Volume-controlled inverse ratio ventilation in oleic acid induced lung injury. Effects on gas exchange, hemodynamics, and computed tomographic lung density.

STUDY OBJECTIVE: To compare volume-controlled inverse ratio ventilation (VCIRV) with volume-controlled ventilation with conventional inspiratory to expiratory (I:E) ratio (VCV PEEP) at equal levels of end-expiratory pressure.

DESIGN: Animal study using an oleic acid lung injury model with random application of VCV PEEP and VCIRV.

SETTING: Experimental investigation at the Department of Clinical Physiology at Uppsala University.

ANIMALS: Seven pigs.

INTERVENTIONS: VCV PEEP, VCIRV at an end-expiratory pressure level of 10 cm H2O.

MEASUREMENTS AND RESULTS: Lung mechanics, hemodynamics, gas exchange, and functional residual capacity. Recruitment of lung tissue, regional lung density, and distribution of inspired gas by computed tomography. Mean and peak airway pressures were 22 +/- 4 and 41 +/- 8 cm H2O with VCIRV and 18 +/- 2 and 45 +/- 7 cm H2O with VCV PEEP. Cardiac output and arterial oxygen tension were equal with VCV PEEP and VCIRV as were static compliance, physiologic dead space, and functional residual capacity. End-expiratory, end-inspiratory, and CT densities during a full ventilatory cycle were not statistically different and the amounts of nonaerated and poorly aerated lung areas were of equal size with VCV PEEP and VCIRV.

CONCLUSIONS: VCIRV was comparable to VCV PEEP at similar PEEP levels in alveolar recruitment, aeration of the lung tissues, and in oxygenating the blood. Since cardiac output also remained unchanged, oxygen delivery to peripheral tissues did not differ significantly between the two modes. Neither method has thus proved superior to the other one.