CVR Physiotherapy › Technique cards › ICU and ventilation
Mechanical ventilation: indications, modes, CPAP and PEEP, complications, weaning
Ventilated patients now appear in long answers (GBS on SIMV in S23, ARDS on SIMV in S24, pneumonia on CMV in W24). You do not set the ventilator, but you must read its settings, know what each mode means for your treatment, and know when the patient is ready to come off it.
- Syllabus
- Ch 9(c) Mechanical ventilator modes; 9(b) Principles of ICU monitoring
- Priority
- High yield. In 7 of 20 papers (2016–2026); an ICU question appears in every paper since 2023.
- Asked as
- LAQ S23 7m S17W19W20 3m S22W21 ×2S24
- Usual split
- 3-mark lists (indications, complications, CPAP vs PEEP); 7-mark modes or weaning; part of ventilated long cases
- Checked against
- International weaning consensus (2007); ACCP/ATS liberation guideline (2017); ARDS Network low tidal volume trial (2000); ICU mobilisation safety consensus (2014). Full list under Sources.
- Content checked
- 19 October 2026. Next review due October 2027.
- My revision
-
1What it is
Mechanical ventilation means a machine moves gas into the lungs with positive pressure when the patient cannot breathe well enough alone. It buys time while the cause is treated; it does not cure anything.
- Invasive: through an endotracheal tube (ETT) or a tracheostomy.
- Non-invasive (NIV): through a tight face or nasal mask: CPAP or bilevel pressure (BiPAP).
| Term | Meaning | Usual adult value |
|---|---|---|
| FiO₂ | Fraction of oxygen in the gas (0.21 = room air, 1.0 = 100%) | The lowest that keeps SpO₂ in the target range |
| Tidal volume (VT) | Volume of each breath | 6–8 mL/kg of predicted body weight; 6 mL/kg in ARDS |
| Rate (f) | Machine breaths per minute | About 12–20 |
| PEEP | Pressure kept in the lungs at the end of breathing out | About 5 cmH₂O; higher in ARDS |
| Peak and plateau pressure | Highest airway pressure in a breath; pressure in the alveoli during a pause | Plateau kept at 30 cmH₂O or less |
| I:E ratio | Time breathing in : time breathing out | About 1:2; longer expiration in COPD and asthma |
| Trigger | The patient's own effort that starts a breath | Set by flow or pressure sensitivity |
| Pressure support | Extra pressure added to each breath the patient starts | 5–8 cmH₂O near the end of weaning |
Minute ventilation = tidal volume × rate (about 5–8 L/min at rest).
2Indications (3 marks in S24)
| Group | Examples |
|---|---|
| Type 1 respiratory failure (low oxygen) | PaO₂ below about 60 mmHg despite high oxygen: pneumonia, ARDS, pulmonary oedema |
| Type 2 respiratory failure (high CO₂ with acidosis) | COPD exacerbation when NIV fails, severe asthma, drug overdose |
| Failure of the breathing pump | Guillain–Barré syndrome, myasthenic crisis, high spinal cord injury, flail chest, exhausted breathing muscles |
| Airway protection | Coma (GCS 8 or less), head injury, stroke, poisoning, burns of the airway |
| Heart and circulation | Cardiac arrest, cardiogenic shock, severe pulmonary oedema |
| Planned | During and after major surgery; when heavy sedation or paralysis is needed; to control CO₂ in raised intracranial pressure |
Warning signs that lead to ventilation: respiratory rate above about 35, exhaustion, falling SpO₂ despite oxygen, rising CO₂ with falling pH, drowsiness, and in neuromuscular disease a falling vital capacity.
