What is the first step in treating a symptomatic diver who has omitted decompression?

The first step in treating a symptomatic diver who has omitted decompression is to administer oxygen or air using the recompression table. This approach is critical because immediate access to oxygen can help alleviate symptoms of decompression sickness (DCS) by facilitating the elimination of nitrogen bubbles that may form in the tissues and bloodstream during the ascent.

When a diver omits decompression, nitrogen can be released from the tissues too quickly, leading to potential symptoms of DCS. Administering oxygen increases the partial pressure of oxygen in the lungs, optimizing the off-gassing of nitrogen and providing urgent care to the diver. It's essential to act promptly, as time is a factor in the successful treatment of decompression illness.

Other actions, such as evaluating vital signs, while important, occur after ensuring that the diver has begun receiving appropriate treatment. Performing a safety stop is not applicable in this scenario, as a diver in distress should not be continuing their ascent. Ascending to the surface quickly is dangerous and might exacerbate the situation, leading to serious complications. Thus, the administration of oxygen according to the recompression protocol is the vital first step in addressing this emergency.