Why this matters: Mechanical ventilation supports patients who cannot maintain oxygenation, ventilation or airway protection. Emergency staff must understand why a patient is ventilated, what each setting does, how to recognise deterioration and how to safely move a ventilated patient between scene, ambulance, emergency department and ICU.
Scope and safety: Ventilator selection and settings are prescribed by trained clinicians and adjusted to the patient, disease and blood gases. Never alter a ventilator blindly. If a ventilated patient deteriorates, immediately assess the patient, manually ventilate with a self-inflating bag and oxygen if necessary, then troubleshoot the machine and circuit.
Learning outcomes
- Explain the difference between oxygenation failure, ventilation failure and airway-protection failure.
- Describe common invasive and non-invasive ventilation modes and the meaning of key settings.
- Recognise high-pressure, low-pressure, apnoea, oxygen-supply and power alarms.
- Apply lung-protective principles, patient–ventilator synchrony, humidification and infection prevention.
- Use clinical assessment, SpO2, ETCO2 and ABG trends to judge response and escalation.
- Prepare safe transport, handover, weaning readiness and emergency disconnection plans.
1. Why patients need ventilatory support
| Indication | Examples | What ventilation must achieve |
|---|---|---|
| Oxygenation failure | Pneumonia, pulmonary oedema, ARDS, severe asthma/COPD, drowning. | Improve alveolar oxygen transfer while avoiding oxygen toxicity and pressure injury. |
| Ventilation failure | Opioid/sedative overdose, neuromuscular weakness, fatigue, severe hypercapnia. | Remove CO2 and correct respiratory acidosis without excessive minute ventilation. |
| Airway protection | Coma, seizures, severe facial trauma, shock or repeated vomiting. | Maintain a secure airway and prevent aspiration. |
| Work-of-breathing failure | Exhaustion, severe obstructive disease, chest wall restriction. | Reduce respiratory muscle load and allow recovery. |
| Raised intracranial pressure | Severe head injury, intracranial haemorrhage. | Prevent hypoxia and harmful hypo/hypercapnia while maintaining cerebral perfusion. |
2. Key terminology
| Term | Meaning | Clinical effect |
|---|---|---|
| Tidal volume (VT) | Volume delivered with each breath. | Too high increases volutrauma; too low may cause inadequate ventilation if not monitored. |
| Respiratory rate | Mandatory or total breaths per minute. | Changes minute ventilation and CO2 clearance. |
| Minute ventilation | VT × respiratory rate, adjusted by dead space. | Major determinant of PaCO2; excessive ventilation can cause alkalosis and lung injury. |
| FiO2 | Fraction of inspired oxygen. | Corrects hypoxaemia; titrate to target rather than leaving high indefinitely. |
| PEEP | Positive pressure remaining at end-expiration. | Recruits alveoli and improves oxygenation but may reduce venous return and blood pressure. |
| Pressure support | Inspiratory assist for spontaneous breaths. | Reduces work of breathing during NIV or weaning. |
| Inspiratory time/flow | How quickly and how long gas enters the lungs. | Changes synchrony, air trapping and peak pressures. |
| Peak/plateau pressure | Peak reflects resistance; plateau approximates alveolar pressure. | High values suggest obstruction, secretions, poor compliance or overdistension. |
3. Common ventilator modes
| Mode | What the ventilator controls | Typical use/limitations |
|---|---|---|
| Volume-controlled assist/control | Set VT and rate; pressure varies with compliance/resistance. | Reliable minute volume; monitor peak/plateau pressure and auto-PEEP. |
| Pressure-controlled assist/control | Set inspiratory pressure and time; delivered VT varies. | Limits pressure; monitor exhaled VT and minute ventilation for changes in compliance. |
| SIMV | Mandatory breaths synchronised with patient plus spontaneous breaths. | May be used during transition; can increase work if poorly synchronised. |
| Pressure support ventilation | Patient triggers every breath; ventilator adds pressure. | Weaning or spontaneous breathing; unsafe in apnoea without backup. |
| CPAP | Continuous positive pressure during spontaneous breathing. | Recruits alveoli; requires alert/cooperative patient with protected airway. |
| NIV BiPAP | Different inspiratory and expiratory pressures via mask. | Selected COPD/respiratory failure; avoid with vomiting, severe agitation or inability to protect airway. |
4. Setting priorities: oxygenation versus ventilation
- Oxygenation: adjust FiO2 and PEEP, treat alveolar collapse/fluid/infection and reassess SpO2/ABG.
