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Schematic traces and simulated values for education only — not a medical device, not for clinical use.
Quick reference
Modes: VC guarantees volume · PC guarantees pressure (volume varies) · PS only boosts breaths the patient starts (no set rate) · AC gives a full breath for every trigger · SIMV mixes mandatory + own breaths · CPAP = one pressure, no boost · BiPAP = IPAP/EPAP, the gap ventilates.
Numbers: Vt 4–8 mL/kg IBW · Pplat < 30 cmH2O · PEEP 5–15 · PS 5–15 · SpO2 92–96% (88–95% COPD/ARDS) · RSBI < 105 · MV = rate × Vt drives CO2 · FiO2 + PEEP drive oxygen.
Alarms: peak↑ plateau OK = resistance (plug, kink, spasm) · peak↑ plateau↑ = compliance (edema, pneumothorax, mainstem) · volumes/pressures falling = leak, disconnect, displaced tube · sudden deterioration = DOPE + hand-bag.
Practice questions
These open the actual NCLEX Trainer question bank — the same questions, answers, rationales, and textbook sources used across DayoRN. Work the respiratory set there to broaden beyond ventilator scenarios.
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Field guide
The complete ventilator reference for this module — modes, settings, monitoring, waveforms, alarms, ABG-driven adjustments, weaning, and prevention. Every practice chain is keyed to this guide, and every section names its source.
The complete ventilator textbook for this module. Every practice chain in this app is keyed to what is written here — if an answer ever seems to disagree with this guide, the guide wins.
1. Ventilation basics
A ventilator is a machine that moves air in and out of the lungs for a patient who cannot do it well enough alone. The most common reason is acute respiratory failure — either hypoxemic (the lungs cannot get oxygen in, PaO2 < 60 mmHg) or hypercapnic (the lungs cannot clear carbon dioxide, PaCO2 > 50 mmHg) — plus airway protection (a patient who cannot protect their own airway), surgery, and severe metabolic problems where breathing is compensating.
The airway. An endotracheal tube (ETT) passes through the mouth into the trachea; a cuff at its tip seals the trachea so air goes through the tube, not around it. Correct placement is confirmed with end-tidal CO2, auscultation of all lobes, and a chest X-ray. A tracheostomy is a surgical opening directly into the trachea — used when ventilation will be prolonged; it is more comfortable, needs less sedation, and makes suctioning and eventual weaning easier.
The circuit is the tubing from ventilator to patient. It carries gas out to the patient and exhaled gas back. Water condensing in the circuit, kinks, and loose connections are everyday troubleshooting items (see Alarms).
Mandatory vs spontaneous breaths. A mandatory breath is started and/or finished by the machine on a schedule. A spontaneous breath is started by the patient's own effort. Modes differ in how they mix the two — that mix is the single most useful way to understand any mode.
📖 Source: OpenStax, Medical-Surgical Nursing — §35.3 Respiratory Concerns · StatPearls — Ventilator Management
2. Modes — what the vent guarantees
Read every mode the same way: what does the ventilator guarantee, what does the patient control, and what can go wrong?
| Mode | The vent guarantees | Patient controls | Used for / watch-outs |
|---|---|---|---|
| Volume Control (VC) | A set tidal volume (Vt) every mandatory breath, whatever pressure it takes | Nothing about the breath size; may trigger extra breaths (in AC) | Predictable minute ventilation. Watch-out: if lungs stiffen, pressures climb — watch plateau pressure. |
| Pressure Control (PC) | A set inspiratory pressure for a set inspiratory time; volume is whatever that pressure delivers | Nothing about volume | Gentle, capped pressures. Watch-out: if compliance falls (stiffer lungs), the same pressure delivers LESS volume — exhaled Vt drifts down. |
| Pressure Support (PS) | A pressure boost added to each breath THE PATIENT starts; the breath ends when the patient's inspiratory flow falls | Rate, timing, and (with the boost) much of the volume | Weaning and spontaneous breathing. There is NO set rate and no machine breaths if the patient makes no effort (except a backup in some setups). Too much PS → oversized volumes; too little → rapid shallow fatigue. |
| Assist Control (AC) | A full mandatory breath (set Vt in AC-VC, or set pressure in AC-PC) at a set minimum rate — AND the same full breath for every patient trigger | Can trigger extra full breaths | Full support for acute respiratory failure; the most common ICU starting mode. Watch-out: a fast patient gets a full breath for every effort → high minute ventilation and respiratory alkalosis. |
