Nitric oxide synthase inhibition restores hypoxic pulmonary vasoconstriction in sepsis

Thoracic epidural analgesia: a new approach for the treatment of acute pancreatitis?

This review article analyzes, through a nonsystematic approach, the pathophysiology of acute pancreatitis (AP) with a focus on the effects of thoracic epidural analgesia (TEA) on the disease. The benefit-risk balance is also discussed. AP has an overall mortality of 1 %, increasing to 30 % in its severe form. The systemic inflammation induces a strong activation of the sympathetic system, with a decrease in the blood flow supply to the gastrointestinal system that can lead to the development of pancreatic necrosis. The current treatment for severe AP is symptomatic and tries to correct the systemic inflammatory response syndrome or the multiorgan dysfunction. Besides the removal of gallstones in biliary pancreatitis, no satisfactory causal treatment exists. TEA is widely used, mainly for its analgesic effect. TEA also induces a targeted sympathectomy in the anesthetized region, which results in splanchnic vasodilatation and an improvement in local microcirculation. Increasing evidence shows benefits of TEA in animal AP: improved splanchnic and pancreatic perfusion, improved pancreatic microcirculation, reduced liver damage, and significantly reduced mortality. Until now, only few clinical studies have been performed on the use of TEA during AP with few available data regarding the effect of TEA on the splanchnic perfusion. Increasing evidence suggests that TEA is a safe procedure and could appear as a new treatment approach for human AP, based on the significant benefits observed in animal studies and safety of use for human. Further clinical studies are required to confirm the clinical benefits observed in animal studies.

Gadolinium chloride modulates bradykinin-induced pulmonary vasoconstriction and hypoxic pulmonary vasoconstriction during polymicrobial abdominal sepsis in rats

BACKGROUND

Macrophages importantly contribute to sepsis-induced lung injury. As their impact on pulmonary endothelial injury and dysregulation of hypoxic pulmonary vasoconstriction (HPV) remains unclear, we assessed pulmonary endothelial dysfunction and HPV by macrophage inhibition via gadolinium chloride (GC) pre-treatment in rats with peritonitis (cecal ligation and puncture [CLP]).

METHODS

The following four study groups were made: Group I: SHAM and group II: SHAM + GC (pre-treatment with NaCl 0.9% or GC 14 mg/kg body weight (b.w.) intravenously 24 hours prior to sham laparotomy); group III: CLP and group IV: CLP + GC (pre-treatment with NaCl 0.9% or GC 14 mg/kg b.w. 24 hours prior to induction of peritonitis). Exhaled nitric oxide (exNO), bradykinin-induced pulmonary vasoconstriction (=surrogate marker of endothelial dysfunction) and HPV were investigated in isolated and perfused lungs (n = 40). Using the same protocol wet to dry lung weight ratio and myeloperoxidase (MPO) activity were investigated in separate rats (n = 28). In additional rats (n = 12) of groups III and IV nitrite levels in alveolar macrophages (AM) were measured.

RESULTS

In sepsis, GC pre-treatment significantly attenuated exNO levels, AM-derived nitrite levels, lung MPO activity, and restored blunted HPV, but severely enhanced endothelial dysfunction in healthy and septic animals.

CONCLUSION

Macrophages exhibit a controversial role in sepsis-induced lung injury. The GC-induced restoration of inflammation parameters to sham levels is clearly limited by the negative impact on CLP-induced endothelial injury in this setting. The exact link between the GC-associated modulation of the NO pathway demonstrated and septic lung injury needs to be determined in future studies.

6-Dehydrogingerdione restrains lipopolysaccharide-induced inflammatory responses in RAW 264.7 macrophages

6-Dehydrogingerdione (6-DG), one important component of ginger, has been reported to possess some medical effects, such as antitumor and antiatherosclerosis. Herein, the anti-inflammatory effects of 6-DG against lipopolysaccharides (LPS) induced pro-inflammation mediators in RAW 264.7 cells were investigated. Results show that 6-DG significantly attenuated inducible nitric oxide synthase (iNOS, NOS2), cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α) in the LPS-mediated murine macrophages (RAW 264.7 cells). 6-DG inhibited LPS-induced phosphorylation of both p38 and nuclear factor of κ light polypeptide gene enhancer in B-cells inhibitor-α (IκBα), which further prevented p-p65 nuclear factor-κB (NF-κB-p65) translocation to the nucleus. Moreover, 6-DG increased the ratio of phosphorylated signal transducers and activators of transcription 1 (p-STAT1)/p-STAT3 and down-regulated the gene expression of IL-1β, IL-6, and IL-10.

Nitric oxide transport in blood: a third gas in the respiratory cycle

The trapping, processing, and delivery of nitric oxide (NO) bioactivity by red blood cells (RBCs) have emerged as a conserved mechanism through which regional blood flow is linked to biochemical cues of perfusion sufficiency. We present here an expanded paradigm for the human respiratory cycle based on the coordinated transport of three gases: NO, O₂, and CO₂. By linking O₂ and NO flux, RBCs couple vessel caliber (and thus blood flow) to O₂ availability in the lung and to O₂ need in the periphery. The elements required for regulated O₂-based signal transduction via controlled NO processing within RBCs are presented herein, including S-nitrosothiol (SNO) synthesis by hemoglobin and O₂-regulated delivery of NO bioactivity (capture, activation, and delivery of NO groups at sites remote from NO synthesis by NO synthase). The role of NO transport in the respiratory cycle at molecular, microcirculatory, and system levels is reviewed. We elucidate the mechanism through which regulated NO transport in blood supports O₂ homeostasis, not only through adaptive regulation of regional systemic blood flow but also by optimizing ventilation-perfusion matching in the lung. Furthermore, we discuss the role of NO transport in the central control of breathing and in baroreceptor control of blood pressure, which subserve O₂ supply to tissue. Additionally, malfunctions of this transport and signaling system that are implicated in a wide array of human pathophysiologies are described. Understanding the (dys)function of NO processing in blood is a prerequisite for the development of novel therapies that target the vasoactive capacities of RBCs.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Mechanistic aspects of inducible nitric oxide synthase-induced lung injury in burn trauma

INTRODUCTION

Although the beneficial effects of inducible nitric oxide synthase (iNOS) inhibition in acute lung injury secondary to cutaneous burn and smoke inhalation were previously demonstrated, the mechanistic aspects are not completely understood. The objective of the present study is to describe the mechanism(s) underlying these favourable effects. We hypothesised that iNOS inhibition prevents formation of excessive reactive nitrogen species and attenuates the activation of poly(ADP) (poly(adenosine diphosphate)) ribose polymerase, thus mitigating the severity of acute lung injury in sheep subjected to combined burn and smoke inhalation.

METHODS

Adult ewes were chronically instrumented for a 24-h study and allocated to groups: sham: not injured, not treated, n = 6; control: injured, not treated, n = 6; and BBS-2: injured treated with iNOS dimerisation inhibitor BBS-2, n = 6. Control and BBS-2 groups received 40% total body surface area 3rd-degree cutaneous burn and cotton smoke insufflation into the lungs under isoflurane anaesthesia.

