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Ventilator modes explained: what each one sets on an adult transport vent

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A ventilator mode is the rule set that decides who starts each breath, what the ventilator holds constant while it delivers that breath, a volume or a pressure, and what ends it. Every mode on an adult transport ventilator combines those three choices, which is why seven acronyms turn out to be two decisions. This page has the ventilator modes explained in one table, then works through what each one changes about the numbers you already set, for adult patients only.

Compare the basic ventilator modes side by side

The five modes commonly taught are assist control, SIMV, pressure support, pressure control, and CPAP. Transport ventilators add BiPAP and, on some models, a volume-targeted pressure mode, which is why the table below carries seven rows instead of five. The first two columns are the whole story: who starts the breath, and whether there’s a set rate underneath it. Everything else follows from those two answers. Run these seven rows against the ventilator settings cheat sheet and field guide this site already walks through, and a mode stops being an acronym and starts being a place those numbers land.

Ventilator modes compared: what starts the breath, what stays fixed, and what you watch
ModeWho starts the breathSet rate?What the vent holds constantWhat varies with the patientWhat you watch
Volume assist control (VC-AC)Ventilator (timer) or patientYes, a minimumTidal volume and inspiratory flowAirway pressurePeak and plateau pressure
Pressure assist control (PC-AC)Ventilator (timer) or patientYes, a minimumInspiratory pressure, held for a set timeTidal volumeDelivered tidal volume
PRVC (volume-targeted pressure)Ventilator (timer) or patientYes, a minimumA target tidal volume, reached by an adjusted inspiratory flowThe pressure the vent is using to get thereWhether the vent is still holding the target
SIMVVentilator for mandatory breaths, synchronized to patient effort; patient in betweenYes, the mandatory countVolume or pressure on the mandatory breathsWhatever the patient adds between themTotal delivered minute ventilation
Pressure support (PSV)Patient onlyNoInspiratory pressure, until flow falls offTidal volume and breath lengthTidal volume and work of breathing
CPAPPatient onlyNoOne continuous airway pressureEverything about the breathWhether the patient is tiring
BiPAP (bilevel NIV)Patient onlyNo by definition; some transport vents add a backup rateTwo set pressures, one for in, one for outTidal volumeMask seal and tolerance

How many ventilator modes are there?

It depends on who’s teaching. Four, five, and six are common groupings, and manufacturers add their own names on top of that: PRVC, PCV-VG, AutoFlow among them. None of those counts is a guideline standard, just teaching shorthand; the two-axis view below stays constant however the list gets counted.

Interpret a mode as two decisions: who starts the breath, what stays fixed

Underneath the acronyms, StatPearls describes every breath by three preset factors: trigger, target, and termination. Trigger is how the breath starts, ventilator timer or patient effort. Target is what the ventilator aims at while delivering the breath, a preset flow or pressure. Termination is what ends inspiration: a set time, a set volume, or the inspiratory flow falling off. Merck frames the same split more simply: volume-cycled ventilation delivers a constant volume and lets pressure vary; pressure-cycled ventilation holds a constant pressure and lets volume vary. Put trigger and target together and the acronym list turns into a grid: who starts the breath against what the vent holds constant. The diagram below places the seven modes from the table on that grid.

Ventilator mode grid: who starts the breath against what the ventilator holds constantA two by three grid. Columns are what the vent holds constant, volume or pressure. Rows are who starts the breath: ventilator timer, either the ventilator or the patient, or the patient only. Both ventilator-timer cells hold CMV, volume-limited on the left and pressure-limited on the right. The volume and either cell holds volume AC and SIMV mandatory breaths. The pressure and either cell holds pressure AC and PRVC. The pressure and patient-only cell holds pressure support and BiPAP, with a smaller sub-cell for CPAP labeled one continuous pressure. The volume and patient-only cell is empty, labeled no volume mode without a set breath.What the vent holds constantWho starts the breathVolumePressureVentilator timerEitherPatient onlyCMV(volume-limited)CMV(pressure-limited)Volume AC,SIMV mandatory breathsPressure AC,PRVCno volume modewithout a set breathPressure support,BiPAPCPAP: one continuous pressure
Seven acronyms, two decisions. CMV is drawn for completeness; StatPearls’ ventilator safety chapter says it should not be used outside the OR.

Compare volume assist control with pressure assist control

Both are assist control: every breath, mandatory or patient-triggered, gets full support at a minimum set rate. The difference is what the vent holds constant. Volume assist control delivers the tidal volume you set and lets airway pressure follow the lungs. Pressure assist control holds the inspiratory pressure you set for a fixed inspiratory time and lets tidal volume follow the lungs instead. Which of the two you’re running also decides which I:E control the mode hands you, inspiratory flow in volume assist control, inspiratory time in pressure assist control. StatPearls’ EMS chapter calls assist control standard across transport ventilators and confines its own discussion to volume AC, and Weingart’s 2016 Annals of Emergency Medicine paper names volume AC as his own chosen mode for both a lung-protective and an obstructive strategy, a stated practice rather than a trial result.

Assist control versus SIMV breath sequenceTwo rows of six breaths each. The top row, assist control at a set rate, shows four timer-triggered full-height breaths and two patient-triggered breaths also drawn full height with a small trigger marker underneath, annotated that every breath gets the full set breath and the set rate is a floor. The bottom row, SIMV at the same set rate with pressure support on, shows four synchronized mandatory breaths at full height and two smaller patient breaths at half height, annotated that mandatory breaths hold the set rate while the patient’s own breaths are smaller.Assist control (set rate 12)patient triggerEvery breath gets the full set breath; the set rate is the floor.SIMV (set rate 12, pressure support on)spontaneous, supportedMandatory breaths hold the set rate; the patient’s own breaths are smaller.
Same set rate, different answer to a patient who breathes over it.

