When a patient is hospitalize in an intensive care unit, it's very important he's surrounded by his dears.
First of all, in a scaring place, the patient is reassured by the presence of his relatives. To face a critical illness is a hard experience, the consciousness of not to be alone is the best way to start the way for a possible recovery.
A relative can even positively contribute improving the recovery of some vital activity (efficient breathing, regular heart beating, blood pressure control..) reducing the anxious component.
Relatives are also the only connection the patient has with the external word, few minutes are enough to maintain a contact with reality. News about the world, family pictures or a gift from a nephew are all important to come back to "normality".