Nitric oxide administration restores the hepatic artery buffer response during porcine endotoxemia

Hepatic blood flow regulation but not oxygen extraction capability is impaired in prolonged experimental abdominal sepsis

Impaired oxygen utilization has been proposed to play a significant role in sepsis-induced liver dysfunction, but its magnitude and temporal course during prolonged resuscitation is controversial. The aim of this study is to evaluate the capability of the liver to increase oxygen extraction in sepsis during repeated acute portal vein blood flow reduction. Twenty anesthetized and mechanically ventilated pigs with hepatic hemodynamic monitoring were randomized to fecal peritonitis or controls (n = 10, each). After 8-h untreated sepsis, the animals were resuscitated for three days. The ability to increase hepatic O₂ extraction was evaluated by repeated, acute decreases in hepatic oxygen delivery (Do₂) via reduction of portal flow. Blood samples for liver function and liver biopsies were obtained repeatedly. Although liver function tests, ATP content, and Do₂ remained unaltered, there were signs of liver injury in blood samples and overt liver cell necrosis in biopsies. With acute portal vein occlusion, hepatic Do₂ decreased more in septic animals compared with controls [max. decrease: 1.66 ± 0.68 mL/min/kg in sepsis vs. 1.19 ± 0.42 mL/min/kg in controls; portal venous flow (Qpv) reduction-sepsis interaction: P = 0.028]. Hepatic arterial buffer response (HABR) was impaired but recovered after 3-day resuscitation, whereas hepatic oxygen extraction increased similarly during the procedures in both groups (max. increase: 0.27 ± 0.13 in sepsis vs. 0.18 ± 0.09 in controls; all P > 0.05). Our data indicate maintained capacity of the liver to acutely increase O₂ extraction, whereas blood flow regulation is transiently impaired with the potential to contribute to liver injury in sepsis.NEW & NOTEWORTHY The capacity to acutely increase hepatic O₂ extraction with portal flow reduction is maintained in sepsis with accompanying liver injury, but hepatic blood flow regulation is impaired.

Serum ammonia levels on admission for predicting sepsis patient mortality at D28 in the emergency department: A 2-center retrospective study

We assessed the predictive value of serum ammonia level on admission for the 28-day mortality of patients with sepsis.We retrospectively included septic patients admitted to the emergency department of West China Hospital, Sichuan University and The Fourth People's Hospital of Zigong city from June 2017 to May 2018. Patients were divided into 2 groups according to 28-day survival. Comparisons of serum ammonia level and sequential organ failure assessment (SOFA) score were made between 2 groups. Multivariate logistic regression models were employed to determine independent risk factors affecting 28-day mortality rate, and receiver operating characteristic (ROC) curve was also used to evaluate the efficacy of risk factors.Total of 316 patients were included into the study, 221 survived to 28 days and 95 were died before 28 days. The 28-day mortality rate was 30.06%. Multivariate logistic regression analyses revealed that the ammonia level, C reactive protein, SOFA score, and the leukocyte were independent risk factors for the 28-day mortality rate. In predicting the 28-day mortality rate, the SOFA score presented an area under the ROC curve (AUC) of 0.815, and the ammonia levels presented the AUC of 0.813.The ammonia level, C reactive protein, SOFA score, and the leukocyte are independent risk factors for 28-day mortality rate in septic patients. Moreover, the serum ammonia and SOFA score have similar predictive values. The serum ammonia level is also a suitable early indicator for prognostic evaluation of patients with sepsis as well.

Effect of Resveratrol on Blood Rheological Properties in LPS-Challenged Rats

Objectives: Abnormal rheological properties induce adverse effects during sepsis. This study sought to investigate the hypothesis that resveratrol (Res) improves blood rheological properties in rats following a lipopolysaccharide (LPS) challenge, and provide a novel approach for treatment of sepsis.

Methods: The rats were intraperitoneally or intramuscularly injected with vehicle, LPS (8 mg/kg), Res (30 mg/kg), or both to yield four groups: control, Res, LPS, and LPS + Res. After 6 h of LPS and/or Res injection, the mean arterial pressure (MAP), regional blood flow, erythrocyte and leukocyte parameters, and blood viscosity were observed.

