Diving medicine Flashcards
physiological changes with free diving
- reduced heart rate
- blood flow
and volume is redistributed towards vital organs by
means of a reflex vasoconstriction - body cooling
- Risk of hypoxic blackout and drowning
How is buoyancy controlled in scuba diving
Buoyancy compensator or buoyancy control device.
Volume of air in the
jacket is varied
ideal gas law
PV = nRT P= absolute pressure, V= volume, n= number of moles, R= universal gas constant, T= temperature
Boyle’s law
P and V inversely related
Gay-Lussac’s law
P and T directly related
Charles law
V and T directly related
implications of the gas laws in diving
Fall in temp: - pressure of the cylinder drops - volume of the air in lungs/BCD jacket drops.
Pressure increases:
- volume of air in lungs/BCD jacket drops.
Dalton’s Law
The total pressure exerted by a mixture of gases is equal to
the sum of the pressures that would be exerted by each of the gases if it alone were present and occupied the total volume.
PTotal= Pp1+ Pp2+
Henry’s Law
The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas that is in contact with the liquid and the solubility coefficient of the gas in the particular liquid
Implications of Dalton’s and Henry’s
law in diving
- For every 10m depth pressure
increases by 1 bar. - Therefore more gas will dissolve into the blood and
body tissues
What causes nitrogen narcosis?
- As depth increases, gas pressure increases –> partial pO2 and PN2 increase
- increased nitrogen into the blood stream
- divers may experience
alterations in reasoning, memory and response time and idea
fixation, overconfidence or calculation errors.
Aetiology of decompression sickness
Increased descent –> increased pressure –>
nitrogen dissolves and accumulate in the lipid component of tissues.
- Diver ascends –> lag –> saturated tissues release
nitrogen back into the blood.
- When a critical amount of nitrogen is dissolved in the tissues, ascending too quickly causes the dissolved nitrogen to return to its gas form while still in the blood or tissues
- Bubbles form- in the tissue–> local problems
- in the blood –> embolisation may result.
Decompression sickness prophylaxis
1- tables/dive computers are used for given depth of water / time a diver can stay down 2- decompression stop (10m/min during ascent) and safety stop (every 5m during descent)
Type I Decompression
sickness (DCS) Sx
- Pain (the bends)- (70-85%) patients with type I
DCS. - Pruritus- mottling/papular violaceous rash.
- Oedema
- Anorexia/excessive fatigue
Type II DCS Sx
- Pulmonary: burning, sub-sternal discomfort on inspiration, nonproductive coughing that can become paroxysmal, and severe
respiratory distress - Circulatory: hypovolemic shock
- Nervous system involvement: low back pain may progress to paresis,
paralysis, paraesthesia, loss of sphincter control, headaches or
visual disturbances, dizziness, tunnel vision, and changes in
mental status. - Pain- only 30% of cases
Sx onset DCS
Usually quick (60% within 3 hours and 98% within the first 24 hours)
Increased risk if –> high altitude within 24h
AGE pathophysiology
Pulmonary over-pressurisation –> large gas emboli –> pulmonary vein –> lodge in coronary, cerebral, and other systemic arterioles.
Gas bubbles continue to expand as ascending
pressure decreases, —> increasing the severity of clinical signs.
Sx Arterial gas Embolisation
Much faster Sx onset (10-20min)
Depends on location of emboli
- coronary artery –> MI
- Cerebral artery –> stroke/seizures
- May occur suddenly or gradually (dizziness,
headache, profound anxiousness)
- More severe symptoms (shock/seizures) = sudden onset
Differentiating cerebral AGE from type II neurologic
DCS
- AGE
- Any type of dive
- onset is immediate (< 10-120 min)
- neurologic deficits
manifest mainly in the brain.
DCS - dive must be of sufficient duration to saturate tissues - onset is latent (0-36 h) - neurologic deficits manifest in spinal cord and brain.
Hx info needed for suspected AGE or DCS
Diving info: Location of the dive, timing of events during the dive and over the prior 72 hours
(length and depth of dives, safety stops, flying, and method of timing used [e.g., watch with tables,
dive computer]) , gases and equipment used (compressed air, rebreathing equipment, mixed gases)
Problems encountered : violation of no–decompression-limit dive tables, equipment, entanglement,
dizziness, marine bites or stings
Patient’s physical condition before, during, and after the dive : fatigue, drug or alcohol intake,
fever, vertigo, nausea, overexertion, pulled muscles
First aid delivered : oxygen, medications, fluids
General symptoms: profound fatigue, weakness, sweating or anorexia
Musculoskeletal symptoms: joint pain, back pain, or heaviness of extremities
Mental-status symptoms: confusion, unconsciousness, changes in personality
Eye and ear symptoms: scotomata , diplopia, tunnel vision, blurring, tinnitus, or partial hearing loss
Skin symptoms: pruritus or mottling
Pulmonary symptoms: dyspnoea, non-productive cough, or haemoptysis
Cardiac symptoms: sharp or burning chest pain
Gastrointestinal symptoms: abdominal pain, faecal incontinence, nausea, or vomiting
Genitourinary symptoms: urinary incontinence or urinary retention
Neurological symptoms: paraesthesia (general or over a joint), paresis, paralysis, migrainous
headache, vertigo, dysarthria, or ataxia
Lymphatic symptoms: oedema
Ix for DCS
No specific tests exist for DCS diagnosis.
