Heterotopic lung transplantation: temporary biologic support for reversible pulmonary insufficiency

The mortality rate resulting from adult respiratory distress syndrome in patients awaiting orthotopic lung transplantation remains high. Providing an "extra" lung may provide a potential solution to support a failing pulmonary system. We hypothesized that using a heterotopic lung transplant can correct hypoxemia and hypercarbia in both the short term and the long term.

Seven mongrel dogs underwent transplantation of a left lung into the abdomen. Anastomosis between the left atrial cuff and the pulmonary artery of the donor lungs was accomplished to systemic venous and arterial circulations, respectively. The main stem bronchus was exteriorized, intubated, and ventilated. Immunosuppression consisted of prednisone and azathioprine both preoperatively and postoperatively. Progressive levels of systemic hypoxemia and hypercarbia were induced. The heterotopic lung transplant augmented oxygenation with a tidal volume of 300 cc, a fraction of inspired oxygen of 50%, and a respiratory rate of 10 and then 20 breaths/min. Four animals were studied again at 48 hours. Flow through the heterotopic lung transplant ranged from 25% to 33% of the cardiac output.

Statistically significant improvements were seen in both systemic oxygenation and ventilation in the short-term experiment. The systemic oxygen pressure improved from 37 +/- 3 mm Hg to 67 +/- 5 mm Hg after ventilation of the heterotopic lung transplant, and the carbon dioxide pressure improved from 56 +/- 1 mm Hg to 43 +/- 2 mm Hg. At 48 hours an improvement in oxygen pressure was noted after ventilation of the heterotopic lung transplant, from 42 +/- 3 mm Hg to 56 +/- 2 mm Hg and an improvement in systemic carbon dioxide pressure was noted after ventilation of the heterotopic lung transplant from 57 +/- 7 mm Hg to 46 +/- 4 mm Hg.

The heterotopic lung transplant was able to provide effective gas exchange and support both oxygenation and ventilation after the induction of acute hypoxemia or hypercarbia, both immediately and at 48 hours after implantation. The heterotopic lung transplant may serve as an alternative mode of temporary support for those with acute respiratory insufficiency or as a bridge for those awaiting orthotopic lung transplantation.