Inhalation injury is one of the main causes of mortality in
burn victims. The tracheobronchial epithelium sloughs and combines with a
protein rich exudate to form casts of the airways that can lead to obstruction. We studied the effects of a continuous infusion of
heparin on the acute
pulmonary injury that occurs after
smoke inhalation injury in sheep. Twelve ewes with
vascular catheters received a standardized
smoke inhalation injury and
mechanical ventilation according to protocol for 72 hours. The
heparin group (n = 6) received a 400 unit per kilogram bolus of
heparin followed by a continuous infusion to maintain the activated clotting time between 250 to 300 seconds. The control group (n = 6) received a
saline solution vehicle. Hemodynamics, blood
gases and plasma samples for conjugated dienes were taken every six hours. At necropsy, pulmonary tissue was collected for histologic findings, polymorphonuclear neutrophil leukosequestration, wet-to-dry weight ratios and conjugated dienes. PaO2 to FIO2 ratios were improved in the
heparin group compared with the control group at 12 to 72 hours after injury, and peak airway pressures were higher in the control group compared with the
heparin group.
Positive end expiratory pressure requirements were higher in the control group compared with the
heparin group. There were significantly fewer airway tracheobronchial casts as determined by our tracheobronchial casts scoring system (2.4 +/- 0.4 versus 0.67 +/- 0.21) and confirmed by histologic examination. Pulmonary blood-free wet-to-dry weight ratios were higher in the control group compared with the
heparin group (6.4 +/- 0.5 versus 5.2 +/- 0.1; p < 0.05). There were no differences in pulmonary tissue or plasma conjugated dienes; likewise, pulmonary leukosequestration was unaffected by
heparin.
Heparin decreases tracheobronchial cast formation, improves oxygenation, minimizes
barotrauma and reduces
pulmonary edema in an ovine model of severe
smoke inhalation injury.
Heparin does not reduce
oxygen free radical activity after
smoke inhalation injury.