Initial hepatic microcirculation correlates with early graft function in human orthotopic liver transplantation

Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 4: Experimental validation of the models of drug concentration in blood

In this final part, the models of drug concentration in blood developed in Part 3 are validated on dogs. Both slow-release gastroretentive fibrous and immediate-release particulate dosage forms containing 200 mg nilotinib were tested. After administering, the fibrous dosage form expanded linearly with time in the stomach, to about 1.5 times the initial radius by 4 h. The expanded dosage form fractured after 10 h, and then passed into the intestines. The drug concentration in blood exhibited a broad peak with a maximum of 0.51 μg/ml and a width at half-height of 10.2 h. By contrast, after administering the immediate-release capsule the drug concentration in blood exhibited a sharp peak with a maximum of 0.68 μg/ml and a width at half-height of just 3.6 h. The experimental data validate the theoretical models reasonably. The gastroretentive fibrous dosage forms designed in this study enable a steady drug concentration in blood for increasing the efficacy and mitigating side effects of drug therapies.

Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 3: Theoretical models of drug concentration in blood

In this part, drug concentration in blood after ingesting slow-release gastroretentive fibrous dosage forms and immediate-release particulate forms is modeled. The tyrosine kinase inhibitor nilotinib, which is slightly soluble in low-pH gastric fluid but practically insoluble in pH-neutral intestinal fluid is used as drug. The models suggest that upon ingestion, the fibrous dosage form expands, is retained in the stomach for prolonged time, and releases drug into the gastric fluid at a constant rate. The released drug molecules flow into the duodenum with the gastric fluid, and are absorbed by the blood. The drug is eliminated from the blood by the liver at a rate proportional to its concentration. Eventually, the elimination and absorption rates will be equal, and the drug concentration in blood plateaus out. After the gastric residence time drug absorption stops, and the drug concentration in blood drops to zero. By contrast, after administering an immediate-release particulate dosage form the drug particles are swept out of the stomach rapidly, and drug absorption stops much earlier. The drug concentration in blood rises and falls without attaining steady state. The gastroretentive fibrous dosage forms enable a constant drug concentration in blood for drugs that are insoluble in intestinal fluids.

The use of pulse pressure variation for predicting impairment of microcirculatory blood flow

Dynamic parameters of preload have been widely recommended to guide fluid therapy based on the principle of fluid responsiveness and with regard to cardiac output. An equally important aspect is however to also avoid volume-overload. This accounts particularly when capillary leakage is present and volume-overload will promote impairment of microcirculatory blood flow. The aim of this study was to evaluate, whether an impairment of intestinal microcirculation caused by volume-load potentially can be predicted using pulse pressure variation in an experimental model of ischemia/reperfusion injury. The study was designed as a prospective explorative large animal pilot study. The study was performed in 8 anesthetized domestic pigs (German landrace). Ischemia/reperfusion was induced during aortic surgery. 6 h after ischemia/reperfusion-injury measurements were performed during 4 consecutive volume-loading-steps, each consisting of 6 ml kg⁻¹ bodyweight⁻¹. Mean microcirculatory blood flow (mean Flux) of the ileum was measured using direct laser-speckle-contrast-imaging. Receiver operating characteristic analysis was performed to determine the ability of pulse pressure variation to predict a decrease in microcirculation. A reduction of ≥ 10% mean Flux was considered a relevant decrease. After ischemia–reperfusion, volume-loading-steps led to a significant increase of cardiac output as well as mean arterial pressure, while pulse pressure variation and mean Flux were significantly reduced (Pairwise comparison ischemia/reperfusion-injury vs. volume loading step no. 4): cardiac output (l min⁻¹) 1.68 (1.02–2.35) versus 2.84 (2.15–3.53), p = 0.002, mean arterial pressure (mmHg) 29.89 (21.65–38.12) versus 52.34 (43.55–61.14), p < 0.001, pulse pressure variation (%) 24.84 (17.45–32.22) versus 9.59 (1.68–17.49), p = 0.004, mean Flux (p.u.) 414.95 (295.18–534.72) versus 327.21 (206.95–447.48), p = 0.006. Receiver operating characteristic analysis revealed an area under the curve of 0.88 (CI 95% 0.73–1.00; p value < 0.001) for pulse pressure variation for predicting a decrease of microcirculatory blood flow. The results of our study show that pulse pressure variation does have the potential to predict decreases of intestinal microcirculatory blood flow due to volume-load after ischemia/reperfusion-injury. This should encourage further translational research and might help to prevent microcirculatory impairment due to excessive fluid resuscitation and to guide fluid therapy in the future.

Real-time observation of microcirculatory leukocytes in patients undergoing major liver resection

Ischemia/reperfusion injury and inflammation are associated with microcirculatory dysfunction, endothelial injury and glycocalyx degradation. This study aimed to assess microcirculation in the sublingual, intestinal and the (remnant) liver in patients undergoing major liver resection, to define microcirculatory leukocyte activation and its association with glycocalyx degradation. In this prospective observational study, the microcirculation was assessed at the beginning of surgery (T0), end of surgery (T1) and 24 h after surgery (T2) using Incident Dark Field imaging. Changes in vessel density, blood flow and leukocyte behaviour were monitored, as well as clinical parameters. Syndecan-1 levels as a parameter of glycocalyx degradation were analysed. 19 patients were included. Sublingual microcirculation showed a significant increase in the number of rolling leukocytes between T0 and T1 (1.5 [0.7-1.8] vs. 3.7 [1.7-5.4] Ls/C-PCV/4 s respectively, p = 0.001), and remained high at T2 when compared to T0 (3.8 [3-8.5] Ls/C-PCV/4 s, p = 0.006). The microvascular flow decreased at T2 (2.4 ± 0.3 vs. baseline 2.8 ± 0.2, respectively, p < 0.01). Duration of vascular inflow occlusion was associated with significantly higher numbers of sublingual microcirculatory rolling leukocytes. Syndecan-1 increased from T0 to T1 (42 [25-56] vs. 107 [86-164] ng/mL, p < 0.001). The microcirculatory perfusion was characterized by low convection capacity and high number of rolling leukocytes. The ability to sublingually monitor the rolling behaviour of the microcirculatory leukocytes allows for early identification of patients at risk of increased inflammatory response following major liver resection.

Intraoperative Imaging Techniques to Visualize Hepatic (Micro)Perfusion: An Overview

The microcirculation plays a crucial role in the distribution of perfusion to organs. Studies have shown that microcirculatory dysfunction is an independent predictor of morbidity and mortality. Hence, assessment of liver perfusion offers valuable information on the (patho)physiological state of the liver. The current review explores techniques in perfusion imaging that can be used intraoperatively. Available modalities include dynamic contrast-enhanced ultrasound, handheld vital microscopes, indocyanine green fluorescence angiography, and laser contrast speckle imaging. Dynamic contrast-enhanced ultrasound relays information on deep tissue perfusion and is a commonly used technique to assess tumor perfusion. Handheld vital microscopes provide direct visualization of the sinusoidal architectural structure of the liver, which is a unique feature of this technique. Intraoperative fluorescence imaging uses indocyanine green, a dye that is administered intravenously to visualize microvascular perfusion when excited using near-infrared light. Laser speckle contrast imaging produces non-contact large surface-based tissue perfusion imaging free from movement- or pressure-related artefacts. In this review, we discuss the intrinsic advantages and disadvantages of these techniques and their clinical and/or scientific applications.

