Mechanical Ventilation

Quick reference: Mechanical Ventilation - Quick Reference

Sub-Notes

• I felt I had to split up this topic otherwise there would be too much to scroll through in one note

Note	Contents
Physiology of Mechanical Ventilation	Lung mechanics, gas exchange, phases of MV, monitoring
Ventilator Modes	AC, SIMV, PCV, PSV, PRVC — trigger/control/cycle, pros/cons, indications
Ventilator Settings	Control variables, targeting schemes, phase variables, FiO₂, VT, RR, PEEP, PS, I:E ratio, initial settings
Ventilator Waveform Interpretation	Pressure and flow waveforms, P-V loops, work of breathing
Lung Protective Ventilation	VALI, barotrauma, biotrauma, ARDS protocol, permissive hypercapnoea
Ventilator Consequences	Effects on gas exchange, haemodynamics, ICP; auto-PEEP, dyssynchrony, VAP
Ventilatory Weaning	SBT readiness, passing/failing SBT, extubation checklist, post-extubation
Ventilator Troubleshooting and Alarms	Crashing patient, DOPES, COPD, all alarm types

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Ventilator Modes Overview

Mode	Control	Trigger	Cycle	Key Use
AC	Volume	Time/P/Flow	Time	Full support, no hyperventilation
SIMV	Volume + Pressure	Time + P/Flow	Time + Flow	Hyperventilating patient, auto-PEEP risk
PCV	Pressure	Time only	Time	High barotrauma risk
PSV	Pressure	P/Flow	Flow	Conscious patient, pre-extubation
PRVC	Adaptive (P→V)	Time	Time	Guarantees VT, minimises P

AC vs SIMV: excess spontaneous breaths get full support in AC, partial support in SIMV

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Initial Settings at a Glance

Parameter	Normal	COPD	ARDS
VT	10 mL/kg IBW	8 mL/kg IBW	6 mL/kg IBW
RR	10–20	Avoid ↑	10–20
FiO₂	Start 100%, wean to ≤60%	←	←
PEEP	5–8 cmH₂O	Low/ZEEP	≥8–12 cmH₂O
I:E	1:2	1:3 or 1:4	1:2

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Pressure Interpretation

$P_{\text{peak}}$	$P_{\text{plateau}}$	Meaning
↑	Normal	↑ Airway resistance (bronchospasm, secretions, kink)
↑	↑	↓ Lung compliance (oedema, pneumothorax, ARDS)

$\text{Compliance}=\frac{V_{\text{T}}}{P_{\text{plateau}}-\text{PEEP}}\text{Driving Pressure}=P_{\text{plateau}}-\text{PEEP}$

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Delirium Prevention

• The FAVoR trial demonstrates a reduction in delirium for ventilated patients receiving scripted family-recorded voice message to re-orientate them
  • There was only a 1.1% improvement in delirium free days, a low number of patients recruited to the trial, and although small the differences in baseline characteristics between the intervention & control groups may be significant given the small difference in outcome. I would therefore want to see further data before pushing for widespread adoption of this technique
  • Delirium Reduction via Scripted Family Voice Recordings in Critically Ill Patients Receiving Mechanical Ventilation CL Munro. Am J Crit Care. 2025; Nov 1;34(6):429-437. doi: 10.4037/ajcc2025486

Sources

• Strong Medicine Playlist: Mechanical Ventilation - YouTube
• ICU One Pager
  • Mechanical Ventilator Basics — ICU One Pager
  • Ventilator Weaning — ICU One Pager
  • Vent Troubleshooting: High Peak Pressures — ICU One Pager
  • Volume Assist/Control Ventilation — ICU One Pager
• Deranged Physiology
  • Flow, volume, pressure, resistance and compliance
  • Phases of a mechanical breath
  • Basics of Mechanical Ventilation
  • Phase variables: triggering, limits, cycling and PEEP
  • Control variables: volume and pressure
  • Triggering of a mechanically supported breath
  • Limit (target) variables in mechanical ventilation
  • Selecting and adjusting PEEP
  • Inspiratory pause, I:E ratio and inspiratory rise time
  • Practical differences between pressure and volume controlled ventilation
  • Mandatory and spontaneous modes of ventilation
• Ventilator Alarm (DOPES) - YouTube
• EMCrit 239 - Vent Alarms = Code Blue
• Ventilator Alarms: Types, Causes, and Troubleshooting (2026)
• Liberation from the ventilator - EMCrit Project