# Shock: Classification and Resuscitation Across Ages

## Introduction

**Shock** is a state of inadequate tissue perfusion and oxygen delivery relative to metabolic demand. While the fundamental pathophysiology is shared across ages, the etiologies, clinical presentations, and resuscitation strategies differ significantly between pediatric and adult patients. Med-peds physicians must recognize the nuances of shock management in neonates, children, and adults to optimize outcomes.

## Classification of Shock

### Hypovolemic Shock

Most common type in children; **gastroenteritis** with dehydration is the leading cause worldwide. In adults, hemorrhage (trauma, GI bleed) is the primary etiology. Characterized by decreased preload, increased SVR, and decreased cardiac output. Pediatric patients compensate longer with tachycardia before hypotension occurs (**compensated shock**)

### Distributive Shock

**Septic shock** is the most common form; gram-negative organisms predominate in adults, while age-dependent pathogens vary in pediatrics. **Anaphylactic shock**: Rapid onset with urticaria, bronchospasm, and hypotension. **Neurogenic shock**: Spinal cord injury causing loss of sympathetic tone with bradycardia and hypotension. In pediatrics, **toxic shock syndrome** (staphylococcal and streptococcal) requires high index of suspicion.

### Cardiogenic Shock

In neonates: ductal-dependent lesions (e.g., **hypoplastic left heart syndrome**, critical coarctation) In children: myocarditis, cardiomyopathy, arrhythmias. In adults: acute myocardial infarction, decompensated heart failure, valvular emergencies. Characterized by elevated filling pressures, decreased cardiac output, and increased SVR.

### Obstructive Shock

**Tension pneumothorax**, **cardiac tamponade**, **massive pulmonary embolism**. In neonates, consider ductal-dependent congenital heart lesions. Requires rapid identification and source-directed intervention.

![Classification of shock types with hemodynamic parameters](illustration-shock-classification-hemodynamics.jpg)

## Age-Specific Considerations in Assessment

### Pediatric Assessment

**Tachycardia** is the earliest and most sensitive sign of shock in children. Hypotension is a **late** finding indicating decompensated shock; defined as <5th percentile for age. Assess capillary refill (normal <2 seconds), skin mottling, mental status, and urine output. Neonates with ductal-dependent lesions may present with shock upon ductal closure (days 3-14 of life) **Prostaglandin E1 (PGE1)** infusion is critical for suspected ductal-dependent cardiac lesions.

### Adult Assessment

**Mean arterial pressure (MAP)** <65 mmHg or systolic BP <90 mmHg defines hypotension. Lactate >2 mmol/L indicates tissue hypoperfusion; >4 mmol/L indicates severe shock. Assess for end-organ dysfunction: altered mental status, oliguria, hepatic dysfunction. **Shock index** (HR/SBP) >1.0 suggests hemodynamic compromise.

## Resuscitation Strategies

### Fluid Resuscitation

**Pediatric**: Isotonic crystalloid (normal saline or lactated Ringer's) 10-20 mL/kg boluses; reassess after each bolus. The **FEAST trial** demonstrated harm from aggressive fluid boluses in febrile children in resource-limited settings, tempering universal aggressive resuscitation. **Adult**: 30 mL/kg crystalloid for septic shock (Surviving Sepsis Campaign), though individualized assessment is preferred. **Balanced crystalloids** (LR, Plasmalyte) are favored over normal saline to reduce hyperchloremic acidosis. In cardiogenic shock, fluid resuscitation should be cautious; small aliquots (5-10 mL/kg in children) with reassessment.

