Metabolic changes in the liver graft monitored continuously with microdialysis during liver transplantation in a pig model

Effects of Subnormothermic Regulated Hepatic Reperfusion on Mitochondrial and Transcriptomic Profiles in a Porcine Model

OBJECTIVE

We sought to investigate the biological effects of pre-reperfusion treatments of the liver after warm and cold ischemic injuries in a porcine donation after circulatory death model.

SUMMARY OF BACKGROUND DATA

Donation after circulatory death represents a severe form of liver ischemia and reperfusion injury that has a profound impact on graft function after liver transplantation.

METHODS

Twenty donor pig livers underwent 60 minutes of in situ warm ischemia after circulatory arrest and 120 minutes of cold static preservation prior to simulated transplantation using an ex vivo perfusion machine. Four reperfusion treatments were compared: Control-Normothermic (N), Control- Subnormothermic (S), regulated hepatic reperfusion (RHR)-N, and RHR-S (n = 5 each). The biochemical, metabolic, and transcriptomic profiles, as well as mitochondrial function were analyzed.

RESULTS

Compared to the other groups, RHR-S treated group showed significantly lower post-reperfusion aspartate aminotransferase levels in the reperfusion effluent and histologic findings of hepatocyte viability and lesser degree of congestion and necrosis. RHR-S resulted in a significantly higher mitochondrial respiratory control index and calcium retention capacity. Transcriptomic profile analysis showed that treatment with RHR-S activated cell survival and viability, cellular homeostasis as well as other biological functions involved in tissue repair such as cytoskeleton or cytoplasm organization, cell migration, transcription, and microtubule dynamics. Furthermore, RHR-S inhibited organismal death, morbidity and mortality, necrosis, and apoptosis.

CONCLUSION

Subnormothermic RHR mitigates IRI and preserves hepatic mitochondrial function after warm and cold hepatic ischemia. This organ resuscitative therapy may also trigger the activation of protective genes against IRI. Sub- normothermic RHR has potential applicability to clinical liver transplantation.

Molecular Mechanisms of Ischaemia-Reperfusion Injury and Regeneration in the Liver-Shock and Surgery-Associated Changes

Hepatic ischemia-reperfusion injury (IRI) represents a major challenge during liver surgery, liver preservation for transplantation, and can cause hemorrhagic shock with severe hypoxemia and trauma. The reduction of blood supply with a concomitant deficit in oxygen delivery initiates various molecular mechanisms involving the innate and adaptive immune response, alterations in gene transcription, induction of cell death programs, and changes in metabolic state and vascular function. Hepatic IRI is a major cause of morbidity and mortality, and is associated with an increased risk for tumor growth and recurrence after oncologic surgery for primary and secondary hepatobiliary malignancies. Therapeutic strategies to prevent or treat hepatic IRI have been investigated in animal models but, for the most part, have failed to provide a protective effect in a clinical setting. This review focuses on the molecular mechanisms underlying hepatic IRI and regeneration, as well as its clinical implications. A better understanding of this complex and highly dynamic process may allow for the development of innovative therapeutic approaches and optimize patient outcomes.

Integrative Network Analysis Revealed Genetic Impact of Pyruvate Kinase L/R on Hepatocyte Proliferation and Graft Survival after Liver Transplantation

Background

Pyruvate kinase L/R (PKLR) has been suggested to affect the proliferation of hepatocytes via regulation of the cell cycle and lipid metabolism. However, its impact on the global metabolome and its clinical implications remain unclear.

Aims

We aimed to clarify the genetic impact of PKLR on the metabolomic profiles of hepatoma cells and its potential effects on grafts for liver transplantation (LT).

Methods

Nontargeted and targeted metabolomic assays were performed in human hepatoma cells transfected with lentiviral vectors causing PKLR overexpression and silencing, respectively. We then constructed a molecular network based on integrative analysis of transcriptomic and metabolomic data. We also assessed the biological functions of PKLR in the global metabolome in LT grafts in patients via a weighted correlation network model.

Results

Multiomic analysis revealed that PKLR perturbations significantly affected the pyruvate, citrate, and glycerophospholipid metabolism pathways, as crucial steps in de novo lipogenesis (DNL). We also confirmed the importance of phosphatidylcholines (PC) and its derivative lyso-PC supply on improved survival of LT grafts in patients. Coexpression analysis revealed beneficial effects of PKLR overexpression on posttransplant prognosis by alleviating arachidonic acid metabolism of the grafts, independent of operational risk factors.

Conclusion

This systems-level analysis indicated that PKLR affected hepatoma cell viability via impacts on the whole process of DNL, from glycolysis to final PC synthesis. PKLR also improved prognosis after LT, possibly via its impact on the increased genesis of beneficial glycerophospholipids.

Clinical assessment of liver metabolism during hypothermic oxygenated machine perfusion using microdialysis

Background

While growing evidence supports the use of hypothermic oxygenated machine perfusion (HOPE) in liver transplantation, its effects on liver metabolism are still incompletely understood.

Methods

To assess liver metabolism during HOPE using microdialysis (MD), we conducted an open‐label, observational pilot study on 10 consecutive grafts treated with dual‐HOPE (D‐HOPE). Microdialysate and perfusate levels of glucose, lactate, pyruvate, glutamate, and flavin mononucleotide (FMN) were measured during back table preparation and D‐HOPE and correlated to graft function and patient outcome.

Results

Median (IQR) MD and D‐HOPE time was 228 (210, 245) and 116 (103, 143) min. Three grafts developed early allograft dysfunction (EAD), with one requiring retransplantation. During D‐HOPE, MD glucose and lactate levels increased (ANOVA = 9.88 [p = 0.01] and 3.71 [p = 0.08]). Their 2nd‐hour levels were higher in EAD group and positively correlated with L‐GrAFT score. 2nd‐hour MD glucose and lactate were also positively correlated with cold ischemia time, macrovesicular steatosis, weight gain during D‐HOPE, and perfusate FMN. These correlations were not apparent when perfusate levels were considered. In contrast, MD FMN levels invariably dropped steeply after D‐HOPE start, whereas perfusate FMN was higher in dysfunctioning grafts.

Conclusion

MD glucose and lactate during D‐HOPE are markers of hepatocellular injury and could represent additional elements of the viability assessment.

Intrahepatic Microdialysis for Monitoring of Metabolic Markers to Detect Rejection Early After Liver Transplantation

OBJECTIVES

The clinical and biochemical manifestations of acute rejection after liver transplantation are nonspecific, and a liver biopsy is often needed to verify the diagnosis. This may delay treatment. The aim of this study was to evaluate whether monitoring of intrahepatic glucose, lactate, pyruvate, and glycerol by microdialysis can be used to predict rejection early after liver transplantation.

METHODS

Seventy-one patients undergoing liver transplantation were included in the study. The patients were monitored using microdialysis for up to 6 days postoperatively. Patients who developed acute rejection within 1 month were identified according to standard protocol. Area under the curve (AUC) was calculated for 12-hour intervals for glucose, lactate, pyruvate, glycerol, and lactate/pyruvate ratio. Patients with and without rejection were compared with respect to these parameters, as well as standard liver blood investigations and time-zero biopsies.

