Basics of Mechanical Ventilation

Introduction

• Key topics:
  • How to initiate mechanical ventilation
  • Different modes of ventilation
  • Weaning patients off ventilators

Indications for Mechanical Ventilation

• Low GCS Score: GCS < 8
• Weak Breathing Effort: GCS < 8 indicates need for ventilation
• Impaired Oxygenation: Inability to maintain saturation despite 100% oxygen
• CO2 Retention: Need for CO2 washing out

Components of Mechanical Ventilation

• Endotracheal Tube (ETT):
  • Tube inserted through the mouth
  • Balloon inflated to hold tube in place
• Ventilator Functionality:
  • Controls breathing (volume, pressure, rate)
  • Provides oxygen mixed with air

Correlation of Volume and Pressure

• Volume Control: Set constant volume (e.g. 500 ml);
  • Ventilator decides pressure to deliver that volume.
• Pressure Control: Set constant pressure;
  • Ventilator decides volume delivered.
• Effect of Lung Compliance:
  • Stiff lungs = higher pressure needed
  • Compliant lungs = lower pressure needed

Modes of Ventilation

Controlled Mandatory Ventilation (CMV)

• For patients with weak breathing efforts, deep coma.
• Entirely controlled by the ventilator.
• Drawbacks:
  • Risk of muscle atrophy from lack of effort
  • Increased risk of barotrauma due to high pressure
  • Accidental disconnection can be fatal.

Assist-Control Ventilation (AC)

• Similar to CMV but allows patient-initiated breaths.
• Ventilator detects breath attempts and assists.
• Always maintains a set minimum rate.
• Drawbacks: Risk of hyperventilation if the patient triggers too many breaths.

Synchronized Intermittent Mandatory Ventilation (SIMV)

• Weaning mode; allows spontaneous breathing.
• Ventilator assists only when necessary.
• Process: Patient breathes independently most of the time, with ventilator support as needed.

Pressure Control Ventilation

• Set constant pressure; volume is variable.
• Used when high pressures are a concern (e.g., ARDS).
• Drawbacks: Risk of lower tidal volumes leading to respiratory acidosis.

Spontaneous Mode

• Patient controls all breathing efforts; ventilator provides pressure support.
• Final step before extubation.

Weaning Patients Off Ventilators

• Process: CMV → AC → SIMV → Spontaneous.
• Reduce sedation and monitor ABGs for readiness to extubate.
• Check mental status and secretions.

Summary

• Reviewed indications, volume/pressure settings, ventilation modes, and weaning processes.
• Importance of monitoring and understanding mode functionalities.