3Modes (7 marks in S17 and W20)
Airway pressure in four common modes
| Mode | How it works | Used for |
|---|---|---|
| Controlled mandatory ventilation (CMV) | Set volume (or pressure) at a set rate; in strict CMV the patient cannot add breaths | Deeply sedated or paralysed patients (W24 pneumonia on CMV) |
| Assist-control (A/C) | Set breath and a minimum rate; if the patient triggers, each extra breath is a full machine breath. Most modern "CMV" settings work this way | Resting tired muscles early in illness. Fast breathing can cause over-breathing and air trapping |
| Synchronised intermittent mandatory ventilation (SIMV) | A set number of machine breaths, timed with the patient's effort; between them the patient breathes alone, usually with pressure support | Partial support (S20, S23, S24 cases). Once used for weaning by lowering the rate, but weaning is slower than with pressure support or daily breathing trials |
| Pressure control (PCV) | Set pressure and inspiratory time; the volume varies with lung stiffness | Limits pressure in stiff lungs (ARDS) |
| Pressure support (PSV) | The patient starts every breath and controls rate and depth; the machine adds a set pressure | Comfortable partial support; weaning by lowering the support to 5–8 cmH₂O |
| CPAP | One continuous positive pressure; no machine breaths; the patient does all the breathing | Weaning on the ventilator; mask CPAP for sleep apnoea, cardiogenic pulmonary oedema, post-operative collapse |
| Bilevel NIV (BiPAP) | Higher pressure on breathing in (IPAP), lower on breathing out (EPAP), by mask | COPD exacerbation with acidosis, after extubation in high-risk patients, neuromuscular disease at night |
Rescue modes in very severe ARDS, such as high-frequency oscillation, are run by the doctors; patients on them are not mobilised out of bed.
Why does the mode matter to a physiotherapist?
It tells you how much work the patient's own muscles do. On CMV or A/C at a high rate the muscles are resting and wasting, so you rely on positioning, passive movement and secretion clearance. On SIMV, PSV or CPAP the patient is breathing, so active exercise, breathing exercises and inspiratory muscle training become possible, and you watch for fatigue.
4CPAP and PEEP (3 marks in W21)
| Point | CPAP | PEEP |
|---|---|---|
| What it is | A mode: positive pressure through the whole breath in a patient who breathes on their own | A setting: positive pressure kept at the end of breathing out, added to any mode with machine breaths |
| Breaths | All spontaneous; no machine breaths | Machine or supported breaths on top of it |
| How given | Mask, nasal interface or ventilator | Ventilator (or a PEEP valve on a bag) |
| Typical use | Sleep apnoea, cardiogenic pulmonary oedema, post-op collapse, weaning | Almost every ventilated patient (about 5 cmH₂O); higher in ARDS |
CPAP = PEEP for a patient who breathes alone
Effects of both: raise the functional residual capacity (FRC), keep small airways and alveoli open, improve oxygenation and lung compliance, and reduce collapse. CPAP also lowers the work of breathing and, in heart failure, the load on the left ventricle.
Side effects of high levels: less blood returns to the heart, so BP can fall; over-stretching and pneumothorax (barotrauma); raised intracranial pressure; mask discomfort, air swallowing and pressure sores with CPAP.
Do not confuse with auto-PEEP (intrinsic PEEP): trapped air when the patient cannot breathe out fully before the next breath, common in COPD and asthma; it lowers BP and makes triggering harder.
5Complications (3 marks in S22 and W21)
| System | Complications | Physio role |
|---|---|---|
| Lungs | Ventilator-induced lung injury (over-stretch, high pressure, repeated opening and closing of alveoli); pneumothorax; ventilator-associated pneumonia (VAP); collapse; oxygen toxicity; auto-PEEP; fighting the ventilator | Head-up position, turning, airway clearance; report sudden high pressures or falling SpO₂ |
| Airway | Tube blocked by secretions, displaced or pulled out; tube in the right main bronchus; damage to the larynx and trachea, later narrowing (stenosis); sinusitis | Humidification, suction; secure the tube during every turn and transfer |
| Heart and circulation | Lower venous return and cardiac output (hypotension), fluid retention | Check BP before and during treatment |
| Muscles and joints | Weak, wasted diaphragm; ICU-acquired weakness; contractures; pressure injuries; DVT | Early mobilisation, ROM, positioning, inspiratory muscle training |
| Other | Stress ulcers and gut bleeding; delirium; poor sleep; anxiety and post-traumatic stress after ICU | Orientation, communication, day–night routine, follow-up rehab |
Long-term ventilation (W21): tracheal stenosis or softening, repeated VAP, diaphragm wasting and ventilator dependence, ICU-acquired weakness, contractures, pressure injuries, and psychological effects. Patients who need the ventilator for more than about 1–2 weeks often get a tracheostomy, which is more comfortable, needs less sedation and makes weaning easier.
