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

Cardiovascular Physiology
Review
-
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

Ohm’s Law
BP = CO x SVR

Pulmonary Capillary Wedge Pressure
(PCWP)
Provides an indirect estimate of left atrial pressure.
Measured with a Swan-Gantz catheter.

Shock
Pathophysiology
- 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
Shock Classification
- Hypovolemic
- Cardiogenic
- Obstructive
- Distributive

Hypovolemic Shock
Pathophysiology
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
Hypovolemic Shock
Etiologies
-
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
Hypovolemic Shock
Parameters

Cardiogenic Shock
Pathophysiology
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)
Cardiogenic Shock
Etiologies
- Myocardial infarction
- Myocarditis
- Arrhythmia
- Valvular ⇒ severe acute aortic or mitral regurgitation
Cardiogenic Shock
Parameters

Obstructive Shock
Pathophysiology
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
Obstructive Shock
Etiologies
-
Conditions that impede venous return
- Tension PTX
- Cardiac tamponade
- Restrictive pericarditis
-
Conditions that obstruct cardiac outflow
- Pulmonary embolism (impacts RV)
- Aortic dissection (impacts LV)
Obstructive Shock
Parameters

Distributive Shock
Pathophysiology
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 ↓
-
Can see ↑ CO during early phase ⇒ ex. septic shock
- CVP and PCWP generally ↓
Distributive Shock
Etiologies
- 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
Distributive Shock
Parameters

Shock Summary

Mixed Shock
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
Shock
Clinical Approach
- 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
- Other management depends on cause
- History and physical critical to determining cause
- Pts usually managed in ICU w/ invasive cardiovascular monitoring
Shock
Physical Exam Pearls
- 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