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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.
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