decompression sickness dr. emilia zainal abidin eoh3202
TRANSCRIPT
DECOMPRESSION DECOMPRESSION SICKNESSSICKNESS
Dr. Emilia Zainal Abidin EOH3202Dr. Emilia Zainal Abidin EOH3202
Pressure
Definition – pressure is force acting on a unit area Pressure = Force/Area Unit of pressure
1 atmosphere = 29.9 inches (760 mm) of Hg= 33 feet (10.08 m) of
seawater= 101.3 kilopascals (kPa)= 14.7 pounds per suare
inch (psi)
Composition of Gases in Atmosphere
Component Composition
Symbol Volume percent
NitrogenOxygenArgonNeonHeliumHydrogenOthers
NOA
NeHeH
(Co, Kr, Xe, etc)
78.09420.9480.934
0.0018180.0005240.00005
0.01
Dalton’s Law
At sea level the total air pressure is 1 atm. or 760 mm Hg. Of this total air pressure, 21% (or .21) is from oxygen, 78% (.78) from nitrogen, and 1% (.01) from other gases. The percentage of an individual gas times the total air pressure gives the pressure of that component gas. Thus, at sea level:
Pressure nomenclature
Absolute pressure, ambient pressure, atmospheric pressure, hydrostatic pressure, partial pressure, design pressure
Dalton's Law states that the total pressure of a gas is equal to the sum of pressures of its individual components.
What happens to inhaled air at depth? At depth all pressure increase Doubling of ambient air pressure occurs
at just 33 feet Tripling of ambient air pressure at 66
feet Boyle’s Law and DivingAir 760 mm
Hg14.7 psi 1 atm
Sea 33 ft 1520 mm Hg
29.4 psi 2 atm
Sea 66 ft 2280 mm Hg
44.1 psi 3 atm
Sea 99 ft 3040 mm Hg
58.8 psi 4 atm
Sea 132 ft 3800 mm Hg
73.5 psi 5 atm
Boyle’s LawBoyle’s Law The mechanical responses to changes in
pressure are in accordance with Boyle's Law, which states that a volume of gas is inversely proportional to the pressure to which it is subjected, temperature remaining constant.
Henry’s LawHenry’s Law The amount of gas in solution is
proportional to the partial pressure of that gas over the solution
As the pressure of the gas above a solution increases, the amount of that gas dissolved in the solution increases
Reverse is also true, as the pressure of the gas above a solution decreases, the amount of gas dissolved in the solution decreases and forms a “bubble” of gas within the solution
Henry’s Law Henry’s Law IllustrationIllustration
Low pressure equilibriumLow concentration
Double the pressure equilibriumDouble the concentration
How does the increased pressure at depth affect gas in the body? The increased pressure of each gas
component at depth means that more of each gas will dissolve into the blood and body tissues, a physical effect predicted by Henry's Law
Inhaled gases are in close contact with blood entering the lungs
Hence, the greater the partial pressure of any inhaled gas, the more that gas will diffuse into the blood.
Hyperbaric work environment Hyperbaric work environment (work below sea level pressure or
in aquatic environment) Together, Boyle's and Henry's laws explain when happens when
compressed air is breathed 1) inhaled PO2 and PN2 increase and 2) the amount of nitrogen and oxygen entering the blood and
tissues also increase. Potential hazards:
Mechanical effects Inert gas narcosis – physical and mental disturbances when
breathing gas contains inert gas under pressure Effects of CO2 accumulation – refer next slide Oxygen toxicity – hyperoxia
Decompression sickness
Inspiration and expiration
Inspiration: When atmospheric pressure is greater than within the lungs, air flows from outside into the lungs.
Expiration: When pressure in the lungs is greater than the atmospheric pressure, air moves from the lungs to the outside.
If surrounding pressure is high, CO2 could not be exhaled thus CO2 accumulated
When does decompression sickness happens? A diver ascends from a dive A worker who is doing underwater logging A worker comes out of a pressurized caisson, or out
of a mine, which has been pressurized to keep water out
An unpressurized aircraft flies upwards The cabin pressurisation system of an aircraft fails. Divers flying in any aircraft after diving Pressurized aircraft are not risk-free, since the cabin
pressure is not maintained at sea-level pressure
Decompression sickness
Decompression sickness (DCS) or diver's disease
Describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurisation
The bends, or caisson disease DCS most commonly refers to a specific type of
underwater diving hazard but may be experienced in other depressurisation events such as caisson working, flying in unpressurised aircraft.
Symptoms of decompression sickness Bends -
DCS Type Bubble LocationSigns & Symptoms (Clinical
Manifestations)
BENDS
Mostly large joints of the body(elbows, shoulders, hip,wrists, knees, ankles)
Localized deep pain, ranging from mild (a "niggle") to excruciating. Sometimes a dull ache, but rarely a sharp pain.