| SIMV | A set number of mandatory breaths; breaths the patient takes in between are their own (often with PS added) | Extra breaths between the mandatory ones | A step-down/weaning structure. Watch-out: unsupported spontaneous breaths through a tube are hard work — add PS, and beware SIMV rates that are neither full support nor a real trial. |
| CPAP | One continuous pressure, all the time (like PEEP for every breath); no inspiratory boost | Everything — rate, timing, volume | Non-invasive (mask) or as a spontaneous trial setting. Helps oxygenation by keeping alveoli open; does NOT directly blow off CO2. |
| BiPAP (NIV) | Two pressures: IPAP on inspiration, EPAP (= PEEP) on expiration; the IPAP–EPAP gap is pressure support by another name | Triggers every breath | Mask ventilation for COPD exacerbation and cardiogenic pulmonary edema. CO2 problem → widen the gap (raise IPAP). Oxygen problem → raise EPAP/FiO2. |
| APRV (overview) | A high CPAP level held most of the time with brief timed releases to a low pressure; the patient may breathe spontaneously throughout | Spontaneous breaths at both levels | A specialist rescue mode for severe ARDS in some centres. You need to recognise it, not set it. |
📖 Source: StatPearls — Assist-Control Ventilation · StatPearls — Ventilator Management
3. Settings
| Setting | What it is | Standard teaching values |
|---|---|---|
| Tidal volume (Vt) | Volume per breath, prescribed against ideal body weight (IBW), never actual weight: IBW (kg) ≈ 50 + 0.91 × (height cm − 152.4) for men; 45.5 + 0.91 × (height cm − 152.4) for women | 4–8 mL/kg IBW (lung-protective; ~6 is the usual starting point) |
| Respiratory rate (RR) | Set breaths per minute (patients may breathe above it in AC/SIMV/PS) | Commonly 12–20 to start; adjusted to the ABG |
| PEEP | Pressure kept in the airways at end-expiration so alveoli stay open | Typical 5–15 cmH2O; an oxygenation lever |
| FiO2 | Fraction of inspired oxygen (room air = 0.21) | Start high in an emergency, then wean promptly — target SpO2 92–96% for most, 88–95% in COPD/ARDS contexts |
| I:E ratio | Inspiratory time vs expiratory time | Commonly 1:2; obstructive patients need a LONGER expiration (1:3, 1:4) |
| Inspiratory pressure | The set pressure in PC (above PEEP) | Titrated to deliver a protective Vt |
| Pressure support level | The boost above PEEP for each spontaneous breath | Typical 5–15 cmH2O |
| Trigger sensitivity | How much effort/flow the patient must generate to start a breath | Too insensitive → missed efforts; too sensitive → the machine self-triggers (auto-triggering) |
| Rise time | How quickly pressure reaches its target at breath start | Comfort/synchrony setting; too slow can cause air hunger in PS |
📖 Source: StatPearls — Acute Respiratory Distress Syndrome (Vt 4–8 mL/kg IBW, SpO2 88–95%, plateau < 30) · StatPearls — Positive End-Expiratory Pressure
4. Monitoring — the numbers that keep lungs safe
Peak pressure (Ppeak) is the highest pressure during the breath — it fights airway resistance AND lung stiffness. Plateau pressure (Pplat), measured with an end-inspiratory hold, is the pressure in the alveoli themselves — the one that stretches lung tissue. Target Pplat < 30 cmH2O. The pattern tells the story: peak up with plateau near normal = a resistance problem (secretions, kink, bronchospasm). Peak AND plateau up = a compliance problem (stiffer lungs — edema, pneumothorax, worsening ARDS).
Driving pressure in plain terms = Pplat − PEEP: how much pressure each breath actually spends stretching the lung. Lower is safer; it rises when you raise Vt or lungs stiffen. Compliance = change in volume ÷ change in pressure — stiff lungs have low compliance. Minute ventilation (MV) = RR × Vt, and it is the master control for CO2. EtCO2 (end-tidal CO2) tracks exhaled CO2 breath by breath: it trends with PaCO2, and SUDDEN loss of EtCO2 means the gas isn't coming back — think displaced tube or disconnect until proven otherwise.
Auto-PEEP (intrinsic PEEP) happens when the next breath starts before exhalation finished, trapping air breath after breath. COPD and asthma patients — narrow airways, slow emptying — are the classic risk, and high rates/short expirations make it worse. Spot it on the flow waveform: expiratory flow never returns to zero before the next breath. Consequences: rising pressures, and the trapped pressure can squeeze venous return and drop blood pressure. Fix = give more expiratory time (lower rate, longer I:E), treat the obstruction.
