United States Naval Flight Surgeon Handbook
2nd Edition 1998

Management Of Decompression Sickness

References:

• U.S. Naval Flight Surgeons Manual

• U.S. Navy Diving Manual (NAVSEA 0994-LP-001-9010 rev.3)

24 Hour Points of Contact:

• Experimental Diving Unit, Panama City, FL
  DSN: 436-4351 Com: (850) 234-4351
  

• Naval Medical Research Institute (NMRI) Bethesda, MD
  DSN: 295-1839/5875 Com: (306) 295-1839/5875

General
Aviation DCS may occur in flight in unpressurized or depressurized aircraft, altitude chamber operations and high altitude high opening parachute operations. DCS does not generally occur with exposure to altitudes below 18,000 feet. Aviators are generally protected from DCS by maintaining cabin altitudes at lower levels by cabin pressurization, by use of pressure suits, by pre-oxygenation to reduce total body nitrogen or a combination of these measures. Currently, the largest numbers of DCS cases seen in Naval Aviation operations involve low pressure chamber activities at the rate of about 1 case per 1000 chamber exposures.

Effects of bubble formation
There are two pathophysiologic effects attributed to the formation of nitrogen bubbles with altitude exposure (or upon decompression from diving):

• A direct mechanical effect of the bubble in distortion of tissue or in vascular obstruction, causing pain, ischemia, infarction or dysfunction.
  

• Tissue-bubble interface activity resulting in denaturation of proteins, platelet aggregation and other biochemical mechanisms causing tissue damage and release of pain mediating substances.

Because these bubbles may form at different locations, there may be multifocal lesions without necessarily following dermatomal or anatomic distributions.

Once bubbles are formed, they expand as dissolved gases continue to come out of solution. Carbon dioxide is highly diffusible and contributes to bubble enlargement, especially if formed in excess by vigorous exercise. For this reason, DCS patients should be kept at rest.

Clinical syndromes of DCS

Type I DCS

Limb pain (musculoskeletal symptoms)

The most common presenting symptom, accounting for 60-70% of altitude related cases and 80-90% of diving cases. Pain usually begins gradually and is poorly localized, but increases in intensity and localizes with time as a throbbing ache. Guarding may be seen. If the painful area is accessible, inflation of a blood pressure cuff over the site may relieve the pain and help distinguish it from pain of ischemia or nerve entrapment which would be made worse by such pressure. Sharp, shooting or encircling pain, migratory pain and tingling or burning trunk pains arise from CNS involvement and should be considered Type II DCS and treated accordingly.

Cutaneous bends

The skin is often affected during and after the decompression event. There are two distinct manifestations; The most common symptom is a transient, multifocal itching, often associated with a scarlatiniform rash, and is not an indication of development of serious sequelae. Itching or crawling sensations usually occur in hyperbaric chamber dives and do not require recompression as a rule. Cutis Marmorata results from venous obstruction and vasospasm and presents as confluent rings of pallor, surrounded by areas of cyanosis which blanche to the touch. This may be the harbinger of more serious forms of DCS and should be treated by recompression.

Lymphatic bends

Rare. Recompression usually provides prompt relief of pain, but swelling of lymphatic tissue may persist after treatment.

Type II DCS
The most severe form of DCS, and may present as neurological, cardiorespiratory or inner ear symptoms, pain or shock. There may be concurrent Type I symptoms in 30-40% of cases. About 10-15 of all altitude DCS cases will be type II.

Early Type II DCS symptoms may seem inconsequential. Fatigue is a very common and early symptom, progressing to weakness, dyscoordination and other difficulties. Many symptoms of Type II DCS are the same as those of arterial gas embolism (AGE), although AGE presents very early, usually within 10 minutes after exposure. Treatment of AGE is also appropriate for DCS.

Unexplained fatigue

This should always alert the examiner to the possibility of DCS.

Neurological symptoms

These may occur at any level of the CNS. There may be paresthesias, numbness or weakness. Symptoms are usually mild and confined to one extremity.

Spinal cord DCS may present with numbness, weakness and paralysis or urinary dysfunction, and occurs in about 10% of Type II altitude DCS cases.

