ABSTRACT
Ventilation is the movement of gas in and out of the lungs. The efficacy of ventilation is measured by the clearance of carbon dioxide from the body via the lungs using arterial blood gases or capnography. Positive-pressure ventilation can hold open alveoli and ensure oxygenation. It also allows the administration of higher concentrations of oxygen. Volume-controlled ventilation delivers a preset volume at a constant flow rate. Pressure-controlled ventilation can improve gas exchange, especially in patients with abnormal lungs because the alveoli are held open for longer. Positive end-expiratory pressure is, as the name suggests, a positive pressure maintained at the end of expiration. It prevents alveolar collapse and re-expansion, which can be damaging. During transfer, external power and piped oxygen may not be available, and portable ventilators should therefore offer efficient use of power and oxygen to avoid consumption of supplies.