Does graft hemodynamics affect the risk of hepatocellular carcinoma recurrence after liver transplantation?

Although experimental studies have reported that hepatic ischemia-reperfusion injury promotes tumor growth and metastases, the impact of graft hemodynamics on the recurrence of hepatocellular carcinoma (HCC) after liver transplantation (LT) is unclear. To investigate the association between graft hemodynamics and HCC recurrence after LT, we conducted a retrospective analysis of 279 patients who underwent LT for HCC. Graft hemodynamics including portal vein flow (PVF), hepatic artery flow (HAF), and total hepatic flow (THF) was analyzed as a predictor of HCC recurrence, using competing risk regression analyses. The cutoff values of PVF, HAF, and THF were set at the lower quartile of distribution. A cumulative recurrence curve demonstrated that low THF (<1511 mL/min, P = .005) was significantly associated with increased recurrence, whereas neither low PVF (<1230 mL/min, P = .150) nor low HAF (<164 mL/min, P = .110) was significant. On multivariate analysis, outside Milan criteria (sub-hazard ratio [SHR] = 3.742; P < .001), microvascular invasion (SHR = 3.698; P < .001), and low THF (SHR = 2.359; P = .010) were independently associated with increased HCC recurrence. In conclusion, our findings suggest that graft hemodynamics may play an important role in HCC recurrence after LT.

Interpatient heterogeneity in hepatic microvascular blood flow during vascular inflow occlusion (Pringle manoeuvre)

BACKGROUND

Vascular inflow occlusion (VIO) during liver resections (Pringle manoeuvre) can be applied to reduce blood loss, however may at the same time, give rise to ischemia-reperfusion injury (IRI). The aim of this study was to assess the characteristics of hepatic microvascular perfusion during VIO in patients undergoing major liver resection.

METHODS

Assessment of hepatic microcirculation was performed using a handheld vital microscope (HVM) at the beginning of surgery, end of VIO (20 minutes) and during reperfusion after the termination of VIO. The microcirculatory parameters assessed were: functional capillary density (FCD), microvascular flow index (MFI) and sinusoidal diameter (SinD).

RESULTS

A total of 15 patients underwent VIO; 8 patients showed hepatic microvascular perfusion despite VIO (partial responders) and 7 patients showed complete cessation of hepatic microvascular perfusion (full responders). Functional microvascular parameters and blood flow levels were significantly higher in the partial responders when compared to the full responders during VIO (FCD: 0.84±0.88 vs. 0.00±0.00 mm/mm2, P<0.03, respectively, and MFI: 0.69-0.22 vs. 0.00±0.00, P<0.01, respectively).

CONCLUSIONS

An interpatient heterogeneous response in hepatic microvascular blood flow was observed upon VIO. This may explain why clinical strategies to protect the liver against IRI lacked consistency.

[Possibilities and perspectives of hyperspectral imaging in visceral surgery]

HyperSpectral Imaging (HSI) technology enables quantitative tissue analyses beyond the limitations of the human eye. Thus, it serves as a new diagnostic tool for optical properties of diverse tissues. In contrast to other intraoperative imaging methods, HSI is contactless, noninvasive, and the administration of a contrast medium is not necessary. The duration of measurements takes only a few seconds and the surgical procedure is only marginally disturbed. Preliminary HSI applications in visceral surgery are promising with the potential of optimized outcomes. Current concepts, possibilities and new perspectives regarding HSI technology together with its limitations are discussed in this article.

Hepatic flow is an intraoperative predictor of early allograft dysfunction in whole-graft deceased donor liver transplantation: An observational cohort study

BACKGROUND

Early allograft dysfunction (EAD) after liver transplantation (LT) is an important cause of morbidity and mortality. To ensure adequate graft function, a critical hepatocellular mass is required in addition to an appropriate blood supply. We hypothesized that intraoperative measurement of portal venous and hepatic arterial flow may serve as a predictor in the diagnosis of EAD.

AIM

To study whether hepatic flow is an independent predictor of EAD following LT.

METHODS

This is an observational cohort study in a single institution. Hepatic arterial blood flow and portal venous blood flow were measured intraoperatively by transit flow. EAD was defined using the Olthoff criteria. Univariate and multivariate analyses were used to determine the intraoperative predictors of EAD. Survival analysis and prognostic factor analysis were performed using the Kaplan-Meier and Cox regression models.

RESULTS

A total of 195 liver transplant procedures were performed between January 2008 and December 2014 in 188 patients. A total of 54 (27.7%) patients developed EAD. The median follow-up was 39 mo. Portal venous flow, hepatic arterial flow (HAF) and total hepatic arterial flow were associated with EAD in both the univariate and multivariate analyses. HAF is an independent prognostic factor for 30-d patient mortality.

CONCLUSION

Intraoperative measurement of blood flow after reperfusion appears to be a predictor of EAD; Moreover, HAF should be considered a predictor of 30-d patient mortality.

Assessment of hepatic microvascular flow and density in patients undergoing preoperative portal vein embolization

BACKGROUND

The microvascular effects occurring after unilateral preoperative portal vein embolization (PVE) are poorly understood. The aim of this study was to assess the microvascular changes in the embolized and the non-embolized lobes after right PVE.

METHODS

Videos of the hepatic microcirculation in patients undergoing right hemihepatectomy following PVE were recorded using a handheld vital microscope (Cytocam) based on incident dark field imaging. Hepatic microcirculation was measured in the embolized and the non-embolized lobes at laparotomy, 3-6 weeks after PVE. The following microcirculatory parameters were assessed: total vessel density (TVD), microcirculatory flow index (MFI), proportion of perfused vessel (PPV), perfused vessel density (PVD), sinusoidal diameter (SinD) and the absolute red blood cell velocity (RBCv).

RESULTS

16 patients after major liver resection were included, 8 with and 8 without preoperative PVE. Microvascular density parameters were higher in the non-embolized lobes when compared to the embolized lobes (TVD: 40.3 ± 8.9 vs. 26.8 ± 4.6 mm/mm² (p < 0.003), PVD: 40.3 ± 8.8 vs. 26.7 ± 4.7 mm/mm² (p < 0.002), SinD: 9.2 ± 1.7 vs. 6.3 ± 0.8 μm (p < 0.040)). RBCv, PPV and the MFI were not significantly different.

CONCLUSION

The non-embolized lobe has a significantly higher microvascular density, however without differences in microvascular flow. These findings indicate increased angiogenesis in the hypertrophic lobe.

Limb remote ischemic conditioning of the recipient protects the liver in a rat model of arterialized orthotopic liver transplantation

Background

Ischemic-reperfusion (IR) injury still represents a major concern in clinical transplantation, especially in the era of extreme organ shortage and extended criteria donor organs. In the present study we aimed to investigate the hepatoprotective effects of remote ischemic conditioning (RIC) in a rat model of arterialized orthotopic liver transplantation (OLT).

Methods

Male Lewis rats were used (n = 144 / 72 OLT cases; 240–340g) as donors and recipients. Livers were flushed and stored in 4°C HTK-solution for 8h before implantation. Recipients were randomly allocated into three experimental groups: RIC 1, RIC 2, Control. In RIC 1, RIC 2 groups, RIC was applied in the recipient before hepatectomy or after reperfusion (4x5-5min IR via clamping the infrarenal aorta), respectively. Animals were sacrificed at 1, 3, 24, 168h post-reperfusion (n = 6 recipient/group/time point). Hepatocellular injury, graft circulation, serum cytokines, tissue redox-stress and adenosine-triphosphate (ATP) levels have been assessed. Additional markers were analyzed, using Western blotting and reverse-transcription polymerase chain reaction.