RESULTS

The lactate/pyruvate ratio was higher at 0 to 12 hours in the group with rejection as compared to the group without rejection. Glucose was lower in the group with rejection at 24 to 48 hours. Also, the intrahepatic lactate levels at 48 to 72 hours and pyruvate levels at 60 to 72 hours after liver transplantation, were higher in the rejection group. The lactate/pyruvate ratio at 0 to 12 hours and lactate at 60 to 72 hours were two independent risk factors for rejection within the first month after liver transplantation. No significant differences in glycerol levels could be detected between the two patient groups.

CONCLUSIONS

Microdialysis monitoring following liver transplantation may be useful in the detection of the metabolic events that precede rejection. The metabolic patterns detected by microdialysis early after transplantation indicate a possible relation between primary ischemia-reperfusion injury and the development of rejection. Identifying these patterns may help to identify patients at risk for the development of acute rejection and may help select those who may benefit from higher dose of immunosuppression early after liver transplantation.

Evaluation of Intrahepatic Lactate/Pyruvate Ratio As a Marker for Ischemic Complications Early After Liver Transplantation-A Clinical Study

Background.

Lactate/pyruvate ratio has been introduced as a sensitive marker for ischemia in the transplanted liver. In the present study, we aimed to evaluate lactate/pyruvate ratio measured in the liver by microdialysis as a marker for ischemic complications early after liver transplantation.

Methods.

Forty-five patients undergoing liver transplantation were included in the study. A microdialysis catheter was placed in the liver graft directly following liver transplantation and the metabolites lactate and pyruvate measured for up to 6 days and the lactate/pyruvate ratio calculated. The association between increased intrahepatic lactate/pyruvate ratio and ischemic complications was studied.

Results.

One of 45 patients developed hepatic arterial thrombosis. Forty-four events with increased lactate/pyruvate ratio were identified in 24 patients. In none of the 24 patients that had a raised lactate/pyruvate ratio could we detect occurrence of any ischemic complication. In the patient that did have hepatic arterial thrombosis, the lactate/pyruvate ratio did not show a significant prolonged rise.

Conclusions.

An increase in the intrahepatic lactate/pyruvate ratio is not necessarily indicative of ischemic complications and is thus not a reliable marker for monitoring of clinically significant ischemia in the liver early after transplantation.

Beneficial effects of the novel marine oxygen carrier M101 during cold preservation of rat and human pancreas

Ischaemia impairs organ quality during preservation in a time‐dependent manner, due to a lack of oxygen supply. Its impact on pancreas and islet transplantation outcome has been demonstrated by a correlation between cold ischaemia time and poor islet isolation efficiency. Our goal in the present study was to improve pancreas and islet quality using a novel natural oxygen carrier (M101, 2 g/L), which has been proven safe and efficient in other clinical applications, including kidney transplantation, and for several pre‐clinical transplantation models. When M101 was added to the preservation solution of rat pancreas during ischaemia, a decrease in oxidative stress (ROS), necrosis (HMGB1), and cellular stress pathway (p38 MAPK)activity was observed. Freshly isolated islets had improved function when M101 was injected in the pancreas. Additionally, human pancreases exposed to M101 for 3 hours had an increase in complex 1 mitochondrial activity, as well as activation of AKT activity, a cell survival marker. Insulin secretion was also up‐regulated for isolated islets. In summary, these results demonstrate a positive effect of the oxygen carrier M101 on rat and human pancreas during preservation, with an overall improvement in post‐isolation islet quality.

Upregulation of Krebs cycle and anaerobic glycolysis activity early after onset of liver ischemia

The liver is a highly vascularized organ receiving a dual input of oxygenated blood from the hepatic artery and portal vein. The impact of decreased blood flow on glucose metabolism and how hepatocytes could adapt to this restrictive environment are still unclear. Using the left portal vein ligation (LPVL) rat model, we found that cellular injury was delayed after the onset of liver ischemia. We hypothesized that a metabolic adaptation by hepatocytes to maintain energy homeostasis could account for this lag phase. Liver glucose metabolism was characterized by ¹³C- and ¹H-NMR spectroscopy and analysis of high-energy metabolites. ALT levels and caspase 3 activity in LPVL animals remained normal during the first 12 h following surgery (P<0.05). Ischemia rapidly led to decreased intrahepatic tissue oxygen tension and blood flow (P<0.05) and increased expression of Hypoxia-inducible factor 1-alpha. Intrahepatic glucose uptake, ATP/ADP ratio and energy charge level remained stable for up to 12 h after ligation. Entry of glucose in the Krebs cycle was impaired with lowered incorporation of ¹³C from [U^-13C]glucose into glutamate and succinate from 0.25 to 12 h after LPVL. However, total hepatic succinate and glutamate increased 6 and 12 h after ischemia (P<0.05). Glycolysis was initially reduced (P<0.05) but reached maximum ¹³C-lactate (P<0.001) and ¹³C-alanine (P<0.01) enrichments 12 h after LPVL. In conclusion, early liver homeostasis stems from an inherent ability of ischemic hepatocytes to metabolically adapt through increased Krebs cycle and glycolysis activity to preserve bioenergetics and cell viability. This metabolic plasticity of hepatocytes could be harnessed to develop novel metabolic strategies to prevent ischemic liver damage.

Comparison of Intraoperative Changes in Blood Glucose According to Model for End-stage Liver Disease Score During Living Donor Liver Transplantation

BACKGROUND

Recipients of liver transplantation (LT) may experience disturbance of blood glucose balance, which is aggravated by various exogenous factors. The Model for End-stage Liver Disease (MELD) score is an indicator of the severity of pretransplantation liver disease. In this study, we investigated the role of the MELD score in intraoperative changes in blood glucose in patients undergoing living donor LT (LDLT).

METHODS

Perioperative data from 280 patients undergoing LDLT were reviewed, including glucose-related data. Intraoperatively, blood glucose levels were checked every hour, and the mean values at each phase of LDLT were calculated. Patients were divided into high and low MELD groups. An unpaired t-test and repeated measures analysis of variance (RMANOVA) were used in intergroup and intragroup comparisons of perioperative blood glucose.

RESULTS

The high MELD group consisted of 79 patients. Both the time sequential change during LDLT and the interaction between perioperative blood glucose and MELD score were significant (RMANOVA with multivariate adjustment; P < .05). Pretransplant blood glucose levels did not differ between the 2 groups, but the mean levels of blood glucose were lower and the incidence of hypoglycemia was higher in the high compared with the low MELD group during all phases of LDLT (P < .05).

CONCLUSIONS

Blood glucose levels progressively increased during LDLT with an interaction with the MELD score. Patients with a high MELD score had low blood glucose levels and a greater incidence of intraoperative hypoglycemia. MELD score is a useful determinant of intraoperative blood glucose levels in LDLT patients.

Outcome of microdialysis sampling on liver surface and parenchyma

BACKGROUND

To investigate whether surface microdialysis (μD) sampling in probes covered by a plastic film, as compared to noncovered and to intraparenchymatous probes, would increase the technique's sensitivity for pathophysiologic events occurring in a liver ischemia-reperfusion model. Placement of μD probes in the parenchyma of an organ, as is conventionally done, may cause adverse effects, e.g., bleeding, possibly influencing outcome.

METHODS

A transient ischemia-reperfusion model of the liver was used in six anesthetized normoventilated pigs. μD probes were placed in the parenchyma and on the liver surface. Surface probes were either left uncovered or were covered by plastic film.

