Diving Medicine Sgn Cdr John Duncan, RNZN Director of Naval Medicine.
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Transcript of Diving Medicine Sgn Cdr John Duncan, RNZN Director of Naval Medicine.
Diving Medicine
Sgn Cdr John Duncan, RNZN
Director of Naval Medicine
Navy Hospital
Slark HBU
HMNZS MANAWANUI
Diving records• 7200 ft and submerged for
two hours
• 2000ft and submerged for an hour
• Free diving ~100m
• No limits 214 Meters
Caisson Disease
Haldane
• 1905-1907 Haldanes work
•Five compartment model•2:1 Ratio•Research with goats•Refined on divers•Ironically a lot of divers today behave like goats•Still basis of tables today
Goat Picture
Dive Profile
-30
-25
-20
-15
-10
-5
0
1 2 3 4 5 6 7
Depth
Tim
e
Diver Numbers
Diver Numbers Slark Hyperbaric Unit
0102030405060708090
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Number
Ye
ar
CAGE - cerebral arterial gas embolism
• Air trapped in lung may expand and burst into arterial system via pulmonary veins – goes to brain
• Massive bubble load may cross to pulmonary veins through lungs – goes to brain
• Presents with rapid onset neurological symptoms
• Patients often recover, then deteriorate
Decompression illness
• Bubbles form in tissue/blood from dissolved N2
on ascent if time / depth of dive was too great, and ascent is too fast
• DCI can be avoided by very slow ascent (but this is sometimes too slow to be practical)
• Bubbles damage vessels and tissue• Variable presentation - pain, weakness, feeling
‘off colour’, breathlessness
16
DECOMPRESSION ILLNESS- evolution of bubbles from dissolved nitrogen
Air breathed at greater pressure during dive Gas solubility increased at greater pressure N2 absorbed into blood and tissues
Amount of gas depends on time and depth N2 solubility declines during ascent (as pressure decreases)
Bubble formation - tissues and blood
17
RISK FACTORS FOR DCI
Too deep / too long – exceed table limits• Rapid ascent• Omitted decompression• Repetitive diving (multiple ascents)• “Bounce dives”• Flying after diving – no flying for 24 hours• Age
RISK FACTORS FOR DCI 2
• Inter-current illness, cold, working hard, etc.• Panic• Gear Failure• Poor planing
Bubbles
tissues
venous blood (some bubble formation)
lungs
*
off-gas arteries organs
Tissue bubbles
• Mechanical effects– compression– stretch
• myelin sheaths, bone, spinal cord, tendon, etc
• Biochemical– activation of complement– coagulation– kinins
Effects
• Reduced microcirculation– ischaemia (haemorrhagic or thrombotic)
– vessel permeability– oedema– inflammation
22
DECOMPRESSION ILLNESS - presentation of disease• Marked variation, from mild constitutional
symptoms to paralysis• Most cases apparent within 24 hours• Only 50% have objective signs• Worst cases are early onset with
progressive neurological symptoms• Diving may not reflect severity• Neurology may not “make sense”
Classification
• Decompression sickness– Type I - musculoskeletal, skin, lymphatic,
constitutional
– Type II - neurological, cardiorespiratory, vestibular
• Arterial gas embolism• Barotrauma
Little diagnostic or prognostic significance
Current classification
• Decompression illness– acute or chronic– static, progressive, relapsing, spontaneously
resolving– organ system involved (cutaneous, cerebral,
spinal, musculoskeletal, lymphatic, etc)– +/- barotrauma
Differentiating between pathological processes
• Decompression illness - due to inert gas load and bubble evolution….
