Reference — Respiratory

Ventilator Modes Reference

Ventilator modes determine how the ventilator delivers breaths — who triggers the breath, what controls the breath delivery, and how much work the patient contributes. Nurses must understand each mode to monitor patients and recognize patient-ventilator dyssynchrony.

Educational use only. Ventilator mode selection and management require provider and respiratory therapy orders. Nurses monitor and respond — they do not independently adjust modes. This reference supports learning, not autonomous clinical decision-making. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.

Assist Control (AC / A-C)

The ventilator delivers a full, preset breath for every patient-initiated effort. If the patient fails to trigger a breath within the set interval, the ventilator delivers a mandatory breath at the set rate anyway.

Settings controlledTidal volume (or pressure), set RR (backup), FiO₂, PEEP, flow rate

Patient workMinimal — ventilator delivers full support for every breath

Typical indicationsAcute respiratory failure; post-operative; apneic or hemodynamically unstable patients; ARDS initial management

Nursing watchAuto-PEEP (breath stacking) if patient over-breathes set rate; respiratory alkalosis; no muscle conditioning

SIMV — Synchronized Intermittent Mandatory Ventilation

The ventilator delivers a preset number of mandatory breaths synchronized with patient efforts. Between mandatory breaths, the patient breathes spontaneously without ventilator support (unless pressure support is added).

Settings controlledMandatory RR, Vt (or pressure), FiO₂, PEEP; optional PS added for spontaneous breaths

Patient workVariable — depends on mandatory rate. Spontaneous breaths are unsupported (unless PS is added).

Typical indicationsTransitional support; weaning by gradual RR reduction; maintaining some respiratory muscle activity

Nursing watchRespiratory muscle fatigue from unsupported spontaneous breaths; dyssynchrony possible; slower weaning than PSV-based trials

Pressure Support Ventilation (PSV / PS)

Each patient-initiated breath receives a preset pressure boost to assist inspiration. The patient controls the timing, respiratory rate, and (partially) the tidal volume. There is no mandatory breath — if the patient stops breathing, no breath is delivered (apnea alarm activates).

Settings controlledPS level (e.g., 5–20 cmH₂O), FiO₂, PEEP; patient determines RR and triggers each breath

Patient workMore patient work than AC or SIMV — patient triggers and drives every breath

Typical indicationsSpontaneous breathing trials (SBTs); weaning; compensation for ETT resistance (PS 5–8 cmH₂O); comfort ventilation

Nursing watchNo backup rate — apnea alarm is the only safety net. Not for apneic or hemodynamically unstable patients. Monitor Vt for adequacy.

CPAP — Continuous Positive Airway Pressure

CPAP delivers a continuous level of pressure throughout the entire breathing cycle (both inspiration and expiration). The patient breathes entirely on their own — no ventilatory assistance is provided. CPAP only maintains oxygenation support, not ventilation.

Settings controlledCPAP pressure level, FiO₂; patient breathes spontaneously

Patient workFull — the patient provides all the work of breathing

Typical indicationsPre-extubation SBT assessment; OSA; non-invasive management of cardiogenic pulmonary edema; NICU applications

Nursing watchNo CO₂ removal support — monitor for CO₂ retention and respiratory fatigue; requires cooperative and hemodynamically stable patient

BiPAP — Bilevel Positive Airway Pressure (Non-Invasive)

BiPAP delivers two different pressure levels: IPAP (inspiratory positive airway pressure) during inhalation and EPAP (expiratory positive airway pressure) during exhalation. The difference between IPAP and EPAP provides the pressure support — assisting ventilation non-invasively through a mask.

Settings controlledIPAP (typically 10–20 cmH₂O), EPAP (typically 4–8 cmH₂O), FiO₂, backup RR

Patient workAssisted — less than breathing alone, more than intubated AC mode

Typical indicationsCOPD exacerbation with respiratory acidosis (first-line); acute cardiogenic pulmonary edema; post-extubation failure risk; OSA

Nursing watchMask fit and pressure tolerance — air leak reduces effectiveness; aspiration risk in altered LOC; monitor closely for BiPAP failure requiring intubation

Support Continuum at a Glance

Mode	Backup Rate	CO₂ Removal	Patient Effort
AC	Yes	Yes (controlled)	Minimal
SIMV	Yes (mandatory breaths)	Yes	Partial
PSV	No (apnea alarm only)	Patient-driven	High (all breaths triggered)
CPAP	No	Patient-driven only	Full
BiPAP (NPPV)	Yes (optional)	Yes (via IPAP−EPAP difference)	Assisted

NCLEX Pearls

›AC mode delivers full support for every breath — minimal patient work, maximum respiratory muscle rest.
›PSV has no backup rate — apnea alarm is the safety net. Not appropriate for apneic patients.
›CPAP provides positive pressure throughout breathing but zero ventilatory assistance — patient does all the work.
›BiPAP is first-line for COPD exacerbation with acute respiratory acidosis — reduces intubation rate.
›SIMV weaning reduces the mandatory rate over time, forcing the patient to do more spontaneous breathing.
›Spontaneous Breathing Trial (SBT) = low PSV (5–8 cmH₂O) + PEEP 5 to assess extubation readiness.

Related Resources

Ventilator Modes Comparison ChartMode, patient effort, advantages, and limitations side by side

Open →

Mechanical Ventilation BasicsPurpose, indications, key settings, and nursing monitoring priorities

Open →

Ventilator Troubleshooting for NursesAlarm types, DOPE mnemonic, and step-by-step response

Open →

ARDS FundamentalsBerlin criteria, lung-protective ventilation, prone positioning

Open →

Standards & sources

Fact-checked Jun 21, 2026

This page is written to align with American Association for Respiratory Care (AARC) · GOLD (COPD) / ATS / CHEST. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →