Undersea Medicine

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Undersea Medicine

• Michael Jacobs MD MPH
• Undersea Medical Officer
• Occupational/Preventive Medicine Physician
• Naval Hospital Great Lakes
• michael.jacobs_at_nhgl.med.navy.mil

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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

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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

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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

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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

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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 earths 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 Pressure D Depth fsw Feet of sea water
P (atm) D (fsw) 1 33 fsw
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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

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Gas Laws

• Boyles 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

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Volume 100

• Sea Level 1 atm Vol1
• 33 fsw 2 atm Vol1/2
• 66 fsw 3 atm Vol1/3
• 99 fsw 4 atm Vol1/4

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33
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As a diver descends, atmospheric pressure
increases and the volume of compressible
tissues/gases decreases (e.g. gas bubbles, lung
tissue)
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Daltons Law

• Ptotal pPa pPb pPc . . . pPn
• (P pressure, pP partial pressure)
• pPa PtotalFa
• (F gas by volume)
• What is the partial pressure of oxygen when
  breathing air at sea level? At 99 fsw?
• pPO2 1 atm (0.21) 0.21 atm
• pPO2 4 atm (0.21) 0.84 atm

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Henrys Law

• The amount of gas that will dissolve in a liquid
  is almost directly proportional to the partial
  pressure of that gas

BLOOD
N2
N2
N2
N2
N2
N2
High pPN2
Dissolve
N2
N2
N2
As a diver descends, inspired gases are more
soluble in blood
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Gas Diffusion

• The difference between the partial pressure of a
  gas inside a liquid and its outside partial
  pressure will cause the gas to diffuse in or out
  of the liquid and will also control the rate of
  diffusion
• Example At 66 fsw, pPN2 3 atm 0.79 2.4
  atm
• Blood Diffusion Direction Tissue
• pPN2 2.4 atm pPN2 0 atm

As a diver descends, inspired gases diffuse into
tissues as a diver ascends, gases diffuse out of
tissues and into the blood
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Diving Gases

• Most recreational divers use compressed air
• 79.1 Nitrogen
• 20.9 Oxygen
• 0.033 Carbon Dioxide
• Various inert and trace gases
• Other options include
• Nitrox (Nitrogen/Oxygen) reduces nitrogen
  narcosis
• Heliox (Helium/Oxygen) reduces DCS
• Trimix (Nitrogen/Helium/Oxygen)
• 100 Oxygen eliminates DCS (special ops use
  with scrubber system to eliminate bubbles)

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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)

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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)

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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

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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

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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

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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 (cont)

• 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

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Type II DCS (cont)

• 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
• Breath holding, bronchospasm, intrinsic
  abnormality
• Excessive pressure disrupts lung parenchyma and
  allows gas into interstitium
• Gas can cause mediastinal/subcutaneous emphysema,
  pneumothorax, or it can enter arterial
  circulation
• Extraalveolar gas enters left side of heart and
  can embolize (to cerebral/coronary vessels, etc.)

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AGE (cont)

• Presents immediately or within minutes of ascent
• Group 1 (5)
• Apnea, unconsciousness, cardiac arrest
• AGE to coronary/cerebral circulation
• Group 2 (95)
• Varying systemic neurologic signs but vital signs
  preserved
• Typical LOC/stupor/confusion, hemiparesis,
  seizures, vertigo, or headache
• Treatment Rapid recompression

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Evaluation of DCIs

• Obtain accurate history
• Dive profile (depth, time, previous dives), rate
  of ascent, time of onset of symptoms
• Physical Exam
• Vital signs, evidence of pulmonary barotrauma
  (PTX), thorough neurologic exam
• Diagnostic tests may not be time
• Differential Diagnosis
• Pain, rash, dyspnea, or neurologic changes after
  a dive should be assumed to be a diving-related
  illness
• Consider other dx for symptoms gt6 hours after dive

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DCI Treatment

• Emergency treatment ABCs first priority
• Oxygen administration (100)
• enhances washout of inert gas (Nitrogen)
• May resolve Sx or improve outcome
• Definitive treatment Recompression
• Reduce bubble size
• Promote bubble resolution
• Delays lead to inflammatory changes, cell death,
  and poorer recovery

