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Understanding CPAP and PEEP Ventilation Modes

Sep 25, 2024

MedCram Lecture: Modes of Ventilation

Introduction

  • Focus on modes of ventilation: CPAP (Continuous Positive Airway Pressure) and PEEP (Positive End Expiratory Pressure).
  • CPAP is used for non-invasive ventilation, typically with a mask.
  • PEEP is used in invasive ventilation.

CPAP and PEEP

  • CPAP:

    • Non-invasive, continuous pressure (5 to 20 cm of water pressure).
    • Used with masks like CPAP or BiPAP.
    • Provides continuous pressure regardless of inhalation or exhalation.
    • Useful in obstructive sleep apnea by keeping the airway open.

  • PEEP:

    • Used in invasive ventilation, measured in mmHg (5 to 20).
    • Maintains pressure in the lungs at the end of exhalation to keep alveoli open.
    • Helps in recruiting alveoli, preventing collapse.

Pressure Support Ventilation (PS)

  • Offers support on inhalation, unlike CPAP which is continuous.
  • Initiated by patient breath; the patient receives a specific pressure.
  • Different from pressure control where the rate can be set.
  • Higher pressure supports result in deeper breaths.
  • Popular weaning mode of ventilation.

Summary of Ventilation Modes

  1. AC (Assist Control):
    • Patient triggers ventilator, receives a set volume.
  2. Pressure Control:
    • Ventilator provides specific pressure.
  3. CPAP:
    • Continuous pressure, independent of breath cycle.
  4. Pressure Support:
    • Provides pressure with patient-initiated breaths.

Writing Vent Orders

  • Four key components:
    1. Mode: e.g., AC (Assist Control).
    2. Backup Rate: Ensures a minimum number of breaths if the patient doesn't initiate.
    3. Tidal Volume: E.g., 550 ml.
    4. FIO2: Fraction of inspired oxygen, e.g., 50%.
    5. PEEP: E.g., 5 cm of water pressure.

Effects on Gas Exchange

  • Carbon Dioxide:
    • Affected by breath rate and tidal volume.
  • Oxygenation:
    • Affected by FIO2 and PEEP.
    • Higher PEEP can recruit more alveoli for better oxygenation.

Pressure-Volume-Flow Graph in AC Mode

  • Pressure:
    • Always a baseline PEEP (e.g., 5).
    • Negative deflection triggers the ventilator.
    • Volume and flow adjust according to set parameters.
  • Compliance and Pressure Alarms:
    • Decreased compliance increases required pressure.
    • Pressure alarms notify of compliance issues (e.g., pulmonary edema, pneumothorax).

Upcoming Topics

  • Discussion on peak and plateau pressures in the next lecture.

Full transcript