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

A region of interest (ROI) was constructed by manually delineating the right lung from the chest wall anteriorly, laterally, and posteriorly and from the mediastinal organs medially. Mean density (Hounsfield units, HU) and area (cm2) within the ROI were measured. Poorly aerated and nonaerated lung regions were defined and quantified as areas occupied by voxels between —200 to —100 HU (poorly aerated) and —100 to +100 HU (nonaerated), respectively.
For analysis of regional density, the right lung was divided into three vertical zones of equal height. Within each zone, a ROI was constructed and analyzed for mean density.
A baseline recording of data was performed prior to induction of lung injury using volume-controlled zero PEEP (VCV ZEEP) ventilation. Lung injury was then produced by oleic acid infusion. Two hours later, when arterial blood gases and CO had remained stable for at least 30 min, the recordings were repeated using the same ventilator setting. The ventilator was then switched in random order to either volume-controlled ventilation using an I:E ratio of 1:2 (VCV PEEP) or to pressure-controlled ventilation with an I:E ratio of 4:1 (PCIRV). A stabilization period of 45 min was allowed to pass before subsequent data registration and blood sampling in detail purchase zyrtec. The pigs that had been receiving VCV PEEP were then switched to PCIRV, and vice versa, and recordings were repeated after 45 min. I:E ratios of 1:2 and 4:1 were obtained by selecting inspiratory times of 33 percent and 80 percent of the ventilatory cycle. An end-inspiratory pause was not used. End-expiratory pressure levels were measured during an end-expiratory hold of 5 s. During PCIRV, inspiratory pressure level was adjusted to maintain normoventilation. Externally applied PEEP was not used with PCIRV. During VCV PEEP, a set PEEP of 10 cm H20 was used. Ventilatory frequency was kept constant at 15 breaths per minute. In seven of the animals, comparisons could be made between VCV ZEEP and VCV PEEP and between VCV PEEP and PCIRV at equal levels of end-expiratory pressure (± 2 cm H2O), and at similar minute ventilation (±0.5 L/min) and results from these are reported in this article.
Statistics were performed using Wilcoxon’s matched pairs test when comparing baseline VCV ZEEP values and VCV ZEEP after oleic acid injection. VCV ZEEP, VCV PEEP, and PCIRV after induction of lung injury were compared by repeated measures analysis of variance (ANOVA) with Fisher’s LSD test for post-hoc comparisons. Statistical significance was considered as p<0.05.

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