Blood volume will return to maximum. Don't worry. Shredders are very similar to L4D2 tanks. When we are far away from him, he will throw gravel at us, and when we are in the middle distance, he will launch a collision. In normal times, the attack will be greatly knocked down by his counterattack.
The way to attack is to lure him to hit the spike, and then attack wildly when he is dizzy. Basically, he can go back and forth three times.
But when the blood volume of the shredder is low, there will be a wave of zombies. Don't be impatient, be patient with this wave of zombies.