Distribution of alveolar edema in ventilated and unventilated canine lung lobes.

RATIONALE AND OBJECTIVES: Pulmonary edema frequently is treated with ventilation but its effects on the distribution of edema, including gravity-dependent gradients as determined by computed tomography (CT) scanning, are unclear. METHODS: To study this, 30 to 50 mL 5% albumin in dextran were instilled in both caudal lobes of supine dogs. They were ventilated only on the left side for 1 minute (n = 4), 30 minutes (n = 6), or 60 minutes (n = 6), and the lobes excised, frozen, and imaged in a CT scanner. Regions of interest were outlined on regional CT slices and tissue from corresponding regions taken for measurements of extravascular lung water (quantity of wet lung [Qwl]/dry quantity of lung [dQl] and for histology to grade interstitial and alveolar edema. RESULTS: After ventilation for 30 and 60 minutes, the CT density of the left caudal lobes was significantly lower than the right caudal lobes (P < 0.05), with no significant differences in their Qwl/dQl. Although gravity-dependent gradients of Qwl/dQl were demonstrated, they were unaffected by ventilation. Histology showed a trend for more interstitial edema in left caudal lobes ventilated for 60 minutes compared with lobes ventilated for 1 minute (P = 0.054). CONCLUSIONS: Ventilation appears to act primarily by maintaining lung aeration and may play a minor role in alveolar fluid clearance.