Hemorrhagic shock prevents lung microvascular permeability and hypoxemia associated with complement activation in the awake sheep.

: The effect of hemorrhagic hypotension on pulmonary dysfunction induced by complement activation was studied in 43 awake sheep, divided into six groups: Group I (n = 6), pulmonary vascular pressure was increased by inflation of a left atrial balloon; group II (n = 9), the complement system was activated by infusion of zymosan activated plasma (ZAP); group III (n = 5), hemorrhagic shock of 50 torr was induced for 3 hr; group IV (n = 10), hemorrhagic shock was induced as in group III, and after 2 hr of shock, ZAP was infused; group V (n = 8), 5 mg/kg of indomethacin was administered before ZAP infusion; group VI (n = 5), pretreatment with indomethacin as in group V, hemorrhagic shock and ZAP as in group IV. ZAP infusion in group II led to a fall in WBC to 2,600/ml (P less than 0.001), and a rise in mean pulmonary artery pressure to 41.1 torr (P less than 0.001) and in pulmonary shunting (QS/QT) to 29.4% (P less than 0.001). Arterial oxygen tension (PaO2) fell to 62.0 torr (P less than 0.001), pulmonary lymph flow (QL) rose to 14.0 ml/hr (P less than 0.01), and lymph protein clearance (L/P.QL) to 8.9 ml/hr (P less than 0.01). Plasma thromboxane B2 (TxB2) increased to 2.43 ng/ml (P less than 0.025) and pulmonary lymph TxB2 to 3.02 ng/ml (P less than 0.005). Hemorrhagic shock was followed by a rise in PaO2 to 97.5 torr (P less than 0.01), a fall in QS/QT to 7.9% (P less than 0.005), QL to 5.0 ml/hr (P less than 0.05), and L/P QL to 2.9 ml/hr (P less than 0.05). During hemorrhage, plasma TxB2 rose to 2.18 ng/ml (P less than 0.005) and lymph TxB2 to 2.32 ng/ml (P less than 0.001). Infusion of ZAP during hemorrhagic shock was followed by a fall in WBC to 2,300/microliter (P less than 0.001); but QS/QT, PaO2, QL, and L/P.QL remained unchanged. After indomethacin and ZAP, WBC fell to 3,210/microliter (P less than 0.001), Ppa rose to 27.0 torr (P less than 0.05), QL rose to 8.3 ml/hr (P less than 0.05), and L/P.QL rose to 5.2 ml/hr (P less than 0.05). PaO2 fell to 75.0 torr (P less than 0.05) and QS/QT increased to 17.1% (P less than 0.005). The protective effect of hemorrhagic shock on ZAP-induced pulmonary dysfunction was not reversed by indomethacin. It is concluded that hemorrhagic shock prevents hypoxemia and increased pulmonary permeability induced by activation of the complement system by ZAP.