Results: LPS administration had no significant effects on the erythrocyte parameters and plasma viscosity. LPS administration reduced the MAP, whole blood viscosity at low and medium shear rates, the blood flow in the spleen and kidney, and the leukocyte content in whole blood when compared to control group, and increased the myeloperoxidase (MPO) activity in lung. Treatment with Res alone had no effects on most of parameters observed except increasing the whole blood relative viscosity. However, Res treatment after LPS resulted in further decrease in whole blood viscosity at high and medium shear rates. Furthermore, Res treatment conversely decreased the red blood cell distribution width-CV, blood flow of stomach, whole blood relative viscosity and MPO activity in lung, and increased the leukocyte content, but did not restore LPS-induced decrease in MAP and the blood flow in the spleen and kidney.

Conclusion: The Res treatment partly reduce the whole blood viscosity and regional blood flow, and increase WBC content in peripheral blood following the LPS challenge, suggesting a favorable role in expanding the quasi-sympathetic effects of LPS in blood viscosity at early stages.

Patterns of Early Allograft Dysfunction in Adult Live Donor Liver Transplantation: The A2ALL Experience

BACKGROUND

Early allograft dysfunction (EAD) after living donor liver transplantation (LDLT) has often been attributed to inadequate graft size, and termed small-for-size syndrome. Early allograft dysfunction definitions include a variable constellation of findings, including hyperbilirubinemia, coagulopathy, encephalopathy, and ascites formation. Among putative causes of EAD after LDLT are excessive portal pressure and/or flow. Our objective was to evaluate patterns of EAD after LDLT.

METHODS

In this study, 631 LDLT recipients were monitored for complications, EAD (defined by postoperative day 7 bilirubin >10 mg/dL or international normalized ratio >1.6), and graft failure. Approximately 200 had portal venous and arterial pressure and flow measurements before and after LDLT. Portal inflow modification (splenic artery ligation, hemiportocaval shunt, or splenectomy) was performed at the discretion of the operating surgeon. Associations between EAD and recipient, donor, and transplant factors were examined using multivariable logistic regression.

RESULTS

Risk of EAD was associated with left lobe grafts, lower graft weight among left lobes, higher preoperative bilirubin, higher portal reperfusion pressure, higher donor age, and higher donor body mass index. The risk of graft loss within the first 90 days was 5.2 times higher for recipients with EAD versus those without EAD (P < 0.001).

CONCLUSIONS

Early allograft dysfunction can be defined using postoperative day 7 laboratory values that are highly predictive of early graft failure within 90 days. Risk factors associated with EAD after LDLT include: graft type and size, preoperative bilirubin, portal reperfusion pressure, donor age, and donor body mass index.

Advances in sepsis-associated liver dysfunction

Recent studies have revealed liver dysfunction as an early event in sepsis. Sepsis-associated liver dysfunction is mainly resulted from systemic or microcirculatory disturbances, spillovers of bacteria and endotoxin (lipopolysaccharide, LPS), and subsequent activation of inflammatory cytokines as well as mediators. Three main cell types of the liver which contribute to the hepatic response in sepsis are Kupffer cells (KCs), hepatocytes and liver sinusoidal endothelial cells (LSECs). In addition, activated neutrophils, which are also recruited to the liver and produce potentially destructive enzymes and oxygen-free radicals, may further enhance acute liver injury. The clinical manifestations of sepsis-associated liver dysfunction can roughly be divided into two categories: Hypoxic hepatitis and jaundice. The latter is much more frequent in the context of sepsis. Hepatic failure is traditionally considered as a late manifestation of sepsis-induced multiple organ dysfunction syndrome. To date, no specific therapeutics for sepsis-associated liver dysfunction are available. Treatment measure is mainly focused on eradication of the underlying infection and management for severe sepsis. A better understanding of the pathophysiology of liver response in sepsis may lead to further increase in survival rates.

Effects of cardiac preload reduction and dobutamine on hepatosplanchnic blood flow regulation in porcine endotoxemia