Cerebral DCS is the most common of Type II DCS. Fatigue is a very common symptom. There may be confusion, odd behavior and personality changes. Headache, tremor, hemiplegia, hemisensory losses and scotomata may also occur. These signs and symptoms may range from mild and seemingly inconsequential to fulminant and life threatening.

Inner ear DCS may mimic round or oval window rupture with vertigo, tinnitus and hearing loss.

Bilateral pain involving the trunk or hips should be considered Type II DCS.

The occurrence of any neurological symptom after a dive or flight should be considered a symptom of Type II DCS or AGE.

Cardiopulmonary symptoms

Symptoms of congestion of pulmonary circulation, the "chokes", are the result of intravascular bubbling, and account for 5-10% of altitude DCS. They are:

• burning substernal pain, worse with inspiration

• cough

• dyspnea

If not treated promptly, the result may be circulatory collapse and death.

Special considerations

Flight after diving

OPNAVINST 3710.7 prohibits flight or low pressure chamber exposure within 24 hours of a SCUBA or compressed air dive or high pressure chamber run. This may be reduced to 12 hours for urgent operational requirements provided there are no symptoms following the dive and the subject is examined and cleared by a flight surgeon.

Diving at altitude

This refers to dives at elevations, such as in mountain lakes and may be a factor in increasing risk for DCS. U.S. Navy dives above 2300 ft. MSL require CNO approval.

Other factors increasing the risk of DCS

• Prior DCS
  

• Occupation. Incidence in chamber inside observers increased.
  

• Age. 3 times higher in 40-45 year old group than 19-25.
  

• Sex. Females 2 times as likely, and may relate to menses as well.
  

• Exercise. Individuals undergoing exposures to altitudes above 18,000 ft. should avoid strenuous activities for 12 hours before and 3-6 hrs. after exposure.
  

• Injuries
  

• Cold temperatures
  

• High body fat appears to be a factor
  

• High C0₂ environments predispose individuals due to high solubilities
  

• Hypoxia
  

• Alcohol, dehydration and fatigue may be associated
  

• Atrial septal defects have been implicated

Pulmonary overinflation syndromes

These are due to trapping of gas in the lung with ascent, producing rupture of alveoli and resulting in:

• Arterial gas embolism (AGE)

• Pneumothorax

• Mediastinal emphysema

• Subcutaneous emphysema

• Pneumopericardium (rare)

These may occur as a result of breath holding on ascent or because of localized pulmonary obstructions secondary to disease processes. Sudden changes in depth while in shallow water can be far more hazardous than equivalent depth changes in deep water. Improper ascent from just a few feet can cause POE syndromes.

Arterial gas embolism (AGE)
Produced by entry of gas emboli into the arterial circulation.

Susceptible organs are the heart and the CNS, in of which bubble emboli are responsible for life threatening symptoms.

Symptoms of AGE usually occur within a minute or two after surfacing.

Unconsciousness upon, or within 10 minutes of surfacing after breathing compressed air including HEEDS bottles must be assumed to be AGE and treated immediately.

CHARACTERISTICS OF AGE:

• Sudden, dramatic onset within seconds or minutes of surfacing

• Chest pain may be noted on ascent

• Weakness, paralysis, large areas of abnormal sensation, visual disturbances and convulsions may occur.

• Coughing of blood may be present

If symptoms of AGE are present and resolve spontaneously, they may recur later with increased severity. Therefor, symptoms of AGE should be treated promptly even if they have spontaneously resolved.

AGE vs DCS

Not always easy to distinguish the difference between the two.

AGE treatment is more lengthy than that of DCS.

If in doubt, err on the side of treatment for AGE, which is always adequate for DCS.

Treatment

General

Treatment tables are time/pressure profiles applied in recompression therapy, and bear numbers which have been assigned as they were developed and so do not necessarily follow a logical sequence. You should be familiar with treatment tables 5,6,6A,4 and 7.

Two basic types of treatment tables:

• AIR. Breathing air mixtures only. Since nitrogen is present and being absorbed, the benefit is from the compression only. Lengthy tables and gradual ascents are required.
  

