Tracheal venous blood and lymph collection: A model to study airway injury in sheep

Airway injury is a frequent result of the inhalation or aspiration of toxic material. Although upper airway damage can be identified endoscopically, pathophysiological changes are difficult to evaluate. This paper describes an animal model in which changes in tracheal blood and lymph flow rates, wet-to-dry weight ratios, and lymph-to-plasma protein ratios can be evaluated after injury. In this model, 12 cm of the cervical trachea were isolated using a double-cuffed endotracheal tube and injured with cotton smoke at near room temperature. Injury to the trachea was evaluated in twenty-five anesthetized sheep 4 (n = 3), 8 (n = 3), 24 (n = 3), 48 (n = 3), 96 (n = 3), and 192 (n = 2) h after smoke exposure and compared with sham control animals (n = 8). A significant increase in tracheal venous blood flow from 1.3 ± 0.4 (SD) ml · min^-1 · cm^-1 for the noninjured trachea to 2.8 ± 1.2 was noted 24 h after injury (P < 0.01). Lymph flow significantly increased from 1.3 ± 0.4 μl · min^-1 · cm^-1 for the noninjured trachea to 9.8 ± 3.3 24 h after injury while wet-to-dry weight ratios were elevated from 3.0 ± 0.2 for noninjured trachea to 4.6 ± 0.9 from 4 to 24 h after injury (P < 0.01) and decreased to 3.7 ± 0.5 by 96 h. Cast material consisting of airway exudate, cellular debris, and intact ciliated epithelial cells was both expectorated and found in the trachea when the animals were killed. Lymph-to-plasma total protein and albumin ratios did not decrease with a sevenfold increase in tracheal lymph flow. This indicates that, in addition to a severe injury to the epithelium, there was a change in the permeability of the trachea microvascular system that was most evident 4-24 h after injury.