Nitric oxide inhibition in the treatment of septic shock

N-Terminal B Natriuretic Peptide as a Prognostic Marker in Sepsis Induced Myocardial Dysfunction

BACKGROUND: Sepsis-induced myocardial dysfunction (SIMD) is an increasingly recognized form of transient cardiac dysfunction in sepsis patients. AIM: The aim of the study was to evaluation of N-terminal pro brain natriuretic peptide (NT-pro BNP) as a predictor of SIMD and poor outcome in patients with sepsis or septic shock. METHODS: Forty patients were enrolled and divided into: Group 1 with sepsis; Group 2 with septic shock. Each group was subdivided according to the presence or absence of cardiomyopathy. Echocardiography, NT-pro BNP - assay on the 1st and 2nd days of admission - were performed. RESULTS: NT-pro BNP level was significant predictor for cardiomyopathy in all case group with 75% sensitivity, 70% specificity (cutoff level >334 pg/ml) on 1st day of admission and 65% sensitivity, and 80% specificity (cutoff level >325 pg/ml) on 2nd day. On subgroup analysis, pro-BNP had 70% sensitivity, 90% specificity; cutoff level >334 pg/ml for prediction of cardiomyopathy in sepsis group and 70% sensitivity and 80% specificity; cutoff level >357pg/ml in septic shock group. Pro-BNP on 2nd day was excellent predictor of mortality in septic shock group with 100% sensitivity and specificity; cutoff level >350 pg/ml. CONCLUSION: N terminal pro-BNP is a good diagnostic and prognostic indicator for cardiomyopathy and mortality in septic patients.

Prolonged methylene blue infusion in refractory septic shock: a case report

PURPOSE

Methylene blue (MB) has been advocated for the treatment of refractory hemodynamic instability in patients with septic shock. However, the use of MB infusions in septic shock is not considered standard treatment, and the available literature describes infusions of short duration, typically less than six hours.

CLINICAL FEATURES

We report a case of septic shock in a 67-yr-old male who required maximal vasopressor support with norepinephrine, epinephrine, and vasopressin. Despite standard protocols for the treatment of septic shock, the patient's hemodynamic status was refractory 80 hr post admission. However, initiation of a MB infusion resulted in the rapid restoration of hemodynamic stability and a subsequent decrease in vasopressor requirements. Multiple attempts to discontinue the MB infusion resulted in immediate and repeated increases in vasopressor requirements, necessitating a continuous infusion with a slow taper of MB for 120 hr. Ultimately, the patient survived the illness and was discharged home. We observed no adverse events that could be attributed to the use of MB.

CONCLUSION

In our patient, the use of MB resulted in hemodynamic stability unattained with standard vasopressor support. Further research is warranted on the use of MB in patients with septic shock.

Selecting a Vasopressor Drug for Vasoplegic Shock After Adult Cardiac Surgery: A Systematic Literature Review

The choice of vasopressors to treat vasodilatory shock after cardiac surgery is a matter of controversy. We have systematically reviewed the literature and found that the data are insufficient to guide choice of agent. However, we found sufficient evidence that when a target blood pressure can not be achieved with a single agent, addition of another is more likely to help achieve the blood pressure target. We also found that there is no evidence that vasopressors induce organ ischemia. Finally, the lack of high quality data indicate that large multicenter trials are needed in this field.

A selective inducible NOS dimerization inhibitor prevents systemic, cardiac, and pulmonary hemodynamic dysfunction in endotoxemic mice