• 100% 0₂. Helps in wash out of nitrogen as well as prevention of further absorption. This permits a more rapid ascent and therefore shorter tables and less risk. Short, air breathing breaks are included in the tables to prevent oxygen toxicity.

Treatment table 5
For Type I DCS only - 2 hrs. 15 min. total time

Pressure is at 60 FSW (ft. sea water) for 2 oxygen periods, gradual ascent to 30 FSW, and 1 period at this depth.

Treatment table 6

For Type I DCS which fails to respond with relief of pain within 10 minutes on TT-5.
For Type II DCS (except inner ear DCS) 4 hrs 45 min. total time.

Similar to TT-5 except that times at 60 FSW and 30 FSW are increased if clinically indicated. Extensions of 2 periods at 60 FSW and 2 periods at 30 FSW may be used if indicated.

Treatment table 6A

For treatment of:

• AGE

• Inner ear DCS

This is like a TT-6 except that the patient is taken to 165 FSW for 30 min. on air to compress intra-arterial bubbles maximally. At this depth, oxygen cannot be used because of toxicity. After this period of deep recompression, the patient is brought slowly to 60 FSW and treatment follows a TT-6 with oxygen.

Treatment table 4

Used for serious cases in which symptoms are refractory to treatment at the 60 FSW level, requiring further compression to 165 FSW for longer periods. This table takes 38 hrs. 11 min. because of the extended time at depth and resultant nitrogen saturation. (Unable to use oxygen until return to 60 FSW)

Treatment table 7

For life threatening DCS unresponsive to treatment. Maximizes the 60 FSW treatment time. This is at least 12 hrs at 60 FSW. Very gradual ascent over 36 hrs. There is no limit on the time at 60 FSW.

Other indications for hyperbaric therapy

• Cyanide or carbon monoxide poisoning

• Smoke inhalation

• Gas gangrene

• Iatrogenic gas embolism

• All other non-diving indications require prior approval of BUMED.

Triage and referral of altitude DCS cases

Type I DCS

If symptoms appear at altitude and resolve on descent, use 100% 0₂ for two hrs and observe for recurrence. If none, light duty only and ground for 1 week. Warn the patient to return promptly if symptoms recur for hyperbaric therapy.

If symptoms develop at altitude and persist, or develop after flight, place the patient on 100% 0₂ while arranging evacuation or recompression. If evacuation is delayed and symptoms resolve, leave on oxygen for 24 hrs. Then, place the patient on limited duty for 1 week, and no physical training for 72 hrs. Recurrence must be treated by hyperbaric therapy.

Current U. S. Navy diving medicine protocols are to treat all patients referred for altitude DCS regardless of whether or not symptoms have resolved.

Type II DCS

All must be recompressed urgently or evacuated promptly for treatment.

Aeromedical evacuation of DCS cases

• Contact receiving facility prior to transport
  

• Medevac aircraft should be pressurized to altitudes of 500 ft. or less.
  

• Place patient on 100% 0₂
  

• Place patient in supine position (unless unconscious) , neutral head position and uncrossed extremities for transport.
  

• Do not allow patient to sleep in order to monitor mental status.
  

• IV of N.S. or Ringers Lactate.
  

• Inflatable cuffs should be filled with WATER rather than air.
  

• Dexamethasone is controversial, but may be given 10 mg. IV if indicated.

Aeromedical disposition

• Type I patients grounded 1 week.
  

• Type II patients grounded 1 month.
  

• Flight surgeon should conduct a fitness to continue exam.
  

• Gas embolism should be worked up for pulmonary bullae and other causes of pulmonary overinflation syndrome and cardiac work up for septal defects.
  

• Persistent neurologic sequelae of DCS or AGE are disqualifying.
  

• Type II DCS or recurrent Type I DCS is disqualifying, but designated personnel may be considered for waiver.
  

• Single Type I DCS is disqualifying but may be considered for waiver in designated and non-designated personnel.
  

• Waiver requests are forwarded to NAMI code 42 for consideration by the Hyperbaric Medicine Committee.

United States Naval Flight Surgeon Handbook: 2nd Edition 1998

The Society of U.S. Naval Flight Surgeons