Pathophysiology refers to the functional and structural changes that occur in the body as a result of disease or injury. In critical care conditions, these changes may develop rapidly and can affect vital organs, requiring continuous assessment and prompt nursing management. The causes and pathophysiology vary according to the underlying condition, but common mechanisms include infection, trauma, hypoxia, circulatory disturbances, metabolic abnormalities, and organ dysfunction. Infections are an important cause of critical illness. Bacterial, viral, or fungal infections may produce a systemic inflammatory response. The release of inflammatory mediators such as cytokines causes vasodilation, increased capillary permeability, and activation of coagulation. Fluid moves from the intravascular space into tissues, resulting in edema and reduced circulating blood volume. Severe infection may progress to sepsis