Hemodynamic Monitoring in ICU

Hemodynamic Basics - Vitals Vigilance

• Goal: Maintain organ perfusion & oxygenation.
• Core Vitals: HR, BP (SBP, DBP, MAP, PP), SpO2.
• Mean Arterial Pressure (MAP):
  • Formula: $MAP = DBP + \frac{1}{3}(SBP - DBP)$
  • Normal: 70-100 mmHg.
  • Target in shock: $\geq \textbf{65}$ mmHg.
• Pulse Pressure (PP):
  • Formula: $PP = SBP - DBP$
  • Normal: 30-50 mmHg.
  • Narrow PP (<25 mmHg or <25% SBP) suggests $\downarrow$ stroke volume.
• Shock Index (SI):
  • Formula: $SI = \frac{HR}{SBP}$
  • Normal: 0.5-0.7.
  • SI > 0.9 indicates shock. 📌 "Heart over Pressure".

⭐ A MAP < 60 mmHg compromises vital organ perfusion, especially coronary, cerebral, and renal flow.

Arterial Monitoring - Arterial Line Lowdown

• Indications: Continuous BP (vasoactive drugs), frequent ABGs, advanced hemodynamics (PPV/SVV).
• Sites:
  • Radial (Allen's test pre-cannulation).
  • Femoral (larger bore; ↑ risk infection/thrombosis).
  • Others: Brachial, axillary, dorsalis pedis.
• Waveform: Systolic upstroke, peak, dicrotic notch (aortic valve closure), diastolic.
  • MAP $\approx DBP + \frac{1}{3} (SBP - DBP)$.
• Complications: Ischemia, thrombosis, hemorrhage, infection, nerve injury. ⚠️ Accidental drug injection.
• Troubleshooting:
  • Damped: ↓SBP, ↑DBP (air, clot, kink).
  • Resonant: ↑SBP, ↓DBP (stiff/long tubing).

⭐ MAP is generally preserved in damping/resonance.

Central Venous Pressure - Central Clues

• Measures right atrial pressure (RAP); estimates RV preload. Normal: 2-8 mmHg.
• Measured via Central Venous Catheter (CVC).
• Sites: Internal Jugular (preferred), Subclavian, Femoral.
• Waveform:
  • a: Atrial contraction.
  • c: Ventricular contraction (tricuspid bulge).
  • x: Atrial relaxation.
  • v: Venous filling.
  • y: Ventricular filling.
• Uses: Volume status, drug admin, TPN.
• Complications: Pneumothorax, infection, thrombosis.

⭐ Cannon 'a' waves on CVP trace suggest atrial contraction against a closed tricuspid valve (e.g., junctional rhythm, complete heart block).

Pulmonary Artery Catheter - Swan's Song Stats

• A balloon-tipped, flow-directed catheter providing key hemodynamic data.
• Measures: Central Venous Pressure (CVP), Pulmonary Artery Pressure (PAP), Pulmonary Capillary Wedge Pressure (PCWP), Cardiac Output (CO), Mixed Venous Oxygen Saturation (SvO2).
• Indications: Differentiating shock types, guiding therapy in severe cardiac/pulmonary dysfunction (e.g., ARDS, cardiogenic shock), major surgeries.
• Risks: Arrhythmias (most common), PA rupture, infection, thromboembolism, valvular damage.

⭐ PCWP is an indirect measure of Left Atrial Pressure (LAP) and Left Ventricular End-Diastolic Pressure (LVEDP), reflecting LV preload. A PCWP >18 mmHg often suggests cardiogenic pulmonary edema.

Functional Hemodynamics - Dynamic Flow View

Dynamic assessment of fluid responsiveness and cardiac output.

• Key Dynamic Indices (Mech. Vent. Pts):
  • Stroke Volume Variation (SVV): If > 10-15%, suggests fluid responsiveness.
  • Pulse Pressure Variation (PPV): If > 10-13%, suggests fluid responsiveness.
• Bedside Echo: IVC variability, LVOT VTI changes.
• Other CO: PiCCO, LiDCO.

⭐ Dynamic indices (SVV, PPV) are superior to static CVP/PAOP for predicting fluid responsiveness in ventilated patients.

High‑Yield Points - ⚡ Biggest Takeaways

• Arterial lines: continuous BP monitoring, frequent ABGs.
• CVP (2-6 mmHg): reflects RV preload; guides fluid status.
• PAC: measures PCWP (6-12 mmHg) for LV preload, CO, SvO2.
• Low SvO2 (<60%): signals impaired tissue oxygen delivery or ↑consumption.
• Elevated lactate: key marker of tissue hypoperfusion & anaerobic metabolism.
• Dynamic indices (PPV, SVV): best predict fluid responsiveness in ventilated patients.
• Use parameters for goal-directed therapy in shock to improve outcomes.