Lung fluid balance evaluated by the rate of change of extravascular lung water content

Lung fluid balance was studied in 27 mongrel dogs by measuring changes in extravascular lung water content (EVLW). The expression delta EVLWi, which is the difference in EVLWi per kilo bodyweight per hour between two measurement occasions, was used as an estimate of the rate of change of EVLW. EVLW was measured by a double-indicator dilution technique (EVLWi) using iced glucose and indocyanine green. In addition, EVLW was determined at the end of each experiment with gravimetric technique (EVLWg), which enabled the calculation of a regression equation between EVLWi and EVLWg. Delta EVLWi was calculated repeatedly during an 8-h period of mechanical ventilation (MV) with no application of a positive end-expiratory pressure (n = 5), during an 8-h period with a positive end-expiratory pressure (PEEP) of 10 cmH2O (1.0 kPa) (n = 5), during the development of oleic acid (OA)-induced pulmonary oedema (n = 7), and hydrostatic pulmonary oedema (left atrial balloon inflation) (n = 9). An increase of EVLW was seen during PEEP 8 h (mean 35%) and after induction of OA and hydrostatic oedema (mean 300%), but no change was found during MV without PEEP. The regression equation was EVLWi = 5.5 + 0.97 x EVLWg (P = 0.001, r = 0.90). OA-induced oedema caused a mean maximum delta EVLWi of 5.1 ml/kg/h, indicating capillary leakage which, however, was self-limiting within 2 h after OA injection. In hydrostatic oedema there was a maximum delta EVLWi of 16.0 ml/kg/h. Delta EVLWi was negative after deflation of the left atrial balloon, indicating reabsorption of oedema.