From the Guidelines
Warm ischemia time (WIT) in renal transplant surgery is defined as the period when the kidney has no blood supply but remains at body temperature, and cold ischemia time (CIT) is the period when the kidney is preserved at hypothermic temperatures in preservation solution. The American Society of Transplant Surgeons recommends standardizing the terminology of warm ischemia time, avoiding the term DWIT due to its ambiguity, and instead using the term f-DWIT with specification of its definition 1. Key factors to be documented in DCD donor procurements include time of WLST, time at which heparin is given, first minute when SpO2 is reduced to <70%, first minute when sBP is reduced to <50 mmHg, time when the patient is determined to have circulatory arrest, time of incision, time of cold flush, time of cross-clamp, time of NRP initiation and termination, and time that each respective organ is removed from the donor 1. In terms of CIT, it typically ranges from 6-24 hours but should ideally be kept under 20 hours, as longer durations increase the risk of delayed graft function, acute rejection, and decreased long-term graft survival 1. Minimizing both WIT and CIT is essential for optimal transplant outcomes, with cold preservation helping to reduce metabolic demands and cellular damage compared to warm ischemia. Some key points to consider in renal transplant surgery include:
- The time from flush/cross-clamp until nephrectomy and placement of the kidneys in hypothermic solution (kidney extraction time) should be ≤ 60 minutes 1.
- Cold ischemia with ice slush safely facilitates longer durations of ischemia and is associated with improved renal functional outcomes 1.
- Longer periods of warm ischemia are associated with diminished postoperative eGFR, whereas the impact of short durations (< 25 minutes) is controversial 1. Therefore, it is crucial to minimize both warm and cold ischemia times to optimize transplant outcomes, with a focus on standardizing terminology and documentation to ensure accurate measurement and comparison of ischemia times across different transplant centers 1.
From the Research
Definition of Warm Ischemia Time and Cold Ischemia Time
- Warm ischemia time refers to the period from organ removal from cold storage to reperfusion with warm blood 2.
- Cold ischemia time refers to the period of hypothermic preservation, which is a prerequisite for kidney exchange in transplantation 3.
Impact of Warm Ischemia Time on Renal Transplant Surgery
- Prolonged warm ischemia time is associated with graft failure and mortality after kidney transplantation 2.
- Warm ischemia time of more than 45 minutes can be a risk factor for poor early graft function, with statistical significance achieved when it exceeds 60 minutes 4.
- Longer warm ischemia times are associated with increased hazard ratios for the composite event of mortality and graft failure 2.
Impact of Cold Ischemia Time on Renal Transplant Surgery
- Prolonged cold ischemia time can lead to delayed graft function, especially in expanded criteria donors, and possibly an increased acute rejection rate 3.
- Cold ischemia time is a significant risk factor for delayed graft function and acute rejection, with each hour of cold ischemia increasing the risk of rejection by 4% 5.
- Simple cold storage up to 50 hours is safe and acceptable, provided that warm ischemia is kept minimal (less than 10 minutes) 6.
Combined Impact of Warm and Cold Ischemia Time
- A combined analysis of warm and cold ischemia shows that it is advisable to keep hypothermic preservation within the limit of 30 hours when warm ischemia time exceeds 10 minutes 6.
- Reducing both warm and cold ischemia times is crucial to improve graft survival and function in renal transplant surgery 2, 3, 5, 4, 6.