Blood glucose control in ICUs and operation rooms has some issues. First, hypoglycemia worsens the neurological prognosis of ICU patients and should definitely be avoided. To avoid hypoglycemic attacks require extensive attention by hospital staff. The two biggest advantages of continuous monitoring are the avoidance of hypoglycemia and the reduced workload for ICU staff. However, to achievement of automating blood glucose control, closed loop continuous glucose monitoring is essential. In this review, topics of blood glucose management in ICUs and operation rooms are introduced and advantages and limitations of closed loop continuous glucose monitoring are discussed.