Inhalation injury and positive pressure ventilation in a sheep model

The mortality rate of inhalation injury was lowered in six chronically instrumented sheep through positive pressure ventilation and positive end-expiratory pressure (PEEP). Six range ewes were prepared for study by implanting catheters to measure lung lymph flow and cardiopulmonary variables. After surgery, these animals were studied in the unanesthetized state and then subjected to an inhalation by insufflating them with smoke from burning cotton. Following the smoking procedure, the animals were studied for 72 hr. All had marked falls in arterial oxygen tension and they developed dyspnea within 24 hr. The inhalation injury produced a marked change in lung lymph flow concomitant with an elevation in the lymph to plasma (L/P) oncotic pressure ratio. This is characteristic of a change in microvascular permeability to protein. A tracheostomy was performed at 72 hr and the animals were connected to positive pressure ventilators with PEEP. All six animals survived. It was concluded that the sheep lung lymph preparation is a very suitable model for the study of inhalation injury and positive pressure ventilation.