Smoke inhalation injury in sheep is caused by the particle phase, not the gas phase.

The inhalation of smoke can produce severe lung injury, particularly to airways. We assessed the role of the toxic compounds in the particle phase vs. those in the gas phase of smoke in the injury process by filtering out all particles > 0.3 micron diam before exposure. Adult sheep (n = 16) were insufflated with a well-characterized cellulose smoke. Mean particle size was 3 +/- 0.4 micron diam. A standardized dose of 12 breaths of whole or filtered smoke (n = 8/group) was given to sheep under anesthesia with a tidal volume of 20 ml/kg. Sheep were awakened and monitored for 24 h and then killed. Peak carboxyhemoglobin levels were 40-45% in both groups. Severe respiratory failure occurred only in the whole-smoke group, as evidenced by an increase in shunt fraction from a control of 0.04 +/- 0.02 to 0.28 +/- 0.05, a decrease in lung compliance of 50%, and histological evidence of severe airway mucosal edema, ulceration, and bronchorrhea. No significant physiological, histological, or biochemical changes were noted in the filtered-smoke group.