The role of the bronchial circulation in the acute lung injury resulting from burn and smoke inhalation

Smoke inhalation in burn patients is a serious medical problem around the world. Inhalation injury increases mortality in addition to increasing infections, ventilator-days, and hospital stays. There are also large numbers of patients subjected to smoke inhalation without burns from cooking fires, burning crops and forest fires. The injury results in a fall in arterial oxygenation as a result of airway blockade, increased pulmonary transvascular fluid flux and loss of hypoxic pulmonary vasoconstriction. The changes in cardiopulmonary function are mediated at least in part by reactive oxygen and nitrogen species. Nitric oxide (NO) is generated by both inducible and constitutive isoforms of nitric oxide synthase (NOS). NO combines with superoxide to form reactive nitrogen species such as peroxynitrite. These reactive nitrogen species can be detected by measuring their reaction products such as 3-nitrotyrosine. The latter is elevated in the airway following smoke/burn injury. The control of NO formation involves poly (ADP ribose) polymerase (PARP) and its ability to up-regulate the activity of nuclear transcription factors through ribosylation. Present data also support a major role for the bronchial circulation in the injury since blockade of bronchial blood flow will also minimize the pulmonary injury. The data suggest that cytotoxins or activated cells are formed in the airway and carried to the parenchyma. These materials cause the formation of oedema and a reduction of PaO₂.