Risks of restrictive red blood cell transfusion strategies in patients with cardiovascular disease (CVD): a meta-analysis

AIM

To evaluate the risks of restrictive red blood cell transfusion strategies (haemoglobin 7-8 g dL^-1 ) in patients with and without known cardiovascular disease (CVD).

BACKGROUND

Recent guidelines recommend restrictive strategies for CVD patients hospitalised for non-CVD indications, patients without known CVD and patients hospitalised for CVD corrective procedures.

METHODS/MATERIALS

Database searches were conducted through December 2017 for randomised clinical trials that enrolled patients with and without known CVD, hospitalised either for CVD-corrective procedures or non-cardiac indications, comparing effects of liberal with restrictive strategies on major adverse coronary events (MACE) and death.

RESULTS

In CVD patients not undergoing cardiac interventions, a liberal strategy decreased (P = 0·01) the relative risk (95% CI) (RR) of MACE [0·50 (0·29-0·86)] (I²  = 0%). Among patients without known CVD, the incidence of MACE was lower (1·7 vs 3·9%), and the effect of a liberal strategy on MACE [0·79, (0·39-1·58)] was smaller and non-significant but not different from CVD patients (P = 0·30). Combining all CVD and non-CVD patients, a liberal strategy decreased MACE [0·59, (0·39-0·91); P = 0·02]. Conversely, among studies reporting mortality, a liberal strategy decreased mortality in CVD patients (11·7% vs·13·3%) but increased mortality (19·2% vs 18·0%) in patients without known CVD [interaction P = 0·05; ratio of RR 0·73, (0·53-1·00)]. A liberal strategy also did not benefit patients undergoing cardiac surgery; data were insufficient for percutaneous cardiac procedures.

CONCLUSIONS

In patients hospitalised for non-cardiac indications, liberal transfusion strategies are associated with a decreased risk of MACE in both those with and without known CVD. However, this only provides a survival benefit to CVD patients not admitted for CVD-corrective procedures.

Bacterial endotoxins and pathogenesis of Gram-negative infections: current status and future direction

100 years after the discovery of a bacterial 'endotoxin', 50 years after the introduction of antibiotics and 25 years after the routine use of intensive care units to support septic shock patients, Gram-negative infections continue to account for significant morbidity and mortality. In the coming decade, basic research on the structure/function of LPS, the cytokine cascade, and receptor-mediated intracellular signalling responses to LPS and cytokines will provide a greater understanding of the molecular, cellular and systemic responses to endotoxin and infection. New therapeutic agents now emerging from research, and better designed clinical trials to assess those agents will contribute to the next significant decline in sepsis- and shock-related morbidity and mortality. This article summarizes the findings of a workshop convened at the National Institutes of Health (NIH) to examine current research on endotoxin and Gram-negative septic shock.

Transfusion of recently donated (fresh) red blood cells (RBCs) does not improve survival in comparison with current practice, while safety of the oldest stored units is yet to be established: a meta-analysis

BACKGROUND AND OBJECTIVES

Preclinical studies generated the hypothesis that older stored red blood cells (RBCs) can increase transfusion risks. To examine the most updated and complete clinical evidence and compare results between two trial designs, we assessed both observational studies and randomized controlled trials (RCTs) studying the effect of RBC storage age on mortality.

MATERIALS AND METHODS

Five databases were searched through December 2014 for studies comparing mortality using transfused RBCs having longer and shorter storage times.

RESULTS

Analysis of six RCTs found no significant differences in survival comparing current practice (average storage age of 2 to 3 weeks) to transfusion of 1- to 10-day-old RBCs (OR 0·91, 95% CI 0·77-1·07). RBC storage age was lower in RCTs vs. observational studies (P = 0·01). The 31 observational studies found an increased risk of death (OR 1·13, 95% CI 1·03-1·24) (P = 0·01) with increasing age of RBCs, a different mortality effect than RCTs (P = 0·02).

