Sleep is very important for cognitive and immune function. However, patients in intensive care unit (ICU) have a very poor sleep.~Almost all ventilated patients in intensive care unit (ICU) take a sedative drug. In Korea, most commonly used sedative drugs are dexmedetomidine and midazolam.~The investigators are going to compare the sleep quality and quantity between dexmedetomidine group and midazolam group using 24 hour polysomnography. And the investigators also compare the incidence of delirium between the two groups.
The investigators are going to compare the sleep quality and quantity between dexmedetomidine group and midazolam group using 24 hour polysomnography in critically ill patients. And the investigators also compare the incidence of delirium between the two groups.