Author Affiliations: Division of Hepatobiliary Pancreatic Surgery (Zhang WJ, Xia WL and Zheng SS), and Geriatrics Center (Pan HY), First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, China

Corresponding Author: Shu-Sen Zheng, MD, PhD, FACS, Division of Hepatobiliary Pancreatic Surgery, First Affiliated Hospital, Zhejiang University School of Medicine, 79 Qingchun Road, Hangzhou 310003, China (Tel: +86-571-87236570; Email: shusenzheng@zju.edu.cn)

 

© 2016, Hepatobiliary Pancreat Dis Int. All rights reserved.

doi: 10.1016/S1499-3872(16)60116-9

Published online July 13, 2016.

 

 

Contributors: ZSS proposed the study. ZWJ wrote the first draft. ZWJ, XWL and PHY collected and analyzed the data. All authors contributed to the design and interpretation of the study and to further drafts. ZSS is the guarantor.

Funding: None.

Ethical approval: This study was approved by the Ethics Committee of the First Affiliated Hospital of Zhejiang University School of Medicine.

Competing interest: No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

 

 

BACKGROUND: With the increasing use of donation after cardiac death (DCD), especially of the graft liver with steatosis or other pathological changes, the frequency of postreperfusion hyperkalemia in liver transplantation has increased significantly. The present study aimed to determine the factors associated with developing postreperfusion hyperkalemia in liver transplantation from DCD.

 

METHODS: One hundred thirty-one consecutive adult patients who underwent orthotopic liver transplantation from DCD were retrospectively studied. Based on serum potassium within 5 minutes after reperfusion, recipients were divided into two groups: hyperkalemia and normokalemia. According to preoperative biopsy results, the DCD graft livers were classified into five categories. Univariate analysis was performed using Chi-square test to identify variables that were significantly different between two groups. Multivariate logistic regression was used to confirm the risk factors of developing hyperkalemia and postreperfusion syndrome. Correlation analysis was used to identify the relationship between the serum concentration of potassium within 5 minutes after reperfusion and the difference in mean arterial pressure values before and within 5 minutes after reperfusion.

 

RESULTS: Twenty-two of 131 liver recipients had hyperkalemia episodes within 5 minutes after reperfusion. The rate of hyperkalemia was significantly higher in recipients of macrosteatotic DCD graft liver (78.6%, P<0.001) than that in recipients of non-macrosteatotic DCD graft liver. The odds ratio of developing postreperfusion hyperkalemia in recipients of macrosteatotic DCD graft liver was 51.3 (P<0.001). Macrosteatosis in the DCD graft liver was an independent risk factor of developing hyperkalemia within 5 minutes after reperfusion. The highest rate of postreperfusion syndrome also occurred in the recipients with macrosteatotic DCD graft liver (71.4%, P<0.001). A strong relationship existed between the serum potassium within 5 minutes after reperfusion and the difference in mean arterial pressure values before and within 5 minutes after reperfusion in macrosteatotic DCD graft liver recipients.

 

CONCLUSION: Macrosteatosis in the DCD graft liver was an independent risk factor of developing hyperkalemia and postreperfusion syndrome in the recipients.

 

(Hepatobiliary Pancreat Dis Int 2016;15:487-492)

 

KEY WORDS: liver transplantation; hyperkalemia; reperfusion injury; macrosteatosis

 

 

Severe hyperkalemia is a serious complication during orthotopic liver transplantation (OLT). Xia et al^[1] showed that it can occur in both prereperfusion and postreperfusion period during OLT operation. Hyperkalemia episodes were also found to be more frequent in early postreperfusion, a short period within 5 minutes after reperfusion of the graft liver, than at other phases during OLT.^{[1, 2]}

 

In general, the causes of hyperkalemia during the early postreperfusion period are considered to be: i) extracellular shift in H⁺ exchange because of severe metabolic acidosis in the anhepatic phase, ii) exogenous potassium with the transfusion of red blood cell (RBC), and iii) the preservative fluid University of Wisconsin (UW) solution, which contains a high potassium concentration, flow into systemic circulation during reperfusion of the graft liver.^[3-5] To prevent potassium flow into system circulation, cold lactated Ringer’s solution with albumin has been routinely used to flush out UW solution, and blood (300-500 mL) was selectively vented via the vena cava before graft reperfusion. Units of intravenous insulin is routinely administered together with the RBC transfusion to transport extracellular potassium into cells and alkalizing agents were administered to counteract the severe metabolic acidosis during the operation period. However, despite these measures, the incidence of hyperkalemia episodes in the early postreperfusion period of OLT did not decrease significantly when using liver grafts from donation after cardiac death (DCD). Several studies^{[1, 6]} have demonstrated that adopting DCD graft liver in OLT was an independent risk factor for postreperfusion hyperkalemia. Warm ischemia time was relatively longer in DCD graft liver than cadaver or brain death grafts, which may result in hypoxic damage to hepatocytes of DCD graft liver. After reperfusion, hepatocyte membrance suffered further damage because of oxygen free radicals which led to potassium release from hepatocytes.^[7-10] Previous studies^{[11, 12]} have also revealed that steatotic DCD graft livers were more sensitive to the ischemia/reperfusion injury.

