01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Boyle's law explains pulmonary over-expansion: as ambient pressure falls on ascent, intrapulmonary gas expands. A closed glottis during panic ascent, equipment-related breath-holding, asthma, mucus plugging, bullae or another local obstruction can prevent gas escape and tear alveoli.
Gas tracking along tissue planes causes pneumomediastinum and subcutaneous emphysema; pleural entry causes pneumothorax. Gas entering pulmonary veins reaches the arterial circulation and can obstruct cerebral or coronary vessels. Neurological AGE and decompression sickness overlap clinically and are grouped operationally as decompression illness because both need urgent hyperbaric expertise.
The central decisions are whether a tension pneumothorax needs immediate decompression, whether neurological symptoms justify emergency recompression, and whether another diving illness or trauma coexists. Dive tables and imaging refine the assessment but never replace ABCDE resuscitation and early specialist contact.
Key points
- Compressed gas expands during ascent, with the greatest proportional volume change near the surface; breath-holding or regional airway trapping can rupture alveoli even after a shallow dive.
- Escaped gas may cause pneumothorax, tension pneumothorax, pneumomediastinum, subcutaneous emphysema or entry into pulmonary veins with arterial gas embolism.
- A stroke-like deficit, seizure, visual change, confusion or loss of consciousness within minutes of surfacing is arterial gas embolism until urgently assessed, even if symptoms improve spontaneously.
- Chest pain, dyspnoea, voice change, neck crepitus or haemoptysis after ascent suggests pulmonary over-expansion injury; normal initial radiography does not exclude small mediastinal gas or gas embolism.
- Give 100% oxygen immediately and call emergency plus diving-medicine services. Oxygen reduces bubble size and improves oxygen delivery; it should continue during transfer whenever safely possible.
- Do not use Trendelenburg positioning, in-water recompression, commercial-air travel or unpressurised altitude transfer unless the diving and retrieval teams explicitly direct the safest option.
- Tension pneumothorax is a resuscitation diagnosis and must be decompressed before hyperbaric chamber treatment because trapped pleural gas can expand and destabilise the patient.
- Do not delay a compelling arterial gas embolism referral for extensive imaging; the hyperbaric specialist should help sequence CT, trauma care and chamber transfer.
- Routine aspirin, anticoagulation, corticosteroid and prophylactic antibiotic treatment is not indicated for gas embolism or uncomplicated pulmonary barotrauma.
- No further diving is permitted until specialist assessment. At-work divers require the HSE return-to-work process; recreational divers need a UKDMC-recognised diving medical opinion.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Breath-holding during ascent
Failure to exhale as ambient pressure falls allows expanding intrapulmonary gas to overdistend and rupture alveoli.
Air trapping
Asthma, mucus plugging, bullae or equipment-related breathing obstruction can create regional gas trapping even when the diver attempts a controlled ascent.
Rapid or uncontrolled ascent
Panic, buoyancy problems and emergency ascent magnify pressure change and reduce time for lung gas to escape safely.
Compressed-gas exposure
Pulmonary over-expansion can occur from shallow depth because relative pressure change is substantial near the surface; great depth is not required.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Expanding alveolar gas
During ascent, decreasing environmental pressure expands gas within the lungs according to pressure-volume relationships, which links the underlying lesion to the observed respiratory dysfunction.
- 2Alveolar rupture
When gas cannot escape, overdistension tears alveolar walls and releases air into interstitial, pleural or vascular compartments.
- 3Arterial gas entry
Gas entering pulmonary veins travels to systemic arteries, where bubbles obstruct cerebral or coronary circulation, which links the underlying lesion to the observed respiratory dysfunction.
- 4Inflammatory vascular injury
Beyond mechanical blockage, bubbles activate endothelium, platelets and inflammation, worsening tissue oedema and ischaemia, which links the underlying lesion to the observed respiratory dysfunction.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
A rapid or uncontrolled ascent, breath-holding, out-of-air emergency or obstructive lung disease followed immediately by chest symptoms strongly supports barotrauma. It can occur despite apparently compliant computer profiles.
