What is the use of ranitidine in icu ?

Lower acid: it lowers stomach acid and can prevent an ulcer. Of course, one would need to know the whole ICU scenario, why the patient is there and what medicines they are on. I just gave you a generic answer.

Ranitidine: Ranitidine is in a group of drugs called histamine-2 blockers. Ranitidine works by reducing the amount of acid your stomach produces. In the ICU setting, there may be other medications that could irritate your stomach lining, so deceasing acid with ranitidine may be prescribed prophylactically. Hope this helps.