Dysbarism Flashcards
Boyle’s Law:
The volume of gas is inversely proportional to the pressure acting on it
Ie. gases and gas-filled cavities expand at low pressure (eg. Plane) and compress at high pressure (eg. Diving)
At 10m, gas volume is halved.
Henry’s Law:
Thee amount of gas that will dissolve into a liquid, is proportional to its partial pressure.
Ie. At depth, nitrogen will dissolve into blood and tissues +. On ascent, it will diffuse out.
Classify complications of diving:
Barotrauma
Decompression illness (DCI)
Nitrogen bubbles in vessels and tissues
Can move venous —> arterial (AGE )
Arterial Gas Embolism (AGE)
—> resulting from either DCI or lung barotrauma
Nitrogen narcosis
Confusion, impaired judgement, poor coordination.
Due to high pp nitrogen at depth
30m+
Oxygen toxicity
Depth of occurrence is dependent on FiO2 of chosen gas
Saltwater aspiration
Diving APO
Drowning/asphyxia
Carbon monoxide (surface supply)
Basis of decompression illness (DCI):
Occurs 1 to 24 hours after surfacing
At depth, nitrogen dissolves into tissues (Henry’s Law)
Slow ascent- nitrogen diffuses out slowly, and is breathed off
Rapid descent- nitrogen ‘bubbles’ out into:
Veins—> problematic if these cross PFO/ lung into arterial system —> AGE - mechanical, Inflamm, thrombotic
Tissues—> distortion, pain, inflammation, functional impairment
Clinical features of DCI:
Usually 1- 24 HOURS after surfacing
Early (<1hr) more serious
Type 1 DCI- MSK/ skin only
- Muscle and joint pain
- Mottling —> cyanotic patches (cutis marmorata)
- Itch
Type 2 DCI- all other
- Nonspec: headache, fatigue
- CNS: amnesia, seizure, memory, personality, ALOC
- PNS: sensory/ motor. Often patchy, nonsensical.
- Vestibular: ataxia, vertigo
- Spinal cord
- Pulmonary: chest pain, SOB, frothy sputum, haemoptysis
Differentials for SOB after a dive:
Barotrauma: PTx
DCI: pulmonary DCI (‘the chokes’)
Saltwater aspiration
Diving APO
Near drowning
Oxygen toxicity
Gas contamination
Marine envenomation
Non-diving related
Arterial Gas Embolism in diving:
Abrupt onset VERY SOON (secs to mins) after surfacing
2 mechanisms:
- Lung barotrauma —> ’big bubbles’
- Venous DCI —> crosses PFO or overwhelms lungs —> arterial —> ’small bubbles’
Often dramatic:
CAGE: LOC, seizure, paralysis, focal deficits - most common re gas rising
Spinal cord
AMI
Organ infarct
SUSPECT IN ANY SYMPTOM WITHIN MINUTES OF SURFACING
APPROACH TO SUSPECTED DIVING ILLNESS:
IMMEDIATE
Keep SUPINE if any suspicion of CAGE
100% O2 via HFNP
Warm
HISTORY
Depth, duration, rapidity of ascent
- >10m O2 tox, >30m nitrogen narcosis
Gas type and equip
- O2 enriched eg Nitrox risks O2 toxicity, CO risk surface supply
Timing of symptom onset
- SECS to MINS= AGE, hours more likely DCI
?Recent/ frequent dives
?Altitude/ heavy exertion post
EXAM
Full exam, incl
-thorough Neuro: MMSE, cerebellar, limbs,
- Skin
INVESTIGATIONS
- PTx imaging is only essential Ix
—> CT or USS cos supine
—> Needed for ?CAGE, and before HBO
- Other Ix guided by Sx
Consider diving DDx: APO/ aspiration/ drowning/ narcosis/ CO etc.
Management of DCI:
100% O2 via HFNP
Fluids
SUPINE until AGE ruled out
—> if any doubt, CT chest (can’t sit up for CXR)
Fly BELOW 300m (or highly pressurised, not commercial)
Hyperbaric O2
Refer ALL for consideration:
—> ASAP. sooner = better outcomes, but can be of benefit any time (up to 14 days)
—> Even if symptoms improved, relapse
DISCHARGE ADVICE:
Not evidence based
Avoid flying 1 week
Avoid diving 4 weeks, and only once asymptomatic
Management of CAGE:
Same as DCI.
PLUS:
Lignocaine infusion 1mg/kg for 48hours
- Reduces neuropsych sequelae
Complications of HBO:
Barotrauma
—> ALL need PTx ruled out or Tx
non emergently, sometimes get grommets
O2/nitrogen toxicity
Claustrophobia
Difficult space for interventions
Contraindications to HBO:
The ONLY absolute is untreated pneumothorax
Lung imaging for all first.
Risk factors for DCI/AGE:
Multiples dives
Multiple ascents within a dive
Cold water
Increasing depth
Longer duration
Rapid ascent
Altitude after dive (eg. Flight)
Heavy exertion after dive
PFO
Differentials for neuro symptoms following a dive:
Neurological DCI (brain, spinal cord, vestibular)
CAGE (or embolus to cord)
Gas contamination
Nitrogen narcosis - *resolves very shortly after surfacing
Oxygen toxicity
Vestibular Barotrauma (vertigo)
Marine envenomation
Non-diving related
Examples of diving Barotrauma:
Pneumothorax
Pneumomediastinum
Middle ear- vertigo
Sinus
‘Mask squeeze’- subconjunctival haemorrhage, skin
Dental pain
