Shock Overview

Definition of Shock

• Shock is a mismatch between tissue perfusion (oxygen and metabolic delivery via bloodstream) and tissue consumption/metabolic needs.

• Hypotension often manifests but is not sufficient to define shock.

Swan-Ganz Catheter (Pulmonary Artery Catheter - PAC)

• Historical measurement tool providing data on shock. Not clinically used routinely anymore.

• Placement:

  • Inserted like a central line, advanced into the right atrium.

  • Pressure monitor at the tip.

• Measurements:

  • Right Atrial Pressure (RAP) / Central Venous Pressure (CVP): Pressure in the right atrium.

  • Right Ventricular Pressure: Pressure in the right ventricle.

  • Pulmonary Artery Pressure: Pressure in the pulmonary artery.

  • Pulmonary Capillary Wedge Pressure (PCWP): Measured by inflating a balloon at the tip of the catheter in the pulmonary artery; serves as a surrogate for left atrial pressure.

Pressure Waves and Normal Values

• CVP/Right Atrium: Low pressure, 2-6 mmHg.

• Right Ventricle: Systolic pressure 20-30 mmHg, diastolic similar to atrial pressure.

• Pulmonary Artery: Pressure peaks of 20-30 mmHg, slightly higher diastolic.

• Pulmonary Capillary Wedge Pressure: Typically 4-12 mmHg.

Mnemonic for Normal Pressures (Read left to right as you are looking at a drawing of the heart)

• Right Atrium (CVP): Nickel ( approx 5 mmHg)

• Left Atrium (PCWP): Dime ( approx 10 mmHg)

• Right Ventricle: Quarter ( approx 25 mmHg systolic)

• Left Ventricle: Dollar ( approx 100 mmHg systolic, normal ~120)

Key Parameters

• Contractility (Pump): Cardiac Output

• Afterload: Systemic Vascular Resistance (SVR)

• Preload: Central Venous Pressure (CVP), measure of volume status

Types of Shock

1. Hemorrhagic: Due to bleeding.

2. Hypovolemic: Includes hemorrhagic, plus other volume losses (vomiting, diarrhea, high ileostomy output).

3. Cardiogenic: Problem with the heart's pumping ability.

4. Distributive:

   • Septic

   • Anaphylactic

5. Neurogenic: Spinal cord injury.

6. Obstructive: Tamponade, pneumothorax.

Hemorrhagic/Hypovolemic Shock

• Problem: Volume (preload) issue.

• Etiology: Trauma, fluid losses.

• Inciting Event reducing volume leads to low CVP (preload).

• Physiology:

  • Cardiac Output: Decreases due to reduced ventricular filling (Frank-Starling curve).

  • Systemic Vascular Resistance: Increases as the body tries to maintain pressure by squeezing capillaries in response to reduced volume.

• Parameters:

  • CVP: Low

  • Pulmonary Capillary Wedge Pressure: Low

  • Cardiac Output: Low

  • SVR: Increased

• Treatment: Fluids and/or blood products. Stop the bleeding if actively bleeding.

Cardiogenic Shock

• Problem: Heart's contractility (pump).

• Etiology: Heart attack leading to heart failure.

• Inciting Event: Decreased contractility/CO.

• Physiology:

  • Systemic Vascular Resistance: Increases to maintain flow.

  • CVP: Increases due to fluid backup.

• Parameters:

  • Cardiac Output: Decreased

  • CVP: Increased

  • Pulmonary Capillary Wedge Pressure: Increased

  • SVR: Increased

• Treatment: Inotropes (epinephrine, dopamine) to improve heart contractility.

Distributive Shock

• Problem: Capillaries (afterload).

• Etiology: Sepsis, anaphylaxis.

• Inciting Event: Drop in SVR (capillary dilation).

• Physiology:

  • Preload: Decreases as fluid shifts into the capillaries.

  • Contractility: Increases due to reduced afterload; heart rate increases.

• Parameters:

  • SVR: Decreased

  • Cardiac Output: Increased

  • CVP: Decreased

  • Pulmonary Capillary Wedge Pressure: Decreased

• Treatment (sepsis):

  • Source control of infection.

  • Broad-spectrum antibiotics.

  • Fluids.

  • Vasopressors (norepinephrine) to increase vascular tone.

Neurogenic Shock

• Etiology: Spinal cord injury (affects sympathetic outflow).

• Diagnosis: Rule out hemorrhagic shock first in trauma patients.

• Physiology:

  • Decreased sympathetic tone leads to vasodilation and decreased SVR.

• Parameters: Similar to distributive shock.

  • SVR: Decreased

  • Cardiac Output: Increased

  • CVP: Decreased

  • Pulmonary Capillary Wedge Pressure: Decreased

• Treatment: Primarily vasopressors; fluids to refill the "tank."

Obstructive Shock

• Etiology: Cardiac tamponade, tension pneumothorax (common in penetrating chest trauma).

• Tamponade: Fluid around the heart restricts filling, usually diagnosed with ultrasound after penetrating injury to the "box" (clavicles, sternal notch, costal margin, and nipples).

• Tension Pneumothorax: Kinking of the IVC due to pressure, restricting venous return.

• Physiology:

  • Increased preload due to blocked venous return.

  • Reduced contractility as ventricles can't fill properly (falling off Frank-Starling curve).

  • Increased afterload as the body tries to maintain pressure.

• Parameters:

  • CVP: Increased (fluid backs up)

  • Pulmonary Capillary Wedge Pressure: Decreased (no volume in the heart)

  • Cardiac Output: Decreased

  • SVR: Increased

• Treatment:

  • Tamponade: Pericardial window.

  • Tension Pneumothorax: Needle decompression can be used initially, chest tube placement is definitive