Critical Illness

Disordered perfusion represents the fundamental pathophysiologic mechanism underlying all forms of critical illness, requiring coordinated management across anesthesia, surgery, and intensive care medicine. Shock manifests in four distinct categories based on underlying etiology: hypovolemic shock from hemorrhage or capillary leak reduces cardiac preload, cardiogenic shock from myocardial failure elevates filling pressures, obstructive shock from mechanical impedance restricts flow, and distributive shock from sepsis or trauma causes vasodilation despite elevated cardiac output. Sepsis and systemic trauma trigger identical inflammatory cascades, with the Surviving Sepsis Campaign providing evidence-based resuscitation protocols including crystalloid administration of at least 30 mL/kg and achievement of mean arterial pressure above 65 mm Hg. Hemorrhagic shock progresses through four grades of blood loss, with Class III hemorrhage causing measurable hypotension and the potential to develop the lethal triad of hypothermia, metabolic acidosis, and disseminated coagulopathy. Damage control resuscitation strategies prioritize permissive hypotension and balanced transfusion ratios of plasma, red cells, and platelets rather than crystalloid-heavy approaches that worsen coagulopathy. Pharmacologic interventions including tranexamic acid within three hours of injury and prothrombin complex concentrates for anticoagulation reversal improve hemostasis and survival. Acute cardiopulmonary emergencies demand rapid recognition of ST-elevation myocardial infarction for reperfusion therapy and immediate needle decompression for tension pneumothorax, while acute respiratory distress syndrome management relies on lung-protective ventilation with low tidal volumes and plateau pressure limitation. Metabolic derangements in critical illness include hyperglycemia requiring glucose targets between 140 and 180 mg/dL, acute kidney injury classified by the KDIGO scoring system, and sick euthyroid syndrome where thyroid hormone replacement offers no benefit. Neurologic complications encompass delirium assessed through standardized tools and associated with poor outcomes, critical illness polyneuropathy from sepsis, and acute neuromuscular weakness from corticosteroid and neuromuscular blocking drug exposure. Perioperative principles emphasize crystalloid superiority over colloids, timely antibiotic prophylaxis, mandatory thromboembolism prevention, active normothermia maintenance, and recognition of abdominal compartment syndrome when intraabdominal pressures exceed 20 mm Hg with concurrent organ dysfunction.