RESULTS

Treatment with iNOS inhibitor BBS-2 significantly improved pulmonary gas exchange (partial pressure of oxygen in the blood/fraction of inspired oxygen (PaO₂/FiO₂) 409 ± 43 mmHg vs. 233 ± 50 mmHg in controls, p < 0.05) and reduced airway pressures (peak pressure 20 ± 1 cm H₂O vs. 28 ± 2 cm H₂O in controls, p < 0.05) and lung water content (lung wet-to-dry ratio 4.1 ± 0.3 vs. 5.2 ± 0.2 in controls, p < 0.05) 24h after the burn and smoke injury. BBS-2 significantly reduced the increases in lung lymph nitrite/nitrate (10 ± 3 μM vs. 26 ± 6 μM in controls, p < 0.05) and 3-nitrotyrosine (109 ± 11 (densitometry value) vs. 151 ± 18 in controls, p < 0.05). Burn/smoke-induced increases in lung tissue nitrite/nitrate, poly(ADP)ribose polymerase, nuclear factor-κB (NF-κB) activity, myeloperoxidase activity and malondialdehyde formation and interleukin (IL)-8 expression were also attenuated with BBS-2.

CONCLUSIONS

The results provide strong evidence that BBS-2 ameliorated acute lung injury by inhibiting the inducible nitric oxide synthase/reactive nitrogen species/poly(ADP-ribose) polymerase (iNOS/RNS/PARP) pathway.

Animal models of sepsis

In this review, we start with a general discussion of relevant factors that can determine the validity of a sepsis animal model. We briefly review some of the currently used animal models of sepsis (small animal models and large animal models). We discuss the clinical relevance of animal models in sepsis research today and address potential reasons for the apparent underperformance of animal models in predicting therapeutic success of novel drugs in clinical trials.

Redistribution of pulmonary blood flow impacts thermodilution-based extravascular lung water measurements in a model of acute lung injury

BACKGROUND

Studies using transthoracic thermodilution have demonstrated increased extravascular lung water (EVLW) measurements attributed to progression of edema and flooding during sepsis and acute lung injury. The authors hypothesized that redistribution of pulmonary blood flow can cause increased apparent EVLW secondary to increased perfusion of thermally silent tissue, not increased lung edema.

METHODS

Anesthetized, mechanically ventilated canines were instrumented with PiCCO (Pulsion Medical, Munich, Germany) catheters and underwent lung injury by repetitive saline lavage. Hemodynamic and respiratory physiologic data were recorded. After stabilized lung injury, endotoxin was administered to inactivate hypoxic pulmonary vasoconstriction. Computed tomographic imaging was performed to quantify in vivo lung volume, total tissue (fluid) and air content, and regional distribution of blood flow.

RESULTS

Lavage injury caused an increase in airway pressures and decreased arterial oxygen content with minimal hemodynamic effects. EVLW and shunt fraction increased after injury and then markedly after endotoxin administration. Computed tomographic measurements quantified an endotoxin-induced increase in pulmonary blood flow to poorly aerated regions with no change in total lung tissue volume.

CONCLUSIONS

The abrupt increase in EVLW and shunt fraction after endotoxin administration is consistent with inactivation of hypoxic pulmonary vasoconstriction and increased perfusion to already flooded lung regions that were previously thermally silent. Computed tomographic studies further demonstrate in vivo alterations in regional blood flow (but not lung water) and account for these alterations in shunt fraction and EVLW.

Inhaled aerosolised recombinant human activated protein C ameliorates endotoxin-induced lung injury in anaesthetised sheep

Introduction

We recently demonstrated that intravenously infused recombinant human activated protein C (APC) attenuates ovine lipopolysaccharide (LPS)-induced lung injury. In this study, our aim was to find out whether treatment with inhaled aerosolised APC (inhAPC) prevents formation of increased lung densities and oedema and derangement of oxygenation during exposure to LPS.

Methods

Sheep were anaesthetised during placement of intravascular introducers. After one to four days of recovery from instrumentation, the animals were re-anaesthetised, endotracheally intubated and mechanically ventilated throughout a six-hour experiment where the sheep underwent quantitative lung computed tomography. Sheep were randomly assigned to one of three groups: a sham-operated group (n = 8) receiving inhaled aerosolised saline from two hours after the start of the experiment; a LPS group (n = 8) receiving an intravenous infusion of LPS 20 ng/kg per hour and, after two hours, inhaled aerosolised saline over the next four hours; a LPS+inhAPC group (n = 8) receiving an intravenous infusion of LPS 20 ng/kg per hour and, after two hours, aerosolised APC 48 μg/kg per hour inhaled throughout the experiment. Data were analysed with analysis of variance; P less than 0.05 was regarded as significant.

Results

An infusion of LPS was associated with a reduction of well-aerated lung volume and a rapid fall in arterial oxygenation that were both significantly antagonised by inhaled APC. Pulmonary vascular pressures and extravascular lung water index increased significantly during exposure to LPS, but inhaled APC had no effect on these changes.

Conclusions

Inhalation of aerosolised APC attenuates LPS-induced lung injury in sheep by preventing a decline in the volume of aerated lung tissue and improving oxygenation.

Combined neuronal and inducible nitric oxide synthase inhibition in ovine acute lung injury

OBJECTIVE

Acute lung injury with subsequent pneumonia and sepsis represents a major cause of morbidity and mortality in thermally injured patients. Production of nitric oxide by the neuronal and inducible nitric oxide synthase may be critically involved in the pathophysiology of the disease process at different time points, and thus specific inhibition at different times may represent an effective treatment regimen.

DESIGN

Prospective, controlled, randomized trial.

SETTING

University research laboratory.

SUBJECTS

Eighteen chronically instrumented, adult, female sheep.

INTERVENTIONS

Following baseline measurements, the animals were allocated to either sham-injured, nontreated controls (sham), injured, nontreated controls (control), or injured animals treated with continuous infusion of 7-nitroindazole, a specific neuronal nitric oxide synthase inhibitor, during the first 12 hrs postinjury and infusion of BBS-2, a specific inducible nitric oxide synthase inhibitor, during the next 12 hrs. Injury was induced by 48 breaths of cotton smoke and subsequent instillation of Pseudomonas aeruginosa into the lungs. All sheep were mechanically ventilated and fluid resuscitated for the entire duration of the 24-hr experiment.

MEASUREMENTS AND MAIN RESULTS

The injury induced severe pulmonary dysfunction, which was associated with increases in lung edema formation, airway obstruction, and vascular endothelial growth factor, 3-nitrotyrosine, and poly(adenosine diphosphate ribose) expression in lung tissue. The treatment reduced the degree of airway obstruction and improved pulmonary gas exchange, whereas the development of lung edema was not affected. The increases in lung tissue vascular endothelial growth factor, 3-nitrotyrosine, and poly(ribose) expression were attenuated by the treatment.

CONCLUSIONS

The combination of early neuronal nitric oxide synthase and delayed inducible nitric oxide synthase inhibition shows potential benefit in ovine acute lung injury by reducing nitrosative stress in the lung and limiting the degree of airway obstruction.

