SURFACTANT NEBULIZATION VERSUS INSTILLATION DURING HIGH-FREQUENCY VENTILATION IN SURFACTANT-DEFICIENT RABBITS

Surfactant nebulization improves lung function at low alveolar doses o f surfactant. However, efficiency of nebulization is low, and lung dep osition seems to depend on lung aeration. High frequency ventilation ( HFV) has been shown to improve lung aeration. We hypothesize that the combination of HFV and surfactant nebulization may benefit lung deposi tion of surfactant and consequently, lung function. The aim of this st udy was to compare the effect of surfactant nebulization versus instil lation during HFV on lung function, surfactant distribution, and cereb ral blood flow. Therefore, severe respiratory failure was induced by l ung lavages in 18 rabbits. HFV was applied: frequency = 8 Hz, mean air way pressure = 12 cm H2O, amplitude = 100%, fraction of inspired O-2 = 1.0. Technetium-99m-labeled surfactant (Alveofact, 100 mg/kg of BW) w as nebulized or instilled (n = 6 each). Six other rabbits did not rece ive surfactant (control, HFV only). We found that after instillation p artial arterial O-2 tension increased from 7.0 kPa (95% confidence int erval, 6.3-8.0 kPa) to 34 kPa (16-51 kPa), and during nebulization fro m 7.0 kPa (6.0-9.0 kPa) to 46 kPa (27-58 kPa). Partial arterial CO, te nsion decreased after instillation from 6.1 kPa (5.3-7.1 kPa) to 4.8 k Pa (3.9-5.6 kPa), and during nebulization, after an initial rise, it d ecreased from 6.3 kPa (5.3-7.4 kPa) to 4.9 kPa (4.4-5.6 kPa). Both tre atments resulted in nonuniform distribution. Surfactant deposition aft er nebulization was 9.8%, Instillation resulted in a drop of mean arte rial blood pressure of 17% (8-31%), and an even more pronounced drop i n cerebral blood flow of 39% (18-57%). Nebulization did not affect blo od pressure. Cerebral blood flow decreased with a maximum of 27% (10-3 7%). We conclude that surfactant nebulization during HFV improves lung function in rabbits with severe respiratory failure, without improvin g distribution, but with less effects on blood pressure and cerebral b lood flow, when compared with surfactant instillation.