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Mechanical ventilation is a process where a ventilator replaces or supports the patient’s own breathing.
The earliest ventilators mimicked the natural activity of the respiratory muscles by creating a negative pressure in the chest and thus causing air to flow into the lungs (inhalation); these “iron lungs” are now very rare. Modern ventilators use invasive or noninvasive interfaces to create positive pressure to force air into the lungs.
Invasive mechanical ventilation (IMV) requires the use of an artificial airway such as an endotracheal tube, supraglottic airway (eg, laryngeal mask), or tracheostomy. This allows for protection of the airway in unconscious patients, facilitates pulmonary toilet via suction or bronchoscopy, and allows for the application of advanced ventilation techniques.
Noninvasive ventilation (NIV) uses other externally applied interfaces such as a facemask (naso-oral or full facemasks), nasal pillows, or helmets, and enables positive pressure ventilation (full support or assisted ventilation) and oxygenation in conscious or semiconscious patients. In contrast to IMV, the interface in NIV can impede effective secretion management.
Two other common respiratory supports are used in the acute setting but are not “mechanical ventilation” in the technical sense, as they do not directly facilitate the patient’s ventilatory efforts. Continuous positive airway pressure (CPAP) uses similar interfaces as NIV but provides single continuous airway pressure, which can prevent upper airway collapse, and increases mean airway pressures, thereby increasing the recruitable lung area for gas exchange. Nasal high-flow therapy (NHFT) provides noninvasive respiratory support by delivering high flows of warmed humidified oxygen or air mixtures (up to 60 L/min). This allows the delivery of up to 100% oxygen, facilitates secretion management, and provides nominal ventilatory support by generating a small amount of positive pressure and washing out dead space from the upper airways. NHFT is often used alongside IMV or NIV.