C-spine is a given. If I'm able to do a sternal rub, he's probably supine. Are initial ventilation attempts successful? Rule out and/or address airway obstruction. Return of spontaneous breathing? If not, intubate. If no witnesses to what happened, perform a rapid trauma exam (track marks? medi-alert bracelet or necklace? DCAP-BTLS...). Log-roll him onto an LSB and initiate priority transport. At this point my paramedic partner will take over in the back of the truck, while I drive to the ER.