Pulmonary surfactant is both deficient and dysfunctional in human infants with AVB (Arch Dis Child 75:133, 1996). We therefore studied the effects of surfactant therapy in the guinea pig model of AVB, testing the hypothesis that surfactant administration would lead to an improvement in pulmonary resistance and airway reactivity. METHODS: Cam-Hartley guinea pigs (270±13 gm, mean±SD) were infected by nasal administration of 100 μL of viral inoculum, containing ≥ 103 plaque-forming units of respiratory syncytial virus. On day 6 post-inoculation, animals were anesthetized, tracheotomized, and ventilated at resp rate 60/min and tidal volume 10 mL/kg in a total body plethysmograph. Transpulmonary pressure (= airway opening - esophageal pressure), and flow (differentiated from plethysmographic volume signal) were recorded, and baseline resistance (RL) determined. Animals then received 1 mL/kg natural surfactant (Survanta®, Abbott Australasia), 0.25 mL/kg surfactant, saline 1mL/kg, or air placebo, instilled via a catheter positioned beyond the tip of the tracheostomy tube. RL was measured 30 mins post-administration, and airway reactivity evaluated using sequentially increasing doses of aerosolized acetylcholine (saline, 0.15, 0.5, 1.5, 5 and 15 mg/mL), with recovery to baseline after each challenge. The provocative concentration of acetylcholine leading to a doubling of RL (PC2) was calculated for each animal. RESULTS (see Table): Baseline RL values were similar across the groups, and there were no significant intergroup differences noted in change in RL at 30 minutes(p=0.37, ANOVA), or PC2 values (p = 0.41). A trend was noted towards increased RL, and greater reactivity (i.e. lower PC2), in the surfactant-treated animals compared to air placebo, which may be explained in part by the fluid volume of the surfactant preparation; a similar effect was seen after saline administration. CONCLUSION: Administration of natural surfactant in 2 different doses did not improve resistance or reactivity in guinea pigs with AVB. These pathophysiological elements of AVB may prove refractory to surfactant therapy.

Table 1 No caption available.
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