As an interjection, 救命 is the standard cry for help in Chinese — like shouting 'Help!' in English. 救命稻草 (life-saving straw) = last resort / clutching at straws.
culture
In Chinese internet slang, 救命 is also used humorously to express exasperation or being overwhelmed: '这道题太难了，救命！' (This question is too hard, help me!).
