IPPB uses a mechanical respirator to deliver a controlled pressure of a gas to assist in ventilation or expansion of the lungs, thereby providing an increased tidal volume for patients with a variety of pulmonary conditions. IPPB machines are also used for the delivery of aerosol medications. The early widespread application of IPPB has dramatically diminished in response to published reports of more recent clinical trials that either question its utility or document its futility in the prophylaxis or treatment of the numerous conditions for which it was commonly prescribed. The effects of IPPB are short-lived, lasting approximately 1 hour, and the long-term consequences have not been adequately evaluated. In no study has IPPB been shown to have unequivocal clinical effectiveness, in terms of morbidity, mortality, or lung function, when used either alone or in combination with other modalities. In general, IPPB is not thought to offer any advantage over simpler therapies in the treatment of COPD or asthma or in preventing or treating postoperative atelectasis. However, IPPB may be useful in the following circumstances: 1) in patients at risk of respiratory failure because of decreased respiratory function secondary to kyphoscoliosis or neuromuscular disorders; 2) in patients with acute severe bronchospasm or exacerbated COPD, who fail to respond to other standard therapy; and 3) in the management of atelectasis that has not improved with simpler therapy (e.g., IS, postural drainage, aerosol therapy).