What do the A and C mean on a ventilator?

Assist: a patient-triggered breath gets the same full breath as a machine-triggered one. Control: if the patient doesn’t trigger, the ventilator delivers the set breath at the set rate. StatPearls’ EMS chapter describes assist control this way and notes that spontaneous breathing, a breath the patient both triggers and does the work of, is not enabled in this mode. The rate you set is a minimum, not the delivered rate, which is the mechanics behind how the ventilator respiratory rate setting behaves once the patient triggers. That same fixed volume and flow can cause dyssynchrony and stack breaths into auto-PEEP, worth knowing as breath stacking in assist control before it shows up on the pressure waveform.

What is the difference between PRVC and volume control?

PRVC is a pressure-targeted breath: the ventilator adjusts the inspiratory flow rate to regulate the pressure delivered to the airways, aiming for a constant tidal volume with a constant inspiratory pressure and a decelerating flow pattern. Volume control instead delivers the volume you set regardless of what pressure that takes. The practical difference for a crew: the number you dial in on PRVC looks like a volume, but the breath the patient feels is a pressure breath the vent keeps adjusting. PRVC, PCV-VG, and AutoFlow are manufacturer names for the same idea.

Compare SIMV and pressure support: when the patient breathes over the set rate

SIMV delivers the set mandatory breaths synchronized to the patient’s own effort, and lets the breaths in between run unsupported or pressure-supported. Pressure support alone has no set rate at all: every breath is patient-triggered, and the ventilator adds a set pressure that ends when the patient’s inspiratory effort falls off. In SIMV, the set rate is the mandatory count, not a floor under every breath, so delivered minute ventilation is the mandatory breaths plus whatever the patient adds, the same delivered-versus-set gap behind how the minute ventilation formula turns into a rate. SIMV is also used for weaning, though the 1995 Esteban trial found a once-daily spontaneous-breathing trial extubated patients faster than intermittent mandatory ventilation did, history rather than an argument for transport. Some crews are trained to default to SIMV; others default to volume assist control. Neither default makes the other wrong, and weaning strategy itself is hospital work past this page’s scope.

Set CPAP or BiPAP on the transport vent as modes, not as a separate device

CPAP is one continuous airway pressure with no mandatory breaths and no per-breath support; the patient does all the work of every breath. BiPAP, bilevel NIV, adds a higher inspiratory pressure above the expiratory one, so each patient-triggered breath gets some support. Both run on the same transport ventilators that run the volume and pressure modes above, ZOLL and Hamilton devices among them, through a mask instead of a tube. In a 2023 meta-analysis of prehospital noninvasive ventilation, CPAP or bilevel pooled together, adults had a lower risk of intubation than with standard oxygen therapy and no mortality difference; cardiogenic pulmonary edema and a COPD exacerbation are the usual indications, including for COPD ventilator settings once the mask is not enough. Picking CPAP or BiPAP over intubation is a protocol and scope-of-practice decision; this page covers what the mode sets on the box already running it, and home CPAP, sleep apnea, mask fitting, and patient coaching stay off it.

What is CPAP mode in a ventilator?

One continuous airway pressure. The patient does all the work of breathing, and there’s no per-breath support and no tidal volume target for the ventilator to steer toward. A tidal volume number has nowhere to land in CPAP.

Verify what your mode changes about the numbers you set

Rapid Vent Calculator names no ventilation mode. It returns an ideal body weight, a tidal volume, a minute ventilation target, and a derived rate, four numbers that land most cleanly on a volume-targeted mode because tidal volume and rate are dialed in directly there. What each mode family does with those four numbers:

  • Volume assist control: tidal volume is set directly, and the set rate is a floor. Watch exhaled tidal volume and EtCO2 once the patient starts triggering on their own.
  • Pressure AC and PRVC: the calculated tidal volume becomes the number you watch, or in PRVC, the number the vent targets for you; rate is still a floor, and pressure is what moves, by your hand in pressure AC and by the vent in PRVC.
  • SIMV: the tidal volume applies to the mandatory breaths; the set rate is the mandatory count, and delivered minute ventilation runs higher than the arithmetic once the patient adds breaths of their own.
  • Pressure support, CPAP, BiPAP: no set rate, so the derived rate has nowhere to go. Tidal volume is watched in pressure support and BiPAP, and CPAP has no per-breath volume target at all.

Every one of those numbers still lives inside the same pressure ceiling, whatever the mode: the plateau pressure ceiling every mode lives under is the limit the volume target sits inside, not a separate rule. The ARDSNet card tells the clinician to select any ventilator mode first, then works down to a volume goal, the same logic behind the ARDSnet protocol settings, written for any mode. The tidal volume itself still comes from the tidal volume target set from ideal body weight, the same figure whichever mode it ends up inside. None of this tells the calculator which mode the box is running. It cannot see the patient or know the protocol, so the clinician picks the mode, then reads the app’s numbers into whatever that mode asks for; the hub’s four-point answer on pressure modes covers that same read in more depth. Once the mode is chosen and the numbers are on the screen, the next step is post-intubation vent management for EMS crews, where those numbers get rechecked against the patient actually breathing on them.

Sources

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