Increased nitric oxide (NO) production by inducible NO synthase (NOS2), an obligate homodimer, is implicated in the cardiovascular sequelae of sepsis. We tested the ability of a highly selective NOS2 dimerization inhibitor (BBS-2) to prevent endotoxin-induced systemic hypotension, myocardial dysfunction, and impaired hypoxic pulmonary vasoconstriction (HPV) in mice. Mice were challenged with Escherichia coli endotoxin before treatment with BBS-2 or vehicle. Systemic blood pressure was measured before and 4 and 7 h after endotoxin challenge, and echocardiographic parameters of myocardial function were measured before and 7 h after endotoxin challenge. The pulmonary vasoconstrictor response to left mainstem bronchus occlusion, which is a measure of HPV, was studied 22 h after endotoxin challenge. BBS-2 treatment alone did not alter baseline hemodynamics. BBS-2 treatment blocked NOS2 dimerization and completely inhibited the endotoxin-induced increase of plasma nitrate and nitrite levels. Treatment with BBS-2 after endotoxin administration prevented systemic hypotension and attenuated myocardial dysfunction. BBS-2 also prevented endotoxin-induced impairment of HPV. In contrast, treatment with NG-nitro-l-arginine methyl ester, which is an inhibitor of all three NOS isoforms, prevented the systemic hypotension but further aggravated the myocardial dysfunction associated with endotoxin challenge. Treatment with BBS-2 prevented endotoxin from causing key features of cardiovascular dysfunction in endotoxemic mice. Selective inhibition of NOS2 dimerization with BBS-2, while sparing the activities of other NOS isoforms, may prove to be a useful treatment strategy in sepsis.

Hemoglobin solutions and tissue oxygenation

Oxygen (O2) delivery to tissues plays an important role in determining microcirulatory autoregulatory responses. The balance between O2 delivery by whole blood and tissue O2 consumption likely has evolved based on regulatory processes designed to accommodate the encapsulation of hemoglobin (Hb) within red blood cells (RBCs). The hemodynamic, rheologic, and physical properties of blood, or an alternate O2-carrying solution, can have important consequences for O2 delivery to tissue. The development of acellular hemoglobin-based oxygen carriers (HBOC) requires reassessment of the O2 loading and unloading charactistics of Hb. the effects of altering the rheologic properties of blood, and the impact of these changes on microcirculatory autoregulation and tissue oxygenation. A variety of experimental and clinical studies have demonstrated beneficial effects of HBOCs. However, mechanisms responsible for HBOC-facilitated, O2-dependent autoregulatory changes in the microcirculation have not been completely elucidated.

A selective inhibitor for inducible nitric oxide synthase improves hypotension and lactic acidosis in canine endotoxic shock

OBJECTIVE

To investigate whether ONO-1714, a putative selective inhibitor for inducible nitric oxide synthase, modulates systemic hemodynamics, arterial blood gases, lactate concentrations, gastric mucosal perfusion, and renal and hepatic functions in endotoxic shock.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Laboratory at a university hospital.

SUBJECTS

Eighteen male beagle dogs (12-19 kg) under pentobarbital anesthesia.

INTERVENTIONS

Dogs were mechanically ventilated and monitored with a pulmonary arterial catheter and a gastric tonometer. They were divided in three groups: a) lipopolysaccharide (LPS) plus vehicle group (n = 6), which received LPS (250 ng/kg/min for 2 hrs) and saline 1 hr later; b) LPS plus ONO (0.05) group (n = 6), which received ONO-1714 (0.05 mg/kg) 1 hr after the start of LPS; c) LPS plus ONO (0.1) group (n = 6), which received ONO-1714 (0.1 mg/kg) 1 hr after the start of LPS.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics, blood gas parameters, gastric intramural pH, urine output, and serum levels of lactate, transaminases, bilirubin, and creatinine were measured during a 6-hr observation period. LPS induced hypotension, lactic acidosis, gastric mucosal acidosis, and renal and hepatic dysfunction. ONO-1714 reversed the LPS-induced hypotension and lactic acidosis without deteriorating cardiac output, oxygen delivery, or gastric mucosal acidosis.

CONCLUSIONS

These findings suggest that ONO-1714 is a useful agent to reverse hypotension and lactic acidosis in a canine endotoxic shock model.

Methylene blue based protein solder for vascular anastomoses: an in vitro burst pressure study

BACKGROUND AND OBJECTIVE

Attempts at sutureless anastomoses have used protein-based solders containing chromophores [Oz et al., J Vasc Surg 1990;11:718; Poppas et al., J Urol 1998150:1052] to enhance the strength of laser anastomoses. Reports have described the use of indocyanine green [Oz et al., Surg Forum 1989;316.], fuschin, and fluorescein isothiocyanate as chromophores [Chuck et al. , Lasers Surg Med 1989;9:471; Vance et al., Lasers Med Sci 1988;3:219]. Methylene blue (MB) is a chromophore with absorption peaks in the 600-700 nm region whose use has not been reported in laser-assisted vascular anastomoses. Therefore, we set out to produce and characterise a MB-containing protein solder. The absorption and burst pressure characteristics have been investigated and described as well as a brief review of the chemical and biological properties of MB.

