Effects of alpha - and beta -adrenergic stimulation on hepatosplanchnic perfusion and oxygen extraction in endotoxic shock

Pathophysiology, mechanisms, and managements of tissue hypoxia

Oxygen is needed to generate aerobic adenosine triphosphate and energy that is required to support vital cellular functions. Oxygen delivery (DO₂) to the tissues is determined by convective and diffusive processes. The ability of the body to adjust oxygen extraction (ERO₂) in response to changes in DO₂ is crucial to maintain constant tissue oxygen consumption (VO₂). The capability to increase ERO₂ is the result of the regulation of the circulation and the effects of the simultaneous activation of both central and local factors. The endothelium plays a crucial role in matching tissue oxygen supply to demand in situations of acute drop in tissue oxygenation. Tissue oxygenation is adequate when tissue oxygen demand is met. When DO₂ is severely compromised, a critical DO₂ value is reached below which VO₂ falls and becomes dependent on DO₂, resulting in tissue hypoxia. The different mechanisms of tissue hypoxia are circulatory, anaemic, and hypoxic, characterised by a diminished DO₂ but preserved capacity of increasing ERO₂. Cytopathic hypoxia is another mechanism of tissue hypoxia that is due to impairment in mitochondrial respiration that can be observed in septic conditions with normal overall DO₂. Sepsis induces microcirculatory alterations with decreased functional capillary density, increased number of stopped-flow capillaries, and marked heterogeneity between the areas with large intercapillary distance, resulting in impairment of the tissue to extract oxygen and to satisfy the increased tissue oxygen demand, leading to the development of tissue hypoxia. Different therapeutic approaches exist to increase DO₂ and improve microcirculation, such as fluid therapy, transfusion, vasopressors, inotropes, and vasodilators. However, the effects of these agents on microcirculation are quite variable.

β₁-adrenergic receptor-mediated HO-1 induction, via PI3K and p38 MAPK, by isoproterenol in RAW 264.7 cells leads to inhibition of HMGB1 release in LPS-activated RAW 264.7 cells and increases in survival rate of CLP-induced septic mice

High mobility group box (HMGB)-1 plays an important role in sepsis-associated death in experimental studies. Heme oxygenase-1 (HO-1) inducers were reported to reduce HMGB1 release in experimental sepsis. Previously, we reported on the importance of the β₁-adrenergic receptor and protein kinase A pathway in the regulation of HO-1 expression by isoproterenol (ISO) in RAW 264.7 cells. We investigated whether ISO reduces HMGB1 release in LPS-activated RAW 264.7 cells and improves survival rate in septic mice due to HO-1 induction. ISO concentration-dependently increased HO-1 via Nrf-2 translocation and inhibited release of HMGB1 through the β₁-adrenergic receptor (β₁-AR) in LPS-activated RAW 264.7 cells. This conclusion was supported by the finding that dobutamine but not salbutamol increased HO-1 expression in both RAW 264.7 cells. ISO failed to inhibit HMGB1 release when HO-1 expression was suppressed by ZnPPIX, an HO-1 inhibitor in RAW 264.7 cells. ISO significantly inhibited phosphorylation of IκB-α and NF-κB-driven luciferase activity in LPS-activated RAW 264.7 cells. In addition, LY294002, a PI3K inhibitor, and SB203580, a p38 MAPK inhibitor, significantly inhibited not only HO-1 induction but also HMGB1 release by ISO. Importantly, ISO increased HO-1 protein expression in heart and lung tissues, reduced HMGB1 in plasma and increased survival rate in CLP-treated septic mice, which was significantly reversed by co-treatment with ZnPPIX. Taken together, we conclude that inhibition of HMGB1 release during sepsis via β₁-AR-mediated HO-1 induction is a novel mechanism for the beneficial effects of ISO in the treatment of sepsis.

Phenylephrine versus norepinephrine for initial hemodynamic support of patients with septic shock: a randomized, controlled trial

Introduction

Previous findings suggest that a delayed administration of phenylephrine replacing norepinephrine in septic shock patients causes a more pronounced hepatosplanchnic vasoconstriction as compared with norepinephrine. Nevertheless, a direct comparison between the two study drugs has not yet been performed. The aim of the present study was, therefore, to investigate the effects of a first-line therapy with either phenylephrine or norepinephrine on systemic and regional hemodynamics in patients with septic shock.

