What Does A Life Sentence Mean?

Came across this little ditty in the news today. There's a guy serving a life sentence in Iowa. He's arguing for release after this happened.

In 2015 this prisoner fell unconscious in his cell after his heart stopped beating. The prison staff took him to the hospital. Where doctors were able to bring him back to life after getting his heart beating again after the fifth try. He is now claiming he's being held illegally because his "life sentence" should have been up four years ago. So far the court disagrees with him.

The judge reasoned dying doesn't earn someone a get out of jail free card. I agree this makes sense, but what does the law say specifically?

Seems to me the law should define exactly what it considers to be a "life sentence". Oft times a judge will require someone convicted to remain behind bars throughout his or her "natural life". This should be clearly defined. If one or neither is not this case deserves additional consideration

I think law should specify whether prison staff is required or not to revive a prisoner serving life. Whether or not be compelled to take such a person to a hospital if their heart stops beating. In my opinion such absence in law (clearly defining such things) needlessly opens up a state to expensive prolonged litigations.