Scubadoc’s Ten Foot Stop

September 23, 2009

Decompression Illness in Sports Divers, Chapter V, Risks for DCS

Filed under: Publication — admin @ 11:12 am

Risks for DCS

by Ernest S Campbell, MD


Self-grading Quiz for Prevention of Decompression Accidents

Some Causes of Decompression Accidents

The best way to categorize the various ways a diver can prevent the occurrence of DCS is by looking for the causes of the accident.

Some predisposing causes for DCS are as follows:

  • Inadequate decompression or violating the no-decompression limits. By surfacing too rapidly and not taking safety stops a diver allows bubbles to form and to get larger as the pressure differential decreases. Nitrogen loads in all the tissues at different pressures and times and violation of the NDL (no-decompression limits) is a major cause of DCS.
  • Inadequate surface intervals (failure to decrease accumulated nitrogen). Surface times are outlined for various diving profiles and failure to adhere to the prescribed length of time does not allow “off-gassing” of onboard nitrogen. The accumulated nitrogen is then added to by the next dive, increasing the risk of DCS.
  • Flying or going to higher altitude soon after diving (12-24 hours), which increases the pressure gradient. This in reality is a continuation of an ascent from a dive. This allows any nitrogen that is in the tissues to come out of solution and form bubbles, leading to DCS.
  • Individual physiological differences that have been traditionally thought of as increasing the risk of DCS are as follows:
    • Dehydration: This is probably the most important of the predisposing factors. Taking in adequate quantities of water (8-10 glasses/day).This is needed to counteract the drying effect of compressed air and the obligatory diuresis that all divers get from immersion. Dehydration, due to any cause (coffee, oral diuretics, alcohol, vomiting and diarrhea states, failure to drink non-alcoholic liquids)
    • Pre-existing illness affecting lung or circulatory efficiency: The lung acts as a filter for the buubles that occur in all divers. Chronic lung disease, heart failure both tend to increase the risk of DCS. Decreased perfusion from any source can increase the possibility of DCS. Intracardiac septal defect (PFO) bypasses the filtering effect of the lungs and increases risk of bubbles. Undeserved DCS (DCS that has no other causative factors) should have investigation for this entity.
    • Scar tissue from previous injury: (scar tissue decreases diffusion). Areas of decreased and increased blood flow have been incriminated in leading to DCS. Whether this is operative in the growth plates of teenagers is unknown. Nitrogen off-gassing is influenced by factors that alter perfusion.
    • Gender; women have been shown to have a slightly higher rate of DCS, particularly during the menses.
    • Obesity (nitrogen is lipid soluble). Several studies have incriminated obesity as a factor in increasing the risk of DCS. Fat is poorly supplied with blood vessels and decreased perfusion (ability to off-gas) can lead to DCS.
    • Fatigue: This clouds the decision making process, often leading to mistakes and DCS. Fatigue is also a subtle symptom of decompression sickness. Exertion during the deep part of the dive is a risk factor.
    • Age: The older diver has long been thought to be have increased tendencies to have DCS. Studies done by the Navy show a definite increase in DCS in older divers (all under 50 years of age). Other studies have not borne this out. Older divers have a higher percentage of body fat. Age and obesity: risk possibly increases in proportion to increase in age. Greater age and higher fat content are traditionally associated with increased incidence of DCS but the evidence is not consistent, recent reports showing no relationship.
    • Poor physical condition: Good physical fitness increases perfusion and ensures good gas exchange.
    • Exercise after diving increases the incidence of DCS from 22% to 46%. Exercise at depth is detrimental, increasing nitrogen uptake. (Requiring three times the decompression). Immersion in cold water with exercise causes increased incidence of DCS. Exercise while decompressing is beneficial.

Environmental factors that are important include the following:

  • Cold water (vasoconstriction decreases nitrogen off-loading). Warm water immersion (vasodilation) and the head down position increases nitrogen elimination.
  • Heavy work (vacuum effect in which tendon use causes gas pockets). Exercise at depth increases nitrogen uptake and is detrimental.
  • Rough sea conditions
  • Heated diving suits (leads to dehydration)
  • Divers who have been chilled on decompression dives (or dives near the no-decompression limit) and take very hot baths or showers may stimulate bubble formation.

Sport divers mainly need to avoid dehydration, dive shallower, ascend slower and spend more time between dives eliminating nitrogen.

Here are some of the factors found to increase the risk of decompression accidents:

      • Repetitive diving
      • Exceeded No-decompression limits
      • Running out of air, rapid ascent
      • Diving on the edge of No-decompression limits
      • Deep or repetitive dives using computer outside the limits of the tables or no-decompression limits
      • Flying after diving
      • Diving at altitude

There are other factors that are thought to increase the chances of getting DCS but have little data in support; some of these are:
  • Alcohol and hangover state (related to dehydration)
  • Medical problems increasing the viscosity of the blood (Sickle cell anemia and trait)
  • Injury to muscle, bone or joint (due to increased blood flow to inflamed area)
  • Rate of ascent
  • Repetitive, multiday dives after a long lay-off; deep prolonged air diving
  • Failure to do safety stops
  • Patent foramen ovale
  • Smoking habits
  • Adaptation or recent diving history
  • Underestimated depth
  • Table “fudging”
  • Neurological DCS symptoms are most common after short, deep dives. less common after altitude exposure, slow saturation decompression and low-pressure caisson exposure.
  • Slow ascent near the surface more effective in reducing neurologic DCS than was slow ascent from depth.
  • Fewer VGE with short safety stops. (venous gas emboli)
  • Off-gassing greatest in subjects tilted head down, immersed in warm water and exercising. Increasing venous return to the thorax increases off-gassing.(Head down tilt)
  • Exercise in warm water immersion decreases DCS (decrease by about 30%)
  • Some believe that the use of aspirin might help prevent the adherence of platelets to bubbles, thereby reducing the chance of bubble damage.

References:
Gorman, Pearce and Webb, Dysbaric illness treated at the Royal Adelaide Hospital, 1987: A factorial analysis. SPUMS Journal 18:95-101, 1988
Wilmshurst PT, Byrne JC, Webb-Peploe MM: Relation between inter-atrial shunts and decompression sickness in divers. Lancet, 2:1302-1306, 1989.

Moon RE, Camporesi EM, Kisslo JA: Patent foramen ovale and decompression sickness in divers. Lancet 1: 513-514, 1989.
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