Releasing high positive end-expiratory pressure to a low level generates a pronounced increase in particle flow from the airways

OBJECTIVES: Detecting particle flow from the airways by a non-invasive analyzing technique might serve as an additional tool to monitor mechanical ventilation. In the present study, we used a customized particles in exhaled air (PExA) technique, which is an optical particle counter for the monitoring of particle flow in exhaled air. We studied particle flow while increasing and releasing positive end-expiratory pressure (PEEP). The aim of this study was to investigate the impact of different levels of PEEP on particle flow in exhaled air in an experimental setting. We hypothesized that gradually increasing PEEP will reduce the particle flow from the airways and releasing PEEP from a high level to a low level will result in increased particle flow. METHODS: Five fully anesthetized domestic pigs received a gradual increase of PEEP from 5 cmH(2)O to a maximum of 25 cmH(2)O during volume-controlled ventilation. The particle count along with vital parameters and ventilator settings were collected continuously and measurements were taken after every increase in PEEP. The particle sizes measured were between 0.41 µm and 4.55 µm. RESULTS: A significant increase in particle count was seen going from all levels of PEEP to release of PEEP. At a PEEP level of 15 cmH(2)O, there was a median particle count of 282 (154–710) compared to release of PEEP to a level of 5 cmH(2)O which led to a median particle count of 3754 (2437–10,606) (p < 0.009). A decrease in blood pressure was seen from baseline to all levels of PEEP and significantly so at a PEEP level of 20 cmH(2)O. CONCLUSIONS: In the present study, a significant increase in particle count was seen on releasing PEEP back to baseline compared to all levels of PEEP, while no changes were seen when gradually increasing PEEP. These findings further explore the significance of changes in particle flow and their part in pathophysiological processes within the lung.