Deep-water blackout

Deep-water blackout is a loss of consciousness caused by cerebral hypoxia towards the end of a deep dive, often on surfacing. It is a significant risk in freediving and spearfishing, but can also occur in scuba diving if the diver holds their breath on ascent.

Causes

Deep-water blackouts occur when a diver, having used up the oxygen in their body during a deep dive, loses consciousness as they ascend towards the surface. This is due to the partial pressure of oxygen in the lungs dropping below the level necessary to maintain consciousness. The risk is increased by hyperventilation prior to the dive, which depletes carbon dioxide levels in the blood and allows the diver to hold their breath for longer, but also reduces the urge to breathe and can mask the onset of hypoxia.

Symptoms and effects

The symptoms of a deep-water blackout include light-headedness, tunnel vision, and a loss of motor control. If the diver does not receive immediate assistance, they can drown. Even if they are rescued, they may suffer brain damage due to lack of oxygen.

Prevention and treatment

Prevention of deep-water blackouts involves careful management of breath-holding and ascent rates. Divers should avoid hyperventilating before a dive, and should ascend slowly, especially in the final stages of the dive. If a diver experiences symptoms of a blackout, they should immediately signal for help and try to reach the surface as quickly and safely as possible.

Treatment for a deep-water blackout involves immediate rescue and resuscitation, followed by medical treatment to address any brain damage or other injuries. This may involve hyperbaric oxygen therapy or other treatments.

See also

• Shallow water blackout
• Hypoxia (medical)
• Diving safety