Possible Risk of Prolonged Mechanical Ventilation in Pressure-support Mode

Overview

The authors describe the possible risk of inpulsion effect arising during conventional ventilation if TI:TE ratio is less than 0.5 (Ti% < 33%).They analyze changes of expiratory time constant, pressure support, TI:TE ratio, ventilation frequency, FiO2, SpO2, static compliance and respiratoryresistance which were monitored during ventilation in pressure support mode (pressure support PS). The authors have found that during prolongeddecrease of Ti < 33% (28 ± 3) there could be observed a decrease of static compliance and increase of respiratory tract resistance, evolving graduallyduring several tens of hours.To maintain the gas exchange (MV) in PS mode there is a need to increase pressure support Pps. Based upon above mentioned findings, there waspostulated a theory of persistent inpulsion effect of mechanical ventilation of the lungs that worsens the drainage function of the lungs especially indistal respiratory airways. To eliminate this inpulsion effect, high-frequency jet ventilation (HFJV) was used intermittently for its expulsion effect.After application of expulsion effect using HFJV, improvement of lung mechanics could be documented. At the end the authors stress the possiblerisk of worsening lung mechanics during ventilation in PS mode (ASB) under the condition that Ti% < 33% is applied for prolonged time.

Key words:
pressure support – inpulsion – expulsion – static compliance – respiratory tract resistance