What is the purpose of giving oxygen to a diver in distress after ascending?

The reason for administering oxygen to a diver in distress after ascending is primarily to enhance respiratory function. When a diver is in distress, especially after a potentially hazardous situation like an incomplete or rapid ascent, the lungs may require assistance in processing oxygen effectively. Providing supplemental oxygen helps to replenish oxygen levels in the blood, facilitating better gas exchange in the lungs. This is critical, particularly if the diver is exhibiting any symptoms of hypoxia or the effects of decompression sickness, which can influence the respiratory system's efficiency.

Although other factors such as blood circulation and overall safety (including drowning prevention) are certainly important considerations in diver care, the immediate physiological need in many distress situations is focused on optimizing oxygenation of the blood and supporting the respiratory system.