Consider (only if doesn’t delay HBO therapy):
- Blood glucose level, FBC, clotting, U+Es,
magnesium, calcium and phosphorous levels
- ETOH and drug screen
-carboxyhaemoglobin level
Oxygen saturation
Mx for AGE/DCS
If shock: resuscitation
Do not delay HBO therapy
- Administer 100% oxygen
- Do not put the patient into the Trendelenburg position
- Consider IV fluids, if available
Transport to the nearest ED and hyperbaric facility and try to
keep all diving gear with the diver
Predisposing factors to DCS- diving factors
- Inadequate decompression (inc increased depth and
duration of dives and repeated dives) - Inadequate surface intervals (i.e. failure to decrease accumulated nitrogen)
- Failure to take recommended safety stops
- Flying or going to higher altitude soon (12-24 h) after diving
- Rapid ascent due to panic. Anxiety traits
Predisposing factors to DCS- individual
Obesity (nitrogen is lipid soluble)
- Fatigue
- Age
- Poor physical condition
- Dehydration
- Illness affecting lung or circulatory efficiency (Patent foramen ovale)
- Prior MSK injury (scar tissue decreases diffusion)
- Smoking
Predisposing factors to DCS- Environmental factors
Cold water (vasoconstriction decreases nitrogen offloading)
- Heavy work
- Rough sea conditions/poor buoyancy
- Heated diving suits (leads to dehydration)
Cylinder content- 3 options
most common = air: 21% oxygen, 78% nitrogen, approximately 1%
other trace gases, primarily argon.
Safe depth limit is about 40 m
Pure oxygen: mainly used to speed the shallow decompression
stops (military and commercial dives)
only safe down to a
depth of 6 m
Nitrox: a mixture of oxygen and air. accelerates
in-water decompression stops or to decrease the risk of
decompression sickness
Sx oxygen toxicity
disorientation, seizures, breathing
problems, vision changes (retinal detachment), death
Oxygen toxicity- pathophysiology
- collapse of the alveoli in the lungs–>
hypoxia - destruction of cell membranes –>
- chemical toxicity + haemolysis –> hepatic and renal
damage, neural toxicity
most common medical problem divers
Barotrauma can affect the external, middle, or inner ear.
Middle ear
barotrauma (MEBT) is the most common (10-30% divers)
Due to insufficient equilibration of the middle ear
inner ear barotrauma Sx
Inner ear barotrauma (IEBT) is less common
Can lead to:
- conductive and sensori- neural hearing loss
- vertigo
- auditory
hypersensitivity.
breath-holding on ascent leads to…
Pulmonary barotrauma
Compressed gas in the lungs expands –>
ruptures lungs
No associated pain.
Adjust buoyancy techniques
Before the dive:
- weights
- wetsuit
- water temperature
During the dive:
- BCD
- exhale/inhale
- swimming position
Leading causes of death diving
- Drowning (80%).
- Asphyxia
- Arterial gas embolism (AGE), caused overwhelmingly by emergency ascent with insufficient gases
>40yr- cardiovascular disease.
Prognosis AGE
Morbidity is directly related to time to HBO treatment.
If recompression with HBO occurs within 5 minutes- death rate is only 5% with little residual morbidity
If delayed 5 hours- mortality increases to 10% with residual symptoms
in 50%
Diving contraindications
Neuro:
- Epilepsy controlled by medication
- unexplained syncopal episodes
- Stroke/TIA
- Intracranial aneurysm, AVM or tumour
- Progressive neurological problems eg severe MS/Parkinson’s/ MND
Severe heart disease: -congenital heart defects - severe valve problems - severe IHD - post-MI with left ventricular dysfunction - medication to control dysrhythmias
Pulmonary:
- bullae
- severe asthma
- COPD
- Hx of spontaneous pneumothorax
Blood disorders:
- severe bleeding disorders (e.g. haemophilia)
- malignancy
- Pregnancy
- MH issues
- Inability to equalise pressure in the middle ear
