Pathophysiology
Clinical meaning
Red flag findings indicate serious or life-threatening pathology requiring urgent action. Neurological: new focal deficit (stroke until proven otherwise), papilledema (elevated ICP), nuchal rigidity with fever (meningitis), cauda equina syndrome (saddle anesthesia, retention, bilateral weakness — surgical emergency). Cardiovascular: new murmur with fever (endocarditis), pulsus paradoxus > 10 mmHg (tamponade), Beck triad (hypotension, JVD, muffled sounds = tamponade), unequal arm BPs > 20 mmHg (aortic dissection). Abdominal: involuntary guarding/rebound (peritonitis), pulsatile mass (AAA), Cullen sign (periumbilical bruising) and Grey Turner sign (flank bruising) = retroperitoneal hemorrhage. Respiratory: tracheal deviation (tension pneumothorax — decompress before imaging), subcutaneous emphysema, stridor (upper airway obstruction). Musculoskeletal: 'worst headache of life' (SAH), progressive bilateral weakness (GBS), hot swollen joint with fever (septic arthritis).