Board Thread:Warhammer 40k Roleplay/@comment-67.141.249.249-20130713231947/@comment-3258762-20130716174427

But they do not use the saw when treating a patient. If the astartes can be saved, stimulants can be injected by the neck joint.

The saw is used to access the Progenoid gland, which is to be removed upon death of the Astartes. As such, it doesn't matter if it cuts into the flesh of the Astartes for a matter of seconds.