Retrosternal pain, dysphagia, voice change, neck swelling or palpable crepitus after surfacing suggests mediastinal and subcutaneous gas. Haemodynamic stability does not exclude an associated pneumothorax or AGE.
Severe respiratory distress, unilateral reduced air entry, hypotension, tachycardia, increasing ventilatory pressure or peri-arrest physiology after ascent requires immediate decompression without waiting for a radiograph.
Abrupt focal weakness, aphasia, visual loss, vertigo, seizure, confusion or coma during ascent or soon after surfacing is characteristic. Rapid spontaneous improvement does not remove the need for hyperbaric assessment.
Chest pain, dysrhythmia, shock or cardiac arrest immediately after ascent may reflect coronary gas, hypoxia or another cardiac event. Treat standard resuscitation needs while contacting hyperbaric medicine.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Dive profile and computer downloadFirst step - Why
- Reconstruct pressure exposure and mechanism without delaying treatment.
- Interpretation and limitations
- Record maximum depth, bottom time, gas mixtures, stops, ascent rate, breath-holding, equipment failure, repetitive dives, flying, symptoms at depth and buddy observations. A normal profile does not exclude AGE.
- 02
Serial full neurological examination - Why
- Detect and track cerebral or spinal decompression illness.
- Interpretation and limitations
- Document consciousness, speech, cranial nerves, vision, limb power, sensation, coordination, gait and bladder function. Repeat before and after oxygen because fluctuating or resolved deficits still matter.
- 03
Chest examination and point-of-care ultrasound - Why
- Identify pneumothorax or haemodynamic compromise immediately.
- Interpretation and limitations
- Absent lung sliding can support pneumothorax but operator and context matter. A clinically unstable tension pneumothorax is decompressed without waiting for ultrasound or radiography.
- 04
Chest radiograph - Why
- Show pneumothorax, mediastinal gas and other pulmonary complications.
- Interpretation and limitations
- A normal film does not exclude small barotrauma or arterial gas embolism. Obtain it when it does not delay urgent recompression and repeat if symptoms evolve.
- 05
CT chest - Why
- Define subtle mediastinal, pleural or parenchymal injury in a stable patient.
- Interpretation and limitations
- CT is more sensitive for small gas collections, bullae and alternative pathology but transfer for compelling AGE should be sequenced with the hyperbaric clinician rather than delayed automatically.
- 06
ECG and cardiac troponin - Why
- Assess coronary embolism, ischaemia and dysrhythmia.
- Interpretation and limitations
- Abnormalities require monitored resuscitation and cardiology input but do not exclude concurrent cerebral AGE. Treatment choices should be coordinated with hyperbaric medicine.
- 07
Blood gas and basic laboratory profile - Why
- Assess oxygenation, ventilation, lactate and organ consequences.
- Interpretation and limitations
- Results support resuscitation but cannot rule out intravascular bubbles. Check glucose, full blood count, renal function and electrolytes for mimics and safe critical-care transfer.
- 08
Trauma and ear examination - Why
- Find concurrent injuries from ascent, impact or pressure change.
- Interpretation and limitations
- Assess cervical mechanism, tympanic membranes, vertigo and facial or chest trauma. Neurological symptoms should not be dismissed as middle-ear barotrauma without a complete examination.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Decompression illness
Inert-gas bubble disease often follows longer or deeper exposure and may cause joint, skin or neurological symptoms, but overlap requires diving-medicine advice.
Primary neurological event
Stroke, seizure or intracranial haemorrhage may occur coincidentally, yet sudden deficits immediately after surfacing strongly raise arterial gas embolism.
Pneumothorax unrelated to barotrauma
Underlying cystic lung disease can cause spontaneous pleural air, though the timing during ascent suggests pressure-related rupture.
Aspiration or immersion pulmonary oedema
Cough and hypoxaemia after a dive without focal neurological signs may reflect water aspiration or immersion-related oedema rather than over-expansion injury.
