Light and electron microscopic analyses for ischaemia-reperfusion lung injury in an ovine cardiopulmonary bypass model

An experiment to study the role of contact-activation leukocyte sequestration in the formation of ischaemia-reperfusion injury (I-R injury) was carried out. The study was conducted using light and electron microscopic analyses in an ovine cardiopulmonary bypass (CPB) model using a membrane oxygenator. Five adult sheep were used in the study. The CPB circuitry consisted of a roller pump and a membrane oxygenator. During CPB, flow rates ranged from 50 to 60 ml/kg/min with mild hypothermia. The CPB time was fixed at 120 min. Ten minutes after the start of CPB, total CPB was established. Thereafter, total CPB was performed for 100 min, followed by another 10 min of partial CPB. Lung biopsy specimens for light and electron microscopy were obtained from the upper lobe of the right lung before CPB, 109 min after the start of CPB (just before reperfusion) and 30 min after weaning (after reperfusion). A portion of the lung biopsy specimen was taken for a water content measurement at the same time intervals. For measuring the left and right atrial leukocyte counts, blood samples were taken before thoracotomy, 5 and 109 min after the start of CPB, and 30 and 120 min after weaning. C3a was measured before thoracotomy, 109 min after the start of CPB, and 30 and 120 min after weaning. Plasma malondialdehyde (MDA) was checked before thoracotomy, 109 min after the start of CPB and 30 min after weaning. On both light and electron microscopic examination, mild to moderate acute lung change was observed after ischaemia-reperfusion. Interstitial oedema, leakage of erythrocytes into the alveolar space and endothelial cell swelling were the main findings. However, few neutrophils were seen. Water content of the lung showed a slight increase after the start of CPB, but there was no statistical significance. Neither significant differences in the transpulmonary gradients of leukocytes nor a significant complement activation, expressed by C3a levels, was observed. The MDA level did not display a significant change related to lung reperfusion despite an increase in MDA after the start of CPB. These findings indicate that I-R injury during CPB may not be from complement-activation leukocyte sequestration, but from another source of oxygen free radicals related to CPB.