A Functional and Morphologic Analysis of Pressure-Controlled Inverse Ratio Ventilation in Oleic Acid-Induced Lung Injury: Gas Exchange

Inverse ratio ventilation tentatively improves recruitment in lung regions with longer time constants (consisting of alveolar units with higher resistance or higher compliance). As a result of smaller airway dimensions, lung units with longer time constants may be more abundant in dependent lung regions. Computer simulations comparing different flow patterns have suggested a more even distribution of ventilation with decelerating flow. However, regional aeration in three vertical zones of the lung were compared and found to be equal between VCV PEEP and PCIRV. There was a tendency toward better aeration with PCIRV in all three zones during dynamic conditions, but the difference was not statistically different.
When comparing mean density between ventilatory modes in static end-inspiratory or end-expiratory conditions (ie, using the hold function of the ventilator), the values obtained may be influenced by gas and pressure equalization during the ventilatory pause. For this reason, in the present study, a dynamic CT scan for a time period equal to the length of the ventilatory cycle (4 s) was performed. No significant difference in lung density between the two ventilatory modes were found during dynamic conditions. Ventolin inhalers website However, it should be stressed that the study period covered 45 to 60 minutes, and thus allows no analysis of possible late effects of a particular ventilator setting.
In the present study, the decrease in FRC caused by oleic acid-induced lung injury was restored by application of PEEP. This volume restoration was accompanied by reduced venous admixture and an increase in PaC>2. PCIRV did not further increase FRC or improve oxygenation despite a higher mean airway pressure. A possible but unproved explanation to the increase in arterial oxygenation with PCIRV that has been reported in some previous studies may be an unrecognized higher level of PEEP.
Cardiac output and mean arterial blood pressure decreased during PCIRV. Mean pulmonary artery pressure and pulmonary vascular resistance were unchanged suggesting that impaired venous return caused the CO reduction.

This entry was posted in Respiratory Failure and tagged , , , .