Results

RIC 1 group showed significantly (p<0.05) improved portal venous and microcirculation flow as well as velocity. RIC has significantly reduced tissue injury according to the serum levels of transaminases and results of histopathological evaluation. Reduced TUNEL-staining (p<0.01 RIC 1–2 vs. Control) and elevated pBAD/BAD ratio was detected in the RIC groups (p<0.01 RIC 1 vs. Control). Supporting findings were obtained from measurements of serum IL-10 as well as tissue malondialdehyde and ATP levels. Hemoxygenase-1 (HO-1) mRNA-expression was significantly higher in RIC 1 compared to Control (p<0.05 RIC 1 vs. Control).

Conclusion

These results suggest that RIC might confer potent protection against the detrimental effects of IR injury including tissue damage, apoptosis, graft circulation, inflammation, tissue energetic status in OLT. HO-1 overexpression might play an orchestrating role in RIC mediated organ protection. An earlier intervention (RIC 1 protocol) was more effective than remote conditioning after graft reperfusion.

Temporary Intraoperative Porto-Caval Shunts in Piggy-Back Liver Transplantation Reduce Intraoperative Blood Loss and Improve Postoperative Transaminases and Renal Function: A Meta-Analysis

BACKGROUND

The value of temporary intraoperative porto-caval shunts (TPCS) in cava-sparing liver transplantation is discussed controversially. Aim of this meta-analysis was to analyze the impact of temporary intraoperative porto-caval shunts on liver injury, primary non-function, time of surgery, transfusion of blood products and length of hospital stay in cava-sparing liver transplantation.

METHODS

A systematic search of MEDLINE/PubMed, EMBASE and PsycINFO retrieved a total of 909 articles, of which six articles were included. The combined effect size and 95 % confidence interval were calculated for each outcome by applying the inverse variance weighting method. Tests for heterogeneity (I ²) were also utilized.

RESULTS

Usage of a TPCS was associated with significantly decreased AST values, significantly fewer transfusions of packed red blood cells and improved postoperative renal function. There were no statistically significant differences in primary graft non-function, length of hospital stay or duration of surgery.

CONCLUSION

This meta-analysis found that temporary intraoperative porto-caval shunts in cava-sparing liver transplantation reduce blood loss as well as hepatic injury and enhance postoperative renal function without prolonging operative time. Randomized controlled trials investigating the use of temporary intraoperative porto-caval shunts are needed to confirm these findings.

POST-REPERFUSION LIVER BIOPSY AND ITS VALUE IN PREDICTING MORTALITY AND GRAFT DYSFUNCTION AFTER LIVER TRANSPLANTATION

Background:

The outcome of the patients after liver transplant is complex and to characterize the risk for complications is not always easy. In this context, the hepatic post-reperfusion biopsy is capable of portraying alterations of prognostic importance.

Aim:

To compare the results of liver transplantation, correlating the different histologic features of the hepatic post-reperfusion biopsy with graft dysfunction, primary non-function and patient survival in the first year after transplantation.

Method:

From the 377 transplants performed from 1996 to 2008, 164 patients were selected. Medical records were reviewed and the following clinical outcomes were registered: mortality in 1, 3, 6 and 12 months, graft dysfunction in varied degrees and primary graft non-function. The post-reperfusion biopsies had been examined by a blinded pathologist for the outcomes. The following histological variables had been evaluated: ischemic alterations, congestion, steatosis, neutrophilic exudate, monomorphonuclear infiltrate and necrosis.

Results:

The variables associated with increased mortality were: steatosis (p=0.02209), monomorphonuclear infiltrate (p=0.03935) and necrosis (p<0.00001). The neutrophilic exudate reduced mortality in this study (p=0.00659). The primary non-function showed significant association (p<0.05) with the necrosis, steatosis and the monomorphonuclear infiltrate.

Conclusion:

Post-reperfusion biopsy is useful tool to foresee complications after liver transplant.

Results of the TOP Study: Prospectively Randomized Multicenter Trial of an Ex Vivo Tacrolimus Rinse Before Transplantation in EDC Livers

Background

Organ shortage results in the transplantation of extended donor criteria (EDC) livers which is associated with increased ischemia-reperfusion injury (IRI). Experimental studies indicate that an organ rinse with the calcineurin inhibitor tacrolimus before implantation protects against IRI. The tacrolimus organ perfusion study was initiated to examine the effects of ex vivo tacrolimus perfusion on IRI in transplantation of EDC livers.

Methods

A prospective randomized multicenter trial comparing ex vivo perfusion of marginal liver grafts (≥2 EDC according to Eurotransplant manual) with tacrolimus (20 ng/mL) or histidine-tryptophane-ketoglutarate solution (control) was carried out at 5 German liver transplant centers (Munich Ludwig-Maximilians University, Berlin, Heidelberg, Mainz, Regensburg) between October 2011 and July 2013. Primary endpoint was the maximum alanine transaminase (ALT) level within 48 hours after transplantation. Secondary endpoints were aspartate transaminase (AST), prothrombine ratio, and graft-patient survival within an observation period of 1 week. After an interim analysis, the study was terminated by the scientific committee after the treatment of 24 patients (tacrolimus n = 11, Control n = 13).

Results

Tacrolimus rinse did not reduce postoperative ALT peaks compared with control (P = 0.207; tacrolimus: median, 812; range, 362-3403 vs control: median, 652; range, 147-2034). Moreover, ALT (P = 0.100), prothrombine ratio (P = 0.553), and bilirubin (P = 0.815) did not differ between the groups. AST was higher in patients treated with tacrolimus (P = 0.011). Survival was comparable in both groups (P > 0.05).

Conclusions

Contrary to experimental findings, tacrolimus rinse failed to improve the primary endpoint of the study (ALT). Because 1 secondary endpoint (AST) was even higher in the intervention group, the study was terminated prematurely. Thus, tacrolimus rinse cannot be recommended in transplantation of EDC livers.

Non-invasive imaging of microcirculation: a technology review

Microcirculation plays a crucial role in physiological processes of tissue oxygenation and nutritional exchange. Measurement of microcirculation can be applied on many organs in various pathologies. In this paper we aim to review the technique of non-invasive methods for imaging of the microcirculation. Methods covered are: videomicroscopy techniques, laser Doppler perfusion imaging, and laser speckle contrast imaging. Videomicroscopy techniques, such as orthogonal polarization spectral imaging and sidestream dark-field imaging, provide a plentitude of information and offer direct visualization of the microcirculation but have the major drawback that they may give pressure artifacts. Both laser Doppler perfusion imaging and laser speckle contrast imaging allow non-contact measurements but have the disadvantage of their sensitivity to motion artifacts and that they are confined to relative measurement comparisons. Ideal would be a non-contact videomicroscopy method with fully automatic analysis software.

