Bronchial cytologic changes during cardiopulmonary bypass: iron transport by histiocytes in low flow states

We previously reported (1) that tracheobronchial secretions of patients in hemorrhagic shock contained significantly more iron laden histiocytes than secretions of matched controls and demonstrated by histiologic studies in rats bled to hemorrhagic shock that these animals' lungs contained significantly more iron laden histiocytes than those of a control group. Two explanations appeared plausible: 1) abnormal hemoglobin breakdown products of systemic hypoperfusion during shock (2, 3, 5) may have accumulated in the pulmonary circulation where they were phagocytozed by pulmonary histiocytes, or 2) circulating iron laden histiocytes may have been arrested in the lung, which is well known to act as a filter during low-flow states (4). The present study reports on assay of bronchial secretions of 12 open-heart surgery patients under cardiopulmonary bypass from specimens obtained 1) immediately after onset of anesthesia; 2) during; and 3) after termination of cardiopulmonary bypass. The percentage of iron laden histiocytes rose from 15.6+/-6.0 after intubation, to 49.6+/-6.8 after 1 hour on bypass with occluded pulmonary arteries (p less than 0.0025), remaining close to the latter value after pulmonary circulation was restored. Hypoperfusion, accumulation of metabolites, or falling pH at the tissue level are probable explanations for these findings.