Kidneys obtained from organ donors necessarily undergo a period of ischemia whereby there is no blood supply or oxygenation of the kidney until the kidney is implanted into the transplant recipient. During organ retrieval, the kidney is flushed with cold preservation fluid, after which it is most commonly placed in cold storage (CS) solution until the kidney is implanted. This method reliably keeps the kidney cool, dropping its metabolic rate and ATP consumption, and aiming to minimize the ischemia-reperfusion injury (IRI) which is one of key determinants of early and longer-term graft outcomes (1).
However, once the kidney is ready for transplantation, it must be removed from CS in preparation for anastomoses in the recipient. The kidney at this stage is exposed to the 37°C environment of the patient's body temperature and begins to re-warm; this interval is known as the second warm ischemic time (SWIT). After it reaches a temperature of 15°C to 18°C, the degree of renal glomerular and tubular metabolic activity results in warm ischemic damage (2-5). The SWIT usually ranges between 15-70 minutes, depending on the number of vessels to be reattached, surgeon experience, and anatomical differences (6-10).
Multiple studies have demonstrated the changes that occur in kidney temperature during the transplantation process. A study by Feuillu et al. (2003) on 65 patients showed that mean kidney temperature at the time of removal from the cold storage was 1.6°C and 6.3°C when the kidney was placed in the recipient (3). Then, kidney temperature increased logarithmically reaching mean kidney temperature of 26.7°C at end of anastomosis (mean SWIT: 45.5 \[22-85\] min). Kidney warming speed was 0.48°C/min and was dependent on the length of time of vascular anastomosis (3). The other series on 152 consecutive adult living donor kidney transplantations showed the mean SWIT was 41.3 ± 10.1 minutes with a temperature of 5.4 °C at baseline which gradually increased to 13.7, 17.4, and 20.2°C after 10, 20, and 30 min, respectively (4). The percentage of kidneys with a temperature of 15°C or higher was 81.2% after 20 min and 97.5% after 30 min (4).
There is large scale registry data that demonstrates the deleterious impact of kidney rewarming during the SWIT on subsequent transplant outcomes. In particular, using large cohorts from Europe, Heylen et al demonstrated: (i) increased risk with respect to higher rates of delayed graft function (defined as the need for dialysis in the 1st week post transplant), quantified as an odds ratio of 1.05 for every additional minute (i.e. 5% additional risk for every minute); (ii) poorer kidney transplant function up to 3 years post-transplant; and (iii) elevated rates of death-censored graft failure (hazard ratio of 1.10) for every additional 10 minutes. This includes outcomes for all types of deceased donor kidneys (8). The longer the SWIT the worse the outcome - this effect is especially pronounced in circulatory death donors.
Maintenance of appropriate renal hypothermia is, therefore, not only important during preservation and transportation, but also when the kidney is removed from its cooled transport media in preparation for anastomoses (8,10). This cannot be achieved using current core cooling methods (i.e. direct intravascular perfusion) during anastomoses but must rely upon external methods and/or devices. Various examples of such devices and/or techniques exist, although they have had limited success, limited generalizability, impede surgical vision, and are prone to inconsistencies. There is currently no commercial product that allows cooling of the kidney to minimise the impacts of the SWIT time.
With this current context, we wish to undertake a trial of a novel device, the Kidney Protective Jacket (KPJ™), which will assess its usability and establish its safety in the clinical setting, and add significantly to worldwide knowledge of this process. Ultimately, this device aims to provide consistent user experience with good thermoregulation leading to minimisation of IRI from the SWIT. We anticipate this will translate into improving the recipient's transplant outcomes.
