Michael Wanecek

The endothelin system in septic and endotoxin shock

The view of the endothelium as a passive barrier has gradually changed as a number of endothelium-derived substances have been discovered. Substances like nitric oxide, prostaglandins and endothelins have potent and important properties, involving not only the circulation as such but also the response to stimuli like inflammation and trauma. The endothelin system, discovered in 1988, has not only strong vasoconstrictor properties, but also immunomodulating, endocrinological and neurological effects exerted through at least two types of receptors. Septic shock, a condition with high mortality, is associated with vast cardiovascular changes, organ dysfunction with microcirculatory disturbances and dysoxia. In the experimental setting, endotoxaemia resembles these changes and is, as well as septic shock, accompanied by a pronounced increase in plasma endothelin levels. The pathophysiology in septic and endotoxin shock remains to be fully elucidated, but several studies indicate that endothelial dysfunction is one contributing mechanism. Activation of the endothelin system is associated with several pathological conditions complicating septic shock, such as acute respiratory distress syndrome, cardiac dysfunction, splanchnic hypoperfusion and disseminated intravascular coagulation. Through the development of both selective and nonselective endothelin receptor antagonists, the endothelin system has been the object of a large number of studies during the last decade. This review highlights systematically the findings of previous studies in the area. It provides strong indications that the endothelin system, apart from being a marker of vascular injury, is directly involved in the pathophysiology of septic and endotoxin shock. Interventions with endothelin receptor antagonists during septic and endotoxin shock have so far only been done in animal studies but the results are interesting and promising.

Effects of levosimendan, a novel inotropic calcium-sensitizing drug, in experimental septic shock.

Objective Levosimendan is a novel inodilator that improves cardiac contractility by sensitizing troponin C to calcium. This drug has proved to be effective in treating advanced congestive heart failure but has not been evaluated in septic settings. The purpose of the present study was to study the effects of this drug in a porcine model of endotoxemia. Design Prospective experimental study. Subjects Fourteen landrace pigs. Interventions All animals were anesthetized and catheterized for measurement of central and pulmonary hemodynamics. Ultrasonic flow probes were placed around the renal artery and portal vein to measure blood flow. A tonometer was placed in the ileum to measure mucosal pH. Levosimendan was given to six animals as a bolus (200 &mgr;g·kg−1) followed by a continuous infusion (200 &mgr;g·kg−1· hr−1). Thirty minutes after onset of levosimendan treatment, all animals received endotoxin (20 &mgr;g·kg−1·hr−1 for 3 hrs). Measurements and Main Results At baseline, levosimendan induced a systemic vasodilation with a reduction in blood pressure and an increase in heart rate. A tendency to an increase in cardiac index did not reach statistical significance (p = .055).Cardiac index and systemic oxygen delivery were markedly improved in the levosimendan group during endotoxemia. Systemic vascular resistance and blood pressure were reduced in the levosimendan group. The latter parameter, however, was only different from the control group during the initial phase of endotoxin shock but not at the late, most pronounced phase of shock. Levosimendan also efficiently attenuated endotoxin-induced pulmonary hypertension. Portal venous blood flow and gut oxygen delivery were improved, but no concomitant reduction in endotoxin-induced intestinal mucosal acidosis was observed. Renal blood flow was unaffected, as was the endotoxin-induced increase in plasma endothelin-1-like immunoreactivity.These findings support previous reports of calcium desensitization as a potential component in septic myocardial depression. Furthermore, the vasodilatory properties of this drug were well tolerated in the current model of hypodynamic endotoxin shock, and they may have contributed to improved regional blood flow as seen in the gut as well as improved systemic perfusion by means of reduced biventricular afterload. Conclusion Pretreatment with levosimendan in pigs subjected to endotoxin shock improved cardiac output and systemic and gut oxygen delivery. In addition, pulmonary hypertension largely was attenuated without any adverse effects on gas exchange. These results are promising in several aspects, but the role of levosimendan in the treating circulatory failure in sepsis remains to be established.

