bubblesize and surface area while providing hyperbaric oxygenation (HBO). HBOreduces edema, blocks WBC adherence, protects and preserves the microcirculation,corrects hypoxia (100% oxygen under pressure produces 7 volume % in theplasma), blocks reperfusion injury, and facilitates the removal of dissolvedgas from the lungs through perfusion.

Outcome. The most recent DAN (Divers Alert Network)report (1994 data) suggests that complete resolution of symptoms occurredin only 56% of cases while 28% of divers had neurologic sequelae and 17%continued to experience pain. Travel after treatment of DCS should be delayedfor at least 48 hours; 72 hours for arterial gas embolism. Recurrence ofsymptoms has occurred with flying more than one week after the initialevent. Diving should not be resumed if there is any residual neurologicaldamage.

Treatment. Decompression sickness is treated withrecompression in a chamber to 60 FSW or deeper associated with hyperbaricoxygen breathing. In the US, this therapy is usually guided by a Navy TreatmentTable. These tables are very effective, especially when recompression isbegun promptly.

The purpose of the therapy called for in the Navy TreatmentTables is two-fold: to promote inert gas elimination and to help causea decrease in bubble size. The treatment outlined by the tables also providesoxygen to the damaged tissues, treats platelet and clotting damage andallows excretion of harmful metabolites. The oxygen reduces CNS edema andprovides a high oxygen gradient (2000 mm Hg) for the ischemic tissues.

Specifics: Recompression treatment of decompressionsickness. First, it is important to take the time for a careful clinicalexam, because true Type I DCS without other manifestations is very rare,and diagnostic tests are of little value.

The initial therapy for Type I and Type II DCS is treatmentin a chamber with Navy Treatment Table 6. Table 6 indicates recompressionto 60 feet for 285 minutes, with intermittent oxygen breathing periodsand slow "ascent to the surface." (The diving tables indicate increasesin pressure with the word "descent" and decreases with "ascent." They alsogive their pressure values in depth-equivalents.) The periods of oxygenbreathing are broken up into intervals to prevent O₂ toxicity.If O₂ seizures occur, turn off the O₂ for 15 minutesand continue the treatment.

In the case of poor response to standard Navy TreatmentTables 6A or 6, Treatment Table 6 can be extended for additional oxygenbreathing periods at 60 or 30 feet. If you are following Treatment Table6A and there is no resolution or the patient is getting worse on ascent,try Treatment Table 4, which indicates staying at 165 feet for 2 hours--thengo to Table 6 at 60 feet with extensions, if necessary.

Treatment Table 7 is used for worsening or unresolvedDCS or AGE. It is a long, involved and dangerous treatment and should notbe used unless adequate support is available. If all else fails, call DiversAlert Network (DAN) at (919) 684-9111, rather than creating your own treatmenttable.

Even after "successful" treatment, some people experiencerelapse of symptoms. Recurrences are treated with Treatment Table 5 orTreatment Table 6 once or twice-daily until no further improvement is observedby the medical director of the facility. Recent evidence indicates thatpersistent neurologic defects may be lessened by repetitive treatmentson Navy Treatment Tables 5, 6 or even with 100% oxygen at 30 FSW for 90minutes bid. Flying should be avoided for a period of 72 hours after treatmentfor DCS or AGE.

Equipment which might be needed in the altered pressureenvironment includes ventilators, bubble traps and pumps for use with intravenouscatheters, endotracheal tube cuffs which inflate with water, and if chesttubes are required, the patient must be vented during descent using #18gauge 1 1/2 " needle.

Treatment of Arterial Gas Embolism

Treatment. Management is generally similar to thatof DCS--recompression and HBO are indicated in all cases as quickly aspossible.

Specifics: Recompression treatment of gas embolism.In contrast to the treatment of decompression sickness, one should notdelay for diagnostic work-up or extensive clinical evaluation. Instead,the first question is whether to use Treatment Table 6A or 6. If thereis a delay greater than 4 hours, Treatment Table 6 should be used initiallyand then proceed to 6A depending on the clinical response. Treatment Table6A allows for rapid compression to 165 feet and is used for major air embolisms.If such a chamber is not available, then one should use a 3 ATA chamber.

For those patients not responding to Navy Table 6, otherchoices are available: US Navy Table Treatment 4 or the Comex Table, whichprescribes 30 minutes breathing 50/50 O₂/N2 mix at 100 feet.Unproven treatment schedules should be avoided, but extensions to the tablesare not experimental and should be used as necessary.

Special Considerations (Difficult circumstances)

1. Diver at 165 feet (50 meters) not responding to 6A,or getting worse on decompression:

a. Continue on USN 4 (165 ft air+oxygen) for 2h at 165feet to 60 ft. and then on extended 6. (Unproven).

b. Duke oxy-nitrogen saturation (Lancet, 7/22/1978)

c. 50 % oxygen by mask while at 165 ft.
 
 

2. Patient at 60 ft. (18 m.) not responding to maximumoxygen or deteriorating on decompression.

a. Continue on air (with additional oxygen sessions) at60 ft. and decompress on saturation table. (USN 7)

b. Compress to 100 ft. (30 m.) on 50% oxygen, Comex TableCX 30.

c. 100 ft and onto the Duke regimen.
 

Other Considerations

USN 5 (for 'pain only') is no longer recommended in commercialdiving. This is due to the overlooking of serious symptoms. This is replacedby USN 6 in many schedules.

Cases from oxy-nitrogen bounce diving should be treatedas though from compressed air. Cases from oxy-nitrogen saturation divingshould be treated as oxy-helium saturation.

Residual manifestations- Table 6 daily, or CX 12 or pO21.7 bar. Continue for as long as there is subjective improvement, witha maximum of ten sessions.

Treatment of Tri-mix or oxy-helium decompression illness

Never use compressed air tables

1. Bounce diving, onset at surface: Table 6 using oxy-heliumin place of air. Continue down to depth of significant relief with chamberpO2 0.4 bar. If a blow up, consider recompression to 3 bar greater thandepth of the dive. Use oxygen rich oxy-helium (pO2 1.5 to 2.5 bar) mixturesby mask intermittently at depth for 2 hours. Decompress without an initialupward excursion but on a saturation table.

2. Bounce diving - onset during decompression: Immediatecompression to depth of relief or full depth of the dive, if necessary.Otherwise treat as in 1. above.

3. After downward excursion in saturation diving - Compressto depth of relief, possibly depth of excursion but not less than threebar. Remain at treatment depth at least 2 hours, or 24 hours if needed.Use saturation decompression with no upward excursion.

4. Onset during saturation decompression - Compress slowlyto depth of relief but by not more than 2 bar (for pain) or 3 bar (forserious) deeper than depth of onset. Remain 2 hours to 6 hours wit up to6 intermittent periods of breathing oxygen rich mixtures for 20 minuteseach.

The condition of the patient should determine the rateof decompression.

References:

DecompressionProblems
DecompressionSickness: Definition and Early Management
Diving Accident Management
FirstAid for Diving Accidents Requiring Immediate Transport

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