- Ventilation: adjust rate, tidal volume and pressure support according to PaCO2/pH, obstructive disease and patient effort.
- Synchrony: optimise trigger sensitivity, flow, inspiratory time and sedation/analgesia so the patient and machine work together.
- Safety: limit excessive pressures, avoid over-oxygenation, monitor blood pressure and prevent ventilator-associated complications.
Lung-protective principle: Use the lowest effective tidal volume and airway pressure, allow adequate exhalation and accept a clinically appropriate CO2 level when necessary rather than causing volutrauma/barotrauma through aggressive ventilation.
5. Non-invasive ventilation (NIV)
| Potential benefit | Candidate features | Contraindications or failure signs |
|---|---|---|
| CPAP | Conscious patient with cardiogenic pulmonary oedema or hypoxaemia who can protect the airway. | Vomiting, shock, reduced consciousness, severe agitation, facial trauma or inability to cooperate. |
| BiPAP/NIV | Hypercapnic COPD exacerbation, increased work of breathing and cooperative patient. | Worsening acidosis, exhaustion, persistent hypoxia, copious secretions or haemodynamic instability. |
| Mask safety | Correct size, leak management, pressure relief and frequent skin checks. | Large leak, pressure sores, panic, aspiration or delayed intubation. |
NIV must be started where trained staff can monitor continuously and intubate if it fails. Explain the mask, sit the patient upright, allow them to hold it initially where possible and reassess work of breathing, mental state, gas exchange and haemodynamics within minutes—not hours.
6. Monitoring the ventilated patient
| Monitor | What it tells you | Limitations |
|---|---|---|
| Clinical examination | Chest rise, breath sounds, synchrony, secretions, distress, skin colour and perfusion. | Can miss silent deterioration; repeat after movement and interventions. |
| SpO2 | Oxygenation trend. | Delayed/false readings with poor perfusion, motion, nail products or carbon monoxide. |
| ETCO2 waveform | Ventilation, tube confirmation, perfusion and sudden changes. | Interpret with circulation, pulmonary disease and equipment status. |
| ABG/VBG | pH, PaCO2, PaO2, bicarbonate, lactate and metabolic status. | Snapshot only; correlate with trends and the clinical picture. |
| Pressures/volumes | Compliance, resistance, air trapping, leaks and delivered VT. | Machine values can mislead when tubing, filters or patient effort change. |
| Haemodynamics | PEEP/positive pressure effects on venous return and shock. | Blood pressure must be assessed with perfusion and urine output. |
7. Ventilator alarms: a systematic response
DOPE for sudden deterioration: Displacement of tube, Obstruction of tube/circuit, Pneumothorax or pulmonary problem, Equipment failure. Assess the patient first; manually ventilate if in doubt.
| Alarm | Common causes | Immediate actions |
|---|---|---|
| High pressure | Biting, kink, secretions, bronchospasm, reduced compliance, pneumothorax, water in tubing. | Assess patient, disconnect and BVM with oxygen if unstable, inspect tubing, suction, check chest and escalate. |
| Low pressure/low volume | Disconnection, cuff leak, tube displacement, circuit leak or inadequate effort. | Check connections/cuff/tube depth, ventilate manually and confirm capnography. |
| Apnoea | No patient trigger, sedation/neuromuscular weakness, disconnection or sensor problem. | Assess consciousness/breathing, ensure backup ventilation and call the airway team. |
| High minute volume | Pain, anxiety, fever, acidosis, hypoxia, sepsis or ventilator dyssynchrony. | Assess cause and synchrony; do not simply suppress respiratory drive without evaluation. |
| Low oxygen supply | Empty cylinder, pipeline disconnection, concentrator failure. | Switch to backup oxygen, check pressure and inform the receiving team. |
| Power/battery | Unplugged device, depleted battery, electrical failure. | Connect power and manually ventilate during transfer or malfunction. |
8. Common complications of mechanical ventilation
- Ventilator-associated pneumonia: hand hygiene, head elevation where appropriate, oral care, suctioning, circuit care and early liberation when safe.