### Vasopressor and Inotrope Selection

| Agent | Mechanism | Primary Indication | Key Notes |
|-------|-----------|-------------------|-----------|
| Epinephrine | Alpha + Beta agonist | First-line pediatric septic shock | Inotropy + vasoconstriction |
| Norepinephrine | Alpha-1 >> Beta-1 | First-line adult septic shock | Strong vasoconstriction |
| Dopamine | Dose-dependent DA/Beta/Alpha | Largely supplanted | Increased arrhythmia risk |
| Dobutamine | Beta-1 > Beta-2 | Cardiogenic shock (low CO) | Inotrope; may cause hypotension |
| Vasopressin | V1 receptor | Adjunct in refractory distributive shock | Catecholamine-sparing |
| Milrinone | PDE-3 inhibitor | Pediatric cardiogenic shock | Inotropy + afterload reduction |

**Epinephrine**: First-line vasopressor in pediatric septic shock (ACCM/SCCM guidelines); provides both inotropy and vasoconstriction. **Norepinephrine**: First-line vasopressor in adult septic shock; strong alpha-1 with moderate beta-1 activity. **Dopamine**: Previously used as first-line; now largely supplanted due to increased arrhythmia risk. **Dobutamine**: Preferred inotrope for cardiogenic shock when systemic perfusion is inadequate. **Vasopressin**: Adjunctive agent in refractory distributive shock. **Milrinone**: Phosphodiesterase-3 inhibitor useful in pediatric cardiogenic shock; provides inotropy and afterload reduction.

### Blood Products

**Hemorrhagic shock**: Initiate massive transfusion protocol with 1:1:1 ratio of pRBCs, FFP, and platelets. **Transfusion thresholds**: Generally Hgb <7 g/dL in hemodynamically stable patients; higher thresholds in active hemorrhage. **Neonatal considerations**: Use irradiated, CMV-negative blood products; volume-based dosing (10-15 mL/kg pRBCs)

![Pediatric vs adult septic shock resuscitation algorithm](illustration-shock-resuscitation-algorithm.jpg)

## Monitoring and Endpoints of Resuscitation

**Clinical targets**: Normalization of heart rate, capillary refill <2 seconds, improved mental status, urine output >1 mL/kg/hr (children) or >0.5 mL/kg/hr (adults) **Lactate clearance**: Target >10% reduction per 2 hours; serial lactate monitoring guides adequacy of resuscitation. **Point-of-care ultrasound (POCUS)**: Assess IVC collapsibility, cardiac function, and volume status. **Invasive monitoring**: Arterial lines, central venous access for CVP and ScvO2 monitoring in refractory shock. **ScvO2 target**: >70% indicates adequate oxygen delivery relative to consumption.

![Point-of-care ultrasound findings in different shock states](illustration-pocus-shock-assessment.jpg)

## Clinical Pearls

Hypotension is a late finding in pediatric shock; tachycardia, poor perfusion, and altered mental status should trigger intervention before blood pressure drops. Prostaglandin E1 should be started empirically in any neonate presenting with shock in the first weeks of life until ductal-dependent cardiac lesions are excluded. Balanced crystalloids are preferred over normal saline for large-volume resuscitation to minimize hyperchloremic metabolic acidosis. Epinephrine is first-line in pediatric septic shock, while norepinephrine is first-line in adult septic shock. Point-of-care ultrasound is invaluable for differentiating shock types and guiding fluid versus vasopressor therapy.

## References

1. Davis AL, Carcillo JA, Aneja RK, et al. American College of Critical Care Medicine clinical practice parameters for hemodynamic support of pediatric and neonatal septic shock. *Crit Care Med*. 2017;45(6):1061-1093.
2. Evans L, Rhodes A, Alhazzani W, et al. Surviving sepsis campaign: international guidelines for management of sepsis and septic shock 2021. *Crit Care Med*. 2021;49(11):e1063-e1143.
3. Maitland K, Kiguli S, Opoka RO, et al. Mortality after fluid bolus in African children with severe infection (FEAST). *N Engl J Med*. 2011;364(26):2483-2495.
4. Semler MW, Self WH, Wanderer JP, et al. Balanced crystalloids versus saline in critically ill adults (SMART). *N Engl J Med*. 2018;378(9):829-839.