Decompression Sickness: Signs, Treatment, and Prevention

What Causes DCS

When you breathe compressed air at depth, nitrogen dissolves into your blood and tissues at a rate proportional to the partial pressure — the higher the pressure (the deeper you are), the more nitrogen dissolves. As you ascend, the pressure drops and the dissolved nitrogen comes back out of solution. If the ascent is slow enough and the nitrogen loading was within no-decompression limits, this off-gassing happens quietly through the lungs without forming bubbles.

If the ascent is too fast, or the nitrogen loading exceeded safe limits, gas comes out of solution faster than the lungs can eliminate it — forming bubbles in the blood vessels, tissues, and joints. This is decompression sickness (DCS), also called 'the bends.'

Types of DCS

Type I DCS (musculoskeletal/cutaneous):

• Joint and limb pain (the 'bends' in the original sense) — most commonly shoulder, elbow, knee
• Skin manifestations: mottled red rash (cutis marmorata), itching, or localised swelling
• Lymphatic obstruction causing swelling

Type I is serious but typically not immediately life-threatening if treated promptly.

Type II DCS (neurological/cardiopulmonary):

• Spinal cord involvement: partial or complete paralysis, loss of bladder control, numbness in limbs
• Brain involvement: vision disturbance, confusion, headache, loss of consciousness
• Inner ear involvement: vertigo, nausea, tinnitus ('staggers')
• Pulmonary involvement (chokes): shortness of breath, chest pain, coughing

Type II DCS is a medical emergency. Neurological symptoms in particular require immediate treatment for the best outcome — permanent paralysis results from delayed treatment.

Signs and Symptoms: When They Appear

90% of DCS cases present symptoms within 6 hours of surfacing; 50% within the first hour. Symptoms appearing more than 24 hours after a dive are rarely DCS. Common presentations and their timing:

• Joint pain: typically 30 minutes to 6 hours post-dive
• Neurological symptoms: can appear within minutes of surfacing, or up to 6 hours later
• Skin manifestations: usually within 1–2 hours

First Aid

1. Administer 100% oxygen immediately via a non-rebreather mask. Oxygen breathing significantly accelerates nitrogen washout and reduces bubble size. This is why every dive operation must carry O₂ emergency equipment.
2. Lay the diver flat — do not elevate the legs (traditional advice) and do not put them in the head-down position; horizontal is appropriate
3. Fluids: Encourage fluid intake (water, sports drinks) if the diver is conscious and able to swallow
4. Do not re-dive: A second dive on an injured diver will worsen the condition
5. Contact DAN (Divers Alert Network) via their emergency line: they provide real-time physician advice and coordinate chamber referral
6. Transport to a hyperbaric chamber — recompression in a hyperbaric chamber is the definitive treatment. Oxygen at 2.8 bar pressure compresses the bubbles and accelerates nitrogen elimination.

Prevention

• Stay within your NDL with margin: Do not push to the limit on multiple repetitive dives
• Ascend slowly: 9–18 metres per minute; most dive computers monitor and alarm
• Safety stop: 3 minutes at 5 metres at the end of every dive below 10 metres
• Surface intervals: At least 60 minutes between dives for recreational multi-dive days
• Avoid flying: Wait 12 hours after a single dive, 18–24 hours after repetitive dives, before flying
• Stay hydrated: Dehydration reduces blood volume and increases DCS risk
• Avoid exertion post-dive: Exercise increases bubble formation from dissolved nitrogen
• Patent Foramen Ovale (PFO): An unclosed opening between heart chambers present in ~25% of people allows venous bubbles to bypass the lungs and enter arterial circulation. Divers with unexplained DCS at conservative profiles should be evaluated for PFO.