Delayed rearterialization unlikely leads to nonanastomotic stricture but causes temporary injury on bile duct after liver transplantation

Nonanastomotic strictures (NAS) are common biliary complications after liver transplantation (LT). Delayed rearterialization induces biliary injury in several hours. However, whether this injury can be prolonged remains unknown. The correlation of this injury with NAS occurrence remains obscure. Different delayed rearterialization times were compared using a porcine LT model. Morphological and functional changes in bile canaliculus were evaluated by transmission electron microscopy and real-time PCR. Immunohistochemistry and TUNEL were performed to validate intrahepatic bile duct injury. Three months after LT was performed, biliary duct stricture was determined by cholangiography; the tissue of common bile duct was detected by real-time PCR. Bile canaliculi were impaired in early postoperative stage and then exacerbated as delayed rearterialization time was prolonged. Nevertheless, damaged bile canaliculi could fully recover in subsequent months. TNF-α and TGF-β expressions and apoptosis cell ratio increased in the intrahepatic bile duct only during early postoperative period in a time-dependent manner. No abnormality was observed by cholangiography and common bile duct examination after 3 months. Delayed rearterialization caused temporary injury to bile canaliculi and intrahepatic bile duct in a time-dependent manner. Injury could be fully treated in succeeding months. Solo delayed rearterialization cannot induce NAS after LT.

Laser speckle contrast imaging for intraoperative assessment of liver microcirculation: a clinical pilot study

Background

Liver microcirculation can be affected by a wide variety of causes relevant to liver transplantation and resectional surgery. Intraoperative assessment of the microcirculation could possibly predict postoperative outcome. The present pilot study introduces laser speckle contrast imaging (LSCI) as a new clinical method for assessing liver microcirculation.

Methods

LSCI measurements of liver microcirculation were performed on ten patients undergoing liver resection. Measurements were made during apnea with and without liver blood inflow occlusion. Hepatic blood flow was assessed by subtracting zero inflow signal from the total signal. Zero inflow signal was obtained after hepatic artery and portal vein occlusion. Perfusion was expressed in laser speckle perfusion units, and intraindividual and interindividual variability in liver perfusion was investigated using the coefficient of variability.

Results

Hepatic microcirculation measurements were successfully made in all patients resulting in analyzable speckle contrast images. Mean hepatic blood flow was 410±36 laser speckle perfusion units. Zero inflow signal amounted to 40%±4% of the total signal. Intraindividual and interindividual coefficients of variability in liver perfusion were 25% and 28%, respectively.

Conclusion

Under the conditions of this pilot study, LSCI allows rapid noncontact measurements of hepatic blood perfusion over wide areas. More studies are needed on methods of handling movement artifacts.

A novel in situ model of liver cold ischemia-reperfusion in rats

BACKGROUND

Orthotopic liver transplantation (OLT) is being used for studying cold ischemia reperfusion (I/R)-induced injury in experimental animals, but the technique is complicated and it does not accurately reflect the pathophysiology. Here, we report a novel model, termed "in situ liver cold ischemia (ISLCI)", in Wistar rats.

METHODS

ISLCI was achieved in rats by establishing a portal-jugular shunt and a cannula shunt in inferior vena cava, and the liver was continuously perfused with lactate Ringer's solution at a speed of 150 mL/h through the portal vein for 60 min. Portal venous pressure, serum levels of total bilirubin, alkaline phosphatase, alanine aminotransferase and γ-glutamyl transpeptidase (GGT), and hepatic histopathology were examined, and compared with rats undergoing OLT, in which the donor liver was subjected to a 60 min cold ischemia.

RESULTS

Livers from ISLCI and OLT rats showed histopathologic changes characteristic of I/R-induced injury when examined on days 1 and 7, with complete recovery 14 d after reperfusion. Compared with OLT rats, ISLCI rats had significantly lower levels of portal venous pressure 1 and 10 min after porta hepatis clamping. They suffered a milder degree of I/R-induced hepatic injury, reflected by significantly lower levels of GGT, alanine aminotransferase, and alkaline phosphatase on day 1, and a significant lower level of GGT and a lower histopathologic score on day 7 after reperfusion.

CONCLUSIONS

Our preliminary results indicate that the ISLCI model is reliable and technically easier, and is superior to OLT for studying cold I/R injury.

Assessment of right liver graft perfusion effectiveness between one and two-catheter infusion methods

Backgrounds/Aims

Conventional graft perfusion method using one small-caliber catheter takes a relatively long time for right liver graft perfusion, thus some modification is needed. In this study, we intended to assess the effectiveness of right liver graft perfusion methods through comparison of different infusion catheters.

Methods

The study consisted of two parts including one bench experiment to obtain data of hydraulic infusion and one clinical trial of 40 cases on graft perfusion with one- versus two-catheter infusion methods. These two graft infusion methods were compared in terms of the perfusion time and washing-out efficiency.

Results

At bench experiment, the infusion flow rate and infusion pressure were 3.3 ml/sec and 1.9 cmH₂0 in one blood transfusion catheter group, and 11.7 ml/sec and 3.1 cmH₂0 in single transurethral resection of prostate irrigation catheter group, and 6.6 ml/sec and 2.0 cmH₂0 in two blood transfusion catheters group, respectively. In clinical trial with 40 right liver grafts, two-catheter group had a shorter graft portal perfusion time for the first 2 L of histidine-tryptophan-ketoglutarate (HTK) solution than the conventional one-catheter group (375±25 seconds vs. 662±34 seconds; p=0.001) and a lower rate of incomplete blood washing-out after the initial 2 L portal perfusion (40% vs. 85%; p=0.03).

Conclusions

The two-catheter infusion method appears to be more effective than the conventional one-catheter infusion method for right liver graft perfusion at the back table. Large size of right liver grafts seems to be its good indication.

Hepatic ischemic preconditioning increases portal vein flow in experimental liver ischemia reperfusion injury

BACKGROUND

Ischemic preconditioning (IPC) has been shown to decrease liver injury and to increase hepatic microvascular perfusion after liver ischemia reperfusion. This study aimed to evaluate the effects of IPC on hemodynamics of the portal venous system.

METHODS

Thirty-two rats were randomized into two groups: IPC group and control group. The rats of the IPC group underwent IPC by 10 minutes of liver ischemia followed by 10 minutes of reperfusion before liver ischemia, and the rats of the control group were subjected to 60 minutes of partial liver ischemia. Non-ischemic lobes were resected immediately after reperfusion. The animals were studied at 4 hours and 12 hours after reperfusion. Mean arterial pressure, heart rate, portal vein flow and pressure were analyzed. Blood was collected for the determination of the levels of aspartate aminotransferase, alanine aminotransferase, calcium, lactate, pH, bicarbonate, and base excess.

RESULTS

IPC increased the mean portal vein flow at 4 hours and 12 hours after reperfusion. IPC recovered 78% of the mean portal vein flow at 12 hours after reperfusion. IPC decreased the levels of aspartate aminotransferase, alanine aminotransferase and lactate, and increased the levels of ionized calcium, bicarbonate and base excess at 12 hours after reperfusion.

CONCLUSIONS

This study demonstrated that IPC increases portal vein flow and enhances hepatoprotective effects in liver ischemia reperfusion. The better recovery of portal vein flow after IPC may be correlated with the lower levels of transaminases and with the better metabolic profile.

