The effects of increasing levels of PEEP on oxygenation and lung perfusion in pigs with unilateral lung injury

Introduction

The effects of PEEP may differ in healthy and diseased parts of the lung. Accordingly, we studied the effects of increasing PEEP-levels on ventilation, lung perfusion, oxygenation, and hemodynamics in an animal model with unilateral lung injury.

Methods

In 8 pigs (25-36 kg) unilateral lung injury was induced by bronchoscopic application of HCl 0.1 m into the left lung (total: 20-35 ml). Twenty-four hours after injury the pigs were anesthetized, endotracheally intubated with a double-lumen tube and mechanically ventilated. Catheters for hemodynamic monitoring were inserted. Volume controlled ventilation (12 ml/kg body weight, FiO₂ 1.0) with ZEEP, PEEP 5 cmH₂O and PEEP 10 cmH₂O was performed in random order in each animal. Measurements after 45 min of hemodynamic stability in each phase included differential lung perfusion using colored microspheres and differential lung ventilation using the double lumen tube. In 6 pigs (control group) the study was performed without preceding lung injury. ANOVA was used for statistical analysis.

Results and conclusion

After lung injury and in comparison to the control group, left side lung compliance and left side tidal volumes were significantly lower (data not shown). With increasing PEEP, MAP, CO and shunt fraction decreased in both groups.

Compared to the control group, perfusion of the left lung decreased after lung damage, but was not changed by PEEP. Our study shows that PEEP depresses the circulation but does not alter the perfusion of the injured lung during unilateral lung injury.

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