Hypovolemic Shock Basics

Hypovolemic shock is a life-threatening condition resulting from inadequate circulating blood volume leading to decreased cardiac output, inadequate tissue perfusion, and cellular hypoxia. It is the most common type of shock. Hemorrhagic causes include trauma, GI bleeding, surgical bleeding, and obstetric hemorrhage. Non-hemorrhagic causes include severe dehydration, extensive burns, pancreatitis, and DKA. The pathophysiology follows the Frank-Starling mechanism: decreased volume → decreased venous return → decreased preload → decreased stroke volume → decreased cardiac output. Compensatory mechanisms include sympathetic activation (tachycardia, vasoconstriction, diaphoresis), RAAS activation (sodium/water retention), and ADH release. Shock is classified by percentage of blood loss: Class I (<15%, compensated), Class II (15-30%, tachycardia with narrowed pulse pressure), Class III (30-40%, hypotension and confusion), Class IV (>40%, life-threatening with obtundation). The 'lethal triad' in hemorrhagic shock is hypothermia, acidosis, and coagulopathy — each worsens the others. Tachycardia is the EARLIEST vital sign change. Hypotension is a LATE sign indicating ≥30% blood volume loss and decompensation.