STUDY DESIGN/MATERIALS AND METHODS

The MB and porcine serum albumin (PSA)-based solder was produced and used to form end-to-end anastomoses in porcine splenic arteries. The solder was activated using a laser diode emitting at 670 nm. The burst pressures of the anastomoses were tested, and the results analysed as a function of MB concentration and absorption. In addition, the relationship between MB concentration and absorption was examined.

RESULTS

A dose-response relationship was found between the measured absorption of the solder and the burst pressure of the anastomoses formed. Burst pressures exceeding physiological levels were found. Changes in MB concentration revealed a marked negative deviation from Beer's law at 670 nm, owing to the monomer-dimer-trimer equilibria.

CONCLUSION

PSA with MB solder is able to form high-quality end-to-end anastomoses, with immediate burst pressure profiles similar to those previously described for sutured [Quigley et al., Microsurgery 1985;6:229], lasered [Quigley et al., Microsurgery 1985;6:229], and soldered anastomoses [Small et al., J Clin Laser Med Surg 1997;15:205]. The relationship between burst pressure strength and chromophore absorption is discussed.

Nitric oxide in the pathogenesis of sepsis

In sepsis and septic shock, inflammatory mediators result in the production of increased concentrations of nitric oxide (NO) from the enzymatic breakdown of the amino acid L-arginine. The increased amounts of NO are responsible for changes in vasomotor tone, decreased vasopressor responsiveness, and decreased myocardial function, characteristic of septic insult. Therapeutic strategies designed to reduce the concentration of NO by inhibiting the action of the nitric oxide synthase enzyme, or by scavenging the excess NO, offer the potential to treat directly the vasomotor abnormalities and myocardial depression seen in sepsis and other inflammatory states. This article reviews the biology of NO in sepsis and discusses strategies for neutralization of the increased NO production, in the setting of severe sepsis and septic shock.

Selective inhibition of inducible nitric oxide synthase: effects on hemodynamics and regional blood flow in healthy and septic sheep

OBJECTIVES

To investigate the effects of S-ethylisothiourea (S-EITU) on hemodynamics, oxygen transport, and regional blood flow in healthy and septic sheep.

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational intensive care unit at a university medical center.

SUBJECTS

Eleven healthy, female adult sheep of the Merino breed, divided into a control group (n = 5) and into a group treated with S-EITU (n = 6).

INTERVENTIONS

All sheep were chronically instrumented. After a 5-day recovery period, they were randomly assigned to either control or S-EITU groups. While control sheep received only saline, S-EITU was administered in increasing doses of 1, 3, and 9 mg/kg/hr over 1 hr each (nonseptic phase). After 2 days of recovery, a continuous infusion of live Pseudomonas aeruginosa (2.5 x 106 colony-forming units/min) was started in all sheep and maintained for the remainder of the experiment. After 24 hrs of sepsis, the sheep again received their assigned treatment (septic phase). In both the nonseptic and septic phases, the sheep received colored microspheres through a left atrial catheter to allow analysis of regional blood flows. All animals were autopsied at the end of the experiments, and organ probes were removed for blood flow analyses.

MEASUREMENTS AND MAIN RESULTS

The administration of S-EITU caused a dose-dependent vasoconstriction in the nonseptic phase. After 24 hrs of Pseudomonas infusion, all sheep developed a hyperdynamic circulatory state, with increased cardiac indices and reduced arterial pressures and systemic vascular resistances. Oxygen extraction decreased significantly, preventing an increase in oxygen consumption, despite an increased oxygen delivery. The hyperdynamic circulation was dose dependently reversed by S-EITU, causing an increase in arterial pressure by peripheral vasoconstriction. Sheep in the control group showed a continuation of the hyperdynamic circulation. The effects of S-EITU on hemodynamics and regional blood flows were comparable under septic and nonseptic conditions.

