Mechanical ventilation

Ventilator modes made simple

Reviewed Nov 2026·2 references
New· views rounded down, updated weekly

Every mode is defined by what the machine controls (volume or pressure), what triggers a breath (time or patient) and what ends it (volume, time or flow). Use assist-control early, pressure support when the patient breathes well, and know what to monitor for each.

At the bedside

Timed steps
  1. 1

    Volume control (VC-AC)

    Know

    Set Vt and flow; pressure varies with compliance and resistance. Monitor peak and plateau pressures. Guaranteed minute ventilation.

  2. 2

    Pressure control (PC-AC)

    Know

    Set inspiratory pressure and Ti; Vt varies with mechanics. Monitor exhaled Vt and minute volume. Decelerating flow, often more comfortable.

  3. 3

    Dual modes (PRVC / VC+ / AutoFlow)

    Know

    Set target Vt; machine adjusts pressure breath to breath. Risk: if the patient pulls hard, the machine lowers support.

  4. 4

    Pressure support (PSV/CPAP)

    Know

    Patient-triggered, flow-cycled (usually 25% of peak flow). Set PS and PEEP. No backup rate: set apnoea ventilation. Used for weaning.

  5. 5

    SIMV

    Know

    Mandatory breaths synchronised with spontaneous breaths. Slows weaning compared with PS or SBTs; avoid as a weaning mode.

  6. 6

    APRV

    Know

    Long high pressure with brief releases; rescue in some ARDS units; needs expertise.

Common modes

ModeSetVariesMonitorUse
VC-ACVt, rate, PEEP, FiO2, flowAirway pressurePeak, plateauDefault initial mode
PC-ACPinsp, Ti, rate, PEEP, FiO2Tidal volumeExhaled Vt, MVAsynchrony, high peak pressures
PRVC / VC+Target Vt, rate, PEEPPressure (auto-adjusted)Vt, pressureConvenience; caution with high drive
PSV / CPAPPS, PEEP, FiO2, trigger, cycle %Vt, rateRR, Vt, RSBIWeaning, comfort
SIMV (+PS)Vt or Pinsp, rate, PSSpontaneous breathsTotal RRNot recommended for weaning
APRVP-high, P-low, T-high, T-lowVtRelease volumesRescue ARDS (experienced units)
Red flag · call your senior now
PSV with no apnoea backup in a sedated patient.
Red flag
Pressure-controlled mode with falling exhaled Vt: compliance has worsened (secretions, oedema, pneumothorax).
Pitfall
Assuming PC is 'safer' for the lung: large Vt can still occur with strong patient effort.
Pearl
Change only one variable at a time and record why.

References

  1. 1

    Boles JM, Bion J, Connors A, et al. Weaning from mechanical ventilation. Eur Respir J. 2007;29(5):1033-1056

  2. 2

    Girard TD, Alhazzani W, Kress JP, et al. An official ATS/ACCP clinical practice guideline: liberation from mechanical ventilation in critically ill adults. Am J Respir Crit Care Med. 2017;195(1):120-133

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Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.