Mechanical Ventilation Basics And Ventilator Modes
Indications for Intubation:
• Failure of NIPPV: No clinical improvement (Intensive Care Med 2001;27:1718)
• Cannot ventilate: PaCO2 >60 with severe acidemia (COPD or other obstruction, sedation, NM disease, respiratory muscle fatigue, trauma)
• Cannot oxygenate: Worsening P:F ratio (PNA, pulmonary edema, ARDS, PE)
• Airway protection/instability: Unconsciousness, AMS, shock, facial/head trauma, nausea/vomiting/UGIB, severe secretions, severe bronchospasm/anaphylaxis
• Persistent increased work of breathing: Severe bronchospasm, airway obstruction, inability to compensate for severe acidemia
• Hemodynamic instability: unstable arrhythmia, HoTN
Ventilator Modes:
AC/VC - Assist Control/Volume Control
• Delivers a breath until set tidal volume is reached
• Pros: ↑control over ventilation (fixed VT prevents barotrauma or atelectrauma, e.g., ARDSNet)
• Cons: fixed inspiratory flow regardless of effort, ↑ pt-vent dyssynchrony
AC/PC - Assist Control/Pressure Control
• Delivers a breath until set pressure is reached
• Pros: variable flow (and variable VT) during inspiration to satisfy patient demand, ↓ dyssynchrony
• Cons: can cause volutrauma as compliance or pt effort changes
PSV - Pressure Support Ventilation
• Delivers a set pressure triggered by patient’s spontaneous breathing
• Pros: better tolerated, less sedation required, used as trial setting prior to extubation (i.e. SBT of 0/0)
• Cons: less control over respiratory parameters, volutrauma possible, no fixed RR (only backup rate)
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