Methods

We performed a prospective, randomized, controlled trial in a multidisciplinary intensive care unit in a university hospital. We enrolled septic shock patients (n = 32) with a mean arterial pressure below 65 mmHg despite adequate volume resuscitation. Patients were randomly allocated to treatment with either norepinephrine or phenylephrine infusion (n = 16 each) titrated to achieve a mean arterial pressure between 65 and 75 mmHg. Data from right heart catheterization, a thermodye dilution catheter, gastric tonometry, acid-base homeostasis, as well as creatinine clearance and cardiac troponin were obtained at baseline and after 12 hours. Differences within and between groups were analyzed using a two-way analysis of variance for repeated measurements with group and time as factors. Time-independent variables were compared with one-way analysis of variance.

Results

No differences were found in any of the investigated parameters.

Conclusions

The present study suggests there are no differences in terms of cardiopulmonary performance, global oxygen transport, and regional hemodynamics when phenylephrine was administered instead of norepinephrine in the initial hemodynamic support of septic shock.

Trial registration

ClinicalTrial.gov NCT00639015

SHORT-TERM EFFECTS OF PHENYLEPHRINE ON SYSTEMIC AND REGIONAL HEMODYNAMICS IN PATIENTS WITH SEPTIC SHOCK

Clinical studies evaluating the use of phenylephrine in septic shock are lacking. The present study was designed as a prospective, crossover pilot study to compare the effects of norepinephrine (NE) and phenylephrine on systemic and regional hemodynamics in patients with catecholamine-dependent septic shock. In 15 septic shock patients, NE (0.82 +/- 0.689 microg x kg(-1) x min(-1)) was replaced with phenylephrine (4.39 +/- 5.23 microg x kg(-1) x min(-1)) titrated to maintain MAP between 65 and 75 mmHg. After 8 h of phenylephrine infusion treatment was switched back to NE. Data from right heart catheterization, acid-base balance, thermo-dye dilution catheter, gastric tonometry, and renal function were obtained before, during, and after replacing NE with phenylephrine. Variables of systemic hemodynamics, global oxygen transport, and acid-base balance remained unchanged after replacing NE with phenylephrine except for a significant decrease in heart rate (phenylephrine, 89 +/- 18 vs. NE, 93 +/- 18 bpm; P < 0.05). However, plasma disappearance rate (phenylephrine, 13.5 +/- 7.1 vs. NE, 16.4 +/- 8.7% x min(-1)) and clearance of indocyanine green (phenylephrine, 330 +/- 197 vs. NE, 380 +/- 227 mL x min(-1) x m(-2)), as well as creatinine clearance (phenylephrine, 81.3 +/- 78.4 vs. NE, 94.3 +/- 93.5 mL x min(-1)) were significantly decreased by phenylephrine infusion (each P < 0.05). In addition, phenylephrine increased arterial lactate concentrations as compared with NE infusion (1.7 +/- 1.0 vs. 1.4 +/- 1.1 mM; P < 0.05). After switching back to NE, all variables returned to values obtained before phenylephrine infusion except creatinine clearance and gastric tonometry values. Our results suggest that for the same MAP, phenylephrine causes a more pronounced hepatosplanchnic vasoconstriction as compared with NE.

Effects of antiglaucoma drugs GLC756, a novel dopamine D2 agonist and D1 antagonist, and timolol on endotoxin-induced TNF-alpha release in serum of rats

PURPOSE

Anti-inflammatory activity of an antiglaucoma drug may be an advantage for long-term treatment of glaucoma since it may reduce the risk of treatment-related inflammatory processes in outer compartments of the eye and probably also prevent or delay progression of glaucomatous retinal neurodegeneration. In this study, the effect of GLC756, a novel mixed dopamine D 2 receptor agonist and dopamine D 1 receptor antagonist, and timolol on endo-toxin-induced cytokine tumor necrosis factor-alpha (TNF-alpha) release in serum was examined.

METHODS

For endotoxin-induced TNF-alpha release, 8-week-old Lewis rats were intravenously injected with 160 microg lipopolysaccharide (LPS) from Salmonella typhimurium. GLC756, timolol, or betamethasone were either systemically (1 mg/kg SC for 5 days) or topically (0.4%, 0.5%, and 0.1%, respectively, 20 microL eye drops given 16 times over 48 hours in left and right eye) administered. TNF-alpha was measured in serum 2 and 48 hours after LPS induction.

RESULTS

A marked TNF-alpha increase in serum was found 2 hours after LPS induction. Administration of GLC756 and betamethasone, systemically and topically, decreased TNF-alpha release. However, due to large scattering of mean values only the effect of systemically administered GLC756 was statistically significant. In contrast, timolol increased TNF-alpha values stronger than LPS alone.