Neuronal nitric oxide synthase inhibition attenuates cardiopulmonary dysfunctions after combined burn and smoke inhalation injury in sheep

OBJECTIVE

We hypothesized that nitric oxide derived from the neuronal nitric oxide synthase (NOS) is responsible for much of the injury resulting from skin burn and smoke inhalation. Therefore, we aimed to examine the effects of selective neuronal NOS inhibition on cardiopulmonary functions and cellular injury in sheep with acute respiratory distress syndrome secondary to combined burn and smoke inhalation injury.

DESIGN

Prospective, randomized, controlled laboratory experiment.

SETTING

Investigational intensive care unit.

SUBJECTS

A total of 22 chronically instrumented adult ewes.

INTERVENTIONS

Sheep were randomly assigned to either healthy controls (sham), injured controls (40% third-degree flame burn; 48 breaths of cotton smoke), or an injury group treated with the specific neuronal NOS inhibitor 7-nitroindazole (1 mg x kg(-1) x hr(-1)) from 1 hr postinjury to the end of the 48-hr study period. Hypoxic pulmonary vasoconstriction was assessed as decrease in left pulmonary blood flow in response to single-lung hypoxic challenges (100% nitrogen) at baseline, 24 hrs, and 48 hrs.

MEASUREMENTS AND MAIN RESULTS

The combination injury contributed to a approximately 90% loss of hypoxic pulmonary vasoconstriction and was associated with significant pulmonary shunting and death of one animal. The increase in nitrate/nitrite plasma levels in injured controls (12 hrs: 17 +/- 2 vs. 6 +/- 1 microM in sham animals; p < .001) was linked to increases in inducible NOS messenger RNA and 3-nitrotyrosine formation in lung tissue (48 hrs: 22 +/- 1 vs. 0.8 +/- 0.3 nM in sham animals; p < .001). 7-Nitroindazole treatment prevented the injury-associated changes in inducible NOS messenger RNA, nitrate/nitrite, and 3-nitrotyrosine, thereby attenuating the loss of hypoxic pulmonary vasoconstriction and improving gas exchange. In addition, 7-nitroindazole decreased lung tissue concentrations of hemoxygenase-1 and ameliorated myocardial depression, airway obstruction, pulmonary edema, ventilatory pressures, and histopathologic changes seen in injured controls.

CONCLUSIONS

The present study provides evidence that neuronal NOS-derived nitric oxide plays a pivotal role in the pathogenesis of acute respiratory distress syndrome resulting from combined burn and smoke inhalation injury.

The Role of Thoracic Epidural Analgesia in Receptor-Dependent and Receptor-Independent Pulmonary Vasoconstriction in Experimental Pancreatitis

BACKGROUND

Acute pancreatitis commonly results in lung injury and deterioration of pulmonary endothelial function and vasoregulation. Despite a variety of potential risks with the use of thoracic epidural analgesia (TEA) in the critically ill, this technique is an important component of pain management in pancreatitis in selected cases. Although there is evidence that epidural analgesia improves lung function through effective pain relief, the influence of continuously applied epidural local anesthetics on pulmonary endothelial dysfunction is still unknown.

METHODS

In an in vivo model of TEA in awake rats with acute pancreatitis, we evaluated blood gas analysis, arterial blood pressure, and exhaled nitric oxide. This was followed by in vitro studies of receptor-dependent and receptor-independent pulmonary vasoconstriction using an isolated perfused lung model. Pulmonary myeloperoxidase activity, indicating leukocyte sequestration into the lungs and wet/dry ratio evaluating pulmonary edema, were also measured.

RESULTS

Deteriorated oxygenation, metabolic and lactate acidosis, as well as exhaled nitric oxide levels occurring during acute pancreatitis, were reduced by TEA to levels observed in sham-operated animals. TEA also partially ameliorated the hypotension occurring in pancreatitis. In isolated perfused lungs, receptor-dependent vasoconstriction due to angiotensin II was reduced during acute pancreatitis, indicating pulmonary vascular smooth muscle cell dysfunction. Hypoxic pulmonary vasoconstriction was likewise abolished. Treatment with TEA partly restored the vasoreactivity to angiotensin II and hypoxia. Bradykinin-induced vasoconstriction, indicating pulmonary endothelial dysfunction, myeloperoxidase activity and the degree of pulmonary edema, was not influenced by TEA.

CONCLUSIONS

Our study demonstrated that TEA improves pancreatitis-associated impairment of pulmonary vasoreactivity and gas exchange.

Pretreatment with N-nitro-L-arginine methyl ester improved oxygenation after inhalation of nitric oxide in newborn piglets with Escherichia coli pneumonia and sepsis

We evaluated the effects of a combined therapy of pre-blockade endogenous nitric oxide synthase (NOS) with N-nitro-L-arginine methyl ester (L-NAME) and continuous inhaled NO (iNO) on the gas exchange and hemodynamics of Escherichia coli pneumonia and sepsis in newborn piglets. Seven to ten day old ventilated newborn piglets were randomized into 5 groups: control, E. coli pneumonia control, pneumonia with iNO 10 ppm, pneumonia pre-treated with L-NAME 10 mg/kg, and pneumonia with the combined therapy of L-NAME pretreatment and iNO. E. coli pneumonia was induced via intratracheal instillation of Escherichia coli, which resulted in progressively decreased cardiac index and oxygen tension; increased pulmonary vascular resistance index (PVRI), intrapulmonary shunting, and developed septicemia at the end of 6 hr experiment. iNO ameliorated the progressive hypoxemia and intrapulmonary shunting without affecting the PVRI. Only two of 8 animals with L-NAME pretreated pneumonia survived. Whereas when iNO was added to infected animals with L-NAME pretreatment, the progressive hypoxemia was abolished as a result of a decrease in intrapulmonary shunting without reverse of the high PVRI and systemic vascular resistance index induced by the L-NAME injection. This result suggests that a NOS blockade may be a possible supportive option for oxygenation by iNO treatment in neonatal Gram-negative bacterial pneumonia and sepsis.

Mechanism of hypoxemia in acute lung injury evaluated by multidetector-row CT

RATIONALE AND OBJECTIVES

Hypoxic pulmonary vasoconstriction (HPV) is a homeostatic mechanism causing pulmonary arterial constriction in response to local hypoxia, redistributing blood flow to lung regions with better oxygenation and ventilation. We present the use of computed tomographic (CT) volume and perfusion imaging to show differences in the mechanisms of hypoxemia from alterations in blood flow distribution within different animal models of acute lung injury (ALI).

MATERIALS AND METHODS

Three anesthetized, instrumented, and ventilated sheep were studied, two with induced ALI and one with native pneumonia. One subject was injured by using intravenous infusion of lipopolysaccharide (LPS), and the other, by repetitive saline lavage. Subjects were imaged using multidetector-row CT (MDCT) before and after injury. Lung volume scans were gated to the respiratory cycle. Contrast injection perfusion images were electrocardiogram gated. Computer-based image analysis quantified regional blood flow and total lung, air, and tissue volumes.