RESULTS

Lactate and glucose levels were significantly higher in plastic film covered probes than in uncovered surface probes throughout the ischemic period. Glycerol levels were significantly higher in plastic film covered probes than in uncovered surface probes at 30 and 45 min into ischemia.

CONCLUSIONS

Covering the μD probe increases the sensibility of the μD-technique in monitoring an ischemic insult and reperfusion in the liver. These findings confirm that the principle of surface μD works, possibly replacing need of intraparenchymatous placement of μD probes. Surface μD seemingly allows, noninvasively from an organ's surface, via the extracellular compartment, assessment of intracellular metabolic events. The finding that covered surface μD probes allows detection of local metabolic changes earlier than do intraparenchymatous probes, merit further investigation focusing on μD probe design.

Predictive roles of intraoperative blood glucose for post-transplant outcomes in liver transplantation

Diabetogenic traits in patients undergoing liver transplantation (LT) are exacerbated intraoperatively by exogenous causes, such as surgical stress, steroids, blood transfusions, and catecholamines, which lead to intraoperative hyperglycemia. In contrast to the strict glucose control performed in the intensive care unit, no systematic protocol has been developed for glucose management during LT. Intraoperative blood glucose concentrations typically exceed 200 mg/dL in LT, and extreme hyperglycemia (> 300 mg/dL) is common during the neohepatic phase. Only a few retrospective studies have examined the relationship between intraoperative hyperglycemia and post-transplant complications, with reports of infectious complications or mortality. However, no prospective studies have been conducted regarding the influence of intraoperative hyperglycemia in LT on post-transplant outcome. In addition to absolute blood glucose values, the temporal patterns in blood glucose levels during LT may serve as prognostic features. Persistent neohepatic hyperglycemia (without a decline) throughout LT is a useful indicator of early graft dysfunction. Moreover, intraoperative variability in glucose levels may predict the need for reoperation for hemorrhage after LT. Thus, there is an urgent need for guidelines for glucose control in these patients, as well as prospective studies on the impact of glucose control on various post-transplant complications. This report highlights some of the recent studies related to perioperative blood glucose management focused on LT and liver disease.

Is microdialysis useful for early detection of acute rejection after kidney transplantation?

INTRODUCTION

Acute rejection following kidney transplantation (KTx) is still one of the challenging complications leading to chronic allograft failure. The aim of this study was to investigate the role of microdialysis (MD) in the early detection of acute graft rejection factor following KTx in porcine model.

METHODS

Sixteen pigs were randomized after KTx into case (n = 8, without immunosuppressant) and control groups (n = 8, with immunosuppressant). The rejection diagnosis in our groups was confirmed by histopathological evidences as "acute borderline rejection". Using MD, we monitored the interstitial concentrations of glucose, lactate, pyruvate, glutamate and glycerol in the transplanted grafts after reperfusion.

RESULTS

In the early post-reperfusion phase the lactate level in our case group was significantly higher comparing to the control group and remained in higher levels until the end of monitoring. The lactate to pyruvate ratio showed a considerable increase in the case group during the post-reperfusion phase. The other metabolites (glucose, glycerol, glutamate) were nearly at the same levels at the end of our monitoring in both study groups.

CONCLUSION

The increase in lactate and lactate to pyruvate ratios seems to be an indicator for early detection of acute rejection after KTx. Therefore, MD as a minimally invasive measurement tool may help to identify the need to immunosuppression adjustment in the early KTx phase before the clinical manifestation of the rejection.

Ischemic injury of the liver in a porcine model of cardiac death assessed by in vivo microdialysis

This study aims to evaluate the ischemic injury of the liver in a porcine model of cardiac death assessed by in vivo microdialysis. A porcine model of cardiac death was established by the suffocation method. Metabolic indicators were monitored using the microdialysis technique during warm ischemia time (WIT) and cold ischemia time (CIT). Pathological changes in ischemic-injured livers were observed by haematoxylin-eosin staining. The predictive values of biochemical parameters regarding the liver donor were evaluated by receiver operating characteristic curve analysis. All statistical analyses were conducted using the SPSS 18.0 software (SPSS Inc, Chicago, Illinois, USA). The degree of warm ischemic injury of the livers increased with prolonged WIT. Serum glucose, glycerol, pyruvate, lactic acid levels and lactate-to-pyruvate (L/P) ratio increased gradually during WIT. Results from Pearson correlation analyses indicated that serum lactate level and L/P ratio were positively associated with the degree of warm ischemic injury of the livers. The degree of cold ischemic injury of the livers gradually increased after 12 h CIT. Serum glucose, lactic acid and L/P ratio achieved a peak after 6-8 h of CIT, but gradually decreased with prolonged CIT. The peak of glycerol occurred after 8 h of CIT, while no changes were found with prolonged CIT. Serum pyruvate level exhibited an increasing trend after 12 h CIT. Our results confirmed that serum glucose and lactate levels were negatively correlated with cold ischemic injury of the liver. However, serum glycerol and pyruvate levels showed positive correlations with cold ischemic injury of the liver. The liver donor was unavailable after 30 min WIT and 24 h CIT. The cut-off value of serum lactate level for warm ischemic injury of the livers was 2.374 with a sensitivity (Sen) of 90 % and specificity (Spe) of 95 %; while the L/P radio was 0.026 (Sen = 80 %, Spe = 83 %). In addition, the cut-off values of serum glucose, lactate, glycerol and pyruvate levels for cold ischemic injury of the livers were 0.339 (Sen = 100 %, Spe = 77 %), 1.172 (Sen = 100 %, Spe = 61 %), 56.359 (Sen = 100 %, Spe = 65 %) and 0.020 (Sen = 100 %, Spe = 67 %), respectively. Our findings provide empirical evidences that serum glucose, lactate levels and L/P ratio may be good indicators for the degree of warm ischemic injury of the livers after cardiac death; while serum glucose, lactate, glycerol and pyruvate levels may be important in predicting cold ischemic injury.

Comparison of energy metabolism in liver grafts from donors after circulatory death and donors after brain death during cold storage and reperfusion

Background

Donation after circulatory death (DCD) liver grafts have supplemented the donor organ pool, but certain adverse outcomes have prevented exploration of the full potential of such organs. The aim of this study was to determine key differences in basic energy metabolism between DCD and donation after brainstem death (DBD) grafts.

Methods

Microdialysis samples from DCD and DBD allograft parenchyma from cold storage to 48 h after reperfusion were analysed by colorimetric methods. Interstitial lactate, pyruvate and glycerol levels were measured and the lactate/pyruvate ratio was calculated to estimate energy depletion of the grafts. Histological features of ischaemia and reperfusion injury were assessed.

Results

Donor age, extent of steatosis and cold ischaemia time were comparable between ten DCD and 20 DBD organs. DCD grafts had higher levels of interstitial lactate (median 11·6 versus 1·2 mmol/l; P = 0·015) and increased lactate/pyruvate ratio (792 versus 38; P = 0·001) during cold storage. There was no significant difference in glycerol levels between DCD and DBD grafts (225·1 versus 127·5 µmol/l respectively; P = 0·700). Rapid restoration of energy levels with lactate clearance, increased pyruvate levels and reduced lactate/pyruvate ratio was seen following reperfusion of functioning DCD grafts, parallel with levels in DBD grafts. Histology revealed more pronounced glycogen depletion in DCD grafts. Three allografts that failed owing to primary non-function showed energy exhaustion with severe glycogen depletion.