📖 Source: StatPearls — ARDS (plateau < 30) · StatPearls — PEEP (intrinsic/auto-PEEP) · StatPearls — Ventilator Management (MV = RR × Vt; compliance)
5. Waveforms & asynchrony
Two traces matter most. The pressure scalar: PC/PS breaths rise quickly to a flat top (square-ish); VC breaths climb through the breath. The flow scalar: VC gives a decelerating inspiratory flow; the expiratory side should always drift back to zero before the next breath.
| Asynchrony | How it looks | Fix the cause |
|---|---|---|
| Double triggering | One patient effort pulls two quick machine breaths — the first breath ended before the patient's demand did | Longer inspiratory time / more support; treat pain, agitation, hunger for air |
| Flow starvation | The pressure curve sags/scoops during a VC breath — the patient is pulling harder than the machine delivers | Increase flow (or switch to a pressure mode); treat the drive (pain, acidosis, anxiety) |
| Ineffective efforts | Small bumps in flow/pressure that never become breaths — the patient tried and the machine didn't notice | Make the trigger more sensitive; reduce auto-PEEP, which forces the patient to overcome trapped pressure first |
📖 Source: StatPearls — Ventilator Management
6. Alarms & troubleshooting
High-pressure alarm — think resistance vs compliance again: secretions/mucus plug, kinked or bitten tube, bronchospasm, water in the circuit (resistance family); pneumothorax, worsening edema/ARDS, right-mainstem intubation (compliance family). Low exhaled volume / low pressure — the gas is escaping: circuit disconnect, cuff leak, or a displaced tube. Apnea alarm — no breaths detected in a spontaneous mode: the backup rate should kick in; check the patient first.
📖 Source: StatPearls — Ventilator Safety · OpenStax — §35.3 (ETT displacement monitoring)
7. ABG-driven adjustments
Two separate problems, two separate toolboxes — never mix them. Ventilation (CO2) problem → change minute ventilation. Respiratory acidosis (high PaCO2, low pH): increase MV — usually raise the rate first, then Vt if it stays inside lung-protective limits. Respiratory alkalosis (low PaCO2, high pH): decrease MV (lower the rate; in AC, also hunt the cause of over-breathing — pain, fever, anxiety). Oxygenation (O2) problem → FiO2 and PEEP. Think of it as a ladder: FiO2 is fast and simple but toxic at 1.0 for long; PEEP recruits and holds alveoli open, so in ARDS the team often climbs the PEEP rungs rather than parking on FiO2 100%.
📖 Source: StatPearls — Ventilator Management (CO2 via Vt/RR; O2 via FiO2/PEEP) · OpenStax — §35.3 (ABG components and interpretation)
8. Weaning & extubation
Weaning starts with a daily readiness screen: the cause of respiratory failure is improving; oxygenation is adequate on modest settings (low FiO2/PEEP); the patient is hemodynamically stable; and they are awake enough to protect their airway. Passing the screen earns a spontaneous breathing trial (SBT) — typically 30 minutes to 2 hours on minimal support (low PS or CPAP) — often paired with a sedation interruption ("sedation vacation").
RSBI (rapid shallow breathing index) = respiratory rate ÷ tidal volume (in litres) during spontaneous breathing. RSBI < 105 predicts success; a rising rate with shrinking volumes (RSBI climbing past 105) is the classic failing pattern. Also weigh: cuff leak (air leaking around a deflated cuff suggests the airway isn't dangerously swollen — absent leak = caution), secretion burden (can they cough and clear?), and mentation. After extubation, high-risk patients often get HFNC or NIV as a bridge. Reintubation risk is highest in the first 24–48 hours — watch work of breathing, rate, and gas exchange, not just SpO2.
📖 Source: StatPearls — Extubation (RSBI < 105, MV < 10 L/min, SBT 30 min–2 h) · OpenStax — §35.3 (SBTs and sedation vacations)
9. Complications & prevention
VAP (ventilator-associated pneumonia) — pneumonia developing more than 48 hours after intubation — is prevented with a bundle: head of bed 30–45°; regular oral care; maintain ETT cuff pressure (about 20–30 cmH2O) and use subglottic suction where available so secretions pooled above the cuff don't leak down; daily sedation vacation + readiness assessment; and DVT and stress-ulcer (GI) prophylaxis — blood thinners and acid suppression, because immobile, critically ill patients clot and bleed.
Lung injury from the vent itself: barotrauma (pressure injury — pneumothorax is the dramatic form) and volutrauma (volume overstretch) are why Vt is prescribed by IBW and plateau pressure is kept under 30. Sedation is titrated to a target on the RASS scale (Richmond Agitation-Sedation Scale) — light is usually better than deep once the patient is stable, because deep sedation prolongs ventilation. Early mobility, even while ventilated, preserves muscle and shortens time on the vent.
📖 Source: OpenStax — §35.3 (VAP bundle; sedation vacations; DVT/ulcer prophylaxis) · StatPearls — Ventilator Safety (HOB 30–45°, cuff 20–30 cmH2O)