EFFECTS OF RAPID COLLOID VOLUME EXPANSION ON PULMONARY MICROVASCULAR PRESSURE AND LUNG WATER IN THE CONSCIOUS SHEEP

Increased pulmonary microvascular pressure (P-mv), in combination with other factors, may cause pulmonary interstitial oedema. Whether incre ased P-mv alone induces alveolar oedema is questionable. In the presen t study we used the heavy water-indocyanine green dilution method to m easure lung water during a rapid intravascular volume expansion in the sheep. Eight conscious sheep were given two 10-min intravenous infusi ons of either 50 ml/kg (N = 2) or 35 ml/kg (N = 6) of dextran 60 with an interval of 10 min between them. At a P-mv of 40 mmHg, respiratory distress was observed in sheep no. 2 which had been given a total amou nt of 100 ml/kg of dextran; this was immediately followed by a lethal pulmonary haemorrhage. Mean P-mv in the remaining seven sheep increase d to 31 (7) mmHg in response to the volume expansion without causing a ny respiratory distress or increase in lung water. These results show that in conscious sheep the lungs have strong protective mechanisms ag ainst hydrostatic oedema. They do not support the hypothesis that incr eased P-mv alone induces alveolar oedema, but suggest that an increase in P-mv to 40 mmHg may cause stress failure of the pulmonary vasculat ure. (C) 1997 Elsevier Science B.V.