RESULTS

Total lung air fraction was decreased in both ALI models. In lavage injury, there was a decrease in perfusion to dependent poorly aerated regions, with perfusion shifting to nondependent regions. Conversely, LPS injury greatly increased perfusion to dependent poorly aerated regions. In the subject with pneumonia, decreasing fraction of inspired oxygen redistributed blood flow into the injured regions.

CONCLUSIONS

MDCT techniques can be used to investigate regional lung perfusion and lung volume distributions to explain physiological mechanisms in ALI. Our findings suggest that after lavage injury, blood flow is redistributed, consistent with preserved HPV and resulting in better oxygenation despite greater lung volume loss compared with LPS injury. In native pneumonia, HPV inactivation can be localized to the injured regions.

Combined burn and smoke inhalation injury impairs ovine hypoxic pulmonary vasoconstriction

OBJECTIVE

To examine the effects of combined burn and smoke inhalation injury on hypoxic pulmonary vasoconstriction, 3-nitrotyrosine formation, and respiratory function in adult sheep.

DESIGN

Prospective, placebo-controlled, randomized, single-blinded trial.

SETTING

University research laboratory.

SUBJECTS

Twelve chronically instrumented ewes.

INTERVENTIONS

Following a baseline measurement, sheep were randomly allocated to either healthy controls (sham) or the injury group, subjected to a 40%, third-degree body surface area burn and 48 breaths of cotton smoke according to an established protocol (n = 6 each). Hypoxic pulmonary vasoconstriction was assessed as changes in pulmonary arterial blood flow (corrected for changes in cardiac index) in response to left lung hypoxic challenges performed at baseline and at 24 and 48 hrs postinjury.

MEASUREMENTS AND MAIN RESULTS

Combined burn and smoke inhalation was associated with increased expression of inducible nitric oxide (NO) synthase, elevated NO2/NO3 (NOx) plasma levels (12 hrs, sham, 6.2 +/- 0.6; injury, 16 +/- 1.6 micromol.L; p < .01) and increased peroxynitrite formation, as indicated by augmented lung tissue 3-nitrotyrosine content (30 +/- 3 vs. 216 +/- 8 nM; p < .001). These biochemical changes occurred in parallel with pulmonary shunting, progressive decreases in Pao2/Fio2 ratio, and a loss of hypoxic pulmonary vasoconstriction (48 hrs, -90.5% vs. baseline; p < .001). Histopathology revealed pulmonary edema and airway obstruction as the morphologic correlates of the deterioration in gas exchange and the increases in airway pressures.

CONCLUSIONS

This study provides evidence for a severe impairment of hypoxic pulmonary vasoconstriction following combined burn and smoke inhalation injury. In addition to airway obstruction, the loss of hypoxic pulmonary vasoconstriction may help to explain why blood gases are within physiologic ranges for a certain time postinjury and then suddenly deteriorate.

Ethyl pyruvate improves systemic and hepatosplanchnic hemodynamics and prevents lipid peroxidation in a porcine model of resuscitated hyperdynamic endotoxemia

OBJECTIVE

To investigate the systemic, pulmonary, and hepatosplanchnic hemodynamic and metabolic effects of delayed treatment with ethyl pyruvate in a long-term porcine model of hyperdynamic endotoxemia.

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Anesthetized, mechanically ventilated, and instrumented pigs.

INTERVENTIONS

After 12 hrs of continuous infusion of lipopolysaccharide and hydroxyethyl starch to keep mean arterial pressure >60 mm Hg, swine randomly received placebo (Ringer's solution; control group, n = 11) or ethyl pyruvate in lactated Ringer's solution (n = 8; 0.03 g.kg(-1) loading dose over 10 mins, thereafter 0.03 g.kg(-1)hr(-1) for 12 hrs).

MEASUREMENTS AND MAIN RESULTS

Whereas mean arterial pressure significantly decreased in control animals, mean arterial pressure was maintained at the baseline level in pigs treated with ethyl pyruvate. Global oxygen uptake was comparable, so that the trend toward a higher oxygen transport and the significantly higher mixed venous hemoglobin oxygen saturation resulted in a significantly lower oxygen extraction in the ethyl pyruvate group. Ethyl pyruvate reduced intrapulmonary venous admixture and resulted in significantly greater Pa(O2)/F(IO2) ratios. Despite comparable urine production in the two groups during the first 18 hrs of endotoxemia, ethyl pyruvate significantly increased diuresis during the last 6 hrs of the study. Lipopolysaccharide-induced systemic and regional venous metabolic acidosis was significantly ameliorated by ethyl pyruvate. Endotoxemia increased both blood nitrate + nitrite and isoprostane concentrations, and ethyl pyruvate attenuated the response of these markers of nitric oxide production and lipid peroxidation.

CONCLUSIONS

Ethyl pyruvate infusion resulted in improved hemodynamic stability and ameliorated acid-base derangements induced by chronic endotoxemia in pigs. Reduced oxidative stress and an decreased nitric oxide release probably contributed to these effects.

Sepsis produced by Pseudomonas bacteremia does not alter plasma volume expansion after 0.9% saline infusion in sheep

Clinicians generally consider sepsis to be a state in which fluid is poorly retained within the vasculature and accumulates within the interstitium. We hypothesized that infusion of 0.9% saline in conscious, chronically instrumented sheep with hyperdynamic bacteremic sepsis would be associated with less plasma volume expansion (PVE) and greater interstitial fluid volume expansion than in conscious, nonseptic sheep. Six conscious adult sheep received an IV infusion of 25 mL/kg of 0.9% saline over 20 min (1.25 mL.kg(-1).min(-1)) in a control nonseptic state and during early and late sepsis (4 and 24 h, respectively, after initiation of a standard infusion of live Pseudomonas aeruginosa). The distribution and elimination of infused fluid were studied by mass balance (after measurement of plasma volume using Evans blue dye) and volume kinetic analysis. Mass balance demonstrated no significant differences in the time-course of PVE between control, early sepsis, and late sepsis. At the end of the infusions, which averaged 1050 +/- 125 mL in sheep weighing an average of 42 +/- 5 kg, calculated PVE was 312 +/- 50 mL, 386 +/- 34 mL, and 400 +/- 51, respectively. Volume kinetic analysis was similar in all three protocols. In both nonseptic and septic sheep, infusion of 0.9% saline resulted in similar peak PVE and resolution of PVE over a 3-h interval and similar kinetic parameters. Contrary to clinical impressions and to our hypothesis, the distribution of 0.9% saline in this animal model was not changed by bacteremia produced by infusion of Pseudomonas aeruginosa.