Conclusion

Liver grafts from DCD donors exhibited depletion of intracellular energy reserves during cold storage. Failed allografts showed severe energy depletion. Modified organ preservation techniques to minimize organ injury related to altered energy metabolism may enable better utilization of donor organs after circulatory death.

Membrane cut-off does not influence results regarding the measurement of small molecules - a comparative study between 20- and 100-kDa catheters in hepatic microdialysis

BACKGROUND

Microdialysis is a method used to monitor hepatic tissue metabolism. Membranes with a molecular cut-off of 20 kilodalton (kDa) are currently used to measure the small metabolites glucose, glycerol, lactate and pyruvate. Using membranes with higher cut-off such as 100 kDa allows the possibility of measuring larger molecules but may affect results regarding small molecules. The aim was to compare microdialysis catheters with a cut-off of 20 and 100 kDa in the measurement of small molecules in a pig liver model.

METHODS

Four microdialysis catheters were inserted into the liver of each pig used in the experiment (n = 6). Two catheters with cut-off of 20 kDa were perfused with Ringer acetate, and two catheters with cut-off of 100 kDa: one perfused with Ringer acetate and one with hydroxyethyl starch (Voluven) at a flow rate of 0·3 μl min(-1). Dialysate samples were collected at 40-min intervals and analysed for glucose, glycerol, lactate and pyruvate.

RESULTS

Compared to the other catheters, the 100-kDa catheters perfused with Ringer acetate tended to measure higher dialysate concentrations of the small molecules, the difference reaching statistical significance in the case of pyruvate. Concentrations measured by the 100-kDa catheters perfused with Voluven were, however, comparable to the 20-kDa catheters.

CONCLUSIONS

Microdialysis catheters with membrane cut-off of 20 and 100 kDa can be used equally in hepatic microdialysis for the monitoring of glucose, glycerol, lactate and pyruvate, and lactate/pyruvate ratio if a high osmotic solution (Voluven) is used to perfuse the 100-kDa catheters.

Early detection of subclinical organ dysfunction by microdialysis of the rectus abdominis muscle in a porcine model of critical intra-abdominal hypertension

The aim of this study was to evaluate microdialysis of the rectus abdominis muscle (RAM) for early detection of subclinical organ dysfunction in a porcine model of critical intra-abdominal hypertension (IAH). Microdialysis catheters for analyses of lactate, pyruvate, and glycerol levels were placed in cervical muscles (control), gastric and jejunal wall, liver, kidney, and RAM of 30 anesthetized mechanically ventilated pigs. Catheters for venous lactate and interleukin 6 samples were placed in the jugular, portal, and femoral vein. Intra-abdominal pressure (IAP) was increased to 20 mmHg (IAH20 group, n = 10) and 30 mmHg (IAH30, n = 10) for 6 h by controlled CO2 insufflation, whereas sham animals (n = 10) exhibited a physiological IAP. In contrast to 20 mmHg, an IAH of 30 mmHg induced pathophysiological alterations consistent with an abdominal compartment syndrome. Microdialysis showed significant increase in the lactate/pyruvate ratio in the RAM of the IAH20 group after 6 h. In the IAH30 group, the strongest increase in lactate/pyruvate ratio was detected in the RAM and less pronounced in the liver and gastric wall. Glycerol increased in the RAM only. After 6 h, there was a significant increase in venous interleukin 6 of the IAH30 group compared with baseline. Venous lactate was increased compared with baseline and shams in the femoral vein of the IAH30 group only. Intra-abdominal pressure-induced ischemic metabolic changes are detected more rapidly and pronounced by microdialysis of the RAM when compared with intra-abdominal organs. Thus, the RAM represents an important and easily accessible site for the early detection of subclinical organ dysfunction during critical IAH.

Early detection of metabolic changes using microdialysis during and after experimental kidney transplantation in a porcine model

BACKGROUND

Microdialysis (MD) can detect organ-related metabolic changes before they become measurable in plasma through the biochemical parameters. This study aims to evaluate the early detection of metabolic changes during experimental kidney transplantation (KTx).

MATERIAL AND METHODS

During preparation of 8 donor kidneys, one MD catheter was inserted in the renal cortex and samples were collected. After a 6-hour cold ischemia time (CIT), kidneys were implanted in the 8 recipient pigs. Throughout the warm ischemia time (WIT) and after reperfusion, kidneys were monitored. The interstitial glucose, lactate, pyruvate, glutamate, and glycerol concentrations were evaluated.

RESULTS

A significant decline in glucose level was observed at the end of CIT. The lactate level was reduced to the minimum point of 0.35 ± 0.08 mmol/L in CIT. After reperfusion, lactate values raised significantly. During the WIT, the pyruvate level increased, continued until the end of the WIT. For glutamate, a steady increase was noted during explantation, CIT, WIT, and early reperfusion phases. The increase of glycerol value continued in the early postreperfusion, which was then followed by a sharp decline.

CONCLUSION

MD is a fast and simple minimally invasive method for measurement of metabolic substrates in renal parenchyma during KTx. MD offers the option of detecting minor changes of interstitial glucose, lactate, pyruvate, glutamate, and glycerol in every stage of KTx. Through the use of MD, metabolic changes can be continuously monitored during the entire procedure of KTx.

N-acetyl cysteine improves glycogenesis after segmental liver ischemia and reperfusion injury in pigs

OBJECTIVE

N-acetylcysteine (NAC) is an antioxidative molecule known to protect liver tissue from oxygen radical species generated during ischemia and reperfusion (IR). Nutritional and toxicology studies have shown that NAC also improves glucose metabolism and glycogen stores. We hypothesized that NAC improves glycogenesis and that impaired glycogenesis is a key element in IR injury.

MATERIAL AND METHODS

In an experimental model, 80 min of segmental liver ischemia was induced in 16 pigs and the reperfusion was followed for 360 min. Eight animals received NAC 150 mg/kg as a bolus injection followed by an infusion of NAC 50 mg/kg/h intravenously.

RESULTS

AST and leukocyte density were lower in the NAC-treated animals, unrelated to the glutathione levels or apoptosis. Glycogen stores returned to a higher degree in the NAC-treated animals and microdialysis revealed lower levels of lactate during the reperfusion phase. Nitrite/Nitrate levels in the NAC group were lower in both serum and microdialysates, indicating that NAC scavenges radical nitrosative species.

CONCLUSIONS

NAC treatment improves glycogenesis after liver IR injury and reduces the level of intraparenchymal lactate during reperfusion, possibly due to the scavenging of radical nitrosative species.

Remote or conventional ischemic preconditioning--local liver metabolism in rats studied with microdialysis

BACKGROUND

Ischemic preconditioning (IPC) of the liver decreases liver injury secondary to ischemia and reperfusion. An attractive alternative to IPC is remote ischemic preconditioning (R-IPC), but these two methods have not previously been compared.

MATERIAL AND METHODS

Eighty-seven rats were randomized into four groups: sham operated (n = 15), 1 h segmental ischemia (IRI, n = 24), preceded by IPC (n = 24), or R-IPC (n = 24) (to the left hindleg). IPC and R-IPC were performed with 10 min ischemia and 10 min of reperfusion. Analyses of liver microdialysate (MD), serum transaminase levels, and liver histology were made.

