Final answer:
If a swimmer unable to progress is not assisted, they may be at risk of drowning. A drowning person can often not shout or wave for help, and CPR must be conducted after removing them from water and on solid ground to be effective.
Step-by-step explanation:
When a swimmer slows down during a lap swim and can no longer make forward progress, there is a concern that they might be experiencing the onset of drowning. Contrary to the popular myth, a person who is drowning may not be able to shout for help or wave their arms; the muscular spasm that seals the airway during drowning prevents both the intake of air and the ability to vocalize. This means that even though someone appears to be calm and not in distress, they might actually be in the final stages before going underwater.
If the swimmer is not assisted, the risk of drowning increases significantly. An unconscious person can still be saved, as long as their airway was protected by a muscular spasm that prevented water from entering the lungs. Immediate rescue and administration of CPR once on stable ground is critical. The sooner CPR is started, the higher the chances of recovery, but after about six minutes without oxygen, the likelihood of brain death increases, except in cases of cold water submersion, where there have been instances of longer survival times.
Furthermore, CPR should only be started after the person is removed from the water. This is because CPR is ineffective in the water and should be performed on stable ground. Once the person is safely removed from the water and on stable ground, it's imperative to commence CPR promptly to maximize the possibility of a successful resuscitation.