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Ann Thorac Surg 1998;66:2155
© 1998 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Wythenshawe Hospital, Southmoor Rd, Manchester M23 9LT, United Kingdom
To the Editor
We thank Drs Rooney and Bonser for their interest in our studies on controlled reperfusion of lung grafts and for their description of the factors governing fluid and solute fluxes across the endothelium. We agree entirely that the increase in albumin leak index demonstrated in stored lungs reperfused at physiologic pressure (group D) could have been influenced by the effects of increased hydrostatic pressure on fluid flux and recruitment of endothelial surface area. However, what was of much greater interest and importance in our study was the comparison between the controlled reperfusion groups E and F. The albumin leak index was significantly elevated between 0 and 5 minutes of reperfusion despite a 50% reduction in perfusion pressure (group E), but was not elevated between 5 and 10 minutes of reperfusion at the same, low, pressure (group F). This change in albumin leakage without any change in hydrostatic pressure is likely to represent a reduction in endothelial permeability. We therefore believe that the observed benefits of controlled reperfusion may in part be through protection from edema during a brief early high-permeability state.
The use of the albumin leak index as a measure of permeability is not ideal, and isogravimetric methods are indeed more accurate. However, the very fact that these methods require an initial period of stable isogravimetric perfusion excluded their use in our studies, as we were interested in early and rapid changes in permeability. The contention that the concentration of albumin presented to the graft may be affected by redistribution into support animal tissues is true but is largely overcome by the use of the graft:blood isotope count index rather than absolute values. As for the effect of isotope retained in blood in the pulmonary vasculature, we attempted in pilot studies to flush the grafts with isotope-free fluids, as has been described by others [1]. We found that even if done using very low pressures, those grafts that had high permeability became flooded with the flush solution, thereby introducing even greater error into the calculation of the leak index. The albumin leak index used widely as a marker of lung endothelial injury [1, 2] was an appropriate tool in our studies, and yielded valid data indicating a mechanism that may contribute to the protection of lung grafts by controlled reperfusion.
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