CARDIOVASCULAR ANESTHESIA: Research Report
The lack of donors has forced transplantation teams to sometimes use marginal quality donors. The liver from cadaveric donors may be injured or damaged before transplantation by cardiovascular instability, endocrine, metabolic, and electrolyte imbalances, hypoxemia, endotoxin release, and hyponutrition, which may result in primary graft failure after liver transplantation (1). Hypernatremia (>155 mEq/L), which is sometimes observed in cadaveric donors, is one of the most dangerous risk factors for graft loss in the clinical setting of orthotopic liver transplantation (OLT) (2,3). The underlying mechanism responsible for this observation is not clear. Animal experiments have shown that the hyperosmolarity associated with diabetes insipidus (DI) alters only hepatocyte structure and function but does not affect the survival after OLT in animal studies (4). Furthermore, there is no controlled study to confirm the evidence that hypernatremia, per se, is a contraindication to organ donation. Only retrospective clinical studies have shown that hypernatremia is one of the risk factors that cause primary graft loss (2,5). However, hypertonic saline is used to resuscitate trauma patients in hemorrhagic shock (6–10) because it provides immediate and long-lasting hemodynamic restoration. It is important to establish the consequence of using liver grafts from hypernatremic donors, because in clinical practice, every terminally injured patient can be considered a potential donor despite the lack of reliable criteria on the use of hypernatremic brain-dead candidates. This study, therefore, aims to evaluate whether the hypernatremia, per se, induced by the injection of hypertonic saline solution in the donors, would affect survival in a rat OLT model.
Materials and Methods
We received permission for our study from the Animal Experimentation Committee at our institution. Principles of laboratory animal care (National Institutes of Health publication No. 86–23, revised 1985) were followed in this study.
A rat model of induced hypernatremia was first established using 15 ether-anesthetized Wistar rats (250–300 g). The penile vein was cannulated, and different concentrations of sodium chloride solution were infused at varying rates using a microinjection pump (Terfusion STC 531, Terumo, Tokyo, Japan). Blood samples were drawn 30 min after termination of infusion, and the level of serum sodium was determined. Once the adequate saline dose to induce hypernatremia of ≥160 mEq/L was determined, 3 rats were used to study the serial changes in serum sodium at 1, 3, and 6 h after the induction of hypernatremia.
After establishment of an adequate hypernatremic rat model, the liver transplant experiments were performed. The techniques of liver graft procurement and OLT without arterialization used herein have been described previously (11,12). At the induction of ether anesthesia in the donors, the infusion of hypertonic sodium chloride solution was started. The donor procurement operation was then begun, and blood samples from the portal vein were obtained and the liver removed approximately 30 min later. The blood samples were sent to the Central Clinical Laboratory of our hospital for determination of aspartate aminotransferase, alanine aminotransferase, total bilirubin, γ glutamyltrans-peptidase, alkaline phosphatase, albumin, and sodium. The liver grafts from six untreated and six hypernatremic Wistar rats were immediately transplanted fresh into normal recipient rats without being preserved in University of Wisconsin (UW) solution. After OLT, the rats were allowed to recover from anesthesia and were observed in a specific pathogen-free facility. The observation period was 7 days, and survival up to this period was regarded as a successful liver transplantation (13). Three other untreated and three hypernatremic liver grafts were preserved in 4°C UW solution before transplantation into normal Wistar rats. Rejection factors are eliminated in this syngeneic rat model, and no immunosuppressive drugs were given.
To study the degree of dehydration or the water content of the liver grafts, the livers removed from three untreated and three hypernatremic donor rats were used. A small piece of liver tissue was taken from each of the livers and promptly weighed to determine the wet weight. The specimen was then place in an oven at 60°C for 24 h to obtain the dry weight. The dry/wet weight ratio represented the water content of the liver tissue and was compared between untreated and hypernatremic livers.
The Mann-Whitney U statistical test for nonparametric data was used to compare the biochemical variables and water content of the liver tissue between groups. P < 0.05 was considered significant. Data were expressed as mean ± sd.
Table 1 shows that the infusion of 10% sodium chloride solution at 0.12 mL/min was adequate to induce a serum sodium ≥160 mEq/L in the Wistar rat. This model was then used to induce hypernatremia in the donors in the transplant experiments. Figure 1 shows the dynamic changes of serum sodium after the induction of hypernatremia at the selected concentration. Hypernatremia lasted for 3 h but returned to normal at 6 h after the infusion of hypertonic saline solution.
