Estimation of the LCt50 of phosgene in sheep.

In all species previously studied, inhalation of toxic doses of phosgene results in varying degrees of pulmonary edema, often after a symptom-free period. The sheep is an anatomically unique animal in which to study the development of pulmonary edema by monitoring the effluent from a catheterized caudal mediastinal lymph node. In addition, the size of the sheep is sufficient to permit placement of vascular monitoring devices and withdrawal of multiple biologic samples for analyses. In spite of this, there appear to be no published reports of sheep having ever been exposed to phosgene. This study was undertaken as a dose-ranging study, in order to permit subsequent studies of phosgene inhalation toxicity in a sheep lung lymph preparation. Accordingly, the LCt50 (24 hours) was estimated to be 13,300 mg.min/m3 (3325 ppm) by "up and down" subsequent dosage selection and moving average interpolation methods.