RESULTS

Rats treated with IPC and R-IPC had significantly lower AST, 71.5 (19.6) IU/L respective 96.6 (12.4) at 4 h reperfusion than those subjected to IRI alone, 155 (20.9), P = 0.0004 and P = 0.04 respectively. IPC also had lower ALT levels, 41.6 (11.3) IU/L than had IRI 107.4 (15.5), P = 0.003. The MD glycerol was significantly higher during ischemia in the R-IPC [759 (84) μM] and the IRI [732 (67)] groups than in the IPC 514 (70) group, P = 0.022 and P = 0.046 respectively. The MD glucose after ischemia was lower in the IPC group 7.1 (1.2) than in the IRI group 12.7 (1.6), P = 0.005. Preconditioning to the liver caused an direct increase in lactate, glucose and glycerol in the ischemic segment compared with the control segment an effect not seen in the R-IPC and IRI groups.

CONCLUSIONS

IPC affects glucose metabolism in the rat liver, observed with MD. IPC reduces liver cell injury during ischemic and reperfusion in rats. R-IPC performed over the same length of time as IPC does not have the same effect as the latter on ALT levels and MD glycerol; this may suggest that R-IPC does not offer the same protection as IPC in this setting of rat liver IRI.

Using microdialysis for early detection of vascular thrombosis after kidney transplantation in an experimental porcine model

BACKGROUND

In kidney transplantation (KTx), vascular thrombosis has a major impact on morbidity and graft survival. The ischaemia, caused by thrombosis, can lead to interstitial metabolite changes. The aim of this experimental study was to create conditions in which the graft would be prone to vascular thrombosis following KTx and then to evaluate the role of microdialysis (MD) for its early detection.

METHODS

Sixteen randomized pigs in the control group received heparin and immunosuppressive drugs, while the case group received none. Based on histopathological evidence of vascular thrombosis, the case group was subdivided into mildly and severely congested subgroups. Using MD, we evaluated the interstitial concentrations of glucose, lactate to pyruvate ratio, glutamate and glycerol in the transplanted grafts during different phases of KTx.

RESULTS

Following reperfusion, we noted considerable changes. The severely congested subgroup showed a low and decreasing level of glucose. Only in this group did the lactate to pyruvate ratio continue to increase until the end of monitoring. The glycerol level increased continuously in the entire case group and this increase was most significant in the severely congested subgroup. In all of the study groups, glutamate concentration remained in a low steady state until the end of monitoring.

CONCLUSION

MD can be an appropriate method for early detection of vascular complications after KTx. Decreasing glucose levels, increased lactate to pyruvate ratio and increased glycerol levels are appropriate indicators for early detection of vascular thromboses following KTx. Particularly, the glycerol level could predict the necessity and urgency of intervention needed to ultimately save the transplanted kidney.

Continuous monitoring of glucose levels in the hepatic vein and systemic circulation during the Pringle maneuver in beagles

Intraoperative continuous glucose monitoring revealed that liver ischemia/reperfusion causes a rapid and profound transition in glucose concentration. We hypothesized that the washout of the glucose stored in the liver leads to a rapid transition in blood glucose concentration. Six female beagles were studied. A portosystemic shunt was established, and the glucose levels in the jugular, hepatic, and portal veins were continuously monitored. All beagles were stabilized for 30 min, and, subsequently, the hepatic artery and portal vein were clamped (the Pringle maneuver). After 30 min of warm hepatic ischemia, the clamp was removed in order to initiate hepatic reperfusion. The endpoint of the experiment was 60 min after the onset of reperfusion. The glucose levels in the abovementioned veins were recorded continuously. The glucose level in the hepatic vein increased 10 min after the start of the Pringle maneuver and was significantly higher than that in the jugular vein and portal vein just before unclamping. The glucose level in the hepatic vein peaked at 2 min after unclamping and that in the portal and jugular veins started to increase after reperfusion. The glucose level in the hepatic vein was significantly higher than that in the jugular and portal veins between 9 min after clamping and 8 min after reperfusion. In conclusion, our study among beagles showed that glucose release from the hepatic vein and sinusoid leads to a rapid elevation in systemic blood glucose levels after liver ischemia/reperfusion. This knowledge might help in the development of new strategies for blood glucose management during hepatectomy.

In vivo proton magnetic resonance spectroscopy of hepatic ischemia/reperfusion injury in an experimental model

RATIONALE AND OBJECTIVES

Hepatic ischemia/reperfusion injury (IRI) occurs during certain hepatobiliary surgeries, hemorrhagic shock, and veno-occlusive disease. Biochemical changes caused by hepatic IRI lead to hepatocellular remodeling, including cellular regeneration or irreversible apoptosis. This study aims to characterize and monitor the metabolic changes in hepatic IRI using proton magnetic resonance spectroscopy (¹H MRS).

MATERIALS AND METHODS

Sprague-Dawley rats (n = 8) were scanned with ¹H MRS using 5.0 × 5.0 × 5.0 mm³ voxel over a homogeneous liver parenchyma at 7 Tesla with a respiratory-gated point-resolved spectroscopy sequence at 1 day before, 6 hours, 1 day, and 1 week after 30 minutes total hepatic IRI. Signal integral ratios of choline-containing compounds (CCC), glycogen and glucose complex (Glyu), methylene proton ((-CH₂-)(n)), and methene proton (-CH=CH-) to lipid (integral sum of methyl proton (-CH₃), (-CH₂-)(n) and -CH=CH-) were quantified by areas under peaks longitudinally.

RESULTS

The CCC-to-lipid and Glyu-to-lipid ratios at 6 hours after IRI were significantly higher than those at 1 day before, 1 day, and 1 week after injury. The (-CH₂-)(n)-to-lipid, and -CH=CH-to-lipid ratios showed no significant differences over different time points. Hepatocellular regeneration was observed at 6 hours after IRI in histology with immunohistochemical technique.

CONCLUSIONS

Changes in CCC-to-lipid and Glyu-to-lipid ratios likely reflect the hepatocellular remodeling and impaired glucose utilization upon hepatic IRI, respectively. The experimental findings in the current study demonstrated that ¹H MRS is a valuable tool for characterizing either global or regional metabolic changes in liver noninvasively and longitudinally. Such capability has the potential to lead to early diagnosis and detection of impaired liver function.

Current state of hypothermic machine perfusion preservation of organs: The clinical perspective

This review focuses on the application of hypothermic perfusion technology as a topic of current interest with the potential to have a salutary impact on the mounting clinical challenges to improve the quantity and quality of donor organs and the outcome of transplantation. The ex vivo perfusion of donor organs on a machine prior to transplant, as opposed to static cold storage on ice, is not a new idea but is being re-visited because of the prospects of making available more and better organs for transplantation. The rationale for pursuing perfusion technology will be discussed in relation to emerging data on clinical outcomes and economic benefits for kidney transplantation. Reference will also be made to on-going research using other organs with special emphasis on the pancreas for both segmental pancreas and isolated islet transplantation. Anticipated and emerging benefits of hypothermic machine perfusion of organs are: (i) maintaining the patency of the vascular bed, (ii) providing nutrients and low demand oxygen to support reduced energy demands, (iii) removal of metabolic by-products and toxins, (iv) provision of access for administration of cytoprotective agents and/or immunomodulatory drugs, (v) increase of available assays for organ viability assessment and tissue matching, (vi) facilitation of a change from emergency to elective scheduled surgery with reduced costs and improved outcomes, (vii) improved clinical outcomes as demonstrated by reduced PNF and DGF parameters, (viii) improved stabilization or rescue of ECD kidneys or organs from NHBD that increase the size of the donor pool, (ix) significant economic benefit for the transplant centers and reduced health care costs, and (x) provision of a technology for ex vivo use of non-transplanted human organs for pharmaceutical development research.