• Barotrauma
• Other diving-related illness
• Depth-time profile gives indication of inert gas load
• Pattern of dive - no. and speed of ascents, etc
• Time of onset of symptoms
• Symptom evolution
• Signs
Making a diagnosis
Cerebral emboli - CAGE
• Usually rapid onset on surfacing
• Loss of consciousness or fitting
• Victims may drown
• Spontaneous recovery of consciousness
• Apparent resolution, then deterioration
Symptom frequencySymptoms after diving are common, DCI is
not• Pain 40%
• Altered sensation 20%
• Dizziness 8%
• Fatigue, headache, weakness 5%
• Nausea, SOB 3%
• Altered LOC 2%
• Rash < 1%
29
DECOMPRESSION ILLNESS classical vs typical patients
THE ‘CLASSICAL’
PATIENT• Exceeds time / depth• Rapid onset of pain• Followed soon after by
weakness and sensory changes
• Presents early
THE ‘TYPICAL’
PATIENT• Borderline time / depth• Initially well• Later, migratory aches,
feels “off colour” and tired• Seeks help several days
after diving
30
DECOMPRESSION ILLNESS - presentation by system
Constitutional Musculo-Skeletal
Skin Heart / Lungs Neurological
“(Anything)”
Fatigue Pain Rash Cough Weakness
Malaise - joints Itch Dyspnoea Sensory change
“Off colour” - limbs Chest pain Bladder and bowel
- girdles
Assessing a diver• A, B, C and if conscious and talking – start
oxygen @ 4L/minute, take blood pressure and pulse
• RECORD EVERYTHING – TIME, etc• Dive profile – depth, time, gas, any events• When did they first notice symptoms?• What were they?• What has happened to the symptoms since?• How do they feel now?• When did they last pass urine?
32
DECOMPRESSION ILLNESS- evaluation in first aid
BRIEF HISTORY BRIEF EXAMINATION
Depth(s) / time(s) Vital signs
Number of ascents Chest
Nature of ascents Neurological
Nature of dive
Symptoms
Temporal relation of
symptoms to dive
Be suspicious if there is any history of altered consciousness, even if transient –
this might be CAGE, which is serious
Refer for treatment
diving emergency services
D.E.S. number (09) 4458454
D.E.S. service• Available 24/7• Call will be answered by Navy Hospital staff -
get basic details• Give contact number• Experienced doctor & consultant on call• Response:
– advice on initial management– transfer immediately (St John coordinate) OR – assess at local hospital OR– review next day
35
DECOMPRESSION ILLNESS - steps in DCI first aid
• ABCs• Position• Oxygen• Fluids• Evaluate• Contact D.E.S.• Evacuate
36
DECOMPRESSION ILLNESS - positioning in first aid
CURRENT ADVICE
• Horizontal• Recovery position if LOC
is decreased• Previous advice was
head down
THE CASE AGAINST
HEAD DOWN• Difficulty• Oral fluid administration
• Increase ICP and cerebral oedema
• Arterialisation of venous bubbles
37
DECOMPRESSION ILLNESS - oxygen in first aid
CURRENT ADVICE RATIONALE
100% Oxygen: damaged valve;
bag/mask/reservoir
Promote N2 outgassing
Record time on / any time off / clinical effects
Promote bubble resolution
Oxygenate ischaemictissue
38
DECOMPRESSION ILLNESS - IV fluids in first aid
CURRENT ADVICE
RATIONALE
0.9% NaCl 1000 ml stat and 100-250 / hr
Divers are usually dehydrated
Titrate against output in long evacuations
DCI= a compromise of the microcirculation
Record fluid balance DCI and dehydration are a bad combination
may need catheter
Adjunctive treatments
• Possible benefit:– NSAIDs (oral, IM)– lignocaine (IV infusion)
• Of no benefit:– heparin or other anticoagulants– steroids
40
DECOMPRESSION ILLNESS- evacuation in first aid
• Not always necessary• Advice from D.E.S. is usually sought first• Minimise altitude – either road, or fixed wing at
normal atmospheric pressure (1 ATA), or rotary (but <300m)
• Maintain oxygen administration• Maintain horizontal posture in acute cases• Avoid pain relief• No entonox
Helicopter vs fixed wing
HELICOPTER• Noisy• Poor access to
patient• Unpressurised• Ideal for short coastal
distances• Good for isolated
areas, boats
FIXED WING• Quieter• Better access
• May be pressurised• Ideal for long haul
over high country• Limited if no strip
Summary: initial management• CPR if necessary• Oxygen - 100% if possible (need rebreather)
• Lie flat• Get advice• Rehydration (fluid balance)
– oral or IV crystalloid– 1L stat, 1L 4-6 hrly
• Evacuate for recompression• NSAIDs if needed
Recompression treatment
• Recompress diver to depth – can use oxygen or oxygen-helium
• bubble compression• increase diffusion gradient so gas leaves
bubble• counter effects of pulmonary AV shunting• deliver high oxygen tensions to damaged
tissue
Recompression therapy
18m
30min
9m
1hr
2hrs surface (0m)
= air ‘breaks’ to reduce oxygen toxicity
(and for convenience, comfort, etc)