GENTAMICIN IMPROVES HEMODYNAMICS IN OVINE SEPTIC SHOCK AFTER SMOKE INHALATION INJURY

Previously, our group developed an ovine model of hyperdynamic sepsis associated with acute lung injury. In this study, we sought to modify this sepsis model by the administration of gentamicin to more closely simulate the symptoms observed in human sepsis in the intensive care unit. In a prospective, controlled, randomized laboratory experiment, 18 female sheep were surgically prepared for chronic study. After a tracheotomy had been performed, the sheep were randomized into sham, control, and gentamicin groups (n = 6 each). Sham animals were surgically prepared for the study but were neither injured nor treated. Control and gentamicin animals received 48 breaths of cotton smoke (<40 degrees C) followed by the instillation (via a bronchoscope) of live Pseudomonas aeruginosa (2-5 x 10(11) colony-forming units) bacteria into the lung. All sheep were mechanically ventilated with 100% O2 for the duration of the 24-h experimental period. Gentamicin (2 mg/kg) was administered at 6, 12, and 18 h after injury. The animals were resuscitated with lactated Ringer's solution to maintain filling pressures and hematocrit on a constant level. Cardiopulmonary variables were stable in sham animals, but in the control group, cardiac index increased significantly after 24 h versus baseline (BL, 5.1 +/- 0.4 L.min(-1).m(-2) vs. 24 h, 7.3 +/- 0.7 L.min(-1).m(-2); P < 0.05); this was associated with a significant drop in mean arterial pressure (BL, 95 +/- 3 mmHg vs. 24 h, 65 +/- 4 mmHg, P < 0.05) and systemic vascular resistance index (BL, 1410 +/- 118 dynes s.cm.m vs. 24 h, 598 +/- 101 dynes s.cm.m, P < 0.05). Treatment with gentamicin stabilized cardiac index (BL, 5.0 +/- 0.4 L.min(-1).m(-2) vs. 24 h, 4.7 +/- 0.4 L.min(-1).m(-2)) and attenuated the decrease in mean arterial pressure (BL, 99 +/- 3 mmHg vs. 24 h, 84 +/- 4 mmHg) and systemic vascular resistance index (BL, 1573 +/- 173 dynes s.cm.m vs. 24 h, 1263 +/- 187 dynes s.cm.m). In addition, the fluid requirement in the gentamicin group was significantly lower than in the control group. Pulmonary function remained stable in sham animals, but the PaO2/FiO2 ratio and shunt fraction deteriorated similarly in the control and the gentamicin groups. Because gentamicin improved hemodynamic variables and reduced the fluid requirement in this ovine model, we believe that this modified sepsis model might provide a clinically relevant and useful new approach for future studies focusing on hemodynamic variables and outcome.

Nitric oxide synthase inhibition in sepsis? Lessons learned from large-animal studies

Nitric Oxide (NO) plays a controversial role in the pathophysiology of sepsis and septic shock. Its vasodilatory effects are well known, but it also has pro- and antiinflammatory properties, assumes crucial importance in antimicrobial host defense, may act as an oxidant as well as an antioxidant, and is said to be a "vital poison" for the immune and inflammatory network. Large amounts of NO and peroxynitrite are responsible for hypotension, vasoplegia, cellular suffocation, apoptosis, lactic acidosis, and ultimately multiorgan failure. Therefore, NO synthase (NOS) inhibitors were developed to reverse the deleterious effects of NO. Studies using these compounds have not met with uniform success however, and a trial using the nonselective NOS inhibitor N(G)-methyl-l-arginine hydrochloride was terminated prematurely because of increased mortality in the treatment arm despite improved shock resolution. Thus, the issue of NOS inhibition in sepsis remains a matter of debate. Several publications have emphasized the differences concerning clinical applicability of data obtained from unresuscitated, hypodynamic rodent models using a pretreatment approach versus resuscitated, hyperdynamic models in high-order species using posttreatment approaches. Therefore, the present review focuses on clinically relevant large-animal studies of endotoxin or living bacteria-induced, hyperdynamic models of sepsis that integrate standard day-to-day care resuscitative measures.

Role of endogenous nitric oxide in endotoxin-induced alteration of hypoxic pulmonary vasoconstriction in mice

Pulmonary vasoconstriction in response to alveolar hypoxia (HPV) is frequently impaired in patients with sepsis or acute respiratory distress syndrome or in animal models of endotoxemia. Pulmonary vasodilation due to overproduction of nitric oxide (NO) by NO synthase 2 (NOS2) may be responsible for this impaired HPV after administration of endotoxin (LPS). We investigated the effects of acute nonspecific (N(G)-nitro-L-arginine methyl ester, L-NAME) and NOS2-specific [L-N6-(1-iminoethyl)lysine, L-NIL] NOS inhibition and congenital deficiency of NOS2 on impaired HPV during endotoxemia. The pulmonary vasoconstrictor response and pulmonary vascular pressure-flow (P-Q) relationship during normoxia and hypoxia were studied in isolated, perfused, and ventilated lungs from LPS-pretreated and untreated wild-type and NOS2-deficient mice with and without L-NAME or L-NIL added to the perfusate. Compared with lungs from untreated mice, lungs from LPS-challenged wild-type mice constricted less in response to hypoxia (69 +/- 17 vs. 3 +/- 7%, respectively, P < 0.001). Perfusion with L-NAME or L-NIL restored this blunted HPV response only in part. In contrast, LPS administration did not impair the vasoconstrictor response to hypoxia in NOS2-deficient mice. Analysis of the pulmonary vascular P-Q relationship suggested that the HPV response may consist of different components that are specifically NOS isoform modulated in untreated and LPS-treated mice. These results demonstrate in a murine model of endotoxemia that NOS2-derived NO production is critical for LPS-mediated development of impaired HPV. Furthermore, impaired HPV during endotoxemia may be at least in part mediated by mechanisms other than simply pulmonary vasodilation by NOS2-derived NO overproduction.

IBC’s 5th Annual Conference on Blood Substitutes

IBC's 5(th) Annual Conference on Blood Substitutes was held on November 20-21, 1997. Approximately 100 medical researchers, academic scientists, blood substitute company speakers and representatives from major pharmaceutical companies with an interest or partner in the field attended. The papers presented focused on the progress in clinical trials for those compounds in human study, on preclinical models for predicting efficacy in humans, and on novel approaches and agents for the delivery of oxygen. Both perfluorocarbons (PFC) and haemoglobin-based oxygen carriers were described. Several lectures addressed the history of the field and future directions for laboratory and clinical investigation. The following is a summary of some of the presentations. This summary is divided into 3 sections. The first section provides a historical overview and discusses the changes in the perceived need for a blood substitute. Section 2 comprises an update of company activities. The final section focuses on likely future directions for laboratory and human clinical study.

