Effects of rapid colloid volume expansion on pulmonary microvascular pressure and lung water in the conscious sheep.

ABSTRACT

Increased pulmonary microvascular pressure (Pmv), in combination with other factors, may cause pulmonary interstitial oedema. Whether increased Pmv alone induces alveolar oedema is questionable. In the present study we used the heavy water-indocyanine green dilution method to measure lung water during a rapid intravascular volume expansion in the sheep. Eight conscious sheep were given two 10-min intravenous infusions 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 Pmv of 40 mmHg, respiratory distress was observed in sheep no. 2 which had been given a total amount of 100 ml/kg of dextran; this was immediately followed by a lethal pulmonary haemorrhage. Mean Pmv in the remaining seven sheep increased to 31 (7) mmHg in response to the volume expansion without causing any respiratory distress or increase in lung water. These results show that in conscious sheep the lungs have strong protective mechanisms against hydrostatic oedema. They do not support the hypothesis that increased Pmv alone induces alveolar oedema, but suggest that an increase in Pmv to 40 mmHg may cause stress failure of the pulmonary vasculature.