Surgical Critical Care: Hemodynamic Monitoring

Arterial Blood Pressure Monitor (Arterial Line/A-Line)

Indications

  • Intraarterial Catheter Used for Continuous Blood Pressure Monitoring
  • Other Possible Indications:
    • Frequent Blood Sampling
    • Arterial Drug Administration
    • Use of an Intra-Aortic Balloon Pump (IABP)

Site Selection

  • Sites:
    • Radial Artery – Generally the Preferred Site
    • Central Arteries (Axillary or Femoral)
    • Brachial Artery – Worst Choice
    • Dorsalis Pedis – Generally Only Used in Children
  • Allen Test
    • Occlude Radial & Ulnar Arteries, Clench Hand 10x, Release Ulnar Artery
    • Positive if Capillary Refill < 6 Seconds
    • Indicates Adequate Contralateral Flow
    • Poor Accuracy

Radial Artery Placement

  • Position: Use a Flexible Board or Rolled Towel to Stabilize the Wrist in Dorsiflexion
  • Placed Using Seldinger Technique
  • Ultrasound Guidance Should be Utilized if Available
    • Benefits:
      • Increased First-Pass Success
      • Decreased Complication Rate
      • Decreased Failure Rate

Arterial Waveform Analysis

  • Arterial Waveform:
    • Systolic Upstroke – Systolic Ventricular Ejection
    • Systolic Decline – Beginning of Decline Before Diastole
    • Dicrotic Notch – Closure of Aortic Valve (Start of Diastole)
    • Diastolic Runoff – Decline During Diastole
  • System Dampening:
    • Over-Dampened System:
      • Waveform Appears Flattened with a Small Amplitude & Loss of Dicrotic Notch
      • Pressure Changes:
        • Decreased Systolic Blood Pressure
        • Increased Diastolic Blood Pressure
        • Decreased Pulse Pressure
      • Causes:
        • Air Bubbles in the Tubing
        • Arterial Thrombus
        • Tube Kinging
    • Under-Dampened System:
      • Waveform Appears Saltatory & Abrupt with Exaggerated Dicrotic Notch
      • Pressure Changes:
        • Increased Systolic Blood Pressure
        • Decreased Diastolic Blood Pressure
        • Increased Pulse Pressure
      • Causes:
        • Excessively Long Tubing Length
        • Multiple Stopcocks
  • Most Reliable Measure: Mean Arterial Pressure (MAP)
    • MAP is Generally Preserved Regardless of Systolic/Diastolic Blood Pressures
    • Systolic Blood Pressure is Greater in Peripheral Vessels than in the Aorta
      • Due to Smaller Diameter

Complications

  • Infection
    • Most Common Source: Skin Colonization
    • Most Common Organism: S. epidermidis
    • Highest Risk Site: Femoral Artery
  • Thrombus
    • Risk Factors:
      • Duration of Use
      • Length & Size of Catheter
      • Hypercoagulable States
    • Clinically Significant Ischemia is Rare (< 1%) – Generally Not a Serious Complication
  • Vasospasm
  • Distal Ischemia
    • Highest Risk Site: Brachial Artery

Arterial Waveform

Arterial Waveform Dampening

Pulmonary Artery (Swan-Ganz) Catheter

Basics

  • Invasive Catheter Placed into the Pulmonary Artery to Allow Direct Hemodynamic Monitoring
  • Catheter Contains 4 Lumens & Thermistor
    • White/Clear: Proximal Port (31 cm) – Used for Infusion
    • Blue: Distal Right Atrial Lumen (30 cm) – Measures CVP & RA Pressure
    • Yellow: Pulmonary Artery Lumen – Measures Pulmonary Artery Pressure & Can Draw Blood for Mixed Venous Oxygen
    • Red: Balloon Port
    • Thermistor (Red/White Connector) – Measures Cardiac Output by Thermodilution
  • Use:
    • Can Help in Determining Etiology of Shock & Guide Treatment
    • There is No Improvement in Mortality – Therefore it Has Generally Fallen Out of Use

Indications

  • Continuous Cardiac Output Monitoring
  • Distinguishing Etiology of Shock
  • Assessment of Volume Status
  • Evaluation of Pulmonary Hypertension
  • Evaluation of Pericardial Illnesses