Effects of a Selective Nitric Oxide Synthase Inhibitor on Endotoxin-Induced Alteration in Hypoxic Pulmonary Vasoconstriction in Sheep

It has been suggested that overproduction of nitric oxide (NO) by nitric oxide synthase (NOS) contributes to blunted hypoxic pulmonary vasoconstriction (HPV) during endotoxemia. We investigated the effect of a selective inducible NOS (iNOS) inhibitor, ONO-1714, on the loss of HPV during endotoxemia in awake sheep to clarify the role of iNOS. We prepared 11 intubated, awake sheep with hemodynamic monitoring. Hypoxic challenges (FiO2; 12%) were performed before, and 5, 24, 48, 72 hours after endotoxin (1 microg/kg) infusion for 15 minutes. Pulmonary artery (Ppa) and left atrial pressure (Pla) were continuously measured and cardiac output (CO) was measured by the thermodilution method. Pulmonary vascular resistance (PVR) was calculated by (Ppa - Pla)/CO. The percent change in PVR (%PVR) before (pre-PVR) and after (post-PVR) hypoxia was calculated as (post-PVR - pre-PVR)/pre-HPV x 100. ONO-1714 (0.1 mg/kg, n=5, Exp 1) or normal saline (n=6, Exp 2) was administered 5 hours before hypoxic challenge every day. ONO-1714 did not affect the baseline pulmonary hemodynamics before endotoxin administration. % PVR before and after hypoxic exposure was significantly decreased 5 hours after endotoxin administration and gradually improved to baseline at 72 hours. Treatment with iNOS inhibition significantly restored % HPV (24.7+/-5.5% in Exp1 versus -3.1+/-3.6% in Exp 2, 5 hours, 25.3+/-2.5% in Exp 1 versus 7.7+/-2.2% in Exp 2, 24 hours). It is suggested that inducible nitric oxide is related to pulmonary vascular hyporesponsiveness to hypoxia during endotoxemia in sheep.

Inhibition of neuronal nitric oxide synthase by 7-nitroindazole attenuates acute lung injury in an ovine model

Nitric oxide (NO) has been shown to play a major role in acute lung injury (ALI) after smoke inhalation. In the present study, we developed an ovine sepsis model, created by exposing sheep to smoke inhalation followed by instillation of bacteria into the airway, that mimics human sepsis and pneumonia. We hypothesized that the inhibition of neuronal NO synthase (nNOS) might be beneficial in treating ALI associated with this model. Female sheep (n = 26) were surgically prepared for the study and given a tracheostomy. This was followed by insufflation of 48 breaths of cotton smoke (40 degrees C) into the airway of each animal and subsequent instillation of live Pseudomonas aeruginosa [5 x 10(11) colony forming units (CFU)] into each sheep's lung. All sheep were mechanically ventilated using 100% O2. Continuous infusion of 7-nitroindazole (7-NI), an nNOS inhibitor, NG-monomethyl-l-arginine (l-NMMA), a nonspecific NOS inhibitor, or aminoguanidine (AG), an inducible NOS inhibitor, was started 1 h after insult. The administration of 7-NI improved pulmonary gas exchange (PaO2/FiO2; where PaO2 is arterial PO2 and FiO2 is fractional inspired oxygen concentration) and pulmonary shunt fraction and attenuated the increase in lung wet-to-dry weight ratio seen in the nontreated sheep. Histologically, 7-NI prevented airway obstruction. The increase in airway blood flow after injury in the nontreated group was significantly inhibited by 7-NI. The increase in plasma concentration of nitrate and nitrite (NOx) was inhibited by 7-NI as well. Posttreatment with l-NMMA improved the pulmonary gas exchange, but AG did not. The results of the present study show that nNOS may be involved in the pathogenesis of ALI after smoke inhalation injury followed by bacterial instillation in the airway.

Pathophysiological basis of smoke inhalation injury

Smoke inhalation injury results in serious respiratory failure. When smoke inhalation injury is combined with burn injury or pneumonia, the physiological responses are different and more severe than those of smoke inhalation injury alone. Treatment strategies should be planned based on these pathophysiological aspects.

The inducible nitric oxide synthase inhibitor BBS-2 prevents acute lung injury in sheep after burn and smoke inhalation injury

In this study we examined the role of inducible nitric oxide synthase (iNOS) in acute respiratory distress syndrome (ARDS) in sheep with severe combined burn and smoke inhalation injury. BBS-2, a potent and highly selective iNOS dimerization inhibitor, was used to exclude effects on the endothelial and neuronal NOS isoforms. Seven days after surgical recovery, sheep were given a burn (40% of total body surface, 3rd degree) and insufflated with cotton smoke (48 breaths, < 40 degrees C) under anesthesia. BBS-2 was provided by constant infusion at 100 microg/kg/hour, beginning 1 hour after injury. During 48 hours, control sheep developed multiple signs of ARDS. These included decreased pulmonary gas exchange, increased pulmonary edema, abnormal lung compliance, and extensive airway obstruction. These pathologies were associated with a large increase in tracheal blood flow and elevated plasma NO2-/NO3- (NOx) levels. These variables were all stable in sham animals. Treatment of injured sheep with BBS-2 attenuated the increases in tracheal blood flow and plasma NOx levels, and significantly attenuated all the pulmonary pathologies that were noted. The results provide definitive evidence that iNOS is a key mediator of pulmonary pathology in sheep with ARDS resulting from combined burn and smoke inhalation injury.

Recombinant antithrombin attenuates pulmonary inflammation following smoke inhalation and pneumonia in sheep

OBJECTIVE

The interaction between coagulation and inflammation has become one of the major topics in critical care medicine. In the present study, we investigated the effect of posttreatment of sepsis with recombinant human antithrombin.

DESIGN

Experimental laboratory in a university hospital.

SETTING

University laboratory.

SUBJECTS

Female merino ewes (n = 16).

INTERVENTIONS

After 1 wk of recovery from the surgical preparation, a tracheotomy was performed followed by insufflation of 48 breaths of cotton smoke (<40 degrees C). Afterward, a stock solution of live (5 x 10(11) colony-forming units) was instilled in the both lung lobes through a bronchoscope. All sheep were mechanically ventilated employing 100% oxygen. An infusion of recombinant human antithrombin (100 units x kg(-1) x 24 hrs(-1), intravenously; n = 6) or saline (n = 6) was started 1 hr after injury. Sham control animals (n = 4) were surgically prepared but not insufflated with smoke and bacteria. Lung histologic changes were evaluated by a scoring system.

MEASUREMENTS AND MAIN RESULTS

The infusion of recombinant human antithrombin maintained the baseline antithrombin activity throughout the study; in the saline-treated group, antithrombin activity decreased significantly. The lung wet/dry weight ratio and the histology score (combined scores for congestion, edema, inflammation, and hemorrhage) were significantly increased by the insult, but recombinant human antithrombin attenuated these responses. More than 30% of both bronchi and bronchioles were obstructed by cast formation after smoke inhalation and pneumonia. The cast was composed of epithelial cells, neutrophils, mucus, and fibrin. The obstruction was significantly improved by recombinant human antithrombin infusion. Arterial pressure and urine output were also attenuated in recombinant human antithrombin-treated animals. The increases in plasma nitrate/nitrite concentrations and pulmonary shunt fraction after the injury were not attenuated by recombinant human antithrombin.

CONCLUSION

Posttreatment by recombinant human antithrombin was effective in treating acute lung injury after smoke inhalation and pneumonia in sheep. We hypothesize that the decrease in antithrombin activity during sepsis might induce severe airway obstruction and that supplementation with antithrombin inhibits this decrease.

