What is the most important first aid measure for decompression sickness and arterial gas embolism after an initial assessment?

Oxygen administration is the most critical first aid measure for decompression sickness (DCS) and arterial gas embolism (AGE) after an initial assessment because it addresses the fundamental problem of nitrogen bubbles forming in the body tissues and bloodstream. In both DCS and AGE, the presence of gas bubbles can lead to tissue ischemia and necrosis, and high concentrations of oxygen help to reduce the size of these bubbles by promoting their reabsorption into the bloodstream. Additionally, breathing pure or high-flow oxygen increases the partial pressure of oxygen in the affected tissues, facilitating the healing process and mitigating the effects of hypoxia.

While the other options, such as wound dressing, fluid replacement, and splinting fractures, have their roles in various medical situations, they do not directly target the critical immediate needs presented by DCS and AGE. Administering oxygen is paramount in helping to stabilize the patient and reduce further complications, making it the most effective first aid intervention in these scenarios.