The two dogs had been play-fighting when Patch got his jaws entangled in Frodo's collar and could not get free.
Unable to breathe, Frodo had been asphyxiated, and appeared lifeless when Tugwell cut through the collar with a knife.
"Patch was dragging Frodo around. Then I noticed that Patch's jaw had become locked in the half-chain collar, pulling it very tight and choking off Frodo's oxygen supply," The Sun quoted Tugwell, as saying.
He then moved Frodo's tongue aside, and gave the dog mouth to mouth resuscitation.
After performing the manoeuvre thrice, Tugwell heaved a sigh of relief when Frodo started breathing.
"He looked a goner. I pulled the tongue to one side, made a cone with my hands, and used the little finger of one of them to place across Frodo's nostrils," Tugwell said.
"I blew three times down the cone and to my amazement I saw Frodo's rib cage started to move.
"I threw him up in the air eight or nine times so his rib cage landed on my hands and that seemed to get him breathing more strongly."
The pooch was then rushed to a vet, and made a full recovery, returning to duty two weeks later.
"We got him to the vet and he was diagnosed with a crushed wind pipe and burst blood vessels in the throat.
"He was off work for two weeks, during which time he made a full recovery. Within three weeks of him returning to duty, Frodo made a major drugs find at the jail."
Tugwell is now set to receive an award at the Prison Service national dog trials on Saturday.