Most modern mechanical ventilators are positive pressure ventilation. An iron lung is an example of negative pressure ventilation. A ventilator is a device used to support, assist or control respiration (inclusive of the weaning period) through the application of positive pressure to the airway when delivered via an artificial airway, specifically oral/nasal endotracheal or tracheostomy tube.
Note: Ventilation and lung expansion devices that deliver positive pressure to the airway (for example: CPAP, Bipap, bi-level, IPPB and PEEP) via non-invasive means (for example: nasal prongs, nasal mask, full face mask, total mask, etc.) are not considered ventilators unless positive pressure is delivered via an artificial airway (oral/nasal endotracheal or tracheostomy tube).
Pressure-cycled ventilators: Gas is allowed to flow into the lungs until a present airway pressure limit is reached, at which time a valve opens allowing exhalation to ensue. The volume delivered by the ventilator varies with changes in airway resistance, lung compliance, and integrity of the ventilatory circuit.
Volume-cycled ventilators: Gas flows to the patient until a preset volume is delivered to the ventilator circuit, even if this entails a very high airway pressure.
It is important for clinical staff working with individuals on mechanical ventilation to understand the different modes. Individuals require mechanical ventilation for different reasons. It is used for individuals with respiratory failure who are unable to breathe on their own. Different modes in mechanical ventilation help to determine how far along a patient is in the weaning process and the patient’s current respiratory status.