Invasive Hemodynamic Monitoring

Arterial Line Lowdown - Pulse Points Probed

• Purpose: Continuous real-time BP; frequent ABGs; vasoactive drug guidance.
• Common Sites:
  • Radial (preferred; Allen's test prior)
  • Femoral (Central; ↑infection risk)
  • Brachial, Axillary, Dorsalis pedis
• Waveform Insights:
  • Upstroke, peak, dicrotic notch (aortic valve closure), runoff.
  • MAP: $MAP = DBP + 1/3 (SBP - DBP)$. Normal 70-100 mmHg.
  • Pulse Pressure (PP): $PP = SBP - DBP$.
• Damping (Square Wave Test):
  • Optimal: 1.5-2 oscillations.
  • Overdamped: Blunted, ↓SBP, ↑DBP. Causes: air, clots, kinks.
  • Underdamped: Sharp, ↑SBP, ↓DBP. Causes: stiff tubing, whip.
• Complications: Ischemia, thrombosis, hematoma, infection, nerve injury, pseudoaneurysm.

⭐ Exam Favourite: Dicrotic notch on arterial waveform: aortic valve closure.

Central Venous Access - Core Pressure Cues

Central Venous Pressure (CVP) estimates right atrial pressure (RAP) & RV preload.

• Normal: 2-8 mmHg. Zero at phlebostatic axis (mid-axillary, 4th ICS).
• Read at end-expiration.

CVP Waveform: (Phases of cardiac cycle) 📌 Mnemonic: All Cows Eat Very Young grass (a, c, x, v, y)

• a wave: Atrial systole. (Absent: AFib; Cannon a: AV dissociation)
• c wave: RV isovolumetric contraction (tricuspid bulge).
• x descent: Atrial relaxation.
• v wave: Atrial filling (tricuspid closed). (Large v: Tricuspid Regurgitation - TR)
• y descent: Early ventricular filling (tricuspid opens). (Blunted: Tamponade, TS)

Interpreting CVP Changes:

• ↑ CVP: Fluid overload, RV failure, PE, tamponade, PEEP.
• ↓ CVP: Hypovolemia, vasodilation.

⭐ Prominent v waves on CVP trace strongly suggest significant tricuspid regurgitation.

Pulmonary Artery Catheter - Swan's In-Depth Scoop

• A.k.a.: Swan-Ganz catheter.
• Function: Monitors Right Atrial (RA), Right Ventricular (RV), Pulmonary Artery (PA) pressures, Pulmonary Capillary Wedge Pressure (PCWP ≈ LVEDP), Cardiac Output (CO), Mixed Venous O2 Saturation (SvO2).
• Key Uses: Complex cardiac surgery, ARDS, cardiogenic/septic shock, guiding fluid/inotrope therapy.
• Catheter Ports:
  • Distal (PA port - typically yellow): Measures PAP, PCWP (balloon inflated), mixed venous blood sampling (SvO2).
  • Proximal (RA port - typically blue): Measures CVP, injectate for CO, fluid/drug administration.
  • Balloon inflation port (typically red): Inflate with ≤1.5 mL air for PCWP; passive deflation.
  • Thermistor connector: Detects temperature change in PA for thermodilution CO.
• CO Measurement: Thermodilution principle; cold saline injectate (e.g., 10 mL at <8°C) in RA, temperature change sensed by PA thermistor.
• Pressure Waveform Progression (During Insertion): RA → RV → PA → PCWP.
• Normal Values (mmHg):
  • RA: 0-8
  • RV: 15-30 / 0-8
  • PA: 15-30 / 8-15 (Mean 10-20)
  • PCWP: 6-12 (approximates Left Atrial Pressure)
• SvO2 (Mixed Venous Oxygen Saturation): Normal 60-80%. Reflects global tissue O2 extraction. ↓SvO2 indicates ↑O2 demand or ↓O2 delivery (e.g., ↓CO, anemia, hypoxia, sepsis).
• Complications: ⚠️ PA rupture (potentially fatal), arrhythmias (VT, RBBB during insertion), pulmonary infarction, catheter knotting, valvular damage, thromboembolism, infection.

⭐ For accurate PCWP measurement, the catheter tip must be in West’s Zone 3 of the lung (where Pa > Pv > PA), ensuring an uninterrupted column of blood between the catheter tip and the left atrium when the balloon is inflated.

High‑Yield Points - ⚡ Biggest Takeaways

• Arterial lines: Continuous BP, ABG access. Allen’s test vital before radial cannulation.
• CVP: Measures RA pressure (normal 2-6 mmHg), guides fluid therapy.
• PAC (Swan-Ganz): Measures PAP, PCWP (estimates LVEDP), CO, SvO2.
• PCWP (normal 6-12 mmHg): Reflects LV preload; elevated in LV failure.
• Low CVP/PCWP: Suggests hypovolemia. High CVP/PCWP: Suggests fluid overload/cardiac dysfunction.
• PAC risks: Arrhythmias, PA rupture, thrombosis, infection.
• Arterial waveform: Overdamping ↓systolic BP; underdamping ↑systolic BP.