Comparison of a single indicator and gravimetric technique for estimation of extravascular lung water in endotoxemic pigs

Objectives:To compare the single thermal indicator dilution (STID) technique for measurement of extravascular lung water (EVLWSTID) with gravimetrically determined EVLW (EVLWGRAV) in anesthetized pigs under sham and endotoxemic conditions. Design:Open experimental comparative animal study. Setting:University animal research laboratory. Subjects:Fifteen anesthetized landrace pigs. Interventions:Endotoxin infusion during 5 hrs in five pigs. Six animals were only anesthetized and rested for 5 hrs. In four additional animals, the impact on EVLWSTID measurements by changes in pulmonary perfusion, ventilation, and the combination of the two was studied. The alterations in ventilation and perfusion were induced by caval balloon inflation, inflation of the pulmonary artery catheter balloon, and bronchial plugging respectively. Measurements and Main Results:The STID technique, with default settings of the intrathoracic blood volume (ITBV) to global end-diastolic volume (GEDV) (i.e., the extrapulmonary intravascular volume between the point of injection of the indicator, and the point of detection) relationship (ITBV = 1.25GEDV), systematically overestimated the EVLW index compared with the gravimetrical method (mean bias of 5.4 mL/kg). By adapting the ITBV to GEDV relationship to the current model (ITBV = 1.52GEDV + 49.7), the accuracy of the STID technique improved. Moreover, the measurement of EVLWSTID proved to be reduced by manipulation of pulmonary perfusion and ventilation. However, the STID technique could detect an increase in EVLW during endotoxemia independent of the ITBV/GEDV relationship used. Conclusion:Despite technological improvement, the dilution techniques for the measurement of EVLW might still be influenced by changes in perfusion and ventilation. The STID technique, in addition, might demand adjustment of the ITBV/GEDV relationship to the particular condition and species subjected to measurement. The STID technique may, however, be a useful tool for monitoring changes of EVLW over time, but further studies are warranted to confirm this.

Bosentan-improved cardiopulmonary vascular performance and increased plasma levels of endothelin-1 in porcine endotoxin shock.

1 To evaluate the possible contribution of endothelin‐1 (ET‐1) to the pathophysiology of porcine septic shock, the non‐peptide, mixed ET‐receptor antagonist, bosentan (RO 47–0203) was administered (5 mg kg−1, i.v.) 30 min before infusion of lipopolysaccharide (LPS) (E. coli., serotype 0111:B4) (15 μg kg−1 h−1) and at 3.5 h of endotoxaemia in six anaesthetized and mechanically ventilated pigs. Six other pigs served as controls and received only LPS infusion. Pulmonary and systemic haemodynamics as well as splenic, renal and intestinal blood flows were measured continuously. Release and synthesis of ET‐1 and Big ET‐1 were also measured. 2 Only three of the six pigs in the control group survived 3 h of LPS infusion while in the bosentan‐treated group all six pigs were alive at that time. A biphasic increase in mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance (PVR) was seen in control pigs. Pretreatment with bosentan did not influence the first peak but markedly attenuated the second, more prolonged increase in MPAP and PVR. The second dose of bosentan completely restored these parameters to pre‐LPS levels. The LPS‐induced changes in mean arterial blood pressure, heart rate and systemic vascular resistance were similar in both groups, while cardiac output (CO) was significantly higher in the bosentan‐treated group. The second bosentan dose increased CO and splenic and intestinal blood flow without further lowering of blood pressure. 3 Bosentan caused an increase of the basal arterial plasma levels of ET‐1‐like immunoreactivity (LI), from 16.8 ± 1.3 pM to 49.6 ± 10.0 pM (n = 6, P < 0.01). However, the rate of the increase of ET‐1 levels during the LPS infusion was not affected by bosentan. Repeated administration of bosentan during LPS infusion caused an additional increase of ET‐1‐LI levels. Neither the basal levels of Big ET‐LI nor the LPS induced 8 fold increase in Big ET‐LI were changed by bosentan. The level of preproET‐1 mRNA in the lung was increased about 3 fold after 4.5 h of LPS treatment. This elevation was not influenced by bosentan. 4 From these studies using bosentan, a non‐peptide, selective and mixed ET‐receptor antagonist, we conclude that during LPS‐induced shock bosentan can abolish the late phase pulmonary hypertension and improve cardiac output as well as increase blood flow to the splenic and intestinal vascular beds without causing a further decrease in mean arterial blood pressure. Further investigations in the clinical setting are needed to evaluate the use of ET‐receptor antagonists, such as bosentan, in treatment of septic shock.