- Barotrauma/volutrauma: pneumothorax, subcutaneous emphysema and high pressures; investigate sudden desaturation or hypotension.
- Hypotension: positive pressure reduces venous return; consider hypovolaemia, excessive PEEP, tension pneumothorax or myocardial dysfunction.
- Auto-PEEP/dynamic hyperinflation: incomplete exhalation in asthma/COPD causes rising pressures, hypotension and worsening distress; allow longer expiratory time and seek expert review.
- Oxygen toxicity/absorption atelectasis: titrate FiO2 to the target and treat underlying lung disease.
- Pressure injuries: inspect lips, nares, ears, cheeks and skin under masks/tapes every shift and after movement.
- Delirium, weakness and deconditioning: orientate, mobilise early when safe, manage pain, avoid unnecessary deep sedation and involve the ICU team.
9. Patient–ventilator synchrony
Dyssynchrony occurs when the ventilator’s timing or flow does not meet the patient’s demand. Clues include grimacing, accessory muscle use, double triggering, missed breaths, high peak pressure, tachycardia or agitation. Check pain, hypoxia, acidosis, fever, secretions, tube position, trigger sensitivity and mode before increasing sedation. Paralysis masks distress and should be used only for a clear indication with adequate analgesia/sedation.
10. Sedation, analgesia and neuromuscular blockade
| Principle | Why it matters |
|---|---|
| Analgesia first | Pain from tube, suction, fractures or procedures can look like agitation and increase oxygen demand. |
| Lightest effective sedation | Allows neurological assessment, synchrony and earlier weaning while reducing delirium and hypotension. |
| Daily review | Check indication, target sedation score, interruptions, delirium, pain and readiness to reduce support. |
| Paralysis is not sedation | A paralysed patient can be awake and terrified; provide analgesia/sedation and eye/skin care. |
| Safety monitoring | BP, ECG, respiratory status, temperature, glucose, urine output and medicine interactions. |
11. Transporting a ventilated patient
- Confirm indication, airway depth/fixation, cuff status, mode/settings, alarms, oxygen reserve and battery life.
- Bring a self-inflating bag with reservoir, backup oxygen, suction, spare tubes/SGA, capnography and emergency medicines.
- Secure all tubing to prevent traction; position the patient with head/neck supported and pressure points protected.
- Use continuous SpO2, ECG, BP and ETCO2 monitoring; assign a clinician to the airway, not just the monitor.
- Before moving, pre-oxygenate if indicated and explain the plan; after every transfer check chest rise, tube depth, capnography and pressures.
- Communicate ventilator settings, recent ABG, secretions, sedation, events and emergency contact pathway to the receiving team.
12. Emergency disconnection or ventilator failure
Patient first: If a ventilated patient becomes hypoxic, hypotensive or unresponsive, disconnect from the ventilator and manually ventilate with a self-inflating bag and oxygen while another team member troubleshoots. If manual ventilation is easy and the patient improves, suspect equipment/tube problems; if difficult, suspect obstruction, bronchospasm or pneumothorax.
- Check oxygen source, power, circuit, filters, water traps and alarm limits.
- Inspect tube depth, cuff, secretions and bite; suction only when indicated.
- Listen for unilateral breath sounds, assess tracheal position and look for tension pneumothorax.
