Positive pressure ventilation using a semiclosed system: a reassessment.

The use of a semidosed system (the Magill attachment) for positive pressure breathing was investigated. Various patterns of ventilation were used and their effects assessed by serial measurement of the arterial carbon dioxide. It was found that this could be kept within limits comparable to those found during normal sleep using a flow of fresh gases as low as 5 l./min. This result was most easily achieved if the tidal volume were large (more than 1 1. for the average adult). Other incidental findings are discussed and it is conduded that semidosed systems provide a safe and economical method for maintaining ventilation when special equipment is not available.