The modes of mechanical ventilation are important for clinicians who work with these patients to understand. An iron lung is an example of negative pressure ventilation. Most modern mechanical ventilators are positive 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. 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 tube or tracheostomy tube).
In mechanical ventilation there are two primary control variables; volume control and pressure control.
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.
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. The indications for mechanical ventilation include airway protection, treatment of hypoxemic respiratory failure (low blood oxygen), treatment of hypercapnic respiratory failure (elevated carbon dioxide in the blood), or treatment of a combined hypoxic and hypercapnic respiratory failure. On some occasions, patients are also intubated and placed on mechanical ventilation for procedures. H
Regardless of the mode of mechanical ventilation, the guiding principals will be to provide lung protection (prevent overdistension), provide adequate gas exchange, unload the respiratory muscles, improving patient comfort and synchrony.