An 18-year-old man with fever and chills is sent home from the emergency room with Tylenol and later dies of sepsis, a blood infection. A 42-year-old woman with chest pains is discharged, only to suffer a heart attack two hours later. A 9-year-old girl's appendix ruptures after doctors rule she's just got a bellyache. Hospitals are drawing on lessons learned from these worst cases of missed or delayed diagnosis to overhaul emergency departments, where errors, oversights and a lack of teamwork between doctors and nurses can harm or kill patients. They are adopting new triage systems to ensure doctors and nurses jointly see at-risk patients soon after they arrive, requiring physicians and nurses to huddle to make sure no information is overlooked, and using time-outs at discharge to prevent patients with unresolved problems from leaving the ER.