Insufficient cardiac preload and impaired contractility are frequent in early sepsis. We explored the effects of acute cardiac preload reduction and dobutamine on hepatic arterial (Qha) and portal venous (Qpv) blood flows during endotoxin infusion. We hypothesized that the hepatic arterial buffer response (HABR) is absent during preload reduction and reduced by dobutamine. In anesthetized pigs, endotoxin or vehicle (n = 12, each) was randomly infused for 18 h. HABR was tested sequentially by constricting superior mesenteric artery (SMA) or inferior vena cava (IVC). Afterward, dobutamine at 2.5, 5.0, and 10.0 μg/kg per minute or another vehicle (n = 6, each) was randomly administered in endotoxemic and control animals, and SMA was constricted during each dose. Systemic (cardiac output, thermodilution) and carotid, splanchnic, and renal blood flows (ultrasound Doppler) and blood pressures were measured before and during administration of each dobutamine dose. HABR was expressed as hepatic arterial pressure/flow ratio. Compared with controls, 18 h of endotoxin infusion was associated with decreased mean arterial blood pressure [49 ± 11 mmHg vs. 58 ± 8 mmHg (mean ± SD); P = 0.034], decreased renal blood flow, metabolic acidosis, and impaired HABR during SMA constriction [0.32 (0.18-1.32) mmHg/ml vs. 0.22 (0.08-0.60) mmHg/ml; P = 0.043]. IVC constriction resulted in decreased Qpv in both groups; whereas Qha remained unchanged in controls, it decreased after 18 h of endotoxemia (P = 0.031; constriction-time-group interaction). One control and four endotoxemic animals died during the subsequent 6 h. The maximal increase of cardiac output during dobutamine infusion was 47% (22-134%) in controls vs. 53% (37-85%) in endotoxemic animals. The maximal Qpv increase was significant only in controls [24% (12-47%) of baseline (P = 0.043) vs. 17% (-7-32%) in endotoxemia (P = 0.109)]. Dobutamine influenced neither Qha nor HABR. Our data suggest that acute cardiac preload reduction is associated with preferential hepatic arterial perfusion initially but not after established endotoxemia. Dobutamine had no effect on the HABR.

Morphological and biomechanical remodeling of the hepatic portal vein in a swine model of portal hypertension

OBJECTIVES

To obtain the morphological and biomechanical remodeling of portal veins in swine with portal hypertension (PHT), so as to provide some mechanical references and theoretical basis for clinical practice about PHT.

METHODS

Twenty white pigs were used in this study, 14 of them were subjected to both carbon tetrachloride- and pentobarbital-containing diet to induce experimental liver cirrhosis and PHT, and the remaining animals served as the normal controls. The morphological remodeling of portal veins was observed. Endothelial nitric oxide synthase expression profile in the vessel wall was assessed at both mRNA and protein level. The biomechanical changes of the hepatic portal veins were evaluated through assessing the following indicators: the incremental elastic modulus, pressure-strain elastic modulus, volume elastic modulus, and the incremental compliance.

RESULTS

The swine PHT model was successfully established. The percentages for the microstructural components and the histological data significantly changed in the experimental group. Endothelial nitric oxide synthase expression was significantly downregulated in the portal veins of the experimental group. Three incremental elastic moduli (the incremental elastic modulus, pressure-strain elastic modulus, and volume elastic modulus) of the portal veins from PHT animals were significantly larger than those of the controls (P < 0.05), whereas the incremental compliance of hepatic portal vein decreased.

CONCLUSIONS

Our study suggests that the morphological and biomechanical properties of swine hepatic portal veins change significantly during the PHT process, which may play a critical role in the development of PHT and serve as potential therapeutic targets during clinical practice.

Morphological and biomechanical remodelling of the hepatic artery in a swine model of portal hypertension

OBJECTIVES

To obtain the biomechanical and morphological remodelling of hepatic arteries in swine with portal hypertension.

METHODS

A number of 20 white pigs was used, of which 14 were subjected to liver cirrhosis and portal hypertension (PHT) induced by carbon tetrachloride and pentobarbital; the rest were used as the control group. The biomechanical remodelling of the hepatic arteries was measured, namely, the incremental elastic modulus (E inc), pressure-strain elastic modulus (E p), volume elastic modulus (E v), the incremental compliance (C), the opening angle and the stained microstructural components of the vessels.

RESULTS

The percentages for the microstructural components and the histologic data significantly changed in the experimental group, three incremental elastic moduli (E inc, E p, and E v) of the experimental group were significantly larger than those of the control group (P < 0.05); the compliance of hepatic arteries decreased greatly (P < 0.05) too. The opening angle (OA) was considerably larger than that of control group (P < 0.05).

CONCLUSIONS

The study suggests that the morphological and biomechanical properties of swine hepatic arteries have changed significantly during the process of portal hypertension and that from biomechanical aspects, the hepatic arteries have also suffered from extensive remodelling, which in turn deteriorates the existing portal hypertension.

Effects of L-arginine pretreatment on nitric oxide metabolism and hepatosplanchnic perfusion during porcine endotoxemia

BACKGROUND

Sepsis is accompanied by an increased need for and a decreased supply of arginine, reflecting a condition of arginine deficiency.

