Diving Medicine
Definitions
Barotrauma: changes in ambient pressure of gas  expansion / contraction within enclosed body cavity;
can affect any non-vented gas containing space; if symptoms occur >24hrs after diving, unlikely to be due
to dive unless ascent to altitude
Boyle’s law: volume = 1 / pressure for given temp
Barometric pressure = at sea level 760mmHg (1 atm);  1 atm per 33ft sea water / 34ft fresh water; 3
atm @ 20m; pressure changes in water are linear, gas volume changes most marked at surface
Henry’s law: Q = Kpgas; @ constant temp, amount of gas that will dissolve in liquid is directly proportional
to partial pressure of gas in contact with that liquid
Dalten’s law: total pressure exerted by mixture of gases = sum of pressures of constituent gases
Diving reflex: causes peripheral vasoconstriction, bradycardia,  CO
Prevent with slow feet-first descent; attention to equilibration; use of Valsalva manouvre
Mask and external ear squeeze: due to external auditory meatal obstruction
 ear pain, tympanic membrane injury, petechiae, conjunctival haemorrhage
Problems of
Descent
Middle ear squeeze: most common medical disorder of diving; in 30% 1st time divers, 10% experienced
divers; due to eustachian tube obstruction  tympanic membrane forced inwards when Valsalva tried;
can occur in opposite direction during ascent; symptoms commence at 1 metre depth; equilibriation
impossible after 1.5m; tympanic membrane rupture at 2-6m
 ear pain, tympanic membrane rupture, vertigo, conductive hearing loss, haemotympanum, middle ear
effusion
 treat with decongestants, analgesia, antibiotics and ENT if perforation
Inner ear barotrauma: rupture of round / oval window, damage of Reissner’s membrane; onset may be
immediate / delayed hours; associated with middle ear squeeze in 2/3
 sensorineural hearing loss, vertigo, tinnitus, N+V; perilymphatic fistula = fluctuating symptoms
exacerbated by positional changes
Differential diagnosis: decompression sickness (onset after emergence from water)
 urgent referral to ENT, head of bed up, no nose blowing
Dental squeeze: dental surgery / decay; treat with recompression, dental drilling
Nitrogen narcosis: during deep dives; disorientation and LOC; prevent by using helium; immediately
reverses on ascent
Immersion induced pulmonary oedema: onset while underwater
Pulmonary barotrauma: air forced across pulmonary capillary membrane when pressure difference
>80mmHg (@ approximately 1m); can occur within only 2m, usually due to panicked ascent;  risk if
asthma, COPD (air trapping)
 SOB, chest pain, interstitial / subcutaneous / mediastinal emphysema, pneumothorax
 Arterial gas embolism (AGE): 50% chance of AGE - always look for neurological symptoms to exclude
AGE (including cognition and memory)
Problems of
Ascent
Arterial gas embolism (AGE, ARTERIAL): 2nd most common cause of death in diving (after drowning)
Pathology: Failure to exhale / regional gas trapping during ascent  pulmonary over-pressurisation 
alveolar rupture  entry of gas into pulmonary capillaries  pass into cerebral circulation (as dependent
on volume of blood flow, not gravity, brain receives 20% blood flow), L atrium, L ventricle, aorta, coronary
arteries  obstruct blood vessels / cause inflammatory response affecting BBB / activates coagulation
cascades /  vascular permeability / vasospasm temporary loss of neuronal function,
ischaemia/infarction, cerebral oedema (within 30mins – 24hrs, peak  ICP at 1hr), interstitial oedema
Causes: diving while breathing compressed gas (eg. Scuba); can occur during short dives
direct entry of gas into circulation (eg. Iatrogenic, trauma)
venous gas embolism  enters arterial circulation through RL shunt (eg. ASD, PFO) or pulmonary
capillary bed; if this is cause of AGE, may be pulmonary oedema due to capillary endothelial leak
Symptoms: occur within 5-20 mins of ascent / in water; may get spontaneous recovery then relapse
 NS (brain only; FND, confusion, altered LOC, seizures (associated with poor prognosis), headache,
visual changes)
 CV (haemoptysis, CV instability (severe shock in 5%, arrhythmia, MI), features of pulmonary
barotrauma)
Investigations: Diagnosis is clinical; CXR may show intravascular air, CT/MRI may show changes, CK may be
marker of severity, degree of haemoconcentration, marker of neurological outcome
Problems of
Ascent (cntd)
Sinus squeeze: less common than ear; usually frontal / maxillary; facial pain; epistaxis on ascent,
infraorbital nerve paraesthesia; treat with decongestants, valsalva
Alternobaric vertigo: unequal ear equalisation; vertigo during ascent (can occur on descent), duration secsmins; no hearing loss
Shallow water blackout: syncope secondary to hypoxia after hyperventilating off CO2; LOC during ascent
