Mechanical Ventilation Modes Lecture

Introduction

• Ventilator Mode: Describes how the mechanical ventilator assists a patient with inspiration.
• Control Variables: Volume control and pressure control.
• Importance: Mode controls how machine functions and assists with breathing pattern.

Control Variables

Volume Control

• Definition: Control the patient's tidal volume.
• Pros: Known minute ventilation; useful for achieving desired PaCO2 levels.
• Cons: High peak pressures with decreased lung compliance; patient-ventilator asynchrony.

Pressure Control

• Definition: Control patient's pressure to achieve desired tidal volume.
• Pros: Helps reach desired PaCO2 levels.
• Cons: Potentially unstable tidal volumes with changes in lung compliance or airway resistance.

Primary Ventilator Modes

Assist Control (AC)

• Function: Delivers preset mandatory breaths; patient can trigger assisted breaths.
• Pros: Full ventilatory support; low work of breathing.
• Cons: Risk of hyperventilation and respiratory alkalosis.

Synchronous Intermittent Mandatory Ventilation (SIMV)

• Function: Delivers preset mandatory breaths; allows spontaneous breaths in between.
• Pros: Maintains respiratory muscle strength; distributes tidal volume evenly; decreases mean airway pressure.
• Cons: Not as high support as AC; used for partial ventilatory support.

Spontaneous Modes

Continuous Positive Airway Pressure (CPAP)

• Function: Delivers continuous pressure; patient must be breathing spontaneously.
• Use: Useful for weaning patients.

Pressure Support Ventilation (PSV)

• Function: Supports spontaneous breaths during inspiration with preset pressure.
• Use: Helps overcome airway resistance, useful in weaning.

Volume Support (VS)

• Function: Delivers supportive breath to reach set tidal volume.
• Use: Often used for weaning patients from anesthesia.

Unconventional (Secondary) Modes

Control Mode Ventilation (CMV)

• Function: Delivers preset tidal volume at set frequency.
• Use: For fully sedated patients with neuromuscular blocking agents.

Airway Pressure Release Ventilation (APRV)

• Function: Two levels of CPAP with intermittent release phase.
• Use: Improves oxygenation, treats refractory hypoxemia, ARDS.

Mandatory Minute Ventilation (MMV)

• Function: Increases mandatory breaths when spontaneous breaths are inadequate.
• Use: Prevents hypercapnia, often used with SIMV.

Inverse Ratio Ventilation (IRV)

• Function: Uses inverse I:E ratio to improve oxygenation.
• Use: Treats ARDS; causes auto-PEEP which improves oxygenation.

Pressure Regulated Volume Control (PRVC)

• Function: Provides volume-controlled breaths at lowest pressure.
• Use: Maintains low peak airway pressure.

Proportional Assist Ventilation (PAV)

• Function: Variable pressure support for spontaneous breaths.
• Use: Adjusts to patient’s work of breathing.

Adaptive Support Ventilation (ASV)

• Function: Changes mandatory breaths and pressure support based on breathing pattern.

Adaptive Pressure Control (APC)

• Function: Pressure-controlled mode with minimum tidal volume maintenance.

Volume Assured Pressure Support (VAPS)

• Function: Stable tidal volume with inspiratory pressure support.
• Use: Watch in patients with obstructive disease to avoid air trapping.

Neurally Adjusted Ventilatory Assist (NAVA)

• Function: Uses diaphragm's electrical activity to guide ventilation.

Automatic Tube Compensation (ATC)

• Function: Compensates for airflow resistance from endotracheal tube.

High-Frequency Oscillatory Ventilation (HFOV)

• Function: Small tidal volumes at high rate to prevent lung injury.
• Use: Improves oxygenation in severe cases like refractory hypoxemia; useful in neonates with specific conditions.

Conclusion

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Resources

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