Inhibition of glycogen synthase kinase (GSK)-3-β improves liver microcirculation and hepatocellular function after hemorrhagic shock

Ischemia and reperfusion may cause liver injury and are characterized by hepatic microperfusion failure and a decreased hepatocellular function. Inhibition of glycogen synthase kinase (GSK)-3β, a serine-threonine kinase that has recently emerged as a key regulator in the modulation of the inflammatory response after stress events, may be protective in conditions like sepsis, inflammation and shock. Therefore, aim of the study was to assess the role of GSK-3β in liver microcirculation and hepatocellular function after hemorrhagic shock and resuscitation (H/R). Anesthetized male Sprague-Dawley rats underwent pretreatment with Ringer´s solution, vehicle (DMSO) or TDZD-8 (1 mg/kg), a selective GSK-3β inhibitor, 30 min before induction of hemorrhagic shock (mean arterial pressure 35±5 mmHg for 90 min) and were resuscitated with shed blood and Ringer´s solution (2h). 5h after resuscitation hepatic microcirculation was assessed by intravital microscopy. Propidium iodide (PI) positive cells, liver enzymes and alpha-GST were measured as indicators of hepatic injury. Liver function was estimated by assessment of indocyanine green plasma disappearance rate. H/R led to a significant decrease in sinusoidal diameters and impairment of liver function compared to sham operation. Furthermore, the number of PI positive cells in the liver as well as serum activities of liver enzymes and alpha-GST increased significantly after H/R. Pretreatment with TDZD-8 prevented the changes in liver microcirculation, hepatocellular injury and liver function after H/R. A significant rise in the plasma level of IL-10 was observed. Thus, inhibition of GSK-3β before hemorrhagic shock modulates the inflammatory response and improves hepatic microcirculation and hepatocellular function.

Protocol TOP-Study (tacrolimus organ perfusion): a prospective randomized multicenter trial to reduce ischemia reperfusion injury in transplantation of marginal liver grafts with an ex vivo tacrolimus perfusion

BACKGROUND

Critical organ shortage results in the utilization of extended donor criteria (EDC) liver grafts. These marginal liver grafts are prone to increased ischemia reperfusion injury (IRI) which may contribute to deteriorated graft function and survival. Experimental data have shown that the calcineurin inhibitor tacrolimus exerts protective effects on hepatic IRI when applied intravenously or directly as a hepatic rinse. Therefore, the aim of the present study is to examine the effects of an ex vivo tacrolimus perfusion on IRI in transplantation of EDC liver grafts.

METHODS/DESIGN

The TOP-Study (tacrolimus organ perfusion) is a randomized multicenter trial comparing the ex vivo tacrolimus perfusion of marginal liver grafts with placebo. We hypothesize that a tacrolimus rinse reduces IRI, potentially improving organ survival following transplantation of EDC livers. The study includes livers with two or more EDC, according to Eurotransplant International Foundation's definition of EDC livers. Prior to implantation, livers randomized to the treatment group are rinsed with tacrolimus at a concentration of 20 ng/ml in 1000 ml Custodiol solution and in the placebo group with Custodiol alone. The primary endpoint is the maximum serum alanine transamninase (ALT) level within the first 48 hours after surgery; however, the study design also includes a 1-year observation period following transplantation. The TOP-Study is an investigator-initiated trial sponsored by the University of Munich Hospital. Seven other German transplant centers are participating (Berlin, Frankfurt, Heidelberg, Mainz, Münster, Regensburg, Tübingen) and aim to include a total of 86 patients.

DISCUSSION

Tacrolimus organ perfusion represents a promising strategy to reduce hepatic IRI following the transplantation of marginal liver grafts. This treatment may help to improve the function of EDC grafts and therefore safely expand the donor pool in light of critical organ shortage.

TRIAL REGISTER

EudraCT number: 2010-021333-31, ClinicalTrials.gov identifier: NCT01564095.

Laser speckle contrast imaging for assessment of liver microcirculation

OBJECTIVE

Laser speckle contrast imaging (LSCI) is a novel technique for microcirculation imaging not previously used in the liver. The aim of the present experimental study was to evaluate the use of LSCI for assessing liver microcirculation.

MATERIALS AND METHODS

In six male Wistar rats, the median liver lobe was exposed through a midline laparotomy. Liver blood perfusion was measured simultaneously with LSCI and sidestream dark-field (SDF) imaging at baseline and during sequential temporary occlusions of the portal vein, hepatic artery, and total blood inflow occlusion. Both the inter-individual variability associated with perfusion sampling area and comparisons in perfusion measurements between both imaging techniques were investigated and validated for the application of LSCI in the liver.

RESULTS

Occlusion of the hepatic artery, portal vein, and total inflow occlusion resulted in a significant decrease in LSCI signal to 74.7±6.4%, 15.0±2.3%, and 10.4±0.5% respectively (p<0.005 vs. baseline). The LSCI perfusion units correlated with sinusoidal blood flow velocity as measured with SDF imaging (Pearson's r=0.94, p<0.001). In a 10 mm diameter region of interest, as measured with LSCI, baseline inter-individual variability measured by the coefficient of variability was 13%.

CONCLUSION

Alterations in LSCI signal during sequential inflow occlusions were in accordance with previously published results on hepatic hemodynamics in the rat and correlated well with our SDF imaging-derived sinusoidal blood flow velocity measurements. We found that LSCI was able to produce reproducible real-time blood perfusion measurements of hepatic microcirculation. Compared to established techniques for liver blood perfusion measurements LSCI holds the advantages of non-contact measurements over large surfaces with a high speed of data acquisition.

Dual cytoprotective effects of splenectomy for small-for-size liver transplantation in rats

The problems associated with small-for-size liver grafts (ie, high mortality rates, postoperative complications, and acute rejection) remain critical issues in partial orthotopic liver transplantation (OLT). In association with partial OLT, splenectomy (SP) is a procedure used to reduce the portal pressure. However, the precise effects of SP on partial OLT have been unclear. In this study, using small-for-size liver grafts in rats, we examined the cytoprotective effects of SP on OLT. Liver grafts were assigned to 2 groups: a control group (OLT alone) and an SP group (OLT after SP). SP significantly increased animal survival and decreased liver damage. SP exerted the following cytoprotective effects: (1) it improved hepatic microcirculation and prevented increases in the portal pressure after OLT, (2) it suppressed the hepatic infiltration of neutrophils and macrophages through the direct elimination of splenic inflammatory cells before OLT, (3) it decreased the hepatic expression of tumor necrosis factor α and interleukin-6, (4) it attenuated sinusoidal endothelial injury, (5) it decreased plasma endothelin 1 levels and increased hepatic heme oxygenase 1 expression, (6) it suppressed hepatocellular apoptosis through the down-regulation of hepatic caspase-3 and caspase-8 activity, and (7) it increased hepatic regeneration. In conclusion, SP for small-for-size grafts exerts dual cytoprotective effects by preventing excessive portal vein hepatic inflow and eliminating splenic inflammatory cell recruitment into the liver; this in turn inhibits hepatocellular apoptosis and improves liver regeneration.