CONCLUSIONS

With the inducible form of nitric oxide synthase expressed under septic, but not under nonseptic conditions, S-EITU was expected to have vasoconstrictive properties only in the septic phase. It produced a comparable vasoconstriction during the nonseptic phase of the experiment. Thus, either S-EITU does not selectively block the inducible nitric oxide synthase in sheep, or other vasodilators besides nitric oxide play an important role in septic vasodilation.

Nitric oxide mediates hepatocyte injury

The degree of acute hepatic failure after severe trauma and sepsis is related to the extent of hepatocyte (HC) damage and cell death resulting from either necrosis or apoptosis. We have previously demonstrated that tumor necrosis factor-alpha (TNF-alpha) and lipopolysaccharide (LPS) can directly lead to HC necrosis, but not apoptosis. To date, the reactive oxygen intermediates (ROI) and nitric oxide (NO) have been shown to play a potential role in the induction of cell apoptosis. However, it is unknown whether ROI and NO are involved in HC cell death. Therefore, in this study we tested the hypothesis that NO and ROI exert different effects on HC cell death. TNF-alpha and LPS alone failed to induce HC apoptosis but when combined with antioxidants resulted in HC apoptosis and DNA fragmentation, which is correlated with an increase in NO production. This effect was attenuated by the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). Moreover, the NO donor sodium nitroprusside resulted in HC apoptosis and cell damage as represented by hepatocellular enzyme release. Antioxidants inhibited TNF-alpha- and LPS-mediated ROI generation and peroxynitrite formation in HC. TNF-alpha- and LPS-induced HC damage could be further reduced by the combination of antioxidants and L-NMMA. These results indicate that NO is involved in HC injury, primarily through the induction of HC apoptosis.

Effect of L-NAME, an inhibitor of nitric oxide synthesis, on cardiopulmonary function in human septic shock

STUDY OBJECTIVES

We tested the effects of continuous infusion of N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, on cardiovascular performance and pulmonary gas exchange in patients with hyperdynamic septic shock.

DESIGN

Prospective clinical study.

SETTING

ICU of a university hospital.

PATIENTS

Eleven critically ill patients with severe refractory septic shock.

INTERVENTIONS

Standard hemodynamic measurements were made and blood samples taken before, during, and after 12 h of continuous infusion of 1 mg/kg/h of L-NAME.

MEASUREMENTS AND RESULTS

Continuous infusion of L-NAME increased mean arterial pressure (MAP) from 65+/-3 (SEM) to 93+/-4 mm Hg and systemic vascular resistance (SVR) from 962+/-121 to 1,563+/-173 dyne x s x cm(-5)/m2. Parallel to this, cardiac index (CI) decreased from 4.8+/-0.4 to 3.9+/-0.4 L/min/m2 and myocardial stroke volume (SV) was reduced from 43+/-3 to 34+/-3 mL/m2. Left ventricular stroke work was increased in the first hour of L-NAME infusion from 31+/-3 to 43+/-4 g x m/m2 (all p<0.01 compared with baseline). Heart rate, cardiac filling pressures, and right ventricular stroke work did not change significantly (p>0.05). L-NAME increased the ratio of arterial PO2 to the fraction of inspired O2 from 167+/-23 to 212+/-27 mm Hg (p<0.05). Venous admixture (QVA/QT) was reduced from 19.4+/-2.6% to 14.2+/-2.1% (p<0.05) and oxygen extraction ratio increased from 21.1+/-2.4% to 25.3+/-2.7% (p<0.05). Oxygen delivery (DO2) was reduced following L-NAME, whereas oxygen uptake and arterial lactate and pH were unchanged.

CONCLUSIONS

Prolonged inhibition of NO synthesis with L-NAME can restore MAP and SVR in patients with severe septic shock. Myocardial SV and CI decrease, probably as a result of increased afterload, since heart rate and stroke work were not reduced. L-NAME can improve pulmonary gas exchange with a concomitant reduction in QVA/QT. L-NAME did not promote anaerobe metabolism despite a reduction in DO2.

