Protective effect of lung inflation in reperfusion-induced lung microvascular injury

We used the isolated-perfused rat lung model to study the influence of pulm onary ventilation and surfactant instillation on the development of postrep erfusion lung microvascular injury. We hypothesized that the state of lung inflation during ischemia contributes to the development of the injury duri ng reperfusion. Pulmonary microvascular injury was assessed by continuously monitoring the wet lung weight and measuring the vessel wall I-125-labeled albumin (I-125-albumin) permeability-surface area product CPS). Sprague-Da wley rats (n = 24) were divided into one control group and five experimenta l groups (n = 4 rats per group). Control lungs were continuously ventilated with 20% O-2 and perfused for 120 min. All lung preparations were ventilat ed with 20% O-2 before the ischemia period and during the reperfusion perio d. The various groups differed only in the ventilatory gas mixtures used du ring the flow cessation: group I, ventilated with 20% O-2; group II, ventil ated with 100% N-2; group III, lungs remained collapsed and unventilated; g roup n: same as group III but pretreated with surfactant (4 ml/kg) instille d into the airway; and group V, same as group III but saline (4 ml/kg) was instilled into the airway. Control lungs remained isogravimetric with basel ine I-125-albumin PS value of 4.9 +/- 0.3 x 10(-3) ml . min(-1) . g wet lun g wt(-1). Lung wet weight in group III increased by 1.45 +/- 0.35 g and alb umin PS increased to 17.7 +/- 2.3 x 10(-3), indicating development of vascu lar injury during the reperfusion period. Lung wet weight and albumin PS di d not increase in groups I and II, indicating that ventilation by either 20 % O-2 or 100% N-2 prevented vascular injury. Pretreatment of collapsed lung s with surfactant before cessation of flow also prevented the vascular inju ry, whereas pretreatment with saline vehicle had no effect. These results i ndicate that the state of lung inflation during ischemia (irrespective of g as mixture used) and supplementation of surfactant prevent reperfusion-indu ced lung microvascular injury.