Effect of detergent combined with large tidal volume ventilation on alveolocapillary permeability

The combined effect of large tidal volume ventilation (LTVV) and detergent-induced surfactant dysfunction on the clearance kinetics of technetium-99m-labelled diethylene triamine pentaacetate was investigated. Four groups of rabbits (n = 6 in each) were studied: (1) controls, (2) detergent, (3) LTVV, and (4) detergent + LTVV. Clearance was measured for 3 h and the kinetics was analysed by fitting mono- and biexponential equations to the clearance curve and was expressed as a half-life (T 1/2). Pulmonary clearance of 99mTc-DTPA was monoexponential in control animals (T 1/2 = 194 min) and in animals ventilated with LTVV (T 1/2 = 43 min, P < 0.01 compared with controls). In contrast, clearance was biexponential after detergent administration with or without LTVV. T 1/2 values of the fast and slow compartments were 5.4 and 80 min, respectively, with the fast fraction comprising 81% of the radioactivity after detergent alone. When detergent was combined with LTVV, clearance was bicompartmental as with detergent alone, with the same size of the fast fraction. However, clearance from each of the slow (P < 0.01) and fast compartments (P < 0.05) increased significantly. Clearance from the slow compartment was thus similar to T 1/2 during LTVV alone. Large tidal volume ventilation induced a faster than normal clearance of a single compartment, whereas detergent induced kinetics that was distinctly bicompartmental. The mechanisms increasing permeability of the alveolocapillary barrier after detergent and during LTVV seem different and may be additive.