Active and passive motion of the joint aggravates the pain.
The pain may be reduced by bending the joint to find a more comfortable position.
If caused by altitude, pain can occur immediately or up to many hours later.
Symptoms of decompression sickness
CHOKES Lungs
Burning deep chest pain (under the sternum)
Pain is aggravated by breathing
Shortness of breath (dyspnea)
Dry constant cough
SKIN BENDS Skin
Itching usually around the ears, face, neck arms, and upper torso
Sensation of tiny insects crawling over the skin
Mottled or marbled skin usually around the shoulders, upper chest and abdomen, with itching
Swelling of the skin, accompanied by tiny scar-like skin depressions (pitting edema)
Symptoms of decompression sickness
NEUROLOGIC
Brain
Confusion or memory loss Headache Spots in visual field (scotoma),
tunnel vision, double vision (diplopia), or blurry vision
Unexplained extreme fatigue or behaviour changes
Seizures, dizziness, vertigo, nausea, vomiting and unconsciousness may occur
Spinal Cord
Abnormal sensations such as burning, stinging, and tingling around the lower chest and back
Symptoms may spread from the feet up and may be accompanied by ascending weakness or paralysis
Girdling abdominal or chest pain
Peripheral Nerves
Urinary and rectal incontinence
Abnormal sensations, such as numbness, burning, stinging and tingling (paresthesia)
Muscle weakness for twitching
Body cavities with trapped gases
When the gases in cavities can't equalize with the ambient environment, the gas is considered to be "trapped" Lungs Middle ear - Middle ear squeezes occur because
of obstruction of the eustachian tube. Sinuses - If openings of sinuses are obstructed
equalization of pressure becomes difficult Tooth cavities - mechanically imperfect fillings Stomach and intestines- gases in the stomach
and intestines expand during ascent
Factors predisposing to decompression sickness Ill health Old age Obesity Exercise/exertion Drugs Alcohol Cold Hypoxia Previous exposure to decompression – several
unpressurized flights or scuba before flight
Hypobaric work environment Work in conditions with reduced pressure – above sea
level For example
Aviation Space industry
As altitude increases, excess nitrogen will begin to try to escape the body to the lower pressure outside. This results in decompression sickness, which can be very painful and even deadly.
Potential hazards Reduction in partial pressure of oxygen Decompression sickness
Manifestation of decompression sickness at 28000 feet altitude Bends – joint pains 74% Creeps – skin rash 7% Chokes – chest discomfort 5% Staggers – neurological complaints 1% Visual disturbances 2% Reduced awareness/comfusion 9%
Dalton’s Law and hypoxia
Ambient air Partial pressure
Alveolar air Partial pressure
Nitrogen 600 mm Hg Nitrogen 570 mm Hg
Oxygen 160 mm Hg Oxygen 103 mm Hg
Carbon dioxide 40 mm Hg
Water vapour 47 mm Hg
Total 760 mm Hg 760 mm Hg
% saturation of hemoglobin varies with changes in partial pressure of alveolar oxygen at various altitudes
CNS effects of increasing hypoxia Feeling tired, sleepy Euphoria Impairment of judgement Dulling of thoughts Light-headedness Tingling of hands and feet Pallor of skin, cyanosis In-coordination of limbs and disorientation Falling of vision Semi-consciousness Unconsciousness
Time of useful consciousness with increasing altitudeAltitude Rapid disconnect of O2 systems
Moderate activity Sitting activity
22,000 5 minutes 10 minutes
25,000 2 minutes 3 minutes
30,000 45 seconds 1 ¼ minutes
35,000 30 seconds 45 seconds
40,000 18 seconds 30 seconds
Role of occupational health professional Advice on health effects of pressure
changes Treatment of pressure related
complications Medical selection of workers to be
engaged in work in hypobaric or hyperbaric environments
Periodic medical examination of diving or aviation personnel
Certification of invalidity for air travel
Middle Ear: Middle Ear: PreventionsPreventions Valsalva maneuver
Valsalva maneuver is performed by closing the mouth, pinching the nostrils closed and blowing air through the nose. This will force air up the eustachian tube and into the middle ear.
Make sure you are in good health with no upper respiratory or sinus problems.
swallowing, yawning, or tensing the muscles of the throat; this will
allow the pressure to equalize
Sinus: PreventionsSinus: Preventions
Equalization of pressure to relieve pain in the sinuses is best accomplished by use of:
the Valsalva procedure, and/or inhalants. Reversing the direction of pressure
change as rapidly as possible may be necessary to clear severe sinus blocks.
GI tract: Preventions GI tract: Preventions
Watch what you eat before you fly. Staying away from foods you know cause
you discomfort or pain in the gastrointestinal tract.
Some of the foods that more commonly disagree with individuals are: onions, cabbage, raw apples, radishes, dried beans, cucumbers, melons-or any food that you know causes you problems.
Thank you