HETEROTOPIC LUNG TRANSPLANTATION - TEMPORARY BIOLOGIC SUPPORT FOR REVERSIBLE PULMONARY-INSUFFICIENCY

Background: The mortality rate resulting from adult respiratory distre ss syndrome in patients awaiting orthotopic lung transplantation remai ns high. Providing an ''extra'' lung may provide a potential solution to support a failing pulmonary system. We hypothesized that using a he terotopic lung transplant can correct hypoxemia and hypercarbia in bot h the short term and the long term. Methods: Seven mongrel dogs underw ent transplantation of a left lung into the abdomen. Anastomosis betwe en the left atrial cuff and the pulmonary artery of the donor lungs wa s accomplished to systemic venous and arterial circulations, respectiv ely. The main stem bronchus was exteriorized, intubated, and ventilate d. Immunosuppression consisted of prednisone and azathioprine both pre operatively and postoperatively. Progressive levels of systemic hypoxe mia and hypercarbia were induced. The heterotopic lung transplant augm ented oxygenation with a tidal volume of 300 cc, a fraction of inspire d 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 heterot opic lung transplant ranged from 25% to 33% of the cardiac output. Res ults: Statistically significant improvements were seen in both systemi c oxygenation and ventilation in the short-term experiment. The system ic oxygen pressure improved from 37 +/- 3 mm Hg to 67 +/- 5 mm Hg afte r ventilation of the heterotopic lung transplant, and the carbon dioxi de pressure improved from 56 +/- 1 mm Hg to 43 +/- 2 mm Hg. At 48 hour s an improvement in oxygen pressure was noted after ventilation of the heterotopic lung transplant, from 42 +/- 3 mm Hg to 56 +/- 2 mm Hg an d an improvement in systemic carbon dioxide pressure was noted after v entilation of the heterotopic lung transplant from 57 +/- 7 mm Hg to 4 6 +/- 4 mm Hg. Conclusions: The heterotopic lung transplant was able t o provide effective gas exchange and support both oxygenation and vent ilation after the induction of acute hypoxemia or hypercarbia, both im mediately and at 48 hours after implantation. The heterotopic lung tra nsplant may serve as an alternative mode of temporary support for thos e with acute respiratory insufficiency or as a bridge for those awaiti ng orthotopic lung transplantation.