Uniformed Services University – Department of Preventive Medicine and Biometrics 1 Undersea Medicine Borrowed heavily from: Michael Jacobs MD MPH Undersea Medical Officer Occupational/Preventive Medicine Physician Naval Hospital Great Lakes [email protected]LTC(P) Michael Lewis, MD, MPH, MBA, FACPM Assistant Professor, Epidemiology, PMB
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Uniformed Services University – Department of Preventive Medicine and Biometrics
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Undersea Medicine
Borrowed heavily from:Michael Jacobs MD MPHUndersea Medical Officer
Occupational/Preventive Medicine PhysicianNaval Hospital Great Lakes
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Learning Objectives
• Understand the scope of undersea medicine practice
• Understand basic principles of diving physiology
• Recognize symptoms and signs of decompression illness
• Understand principles of treatment for decompression
illness
• Identify medical contraindications for diving
Uniformed Services University – Department of Preventive Medicine and Biometrics
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What is Undersea Medicine?
• Also known as “Diving Medicine”
• Field of medicine that deals with the effects of the undersea environment on health
• Prevention and treatment of diving-related injuries/illnesses
• Pre-employment/Pre-placement examinations
• Fitness-for-diving evaluations
• NOT management of chronic medical conditions
• “Undersea and Hyperbaric Medicine” – board certification offered by the American Board of Preventive Medicine
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Examples of Diving-Related Injuries/Illnesses
• Decompression Sickness (“The Bends”)
• Arterial Gas Embolism
• Sinus/Aural barotrauma
• Pneumothorax
• Nitrogen Narcosis
• Drowning/Near Drowning
• Hypothermia
• Bites/Envenomations
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Who sees a “diving doctor”?
• Recreational divers
• Professional/Commercial divers
• Dive instructors/Dive Masters
• Military/Police/Technical divers
• Inshore professionals – Oceanographers,
Marine biologists, Engineers, Salvors
• Offshore professionals – Saturation
welders, Mixed-gas construction teams
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Diving Physics
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Pressure• Pressure – force applied per unit area
• Atmosphere (atm): pressure exerted on all bodies/structures by earth’s atmosphere
• Sea Level = 1 atm = 14.7 psi (lb/in2)
• Pressure under water
• Every 33 ft of depth (sea water) = 1 atm or 14.7 psi
• Example: Diver at depth of 66 ft
• 1 atm (sea level) + 2 atm (water depth) = 3 atm
• Diver at 66ft is under 3 atm pressure
P (atm) = D (fsw) + 133 fsw
P = PressureD = Depthfsw = Feet of sea water
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Buoyancy• Object in liquid floats or sinks depending on density
of object relative to liquid• Your pet rock will sink in water• Your rubber ducky will float
• State of “neutral buoyancy” – object neither floats nor sinks
• Divers use various methods to maintain neutral buoyancy throughout a dive• If it feels like you are sinking – negatively buoyant• If it feels like you are floating up - positively
buoyant• Both cause extra effort and potential injuries
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Gas Laws
• Boyle’s Law: P1V1 = P2V2
A rubber balloon with a volume of 1 cf at the surface is submerged to a depth of 33 fsw. What is the volume of the balloon now?
P1V1 = P2V2 P1 = atmospheric press.
1 atm x 1 cf = 2 atm x V2 V1 = volume at P1
0.5 cf = V2 P2 = press at 33 fsw
V2 = volume at 33 fsw
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Sea Level 1 atm Vol=1
33 fsw 2 atm Vol=1/2
66 fsw 3 atm Vol=1/3
99 fsw 4 atm Vol=1/4
Volume100%
50%
33%
25%
As a diver descends, atmospheric pressure increases and the volume of compressible tissues/gases decreases (e.g. gas bubbles, lung tissue)
Uniformed Services University – Department of Preventive Medicine and Biometrics
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Diving Gases• Nitrogen
• colorless, odorless, tasteless, inert
• under pressure
• soluble in body tissues
• Anesthetic/intoxicant on CNS
• “Nitrogen Narcosis”: (50 ft = 1 martini)
• Oxygen
• Colorless, odorless, tasteless
• Too little (low Partial Press.) = hypoxia
• Too much (high Partial Press.) = CNS toxicity (seizures)
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Diving Gases• Carbon Dioxide
• Principal stimulant for respiration• Slight elevations cause headache, dizziness• High concentrations cause unconsciousness, death
• Carbon Monoxide• Product of incomplete combustion• Toxic, asphyxiant
• Helium• Inert and nontoxic• Often used as a nitrogen substitute for deep-diving
divers to prevent nitrogen narcosis• Associated with High Pressure Nervous Syndrome
(HPNS)
Uniformed Services University – Department of Preventive Medicine and Biometrics
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In 1900, a Royal Navy diver descended to 150 fsw in 40 minutes, spent 40 minutes at depth searching for a torpedo, and ascended to the surface in 20 minutes with no apparent difficulty. Ten minutes later he complained of abdominal pain and fainted. His breathing was labored, he was cyanotic, and he died after seven minutes. An autopsy the next day revealed the organs to be healthy, but gas was present in the liver, spleen, heart, cardiac veins, venous system, subcutaneous fat, and cerebral veins and ventricles. By present U.S. Navy Standard Air Decompression Tables, this diver should have had 174 minutes of decompression time before reaching the surface.