Implantable sensor for blood flow monitoring after transplant surgery

A limited number of techniques are employed in clinical medicine for regional tissue perfusion assessment. These methods are marginally effective and are not well suited for implantation due to the inability to miniaturize the associated technologies. Consequently, no standardized techniques exist for real-time, continuous monitoring of organ perfusion following transplantation. In this paper, a brief overview of the relevant clinical techniques employed for regional tissue perfusion assessment is given with particular emphasis on post-surgical monitoring of transplanted organs. The ideal characteristics for a perfusion monitoring system are discussed and the development of a new, completely implanted local tissue monitoring system is summarized. <I>In vivo</I> and <I>in vitro</I> data are presented that establish the efficacy of this new technology, which is a photonics-based sensor system uniquely suited for continuous tissue monitoring and real-time data reporting. The suitablity of this sensor technology for miniaturization, which enables implantation for monitoring localized tissue perfusion, is discussed.

Hemodynamic alterations during orthotopic liver experimental transplantation in pigs

PURPOSE

To describe the hemodynamic alterations during orthotopic liver transplantation in pigs.

METHODS

In the period from April 2004 to December 2005, forty-four female Landrace pigs, weighting between 32 and 38 Kg underwent orthotopic liver transplantation. The animals were divided into two groups, donor and recipient pairs, which received whole liver grafts. The surgical procedure was divided into four parts: harvested, back-table, hepatectomy of the recipient and implantation. We analyzed heart rate, blood gas, mean systemic arterial pressure (MAP-mmHg), central venous pressure, pH, Na-, K+, Cl-, Ca+ and urinary output.

RESULTS

The mean anhepatic time was 69 min, cold ischemia was 252.2 min and back-table was 56.6 min. Blood pressure and heart rate dropped significantly during anhepatic phase and after revascularization. Blood gas and electrolytes alterations were observed during anhepatic and reperfusion phases. Although alterations were noted during these phases, the hemodynamic status was recovered and stabilized in the end of the surgery.

CONCLUSIONS

Simplified technique of liver transplant was achieved and description of hemodynamic alterations was possible in pigs.

Microdialysis monitoring of porcine liver metabolism during warm ischemia with arterial and portal clamping

Early detection of vascular complications following liver surgery is crucial. In the present study, intrahepatic microdialysis was used for continuous monitoring of porcine liver metabolism during occlusion of either the portal vein or the hepatic artery. Our aim was to assess whether microdialysis can be used to detect impaired vascular inflow by metabolic changes in the liver. Changes in metabolite concentrations in the hepatic interstitium were taken as markers for metabolic changes. After laparotomy, microdialysis catheters were introduced directly into the liver, enabling repeated measurements of local metabolism. Glucose, lactate, pyruvate, and glycerol were analyzed at bedside every 20 minutes, and the lactate/pyruvate ratio was calculated. In the arterial clamping group, the glucose, lactate, glycerol, and lactate/pyruvate ratio significantly increased during the 2-hour vessel occlusion and returned to baseline levels during the 3-hour reperfusion. In the portal occlusion group and in the control group, the measured metabolites were stable throughout the experiment. Our findings show that liver metabolism, as reflected by changes in the concentrations of glucose, lactate, and glycerol and in the lactate/pyruvate ratio, is markedly affected by occlusion of the hepatic artery. Surprisingly, portal occlusion resulted in no major metabolic changes. In conclusion, the microdialysis technique can detect and monitor arterial vascular complications of liver surgery, whereas potential metabolic changes in the liver induced by portal occlusion were not seen in the current study. Microdialysis may thus be suitable for use in liver surgery to monitor intrahepatic metabolic changes.

Current approach to intraoperative monitoring in liver transplantation

PURPOSE OF REVIEW

Although liver transplantation has become a standardized treatment and the only established definite therapy for end-stage liver disease it remains a unique clinical procedure. Increased understanding of the specific pathophysiological changes in end-stage liver disease and the transplantation procedure have led to the adaptation of concepts including overall monitoring of the patient and assessment of specific organ function.

RECENT FINDINGS

Major emphasis is placed on adequate monitoring during perioperative care of liver transplantation patients in order to ensure optimal hemodynamic and respiratory performance. The immediate assessment of metabolism and graft function will also serve to guide therapy according to the individual patient's needs.

SUMMARY

The evolution of monitoring during standardized liver transplantation, as well as currently recommended novel devices and concepts, are described and discussed.

The influence of preconditioning on metabolic changes in the pig liver before, during, and after warm liver ischemia measured by microdialysis

PURPOSE

Ischemia-reperfusion injury induced by the Pringle maneuver is a well-known problem after liver surgery. The aim of this study was to monitor metabolic changes in the pig liver during warm ischemia and the following reperfusion preceded by ischemic preconditioning (IPC).

METHODS

Eight Landrace pigs underwent laparotomy. Two microdialysis catheters were inserted in the liver, one in the left lobe and another in the right lobe. A reference catheter was inserted in the right biceps femoris muscle. Microdialysis samples were collected every 30 min during the study. After 2 h of baseline measurement, IPC was performed by subjecting pigs to 10 min of ischemia, followed by 10 min of reperfusion. Total ischemia for 60 min was followed by 3 h of reperfusion. The samples were analyzed for glucose, lactate, pyruvate, and glycerol. Blood samples were drawn three times to determine standard liver parameters.

RESULTS

All parameters remained stable during baseline. Glycerol and glucose levels increased significantly during ischemia, followed by a decrease from the start of reperfusion. During the ischemic period, lactate levels increased significantly and decreased during reperfusion. The lactate-pyruvate ratio increased significantly during ischemia and decreased rapidly during reperfusion. Only minor changes were observed in standard liver parameters.

CONCLUSIONS

The present study demonstrated profound metabolic changes before, during, and after warm liver ischemia under the influence of IPC. Compared with a similar study without IPC, the metabolic changes seem to be unaffected by preconditioning.

Metabolic changes in the pig liver during warm ischemia and reperfusion measured by microdialysis

AIM

Portal triad clamping can cause ischemia-reperfusion injury. The aim of the study was to monitor metabolic changes by microdialysis before, during, and after warm ischemia in the pigliver.

MATERIAL AND METHODS

Eight pigs underwent laparotomy followed by ischemia by Pringle's maneuver. One microdialysis catheter was placed in each of four liver lobes. A reference catheter was placed in a muscle. Microdialysis samples were collected at intervals of 30 min starting 2 h before 1 h of total ischemia followed by 3 h of reperfusion. Glucose, lactate, pyruvate, and glycerol concentrations were measured. Blood samples were drawn for determination of alanine aminotransferase, alkaline phosphatase, and bilirubin together with total leukocytes and prothrombin time.

RESULTS

All parameters were stable during the baseline period. During the ischemic period, lactate levels increased significantly (P < 0.05) followed by a rapid decrease after reperfusion. A transient increase was observed for glucose and glycerol. Pyruvate showed a slight increase from the time of ischemia. The lactate-pyruvate ratio increased rapidly after initiating ischemia and decreased immediately after reperfusion. A slight increase in transaminase levels was observed.