Contraindications

  • Absolute Contraindications:
    • Presence of a Right Ventricular Assist Device
    • Infection at Insertion Site
    • Insertion During Cardiopulmonary Bypass
  • Relative Contraindications:
    • Left Bundle Branch Block (Can Induce RBBB Causing Complete Heart Block)
    • Pneumonectomy
    • Pacemaker or Defibrillator
    • Right-Sided Mechanical Valve
    • Right-Sided Endocarditis, Tumors or Masses – Can Cause Embolization (Some Consider an Absolute Contraindication)
    • Severe Coagulopathy or Thrombocytopenia

Placement

  • Done at Bedside or Under Fluoroscopy (Most Common)
  • Insertion Site is Similar to CVC (Right IJ Generally Preferred)
  • Confirm Appropriate Position on CXR: West Zone III (Lower Lung Has Less Respiratory Influence)
  • Waveforms:
    • Right Atrium:
      • A Wave (Atrial Contraction) with X Descent
        • May Have a Small C Wave (Tricuspid Closure) During X Descent
      • V Wave (Ventricular Contraction) with Y Descent
    • Right Ventricle: Sharp Systolic Rise/Fall with QRS & Gradual Increase Between
    • Pulmonary Artery: Primary Systolic Wave Followed by Gradual Decline with Dicrotic Notch
      • Similar to Arterial-Line Waveform
    • Pulmonary Artery Wedge Pressure: Similar to Right Atrium but at Higher Pressure
      • No C Wave (Tricuspid Closure) During X Descent

Measures

  • Measure At: End-Expiration (Lowest Intrathoracic Pressure)
  • Measured Values:
    • Cardiac Output/Cardiac Index (CO/CI)
    • Central Venous Pressure (CVP)
    • Pulmonary Artery Wedge Pressure (PAWP)
    • Pulmonary Artery Pressure (PAP)
    • Mixed Venous Oxygen Saturation (SvO2)
    • Temperature
  • Calculated Values:
    • Stroke Volume (SV)
    • Systemic Vascular Resistance (SVR)
    • Pulmonary Vascular Resistance (PVR)

Hemodynamic Changes & Shock Differentiation

Complications

  • Same Complications as Central Venous Catheters
  • Pulmonary Artery Rupture
    • Risk: 0.2%
    • 30-70% Mortality
    • Presentation: Massive Hemoptysis
    • Pseudoaneurysm May Form if Initial Injury is Self-Limiting
    • Treatment: Leave Balloon Inflated (Tamponade) & Emergent Angiography
      • If Fails: Lobectomy

PAC Waveforms

FloTrac/Vigileo

Basics

  • Allows for Continuous Minimally Invasive Hemodynamic Monitoring
  • Analyzes Arterial Pressure Waveform to Calculate Stroke Volume & Cardiac Output
  • Minimally Invasive
    • Attaches to an Arterial Line
    • Allows Avoidance of Invasive Pulmonary Artery Catheters
  • Components:
    • FloTrac – Sensor that Connects to the Arterial Line
    • Vigileo – Monitor

Measures

  • Mean Arterial Pressure (MAP)
  • Stroke Volume (SV)
  • Cardiac Output/Cardiac Index (CO/CI)
  • Stroke Volume Variation (SVV)
  • Systemic Vascular Resistance (SVR)

Use

  • Generally Accurate in Stable Patients
  • SVV if Often Used in Determining Fluid Responsiveness
  • Accuracy is Controversial for Patients with Low SVR
    • Includes: Septic Shock, Hepatic Cirrhosis, Aortic Regurgitation or IABP Counter-Pulsion

Bioreactance/Bioimpedance Analysis (Cheetah NICOM)

Basics

  • Allows for Continuous Noninvasive Hemodynamic Monitoring
  • Analyzes the “Phase Shifts” When Alternating Current Through the Thorax
  • Accurately Measures the Stroke Volume & Heart Rate to Calculate the Cardiac Output
  • Noninvasive
    • Uses Four External Sensors Over the Thorax
    • Allows Avoidance of Invasive Pulmonary Artery Catheters

Measures

  • Heart Rate (HR) – Directly Measured
  • Stroke Volume (SV) – Calculated Based on Flow (dX/dt) & Ventricular Ejection Time (VET)
    • Age & Body Surface Area (Weight & Height) Affect Signal Propagation & Are to Modify the Calculation
  • Cardiac Output (CO) – Calculated from HR & SV
    • CO = SV x HR = f(dX/dt,VET,HR,Weight,Height,Age)