Smoke Inhalation Injury

Twenty-two adult male sheep (21-50 kg body wt) were used and prepared for the experimental study through the following proce­dures: preparation of chronic lung lymph fistula was performed for the study of pulmonary fluid and protein exchange according to the methods of Staub et al.

Smoke inhalation injury was performed five to six days after the establishment of lung lymph fistula. Prior to smoke inhalation, cardiovascular catheterizations were done. Twenty four hours later, food and water were withheld for 12 h. Under anesthesia with 3 percent sodium pentobarbital (15 mg/kg/wt) IV, the sheep were insufflated with pine smoke through an endotracheal tube for 6 min with insertion of oxygen insufflation for 30 s after every 1 min of smoke inhalation. At the end of smoke inhalation, oxygen supply continued for 5 min. The procedures were performed by the aid of a smoke inhalation apparatus (Fig 1) which consists of a synchronous positive-pressure respirator (15 breaths/min and 0.98 kPa of peak airway pressure) for oxygen support and a set of smoke generation equipment. An electric stove (2,000 w), fixed at the bottom of a smoke generator, was employed to heat pine sawdust (180 g) in an aluminum basin pre-heated in an electric oven (80°C) for 12 h. There is an inlet on the wall of the smoke generator near its base linked to a volume-calibrated respirator (tidal volume 750 ml, rate 16 times/min) for air supply, and an outlet on its lid in contact with a smoke tube. After 15 min the electric stove worked and the temperature in the smoke generator went up to about 200°C. Then the aluminum basin with pine sawdust was placed on the stove and the lid of the generator fixed. Another 15 min later, the volume respirator was turned on for 3 min; then the smoke tube was linked to an endotracheal tube and began to introduce smoke inhalation.

Measurements

Before and after smoke inhalation, respiratory rate, and lung physical signs were observed. The temperature of the smoke inhaled was recorded by an indwelling thermistor placed near the inlet of the endotracheal tube. The volumes of CO and 02 in room air and smoke inhaled at 2, 4 and 6 min during the procedure taken from the smoke tube were analyzed by gas chromatography. Blood samples were taken from both the pulmonary artery and aorta before, during and after smoke inhalation. Blood gas analysis was performed immediately after the sampling using a pH blood gas analyzer (model 1303, Instrumentation Laboratory, USA). Arterial hemoglobin (Hb), carboxyhemoglobin (HbCO), oxyhemoglobin (HbOJ, metamorphous globin (HbMet) and oxygen saturation (SaOJ were determined by a СО-oximeter (model 282, Instrumentation Laboratory, Inc). Alveolar-arterial 02 gradient (P[A-a]Oa) and pul­monary shunt (Qs/Qt) were calculated. A funnel-shaped rubber mask was specially made to collect and direct air flow to a pneumotachograph (model MFF-1200M, Nihon Kohden Corpora­tion, Japan), then intrapleural pressure and lung volume were monitored simultaneously, and pulmonary dynamic compliance (Cdyn) was measured geometrically and calculated according to the formula Cdyn = DY/DP (L/0.098 kPa).

FIGURE 1. A diagram of the smoke inhalation apparatus. VR, volume respirator; S, smoke tube; C, connection tube; G, smoke generator; B, aluminium basin; ES, electron stove; PR, pressure respirator; O, oxygen bottle.

Bjthology Studies

Gross examination (GE) and light microscopy (LM) of the tracheobroncheal tree and lung and transmission electron micros­copy (ТЕМ) of the lung were performed in 22 sheep with smoke inhalation that were killed or died after smoke inhalation, and four remaining alive as normal controls. Immediately after the killing, samples were taken for ТЕМ at first, then for LM. For ТЕМ, sections of lung were fixed in phosphate-buffered 3 percent gluta- raldehyde (pH 7.4) for 24 h, then postfixed with 1 percent 0s04 solution for 2 h, dehydrated in incremental alcohol concentration, fixed in Epon 812, sectioned with a LKB ultramicrotor, (model 2088 V), stained with lead citrate and uranyl acetate and observed and photographed in an electron microscope (model H-300, Hitachi, Japan). For LM, the sections were fixed with 10 percent phosphate buffered formalin, dehydrated in increment alcohol, embedded in paraffin, and stained with hematoxylin-eosin.

Statistical Analysis

All variables obtained during and after smoke inhalation were compared with the sheeps own baseline values established before smoke inhalation injury in a stable condition physiologically by using the paired t test. Probabilities <0.05 and <0.01 were considered significant (-I-) and very significant (+ +) respectively.