CONCLUSIONS

During and after warm ischemia, there were profound metabolic changes in the pigliver observed with an increase in lactate, glucose, glycerol, and the lactate-pyruvate ratio. There were no differences between the four liver lobes, indicating the piglivers homogeneity.

Microdialysis monitoring for evaluation of the influence exerted by pneumoperitoneum on the kidney: an experimental study

BACKGROUND

Laparoscopic donor nephrectomy has become the first choice for living donor kidney transplantation, offering advantages over open donor nephrectomy. This study aimed to evaluate kidney tissue metabolism during and after pneumoperitoneum using a microdialysis technique.

METHODS

Eight pigs underwent laparotomy and implantation of two microdialysis catheters: one in the cortex and one in the medulla of the left kidney. After laparotomy, the abdominal wall was closed, and pneumoperitoneum was induced with a constant standard pressure of 16 to 18 mmHg for 4 h, followed by rapid desufflation. In microdialysis samples collected from intrarenal catheters, markers of ischemia (glucose, lactate, pyruvate, and lactate-pyruvate ratio) and the marker of cell membrane injury (glycerol) were monitored.

RESULTS

There were no changes in glucose, lactate, or pyruvate level before, during, or after pneumoperitoneum, either in the cortex or in the medulla. Additionally, the calculated lactate-pyruvate ratio did not show signs of ischemia during or after pneumoperitoneum. However, with regard to the marker of cell injury, glycerol increased in the medulla after decompression from 22.57 +/- 3.76 to 35.67 +/- 5.43 mmol/l (p < 0.01). This release of glycerol in the medulla was significantly higher than in the cortex (area under the curve [AUC], 22.18 +/- 4.87 vs 34.79 +/- 7.88 mmol/l; p < 0.01).

CONCLUSIONS

The pattern of metabolic changes monitored in the kidney during and after pneumoperitoneum indicates some kind of cell injury predominant in the medulla without any signs of kidney ischemia. This nonischemic injury could be related to hyperperfusion of the kidney after decompression or injury to cells attributable to mechanical cell expansion at the point of rapid decompression.

Microdialysis of the rectus abdominis muscle for early detection of impending abdominal compartment syndrome

OBJECTIVE

To investigate whether microdialysis is capable of assessing metabolic derangements during intra-abdominal hypertension (IAH), and whether monitoring of the rectus abdominis muscle (RAM) by microdialysis represents a reliable approach in the early detection of organ dysfunctions in abdominal compartment syndrome (ACS).

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University animal research facility.

SUBJECTS

Fifteen isoflurane-anesthetized and mechanically ventilated Sprague-Dawley rats.

INTERVENTIONS

IAH of 20 mmHg was induced for 3 h and followed by decompression and reperfusion for another 3-h period (n = 10). Five sham-operated animals served as controls. Microdialysis was performed in the anterior gastric wall, liver, kidney, and RAM. The anterior cervical muscles served as distant reference. Glucose, lactate, pyruvate, and glycerol was analyzed throughout the 6-h experiment.

MEASUREMENTS AND MAIN RESULTS

Prolonged IAH induced significant cardiopulmonary dysfunction and persistent abdominal organ injury. Microdialysis revealed a significant increase of lactate/pyruvate and glycerol in kidney, intestine and liver, indicating ischemia, energy failure, and cell membrane damage. In addition, at 3 h IAH glucose was significantly decreased in all organs studied. The distant reference did not show any alteration of lactate/pyruvate, glycerol, and glucose over the entire 6-h observation period. In contrast to the other organs, microdialysis of the RAM showed an early and more pronounced increase of lactate, lactate/pyruvate and glycerol already at 1 h IAH. It is noteworthy that lactate, glycerol, and glucose did not completely recover upon decompression of IAH.

CONCLUSIONS

Our data suggest that continuous microdialysis in the RAM may represent a promising tool for early detecting IAH-induced metabolic derangements.

Effect of extended cold ischemia time on glucose metabolism in liver grafts: experimental study in pigs

BACKGROUND/PURPOSE

Recovery of normal carbohydrate metabolism in the liver after transplantation is highly important. The aim of the present study was to evaluate how short and long cold ischemia (CI) time followed by warm ischemia (WI) impact intrahepatic glucose metabolism in a pig liver transplantation model.

METHODS

Twenty-six animals were divided into two transplantation groups: group I with a liver ischemia time of 5 h (n = 6), and group II with 15 h of liver ischemia (n = 7). Intrahepatic microdialysis samples were collected throughout the experiment at 20-min intervals, during the donor operation, cold preservation, liver implantation, and liver reperfusion in the recipient. Glucose, lactate, and pyruvate concentrations were analyzed and the lactate/pyruvate ratio (L/Pr) was calculated.

RESULT

There were no changes in glucose levels during CI. However, during WI, glucose and lactate increased and the increase was significantly higher in the group with longer CI (P < 0.01). The L/Pr increased at the beginning of CI but accelerated to increase during WI in both groups, with significantly prolonged and higher levels in the group with longer CI (P < 0.01).

CONCLUSIONS

Extended CI results in increased intrahepatic glycogenolysis, delayed restoration of aerobic glycolysis, and prolonged anaerobic glycolysis shortly after reperfusion. Improvements in glycogen protection and faster restoration of aerobic metabolism during preservation and reperfusion time seem to be necessary in order to improve liver preservation protocols per se.

Total body propofol clearance (TBPC) after living-donor liver transplantation (LDLT) surgery is decreased in patients with a long warm ischemic time

Metabolic capacity after liver transplant surgery may be affected by the graft size and by hepatic injury during the surgery. This study was carried out to investigate the postoperative total body propofol clearance (TBPC) in living-donor liver transplantation (LDLT) patients and to investigate the major factors that contribute to decreased postoperative TBPC in LDLT patients. Fourteen patients scheduled for LDLT were included in this study. Propofol was administered at a rate of 2.0 mg.kg(-1).h(-1) as a sedative in the intensive care unit (ICU) setting. To calculate TBPC, propofol arterial blood concentration was measured by HPLC. Five variables were selected as factors affecting postoperative TBPC; bleeding volume (BLD), warm ischemic time (WIT), cold ischemic time (CIT), graft weight/standard liver volume ratio (GW/SLV), and portal blood flow after surgery (PBF). After factor analysis of six variables, including TBPC, varimax rotation was carried out, and this yielded three interpretable factors that accounted for 75.5% of the total variance in the data set. TBPC, WIT, CIT, and BLD were loaded on the first factor, PBF on the second factor, and GW/SLV on the third factor. The adjusted correlation coefficient between TBPC and WIT showed the highest value (r = -0.61) in the first factor. The LDLT patients were divided into two groups according to WIT; group A (WIT > 100 min) and group B (WIT < 100 min). Mean TBPC values in group A and group B were 14.6 +/- 2.1 and 28.5 +/- 4.1 ml.kg(-1).min(-1), respectively (P < 0.0001). These data suggest that LDLT patients with a long WIT have a risk of deteriorated drug metabolism.

Interstitial Lactic Acidosis in the Graft During Organ Harvest, Cold Storage, and Reperfusion of Human Liver Allografts Predicts Subsequent Ischemia Reperfusion Injury

BACKGROUND

The impact of the process of liver transplantation on glucose metabolism in the graft was studied using microdialysis.

