Understanding Hemodynamic Principles

Sep 25, 2024

Hemodynamic Principles Review

Introduction

  • Hemodynamics: Movement of blood.
    • Importance: Proper hemodynamics are crucial for achieving desirable patient outcomes.

Key Definitions

  • Cardiac Output: Volume of blood ejected per minute during ventricular contractions.
  • Cardiac Index: Cardiac output adjusted for patient's body size.
  • Stroke Volume: Volume of blood ejected during ventricular systole.
  • Ejection Fraction: Percentage of blood pumped out of the left ventricle during systole.
  • Systemic Vascular Resistance (SVR): Tone of the vessels affecting blood flow.

Factors Affecting Blood Pressure

  • Blood Pressure Equation: Cardiac Output x SVR
  • Cardiac Output Components: Heart rate and stroke volume.
    • Stroke Volume Components: Preload, contractility, afterload.

Preload

  • Definition: Volume of blood returning to the heart from the venous side.
  • Measurement: CVP (central venous pressure).
    • Influences: Volume status, venous return.
  • Starling's Law: Optimal stretch of heart muscle results in more forceful contractions.
  • **Agents Affecting Preload: **
    • Reduce: Lasix, nitroglycerin.
    • Increase: Crystalloids (e.g., normal saline).

Contractility

  • Definition: Force of the heart's contraction.
  • Influences: Preload, oxygenation, electrolyte balance, pH.
  • Decrement Factors: Low potassium, magnesium, calcium, hypoxia, MI.
  • Increment Factors: Inotropes (dobutamine, dopamine, epinephrine).

Afterload

  • Definition: Resistance the heart must work against to eject blood.
  • Measurement: SVR or PVR.
  • Influences: Vessel status (tone, clamp status).
  • Agents Affecting Afterload:
    • Reduce: Vasodilators (nipride, nitroglycerin).
    • Increase: Vasoconstrictors (norepinephrine).

Clinical Example - Septic Shock

  • Case Description: Patient with hypotension, tachycardia, altered mental status.
  • Causes of Hypotension: Decreased SVR and preload due to vasodilation and increased tank size.
  • Cardiac Output: Typically high in septic shock due to compensatory mechanisms.
  • Treatment Protocols:
    • Oxygen, mechanical ventilation.
    • Fluids to increase preload.
    • Vasopressors to stabilize blood pressure.
    • Antibiotics for infection control.

Summary

  • Preload: Volume returning to the heart (affected by volume status and vasodilators).
  • Contractility: Force of contraction (affected by inotropes and electrolyte balance).
  • Afterload: Resistance due to vessel tone (affected by vasodilators and vasoconstrictors).
  • Overall: The balance of preload, contractility, and afterload is crucial for effective cardiovascular function.