CONCLUSIONS

The significant suppression of LPS-induced TNF-alpha increase by GLC756 suggests an additional anti-inflammatory potential of the dopaminergic compound in the treatment of glaucoma.

Critical oxygen delivery during cardiopulmonary bypass in dogs

BACKGROUND AND OBJECTIVE

To determine the minimal oxygen delivery and pump flow that can maintain systemic oxygen uptake during normothermic (37 degrees C) pulsatile and non-pulsatile cardiopulmonary bypass in dogs.

METHODS

Eighteen anaesthetized dogs were randomly assigned to receive either non-pulsatile (Group C; n = 9) or pulsatile bypass flow (Group P; n = 9). Oxygen delivery was reduced by a progressive decrease in pump flow, while arterial oxygen content was maintained constant. In each animal, critical oxygen delivery was determined from plots of oxygen uptake vs. oxygen delivery and from plots of blood lactate vs. oxygen delivery using a least sum of squares technique. Critical pump flow was determined from plots of lactate vs. pump flow.

RESULTS

At the critical point, oxygen delivery obtained from oxygen uptake was 7.7 +/- 1.1 mL min(-1) kg(-1) in Group C and 6.8 +/- 1.8 mL min(-1) kg(-1) in Group P (n.s.). These values were similar to those obtained from lactate measurements (Group C: 7.8 +/- 1.6 mL min(-1) kg(-1); Group P: 7.6 +/- 2.0 mL min(-1) kg(-1)). Critical pump flows determined from lactate measurements were 55.6 +/- 13.8 mL min(-1) kg(-1) in Group C and 60.8 +/- 13.9 mL min(-1) kg(-1) in Group P (n.s.).

CONCLUSIONS

Oxygen delivery values greater than 7-8 mL min(-1) kg(-1) were required to maintain oxygen uptake during normothermic cardiopulmonary bypass with either pulsatile or non-pulsatile blood flow. Elevation of blood lactate levels during bypass helps to identify inadequate tissue oxygen delivery related to insufficient pump flow.

Renal blood flow in sepsis

Introduction

To assess changes in renal blood flow (RBF) in human and experimental sepsis, and to identify determinants of RBF.

Method

Using specific search terms we systematically interrogated two electronic reference libraries to identify experimental and human studies of sepsis and septic acute renal failure in which RBF was measured. In the retrieved studies, we assessed the influence of various factors on RBF during sepsis using statistical methods.

Results

We found no human studies in which RBF was measured with suitably accurate direct methods. Where it was measured in humans with sepsis, however, RBF was increased compared with normal. Of the 159 animal studies identified, 99 reported decreased RBF and 60 reported unchanged or increased RBF. The size of animal, technique of measurement, duration of measurement, method of induction of sepsis, and fluid administration had no effect on RBF. In contrast, on univariate analysis, state of consciousness of animals (P = 0.005), recovery after surgery (P < 0.001), haemodynamic pattern (hypodynamic or hyperdynamic state; P < 0.001) and cardiac output (P < 0.001) influenced RBF. However, multivariate analysis showed that only cardiac output remained an independent determinant of RBF (P < 0.001).

Conclusion

The impact of sepsis on RBF in humans is unknown. In experimental sepsis, RBF was reported to be decreased in two-thirds of studies (62 %) and unchanged or increased in one-third (38%). On univariate analysis, several factors not directly related to sepsis appear to influence RBF. However, multivariate analysis suggests that cardiac output has a dominant effect on RBF during sepsis, such that, in the presence of a decreased cardiac output, RBF is typically decreased, whereas in the presence of a preserved or increased cardiac output RBF is typically maintained or increased.

Is there a place for N-acetylcysteine in the treatment of septic shock?

Excessive inflammatory responses and impaired oxygen utilization because of microcirculatory failure are implicated in septic shock. Recent studies have pointed out some beneficial effects in the treatment of septic shock of several vasodilators that exert anti-inflammatory properties. In particular, the antioxidant N-acetylcysteine has been demonstrated to enhance cardiac performance, and to improve hepatosplanchnic perfusion and liver function in patients with established septic shock. These clinical observations may lead us to examine further the role of antioxidant agents in developing novel therapies for septic shock.