 

The present study was to identify the pathological characteristics in DCD graft liver associated with postreperfusion hyperkalemia in adult recipients. We hypothesized that preexisting pathological changes in the DCD graft livers are associated with high incidence of postreperfusion hyperkalemia in the liver recipients.

 

 

The study population consisted of adult patients who underwent OLT from DCD in our hospital between March 1, 2011 and March 31, 2014. All recipients provided informed consent and the study was approved by the hospital ethics review committee. Recipient variables including age, gender, weight, model for end-stage liver disease (MELD) score, blood urea nitrogen, blood creatinine, baseline serum concentration of potassium and etiology of liver diseases were recorded and stored in our OLT database. Intraoperative variables including the units of transfused RBCs before reperfusion, anhepatic time, mean arterial pressure (MAP) and blood gas including pH, serum lactate level and base excess, were recorded and stored in our OLT database. Baseline serum potassium concentration was defined as the first intraoperative laboratory value or the value measured immediately before operation. MAP was measured directly via a catheter inserted into the radial artery. The difference in MAP values before and within 5 minutes after reperfusion was calculated and a 30% decrease in MAP during this period was considered postreperfusion syndrome (PRS). In addition to the routine check every hour, MAP, blood gas and serum potassium concentration were measured within 5 minutes after DCD graft liver reperfusion. Hyperkalemia was defined as serum potassium concentration >5.5 mmol/L.

 

The donor variables including liver biopsy before operation, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TB), intensive care unit (ICU) days, vasopressor administration, cold ischemia time (CIT) and warm ischemia time (WIT) were recorded in our OLT donor database. DCD donors were generally younger than 55 years with body mass index (BMI) lower than 30 kg/m², and serum aminotransferase levels at procurement were less than twice of the normal values. The CIT of DCD grafts was less than 12 hours. Artificial life supports of all DCD donors had a planned withdrawal in the operating room or ICU. An independent physician from the donor hospital was assigned to declare death. Following a 5-minute mandatory waiting period after asystole, procurement began. Livers were stored at 4 �� for transport after flushed with 4-6 L of cold UW solution via both the abdominal aorta and inferior mesenteric vein. In our study, graft procurement WIT started when the life support was withdrawn and ended when cold perfusion started. Biopsy of the DCD graft liver was routinely completed before OLT operation.

 

Recipients were divided into two groups according to serum potassium level within 5 minutes after reperfusion. Hyperkalemia group consisted of recipients with a serum potassium level >5.5 mmol/L; Normokalemia group with a serum potassium level ≤5.5 mmol/L. According to the results of routine biopsy before operation, the pathological characteristics of DCD graft livers were classified as 1) macrosteatosis, with ≥20% of hepatocytes demonstrating macrosteatosis; 2) microsteatosis, with ≥20% of hepatocytes demonstrating microsteatosis; 3) piecemeal necrosis of hepatocytes; 4) diffused swelling of hepatocytes; and 5) normal DCD liver with no significant pathologic changes. According the pathological classification of the adopted DCD graft liver, the recipients were also divided correspondingly into the following groups: 1) macrosteatosis group, 2) microsteatosis group, 3) piecemeal necrosis group, 4) diffused swelling group and 5) normal DCD liver group.

 

Data were expressed as mean±SD and median values for continuous variables, or as proportions for nonparametric variables. Chi-square test was performed to identify variables that demonstrated significant difference between hyperkalemia and normokalemia groups. Multivariate forward and backward-stepwise logistic regression modeling was then adopted to identify independent risk factor for developing hyperkalemia and PRS. The odds ratio (OR) and 95% confidence interval (CI) with associated P values for pathological variables were determined in the logistic models. A P<0.05 was considered statistically significant. Correlation analysis was used to identify the relationship between the serum concentration of potassium within 5 minutes after reperfusion and the difference in MAP values before and after reperfusion in the same period.

