Shock Pathophysiology

Question 1

Shock

Definition

Answer 1

The clinical condition of organ dysfunction resulting from an imbalance between cellular oxygen supply and demand.

Question 2

Cardiovascular Physiology

Review

Answer 2

• Oxygen delivery primarily determined by CO and arterial oxygen content
  
  • CO = HR x SV
  • Arterial O₂ content = O₂ on Hb + dissolved O₂
• Stroke volume determined by:
  
  • Heart size
  • Contractility
  • Preload ⇒ end-diastolic volume
    
    • Inc. w/ inc. blood volume or rate of return
  • Afterload ⇒ systemic vascular resistance
    
    • Controlled primarily by arterioles

Question 3

Ohm’s Law

Answer 3

BP = CO x SVR

Question 4

Pulmonary Capillary Wedge Pressure

(PCWP)

Answer 4

Provides an indirect estimate of left atrial pressure.

Measured with a Swan-Gantz catheter.

Question 5

Shock

Pathophysiology

Answer 5

• Imbalance in oxygen supply and demand
• Inability of cells to use O₂ to generate ATP through oxidative phosphorylation
• Cells must rely on anaerobic metabolism ⇒ dec. ATP production
• Results in cellular death and organ system dysfunction
  
  • Organ dysfunction reversible early in shock if O₂ supply quickly restored
  • As shock progresses, dysfunction becomes irreversible and risk of death is high

Question 6

Shock Classification

Answer 6

• Hypovolemic
• Cardiogenic
• Obstructive
• Distributive

Question 7

Hypovolemic Shock

Pathophysiology

Answer 7

Acute loss of intravascular volume ⇒ ↓ preload ⇒ ↓ CO ⇒ ↓ O₂ delivery

• ↓ SVP and PCWP due to ↓ intravascular volume
• ↑ SVR in response to ↓ intravascular volume
  
  • Attempt to restore BP

Question 8

Hypovolemic Shock

Etiologies

Answer 8

• Most commonly related to hemorrhage
  
  • Can be external (trauma) or internal (GI bleed)
• Profound GI volume loss (V/D)
• Renal losses ⇒ osmotic diuresis due to DKA or Diabetes insipidus
• Skin losses ⇒ severe burns or inflammatory conditions such as Stevens-Johnson

Question 9

Hypovolemic Shock

Parameters

Answer 9

Question 10

Cardiogenic Shock

Pathophysiology

Answer 10

A primary cardiac problem resulting in ↓ CO ⇒ ↓ O₂ delivery.

• Usually ↑ SVR as compensatory response to ↓ BP from ↓ CO
• When LV involved ⇒ ↑ PCWP
• When RV involved ⇒ ↑ CVP
• If condition affects myocardial contractility or a valve ⇒ ± ↓ SV
• Often ↑ HR in response to ↓ CO
  
  • Unless caused by bradyarrhythmia or other condition that ↓ HR (ex. excess β-blocker)

Question 11

Cardiogenic Shock

Etiologies

Answer 11

• Myocardial infarction
• Myocarditis
• Arrhythmia
• Valvular ⇒ severe acute aortic or mitral regurgitation

Question 12

Cardiogenic Shock

Parameters

Answer 12

Question 13

Obstructive Shock

Pathophysiology

Answer 13

Impaired blood flow from extracardiac process ⇒ ↓ CO ⇒ ↓ O₂ delivery

• Obstruction may result in:
  
  • ↓ return to the heart
  • ↓ blood leaving the heart
• ↑ SVR in response to ↓ CO
• PCWP will vary
  
  • ↑ PCWP if etiology causes outflow obstruction
  • Normal if issue is with venous return
• Usually ↑ CVP

Question 14

Obstructive Shock

Etiologies

Answer 14

• Conditions that impede venous return
  
  • Tension PTX
  • Cardiac tamponade
  • Restrictive pericarditis
• Conditions that obstruct cardiac outflow
  
  • Pulmonary embolism (impacts RV)
  • Aortic dissection (impacts LV)

Question 15

Obstructive Shock

Parameters

Answer 15

Question 16

Distributive Shock

Pathophysiology

Answer 16

Stressor ⇒ body response ⇒ dysregulated state ⇒ inappropriate distribution of blood

• Vasodilation ⇒ ↓ SVR ⇒ shunting of blood from vital organs
• Many different underlying mechanisms
• CO varies based on cause
  
  • Can see ↑ CO during early phase ⇒ ex. septic shock
    
    • Only shock pathology whee you may see high CO
  • CO will eventually ↓
• CVP and PCWP generally ↓

Question 17

Distributive Shock

Etiologies

Answer 17

• Sepsis ⇒ most common cause
• Pancreatitis
• Severe burns
• Liver failure
• Anaphylaxis ⇒ IgE-mediated allergic rxn w/ venous and arterial vasodilation
• Neurogenic causes ⇒ brain or spinal cord injury → autonomic dysfunction → vascular tone dysregulation → ↓ SVR
• Adrenal insufficiency ⇒ inability to inc. cortisol during times of stress → vasodilation → aldosterone deficiency mediated hypovolemia

Question 18

Distributive Shock

Parameters

Answer 18

Question 19

Shock Summary

Answer 19

Question 20

Mixed Shock

Answer 20

Pts may present with more than one type of shock.

• Ex. Distributive shock 2/2 sepsis
  
  • Results in heart damage d/t reduced perfusion
  • Leads to cardiogenic shock

Question 21

Shock

Clinical Approach

Answer 21

• Must determine type of shock and etiology
• Management depends on underlying cause
  
  • Hypovolemic → give fluids, fix underlying problem
  • Cardiogenic → diuretics and inotropic agents
  • Obstructive → fix cause of obstruction
  • Distributive → IV fluids, pressors for BP
    
    • Other management depends on cause
      
      • Abx for sepsis
      • Epinephrine for anaphylaxis
• History and physical critical to determining cause
• Pts usually managed in ICU w/ invasive cardiovascular monitoring

Question 22

Shock

Physical Exam Pearls

Answer 22

• Look closely for signs of infection
• Assess jugular venous pulsations
  
  • Non-invasive estimate of right atrial pressure and CVP
• Feel the extremities
  
  • Warm fingers/toes suggestive of a distributive etiology