Decompression Sickness and Hyperbaric Medicine
On this page
Direct answer
Decompression sickness is a condition in which dissolved inert gas, mainly nitrogen, forms bubbles in tissues and blood when a diver or caisson worker ascends too quickly after pressurised exposure. Type I involves the skin, joints and lymphatics and is usually milder, whereas type II involves the central nervous system, lungs or inner ear and is more serious. First-line management is high-concentration oxygen and urgent recompression in a hyperbaric chamber.
What you must remember
- Mechanism: under Henry's law, gas dissolves more at higher pressure, and rapid ascent releases it as bubbles.
- Type I: pain in joints, skin mottling or itching and lymphatic swelling, usually less severe than type II.
- Type II: neurological deficits such as spinal cord signs, vestibular symptoms and cerebral features, or pulmonary involvement.
- Arterial gas embolism: caused by pulmonary barotrauma from breath-holding on ascent, with cerebral symptoms within minutes of surfacing.
- Barotrauma of ascent: pneumothorax and mediastinal emphysema, which need their own immediate treatment.
- Barotrauma of descent: middle ear and sinus squeeze during descent, a different entity from bubble formation on ascent.
- Recompression principle: raising pressure shrinks bubbles and increases oxygen delivery to ischaemic tissue.
A pathway from a diving accident to the chamber
A 30-year-old diver surfaces rapidly after a deep dive and reports joint pain and tingling in both legs within an hour. The sequence below sets the priorities, because delay in recompression worsens the outcome.
- Recognise the pattern: pain, numbness, weakness, vertigo or breathlessness after diving or caisson work suggests decompression illness.
- Separate barotrauma: pneumothorax or arterial gas embolism needs its own first-line action, so the chest and neurological state are examined at once.
- Give oxygen: high-concentration oxygen by a non-rebreather mask, the patient lying flat, and intravenous fluids while transfer is arranged.
- Recompress urgently: refer to a hyperbaric chamber, where the treatment table is run under a standard schedule, because delay worsens the outcome.
- Monitor the course: repeat neurological assessment and watch for residual deficits during and after the treatment course.
- Counsel for future dives: advise against repeat diving without medical clearance and avoid flying for a period after diving.
Where the exam tries to catch you
Decompression questions test the difference between bubble disease, barotrauma and the appropriate treatment for each.
- Trap: treating decompression sickness with fluids and rest alone Correct: recompression with oxygen is definitive, and fluids and rest are supportive only.
- Trap: dismissing neurological symptoms as tiredness after a dive Correct: cerebral or spinal signs indicate type II disease or arterial gas embolism and need urgent recompression.
- Trap: using hyperbaric oxygen for any non-healing wound Correct: hyperbaric oxygen is reserved for approved indications with evidence, and use outside them is not justified.
- Trap: labelling ear pain on descent as decompression sickness Correct: that is barotrauma of descent from middle ear squeeze, not bubble formation during ascent.
Frequently asked questions
What is the difference between type I and type II decompression sickness?
Type I decompression sickness involves the skin, joints and lymphatics and is usually less severe. Type II decompression sickness involves the central nervous system, lungs or inner ear and needs urgent recompression.
Why is arterial gas embolism treated as an emergency?
Arterial gas embolism causes cerebral symptoms within minutes of surfacing and can be rapidly fatal. Recompression is started without delay because the bubbles block cerebral and coronary circulation.
What is the first aid for suspected decompression sickness?
First aid for suspected decompression sickness is high-concentration oxygen, lying flat, intravenous fluids and immediate transfer for recompression. The patient should not be given further dives or be allowed to exert themselves.
Which conditions are approved indications for hyperbaric oxygen therapy?
Decompression sickness, arterial gas embolism and carbon monoxide poisoning are among the established indications for hyperbaric oxygen therapy. Other indications, such as gas gangrene and selected wounds, are listed by specialist bodies and used under strict criteria.
How does hyperbaric oxygen help decompression sickness?
Hyperbaric oxygen raises pressure, which shrinks gas bubbles and allows oxygen to dissolve in plasma at high concentrations. This improves oxygen delivery to ischaemic tissue and helps the body clear the bubbles over the treatment course.