Unquestionably the single most important function of the lung is to govern the exchange of respiratory gases, oxygen, and carbon dioxide between the ambient environment and arterial blood. Although gas exchange usually occurs at the microscopic level along the alveolar–pulmonary capillary membrane, overall gas transport is the result of complex interactions of diffusion and convection occurring in the airways. Gas flow patterns and gas mixing in the airways are highly dependent on local airway geometry, mechanical properties such as wall stiffness and parenchymal elasticity, and the underlying pattern of ventilation. Illness, disease, or injury involving the upper airway, lung, chest, abdomen, diaphragm, or neurologic system may alter these factors so that some form of respiratory support is required.

The mainstay of clinical care for patients requiring ventilatory support is endotracheal intubation (oral, nasal or by tracheostomy) and institution of some form of mechanical ventilation by the use of intermittent positive pressure. Generally, intubation assures gas exchange and provides a portal for airway care, but it is not without side effects or risks to the patient. Endotracheal intubation limits the patient's ability to talk, swallow, and cough effectively. There can be tracheal mucosal irritation or injury leading to tracheomalacia or tracheal stenosis. Positive pressure ventilation may cause hemodynamic embarrassment or lead to lung injury by volutrauma. For most individuals, such as those patients undergoing a general anesthetic, a brief period of endotracheal intubation and mechanical ventilation remains safe and is generally performed without the development of any significant clinical sequelae.

Few methods have been developed to increase alveolar ventilation that do not require the placement of an artificial endotracheal airway. One method to improve ventilation without endotracheal intubation involves the application of subatmospheric intermittent external pressure to the chest wall or whole body using a chest–abdomen cuirass or an iron lung. Patients also may be placed in a rocking bed, which uses gravity to induce gas flow in the airways by intermittently changing the transdiaphragmatic pressure. These techniques historically have been used for the care of patients with normal lungs but a chronic need for ventilatory support because of neurologic or neuromuscular failure, such as occurs after polio or with myasthenia gravis or spinal cord injury.

One additional technique that can be used partially to support gas exchange is transtracheal oxygen therapy or tracheal gas insufflation (TGI). Low flow (in the range of 2 to 10 L/min) oxygen insufflation is delivered directly into the trachea through a narrow catheter. Typically, the catheter rests in the airway with its tip within the trachea, 1 cm or 2 cm proximal to the carina. The method of placement of the catheter, the position of the catheter tip, the orientation of the direction of gas flow, and the synchronization of flow with the ventilatory cycle may depend on the clinical scenario for which tracheal gas insufflation has been chosen. The details for different clinical applications are discussed elsewhere in this article. Broadly, transtracheal insufflation has three main uses: (1) it can be used for chronic oxygen therapy; (2) it can be added to mechanical ventilation as an adjunct measure to enhance CO₂ exchange; and (3) it can be instituted as an emergency intervention in the patient who can be neither intubated nor ventilated.