Diagnosis: Decompression Sickness (DCS)
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History• DCS recognized in divers and compressed air
workers since late 1800s
• Prevailing guideline was to ascend slowly
• Standards ranged from 1.5 ft/min to 5 ft/min
• DCS still occurred but less frequently
• Bert*: DCS associated with nitrogen bubbles
• Haldane: Shorter/shallower dives associated
with less frequent/less severe DCS
*Bert P. Barometric pressure. Researches in experimental physiology. Bethesda, MD. Undersea
Medical Society, 1878.
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Decompression Theory• Body tissues absorbs nitrogen at depth
• Each tissue type absorbs nitrogen at different rate• Slow, staged ascent (“decompression”) releases
nitrogen harmlessly and is exhaled• Stages determined by time/depth of each dive
• Ascent without adequate decompression causes nitrogen bubble formation• Clinical manifestations = “Decompression Sickness”• Origin of bubbles is controversial• Form in extra vascular spaces, such as skin and
joints (including spine)• Reach venous circulation through lymphatics
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Decompression Illness (DCI)
• Decompression Sickness (DCS)
• Typically presents minutes to hours after dive
• 95% within 6 hours
• Nitrogen bubble formation from inadequate
decompression
• Onsite treatment: ABCs, Oxygen
• Definitive treatment: Recompression
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Type I DCS
• Musculoskeletal pain (Limb bends)
• Most common manifestation of DCS
• Dull pain, not well localized; no change with movement
• Knees, elbows, or shoulders most commonly involved
• Cutaneous DCS (Skin bends)
• Pruritis and erythema of trunk
• Cutis marmorata (mottling appearance of skin)
• Treatment: Recompression
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Type II DCS
• Risk of permanent disability or death
• Pulmonary DCS (“Chokes”)
• Venous gas emboli clog pulmonary arterial circulation
• Rare; occurs with rapid ascent from deep dive
• Substernal discomfort, cough; worse with deep inspiration
• May lead to right-sided heart failure and cardiovascular collapse
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Type II DCS (con’t)• Neurologic DCS
• Predilection for spinal cord • Recreational divers doing short, deep dives• Syndrome – over minutes to hours after ascent
• Tingling in trunk• Progressive numbness and paresthesias• Ascending motor weakness• Bowel/bladder incontinence• Severe cases may present with LOC/paraplegia• Cerebral Sx: memory impairment, aphasias,
visual disturbances, personality changes
Uniformed Services University – Department of Preventive Medicine and Biometrics
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Type II DCS (con’t)
• Vestibular DCS (“Staggers”)• Sudden onset of dizziness, nausea,
vomiting, nystagmus, +/- hearing loss and tinnitus
• Not common in recreational divers• Confused with middle ear barotrauma
• Treatment of Type II DCS:• Rapid recompression with hyperbaric
oxygen • Supportive care: Fluids, pressors
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You and your dive buddy are out on the Great Barrier Reef.
Your dive buddy is a novice diver on his first “real” diving
trip. Your first dive is planned to a depth of 60 fsw for 45
minutes. Thirty-five minutes into your dive, your dive
buddy points frantically toward a beautiful nine foot reef
shark. After observing the shark for a few moments, you
turn back to see your dive buddy swimming quickly for the
surface. By the time you reach him on the surface, he is
unconscious. The boat crew brings him on board and
finds him unresponsive with a weak pulse. A review of
your diving profile reveals that the dive was well within the
decompression limits for a 60 ft dive. All other divers on
the boat had no complications from their dives. What is
the most likely diagnosis?
Diagnosis: Arterial Gas Embolism
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Arterial Gas Embolism (AGE)• 2nd only to drowning as most common cause of death in
recreational divers• More common in novice divers• Pathophyisiology
• Usually secondary to pulmonary barotrauma (PBT)• Lung overinflation from diving activities