- Call the airway/critical-care clinician early; do not silence alarms without finding the cause.
13. Weaning and liberation
Weaning begins when the cause of respiratory failure improves and the patient can maintain airway protection, adequate oxygenation and ventilation with reduced support. The ICU team considers mental state, cough, secretions, haemodynamics, gas exchange, respiratory muscle strength and a spontaneous breathing trial. Extubation requires a plan for reintubation and post-extubation support.
| Readiness feature | Questions |
|---|---|
| Cause improved | Has pneumonia, shock, overdose, trauma or surgery stabilised? |
| Oxygenation | Can target oxygenation be maintained on low/moderate FiO2 and PEEP? |
| Ventilation | Is pH/PaCO2 acceptable with manageable work of breathing? |
| Neurological state | Can the patient wake, follow commands, cough and protect the airway? |
| Haemodynamics | Is blood pressure stable without escalating vasopressor support? |
| Secretions | Can the patient clear secretions and maintain airway hygiene? |
14. Clinical scenarios
Scenario 1 — High-pressure alarm: A ventilated COPD patient suddenly alarms high pressure and becomes hypotensive. Assess the patient, disconnect and BVM with oxygen, check for kink/secretions/bronchospasm, allow exhalation and urgently exclude tension pneumothorax and auto-PEEP.
Scenario 2 — Low-volume alarm: After ambulance transfer, the low-volume alarm sounds and the waveform disappears. Manually ventilate, check connections and tube depth, assess cuff/circuit leak and confirm placement with capnography.
Scenario 3 — NIV failure: A patient on BiPAP is increasingly drowsy, vomiting and has falling SpO2. Remove the mask, suction/protect the airway, ventilate with BVM and call the advanced airway team; do not persist with NIV.
Scenario 4 — Sudden hypotension after PEEP increase: A septic patient becomes hypotensive after a pressure change. Reassess preload, right-heart function, pneumothorax, bleeding and sedation; involve the clinician rather than independently returning to arbitrary settings.
Scenario 5 — Transport disconnect: During movement, ETCO2 falls to zero. Stop, BVM with oxygen, check the tube/circuit, reconnect only after confirming function and reassess chest rise, SpO2 and waveform.
15. Ventilator handover checklist
- Indication for ventilation, diagnosis, airway type/size/depth, cuff status and last confirmation.
- Mode, FiO2, VT or pressure, rate, PEEP, pressure support, alarms and recent changes.
- Latest SpO2/ETCO2/ABG, respiratory examination, secretions and suction frequency.
- Analgesia, sedation, neuromuscular blockade, infusions, allergies and haemodynamic support.
- Events during transfer, alarm causes, circuit changes, complications and response.
- Plan for repeat gases, imaging, weaning, extubation or escalation.
16. Revision questions
- What is the difference between oxygenation failure and ventilation failure?
- Why can PEEP improve oxygenation but lower blood pressure?
- What does the DOPE mnemonic stand for?
- How do high-pressure and low-pressure alarms differ?
- When is NIV unsafe or failing?
- Why is paralysis not the same as sedation?
- What must be carried during transport of an intubated patient?
- What findings suggest auto-PEEP in asthma/COPD?
- What are the main components of weaning readiness?
- Why should an unstable ventilated patient be manually ventilated while troubleshooting?
17. Key take-home points
- Mechanical ventilation supports oxygenation, ventilation and airway protection; it does not treat the underlying cause by itself.
- Assess the patient before the machine, then use DOPE to troubleshoot sudden deterioration.
- Protect the lung with appropriate volumes, pressures, PEEP, oxygen targets and adequate exhalation.
- Monitor the full picture: chest movement, SpO2, ETCO2, ABG, pressures, haemodynamics and mental state.
- Every transport needs a backup BVM, oxygen, suction, monitoring and a clear airway plan.
Selected authoritative resources
For EMT practice: Know the machine, but always treat the patient. When the ventilator alarms, call for help, maintain manual oxygenation and find the cause before changing settings.