6Weaning (7 marks in W19)
Weaning is the process of freeing the patient from the ventilator. It starts with a daily check of readiness, then a spontaneous breathing trial (SBT), then extubation.
Ready to try? (daily screen)
- The cause of respiratory failure is improving.
- Oxygenation: SpO₂ 90% or more on FiO₂ 0.4–0.5 or less and PEEP 5–8 cmH₂O or less (PaO₂/FiO₂ ratio above about 150–200).
- Circulation: stable heart rate and BP, no or low-dose drugs to support BP, no active ischaemia.
- Brain: awake or easily roused, follows commands; can cough and protect the airway.
- Breathing: breathes on their own; pH 7.25 or more; few secretions; no fever, normal electrolytes.
| Measure | Favours weaning |
|---|---|
| Rapid shallow breathing index (RSBI = rate ÷ tidal volume in litres) | Below 105 breaths/min/L |
| Maximal inspiratory pressure (MIP) | Stronger than about −20 to −30 cmH₂O |
| Vital capacity | More than about 10 mL/kg |
| Minute ventilation | Below about 10 L/min |
Why does a high RSBI predict failure?
A tiring patient breathes fast and shallow: rate goes up, tidal volume goes down, so the ratio rises. Example: 35 breaths of 0.25 L gives 140 (likely to fail); 20 breaths of 0.5 L gives 40 (likely to succeed).
The breathing trial
- 30–120 minutes on low pressure support (5–8 cmH₂O) or a T-piece. The 2017 ACCP/ATS guideline suggests using low pressure support for the trial.
- Stop the trial if: breathing rate above 35 for more than 5 minutes; SpO₂ below 90%; heart rate above 140 or a change of more than 20%; systolic BP above 180 or below 90 mmHg; agitation, sweating, use of accessory muscles or see-saw breathing.
- Passed: the team considers extubation (with a cough and secretion check). High-risk patients may go onto NIV straight after extubation.
| Group | Meaning |
|---|---|
| Simple | Extubated after the first trial |
| Difficult | Needed up to 3 trials or up to 7 days |
| Prolonged | More than 3 trials or more than 7 days |
The physiotherapist's part in weaning
- Keep the airways clear: positioning, manual techniques, hyperinflation and suction.
- Sit the patient upright for trials: the diaphragm works better and lung volume is larger.
- Inspiratory muscle training for patients who fail weaning: it strengthens the inspiratory muscles and may shorten weaning (systematic review, 2015).
- Early mobilisation builds the strength and endurance needed to breathe alone.
- After extubation: deep breathing, huffing and supported cough, early walking.
7Reading the settings in a case
Before treatment, note the mode, FiO₂, PEEP, set and actual tidal volume, rate, peak pressure, SpO₂ and the latest ABG, and whether these are getting better or worse. Rising FiO₂ or PEEP means the lungs are getting worse.
| Case | Settings | What it tells you |
|---|---|---|
| S23: GBS, 45-year-old teacher | SIMV, PEEP 6, FiO₂ 0.4 | Moderate support for weak breathing muscles; lungs not badly affected; safe for active treatment as strength returns |
| S24: ARDS, 30-year-old woman | SIMV, PEEP 5, FiO₂ 0.4 | Mild to moderate support; oxygenation improving or mild disease; in-bed and out-of-bed activity possible if other signs are stable |
| W24: pneumonia, 35-year-old man | CMV, PEEP 10, FiO₂ 0.6, day 3 | High support, deeply sedated; at the limit for mobilising; avoid disconnection (closed suction) |
- High-pressure alarm: coughing, secretions, biting the tube, kinked tubing, bronchospasm, the patient fighting the ventilator, or a pneumothorax.
