Introduction: Ischemia-free techniques for organ preservation from procurement to graft implantation using Normothermic Machine Perfusion (NMP) have been used for marginal liver intra-facility transplantation [1]. However, it requires an expensive perfusion device and a dedicated perfusionist, and to overcome these limitations, we have explored the benefits of a continuous slow cold flush in an intravenous (IV) drip fashion using the University of Wisconsin Cold Storage Solution (UW-CSS) oxygenated with Hemopure (HBOC-201), a hemoglobin-based oxygen carrier (HBOC). 
Cold continuous oxygenated flush removes metabolic waste without the need for a dialysis system while still meeting the lower O₂ demand at 4^oC [2,3]. This protocol helps to achieve simplified & cost-effective hypothermic ischemia-free conditions during simulated procurement and back-benching, decreasing cold ischemic time (CIT) and warm ischemic time (WIT) during gradual rewarming in simulated graft implantation in the recipient. 
Oxygenated solutions will help prevent primary graft dysfunction from Ischemia-Reperfusion Injury (IRI) by minimizing CIT and WIT, ultimately resulting in better graft utilization from an already limited available donor pool. 

Methods:
1. Initial Flush during procurement (after cross-clamping): 15min @ 0.3ml/min/g

• Control: UW-CSS without oxygenation
• Experimental Group (OxyFlush): UW-CSS with oxygenation

2. For the next 3hrs:  Simulated 2hr CIT of procurement + back-benching and 1hr WIT of Graft Implantation (simulated sew-in) with controlled gradual rewarming

• Control: mimicking classical clinical transplantation protocol; UW-CSS without oxygenation for 2hr CIT followed by flushing-out UW-CSS using 10ml normal saline (NS) just before the start of implantation phase with 1 hr WIT.
• OxyFlush: all 3 phases with continuous slow (0.05ml/min/g) flush with oxygenated solution: HBOC-201 + UW-CSS (25-75% V/V).

Flushing out preservative solutions with 10ml NS just before the start of NMP in both groups.

3. NMP: 6hrs for assessment using rat liver portal perfusion

Results:

• O₂ extraction ratio and uptake during initial 15min flush after cross-clamp are significantly higher with oxygenated UW-CSS.
• Livers treated with oxygenated solution (UW+HBOC) have lower edema & vascular resistance, higher O₂ uptake & cumulative bile production, as well as lower lactate & glucose in effluent drainage indicating less ischemic damage.

Conclusion:

• Hypothermic oxygenated slow continuous flushing minimizes CIT & WIT to decrease IRI.
• Although gradual temperature rise for both groups during WIT has been kept similar, clinical application of this protocol has the potential to keep the graft core temperature lower further decreasing warm ischemic damage.
•  The future direction is to try oxygenated hemopure-based UW in intermittent vs. continuous slow flush for 48hrs of static cold storage simulating transportation phase to explore IRI minimization using low volume.