Basics of Mechanical Ventilation and Ventilators

Introduction

• Third module in a series on mechanical ventilation.
• Prerequisite: Complete previous modules on lung ventilation and ventilator system concepts.

Objectives

• Understand essential variables and mechanical breath types.
• Explain concepts like breath cycle time, inspiratory/expiratory time, and more.

Essential Variables

• Foundation of mechanical breaths and ventilation modes.
• Key components of intermittent positive pressure ventilation (IPPV).
• Major ventilator control parameters.

Key Questions

• Define breath cycle time, inspiratory time (Ti), expiratory time (Te).
• Explain triggering, cycling, controlling, targeting, and baseline pressure.
• Understand mechanical breath and properties of eight mechanical breath types.

Mechanical Breath and Timing

• Mechanical ventilation: a series of mechanical breaths.
• Breath Cycle Time (BCT) includes inspiratory (Ti) and expiratory time (Te).

Triggering and Cycling

• Triggering: When inspiration starts.
• Cycling: When inspiration ends.
• Triggering mechanisms: time, pressure, flow.
• Cycling mechanisms: time cycling, flow cycling.

Triggering Mechanisms

• Time Triggering: Based on set rate; machine-triggered.
• Pressure Triggering: Patient-triggered; relies on airway pressure monitoring.
• Flow Triggering: Patient-triggered; relies on airway flow monitoring.

Abnormal Patient Triggering

• Failure forms: Weak patient effort or overly sensitive trigger settings.
• Auto-triggering: Triggering without patient inhalation, often caused by external factors.

Controlling

• Mechanisms by which a ventilator controls gas delivery.
• Types: Volume controlling, Pressure controlling, Adaptive controlling.

Volume Controlling

• Controls inspiratory gas flow.
• Advantages: Stable tidal volume.
• Disadvantages: Potential asynchrony, variable peak pressure, invisible volume loss.

Pressure Controlling

• Adjusts inspiratory flow to maintain target pressure.
• Advantages: Synchrony, leak compensation.
• Disadvantages: Variable tidal volume.

Adaptive Controlling

• Automatic regulation of inspiratory pressure.
• Advantages: Stable tidal volume in passive patients.

Hybrid Controlling

• Combines volume and pressure controlling.
• Not widely popularized.

Targeting

• Defines size of a mechanical breath.
• Paired with controlling type.
• Involves tidal volume, inspiratory pressure, or target tidal volume.

PEEP (Positive End Expiratory Pressure)

• Baseline pressure above atmospheric level.
• Therapeutic benefits: Improves lung function.
• Typically constant in ventilation modes.

Mechanical Breath Types

• Classification based on triggering, cycling, controlling.
• Eight Breath Types:
  • Volume Control Breath: Time-triggered, time-cycled, volume-controlled.
  • Pressure Control Breath: Time-triggered, time-cycled, pressure-controlled.
  • Adaptive Control Breath: Time-triggered, time-cycled, adaptive-controlled.
  • Volume Assist Breath: Patient-triggered, time-cycled, volume-controlled.
  • Pressure Assist Breath: Patient-triggered, time-cycled, pressure-controlled.
  • Adaptive Assist Breath: Patient-triggered, time-cycled, adaptive controlled.
  • Pressure Support Breath: Patient-triggered, flow-cycled, pressure-controlled.
  • Adaptive Support Breath: Patient-triggered, flow-cycled, adaptive controlled.

Conclusion

• Understanding essential variables and breath types is crucial.
• Prepare to advance to mechanical ventilation modes.