Hepatic blood flow plays an important role in ischemia-reperfusion injury

Severe ischemia/reperfusion (IR) injury is associated with poor hepatic microperfusion. The aim of this study was to investigate the role of hepatic artery flow (HAF) and portal vein flow (PVF) in IR injury. From January 2004 to June 2008, 566 patients underwent orthotopic liver transplantation (OLT). The data were retrospectively reviewed via the transplant database. Patients with hepatic artery (HA) or portal vein (PV) thrombosis and retransplant patients were excluded. Intraoperative PVF and HAF values and graft weights were measured routinely, and the central venous pressure, mean arterial pressure, cardiac output, and cardiac index were recorded with hepatic blood flow measurements. Complete data were available for 312 primary OLT recipients (215 males and 97 females; mean age = 54 ± 10 years). The patients' follow-up ranged from 215 to 1746 days (705 ± 408 days). IR injury was defined by the aspartate aminotransferase (AST) level on postoperative day (POD) 2, and the patients were divided into 3 groups: (1) mild IR injury [AST < 500 U/L; n = 160 (51%)], (2) moderate IR injury [AST = 500-1000 U/L; n = 85 (27%)], and (3) severe IR injury [AST > 1000 U/L; n = 67 (21%)]. The demographics and pre-OLT variables (the Model for End-Stage Liver Disease score (MELD), platelet counts, PV thrombosis, transjugular intrahepatic portosystemic shunts, and shunts on computed tomography scans) were similar in all groups. The graft survival rate was 99% in group 1, 95.2% in group 2 (P = 0.02), and 92.3% in group 3 (P = 0.016). The patient survival rates were similar in the 3 groups. The cold ischemia time (CIT) was significantly higher in group 3 versus group 1 (P < 0.007). In the statistical analysis, low HAF, PVF, total liver blood flow (TLBF), and augmented HAF values were associated with a greater likelihood of elevated AST levels on POD 2. The strongest univariate predictors of AST were reduced augmented HAF (mL/minute/100 g) values (P < 0.001) and reduced TLBF (mL/minute/100 g) values (P < 0.001). In a covariate analysis with adjustments for CIT and donor variables, the blood flow parameters remained important predictors of graft function. In conclusion, this report demonstrates for the first time that reduced hepatic blood flow is a significant finding in patients with severe hepatic IR injury.

Arterial blood flow predicts graft survival in liver transplant patients

Proper liver perfusion is essential for sufficient organ function after liver transplantation. The aim of this study was to determine the effects of portal and arterial blood flow on liver function and organ survival after liver transplantation. The arterial and portal venous blood flow was measured intraoperatively by transit time flow measurement after reperfusion for 290 consecutive liver transplants. The graft survival, hepatic cell damage (alanine aminotransferase and aspartate aminotransferase), and liver function (prothrombin ratio and bilirubin) were determined. Grafts were stratified into groups according to arterial blood flow measurements [<100 mL/minute for arterial blood flow group I (ART I), 100-240 mL/minute for ART II, and ≥ 240 mL/minute for ART III] and portal venous blood flow measurements (<1300 mL/minute for portal venous blood flow group I and ≥ 1300 mL/minute for portal venous blood flow group II). With multivariate analysis, the impact of blood flow on graft survival was determined, and potential confounders were considered. Decreased portal venous blood flow was associated with significantly less organ survival in univariate analysis but not in multivariate analysis. In contrast, the arterial blood flow was significantly correlated with organ survival after liver transplantation in univariate and multivariate analyses [hazard rate ratio = 2.5, confidence interval = 1.6-4.1, P < 0.001, median survival = 56.6 (ART I), 82.7 (ART II), or 100.7 months (ART III)]. Moreover, low arterial blood flow resulted in impaired postoperative organ function and higher rates of primary nonfunction. Biliary complications were not affected by blood flow. Other risk factors for graft failure that were identified by multivariate analysis included retransplantation, histidine tryptophan ketoglutarate solution versus University of Wisconsin solution, and donor treatment with epinephrine. Impaired arterial blood flow after reperfusion represents a significant predictor of primary graft nonfunction and is associated with impaired graft survival. Whether the intraoperative measurement of hepatic arterial flow is predictive of graft survival should be evaluated in a prospective trial.

Anesthesia care for liver transplantation

Intraoperative transfusion practices for liver transplantation have evolved dramatically since the first transplants of the 1960s. It is important for today's clinicians to be current in their understanding of how transplant patients should be managed with regard to their coagulation profile, volume status, and general hemodynamic state. The anesthesia team is presented with the unique task of manipulating this tenuous balance in a rapid and precise manner when managing patients undergoing liver transplantation. Although significant progress has been made in reducing blood product administration, it is still common to encounter large volume blood loss in these cases. Increasingly, clinicians are challenged to justify transfusion practices with a stronger evidentiary base. The current state of the literature for transfusion guidelines and blood product management in this particular patient subset will be discussed, as well as a variety of means (both pharmacologic and otherwise) used to reduce the need for transfusion. The aim was to review the latest evidence on these topics, as well as to highlight areas that need further clarification regarding their role in the optimal care of these patients.

The role of calcium and nitric oxide during liver enzyme release induced by increased physical forces as evidenced in partially hepatectomized rats

Although increased plasma enzyme activities could be diagnostic for tissue damage, the mechanisms controlling cellular enzyme release remain poorly understood. We found a selective and drastic elevation of serum enzyme activities accompanying rat liver regeneration after partial hepatectomy (PH), apparently controlled by a mechanism dependent on flow-bearing physical forces. In fact, this study assesses a putative role of calcium mobilization and nitric oxide (NO) production underlying rat liver enzyme release. The role of increased shear stress (by enhancing viscosity during perfusion) and the participation of cell calcium and NO were tested in isolated livers subjected to increasing flow rate. After PH, there was a drastic elevation of serum activities for liver enzyme markers, clearly predominating those of mitochondrial localization. Liver enzyme release largely depended on extracellular calcium entry, probably mediated by stretch-sensitive calcium channels, as well as by increasing NO production. However, these effects were differentially observed when comparing liver enzymes from cytoplasmic or mitochondrial compartments. Moreover, a possible role for cell-mediated mechanotransduction in liver enzyme release was suggested by increasing shear stress (high viscosity), which also selectively affected the release of the enzymes tested. Therefore, we show, for the first time, that flow-induced shear stress can control the amount of hepatic enzymes released into the bloodstream, which is largely regulated through modifications in cell calcium mobilization and production of liver NO, events markedly elevated in the proliferating rat liver.

Impact of preexisting diabetes mellitus on outcome after liver transplantation in patients with hepatitis B virus-related liver disease

BACKGROUND

Preexisting diabetes mellitus (DM) has been reported to have an adverse consequence on patient prognosis after liver transplantation in the West. So far, there are few reports on the effect of preexisting DM on outcome of liver transplant recipients with HBV infection.

AIMS

We aimed to examine the impact of preexisting DM on post-transplant outcome in Chinese patients with HBV-related liver disease.

METHODS

The post-transplant morbidities and patient survival were compared between 48 diabetes patients (DM group) and 96 non-diabetes patients (control group) matched for age, gender, primary disease and model for end-stage liver diseases score. The DM group was further divided into hyperglycemia patients (fasting blood glucose >8.0 mmol/L, n = 22) and non-hyperglycemia patients (fasting blood glucose ≤8.0 mmol/L, n = 26).

RESULTS

Patient characteristics were comparable between both groups, except a higher incidence of hepatic encephalopathy in the DM group than that in the control group (22.9% vs. 10.4%, P = 0.045). The incidences of post-transplant complications and patient survival did not differ significantly between the DM and control groups, or between non-hyperglycemia patients and their matched case controls. Hyperglycemia patients showed a higher incidence of post-transplant sepsis (18.2% vs. 2.3%, P = 0.039) and biliary complications (31.8% vs. 6.8%, P = 0.012) than their matched case controls.

CONCLUSIONS

Preexisting DM is not a contraindication for liver transplantation in patients with HBV-related liver disease. A tight control of blood glucose to a level of ≤8.0 mmol/L was necessary to reduce the risk of complications after liver transplantation.

In vivo assessment of the hepatic microcirculation after mesenterico-portal bypass (REX-shunt) using orthogonal polarization spectral imaging

BACKGROUND

Extrahepatic portal vein thrombosis, not associated with cirrhosis or tumours, is the second most frequent cause of portal hypertension worldwide. Especially in children, anatomic mesenterico-portal interposition (REX-shunt) has become an established treatment. The changes in hepatic microcirculation after reperfusion of the shunt have not been investigated so far.

