The nurse serves as the clinical leader in psychiatric crisis situations, making rapid assessments, directing the team response, implementing graduated intervention protocols, and managing post-crisis care. Advanced crisis assessment includes differentiation between psychiatric agitation and medical emergencies presenting as behavioral disturbance. Common medical causes of acute agitation: delirium (fluctuating level of consciousness -- most commonly missed medical diagnosis in agitated patients), hypoglycemia, hypoxia, infection/sepsis (especially UTI in elderly), stroke, head injury, medication toxicity (anticholinergic toxicity, serotonin syndrome, NMS), substance intoxication/withdrawal, urinary retention, and severe pain. The nurse implements the Sequential Intercept Model for crisis intervention: Prevention (identify at-risk patients, modify environment, address unmet needs) -> Recognition (early warning signs of escalation) -> De-escalation (verbal techniques, environmental modification) -> Voluntary medication (offer PRN oral medication) -> Involuntary medication (IM medication when safety requires) -> Physical management (restraint as absolute last resort). Each step is documented with clinical rationale for escalation to the next level.