MedCram Lecture: Modes of Ventilation

Introduction

• Focus on additional modes of ventilation: CPAP and PEEP.
• Difference between non-invasive (CPAP) and invasive (PEEP) ventilation.

CPAP and PEEP

• CPAP: Stands for Continuous Positive Airway Pressure.

  • Used in non-invasive ventilation (e.g., BiPAP or CPAP masks).
  • Continuous pressure: Same pressure during inhalation and exhalation.
  • Settings range from 5 to 20 cm of water pressure.
  • Useful for obstructive sleep apnea.

• PEEP: Stands for Positive End Expiratory Pressure.

  • Used in invasive ventilation.
  • Measured in mmHg, ranging from 5 to 20.
  • Maintains pressure even at end of exhalation.
  • Keeps alveoli open and recruited.

Pressure Support Ventilation (PSV)

• Similar to CPAP but only occurs on inhalation.
• Delivers specific pressure support for each breath.
• Patient initiates all breaths.
• Popular for weaning.

Review of Ventilation Modes

• Assist Control (AC):

  • Patient triggers the ventilator to provide a specific volume.
  • Backup rate ensures patient gets a minimum number of breaths.

• Pressure Control:

  • Set specific pressure, patient or ventilator initiates.

• CPAP:

  • Continuous pressure, independent of breaths.

• Pressure Support Ventilation (PS):

  • Specific pressure on each patient-initiated breath.

Writing Vent Orders

• Mode: E.g., AC (Assist Control).
• Backup Rate: Ensures a minimum breath rate (e.g., 16 breaths/min).
• Tidal Volume: Amount of air per breath (e.g., 550 ml).
• FiO2: Fractional inspiration of oxygen (e.g., 50%).
• PEEP: Positive end expiratory pressure (e.g., 5).

Impact on Ventilation and Oxygenation

• Tidal volume and rate affect carbon dioxide levels.
• FiO2 and PEEP affect oxygenation.

Pressure-Volume Flow Graphs

• Demonstrates how pressure, volume, and flow are related in AC mode.
• Key concepts:
  • PEEP: Maintains constant pressure in the circuit.
  • Tidal Volume: Preset target volume.
  • Triggering Breaths: Patient-initiated vs. ventilator-initiated.

Compliance and Pressure Alarms

• Compliance Issues:

  • Decreased lung compliance may increase pressure.
  • Set pressure alarm can alert staff to compliance issues.

• Types of Pressure:

  • Peak pressure vs. plateau pressure (to be covered in next lecture).