AIMS

This study investigates the hepatic microcirculation before and after REX-shunt interposition using orthogonal polarization spectral imaging (OPS).

PATIENTS AND METHODS

Since 2004, three consecutive patients with extrahepatic portal vein thrombosis underwent REX-shunt interposition. We measured the hepatic microcirculation by OPS before and directly after REX-shunt reperfusion and analysed the capillary vessel diameter, red blood cell velocity, functional capillary density and volumetric blood flow. Furthermore, we compared our values with the physiological values of the hepatic microcirculation defined previously by other investigators.

RESULTS

All shunts showed an excellent function in the follow-up investigations. The intra-individual microcirculatory analysis revealed a reduction in the red blood cell velocity after shunt reperfusion in particular.

CONCLUSIONS

Our results provide preliminary evidence for the reversal of the hepatic arterial buffer response following the restoration of the portal venous blood flow. This may be a short-term effect because of the restored portal venous blood flow.

Ischemic preconditioning-induced hyperperfusion correlates with hepatoprotection after liver resection

AIM: To characterize the impact of the Pringle maneuver (PM) and ischemic preconditioning (IP) on total blood supply to the liver following hepatectomies.

METHODS: Sixty one consecutive patients who underwent hepatic resection under inflow occlusion were randomized either to receive PM alone (n = 31) or IP (10 min of ischemia followed by 10 min of reperfusion) prior to PM (n = 30). Quantification of liver perfusion was measured by Doppler probes at the hepatic artery and portal vein at various time points after reperfusion of remnant livers.

RESULTS: Occlusion times of 33 ± 12 min (mean ± SD) and 34 ± 14 min and the extent of resected liver tissue (2.7 segments) were similar in both groups. In controls (PM), on reperfusion of liver remnants for 15 min, portal perfusion markedly decreased by 29% while there was a slight increase of 8% in the arterial blood flow. In contrast, following IP + PM the portal vein flow remained unchanged during reperfusion and a significantly increased arterial blood flow (+56% vs baseline) was observed. In accordance with a better postischemic blood supply of the liver, hepatocellular injury, as measured by alanine aminotransferase (ALT) levels on day 1 was considerably lower in group B compared to group A (247 ± 210 U/I vs 550 ± 650 U/I, P < 0.05). Additionally, ALT levels were significantly correlated to the hepatic artery inflow.

CONCLUSION: IP prevents postischemic flow reduction of the portal vein and simultaneously increases arterial perfusion, suggesting that improved hepatic macrocirculation is a protective mechanism following hepatectomy.

Is impaired hepatic arterial buffer response a risk factor for biliary anastomotic stricture in liver transplant recipients?

BACKGROUND

Blood flow to the liver is partly maintained by the hepatic arterial buffer response (HABR), which is an intrinsic autoregulatory mechanism. Temporary clamping of the portal vein (PV) results in augmentation in hepatic artery flow (augHAF). Portal hyperperfusion impairs HAF due to the HABR in liver transplantation (LT). The aim of this study is to examine the effect of the HABR on biliary anastomotic stricture (BAS).

METHODS

In 234 cadaveric whole LTs, PV flow (PVF), basal HAF, and augHAF were measured intra-operatively after allograft implantation. All recipients with a vascular complication were excluded. Buffer capacity (BC) was calculated as (augHAF - basal HAF)/PVF to quantify the HABR. Recipients were divided into 2 groups based on their BC: low BC (<0.074; n = 117) or high BC (> or =0.074; n = 117).

RESULTS

Of the 234 recipients, 23 (9.8%) had early BAS (< or =60 days after LT) and 18 (7.7%) had late BAS (>60 days after LT). The incidence of late BAS and bile leakage was similar between the groups; however, the incidence of early BAS in the low BC group was greater than that in the high BC group (15% vs 5.1%; P = .0168). In the multivariate analysis, low BC (P = .0325) and bile leakage (P = .0002) were found to be independent risk factors affecting early BAS.

CONCLUSION

Recipients with low BC who may have impaired HABR are at greater risk of early BAS after LT. Intraoperative measurements of blood flow help predict the risk of BAS.

The cytoprotective effects of addition of activated protein C into preservation solution on small-for-size grafts in rats

Small-for-size liver grafts are a serious obstacle for partial orthotopic liver transplantation. Activated protein C (APC), a potent anticoagulant serine protease, is known to have cell-protective properties due to its anti-inflammatory and antiapoptotic activities. This study was designed to examine the cytoprotective effects of a preservation solution containing APC on small-for-size liver grafts, with special attention paid to ischemia-reperfusion injury and shear stress in rats. APC exerted cytoprotective effects, as evidenced by (1) increased 7-day graft survival; (2) decreased initial portal pressure and improved hepatic microcirculation; (3) decreased levels of aminotransferase and improved histological features of hepatic ischemia-reperfusion injury; (4) suppressed infiltration of neutrophils and monocytes/macrophages; (5) reduced hepatic expression of tumor necrosis factor alpha and interleukin 6; (6) decreased serum levels of hyaluronic acid, which indicated attenuation of sinusoidal endothelial cell injury; (7) increased hepatic levels of nitric oxide via up-regulated hepatic endothelial nitric oxide synthesis expression together with down-regulated hepatic inducible nitric oxide synthase expression; (8) decreased hepatic levels of endothelin 1; and (9) reduced hepatocellular apoptosis by down-regulated caspase-8 and caspase-3 activities. These results suggest that a preservation solution containing APC is a potential novel and safe product for small-for-size liver transplantation, alleviating graft injury via anti-inflammatory and antiapoptotic effects and vasorelaxing conditions.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Pathophysiology of renal hemodynamics and renal cortical microcirculation in a porcine model of elevated intra-abdominal pressure

BACKGROUND

Elevated intra-abdominal pressure (IAP) has been shown to impair renal perfusion and renal function. This study was designed to further investigate the effects of elevated IAP on renal venous hemodynamics and renal perfusion pressure (RPP). Another aim was to evaluate the renal cortical microcirculation by sidestream dark field (SDF) imaging in a porcine model of elevated IAP.

METHODS

In 11 pigs, IAP was increased stepwise while renal hemodynamics and urinary output were recorded. RPP (RPP = mean arterial pressure minus IAP) and renal filtration gradient (RFG = mean arterial pressure minus 2xIAP) were calculated. Renal cortical microcirculatory perfusion was assessed by calculating the microvascular flow index (MFI) based on SDF data.

RESULTS

With IAP elevated to 30 mm Hg, renal arterial and venous flow decreased in parallel by 34% (p < 0.05) and RPP decreased by 12% (p < 0.05). With increasing IAP, renal vascular resistance increased and MFI decreased significantly. RFG showed a moderate correlation with renal blood flow (r = 0.39, p < 0.05) and MFI (r = 0.46, p < 0.005), whereas RPP did not.

CONCLUSIONS

In a porcine model of IAP-induced renal impairment, we observed a parallel decrease in renal venous and arterial blood flow together with blood flow redistribution away from the kidney. SDF imaging was used for the first time to assess renal cortical microcirculation and MFI was found to decrease with increasing IAP. RFG, as a clinical estimator of renal perfusion, correlated moderately with renal blood flow and microcirculatory perfusion, whereas RPP did not. Increased renal vascular resistance with elevated IAP might account for this.

