To establish serious, critical and extra-critical model of severe inhalation injury induced by steam in rabbits.

One hundred and thirty six New Zealand white rabbits were randomly divided into the injury groups with 102 rabbits and the sham group with 34 rabbits. According to the injury time the injury groups were randomly divided into 3 groups and each group included 34 rabbits and those groups were respectively named the group of 0.25 s, 0.50 s, 1.00 s. After placed a 5-mm inside diameter tracheal tube, animals in the injury groups were vulnerated by steam that came from an "automatic control time and pressure scald instrument" made at our lab which ensured the steam pressure 0.02 Mp/cm² and temperature 105 ℃. In the injury groups the injury time was respectively 0.25 s, 0.50 s, 1.00 s. Except inhalation injury induced by steam, the same treatment was given to the sham group with 34 animals as the injury groups. Throughout the experiment, We measured PaO₂, PaCO₂ of arterial blood sample using an automatic blood gas system in each group with 6 rabbits at each post injury time point (1 h, 4 h, 12 h, 24 h). we also examined the lung histopathology, the lung dry/wet weight ratio in each group with 6 rabbits at each post injury time point (1 h, 4 h, 12 h, 24 h). We recorded the mortality rate in each group with additional 10 rabbits at various post injury time point (6 h, 12 h, 24 h).

At 1 h of post injury the group of 1.00 s appeared the changes that included significant pulmonary congestion, edema , bleeding, hypoxia and inflammatory cells infiltration. The above changes were gradually aggravated with time and the mortality of rabbits at 6 h of post injury was 100%. At 1 h of post injury the group of 0.50 s also appeared the changes that included pulmonary congestion, edema, bleeding, hypoxia. The above changes were gradually aggravated at 4 h of post injury and inflammatory cells infiltrated into the lung tissue. PaO₂ in the group of 0.50 s was higher than the group of 1.00 s at 1 h, 4 h of post injury, which indicated a statistical significance (P<0.05). The mortality of rabbits of the group of 0.50 s at 12 h, 24 h of post injury was 25%, 75%. In the group of 0.25 s, pulmonary congestion, edema and hypoxia were observed at 4 h of post injury. At 12 h of post injury , pulmonary congestion and edema combined with pulmonary bleeding, hypoxia and inflammatory cells infiltration were gradually aggravated in the group of 0.25 s. PaO₂ in the group of 0.25 s decreased to a level of less than 60 mmHg at 4 h, 12 h, 24 h of postinjury. PaO₂ in the group of 0.25 s was higher than the group of 0.50 s at the same time-point of post injury, which indicated a statistical significance (P<0.05). PaO₂ in the group of 0.25 s was lower than the sham group at the same time-point of post injury (P<0.01). The mortality of rabbits of the group of 0.25 s at 24 h of postinjury was 25%.

By inhaling the steam of 0.25 s, 0.50 s, 1.00 s that the steam pressure was 0.02 Mp/cm² and temperature was 105 ℃, the stable serious, critical and extra-critical model of inhalation injury induced by steam can be reproduced in rabbits.