Decompression illness = decompression sickness or AGE
Decompression
Illness /
Sickness
Decompression sickness (DCS, VENOUS): injury due to bubble formation in blood and tissues; incidence in
recreational scuba divers 2-3/10,000 dives
Risk factors = obese, smoker, ETOH, exercise, cold, dehydration, previous joint injury, old, binge drinking
night before, other medical illness, female, aerobic capacity, local physical injury;  dive duration / depth
(>18 metres), multiple dives, rate of ascent, no decompression stops, ascent to altitude soon after diving,
cold water
Pathology: inert gas (especially nitrogen) dissolved  dissolved nitrogen forms bubbles on ascent (in veins,
lymphatics, tissues)  tissue injury by same mechanism as AGE  lungs act as filter (off-gassing),
preventing bubble entry to systemic circulation
 symptoms occur if: pulmonary circulation overwhelmed (usually self limiting but indicates large bubble
load)
RL shunt (eg. PFO, ASD)  AGE
Pulmonary barotrauma so severe that bubbles enter pulmonary circulation
Symptoms: onset may be delayed - 50% onset within 1 hour, 90% within 6 hours (occasionally longer); may
be progressive, stable, relapsing and remitting, minor, Severe
Type I (non-systemic, musculoskeletal): joint pain, rash (skin marbling; usually resolves in 12-24hrs), itching;
maybe transient symptoms, poorly localised; may be no signs of inflammation; most common shoulder /
elbow / knees; usually single joint; relieved by pressure
Type II (neurological / systemic): affects NS (SC (in 60%) or CNS)
NS: starts with feeling of truncal constriction  numb feet, dizziness, weakness, gait probs, ascending
paralysis, autonomic; maybe patchy and multiple sites; spinal cord symptoms, distended bladder;
poor prognosis if sphincter involvement / psychiatric; associated with aching pain
Vestibular (the staggers): symptoms after emergence (as opposed to inner ear barotrauma)  vertigo,
nystagmus, tinnitus, N+V
Pulmonary (the chokes): rare; due to massive pulmonary gas embolism CP, cough, SOB, haemoptysis, CV
collapse
Type III: DCS + AGE = type II + stroke symptoms
Supine position (no leg elevation; head down position may  gas bubbles to coronary arteries)
B: 100% O2 (even if not hypoxic; enhances inert gas elimination and bubble resolution, symptoms may
resolve but frequently recur)
C: IVF (maintain hydration to prevent 2Y ischaemic insult, avoid dextrose as may worsen neurological
injury); Treat arrhythmias (usually refractory to standard treatment)
D: Mannitol if impending cerebral herniation
E: Transport at sea level (or at least <1000ft or pressurised aircraft)
Lignocaine may improve outcome if treatment delayed (give for 48 hours)
Not useful: anticoagulation ( risk of spinal cord haemorrhage), steroids, aspirin
Management
Hyperbaric Oxygen: 100% O2 at 2.8atm (18m, p O2 2000mmHg, 13x room air); usually require 1-2
treatment of 1 hour; early in type I, immediate in type II; reduces bubble volume, promotes nitrogen
reabsorption and excretion, inhibits secondary inflammation and reperfusion injury, improves
oxygenation of tissue, reduces ICP, improves brain metabolism; effectiveness in barotrauma strongly
supported by research; place chest drain 1st if pneumothorax; early treatment = better outcome; requires
close neurological monitoring in chamber; NSAIDs may  number of sessions needed
Indications: decompression illness / AGE: if any symptoms (even if become asymptomatic with 1st aid) and
no contraindications; best if started within 72 hours; 55% resolve with 1 treatment, 75%
with all treatments; if symptoms not responding significantly within 10-20 minutes, go
deeper/longer; extend treatment if symptom recurrence during treatment
CO poisoning: COHb >20, CV / NS signs; lower threshold if respiratory disease / pregnancy
Other: cyanide, H2S, CCl4, clostridial infection
Side Effects: O2 toxicity (formation of O2 free radicals  cerebral toxicity (muscle twitching, apprehension,
vertigo, visual problems, nausea, confusion, dizziness, seizures), pulmonary toxicity (cough, retrosternal
pain,  vital capacity); middle ear barotrauma, claustrophobia
Prognosis
Decompression Sickness: complete recovery possible despite severe symptoms; residual deficit 25% (more
likely if delayed treatment); worse outcome if spinal cord symptoms
Flying after diving: delay at least 12 hours after single non-decompression dive
At least 18 hours after multiple dives / multiple days of diving
>>18 hours for any decompression dives
At least 1/52 if treatment for decompression illness
More diving: congestion of tympani membrane  1-3/7 off diving
Tympanic membrane haemorrhage  1/52 off diving
Haemotympanum  6/52 off diving