Medical ventilation
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Medical ventilation means supporting or replacing a patient’s breathing when they cannot maintain adequate oxygenation, carbon dioxide removal, or respiratory effort.
1. Types
- Oxygen therapy: nasal cannula, face mask, high-flow nasal oxygen. Adds oxygen but does not directly provide ventilatory breaths.
- Non-invasive ventilation (NIV): a tight face or nasal mask provides positive pressure.
- CPAP: one continuous pressure, mainly improves oxygenation by keeping alveoli open.
- BiPAP: higher inspiratory than expiratory pressure, helping both ventilation and oxygenation. Often used in selected COPD exacerbation or cardiogenic pulmonary edema cases.
- Invasive mechanical ventilation: a ventilator is connected via an endotracheal tube or tracheostomy. It is used when airway protection or full respiratory support is needed.
2. Why it is used
Common indications include:
- Severe hypoxemic respiratory failure
- Hypercapnic respiratory failure with acidosis or fatigue
- Apnea, respiratory arrest, or severe work of breathing
- Reduced consciousness with inability to protect the airway
- Need for airway control during critical illness or major surgery
The decision is clinical, not based on one arterial blood gas value alone.
3. Main ventilator controls
| Control | What it does |
|---|---|
| FiO₂ | Fraction of inspired oxygen, adjusted to correct hypoxemia while avoiding unnecessary oxygen excess |
| Tidal volume (VT) | Volume delivered per breath |
| Respiratory rate | Mandatory breaths per minute |
| PEEP | Pressure retained at end-expiration to prevent alveolar collapse and improve oxygenation |
| Inspiratory pressure / pressure support | Pressure used to deliver or assist inspiration |
| Inspiratory time and flow | Influence breath delivery and time available for exhalation |
Minute ventilation is roughly tidal volume × respiratory rate. Increasing it usually reduces PaCO₂, while reducing it raises PaCO₂, though dead space and patient-ventilator synchrony also matter.
4. Common modes
- Volume-controlled ventilation: a set tidal volume is delivered. Airway pressure varies with lung mechanics.
- Pressure-controlled ventilation: a set inspiratory pressure is delivered. Tidal volume varies with compliance and resistance.
- Assist-control: every triggered or mandatory breath receives full preset support.
- SIMV: fixed mandatory breaths plus possible spontaneous breaths.
- Pressure-support ventilation: patient initiates breaths; ventilator adds preset pressure. Common during weaning.
- CPAP: spontaneous breathing with continuous positive pressure.
5. Core principle: lung-protective ventilation
Ventilation can itself harm lungs through overdistension, repeated alveolar opening and closing, excess oxygen exposure, and high pressures. Thus clinicians often use smaller tidal volumes and accept some elevation in CO₂, called permissive hypercapnia, when safe, rather than force normal blood gases. Goldman-Cecil Medicine describes the goals as adequate gas exchange with minimal ventilator-related harm, including auto-PEEP, infection, oxygen toxicity, and ventilator-induced lung injury (Chapter 91).
A common educational starting framework for many intubated adults is a controlled mode, tidal volume around 6-8 mL/kg predicted body weight, an individualized respiratory rate, FiO₂ titrated down once oxygenation is acceptable, and PEEP individualized to the clinical problem. These are not universal prescriptions. ARDS, COPD/asthma, brain injury, pregnancy, metabolic acidosis, and shock need different strategies. The ventilator setup overview summarizes these controls and common initial ranges.
6. Disease-specific priorities
- ARDS: protective low tidal volume ventilation, appropriate PEEP, avoidance of excessive driving/plateau pressures.
- COPD or severe asthma: allow a long expiratory time to prevent air trapping and auto-PEEP. Correcting CO₂ immediately is less important than avoiding hyperinflation and hypotension.
- Cardiogenic pulmonary edema: CPAP or BiPAP may reduce work of breathing and improve oxygenation if the patient is alert and can protect their airway.
- Neuromuscular weakness: ventilation may be needed because of inadequate respiratory muscle force, even if lungs themselves are relatively clear.
7. Monitoring and complications
Monitor clinical appearance, pulse oximetry, end-tidal CO₂ when applicable, arterial blood gases, airway pressures, ventilator waveforms, chest imaging, and hemodynamics.
Potential complications:
- Barotrauma or pneumothorax
- Volutrauma and ventilator-induced lung injury
- Auto-PEEP and dynamic hyperinflation
- Hypotension from increased intrathoracic pressure
- Ventilator-associated pneumonia
- Delirium, sedation-related harm, muscle weakness, and diaphragm deconditioning
- Patient-ventilator dyssynchrony
8. Weaning and extubation
Support should be reduced once the underlying problem improves. Readiness usually involves adequate oxygenation on modest support, stable circulation, improving consciousness, manageable secretions, and a spontaneous breathing trial. Passing a trial does not automatically mean extubation is safe: airway protection and cough strength still matter.
NIV should only be used in appropriately selected, monitored patients. It is not a replacement for intubation in someone with worsening consciousness, absent airway reflexes, arrest, refractory hypoxemia, or NIV failure.
Recent evidence continues to focus on limiting the total mechanical energy delivered to the lungs, called “mechanical power,” as a possible contributor to ventilator-induced lung injury. This remains an evolving area rather than a standalone bedside target, as noted in a 2025 systematic review.
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