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Recompression Chamber
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Recompression

• Increased ambient pressure shrinks bubbles
• Can often reduce symptoms
• Controlled decompression allows dissipation of
  bubbles
• Breathing gases
• Air Acceptable, but leads to additional
  nitrogen uptake and potential for additional DCS
• Oxygen Enhances diffusion of nitrogen out of
  tissues (Oxygen window)
• Oxygenates ischemic tissue
• Reduces cerebral edema
• Probably inhibits endothelial leukocyte
  accumulation

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Treatment Tables

• Designed to allow 100 oxygen breathing at
  highest practical ambient pressure
• Oxygen toxicity occurs above 3 atm
• Typical treatments max depth 60 ft (2.8 atm)
• Minimize nitrogen absorption
• Type of treatment depends on type/severity of DCI

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U.S. Navy Dive Table 5
U.S. Navy Diving Manual Revision 4, March 2001
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Example Treatment Table 5

• Used for Type 1 DCS (pain only)
• All symptoms must resolve within 10 minutes of
  reaching 60 ft in chamber
• Other cases treated with similar tables, but
  longer duration

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Effectiveness of Recompression for DCS

• Workman1
• Military divers 110 of 114 cases (96.3)
  completely resolved
• Civilians divers 70 resolution
• Divers Alert Network (DAN) 19942
• Recreational divers 56 resolution
• 30-90 days later residual Sx in 33 pain-only
  DCS 46 in mild neurologic DCS 75 in severe
  neurologic DCS

• Workman RD, Aerospace Medicine 1968.
• DAN, 1996.

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Other injuries and illnesses are much more common
during a typical dive
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Potential problems during a dive

• 1) Descent
• Aural/Sinus barotrauma
• Injury
• 2) On bottom
• Nitrogen Narcosis
• Injury

• 3) Ascent
• Aural/Sinus barotrauma
• CO poisoning
• Injury
• AGE
• PTX
• 4) After surfacing
• DCS
• AGE (within 10 min)
• PTX (within 10 min)
• Injury

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Medical Evaluation of Divers
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Contraindications to Diving(Recreational Divers)

• Relate to pressure changes and need to be
  completely comfortable in surroundings
  (underwater, heavy gear, away from land/medical
  treatment)
• Absolute (typically)
• Neuro Severe brain damage (e.g. following head
  injury), seizure disorders, illnesses causing
  significant neurological deficits (stroke)
• Endocrine Diabetes with end-organ disease or
  symptomatic hyper/hypoglycemia
• Gastrointestinal Achalasia, symptomatic hernias,
  gastric-outlet syndrome, SBO
• Pulmonary Uncontrolled asthma, COPD, spontaneous
  PTX
• Cardiac Unstable angina, Septal defects
• Medications Decision usually relates to
  underlying condition
• Relative contraindications are numerous and may
  require thorough evaluation/discussion with
  specialist

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Commercial Divers

• Initial/periodic exams usually required
• Very thorough evaluation (neurologic, pulmonary)
• Functional testing may be required (Exercise
  Treadmill Test, Pulmonary Function Test)
• Contraindications similar but much more strict
  than for recreational divers

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Related topics

• Other diving-related disorders
• Nitrogen narcosis, High pressure nervous
  syndrome, gas toxicity, hypothermia, marine
  animal injuries
• Mixed gas diving (Nitrox, Trimix, 100 oxygen)
• Hyperbaric Oxygen Therapy (HBOT)
• Non diving injuries/illnesses
• Poor wound healing
• CO poisoning
• Necrotizing fasciitis
• Radiation necrosis
• Benefit derives from increased oxygen delivery to
  tissues
• Area of active research

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Resources

• Bove AA. Bove and Davis Diving Medicine, 4th
  edition. WB Saunders, Philadelphia, 2004.
• Navy Diving Manual, 4th edition. 2001.
  (www.vnh.org/DivingManual/DMTOC.html)
• www.dive.noaa.gov (NOAA)
• www.scubamed.com (Underwater Medicine Associates)
• www.diversalertnetwork.org (DAN)