Among the four types of shock, which is the most common cause of shock in the general population and in trauma settings?

Explanation

## Hypovolemic Shock: The Most Common Type **Key Point:** Hypovolemic shock is the most frequent type of shock encountered in clinical practice, particularly in trauma, hemorrhage, and severe dehydration. It accounts for the majority of shock cases in both civilian and military trauma settings. ### Definition and Causes Hypovolemic shock results from inadequate circulating blood volume, reducing venous return and cardiac output below the threshold needed for tissue perfusion. ### Major Causes of Hypovolemic Shock | Category | Examples | | --- | --- | | **Hemorrhagic** | Trauma, GI bleed, ruptured AAA, postpartum hemorrhage | | **Non-hemorrhagic fluid loss** | Severe diarrhea, vomiting, burns, pancreatitis, peritonitis | | **Third-spacing** | Sepsis, cirrhosis, nephrotic syndrome, intestinal obstruction | ### Hemodynamic Profile - Cardiac Index: < 2.2 L/min/m² - PCWP: < 18 mmHg (low, unlike cardiogenic shock) - SVR: Elevated (compensatory vasoconstriction) - CVP: Low (< 5 cmH₂O) ### Pathophysiology Sequence 1. Blood/fluid loss → reduced intravascular volume 2. Decreased venous return → reduced preload 3. Reduced cardiac output (by Frank-Starling mechanism) 4. Sympathetic activation → tachycardia, vasoconstriction, increased SVR 5. Tissue hypoperfusion → anaerobic metabolism → lactic acidosis **High-Yield:** The key distinguishing feature of hypovolemic shock is LOW PCWP (or CVP), which differentiates it from cardiogenic shock (high PCWP) and septic shock (variable PCWP with low SVR). **Mnemonic:** **CRASH** for hemorrhagic hypovolemic shock causes: - **C**ontusion (trauma) - **R**uptured vessels (AAA, splenic, hepatic) - **A**ccidents (trauma) - **S**urgical bleeding - **H**emorrhage (GI, postpartum) **Clinical Pearl:** In trauma, hypovolemic shock is the most common type; septic shock is rare in the acute phase unless there is pre-existing infection or delayed presentation. Rapid fluid resuscitation (crystalloids, then blood products if hemorrhagic) is the cornerstone of management. [cite:Robbins 10e Ch 4]