PARALYSIS OF THE PRETERM RABBIT FETUS INHIBITS THE PULMONARY UPTAKE OF INTRAAMNIOTIC IRON DEXTRAN

OBJECTIVE: Whether fetal breathing movements or gasping result in the movement of amniotic fluid substances into the distal airways remains controversial. We evaluated the effect of paralysis of the preterm rab bit fetus on the pulmonary distribution of iron dextran. STUDY DESIGN: Laparotomy was performed on 10 New Zealand White rabbits of 25 days' gestation (term 31 days) under general anesthesia. Fetuses in one uter ine horn were given an intramuscular injection of pancuronium (1.5 mg/ kg) and fetuses in the other horn were given an equal volume of normal saline solution as controls. A 1 mi volume of iron dextran (100 mg/ml ) was injected into the amniotic sac of all fetuses. The laparotomy wa s closed, and 20 to 24 hours later the fetuses were removed by hystero tomy and assessed for paralysis. Necropsy was performed. Lungs were st ained with prussian blue and evaluated histologically for the presence of iron. RESULTS: A total of 92 pups were delivered (49 given pancuro nium, 43 given normal saline solution), of which 64 were born alive. T here were no differences between groups for live births (31 pancuroniu m, 33 normal saline solution), pup body weight, or lung weight. Pups g iven normal saline solution demonstrated more breathing motions, spont aneous movement, and brown (color of iron dextran) stomach contents th an did the pups given pancuronium (p < 0.001). At necropsy a greater n umber or control pups (31/33) had brown lungs grossly compared with pu ps given pancuronium (2/31, p < 0.001). Lung histologic examination sh owed that more control pups (29/29) had iron in the trachea and main b ronchi compared with pancuronium pups (0/27, p < 0.001), and more cont rol pups (29/29) had iron in the distal lung airways compared with pan curonium pups (0/27, p < 0.001). With use of the Optimas Image Analysi s System, iron in the lungs of control pups was found to be equally di stributed between right Versus left lungs, upper half versus lower hal f lungs, and anterior versus posterior lung sections. More iron was id entified in the central airways than in the periphery (p < 0.001). CON CLUSION: We conclude that paralysis prevents the uptake of iron dextra n into the main and distal airways of the rabbit fetus. Although lung fluid production results in a net efflux of fluid, we speculate that f etal breathing movements can result in the movement of fluid into dist al airways and potentially provide fetal therapy.