Table 2 shows the results of the experiments comparing OLT using grafts from hypernatremic donors (Group I) and from untreated donors (Group II). There was no significant difference in liver function in the donors and water content of the graft between the two groups. There was, likewise, no significant difference in liver function between Group I and Group II recipients at Day 7 after OLT, although the liver enzymes and total bilirubin in all rats were much higher compared with the values in the donors. All the recipients from both groups remained alive at 7 days after OLT, suggesting that peritransplant acute hypernatremia did not affect survival.
In a retrospective study, Figueras et al. (2) concluded that hypernatremia is one of the most dangerous risk factors for graft loss in liver transplantation. Therefore, they recommended that the suitability of liver grafts should be carefully evaluated when the serum sodium of the potential donor is more than 155 mEq/L (2). Two reports have shown that the correction of hypernatremia in cadaveric donors before OLT improved the graft survival rate (5,14). Considering this risk factor, the decision to resuscitate trauma patients with hypertonic saline solution is then questionable because they are potentially valuable organ donors. Hypernatremia more than 161 mEq/L is found after such resuscitation (15), but associated complications have not been reported (7–9,16). Permanent liver damage (17) or brain damage (18) has also not been reported in patients who survived hypernatremia. It has, likewise, been reported that the induction of liver cell apoptosis was significantly decreased by using hypertonic saline solution instead of Ringer’s lactate in the resuscitation for hemorrhagic shock in a rat model (19). Our findings also showed that hypernatremia did not significantly affect liver function of the donors at the time of liver removal. This implies that resuscitation of patients in shock, who could be potential organ donors, with hypertonic saline need not be considered a contraindication or deterrent to liver donation. Furthermore, contrary to previous reports (5,14), correction of the hypernatremia in a potential organ donor may not always be required. This may be relevant in the clinical setting, because the urgency of the situation will often not allow time for correction of all electrolyte imbalances.
Posttransplant liver function variables between recipients of the two groups were comparable, although they remained high because there was no re-arterialization of the graft in the rat OLT model used (11,12). The survival rate after OLT was apparently not affected by hypernatremia in the donors because recipient rats in both groups survived 100%. Preservation of liver grafts in UW solution with a six-hour delay to implantation also did not adversely affect survival. The reason why our findings do not correlate with the observation in human OLT using organs from hypernatremic donors (2,3,5) is not clear but may be because of the short duration of the induced hypernatremic state in the rat. Increased serum sodium induced by the administration of 10% hypertonic saline solution lasted only approximately three hours after the infusion and normalized on the sixth hour (Fig. 1). On the contrary, the hypernatremia seen in brain-dead patients is long lasting and usually caused by DI (20–23) instead of improper crystalloid administration (24). Nevertheless, in this experiment, the graft was still in a hypernatremic environment at the time of procurement.
Hypernatremia primarily affects central nervous system function by causing cellular dehydration (25). Because sodium ions cannot freely cross the cell membrane, intracellular water shifts into the extracellular space with subsequent cellular dehydration. Severe brain dehydration leads to mechanical traction on cerebral blood vessels and may cause bleeding (26). The clinical features of hypernatremia are mainly neurologic and include impaired mentation, weakness, lethargy, obtundation, coma, seizures, and death (17,24,26). However, the mechanism of how hypernatremia leads to cellular damage in hepatocytes is not yet clear. The hypothesis proposed by Gonzalez et al. (3) –that sudden change of extracellular osmolarity immediately after reperfusion of a liver graft obtained from a hypernatremic donor could cause intracellular water accumulation and hepatocyte injury–could not be confirmed in our study. The hypernatremia that we induced did not affect the water content of the liver or the liver enzymes of the donors (Table 2).
Another drawback in this study is that the donor rats were neither in shock nor in a brain-dead state at the time of liver procurement. However, our results concur with those reported by Florman et al. (4) who also demonstrated that hyperosmolarity-induced DI did not affect survival after liver transplantation in nonbrain-dead rats. Therefore, hypernatremia and hyperosmolarity associated with DI itself do not seem to be the major determinants of primary graft loss after OLT (2). Hypernatremia must at least be associated with brain death, which is a more complex process producing profound alterations of the endocrine system and electrolyte balance (27) affecting all organ systems in a complicated way. Graft survival may well be affected by conditions in the recipient. Wang et al. (28) have suggested that liver graft survival in rats is a function of disease in the recipient rather than donor-related factors. This observation is also often true in the clinical setting.
In conclusion, our rat model demonstrated that acute donor hypernatremia induced by an IV infusion of 10% saline solution before graft procurement did not affect the survival of recipient rats after OLT. It seems that the administration of hypernatremic solution itself does not affect the quality of the liver in nonbrain-dead rats.
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© 2002 International Anesthesia Research Society
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