Additional chapter-specific clues
Decompression sickness, immersion pulmonary oedema, aspiration, salt-water inhalation, myocardial ischaemia, stroke, seizure, hypoglycaemia and trauma can mimic or coexist; none justifies withholding emergency oxygen or specialist advice.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Dive incidentStart oxygen and specialist contactFirst stepAny serious chest, neurological or cardiorespiratory symptom during ascent or after surfacing.+
- 1Call 999 or Coastguard at sea, give 100% oxygen by tight-fitting mask, keep the casualty lying horizontally, warm and monitored, and use the live BHA emergency contact.
- 2Perform ABCDE assessment with glucose and a documented neurological examination, treating arrest, hypoxaemia, seizure, trauma and shock in parallel.
- 3Preserve the dive computer and record profile, gas and symptom timing, but do not postpone evacuation or oxygen to complete a perfect history.
- 4Agree destination, imaging and pressure-safe transport with the diving physician; avoid altitude exposure and never attempt in-water recompression.
02TensionRelieve pressure before chamber transferHaemodynamic or severe respiratory compromise with suspected pneumothorax after ascent.+
- 1Diagnose clinically, continue high-concentration oxygen and perform immediate pleural decompression using the current trauma protocol and trained operator.
- 2DefinitiveInsert definitive thoracic drainage when indicated and secure it for transport, checking function and recurrence rather than clamping a bubbling system casually.
- 3Inform the hyperbaric service because AGE and decompression sickness may coexist; an untreated tension pneumothorax makes pressure changes dangerous.
- 4Use lung-protective ventilation if intubation is required and reassess for bilateral injury, mediastinal gas, haemorrhage and equipment-related complications.
03Neurological AGEExpedite recompression assessmentFocal deficit, seizure, confusion, visual disturbance or loss of consciousness at or soon after surfacing.+
- 1Continue 100% oxygen, place supine or in a comfortable horizontal position, protect the airway and treat seizures while avoiding head-down positioning.
- 2Contact the National Diving Accident service immediately and describe the exact onset, evolution, examination, dive profile and possible pneumothorax.
- 3Do not cancel referral because symptoms resolve or CT brain is normal; bubbles may have moved while tissue injury remains and early HBOT can still be indicated.
- 4Coordinate imaging for trauma or haemorrhage only when it changes immediate safety, with the hyperbaric and retrieval teams controlling any delay to recompression.
04RecoveryPrevent premature return to divingAcute symptoms have resolved after conservative care, drainage or HBOT.+
- 1Arrange follow-up with a diving-medicine physician to review lung imaging, pulmonary function, mechanism, neurological recovery and risk of recurrence.
- 2Prohibit diving, flying and altitude exposure for the interval specified by the treating hyperbaric team; generic waiting periods are unsafe after serious injury.
- 3For a diver at work, use an HSE Approved Medical Examiner of Divers and statutory return-to-work process; recreational clearance follows current UKDMC standards.
- 4Address asthma, bullae, smoking, equipment practice, panic or training issues before any decision about future compressed-gas exposure.
Key medicines and prescribing safety5 treatments · regimens, roles and cautions+
Normobaric 100% oxygen
Deliver continuously through a tight-fitting non-rebreather or secured airway at the highest feasible inspired concentration during transfer and consultation.Do not interrupt for unnecessary tests. Ensure adequate cylinder supply and ventilation, observe fire precautions, and remember oxygen does not decompress a tension pneumothorax.
Isotonic crystalloid
Give cautious boluses or maintenance guided by perfusion, oral tolerance, urine output and the diving or critical-care specialist plan.Avoid routine aggressive loading, particularly with pulmonary oedema or cardiac disease. Oral electrolyte fluid is suitable only if fully alert with safe swallowing and no urgent anaesthetic need.
Analgesia
Titrate paracetamol or an opioid to pain and physiology under the emergency formulary, preserving serial neurological assessment and ventilation.Sedation can obscure neurological deterioration and suppress breathing. Avoid nitrous oxide because it can expand trapped gas spaces; adjust opioid choice for shock and renal function.
