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Ventilator Peak and Plateau Pressures

Jul 12, 2024

Ventilator Peak and Plateau Pressures

Case Introduction

  • 50-year-old patient with COPD and ARDS, on volume control mode of ventilation
  • High-pressure alarm is sounding; oxygen saturation is 84% on 100% FiO2
  • Current peak pressures: 45-50

Objectives

  1. How to obtain plateau pressure for patients on mechanical ventilation
  2. Concept of lung compliance
  3. Framework for addressing elevated peak and plateau pressures

Understanding Pressure Waveforms

  • Peak Inspiratory Pressure (PIP): pressure at the end of inspiration
    • Determined by:
      • Inspiratory flow rate and flow pattern
      • Airway resistance
      • Compliance of the respiratory system
      • Total Positive End Expiratory Pressure (PEEP)

Changes in PIP

  • Assuming inspiratory flow rate and PEEP are constant, changes in PIP indicate changes in either airway resistance or compliance
  • Inspiratory Hold/Pause: Stops flow briefly (0.5 - 1 second)
    • By removing flow, we focus on measuring compliance by determining the plateau pressure (Pplat)
    • Compliance = ability to distend or increase volume when pressure is applied

Compliance Equation

  • Compliance (C) = ΔVolume / ΔPressure
    • For ventilated lungs: C = Tidal Volume / (Plateau Pressure - PEEP)
  • Normal lung compliance: ~100 mL/cm H2O
  • ARDS lung compliance: 10-50 mL/cm H2O
  • Higher compliance = easy to inflate; Lower compliance = stiff lungs

Determining Cause of Increased PIP

  • Increase in PIP with increased Pplat: Indicates decreased compliance
  • Increase in PIP without change in Pplat: Indicates increased resistance

Framework for Elevated PIP

Increased Resistance

  • Factors decreasing diameter of the ventilator tubing, endotracheal tube, or major airways
  • Ventilator to Alveoli Framework:
    1. Ventilator Tubing: Check for kinks or obstructions
    2. Endotracheal Tube: Biting the tube
    • Add bite block or increase sedation
    1. Airway Secretions/Mucous Plugs: Inline suction catheter
    2. Bronchospasm: Inhaled bronchodilators (e.g., in asthma, COPD exacerbations)

Decreased Compliance

  • Processes affecting alveoli through filling or preventing expansion
    • Alveolar Filling:
      • Blood (hemorrhage), Pus (pneumonia, ARDS), Water (edema)
    • Preventing Alveolar Expansion:
      • Intrathoracic: Pneumothorax, pleural effusion, Auto-PEEP
      • Extrathoracic: Abdominal compartment syndrome, ascites
    • Chronic Cause: Fibrotic lung disease

Acute Management

  • Identify and address underlying disease processes causing increased Pplat or PIP
  • Multiple issues can coexist, need to consider a holistic approach

Case Follow-Up

  • Inspiratory Hold Results: PIP 45, Pplat 24 (unchanged)
  • Intervention: Suctioning to remove thick secretions
  • Outcome: PIP decreased to 32, oxygen saturation improved to 94%

Summary

  • Described obtaining plateau pressure via inspiratory hold
  • Discussed lung compliance and its calculation
  • Provided a framework for handling elevated PIP and Pplat

Thank you for watching.

Full transcript