Hypothermic Perfusion of the Warm Ischemic Kidney: Is 32 °C Better Than 4 °C?

Abstract

To the Editor: Brasile et al. (1) have developed an oxygen-carrying perfusion solution that can be used at 32°C to perfuse dog kidneys successfully after being exposed to 30 min of warm ischemia. This is a unique and meritorious achievement. The title of the article, ‘Hypothermia – a limiting factor in using warm ischemically damaged kidneys’, and their conclusion that hypothermia is the limiting factor, however, is unsupported by the evidence. In their experimental design they varied three parameters simultaneously (temperature, method of preservation, and solution). Thus, to conclude that the temperature was the limiting factor is premature and requires a better experimental design. Furthermore, 32°C is actually hypothermic compared with normal body temperature. Previous experimental and clinical experience has shown that hypothermia (0–4°C) can be safely used to preserve kidneys exposed to at least 30 min of warm ischemia. The development by Belzer in the late 1960s of a method to preserve kidneys for 3 d by continuous hypothermic perfusion (4–8°C) was used during the 1970s for human kidneys that often came from nonheart-beating donors. This was due to the lack of standard brain death criteria for organ donors and many donors were nonheart-beating. Thus, many kidneys had 25–40 min of warm ischemia. However, many of these organs were safely preserved for up to 24 h or more and transplanted after hypothermic perfusion. In our clinic at the University of Wisconsin Hospital, we continue to perfuse kidneys hypothermically (0–4°C), both from nonheart-beating (NHBD) and heart-beating cadavers (HBD). The delayed graft function rate for the NHBD kidneys that are machine-perfused is similar to the national average for HBD kidneys that are cold stored (about 25%). The warm ischemic period is variable and may range from 15 to 45 min. Early work by many authors showed that hypothermic perfusion (4–8°C) was superior to simple cold storage (0–4°C) for preservation of the dog kidney exposed to 30 min of warm ischemia. Our laboratory has successfully hypothermically preserved dog kidneys exposed to 45–60 min of warm ischemia by machine perfusion with the UW solution. Some transplant centers that have regularly used hypothermic (0–4°C) machine perfusion for kidney preservation often report significantly lower delayed graft function rates than centers that use simple cold storage. Hypothermic machine perfusion can lower delayed graft function rates of the ideal kidney to less than 10% and is suitable for the warm ischemically damaged kidney. Despite the benefits of machine perfusion, most kidneys continue to be preserved by simple cold storage. Matas and Delmonico (2) argue in the same issue of the journal that improvements in preservation (by shortening the cold ischemic time) could lower the discard rate for kidneys. One improvement in preservation that might achieve the same result as lowering cold ischemic time is the use of hypothermic (0–4°C) perfusion preservation. If more centers perfected this technology, an improvement in kidney transplant results might be achieved without the need for moderate (32°C) hypothermic preservation, both for HB and NHB cadaver kidneys. Anthony M. D'Alessandro and James H. Southard Department of Surgery, University of Wisconsin Medical School, Madison, WI, USA