Final answer:
Firstly, assess for unresponsiveness when finding a patient lying supine. Perform a head tilt/chin lift if unresponsive and begin CPR if necessary. Use the Heimlich maneuver for choking, and always seek emergency medical assistance as needed.
Step-by-step explanation:
The correct first step when you find a patient lying supine along a roadside with no witnesses is to assess for unresponsiveness. This involves checking whether the patient is conscious and can respond to verbal or tactile stimuli. If the patient is unresponsive, subsequent steps would include calling for emergency assistance, opening the airway with a head tilt/chin lift maneuver, checking for breathing, and if necessary, starting CPR.
It is important not to move the patient unnecessarily before assessing their condition to avoid causing further injury. In case of a suspected drowning, the first priority would always be to get the person out of the water before attempting CPR, as administering CPR in the water is ineffective.
When someone is choking, it's critical to act quickly to restore breathing. If an infant is choking, appropriate back slaps may dislodge the object. For adults, back slaps and the Heimlich maneuver are recommended. If these fail, seek emergency medical assistance immediately.