Core Content: Shock

Shock – What Every Provider Must Know

Shock is not just a drop in blood pressure—it's a life-threatening cellular crisis. In this episode of Pulmcast, we break down what every clinician needs to know about shock. From real-world cases to essential pathophysiology, you’ll walk away with a clearer understanding of oxygen delivery, shock subtypes, and bedside management tips for any critical care environment.

What Is Shock?

Shock is defined as a failure of circulatory function leading to inadequate oxygen delivery to meet tissue demands. It represents a mismatch between oxygen delivery (DO₂) and consumption (VO₂).

• At the cellular level, cells shift from aerobic to anaerobic metabolism → leading to lactate buildup and energy deficit.

• If uncorrected, this cascade results in organ dysfunction and ultimately death.

Key determinants of oxygen delivery (DO₂):

• Cardiac output = Heart Rate × Stroke Volume

• Arterial oxygen content = Hemoglobin × SpO₂ × (small contribution from PaO₂)

1. Arterial oxygen content (Arterial O2 sat + Hgb)

2. Cardiac output (HR x SV)

   • stroke volume determined by:

     • preload (how much blood is in the ventricle at the end of diastole)

     • afterload (or the force the heart has to pump against)

     • inotropy (how hard the heart is squeezing)

The Four Major Types of Shock

1. Distributive Shock

Primary Cause: Systemic vasodilation
Examples: Septic shock, anaphylaxis, neurogenic shock
Hemodynamics: ↓ SVR, ↑ or ↓ CO, normal preload
Case Insight: Normotensive septic patient with lactate >5.5 – always look beyond blood pressure!
Treatment:

• IV fluids

• Vasopressors (e.g., norepinephrine)

• Inotropes if needed

• Point-of-care ultrasound (POCUS) for volume status and cardiac function

2. Cardiogenic Shock

Primary Cause: Failure of the heart to pump effectively
Examples: MI, arrhythmias, myocarditis, valve failure
Hemodynamics: ↑ preload, ↓ CO, ↑ afterload
Case Insight: Pulmonary edema, JVD, hypotension → classic sick-heart profile
Treatment:

• Non-invasive ventilation or intubation

• Inotropes (e.g., dobutamine, milrinone)

• Vasopressors only if needed to maintain MAP

• Address the underlying cause: e.g., PCI, surgery

3. Obstructive Shock

Primary Cause: Mechanical obstruction to cardiac filling/output
Examples: PE, tamponade, tension pneumothorax
Hemodynamics: ↓ CO, ↑ SVR, variable preload
Case Insight: Post-op patient with McConnell’s sign → RV strain due to PE
Treatment:

• Thrombolysis or thrombectomy (PE)

• Pericardiocentesis (tamponade)

• Needle decompression (pneumothorax) - check out our blog post on this

4. Hypovolemic Shock

Primary Cause: Loss of circulating volume
Examples: Hemorrhage, diarrhea, burns
Hemodynamics: ↓ preload, ↓ CO, ↑ SVR
Case Insight: Elderly patient with profuse diarrhea, dry mucosa, MAP 43
Treatment:

• Replace lost volume with appropriate fluids

• Use vasopressors early if MAP is dangerously low

• Distinguish between hemorrhagic vs. non-hemorrhagic 

Mixed Shock & Non-Response to Vasopressors

• Patients may present with elements of multiple shock types

• Always reassess when a patient isn’t responding to norepinephrine

• Causes include:

  • Acidosis

  • Adrenal insufficiency

  • Hypocalcemia

  • Occult bleeding

  • Secondary shock subtype (e.g., obstructive + distributive)

Remember: The cognitive response to hypotension is NOT just “start another presser.”

DIAGNOSTIC PEARLS

Use the Shock Index = HR / SBP > 0.9 = occult shock

1. Bedside ultrasound is the great differentiator

   • RUSH exam (Rapid Ultrasound for Shock and Hypotension)

   • Look at IVC, cardiac function, lung sliding, free fluid

   • Shock Index Literature: https://www.ncbi.nlm.nih.gov/pubmed/23599863/

Occult Causes of non-response to vasopressors

Don't just place CVL and forget about it. http://rebelem.com/occult-causes-of-non-response-to-vasopressors/

• Valuable tools:

  • POCUS

  • RUSH exam --> Rapid ultrasound in shock. Checking the pump, tank and pipes for causes of hypotension

    • Original RUSH Article

    • Emcrit on RUSH

 Quick Takeaways

• Shock = imbalance of DO₂ vs VO₂

• 4 Types: Distributive, Cardiogenic, Obstructive, Hypovolemic

• Shock can occur even with a normal BP

• Ultrasound is essential in early differentiation

• Vasopressors are not a cure — treat the underlying cause

If you treat critically ill patients, understanding shock isn't optional—it’s vital.

Listen to the full episode on Pulmcast: Shock Core Content

Frequently Asked Questions (FAQ)

1. What is shock in medical terms?

Shock is a critical condition where oxygen delivery fails to meet cellular demand, leading to organ dysfunction and, if uncorrected, death.

2. What are the 4 types of shock?

The major types of shock are distributive, cardiogenic, obstructive, and hypovolemic shock.

3. Is normal blood pressure a sign a patient is not in shock?

No. Patients can be in shock with normal blood pressure. Look for other signs such as lactic acidosis, poor perfusion, and altered mental status.

4. What is the Shock Index and how is it used?

The Shock Index is calculated by dividing heart rate by systolic blood pressure. A value over 0.9 may suggest occult shock and the need for closer monitoring or intervention.

5. What tools help diagnose shock at the bedside?

Bedside tools include point-of-care ultrasound (RUSH exam), lactate levels, perfusion markers, and clinical examination findings.

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