In EMS, what defines a patient being in shock?

Definition of Shock in EMS

In EMS, a patient is "in shock" when they have acute circulatory failure causing inadequate tissue perfusion and oxygen delivery to meet metabolic demands, manifesting as hypotension (systolic BP <90 mmHg) combined with signs of end-organ hypoperfusion. 1

Core Diagnostic Criteria

Shock requires BOTH hemodynamic instability AND evidence of tissue hypoperfusion:

Hemodynamic Component

• Systolic blood pressure <90 mmHg sustained for >30 minutes 1
• Mean arterial pressure <60 mmHg 1
• Often accompanied by tachycardia as the body attempts to compensate 2

End-Organ Hypoperfusion Signs (Must Have at Least One)

• Altered mental status (confusion, decreased responsiveness) 1
• Cold, clammy extremities with poor capillary refill 1
• Oliguria (urine output <30 mL/h or <0.5 mL/kg/h) 1
• Elevated lactate >2 mmol/L (if available in field) 1
• Acute organ injury (kidney, liver dysfunction on labs) 1

Four Categories of Shock

Understanding the mechanism helps guide immediate treatment 1, 3:

1. Hypovolemic Shock

• Loss of intravascular volume from hemorrhage, dehydration, or fluid losses 4, 3
• Most common in trauma patients 4

2. Distributive Shock

• Inappropriate vasodilation causing maldistribution of blood flow 3, 2
• Includes septic shock, anaphylaxis, neurogenic shock 3

3. Cardiogenic Shock

• Primary pump failure from myocardial infarction, arrhythmias, or heart failure 1, 3

4. Obstructive Shock

• Mechanical obstruction to blood flow (tension pneumothorax, massive PE, cardiac tamponade) 3, 2

Critical EMS Recognition Points

The key distinction is that shock represents a STATE, not just low blood pressure alone 5, 2:

• Hypotension without signs of hypoperfusion may not be shock (e.g., baseline low BP in some patients) 2
• Conversely, early shock can occur with normal or near-normal BP due to compensatory mechanisms, especially in young, healthy patients 4
• Look for the combination: inadequate perfusion pressure PLUS evidence that tissues aren't getting enough oxygen 5, 2

Immediate EMS Positioning Guidance

For patients showing evidence of shock who are responsive and breathing normally, maintain or place them in a supine position 6:

• If no evidence of trauma, raising the feet 6-12 inches (30-60 degrees) may be considered while awaiting advanced care 6
• Do NOT raise feet if movement causes pain 6
• If trauma/spinal injury suspected, leave patient in position found unless airway compromised or area unsafe 6

Common EMS Pitfalls

Do not wait for profound hypotension to recognize shock - early identification when compensatory mechanisms are still working improves outcomes 4, 2:

• Tachycardia, anxiety, and cool extremities may be the only early signs 4
• Elderly patients and those on beta-blockers may not mount typical tachycardic response 4
• Shock can coexist with multiple mechanisms simultaneously (e.g., trauma patient with both hemorrhagic and obstructive shock from tension pneumothorax) 4, 3

Physiologic Understanding

Shock represents "malfunction or cessation of the electrical and mechanical activity of the heart, resulting in almost instantaneous loss of consciousness and collapse" when referring to sudden cardiac arrest 6, but more broadly in EMS practice, shock is the clinical syndrome where circulatory failure leads to cellular hypoxia, anaerobic metabolism, lactic acidosis, and progressive organ dysfunction that becomes irreversible if untreated 5, 7.