We designed a positive expiratory pressure (PEP) generator for prevention of occurrence of atelectasis and promotion of oxygenation during anesthesia. This device superimposes end-expiratory pressure on spontaneous breathing by using a glass bottle including water. In this report, we planned to assure that PEP increases the functional residual capacity, and contributes to prevention of atelectasis and promotion of oxygenation. Patients were 12 people with disabilities who required outpatient anesthesia using a laryngeal mask airway for dental treatment. The patients were divided into two groups, one was a zero expiratory pressure (ZEP) group and the other was a PEP group, in which airway pressure at end-expiratory periods was raised by 5cmH₂O using the PEP generator. Measurements of the valuables of respiratory mechanics were performed with the NICO monitor 7300. In both groups, measurements were performed two times with a 20 minute interval with or without 5cmH₂O PEP, which included arterial blood gas analyses, regular monitors in respiratory and circulation, and valuables in respiratory mechanics, and the results were as follows: 1) inspiratory-expiratory ratio (ZEP, 1.5±0.2; PEP, 2.1±0.4) and work on breathing (ZEP, 416±179; PEP, 929±290 mL・mH₂O) increased in PEP group significantly. 2) in PEP group, airway dead space (1st, 118±14.3; 2nd, 125±13.6 mL) and ratio of dead space to tidal volume (lst, 0.59±0.09; 2nd, 0.63±0.08) increased. 3) in PEP group, oxygen pressure in arterial blood decreased (1st, 250±29; 2nd, 230±23 mmHg). 4) in PEP group, increasing tendency in blood pressure was restrained. Application of PEP is expected to be effective in raising functional residual capacity and prevention of atelectasis. However, PEP causes an increase in breathing effort, which requires vigorous monitoring.

View full abstract