OBJECTIVE

The objective was to evaluate the effects of l-arginine pretreatment on arginine-nitric oxide (NO) production and hepatosplanchnic perfusion during subsequent endotoxemia.

DESIGN

In a randomized controlled trial, pigs (20-25 kg) received 3 μg . kg(-1) . min(-1) lipopolysaccharide (LPS; 5 endotoxin units/ng) intravenously and saline resuscitation. l-Arginine (n = 8; 5.3 μmol . kg(-1) . min(-1)) or saline (n = 8) was infused starting 12 h before LPS infusion and continued for 24 h after the endotoxin infusion ended. Whole-body appearance rates, portal-drained viscera (PDV), and liver fluxes of arginine, citrulline, NO, and arginine de novo synthesis were measured by using stable-isotope infusion of [(15)N(2)]arginine and [(13)C-(2)H(2)]citrulline. Hepatosplanchnic perfusion was assessed by using a primed continuous infusion of para-aminohippuric acid and jejunal intramucosal partial pressure of carbon dioxide and was related to systemic hemodynamics.

RESULTS

Arginine supplementation before LPS increased whole-body NO production in the PDV but not in the liver. Furthermore, it increased blood flow in the portal vein but not in the aorta and hepatic artery. During endotoxin infusion, arginine pretreatment was associated with an increased whole-body arginine appearance and NO production in the gut. Additional effects included a preserved mean arterial pressure, the prevention of an increase in pulmonary arterial pressure, an attenuated metabolic acidosis, and an attenuated increase in the intramucosal partial pressure of carbon dioxide.

CONCLUSION

Arginine treatment starting before endotoxemia appears to be beneficial because it improves hepatosplanchnic perfusion and oxygenation during prolonged endotoxemia, probably through an enhancement in NO synthesis, without causing deleterious systemic side effects.

Regulation of hepatic blood flow: The hepatic arterial buffer response revisited

The interest in the liver dates back to ancient times when it was considered to be the seat of life processes. The liver is indeed essential to life, not only due to its complex functions in biosynthesis, metabolism and clearance, but also its dramatic role as the blood volume reservoir. Among parenchymal organs, blood flow to the liver is unique due to the dual supply from the portal vein and the hepatic artery. Knowledge of the mutual communication of both the hepatic artery and the portal vein is essential to understand hepatic physiology and pathophysiology. To distinguish the individual importance of each of these inflows in normal and abnormal states is still a challenging task and the subject of ongoing research. A central mechanism that controls and allows constancy of hepatic blood flow is the hepatic arterial buffer response. The current paper reviews the relevance of this intimate hepatic blood flow regulatory system in health and disease. We exclusively focus on the endogenous interrelationship between the hepatic arterial and portal venous inflow circuits in liver resection and transplantation, as well as inflammatory and chronic liver diseases. We do not consider the hepatic microvascular anatomy, as this has been the subject of another recent review.

Effects of nitric oxide donor on hepatic arterial buffer response in anesthetized pigs

The effects of systemic administration of exogenous nitric oxide (NO) donor on hepatic arterial buffer response (HABR) have not yet been studied in an anesthetized model. In this study, 28 anesthetized pigs received administration of sodium nitroprusside (SNP) or nitroglycerin (NTG) as exogenous NO donors. Pressure-flow (P-Q) relationships in the hepatic artery defined the pressure at zero flow (P(Qha = 0)) and flow-dependent resistance (R). The magnitude of HABR was evaluated by comparing the change in hepatic arterial blood flow (DeltaQha) divided by the change in portal venous blood flow (DeltaQpv), using the index of change in blood flow (DeltaQha/DeltaQpv). Mean arterial pressure decreased from baseline (95.6 +/- 3.8 mmHg) to SNP condition (68.3 +/- 1.9 mmHg) and decreased from baseline (92.7 +/- 4.4 mmHg) to NTG condition (66.2 +/- 1.7 mmHg). Mean index of change in blood flow (DeltaQha/DeltaQpv) was also significantly increased from baseline (0.19 +/- 0.12) to SNP condition (0.28 +/- 0.17; p = .009) and from baseline (0.18 +/- 0.17) to NTG (0.28 +/- 0.20; p < .05). In conclusion, systemic administration of SNP and NTG increases HABR with reduced hepatic arterial tone under decreased mean arterial pressure, presumably via exogenous NO enhancing another regulatory system and reducing the pressure gradient for sinusoidal washout.

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.