 

 

The preoperative characteristics of hyperkalemia and normokalemia groups were shown in Table 1. There were no significant differences of age, gender, weight, MELD score, blood urea nitrogen, blood creatinine or baseline potassium in the two groups. The predominant indications for OLT in all of these recipients were cirrhosis and hepatocellular carcinoma. One patient with fulminant hepatitis in hyperkalemia group and four in normokalemia group received OLT.

 

Intraoperative variables were shown in Table 2. The mean serum concentration of potassium within 5 minutes after reperfusion was 6.36±0.38 mmol/L in hyperkalemia group. The highest recorded potassium concentration in that group was 7.75 mmol/L, and hyperkalemic cardiac arrest occurred in 3 of 22 patients. The mean serum concentration of potassium in the same period was significantly lower, 3.64±0.59 mmol/L, in normokalemia group (P<0.001). The incidence of PRS was also significantly higher in hyperkalemia group (72.7%) than that in normokalemia group (24.8%, P<0.001). There were no significant differences of pH, base excess and serum lactate levels within 5 minutes after reperfusion in these two groups. The volume of RBC administration in the prereperfusion period, 4.36±2.61 U in hyperkalemia group and 4.09±3.47 U in normokalemia group, was not significantly different in these two groups. The anhepatic time was also demonstrated no significant difference.

 

The donor variables were shown in Table 3. In hyperkalemia group, 50.0% of the DCD graft livers demonstrated macrosteatosis, while the macrosteatosis rate in normokalemia group was significantly lower at 2.8% (P<0.001). The percentage of recipients with normal DCD graft liver was significantly different between hyperkalemia group (22.7%, 5/22) and normokalemia group (64.2%, 70/109, P<0.001). There were no significant differences of other variables in the two groups.

 

Because half of the recipients in the hyperkalemia group had macrosteatotic DCD graft liver, the incidence of early postreperfusion hyperkalemia and PRS in recipients were further analyzed according to pathological classification (Table 4).

 

The percentage of recipients with early postreperfusion hypekalemia was 78.6% in macrosteatosis group and 6.7% in normal DCD liver group (P<0.001).

 

The incidence of PRS in those of macrosteatosis (71.4%), microsteatosis (63.6%) and diffused swelling (59.1%) livers were significantly higher than that in the normal DCD liver (13.3%) (P<0.01). However, no significant difference in the incidence of PRS was detected among those of macrosteatosis, microsteatosis and diffused swelling livers.

 

Because the rates of both hyperkalemia and PRS were the highest in macrosteatotic group, the relationship between the level of serum potassium within 5 minutes after reperfusion and the difference in MAP values before and after reperfusion in the same period was analyzed in recipients of macrosteatotic DCD graft liver and all enrolled recipients. The Pearson correlation values were 0.60 (P=0.024) and 0.35 (P<0.001) in recipients with macrosteatotic DCD graft livers and all enrolled recipients, respectively. These results indicated a strong correlation between the level of the serum potassium within 5 minutes after reperfusion and the difference in MAP values before and after reperfusion in the same period in macrosteatotic DCD graft liver recipients and weak correlation in all enrolled recipients.

 

The biopsy results of DCD graft livers were included in multivariate logistic regression model to identify risk factors of developing hyperkalemia and PRS (Table 5). We found that macrosteatosis in DCD graft liver was the only predictor of the early postreperfusion hyperkalemia. The odds ratio of the developing early postreperfusion hyperkalemia in recipients of macrosteatotic DCD graft liver was 51.3 (P<0.001). Recipients of DCD graft liver with macrosteatosis had more than 50-fold increased odds of developing early postreperfusion hyperkalemia when compared with recipients of no macrosteatosis DCD graft liver.

 

The odds ratio of developing PRS in recipients with macrosteatosis, microsteatosis and diffuse swelling were 14.5, 10.2 and 8.4, respectively. Compared with recipients of no macrosteatosis DCD graft liver, recipients of macrosteatotic DCD graft liver had more than 14-fold increased odds of developing PRS; recipients of significant microsteatosis and diffused swelling DCD graft liver had 8-10 folds increased odds of developing PRS during OLT. Macrosteatosis, microsteatosis and diffused swelling in DCD graft liver were all independent predictors of developing PRS in OLT.