Combination of intravenously infused methylene blue and inhaled nitric oxide ameliorates endotoxin-induced lung injury in awake sheep

OBJECTIVE

To evaluate the effects of a combination of methylene blue, an inhibitor of the nitric oxide pathway, and inhaled nitric oxide on endotoxin-induced acute lung injury in awake sheep.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University animal laboratory.

SUBJECTS

Twenty-four yearling, awake sheep.

INTERVENTIONS

The sheep were anesthetized and instrumented with vascular catheters. After 1 wk of recovery, the animals underwent tracheotomy and were subjected to intravenous infusions of endotoxin 10 ng x kg-1 x min-1 and isotonic saline 3 mL x kg-1 x hr-1 for 8 hrs. The sheep were randomly assigned to three groups of eight animals each: a) the control group received endotoxin and saline; b) the INO group received endotoxin, saline, and inhaled nitric oxide 40 ppm for 5 hrs; and c) the MB/INO group received endotoxin, saline, and methylene blue 3 mg/kg as an intravenous bolus injection followed by a continuous infusion of 3 mg x kg-1 x min-1 for 6 hrs in combination with inhaled nitric oxide 40 ppm for 5 hrs.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables and blood gases were determined hourly. In the early phase of endotoxemia (0-2 hrs), methylene blue/inhaled nitric oxide reduced the increments in pulmonary arterial pressure, pulmonary microvascular pressure, and pulmonary vascular resistance index by 60% compared with the controls and to a greater extent than did inhaled nitric oxide alone. During the late phase, all the preceding variables returned closely to baseline following inhaled nitric oxide or methylene blue/inhaled nitric oxide but remained remarkably elevated in the control group. Inhaled nitric oxide and methylene blue/inhaled nitric oxide reduced the increase in extravascular lung water by 40% and 80%, respectively. Inhaled nitric oxide transiently attenuated the increase in venous admixture and did not prevent a decrease in arterial oxygenation. In the methylene blue/inhaled nitric oxide group, blood gases remained unchanged from baseline.

CONCLUSIONS

In sheep, methylene blue/inhaled nitric oxide protects more efficiently against acute lung injury than inhaled nitric oxide alone, as indicated by a milder pulmonary hypertension, less extravascular lung water accumulation, and maintained gas exchange.

Abnormal pulmonary vascular tone in canine oleic acid lung injury

OBJECTIVE

To characterize the endothelium-dependent and endothelium-independent components of abnormal pulmonary vascular tone in canine oleic acid lung injury.

DESIGN

Prospective, interventional study.

SETTING

University laboratory.

SUBJECTS

Twenty anesthetized mongrel dogs.

INTERVENTIONS

Right heart catheterization was performed to measure pulmonary vascular resistance before and after induction of oleic acid lung injury in ten anesthetized and ventilated dogs. Pulmonary and internal mammary artery rings were sampled in these ten dogs with oleic acid injury and in ten anesthetized healthy control dogs. We also studied the responses to acetylcholine, to phenylephrine, and to hypoxia of the intact or endothelium-denuded rings mounted in organ baths.

MEASUREMENTS AND MAIN RESULTS

Oleic acid lung injury was associated with an increase in pulmonary vascular resistance from 118 +/- 11 to 245 +/- 47 dyne.sec.cm-5.m-2 and a decrease in the Pao2/Fio2 ratio from 451 +/- 42 to 139 +/- 26 mm Hg (mean +/- se, p <.05 and p <.01, respectively). Acetylcholine-induced relaxation was decreased in the oleic acid pulmonary artery rings compared with the controls (85 +/- 3% vs. 99 +/- 6% of precontraction level, p <.05). Phenylephrine-induced contraction was decreased in denuded oleic acid pulmonary artery rings compared with the controls (81 +/- 8% vs. 102 +/- 10% of contraction to KCl 120 mM, p <.05). In vitro hypoxia induced a small endothelium-dependent contraction followed by an endothelium-independent relaxation. These responses were not different in oleic acid lung artery rings and in controls, except for a decrease in hypoxic contraction in the oleic acid pulmonary artery rings. In vitro hypoxic pulmonary vasoconstriction and relaxation were, respectively, directly (r =.48) and inversely (r = -.67) correlated with oleic acid-induced increase in pulmonary vascular resistance. There was no correlation between in vitro internal mammary artery reactivity and oleic acid-induced increase in pulmonary vascular resistance.

CONCLUSIONS

Oleic acid-induced lung injury slightly impairs pulmonary arterial endothelium-dependent relaxation and endothelium-independent contraction. In vitro hypoxic pulmonary vasoreactivity is related to in vivo oleic acid-induced increase in pulmonary vascular resistance.

Continuously infused methylene blue modulates the early cardiopulmonary response to endotoxin in awake sheep

BACKGROUND

In endotoxemia and septic shock, enhanced generation of endogenous nitric oxide (NO) contributes to myocardial depression, hypotension, and derangement of gas exchange. We hypothesized that continuous infusion of methylene blue (MB), an inhibitor of the NO pathway, would counteract these effects in endotoxemic sheep.

METHODS

Twenty-one sheep were anesthetized and instrumented for a chronic study with vascular catheters. On the day of the experiment, 18 conscious animals randomly received either an intravenous injection of MB 10 mg x kg(-1) or isotonic saline. Thirty minutes later, sheep received a 20-min intravenous infusion of Escherichia coli endotoxin 1 microg x kg(-1) and either an intravenous infusion of MB 2.5 mg x kg(-1) x h(-1) or isotonic saline, respectively, for 5 h. In addition, 3 animals were exposed to the same dose of MB alone.

RESULTS

MB reduced the early endotoxin-induced declines in stroke volume, left ventricular stroke work and cardiac indices, and prevented mean arterial pressure from falling. Moreover, MB ameliorated the increases in pulmonary arterial pressure and pulmonary vascular resistance index. In addition, MB reduced the increments in venous admixture and AaPO2, decreased the falls in PaO2, SaO2, and oxygen delivery, and maintained oxygen consumption. MB also prevented the rises in body temperature and plasma nitrites and nitrates, and delayed the elevation of plasma lactate. When given alone to healthy sheep, MB transiently reduced plasma lactate and PaO2, and increased AaPO2.

CONCLUSION

In ovine endotoxemia, continuously infused MB counteracts the early myocardial dysfunction and derangement of hemodynamics and gas exchange.

Management of one-lung ventilation

The practice of thoracic anesthesia requires a clear understanding of the techniques of lung separation and the technical skills necessary to apply such techniques. Customarily they are classified as absolute or relative.

Is nitric oxide overproduction the target of choice for the management of septic shock?

Sepsis is a heterogeneous class of syndromes caused by a systemic inflammatory response to infection. Septic shock, a severe form of sepsis, is associated with the development of progressive damage in multiple organs, and is a leading cause of patient mortality in intensive care units. Despite important advances in understanding its pathophysiology, therapy remains largely symptomatic and supportive. A decade ago, the overproduction of nitric oxide (NO) had been discovered as a potentially important event in this condition. As a result, great hopes arose that the pharmacological inhibition of NO synthesis could be developed into an efficient, mechanism-based therapeutic approach. Since then, an extraordinary effort by the scientific community has brought a deeper insight regarding the feasibility of this goal. Here we present in summary form the present state of knowledge of the biological chemistry and physiology of NO. We then proceed to a systematic review of experimental and clinical data, indicating an up-regulation of NO production in septic shock; information on the role of NO in septic shock, as provided by experiments in transgenic mice that lack the ability to up-regulate NO production; effects of pharmacological inhibitors of NO production in various experimental models of septic shock; and relevant clinical experience. The accrued evidence suggests that the contribution of NO to the pathophysiology of septic shock is highly heterogeneous and, therefore, difficult to target therapeutically without appropriate monitoring tools, which do not exist at present.

