Delirium, Agitation and Behavioral Emergencies

Clinical Assessment and Features of ICU Delirium

Delirium is an acute, fluctuating disturbance in attention and awareness accompanied by additional cognitive changes. In the intensive care unit, this syndrome presents along a spectrum of psychomotor behaviors. Hypoactive delirium is common, is often underrecognized in the ICU, and remains independently associated with adverse outcomes. Because quiet, hypoactive patients do not disrupt care or display visible agitation, critical care nurses must systematically evaluate cognitive status rather than assuming calm behavior represents normal baseline mentation.

The standard validated assessment tool is the Confusion Assessment Method for the ICU (CAM-ICU), which evaluates four core features: Feature 1 (acute onset or fluctuating course), Feature 2 (inattention), Feature 3 (altered level of consciousness), and Feature 4 (disorganized thinking). To be categorized as CAM-ICU positive, a patient must demonstrate both Feature 1 and Feature 2, along with either Feature 3 or Feature 4. An everyday way to think of this algorithm is a two-door entry gate: both Feature 1 and Feature 2 must be unlocked before evaluating whether Feature 3 or Feature 4 is present to confirm delirium.

Clinical testing of Feature 2 is commonly performed at the bedside by asking the patient to squeeze the nurse's hand on a designated letter during a ten-letter sequence. Before assessing delirium, the nurse determines the level of consciousness using the Richmond Agitation-Sedation Scale (RASS). A RASS score of 0 makes CAM-ICU Feature 3 negative; evaluate Feature 4 if Features 1 and 2 are positive. Conversely, patients who are deeply sedated with a RASS score of −4 or −5 cannot be assessed with the CAM-ICU, even though a patient at −4 may still respond to physical stimulation.