Cardiopulmonary Dysfunction During Porcine Endotoxin Shock Is Effectively Counteracted By The Endothelin Receptor Antagonist Bosentan

In a porcine endotoxin shock model, the mixed nonpeptide endothelin receptor antagonist bosentan was administered 2 h after onset of endotoxemia (n = 8). Cardiopulmonary vascular changes, oxygen-related variables, and plasma levels of endothelin-1-like immunoreactivity were compared with a control group that received only endotoxin (n = 8). Bosentan abolished the progressive increase in mean pulmonary artery pressure and pulmonary vascular resistance seen in controls. Possible mechanisms include blockade of vasoconstrictive endothelin receptors, and a lesser degree of edema and inflammation indicated by less alveolar protein and a lower inflammatory cell count observed in bronchoalveolar lavage. Further, bosentan restored cardiac index to the pre-endotoxin level by an increase in stroke volume index, improved systemic oxygen delivery, and acid base balance. Because mean arterial blood pressure was unaffected, bosentan reduced systemic vascular resistance. Endotoxemia resulted in an increase in tumor necrosis factor-α and endothelin-1-like immunoreactivity plasma levels, the latter being further increased by bosentan. In conclusion, in porcine endotoxemia, treatment with the endothelin receptor antagonist bosentan, administered during fulminate shock, abolished pulmonary hypertension and restored cardiac index. These findings suggest that bosentan could be an effective treatment for reversing a deteriorated cardiopulmonary state during septic shock.

The endothelin receptor antagonist, bosentan, in combination with the cyclooxygenase inhibitor, diclofenac, counteracts pulmonary hypertension in porcine endotoxin shock.

OBJECTIVE To prevent endotoxin-induced pulmonary hypertension in the pig with a combination of a nonpeptide mixed endothelin receptor antagonist, bosentan, and a cyclooxygenase inhibitor, diclofenac. DESIGN Prospective, controlled trial. SETTING Animal laboratory at a large university medical center. SUBJECTS Twelve domestic pigs, weighing 17.5 to 27 kg. INTERVENTIONS Endotoxin shock was induced by intravenous infusion of Escherichia coli lipopolysaccharide endotoxin (15 micrograms/kg/hr). Six pigs receiving only endotoxin served as controls. Six pigs were pretreated with intravenous bolus injections of bosentan (5 mg/kg) and diclofenac (3 mg/kg) followed by a continuous bosentan infusion (2.5 mg/kg/hr). MEASUREMENTS AND MAIN RESULTS Systemic hemodynamics and regional circulation were measured using ultrasonic flow probes. Arterial and mixed venous blood samples were collected regularty for determination of Big endothelin-1-like immunoreactivity, endothelin-1-like immunoreactivity, norepinephrine, and blood gases. The bosentan/diclofenac pretreatment per se significantly decreased mean pulmonary arterial pressure (p < .001), pulmonary vascular resistance index (p < .001), and mean arterial blood pressure (p < .001), but cardiac index did not change. Splenic blood flow increased (p < .01) while renal blood flow decreased (p < .001). In addition, intestinal blood flow decreased slightly (p < .05). In the control group, only three animals survived the 3 hrs of endotoxin infusion, while all pretreated animals survived. The biphasic increase in mean pulmonary arterial pressure and pulmonary vascular resistance index seen in control animals during endotoxemia was markedly attenuated in animals pretreated with the bosentan/diclofenac combination. The pretreated group generally showed a favorable hemodynamic course, with a relatively higher cardiac index, stroke volume index, and splenic and renal blood flow. In control animals, a pronounced metabolic acidosis developed during endotoxin infusion. A relatively higher arterial plasma concentration of endothelin-1-like immunoreactivity was reached in pretreated animals, while the Big endothelin-1-like immunoreactivity plasma increase was similar in both groups. Arterial concentrations of norepinephrine were significantly (p < .01) higher in control animals when compared with diclofenac/bosentan-treated animals. CONCLUSIONS The combination of bosentan and diclofenac induced systemic and pulmonary vasodilation in the intrinsic state. During endotoxin shock, this drug combination efficiently counteracts pulmonary hypertension and improves cardiac performance and splenic and renal blood flow. These favorable circulatory effects may have resulted in a reduction of both sympathetic nervous system activation and metabolic acidosis. Thus, we conclude that the endothelin receptors participate in intrinsic regulation of vascular tone in the anesthetized pig. During endotoxin shock, blockade of these receptors, as well as inhibition of the cyclooxygenase enzymes, contributes to a less adverse effect on the systemic and pulmonary circulation.

