A RABBIT MODEL OF INHALATION INJURY

In the course of developing a model of inhalation injury, the relation ship between the severity of pulmonary injury and specific techniques and doses of smoke exposure was examined in pairs of rabbits simultane ously exposed to smoke. In group I (5 pairs), one animal in each pair was exposed to smoke with a breath hold (BH) at the end of each exposu re; the second animal received an exposure producing the same level of carboxyhemoglobin without BH. In group II (6 pairs), both animals wer e exposed to 25 units of smoke simultaneously, with BH. In group III ( 3 pairs), one animal received a 20-unit exposure and the other a 25-un it exposure, both with BH. In group IV, 9 animals received 25-unit exp osures with BH and were observed for 4 days. Groups V and VI served as controls. Smoke exposure with BH regularly produced severe injury in terms of decreased PaO2 and histopathologic changes, while exposure wi thout BH did not, despite high levels of carboxyhemoglobin after smoke inhalation. The mean differences in percent residual PaO2 (PaO2 at 48 hours x 100/pre-injury PaO2) and in extravascular lung water (EVLW) a t 48 hours within pairs of animals receiving 25 units with BH were 12. 3% +/- 5.33%, and 0.271 +/- 0.157 mL/g, respectively. Histologic findi ngs such as necrotic tracheobronchitis with pseudomembrane were consis tently present. No differences were observed between animals receiving exposures of 20 and 25 units. During the 4 days of observation, three animals in group IV died. PaO2 was lowest on the second day and rose thereafter in all surviving animals except in one that had massive pne umonia Extravascular lung water levels were still elevated on the four th day after injury. Histologically, the destroyed surface epithelium in the airway was covered by a nonciliated epithelium, and focal pneum onia was found frequently in the pulmonary parenchyma. These results i ndicate an advantage of the extended exposure afforded by BH in creati ng consistent, severe injury and the important part played by pneumoni a in determining prognosis beyond the second postinjury day. The model appears useful for evaluating the effects of inhalation injury with c oncurrent cutaneous bum or wound infection, and for assessing various regimens for the treatment of inhalation injury.