Continuous Therapeutic Epinephrine but not Norepinephrine Prolongs Splanchnic IL-6 Production in Porcine Endotoxic Shock

Catecholamines play a central role in the treatment of sepsis-associated hypotension. However, these hormones have also been shown to modulate the lipopolysaccharide (LPS)-induced induction of cytokines such as tumor necrosis factor alpha, interleukin (IL)-10, and IL-6 in vitro and in human endotoxemia. We hypothesized that catecholamines applied therapeutically in septic shock also influence cytokine patterns. We studied the cytokine response in tissues of the splanchnic compartment in a porcine endotoxin shock model up to 4 h. Shock was induced by a short infusion of LPS, and animals were treated either with fluid resuscitation alone or in combination with continuous epinephrine or norepinephrine. Animals, receiving epinephrine therapy, showed a significantly prolonged upregulation of IL-6 mRNA expression at 4 h after LPS application in liver (P = 0.0014), spleen (P < 0.0001), and mesenteric lymph nodes (P = 0.0078) as compared with animals treated with norepinephrine or fluid resuscitation. Serum IL-6 increased over time in all groups. The total concentration of the cytokine (area under the curve) was significantly higher in the epinephrine group as compared with the norepinephrine and fluid resuscitation groups (P = 0.017). The peak of serum tumor necrosis factor alpha at 1 h after LPS application was already significantly reduced by epinephrine, which was only administered at a mean of less than 0.05 microg/kg/min at this time point (P < 0.01). None of the catecholamines had a significant effect on IL-10 serum levels when compared with animals receiving fluid resuscitation alone. Our data suggest that the therapeutic application of epinephrine but not of norepinephrine is associated with a profound effect on the IL-6 response of splanchnic reticuloendothelial tissues.

Dopamine does not correct oxygen consumption/oxygen delivery relation abnormality during vasomotor shock induced by interleukin-1beta

We previously showed that interleukin 1beta (IL-1beta) induces vasomotor shock and impairs the oxygen consumption (VO2)/oxygen delivery (DO2) relation by increasing the slope of the supply-independent line in rabbits. In the present study, we investigated the inotropic effect of dopamine on the VO2/DO2 abnormality induced by IL-1beta. Twelve rabbits were divided into two groups (n = 6, each) and were given 10 microg/kg of IL-1beta or saline (control) intravenously. After baseline measurements were obtained, dopamine was infused continuously at a rate of 20 microg/kg/min throughout the study in both groups. All rabbits were subjected to stepwise cardiac tamponade to reduce the DO2 to <5 mL/min/kg by inflation of a handmade balloon placed into the pericardial sac. The VO2/DO2 relation was then analyzed by the dual-line method. Dopamine failed to correct the IL-1beta-induced decrease in mean arterial pressure to the baseline level. Dopamine significantly increased cardiac index in both groups, resulting in significant increases in DO2 (IL-1beta, 28.5 +/- 6.0 mL/min/kg from baseline 24.1 +/- 3.5 mL/min/kg; control, 27.7 +/- 2.9 mL/min/kg from baseline 22.9 +/- 2.9 mL/min/kg), but did not affect VO2 (IL-1beta, 10.0 +/- 0.5 mL/min/kg from baseline 9.9 +/- 0.7 mL/min/kg; control, 10.2 +/- 0.4 mL/min/kg from baseline 10.2 +/- 0.2 mL/min/kg). The IL-1beta group showed a significantly greater supply-independent line slope than that of controls (IL-1beta, y = 0.14x + 6.3; control, y = 0.06x + 8.6) during stepwise decreases in DO2. These results indicate that continuous infusion of dopamine at 20 microg/kg/min increases DO2 but does not correct the vasomotor disturbance or VO2/DO2 abnormality caused by IL-1beta.

New management strategies in ARDS. Immunomodulation

Acute respiratory distress syndrome is a common condition among the critically ill and is associated with high morbidity and mortality [table: see text] rates. Improved understanding of the underlying inflammatory pathogenetics has encouraged the search for strategies that, by modifying this immune response, can improve outcome for this group of patients. Some agents are obviously anti-inflammatory. Others have been used primarily for other purposes; their immune effects are incidental, but no less important. Although immunomodulatory strategies have been discussed for many years, they now are beginning to show positive results, as in the study using activated protein C. Most patients with ARDS die with ARDS, rather than from ARDS. The approach to treatment must not be lung-limited but must take into account the systemic effects of the inflammatory response. The complex nature of the syndrome makes it likely that no single agent will provide the long-desired cure. Rather, it is probable that an individual patient will require a combination of several agents or different agents at different times during the disease process (Table 1). Mortality rates from ARDS already are beginning to fall with improved nutritional and ventilatory support. Positive results from trials using immunomodulatory agents are being reported, and soon such agents will form part of the routine management of patients with ARDS, further improving the outlook for these patients.