A headache during or after a dive is most consistent with which condition?

• A. Hypercapnia
• B. Decompression sickness
• C. Nitrogen narcosis
• D. Barotrauma

Answer: (A)

When a headache appears during or right after a dive, the most consistent cause is hypercapnia—elevated carbon dioxide levels in the body. In closed-circuit diving, this often points to CO2 retention from inadequate ventilation or a fault in the gas handling system, such as an exhausted CO2 scrubber or poor gas exchange in the mouthpiece/regulator. CO2 buildup raises cerebral blood flow and intracranial pressure, which commonly produces a headache and can accompany feelings of shortness of breath or a sense of not getting enough air.

Decompression sickness can also cause headaches, but it typically comes with other signs like joint or muscle pain, skin changes, dizziness, or neurologic symptoms, and may not be as tightly linked to the immediate dive ventilation. Nitrogen narcosis produces cognitive changes and altered judgment under depth, with headache not being the defining feature. Barotrauma causes local pressure-related pain in the ears or sinuses, with the primary signs being ear fullness or sharp pain, not a primary headache pattern.

So the headache pattern most directly aligns with CO2 buildup from ventilation or gas-handling issues, i.e., hypercapnia. If suspected, address ventilation and gas exchange immediately and reassess the dive system to prevent further CO2 retention.