Assessment of ventilation inhomogeneity and gas exchange with volume controlled ventilation and pressure regulated volume controlled ventilation on pigs with surfactant depleted lungs.

Abstract

In adult respiratory distress syndrome (ARDS), whilst a great fraction of the lung is affected by the disease, some parts, still function normally creating a non-homogeneous distribution of lung pathology. This unequal distribution results in increased differences in time constants of different lung units (1–3). Conventional volume controlled ventilation (VCV) with positive end expiratory pressure (PEEP) with a standard inspiration/expiration (I/E) ratio of 1:2 may be inadequate to ventilate these affected lung units equally, as they tend to open later and close earlier compared to healthy alveoli due to high retractive forces. Prolonging the inspiration time of the respiratory cycle is suggested to overcome these time-constant inequalities within the ARDS lungs, ventilate all alveoli despite different retraction forces in the airways and improve the gas exchange (4,5). Furthermore, the application of pressure controlled inverse ratio ventilation (PC-IRV) is shown to provide better gas exchange with significantly lower peak inspiratory pressures (PIP) (4).