Warm Ischemia Time in Kidney Transplantation
For donation after circulatory death (DCD) kidney transplantation, total warm ischemia time should not exceed 45-60 minutes to minimize complications, with kidney extraction time kept under 60 minutes from cold flush to placement in hypothermic solution. 1, 2
Definition and Measurement
Warm ischemia time (WIT) refers to the period when organs experience ischemic injury at body temperature. The American Society of Transplant Surgeons recommends standardized documentation of specific time points during DCD procurement, including the first minute when systolic blood pressure drops below 50 mmHg, time of cold flush, and time of organ removal. 1, 2
Two key WIT measurements exist for DCD kidneys:
- Total warm ischemia time: Interval from withdrawal of life-sustaining treatment to initiation of cold perfusion 1
- Functional warm ischemia time (f-DWIT): Time from systolic blood pressure <50 mmHg until cold flush/cross-clamp 1
Recommended Time Thresholds
Maximum Acceptable Limits
Total warm ischemia time exceeding 45-60 minutes is associated with increased complications in DCD kidney transplantation. 1, 2 This represents a hard threshold beyond which graft outcomes deteriorate significantly.
Kidney extraction time (from cold flush/cross-clamp to placement in hypothermic solution) should be ≤60 minutes. 1, 2 Longer extraction times independently predict delayed graft function and death-censored graft failure, with each 10-minute increase raising graft failure odds by 5%. 1
Cold Ischemia Time
Cold ischemia time should not exceed 24 hours for kidney transplantation. 1, 2 This represents the period from cold preservation initiation to reperfusion in the recipient.
Impact on Outcomes
Delayed Graft Function
Prolonged WIT significantly increases delayed graft function (DGF) rates. DCD kidneys with hypoperfusion WIT ≤30 minutes show DGF rates around 40%, while those with HWIT >30 minutes experience DGF rates approaching 60%. 3 For comparison, donation after brain death (DBD) kidneys have DGF rates of approximately 21.7%. 3
Long-term Graft Survival
Even in deceased donor kidney transplantation, WIT (defined as time from cold storage removal to reperfusion) demonstrates a dose-dependent relationship with mortality and graft failure. 4 Compared to 10-20 minute WIT, times of 30-40-50-60, and ≥60 minutes show hazard ratios of 1.13,1.17,1.20, and 1.23 respectively for the composite outcome of death or graft failure. 4
Strategies to Minimize Warm Ischemia Time
Procedural Optimization
Withdrawal of life support should preferentially occur in the operating room after prepping and draping. 1, 2 This eliminates transport time and allows immediate procurement following circulatory arrest declaration.
Heparin should be administered before withdrawal of life support rather than during the agonal phase. 1, 2 This ensures adequate anticoagulation is established before circulatory compromise begins.
The mandatory "no-touch" period after circulatory arrest declaration should be limited to ≤5 minutes. 1, 2 Longer waiting periods unnecessarily extend warm ischemia without improving death determination accuracy.
Monitoring Requirements
Blood pressure, heart rate, and oxygen saturation must be monitored and recorded every minute during the agonal phase. 1, 2 This documentation allows accurate determination of functional warm ischemia time for all transplant centers involved.
Surgical Technique
DCD procurements should be performed by experienced surgical teams familiar with rapid recovery techniques. 1 Surgical expertise directly impacts extraction time and overall warm ischemia duration.
Important Caveats and Risk Factors
Modifiable Risk Factors
Recipient obesity significantly prolongs WIT, with BMI >35 associated with an odds ratio of 1.57 for prolonged WIT. 5 Transplanting a right kidney into an obese recipient further extends WIT by 11.0% compared to other combinations. 5
Right donor kidneys experience longer WIT than left kidneys (OR 1.14). 5 This likely reflects the more challenging surgical dissection required for right kidney procurement.
Compounding Risk Factors
The combination of prolonged WIT with other risk factors—including donor age ≥65 years, cold ischemia time >8 hours, or hepatic steatosis—significantly compounds graft failure risk. 2 These factors should be carefully considered when evaluating marginal DCD kidneys with borderline WIT.
Extended Time Considerations
**Recent data suggest that waiting up to 4 hours for DCD kidney donation may be acceptable if functional WIT remains low (<30 minutes).** 6 Among potential donors who did not donate due to total WIT >2 hours, 20.8% died between 2-4 hours, representing missed opportunities when functional WIT criteria were likely met. 6
Partial Nephrectomy Context
For partial nephrectomy procedures, when WIT is expected to exceed 20-30 minutes, local renal hypothermia should be employed. 7 This recommendation applies particularly to patients with baseline characteristics suggesting higher risk of ischemic damage, though the exact threshold remains controversial. 7