Anticonvulsant rescue treatment
Treat an ongoing seizure using the current emergency benzodiazepine and status-epilepticus protocol while securing oxygenation and expert help.Respiratory depression may necessitate intubation. Seizure control does not treat the gas embolism and must not delay hyperbaric referral or pneumothorax assessment.
Anticoagulants and corticosteroids
Do not administer routinely for pulmonary barotrauma or arterial gas embolism unless a separate confirmed indication has specialist support.Anticoagulation can worsen traumatic or pulmonary bleeding, while steroid toxicity adds risk without replacing oxygen and HBOT. Investigate alternative stroke or thrombotic diagnoses carefully.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Cerebral arterial gas embolism
Bubbles in cerebral vessels cause abrupt confusion, focal deficits, seizure, coma or death and require immediate specialist hyperbaric coordination.
Coronary gas embolism
Gas entering coronary arteries may cause myocardial ischaemia, arrhythmia and cardiac arrest, with severity determined by its extent and the patient's underlying reserve.
Tension pneumothorax
Pleural air can expand further during ascent or positive-pressure ventilation and produce obstructive shock, and potentially prolonging treatment and functional recovery.
Pneumomediastinum
Interstitial air may track centrally into the mediastinum and neck, causing chest pain, voice change and subcutaneous emphysema.
Persistent neurological disability
Delayed bubble clearance and secondary inflammation can leave cognitive, motor or balance impairment despite initial stabilisation.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Repeat a structured neurological examination during oxygen, transport and after HBOT; transient recovery does not mean the emergency has resolved.
- Track respiratory rate, SpO2, work of breathing, chest symmetry, crepitus and haemodynamics for evolving or recurrent pneumothorax and pulmonary oedema.
- If a chest drain is present, monitor swinging, bubbling, output, connections and securement across pressure and transport changes under the specialist plan.
- Use continuous ECG monitoring when there is collapse, chest pain, dysrhythmia or possible coronary gas, trending troponin and perfusion as indicated.
- Document oxygen concentration and cylinder reserve throughout retrieval so treatment is not inadvertently interrupted during transfer between services.
- After treatment, follow cognitive, vestibular, pulmonary and functional recovery and ensure written restrictions on diving, flying, work and driving are explicit.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
The last metres carry large expansion
Ambient pressure changes proportionally most near the surface, so a shallow emergency ascent with a held breath can cause major over-expansion despite a modest maximum depth.
A compliant profile does not exclude AGE
Decompression computers model inert-gas exposure; they cannot prevent a local lung segment from trapping expanding gas during ascent. Mechanism and immediate symptoms remain decisive.
Improvement does not cancel recompression
Arterial bubbles can move or fragment and neurological findings can fluctuate. Tissue ischaemia and inflammatory injury may persist after a normal examination returns.
Chest gas and neurological gas coexist
The same alveolar rupture can produce pneumothorax and AGE. Searching for pleural pressure is essential before chamber pressurisation or altitude transfer.
Immersion pulmonary oedema is different
Dyspnoea and frothy sputum developing during a dive without ascent injury may reflect immersion pulmonary oedema. It still needs emergency oxygen and assessment but has different recurrence evaluation.
11Common pitfallsFrequent interpretation and management errors.
- 01
Withholding oxygen because pulse oximetry is normal or neurological symptoms have improved.
- 02
Placing a patient head-down in the outdated belief that it keeps bubbles away from the brain.
- 03
Waiting for CT brain or a visible bubble before contacting hyperbaric medicine.
- 04
Sending an unstable tension pneumothorax into a chamber or altitude transfer before decompression.
- 05
Attempting in-water recompression without a specialist operational system and creating drowning or hypothermia risk.
- 06
Assuming a normal dive-computer profile excludes pulmonary barotrauma or AGE.
- 07
Giving aspirin, anticoagulation or corticosteroid reflexively for a stroke-like presentation caused by gas.
- 08
Allowing return to recreational or occupational diving without the appropriate diving-medicine clearance.