Prolonged inhibition of nitric oxide synthesis in severe septic shock: a clinical study

OBJECTIVES

Inhibitors of nitric oxide synthesis have been suggested to be of value in the treatment of hypotension during sepsis. However, earlier clinical reports only describe the initial effects of these nitric oxide inhibitors. This study was designed to examine the effects of the prolonged inhibition of nitric oxide synthesis with N(omega)-nitro-L-arginine methyl ester (L-NAME) in patients with severe septic shock.

DESIGN

Prospective, nonrandomized, clinical study.

SETTING

Medical-surgical intensive care unit in a university hospital.

PATIENTS

Eleven consecutive patients with ongoing hyperdynamic septic shock that was unresponsive to fluid resuscitation and vasopressor therapy.

INTERVENTIONS

Measurements of hemodynamic, hematologic, and biochemical variables were made before, during, and after the start of a continuous intravenous infusion of 1 mg/kg/hr of L-NAME, an inhibitor of nitric oxide synthesis, for a period of 12 hrs.

MEASUREMENTS AND MAIN RESULTS

Continuous infusion of L-NAME resulted in a direct increase in mean arterial pressure from 65 +/- 3 (SEM) to 93 +/- 4 mm Hg and an increase in systemic vascular resistance from 426 +/- 54 to 700 +/- 75 dyne x sec/cm5, reaching a maximum at 0.5 hr. Pulmonary arterial pressure was increased from 31 +/- 2 to a maximum of 36 +/- 2 mm Hg at 1 hr, and pulmonary vascular resistance increased from 146 +/- 13 to a maximum of 210 +/- 23 dyne x sec/cm5 at 3 hrs. Paralleling these changes, cardiac output decreased from 10.8 +/- 0.8 to 8.7 +/- 0.7 L/min and oxygen delivery decreased from 1600 +/- 160 to 1370 +/- 130 mL/min (for all changes p < .05 as compared with the baseline value). Heart rate, cardiac filling pressures, oxygen consumption, urine production, arterial lactate concentration, and other biochemical parameters were not significantly changed by L-NAME administration (all p > .05). Arterial oxygenation was improved during L-NAME infusion, and the dosage of catecholamines could be reduced (both p< .05). Although sustained hemodynamic effects were seen, L-NAME was most effective during the early stages of administration, and the effect of L-NAME on blood pressure and vascular resistance tended to diminish throughout the continuous infusion of L-NAME. Seven of 11 patients ultimately died, with survival time ranging from 2 to 34 days.

CONCLUSIONS

Nitric oxide appears to play a role in cardiovascular derangements during human sepsis. The increased blood pressure and vascular resistance values are sustained during prolonged inhibition of nitric oxide synthesis with L-NAME in patients with severe septic shock, although the hemodynamic changes are most significant in the early stages of L-NAME infusion. The high mortality rate in these patients may suggest that L-NAME has only limited effects on outcome.

Initial evaluation of diaspirin cross-linked hemoglobin (DCLHb) as a vasopressor in critically ill patients

OBJECTIVE

To evaluate the hemodynamic effects and any toxicologic effects of diaspirin cross-linked hemoglobin (DCLHb) in critically ill patients.

DESIGN

A prospective, observational study.

SETTING

A seven-bed intensive care unit (ICU) in a University teaching hospital.

PATIENTS

Fourteen critically ill patients requiring vasopressor therapy to maintain adequate mean arterial pressure (MAP). All patients had secondary organ dysfunction.