 

 

In OLT from DCD, severe hyperkalemia episode occurs most frequent in early postreperfusion period, which was defined as 1-5 minutes after reperfusion.^{[1, 2, 6]} The ischemic reperfusion injury has been considered one of the main reasons for the hyperkalemia episode during this period.^[13-17] Several factors have been proposed as responsible for warm ischemic injury of the DCD graft liver during OLT. The first is the hypoperfusion of the graft liver, because of the hypo-volume of system circulation in DCD donors.^{[16, 17]} The second is the vasopressor administration of donors during ICU treatment, which could exacerbate the hypoperfusion of the grafts by the effect of vasoconstriction.^{[16, 17]} The third is the 5-minute waiting period after asystole, which is mandatory before the procurement started.^[7] Based on these factors, the degree of warm ischemic injury is more significant in DCD graft livers than that in the donation from cadaver or brain death graft livers. Due to the effect of the warm ischemic reperfusion injury, the membranes of hepatocytes in DCD graft livers were damaged after reperfusion, resulting in the release of intracellular potassium to systemic circulation and ultimately to the marked increase in serum potassium level over a short period of time.^[8-10] In addition, preexisting pathological changes such as steatosis and diffuse swelling can make hepatocytes more sensitive to reactive oxygen radicals derived from ischemia/reperfusion.^{[11, 12, 15]} Han et al^[11] and Nativ et al^[12] reported that macrosteatotic livers exhibit elevated intrahepatic triglyceride levels in the form of large lipid droplets, reduced ATP levels, and elevated levels of reactive oxygen species, which contribute to their elevated sensitivity to ischemia/reperfusion injury during transplantation. Based on these previous studies and results in our study, we believed that warm ischemia/reperfusion injury is more serious in steatotic DCD graft liver and thus results in greater rates of hyperkalemia in the early postreperfusion period.

 

In the present study, the rates of both hyperkalemia and PRS were the highest in macrosteatotic group. Multivariate logistic regression analysis demonstrated that macrosteatosis in DCD graft liver is an independent risk factor of both developing PRS and hyperkalemia in early reperfusion period in OLT.

 

During ischemia/reperfusion period of the graft liver, the activation of the inflammatory cytokines, the kallikrein-kinin system, and nitric oxide synthase have been considered the most likely cause of PRS.^[18-21] Xia et al^[1] also reported that liver can release a large amount of intracellular potassium into systemic circulation when subjected to stress causing ischemia/reperfusion injury. In this study, correlation analysis revealed a strong relationship between serum potassium within 5 minutes after reperfusion and the difference in MAP values before and after reperfusion in the same period in macrosteatotic DCD graft liver recipients. These results indicated that recipients of macrosteatotic DCD graft liver may be more prone to early postreperfusion hyperkalemia and PRS.

 

Since this study is purely clinical retrospective study, the exact mechanism of correlation between warm ischemia reperfusion injury and hyperkalemia within 5 minutes after reperfusion was no explored. Previous studies^[13-15] revealed that oxygen-derived free radicals play an important role in the genesis of PRS.

 

Multivariate logistic regression analysis also demonstrated that significant microsteatosis and diffuse swelling in DCD graft liver were independent risk factors of developing PRS but not early postreperfusion hyperkalemia. Insulin administration during OLT may be responsible for this phenomenon. In the present study, to prevent hyperkalemia after reperfusion, bolus of regular insulin was routinely administered intravenously during the anhepatic stage, especially in patients with a base serum potassium level above 4.0 mmol/L. Our findings implied that the administration of regular insulin efficiently prevent postreperfusion hyperkalemia in recipients of DCD liver with microsteatosis or diffuse swelling, while it did not work efficiently in recipients of macrosteatotic DCD graft livers.

 

Other factors including MELD score, graft CIT and WIT, vasopressor administration, RBC transfusion, and ICU days before procurement were also compared between the hyperkalemia and normokalemia groups, and no significant difference in these factors were observed between recipients with and without early postreperfusion hyperkalemia.

 

Severe metabolic acidosis in the anhepatic phase may also contribute to hyperkalemia after reperfusion. In our study, sodium bicarbonate was used to correct metabolic acidosis (base excess <4), and no significant difference in the blood gas within 5 minutes after reperfusion, including pH, base excess and serum lactate level, was found between groups with and without early postreperfusion hyperkalemia. Furthermore, the hyperkalemia and nomokalemia groups, did not significantly differ in an-hepatic time. These results suggested that the factor of severe metabolic acidosis had no effects on development of early postreperfusion hyperkalemia in all enrolled recipients in our study.

 

In conclusion, significant macrosteatosis in DCD graft liver was an independent risk factor of developing hyperkalemia episode within 5 minutes after reperfusion, and it was not prevented efficiently by the insulin administration.

 

 

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