Effects on haemodynamics by selective endothelin ETB receptor and combined endothelin ETA/ETB receptor antagonism during endotoxin shock

The endothelin system is highly activated during endotoxin and septic shock. To investigate this matter the selective non-peptide endothelin ET(B) receptor antagonist A-192621 ([2R-(2alpha,3beta, 4alpha)]-4-(1,3-benzodioxol-5-yl)-1-[2-[2, 6-diethylphenyl)amino]-2-oxoethyl]-2-(4-propoxy-phenyl)-3-py rrolidine carboxylic acid) was administered alone and in combination with the selective non-peptide endothelin ET(A) receptor antagonist PD 155080 (sodium 2-benzo[1, 3]dioxol-5-yl-3-benzyl-4-(4-methoxy-phenyl)-4-oxobut-2-enoat e) during established porcine endotoxin shock. Cardiopulmonary vascular function, metabolic parameters and plasma endothelin-1-like immunoreactivity levels were compared to a control group only receiving endotoxin. Administration of A-192621 alone resulted in cardiovascular collapse and death whereas combining A-192621 with PD 155080 abolished endotoxin induced pulmonary hypertension, enhanced cardiac performance and improved systemic oxygen delivery and acid-base balance. The beneficial effects of mixed endothelin ET(A)/ET(B) receptor antagonisms on the pulmonary and cardiovascular systems may result from blockage of constrictive endothelin receptors in and pulmonary circulation, reduced afterload and a direct inotropic effect. Possible mechanisms for the devastating effects by selective endothelin ET(B) receptor antagonism include increased endothelin ET(A) receptor-mediated vasoconstriction due to lack of endothelin ET(B) receptormediated vasodilation and decreased endothelin clearance from endothelin ET(B) receptor blockade. In conclusion, selective endothelin ET(B) receptor antagonism is deleterious whereas combined endothelin ET(A) and ET(B) receptor antagonism has favourable effects on haemodynamics, suggesting participation of the endothelin system in cardiopulmonary dysfunction during endotoxin shock.

Analyses of cerebral microdialysis in patients with traumatic brain injury: relations to intracranial pressure, cerebral perfusion pressure and catheter placement.

BackgroundCerebral microdialysis (MD) is used to monitor local brain chemistry of patients with traumatic brain injury (TBI). Despite an extensive literature on cerebral MD in the clinical setting, it remains unclear how individual levels of real-time MD data are to be interpreted. Intracranial pressure (ICP) and cerebral perfusion pressure (CPP) are important continuous brain monitors in neurointensive care. They are used as surrogate monitors of cerebral blood flow and have an established relation to outcome. The purpose of this study was to investigate the relations between MD parameters and ICP and/or CPP in patients with TBI.MethodsCerebral MD, ICP and CPP were monitored in 90 patients with TBI. Data were extensively analyzed, using over 7,350 samples of complete (hourly) MD data sets (glucose, lactate, pyruvate and glycerol) to seek representations of ICP, CPP and MD that were best correlated. MD catheter positions were located on computed tomography scans as pericontusional or nonpericontusional. MD markers were analyzed for correlations to ICP and CPP using time series regression analysis, mixed effects models and nonlinear (artificial neural networks) computer-based pattern recognition methods.ResultsDespite much data indicating highly perturbed metabolism, MD shows weak correlations to ICP and CPP. In contrast, the autocorrelation of MD is high for all markers, even at up to 30 future hours. Consequently, subject identity alone explains 52% to 75% of MD marker variance. This indicates that the dominant metabolic processes monitored with MD are long-term, spanning days or longer. In comparison, short-term (differenced or Δ) changes of MD vs. CPP are significantly correlated in pericontusional locations, but with less than 1% explained variance. Moreover, CPP and ICP were significantly related to outcome based on Glasgow Outcome Scale scores, while no significant relations were found between outcome and MD.ConclusionsThe multitude of highly perturbed local chemistry seen with MD in patients with TBI predominately represents long-term metabolic patterns and is weakly correlated to ICP and CPP. This suggests that disturbances other than pressure and/or flow have a dominant influence on MD levels in patients with TBI.

