Effect of norepinephrine and fluid administration on pulmonary extravascular water volume in dogs

The effects of norepinephrine-induced vasoconstriction on pulmonary extravascular water volume (PEWV) and central volume were studied before and after intravenous volume expansion with 5% dextrose and water (20 ml/kg body weight). PEWV was measured by double isotope dilution and gravimetric analysis and assessed by electron photomicrography. Comparisons were made with saline-treated control dogs. Thirty-six dogs were studied after they had been anesthetized with sodium pentobarbital. PEWV determined by indicator dilution increased during norepinephrine infusion, especially after volume expansion; in contrast, PEWV in control dogs was constant despite similar increases in pulmonary arterial and left atrial pressures. However, measurements of PEWV by gravimetric analysis and inspection of electron photomicrographs failed to reveal extravascular accumulation of water in vasoconstricted dogs. Thus, it was concluded that the increased PEWV measured by indicator dilution in norepinephrine-treated dogs compared with that in saline-treated dogs reflects more complete perfusion of pulmonary capillaries and access of the diffusible indicator to additional lung tissues and spaces. Improved capillary filling presumably is attributable to peripheral vasoconstriction and redistribution of blood into the thorax. PEWV determined by gravimetric analysis in dogs that had had open-chest procedures for lung biopsy and electron photomicrography was significantly less than that in dogs with their chests closed throughout the experiments. Although the mechanism for the water loss in unknown, the difference must be recognized when the results from various types of experiments are compared.