INTERVENTIONS

Administration of 100 mL boluses of 10% diaspirin cross-linked hemoglobin, up to a maximum of 500 mL, given over 15 mins and separated by 60 to 90 mins.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic parameters, norepinephrine and inotropic requirements, arterial and mixed venous blood gases, urine output, and biochemical and hematologic analyses were measured before diaspirin cross-linked hemoglobin administration and at multiple time points up to 72 hrs. MAP was maintained at approximately preinfusion values and the reduction in norepinephrine requirements was used as the main end point to assess the efficacy of diaspirin cross-linked hemoglobin as a vasopressor. Diaspirin cross-linked hemoglobin demonstrated a marked vasopressor action, allowing norepinephrine requirements to be reduced from 0.29 +/- 0.15 (SD) microgram/kg/min to 0.15 +/- 0.14 and 0.07 +/- 0.10 microgram/kg/min after the first (at 1.5 hrs, p < .001) and last (at 7.5 hrs, p < .0001) boluses, respectively. These reductions in norepinephrine requirements were maintained at 24, 48, and 72 hrs (p < .01 at all time points). These hemodynamic changes began within 5 mins of starting the diaspirin cross-linked hemoglobin infusion. MAP, heart rate, central venous pressure, pulmonary artery occlusion pressure, mean pulmonary arterial pressure (MPAP), systemic vascular resistance index, and urine output did not demonstrate any significant changes from preinfusion values. Pulmonary vascular resistance index increased at 7.5 hrs despite nonsignificant increases in MPAP. Cardiac index and oxygen delivery index decreased significantly at 7.5 hrs and 24 hrs. Total plasma bilirubin increased significantly from baseline at 24 and 48 hrs, before returning to baseline values within 5 days. Platelet count was significantly reduced at 6 and 24 hrs. No other biochemical or hematologic analyses were altered significantly post diaspirin cross-linked hemoglobin.

CONCLUSIONS

This preliminary study demonstrated that diaspirin cross-linked hemoglobin is a potent vasopressor agent in critically ill patients with septicemic shock or systemic inflammatory response syndrome. This vasopressor characteristic of diaspirin cross-linked hemoglobin may have future clinical applications.

Downregulation of renin gene expression by interleukin-1

The As4.1 cell line was established from a mouse kidney tumor by transgene-targeted tumorogenesis. These cells express high levels of renin mRNA from their endogenous renin gene and release approximately eightfold-more prorenin than active renin in culture. Levels of renin mRNA in As4.1 cells are decreased in a dose-dependent manner by the addition of physiological concentrations of cytokine interleukin-1 to the media. Stability of renin mRNA and initial rates of release of active renin and prorenin were not significantly altered by interleukin-1. In contrast, transcription initiated from a construct that consisted of 4.1 kilobases of renin 5' flanking sequence fused to a reporter gene (chloramphenicol acetyltransferase) was markedly inhibited by interleukin-1. On the basis of our findings, we conclude that downregulation of renin synthesis caused by interleukin-1 occurs primarily at the level of transcription and that DNA sequence or sequences mediating that effect are positioned within 4.1 kilobases upstream of the renin gene. The physiological relevance of this regulation is related to the events that occur during septic shock, characterized by hypotension, cardiovascular collapse, multiple organ failure, and high mortality. Unexpectedly, hypotension associated with septic shock does not lead to activation of the renin-angiotensin system. The hypotension in septicemia is believed to be mediated by the combined action of many modulators including cytokines, and data presented here suggest direct involvement of interleukin-1 in this process.

Activation of the L-arginine nitric oxide pathway in severe sepsis

AIMS

To determine in children with sepsis syndrome and septic shock the time course of nitric oxide metabolites: nitrate and nitrite (nitrogen oxides). To determine whether serum concentrations of nitrogen oxides distinguished those children who died from sepsis from those who survived; those who required prolonged inotropic support compared with those who did not; and whether there was any relationship of the levels of nitrogen oxides to markers of tissue perfusion.

METHODS

Nitrogen oxides were measured in 30 children with sepsis syndrome or septic shock at admission, 12, 24, and 48 hours. A non-septic control group had serum nitrogen oxides measured at admission. Markers of haemodynamics and tissue perfusion measured were mean arterial pressure, blood lactate, base deficit, gastric intramucosal pH, and deltaCO2 (DCO2: the difference between arterial and gastric intraluminal carbon dioxide tensions). Inotrope doses, number of organ systems failing at 48 hours, and outcome as survival were recorded.

RESULTS

Children with sepsis had increased nitrogen oxide concentrations at presentation compared with a group of non-septic controls. Children with organ failure at 48 hours had higher serum nitrogen oxide concentrations than those with sepsis uncomplicated by organ failure at 48 hours. There was no difference in nitrogen oxide when patients were subgrouped according to the receipt of inotropes at 48 hours, and no association with markers of tissue perfusion, or survival.

CONCLUSIONS

While this study shows that nitric oxide production is increased in sepsis in children, there was a limited relationship with clinically important markers of illness severity and no relationship to survival.