Complex sentence: Determined to hold out for rescue, he goes to horrifying lengths to survive, using his surgical training to amputate his own limbs to use as a food source, ingesting the heroin for anesthesia during the operations.
Split into simpler sentences: Determined to hold out for rescue, he goes to horrifying lengths to survive. He continues to amputate his own limbs to use as a food source, ingesting the heroin for anesthesia during the operations.