Just something I've tried with success in the past, when the blood trail peters out, I spiral search instead of keep looking in the direction of travel. If they aren't heading towards a known heavy cover safe spot, half the time they are doubling back in the direction they came from. They may head off in a direction then loop back the way the came from.
Most any Dog is going to pick up that fine lung spray and go nuts. My Dogs would follow a trail like that at 30 MPH if you let them, the scent is so strong they don't need to sniff the ground.
I'm not particularly good or talented at tracking, I make up for it with perseverance.