A functional and morphologic analysis of pressure-controlled inverse ratio ventilation in oleic acid-induced lung injury.

STUDY OBJECTIVE

To compare volume-controlled ventilation (VCV PEEP) with pressure-controlled inverse ratio ventilation (PCIRV) at equal levels of end-expiratory pressure.

DESIGN

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

SETTING

Experimental laboratory investigation at the Department of Clinical Physiology at Uppsala University.

ANIMALS

Twelve pigs.

INTERVENTIONS

VCV PEEP and PCIRV at an end-expiratory pressure level of 10 cm H2O.

MEASUREMENTS AND RESULTS

Lung mechanics, hemodynamics, and gas exchange. Recruitment of lung tissue, regional lung density, and distribution of inspired gas by computed tomography. Mean and peak airway pressures were 29 and 35 cm H2O with PCIRV and 17 and 45 cm H2O with VCV PEEP. Cardiac output and mean systemic blood pressure were lower with PCIRV (2.5 L/min and 82 mm Hg) than with VCV PEEP (3.1 L/min and 97 mm Hg). Physiologic dead space was 24 percent with VCV PEEP and 20 percent with PCIRV. Static compliance, arterial oxygen tension, and functional residual capacity were equal between the two ventilatory modes. End-expiratory, end-inspiratory, and dynamic computed tomographic densities were equal between VCV PEEP and PCIRV. Nonaerated and poorly aerated lung areas were of equal size with VCV PEEP and PCIRV.

CONCLUSIONS

PCIRV was no better than VCV with similar PEEP levels in alveolar recruitment and aeration of the lung tissues or in oxygenating the blood. Cardiac output was lower with PCIRV than with VCV, causing lower oxygen delivery to peripheral tissues. PCIRV does allow for a reduction in minute ventilation and for lowering peak airway pressure.