Basics of Mechanical Ventilation and Ventilators

Introduction

• Third module in series on mechanical ventilation.
• Covers essential variables and mechanical breath types.
• Essential variables are core to mechanical breaths and ventilation modes.

Learning Objectives

• Understand breath cycle time, inspiratory time, and expiratory time.
• Learn about triggering, cycling, controlling, targeting, and baseline pressure.
• Identify properties of eight mechanical breath types.

Mechanical Breath and Timing

• Mechanical ventilation consists of mechanical breaths realized through a ventilator system.
• Breath Cycle Time (BCT): Duration of a mechanical breath.
  • Includes Inspiratory Time (Ti) and Expiratory Time (Te).
• Triggering and Cycling:
  • Triggering: Start of inspiration.
  • Cycling: End of inspiration.
  • BCT = duration from one triggering point to the next.

Types of Triggering

• Time Triggering: Machine-triggered based on BCT.
• Pressure Triggering: Patient-triggered based on airway pressure drop.
• Flow Triggering: Patient-triggered based on difference between circuit flow measurements.
• Abnormal Triggering: Can fail by not responding to patient effort or by auto-triggering.

Cycling Mechanisms

• Time Cycling: Ends inspiration after a set time or ratio.
  • Methods include setting Ti, I:E ratio, or peak flow.
• Flow Cycling: Ends inspiration when inspiratory flow drops to a preset level.

Controlling Mechanisms

• Volume Controlling: Sets tidal volume, stable volume delivery.
  • Disadvantages include possible patient-ventilator asynchrony.
• Pressure Controlling: Sets pressure, allows variable tidal volume.
• Adaptive Controlling: Regulates inspiratory pressure to maintain target volume.
• Hybrid Controlling: Combines pressure and volume controlling.

Targeting and PEEP

• Targeting (Limiting): Defines size of mechanical breath paired with controlling type.
• PEEP (Positive End Expiratory Pressure): Baseline pressure, therapeutic benefits, adjustable.

Mechanical Breath Types

• Classified based on triggering, cycling, and controlling dimensions.
• Breath Types Include:
  • Volume Control Breath
  • Pressure Control Breath
  • Adaptive Control Breath
  • Volume Assist Breath
  • Pressure Assist Breath
  • Adaptive Assist Breath
  • Pressure Support Breath
  • Adaptive Support Breath

Conclusion

• Understanding essential variables and mechanical breath types prepares for learning different ventilation modes.