When JD hides in a body bag in the elevator and startles Doug into hitting him with a fire extinguisher, Doug then clings to the extinguisher and you can clearly see it's made out of foam.
Part of the plot surrounds a family agonizing over a decision to "pull the plug" on their brain-dead son. If a patient is brain-dead, there is never a question as to whether to withdraw life support. A brain-dead patient is medically and legally dead.
When Kelso is talking to the surgeons he claims the brain dead patient did not have a donor card. Later when the father is talking to J.D. he shows him his sons donor card.