止血 is a verb-object compound meaning 'to stop bleeding'. As a separable verb (离合词), you can insert measure words, durations, or other elements between 止 and 血, e.g., 止了五分钟的血 ('stopped the bleeding for five minutes'). It's used in medical contexts — both for self-treatment and clinical procedures. The object 血 is normally kept together with 止, but when you need to quantify or specify, it splits.