METHODS

Microdialysis catheters were inserted into 15 human livers to monitor metabolic changes that took place during organ harvest, the process of backtable preparation of the graft, and following implantation in the recipient where it remained in situ for 48 hours. The cannula was perfused with isotonic solution and hourly samples of perfusate were collected and analyzed.

RESULTS

Six livers showed serum biochemical evidence of ischemia/reperfusion (IR) injury with 24 hours aspartate transaminase (AST) levels >2000 IU/L (Group A) whereas the remaining patients showed little evidence of IR injury (Group B). In Group A, lactate levels in the donor microdialysate rose to >6 mM (P < 0.05), were significantly higher during backtable preparation of the liver (>15 mM; P < 0.03), and took longer to normalize in the recipient following implantation (18 vs. 8 hours, P < 0.03) than lactate levels of the livers of patients in Group B who did not develop ischemia reperfusion injury. No significant differences were observed in glucose, pyruvate, or glycerol concentrations between the two groups.

CONCLUSIONS

Interstitial lactic acidosis in the donor allograft is associated with significant reperfusion injury on implantation.

Microdialysis in Clinical Practice

Clinical examination is still the gold standard of postoperative free flap monitoring, but with intraorally situated and/or buried flaps, it can be difficult or impossible. Microdialysis is a sampling technique which offers the possibility to monitor the metabolism of a flap continuously. Ischemia can be detected by monitoring the changes in glucose, lactate, and pyruvate levels in interstitial fluid of the specific tissue. Our aim was to use microdialysis to monitor the metabolism of free flaps used for reconstructions inside the oral cavity/oropharynx and to evaluate the reliability and usefulness of this new monitoring method.Twenty-five consecutive patients who underwent oral cavity/oropharynx cancer resection and immediate reconstruction with free flap were included in the study. A microdialysis catheter was placed into the subcutaneous adipose tissue of the flap in the end of the surgical procedure. Dialysate samples were taken on an hourly basis for 72 hours postoperatively. Routine clinical monitoring was carried out by experienced nursing staff. Clinical findings were recorded and later compared with microdialysis values. Two flaps out of 25 failed in spite of reoperations. In both problem cases, microdialysis indicated ischemia 1 to 2 hours before it became clinically evident. During flap ischemia, the lactate/pyruvate ratio increased, glucose concentrations reduced, whereas lactate level increased when compared with normal values. Our results indicate that microdialysis is safe for the patient and the flap. It can reliably detect flap ischemia at an early stage. This is especially useful in buried flaps when clinical monitoring is difficult. Microdialysis may also reduce the patient discomfort caused by repeated clinical examination of the flap.

K(ICG) value, a reliable real-time estimator of graft function, accurately predicts outcomes in adult living-donor liver transplantation

Reliable monitoring enabling evaluation of graft function is crucial after living-donor liver transplantation (LDLT). A method to identify poor graft function at an early postoperative period would allow opportune intensive clinical management to bring about further improvements in LDLT outcomes. This study assessed the reliability of the indocyanine green (ICG) elimination rate constant (K(ICG)) value as an estimator of graft function and determined the actual temporal changes of K(ICG) after LDLT. K(ICG) values were measured using a noninvasive method in 30 adult recipients up to 28 days after LDLT. The receptor index (LHL15) based on liver scintigraphy, and graft parenchymal damage score based on histopathological findings were evaluated after LDLT and correlated well with simultaneous K(ICG). Thus, K(ICG) measured by noninvasive method was confirmed as accurately evaluating graft function. Changes of K(ICG) after LDLT in recipients with good graft function were maintained, after some falls in the early periods, and had a significant difference compared with those for recipients without good graft function; moreover, there were already significant differences in K(ICG) 24 hours after LDLT. Mean transit time reflecting systemic hemodynamics revealed that recipients without good outcomes fell into an unstable systemic hemodynamic state, and effective hepatic blood flow has a large influence on liver regeneration after LDLT. In conclusion, we suggested that K(ICG) values can predict clinical outcomes at the early postoperative period after LDLT by sharply reflecting the influence of systemic dynamics on splanchnic circulation.

24-h storage of pig livers in UW, HTK, hydroxyethyl starch, and saline solution: is microdialysis an appropriate method for the continuous graft monitoring during preservation?

Recent studies demonstrate the feasibility of microdialysis to monitor metabolism in ischemic livers. Whether these parameters correlate with markers of liver cell integrity in an experimental model using pig livers and different preservation solutions was an aim of this study. Pig livers were flushed with either 4 degrees C Histidine-Typtophan-Ketoglutarate solution (HTK) (Custodiol), University of Wisconsin solution (ViaSpan), and hydroxyethyl starch, or 12 degrees C saline solution. After 24-h storage, the livers were rinsed with saline to measure liver enzymes and lactate from the effluate. Utilizing microdialysis, intraparenchymal lactate, pyruvate, glucose, and glycerol was monitored. Tissue biopsies were taken for histological examinations. Cold preservation resulted in a decrease of metabolic activity measured by intrahepatic glucose, lactate, and pyruvate levels, as well as lactate in the effluate, independently of the solution used. Of particular interest, glycerol levels partially reflected the extent of hepatocellular damage and liver enzyme release. Glycerol levels partially discriminated preservation of different quality and were in accordance to histological findings and liver enzyme release. Lactate, pyruvate, and glucose levels were not appropriate as markers during cold storage. Whether or not glycerol monitoring could represent an additional and rational complementation to the current practice of macroscopic, microscopic and donor evaluation has to be clarified by further studies.

A Study of the Metabolites of Ischemia-Reperfusion Injury and Selected Amino Acids in the Liver Using Microdialysis during Transplantation

BACKGROUND

Preservation and ischemia-reperfusion injury still impact the outcome of orthotopic liver transplantation. The authors used microdialysis with a view to monitoring its effect on graft function.

METHODS

A microdialysis catheter was inserted into the graft immediately after reperfusion and perfused with an isotonic solution for 48 hr. Metabolites of the ischemia-reperfusion injury and selected amino acids were studied. There were 18 patients, with a median age of 52 years (range, 38-62 years), 8 of whom were men. Lactate, pyruvate, glycerol, and glucose levels were measured. In addition, alanine, arginine, citrulline, gamma-aminobutyric acid (GABA), glutamate, glutamine, glycine, and taurine were determined.

RESULTS

All grafts functioned well. High lactate, pyruvate, and glycerol levels were observed in the immediate postoperative period. These showed a significant rapid decrease and stabilized to baseline levels. Alanine, glutamate, GABA, and taurine levels declined significantly to baseline values. Arginine levels were low immediately postreperfusion and then increased, reaching significantly higher values beyond 19 hr.

CONCLUSIONS

These data may represent "normal" changes seen in the immediate posttransplant period because all grafts functioned well. Two important metabolic fates of arginine in the liver are in the detoxification of ammonia by means of the urea cycle, and in the synthesis of nitric oxide (NO). Low extracellular arginine may reflect influx of the amino acid into hepatocytes, resulting in formation of NO in the presence of inducible NO synthase or conversion to ornithine in the presence of arginase in the urea cycle. As the organ stabilizes, restriction of arginine uptake may give rise to the observed increase in extracellular arginine.