The Effects of Intravenous Infusion of Saline on Lung Density, Lung Volumes, Nitrogen Washout, Computed Tomographic Scans, and Chest Radiographs in Humans1–3

Abstract

In this study we examined the effect of a 15% increase in extracellular fluid volume on lung density, lung volumes, nitrogen washout, chest radiographs, and computerized tomographic (CT) scans of the thorax in 5 volunteers. The objective of the study was to determine the sensitivity of these techniques in detecting small changes in lung water. Lung density was measured by a gamma ray Compton scatter technique and with an Ohio nuclear delta 2020 CT scanner. We measured or derived functional residual capacity, residual volume (RV), vital capacity (VC), and total lung capacity by helium dilution. Single-breath nitrogen washout was used to measure closing volume and the slope of phase III nitrogen washout (ΔN₂). Chest radiographs were taken in the posteroanterior and lateral projections. With the CT scanner we obtained slices 1 cm thick through the bases of the lungs and at 6 and 12 cm up from the bases. All these measurements were made before and 20 to 90 min after the intravenous infusion of 30 ml/kg body weight of warm saline over a period of 20 min. The most striking findings were a 24% increase in ΔN₂, a 14% increase in RV, and a 4.5% decrease in VC. Chest radiographs and the CT scans showed an increase in the size of the azygos veins. There was no change in Compton scatter density or the CT numbers. These results suggest that (1) tests of small airway function, such as RV and ΔN₂, are more sensitive than radiographic techniques to small increases in lung water, (2) there is some protection of the lung to increases in extracellular fluid volume.