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.