Hemodynamic Terminology Lecture

Introduction

• Understanding hemodynamic terms is crucial in clinical settings, especially with critically ill patients.

Preload

• Definition: Amount of blood in the ventricles at end diastole.
• Patients with Elevated Preload: Congestive heart failure patients.
• Preload Reducers:
  • Diuretic therapy.
  • Venous vasodilators like nitroglycerin.
  • Morphine sulfate (opioid that dilates the venous system).
• Increasing Preload: Used in patients with low flow states or shock to increase intravascular volume.
• Measurement: Central venous pressure (CVP) or right atrial pressure (RAP).

Afterload

• Definition: Resistance the ventricles face during systolic ejection.
• Patients with High Afterload: Hypertension patients.
• Afterload Reducers: ACE inhibitors (prevent conversion of angiotensin 1 to 2).
• Increasing Afterload: Needed in distributive shock states (anaphylactic, septic, neurogenic).
• Measurement: Systemic vascular resistance (SVR) using invasive devices like PA catheter.

Cardiac Output

• Definition: Blood pumped in liters per minute (normal: 4-8 L/min).
• Calculation: Stroke volume (blood per systolic ejection) x Heart rate.
• Cardiac Index: Factors in body surface area for more accurate assessment.
  • Normal Cardiac Index: 2.5 to 4 L/min/m².

Mean Arterial Pressure (MAP)

• Definition: A composite of systolic and diastolic blood pressure.
• Calculation: (Systolic BP + 2 x Diastolic BP) / 3.
• Clinical Relevance: Used to ensure adequate organ perfusion in shock states (target MAP ≥ 65).

Contractility

• Definition: Force of heart contraction, also known as inotropy.
• Positive Inotropes:
  • Dobutamine: Increases cardiac output.
  • Digitalis/Digoxin: Increases contractility while reducing heart rate.
• Negative Inotropes:
  • Beta blockers: Used post-MI to reduce myocardial oxygen consumption.

Pulmonary Capillary Wedge Pressure (PCWP)

• Definition: Measurement of left heart pressures using the Swan-Ganz catheter.
• Procedure:
  • Catheter inserted via internal jugular to pulmonary artery.
  • Balloon inflation causes it to wedge, isolating left heart pressures.
  • Normal PCWP: 6-12 mmHg.
• Waveforms:
  • Different chambers exhibit unique pressure waveforms, useful for catheter positioning.

Conclusion

• Understanding these hemodynamic parameters and their clinical implications is essential for effectively managing critically ill patients.