- Low-pressure or low-volume alarm: disconnection or a leak around the cuff.
- If the cause is not obvious, or SpO₂ falls, stop and call the nurse or doctor. Never silence an alarm you do not understand.
8Exam corner
Past questions (MUHS, 2016–2026)
- S23 Q4(b), 15 marks45-year-old schoolteacher with Guillain–Barré syndrome on a ventilator: SIMV, PEEP 6, FiO₂ 0.4. Discuss his impairments and ventilator management. Worked on the ICU physiotherapy card.
- 7-mark questionsModes of ventilation and the role of physiotherapy in ICU (S17). Criteria for weaning a patient off the ventilator (W19). Modes of mechanical ventilation (W20).
- 3-mark questionsRespiratory complications of mechanical ventilation (S22). Complications of long-term mechanical ventilation (W21). Difference between CPAP and PEEP (W21). Three indications for mechanical ventilation (S24).
Answer skeletons
- [Modes, 7] Definition of mechanical ventilation → the four traces sketched → table of CMV/A-C, SIMV, pressure control, pressure support, CPAP, BiPAP with one use each → one line on why the mode matters to physiotherapy.
- [Weaning, 7] Definition → readiness criteria (cause, oxygenation, circulation, brain, breathing) → RSBI and MIP with values → breathing trial and its stop criteria → simple, difficult, prolonged → physiotherapy role.
- [CPAP vs PEEP, 3] Three rows: mode vs setting, spontaneous vs machine breaths, typical use.
Test yourself
3 mGive three differences between CPAP and PEEP.
CPAP is a mode, PEEP is a setting. CPAP applies pressure throughout the breath in a patient who breathes alone, with no machine breaths; PEEP is pressure kept at the end of expiration during machine or supported breaths. CPAP is often given by mask (sleep apnoea, pulmonary oedema); PEEP is given through the ventilator to almost every ventilated patient.
3 mA patient on a breathing trial breathes 32 times a minute with a tidal volume of 0.4 L. Calculate the RSBI and interpret it.
32 ÷ 0.4 = 80 breaths/min/L. Below 105, so it favours successful weaning (other criteria must also be met).
MCQIn which mode does the patient breathe spontaneously between a set number of machine breaths?A. CMVB. SIMVC. CPAPD. Pressure control
B. SIMV gives a set number of synchronised machine breaths; between them the patient breathes alone, usually with pressure support.
MCQDuring a spontaneous breathing trial, which finding means the trial should be stopped?A. SpO₂ 94%B. Breathing rate 38 for 6 minutesC. Heart rate rising from 90 to 100D. Systolic BP 130 mmHg
B. A rate above 35 for more than 5 minutes means the patient is tiring.
Sources
Notes written in original words. The mode diagram is a simplified drawing made for this site.
- MUHS BPTh syllabus (2012) and MUHS IV BPTh question papers 2016–2026 (muhsonline.com, unofficial archive; Dhole Patil College of Physiotherapy past-paper page).
- Boles JM, et al. Weaning from mechanical ventilation. Eur Respir J 2007;29:1033–56 (international consensus conference).
- Schmidt GA, et al. Liberation from mechanical ventilation in critically ill adults: an official ATS/ACCP clinical practice guideline. Am J Respir Crit Care Med 2017; Ouellette DR, et al. Chest 2017.
- Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med 1991;324:1445–50.
- The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and ARDS. N Engl J Med 2000;342:1301–8.
- Hodgson CL, et al. Expert consensus and recommendations on safety criteria for active mobilization of mechanically ventilated critically ill adults. Crit Care 2014;18:658.
- Elkins M, Dentice R. Inspiratory muscle training facilitates weaning from mechanical ventilation among patients in the intensive care unit: a systematic review. J Physiother 2015.
- Structure and classical content: Hough, Physiotherapy in Respiratory and Cardiac Care; Main & Denehy (2016); Pryor & Prasad (2008).
Educational notes for exam preparation. Not medical advice.
Version 1. Content checked 19 October 2026. Next review October 2027.