Because we're with those sick and vulnerable people more than anybody else, we tend to take the responsibility for their deaths on ourselves--even when it's doubtful that anything we did or didn't do led to that death.
I have my own story: an older guy, in his eighties, with a blood calcium level that was horrendously low, had a cardiac arrest. He couldn't have gotten calcium IV, because he was already in physical rehab, where peripheral IVs don't exist. Further, because of his history of chemo in peripheral veins (that's how they did it back in the day), he was an impossible stick and refused to consent to a central line. And he wouldn't take the calcium supplements by mouth that I'd been ordered to give.
I rode his chest down to the CCU, doing hundred-per-minute compressions the entire way. He died anyhow. For a time I believed that I, Nurse Jo, had killed the guy. Whenever I had a brand-new nurse under my wing and something went Seriously Wrong, I would consider telling them about That Guy Who Died. Once, I think I did.
Thank God for CCU training. It helped me understand that all the oral calcium supplements in the world wouldn't have brought his blood calcium levels up enough to make a difference.
And thank God for further experience. His decision to forego a central line was his; pushing one on him would've been unethical at best.
Yes, the patient died. I thought I had killed him. Maybe I contributed to his death: maybe I could've been more convincing, or pushier, or more skilled at making him realize that what I wanted him to do was really necessary. At the end of the day, though, he was sound of mind, if not body, and made his own decisions. The fact that he couldn't have known that those decisions would lead to his heart stopping is kind of beside the point: we don't overrule personal autonomy for might-bes.
It's a dirty little secret of nursing: Sometimes, we kill people. Sometimes we only think we do. Sometimes, we're unsure...and that uncertainty is worst of all.