Differentiated and dose-related cardiovascular effects of a dual endothelin receptor antagonist in endotoxin shock.

Objective:To evaluate the effects of endothelin receptor antagonism on cardiac performance in endotoxin shock. Design:Prospective, experimental study. Setting:A university-affiliated research institution. Subjects:Domestic anesthetized landrace pigs. Interventions:Thirty-seven pigs were anesthetized and subjected to echocardiography, coronary sinus catheterization, and monitoring of central and regional hemodynamics in order to assess cardiac performance. All animals received endotoxin for 5 hrs. Twenty pigs served as endotoxin controls. Tezosentan, a dual endothelin-A and -B receptor antagonist, was administered during established endotoxemic shock. Seven pigs received an infusion of tezosentan of 1·mg·kg−1·hr−1 (tezo1), and an additional ten pigs received a higher dose of 10 mg·kg−1·hr−1 (tezo10). Measurements and Main Results:Endotoxemia evoked a state of shock with pulmonary hypertension and metabolic acidosis. A decrease in stroke volume and coronary perfusion pressure as well as an increase in troponin I was also noted. Tezosentan administration resulted in a significant increase in cardiac index, stroke volume index, left ventricular stroke work index, and left ventricular end-diastolic area index. Decreases in systemic and pulmonary vascular resistance indexes were also evident after intervention. This was achieved without changes in heart rate or systemic arterial or pulmonary artery occlusion pressures in tezo1 animals compared with controls. In addition, metabolic variables were improved by tezosentan. These effects were sustained only in the tezo1 group. In the higher dosage, tezosentan resulted in a deterioration of cardiac performance and 50% mortality rate. The endotoxin-induced increase in troponin I was attenuated in the tezo1 group compared with controls. Conclusions:In this porcine model of volume-resuscitated, endotoxemic shock, endothelin-receptor blockade with tezosentan improved cardiac performance. However, the effect was not sustained with higher doses of tezosentan, possibly due to reduced coronary perfusion pressure. These findings show differentiated, dose-dependent effects by dual endothelin receptor blockade on endotoxin-induced cardiovascular dysfunction.

Tezosentan counteracts endotoxin-induced pulmonary edema and improves gas exchange

Sepsis-induced acute lung injury is still associated with high morbidity and mortality. The pathophysiology is complex, and markers of injury include increased extravascular lung water. To evaluate the effects of the novel dual endothelin receptor antagonist tezosentan on endotoxin-induced changes in extravascular lung water and gas exchange, 16 pigs were anaesthetized and catheterized. Twelve animals were subjected to 5 h of endotoxemia. After 2 h, six of these animals received a bolus of tezosentan 1 mg kg−1 followed by a continuous infusion of 1 mg kg−1 h−1 to the end of the experiment at 5 h. Conventional pulmonary and hemodynamic parameters were measured. Extravascular lung water was determined in these pigs after 5 h of endotoxemia, as well as in the four additional nonendotoxemic sham animals. Tezosentan in the current dosage counteracted the deterioration of lung function caused by endotoxin, as measured by dead space, venous admixture, and compliance. In addition, pulmonary hypertension was attenuated. Tezosentan had a marked effect on the endotoxin-induced increase in extravascular lung water that was reduced to levels observed in nonendotoxemic sham animals. These results suggest that endothelin is involved in endotoxin-induced lung injury and the development of pulmonary edema. Dual endothelin receptor antagonism may be of value in the treatment of sepsis-related acute lung injury.