PALS | Pediatric Shock Extended

. Core Physiology & Definition

• Definition: Shock is inadequate tissue perfusion to meet metabolic demands and oxygenation needs1. Hypotension is not required for diagnosis; shock exists with normal, high, or low SBP1.
• Pediatric Focus: Infants have fixed stroke volume and depend on elevated heart rate to maintain CO3.
• Stroke Volume: Preload (volume), Contractility (pump force), and Afterload (resistance)34.

2. Severity & Compensatory Continuum

• Compensated Shock: Body mechanisms (tachycardia, elevated SVR, venoconstriction) maintain normal SBP despite hypoperfusion56. Key signs: tachycardia, delayed refill, cool skin, oliguria67.
• Hypotensive Shock: Compensatory mechanisms fail, causing low SBP and imminent arrest7. Hypotension is a late finding in most shock types, except septic shock where SVR drops early7.
• Progression: Compensated shock can last hours, but hypotensive shock deteriorates in minutes8.

3. The 4 Shock Types: Differential Pattern Recognition

A. Hypovolemic Shock (Most Common)

• Mechanism: Intravascular volume loss (fluid loss) causing low preload and CO9.
• Signs: "Quiet tachypnea" (rapid breathing without retractions), narrow pulse pressure, pale/cool skin, delayed refill, weak pulses910.

B. Distributive Shock

• Mechanism: Vasodilation causing blood maldistribution and relative hypovolemia110.
• Septic Shock: Commonest form11. Warm Shock: Low SVR, bounding pulses, flushed skin, wide pulse pressure1213. Cold Shock: High SVR, weak pulses, cool skin1213.
• Anaphylactic Shock: Histamine release causes bronchospasm, upper airway edema (stridor), hives, vasodilation14.
• Neurogenic Shock: High spinal injury causes loss of sympathetic tone hypotension without tachycardia (normal HR or bradycardia)15.

C. Cardiogenic Shock

• Mechanism: Primary pump failure with low contractility, high afterload.
• Signs: Tachypnea with increased work of breathing (retractions, grunting, crackles), hepatomegaly, cyanosis1617.

D. Obstructive Shock

• Mechanism: Physical restriction of venous return or cardiac outflow18.
• Tension Pneumothorax: Tracheal deviation, hyperresonance, absent breath sounds19.
• Cardiac Tamponade: Muffled heart sounds, pulsus paradoxus (>10 mmHg SBP drop on inspiration)20.
• Ductal Lesions: Neonatal presentation with differential pre/post-ductal SBP/SpO221.
• Massive PE: Systemic venous congestion and RV failure22.