**4.1 Pre-reperfusion volume status**

The liver is an important reservoir of blood, containing a total of about 250-500ml or 18- 30ml/100g of blood. In liver transplantation, the donor liver graft will be rapidly filled with recipient blood following revascularization of the portal vein, resulting in immediate volume shifts and occasionally, hypotension. De La Morena et al. determined that an insufficient increase in preload is a main causative factor of PRS (or reperfusion hypotension) in an observational study using transesophageal echocardiography (TEE). Maintaining a high cardiac output is essential to ensure adequate perfusion of organs in liver transplantation. However, high cardiac output can be accomplished by maintaining preload, which may be difficult given that the operation itself is associated with major changes in volume and afterload, in addition to blood loss, third space losses, and ongoing ascites production. This result will support the hypothesis that volume shift is one of the main components of reperfusion hypotension and maintaining adequate preload before reperfusion is crucial. Also, size mismatch between donor and recipient can cause additional volume shifts, as evidenced by the fact that a large-for-size donor relative to recipient body size causes more severe reperfusion hypotension. The BSA index (BSAi) may help to more accurately match donor and recipient organs in whole organ liver transplantation.

#### **4.2 Myocardial performance**

In addition to volume shifts, a change in myocardial performance is another component of reperfusion hypotension/PRS. Myocardial performance is reduced by a decrease in temperature, acid-base and electrolyte disturbances, which are all caused by the flushing of residual preservation solution into the systemic circulation after revascularization of the graft. Acidosis following reperfusion due to release of acidic fluid from ischemic bowel and liver graft is a common finding in liver transplantation. Acute acidosis can cause tachycardia, dysrrythmias, and severe myocardial depression by producing changes in resting membrane potential and threshold potential and an increase in the rate of phase IV depolarization. Therefore the use of VVB has been proposed to decrease the incidence of PRS by minimizing small bowel edema/ischemia with varying results.

#### **4.3 Donor factors**

Lastly, the release of inflammatory factors from the post-ischemic donor liver graft into the recipient systemic circulation also can trigger a systemic inflammatory chain reaction that can lead to systemic hypotension and multi-organ dysfunction. Therefore, the quality of the donor can be a risk factor for PRS, and postoperative graft function (primary non-function, and graft survival). A donor organ with certain characteristics such as extreme age, adverse past medical history, preexisting liver damage or disease, obesity, hemodynamic instabilities, deceased cardiac donor (DCD), risk of sepsis and malignancies, hypernatremia, and prolonged ICU stay, may be more susceptible to ischemia, and more likely to have higher incidence of primary non-function (PNF), delayed function or subsequent risk for reduction in long-term graft survival. Similarly, several studies have attempted to identify donor risk factors for PRS. Hilmi et al reported warm ischemia time as a risk factor and more recently Paugam-Burtz, et al reported cold ischemia time is also a risk for PRS. In addition to those prior studies, donor age is an important risk factor for PRS. The older donor graft has a lower tolerance for hypoxia, and a greater susceptibility to reperfusion injury, probably due to metabolic changes associated with senescence, age related atherosclerotic changes in vascular structures , or steatotic changes of the parenchyma. The type of preservation solution and the graft flushing techniques have also been shown to affect the severity of PRS.

### **5. Strategy for the intraoperative management of PRS**

Warm recipient blood flows into the cold organ after revascularization of the portal vein, causing immediate volume shifts, re-oxygenation of the ischemic organ, and outflow of cold preservation solution saturated with vasoactive pro-inflammatory factors. Optimization of volume status in the recipient prior to reperfusion may minimize hemodynamic changes related to volume shifts by maximizing hemodynamic capacity to maintain good perfusion pressure throughout the liver graft, especially the large-for-size graft. TEE coupled with close monitoring of hemodynamic parameters with continuous cardiac output (CO)/SvO2, and standard cardiac monitors are particularly helpful to ensure hemodynamic integrity of the recipient. To obtain sufficient perfusion of the liver graft, especially through the hepatic microcirculation, vasodilating agents such as prostaglandin or calcium channel blockers can be used but with caution since those agents can aggravate hemodynamic instability. To minimize the sudden outflow of preservation solution from the liver graft, flushing the organ prior to reperfusion has been used and currently proposed as the most effective way of preventing hemodynamic instability associated with the inadvertent release of preservation solution. Ingredients of the flush solution as well as rate of infusion, temperature of flush solution, and amount of solution are still under investigation. Gradual and homogeneous perfusion of the organ by machine perfusion immediately prior to implantation may improve graft function by effectively removing the pro-inflammatory factors from the graft microcirculation, may reduce PRS and improve short and long term graft survival, especially in the ECD. Preemptive use of vasopressors may help maintain the systemic blood pressure but may not improve the % change in blood pressure or graft outcome. Preemptive use of oxidative free radical scavenging agents or attempts at counteracting vasoactive inflammatory factors is another area of research. For example, methylene blue has been used to scavenge nitric oxide related vasodilation in various shock states. Also, several oxidative free radical scavengers, vasodilators (inhaled nitric oxide, prostaglandin E), and Ibuprofen (cyclooxygenase inhibitor) have been studied as a way to suppress the pro-inflammatory cascade post-reperfusion. The benefits of these treatment strategies on PRS and postoperative graft function are inconclusive, and larger clinical trials are needed. This will require a consortium of leading academic liver transplant centers to conduct multicenter clinical trials. To minimize the impairment of cardiac performance following reperfusion, electrolyte abnormalities, especially hypocalcemia and hyperkalemia need to be corrected prior to reperfusion. Magnesium replacement may need to be considered, especially when there is hypocalcemia due to intraoperative transfusion and citrate intoxication. Citrate binds magnesium as well as calcium, causing acute hypomagnesemia.