Effect of aminoguanidine on lung fluid filtration after endotoxin in awake sheep

It has been suggested that enhanced generation of nitric oxide by inducible nitric oxide synthase (iNOS) may contribute to acute lung injury. We hypothesized that aminoguanidine (AG), a proposed selective inhibitor of iNOS, would alter pulmonary hemodynamics, fluid filtration, and gas exchange after endotoxin in chronically instrumented awake sheep. Eighteen sheep were randomly assigned to receive either AG (10 mg/kg + 1 mg/kg/h), or NaCl 0.9% intravenously for 4 h, beginning 2 h after injection of Escherichia coli endotoxin (1 microgram/kg). After endotoxin, pulmonary artery pressure (Ppa), capillary pressure (Pc), and vascular resistance index (PVRI) rose concomitantly with six-fold increments in lung lymph flow (Q L) and protein clearance (CL). Extravascular lung water (EVLW) doubled, as assessed with the thermal dye dilution technique; Pa(O(2)) decreased, AaPO(2) and venous admixture (Q S/Q T) increased. After AG, Q L and CL increased further by approximately 30%, whereas EVLW remained unchanged, despite an additional increase in Pc. Ppa, PVRI, and systemic vascular resistance index rose, whereas cardiac index and pulmonary blood volume index declined. In addition, Pa(O(2)) rose, and AaPO(2) and Q S/Q T decreased. We conclude that in endotoxemic sheep, AG improves gas exchange and increases Q L and CL, whereas EVLW remains unchanged in spite of enhanced Pc. Apparently, increased lymphatic drainage prevents EVLW from rising after AG.

Hypoxic pulmonary blood flow redistribution and arterial oxygenation in endotoxin-challenged NOS2-deficient mice

Sepsis and endotoxemia impair hypoxic pulmonary vasoconstriction (HPV), thereby reducing arterial oxygenation and enhancing hypoxemia. Endotoxin induces nitric oxide (NO) production by NO synthase 2 (NOS2). To assess the role of NO and NOS2 in the impairment of HPV during endotoxemia, we measured in vivo the distribution of total pulmonary blood flow (QPA) between the right (QRPA) and left (QLPA) pulmonary arteries before and after left mainstem bronchus occlusion (LMBO) in mice with and without a congenital deficiency of NOS2. LMBO reduced QLPA/QPA equally in saline-treated wild-type and NOS2-deficient mice. However, prior challenge with Escherichia coli endotoxin markedly impaired the ability of LMBO to reduce QLPA/QPA in wild-type, but not in NOS2-deficient, mice. After endotoxin challenge and LMBO, systemic oxygenation was impaired to a greater extent in wild-type than in NOS2-deficient mice. When administered shortly after endotoxin treatment, the selective NOS2 inhibitor L-NIL preserved HPV in wild-type mice. High concentrations of inhaled NO attenuated HPV in NOS2-deficient mice challenged with endotoxin. These findings demonstrate that increased pulmonary NO levels (produced by NOS2 or inhaled at high levels from exogenous sources) are necessary during the septic process to impair HPV, ventilation/perfusion matching and arterial oxygenation in a murine sepsis model.

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.

Changes in the functional properties of bovine hemoglobin induced by covalent modification with polyethylene glycol

Polyethylene glycol conjugation to proteins and peptides (PEGylation) has been shown to promote increased retention time in the circulation as well as to blunt immune or allergic reactions. PEGylated bovine hemoglobin (PEG-Hb) is being explored in human clinical trials as an oxygen delivering agent for the sensitization of solid tumors to radiation therapy. In this study the functional properties of PEG-Hb were compared to those of bovine hemoglobin (Hb), the mutant human hemoglobin Rothchild and bovine hemoglobin crosslinked between the beta chains. The rate of heme transfer from Hb to serum albumin at pH 9.0 was greatly increased by PEGylation, suggesting destabilization of the heme-globin linkage and of the bonds between alpha beta dimers. Measurement of oxygen binding equilibrium showed that the oxygen affinity of Hb became unusually dependent on temperature and Hb concentration after PEGylation. Evidence is presented to suggest that PEGylation of lysine beta-81 at the entrance to the central cavity of the Hb tetramer might be responsible for these observations. The alterations of the functional properties of Hb induced by PEGylation are consistent with the beneficial effects of PEG-Hb in exchange transfusion and radiation sensitization models of human conditions.

Inhibition of cyclooxygenase and nitric oxide synthase in hypoxic vasoconstriction and oleic acid-induced lung injury

Cyclooxygenase (COX) products and nitric oxide (NO) inhibit hypoxic pulmonary vasoconstriction (HPV), and their release could contribute to alterations in gas exchange in lung injury. We tested the hypothesis that combined blockade of COX and NO synthase (NOS) could further increase HPV and better protect gas exchange in lung injury than could blockade of either COX or NOS alone. We determined pulmonary vascular pressure-flow relationships in pentobarbital-anesthetized and ventilated dogs submitted to hypoxic challenges before and after administration of solvent (n = 4), indomethacin alone (2 mg/kg intravenously, n = 8), Nomega-nitro-L-arginine (L-NA) alone (10 mg/kg intravenoulsy, n = 8), indomethacin followed by L-NA (n = 8), and L-NA followed by indomethacin (n = 8). All of the dogs so treated then received oleic acid (0.06 ml/kg intravenously) to induce lung injury. Blood flow was manipulated by establishing a femoral arteriovenous bypass or by inflating an inferior vena caval balloon. Gas exchange was evaluated by measuring arterial PO2 and intrapulmonary shunt (using the inert gas sulfur hexafluoride) at identical cardiac outputs. The magnitude of HPV was not affected by solvent. Indomethacin and L-NA given separately enhanced HPV. L-NA added to indomethacin further enhanced HPV, as did indomethacin added to L-NA. After oleic acid-induced lung injury, gas exchange deteriorated less in dogs pretreated with indomethacin than in dogs pretreated with solvent or with L-NA alone. These results suggest that in pentobarbital-anesthetized dogs: (1) the magnitude of HPV is limited by the corelease of COX metabolites and of NO; and (2) inhibition of COX, but not of NOS, attenuates the deterioration of gas exchange in oleic acid-induced lung injury.

Hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction is a local reflex in the lung that diverts blood away from poorly oxygenated regions. Improvements in understanding of modulators of this response have led to pharmacologic methods whereby V/Q matching may potentially be improved in certain types of pulmonary pathology and during anesthesia for thoracic surgical procedures.