The impact of a micro-lightguide spectrophotometer on the intraoperative assessment of hepatic microcirculation: a pilot study

INTRODUCTION

The intraoperative measurement of the peripheral microperfusion after liver transplantation is connected with quite an effort and a continuous evaluation in the postoperative follow up is not possible till now.

PATIENTS AND METHODS

Before mobilization of the liver during surgical intervention the following parameters were measured on the surface of the right (segment 7/8) and the left (segment 2/3) liver lobe with a probe, combining laser-Doppler-flowmetry and tissue-spectrometry: the oxygen saturation (SO2), the relative capillary hemoglobin concentration (rHB), the blood flow (flow) and the blood flow velocity (velo). In addition the peripheral oxygen saturation (SPO2), the central venous pressure (ZVP), the positive endexspiratory pressure (PEEP) and the hemoglobin (HB) were documented.

RESULTS

9 patients (median age 75 years) were included in the study. SPO2, ZVP, PEEP and HB were regular. The parameters SO2, rHB, flow and velo showed no significant changes between the right and the left liver lobe.

CONCLUSIONS

The O2C-method allows a reproducible intraoperative evaluation of the hepatic microcirculation.

Improved microcirculation by low-viscosity histidine- tryptophan-ketoglutarate graft flush and subsequent cold storage in University of Wisconsin solution: results of an orthotopic rat liver transplantation model

As previously shown in a model of isolated rat liver perfusion, the combined use of an initial graft flush with low-viscosity histidine-tryptophan-ketoglutarate (HTK) solution followed by cold storage in University of Wisconsin (UW) solution markedly improved the preservation during an extended cold storage period. In this study, we aimed to transfer our results into an in vivo model of orthotopic rat liver transplantation, and to elucidate the potential mechanism of the improved preservation by focusing on the hepatic microcirculation. Livers were harvested from male Wistar rats. Aortic perfusion with a pressure of 100 cm H(2)O was performed with either UW (group UW) or HTK (groups UW and HTK_UW), followed by additional back-table perfusion with UW (group HTK_UW). After 20-h cold storage at 4 degrees C, livers were orthotopically transplanted with reconstructing the hepatic artery. As measured by bile flow and liver enzymes, HTK flush followed by UW storage was superior compared to single use of either UW or HTK solution. The hepatic microcirculation was significantly improved, as shown by the increased percentage of reperfused sinusoids and reduced sinusoidal leucostasis. HTK and UW effectively reduce ischaemia-reperfusion injury after liver transplantation. By combining the comparative advantages of both solutions, a cumulative effect resulting in an improved preservation was shown. Thus, this mechanism improves microcirculatory reperfusion.

Microcirculatory function monitoring at the bedside--a view from the intensive care

Microcirculatory dysfunction plays a key role in the pathophysiology of various disease states and may consequently impact patient outcome. Until recently, the evaluation of the microcirculation using different measurement techniques has been mostly limited to animal and human research. With technical advances, microcirculatory monitoring nowadays becomes more and more available for application in clinical praxis. Unfortunately, measurements within the microcirculation are mostly limited to easily accessible surfaces, such as skin, muscle and tongue. Due to major differences in the physiologic regulation of microcirculatory blood flow and in metabolism between organs and even within different tissues in one organ, the clinical importance of regional microcirculatory measurements remains to be determined. In addition, technical methods available demonstrate large differences in the measured parameters and sampling volume, making interpretation of data even more difficult. Nonetheless, the monitoring of the microcirculation may, ahead of time, alert physicians that tissue oxygen supply becomes compromised and it may lead to a better understanding of basic pathophysiological aspects of disease. In the present review, we describe available non-invasive microcirculatory measurement techniques which can be applied clinically at the bedside. After a short discussion of physiologic and pathophysiologic basics related to microcirculatory monitoring, the measuring principles, applications, strengths and limitations of different monitoring systems are discussed.

Signs of reperfusion injury following CO2 pneumoperitoneum: an in vivo microscopy study

BACKGROUND

During laparoscopic surgery, pneumoperitoneum is generally established by means of carbon dioxide (CO(2)) insufflation which may disturb hepatic microperfusion. It has been suggested that the desufflation at the end of the procedure creates a model of reperfusion in a previously ischemic liver, thus predisposing it to reperfusion injury.

METHODS

To study the effects of pneumoperitoneum on hepatic microcirculation, Sprague-Dawley rats underwent pneumoperitoneum with an intraabdominal pressure of 8 or 12 mmHg for 90 min. Subsequently, in vivo microscopy was performed to assess intrahepatic microcirculation and transaminases were measured to index liver injury.

RESULTS

A CO(2) pneumoperitoneum of 8 mmHg did not change serum transaminases; however, further increase of intraperitoneal pressure to 12 mmHg significantly increased AST, ALT, and LDH measured after desufflation to almost 1.5 times as much as control values of 49 +/- 5 U/L, 31 +/- 3 U/L, and 114 +/- 12 U/L. In parallel, in all subacinar zones the permanent adherence of both leukocytes and platelets to the endothelium increased by about sixfold and threefold, respectively. Furthermore, Kupffer cells labeled with latex beads as an index for their activation were significantly increased compared to controls.

CONCLUSION

This in vivo observation demonstrated traces of reperfusion injury in liver induced by the insufflation and desufflation of CO(2 )pneumoperitoneum. The clinical relevance of this finding and the issue of using hepatoprotective substances to prevent this injury should be further investigated.

Protective effect of taurine against ischemia and reperfusion injury of transplanted pancreas in rats

AIM: To investigate the protective effect of taurine (TAU) on the ischemia and reperfusion injury during pancreas transplantation and its mechanism in rats.

METHODS: Rat models of pancreatic-duodenal transplantation were used in this study. Thirty Wistar rats were randomly allocated into 3 groups (n = 10), including control group (CMU-1 preservation solution), experiment group A (CMU-1 + TAU 5 mmol/L) and experiment group B (CMU-1 + TAU 10 mmol/L) (The liquid CMU-1 is multi-organ preservation solution produced in our laboratory). Blood samples were collected 6 hours after reperfusion for examination of serum amylase level. Pancreatic tissues were collect for pathologic observation. The expression of tumor necrosis factor-α (TNF-α) and interleukin-1b (IL-1β) were determined by immunohistochemistry using integrated optical density (IOD).

RESULTS: In comparison with that in control group, the level of serum amylase was increased 6 hours after reperfusion in experiment group A and B (911.2 ± 9.9, 959.9 ± 12.5 U/L vs 1239.5 ± 68.3 U/L, both P < 0.05). The effect of TAU was enhanced with the increased of concentrations. Immunohistochemistry showed that both TNF-α and IL-1β were expressed in pancreatic tissues 6 hours after transplantation, and TAU significantly inhibited TNF-α (12 346.4 ± 4933.69, 16 016.33 ± 4592.06 vs 22 039.71 ± 4782.62, both P < 0.05) and IL-1β (12 417.4 ± 2222.9, 15 047.68 ± 4484.4 vs 19 284.46 ± 3178.19, both P < 0.05) expression in experiment group A and B. Taurine treatment markedly ameliorated the inflammatory reaction of pancreatic tissues.

CONCLUSION: As a kind of cell-protection agent, TAU can inhibit the production of TNF-α and IL-1β, resist cell edema and alleviate ischemia/reperfusion-induced injury and pancreatitis.