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Annex 1:

Practical Preventive Measures and Treatment of DCS in High Altitude Glider Flying above 22000 ft/6000 m


Glider pilots, who fly above 20 000 ft / 6000 m must understand the basic principles of Henry’s Gas Law in order to be prepared to counter and treat DECOMPRESSION SICKNESS (DCS). - Reviewing the latest literature in ASMA Journal, Vol. 69, April 1998 (Aviation Space and Environmental Medicine), some new scientific articles were presented on DCS, also called "Divers Sickness". They highlight some valuable points worth considering, as follows:

  1.     Nitrogen bubble formation in the human body is generated through hypobaric pressure; as a rough rule above 1/2 of the original permanent pressure. This is e.g. if 1 Atmosphere at sea-level with 29,92 inch / 760 mm Hg is reduced to 14,96 inch / 380 mm Hg at an altitude of 18 000 ft / 5500 m . (This is to compare with the generation of CO2 bubbles, when a bottle of carbonated water is opened.- "Hypobaric" pressure is below atmospheric pressure and allows air bubbles to be released from the blood serum.)
  2.     The formation of gas bubbles is dependent of ascent rate, time at altitude and De-Nitrogenisation before the climb with 100% oxygen. (For example: One half atmosphere is reached in 18000 ft / 5500 m, or diving in water from 33 ft / 10 m to sea-level.)
  3.     Scientifically there are great interpersonal differences and situational variations, which contribute, like age, weight, muscle activity, recurrence of ascent, time at altitude or other individual predispositions.
  4.     Scientific knowledge is still under consideration, as many problems are still not completely understood and solved (space suits, space travel). Nevertheless, several empirical limits and insights have to be followed to prevent possible disastrous health consequences!
  5.     It is possible to be killed through DCS!
  6.     DCS in glider flying is a new subject. The professional aviation world knows how to deal with DCS, but it wasn't considered to be a problem in the glider world. In 1994 LTC Bob Weien, MD, FS USARMY discussed the first time high altitude glider flight and DCS risk. Symptoms were reported regularly, but not identified as DCS. -Scientifically Glider Flying DCS is a new problem.
  7.     The scientific barrier for DCS Symptoms without pre-breathing oxygen and with a climb of 5000 ft per minute / 25 m per second is 21000 ft / 6300 m.
  8.     Above this altitude about 5% of pilots without a pressurized cabin will experience DCS Symptoms (which are muscular, skeletal, pulmonary, and minor or major neurological symptoms). Most pilots below this won’t experience any symptoms at all.
  9.     In case of pre-breathing 100% oxygen, depending also on the time flown at lower altitude, the barrier goes up. The longer 100% oxygen is administered on the ground, the higher you can go without DCS.
  10.     The two main DCS symptoms must be differentiated as follows: Type I DCS: Symptoms are primarily bends; pain in the joints; considered minor! Type II DCS: Symptoms are of neurological nature, brain and nerve-malfunction, considered severe!
  11.     Most important are the variables, like elapsed time, altitude, intensity, quality of onset etc., which determine outcome! - Sudden incapacitation in flight, like hearing-loss or striking headache with vision-problems need immediate care and special medical treatment for survival! (Hyperbaric Pressure Chamber! " Hyperbaric "pressure is above atmospheric pressure and forces air bubbles into the blood serum. See also No 1!) - Bends at altitude slowly developing with minor intensity, disappearing at descent requires 100% oxygen!
  12.     All DCS symptoms need to be surveyed as they can return in the next 24 h and might require hyperbaric pressure therapy to resolve.
  13.     Hyperbaric pressure chambers exist, -portable and fixed based-, with the Navy, Airforce and with Diving Companies. They can save life and provide routine therapy in diver / DCS accidents.
  14.     First Aid, if DCS symptoms appear, is: a. always 100% OXYGEN, b. HYDRATION by drinking isotone solutions (water with 1/3 apple-juice, 1/2-teaspoon saline). c. transport to a HYPERBARIC CHAMBER, "dive" to 3 ATA for 2 to 5 hours, which hopefully will resolve the problem!
  15.     In-flight pre-breathing times of 100% oxygen, between 13-16 000 feet (not higher!) don’t prevent minor DCS symptoms, but prevent the most dangerous Type II DCS symptoms. The longer 100% O2 is inhaled, the more useful is it for the body!
  16.     High altitudes above 30 000 ft / 10 Km require as a rule 1 to 2 hours pre-breathing 100% O2 on the ground. One hour breathing 100% O2 flying at an altitude of 13 000 ft / 4000 m seems to have a similar effect!
  17.     If glider pilots fly high above 20 000 ft / 6000 m, it is important to go higher stepwise by ascending slowly, preferably for hours, than only in a few minutes. This reduces the DCS Risk!
  18.     Going up fast, staying up long at high altitude (i.g. 4 hours over 25000 ft / 7500 m) without pre-breathing will most probably cause DCS to develop. 75% of all U 2 Pilots who fly at cabin altitudes of 30 000 ft / 9000 m experienced DCS at least once in their flying career, even with 100% oxygen breathing and with part time pre-breathing in advance!
  19.     DCS develops in general after one hour after ascent! If it is experienced, the pilot must descend immediately!
  20.     After DCS-symptoms have appeared, pilots have to descend and breath 100% oxygen, for 2 hours or even longer, after landing. This method should also be applied as a safety procedure, even when symptoms disappeare during descent.
  21.     Rule is: No Flight the Next Day, after a high altitude flight and if DCS Symptoms occurred during flight!
  22.     For follow up of DCS mishaps it is essential to document all important data on a protocol. Debriefing after flight and a second protocol the next day is recommended.
  23.     If in doubt: Ask a doctor/diving doctor or flight surgeon over the phone for consultation, (Airforce, Navy) or over one of the 24 hours worldwide civilian DCS emergency numbers: like DAN Suisse 0041 32-3223823 or DAN Europe 0039 085 8930333 (all languages)!