CONCLUSION

RCTs established that transfusion of 1- to 10-day-old stored RBCs is not superior to current practice. The apparent discrepancy in mortality between analyses of RCTs and observational studies may in part relate to differences in hypotheses tested and ages of stored RBCs studied. Further trials investigating 1- to 10-day-old stored RBC benefits would seem of lower priority than studies to determine whether 4- to 6-week stored units have safety and efficacy equivalent to the 2- to 3-week-old stored RBCs commonly transfused today.

Transfusion of fresh vs. older red blood cells in the context of infection

The red blood cell (RBC) storage interval has been extended from less than a week to the current storage interval of 6-8 weeks. Regulatory criteria for extending storage rely upon a minimal degree of hemolysis and acceptable in vivo 24-h post transfusion recovery. Clinical studies of safety and efficacy have never been required. Concerns have arisen that RBC toward the end of storage develop a 'storage lesion' with previously unrecognized toxicity. Of the several mechanisms proposed, the bolus of iron delivered to macrophages as a result of hemolysis of stored RBC might pose a particular risk to patients with existing infections. We developed a canine model of pneumonia to compare the toxicity of stored RBC transfusion. We described increased mortality after transfusion of old RBC. We found that transfused older RBC increased mortality, in vivo hemolysis, circulating cell-free hemoglobin that scavenges nitric oxide, and elevations of non-transferrin bound and plasma labile iron. Disappearance of circulating iron correlated with increased mortality, worsening pulmonary function, and bacterial proliferation. Washing decreased the mortality associated with transfusing older RBC, but had the opposite effect on fresher blood. With low doses of bacteria, survival was unaffected by the age of blood, whereas high bacteria doses masked any effect of RBC age on mortality. Older RBC may have adverse effects, but the patient's clinical status, the age, volume and method of preparation of the RBC may be critical variables. Several mechanisms may account for this toxicity, but in the presence of bacterial infection, availability of iron likely plays a major role.

The effects of steroids during sepsis depend on dose and severity of illness: an updated meta-analysis

A previous meta-analysis determined that the effects of steroids during sepsis were dose-dependent; since then, additional trials have been published. The current analysis updates our previous analysis examining the effects of steroids during sepsis. A literature search from 2004 to 2008 identified seven randomized controlled trials in adult patients; these were added to 14 previously identified trials. The effects of steroids on mortality were highly variable among the 21 trials (p <0.001, I(2) = 60%). In trials published before 1989, which involved short courses of high-dose steroids, steroids increased mortality (n = 8, I(2) = 14%, OR of death 1.39 (95% CI 1.04-1.86), p 0.03). In trials published after 1997, which involved longer courses of lower-dose steroids, steroids consistently improved shock reversal (n = 7, I(2) = 0%, OR of shock reversal 1.66 [95% CI 1.25-2.20), p <0.001), but demonstrated a more heterogeneous beneficial effect on mortality (n = 12, I(2) = 25%, OR of death 0.64 (95% CI 0.45-0.93), p 0.02). An inverse linear relationship between severity of illness and the effects of steroids on mortality was identified across all trials (p 0.03) and within the subgroup of trials published after 1997 (p 0.03); steroids were harmful in less severely ill patient populations and beneficial in more severely ill patient populations. There was no effect of response to adrenocorticotrophic hormone (ACTH) stimulation testing concerning the effects of steroids and no increase in steroid-associated adverse events. Low-dose steroids appear to improve mortality rates in patients with septic shock who are at high risk of death; however, additional trials in this subpopulation are necessary to definitively determine the role of low-dose steroids during sepsis.

Clinical trials in sepsis: an update

In this article, we place clinical sepsis trials from the past year in the context of similar sepsis trials run over the past three decades. These recent clinical sepsis trials include studies of agents administered to limit the effects of specific host proinflammatory mediators (tumor necrosis factor, platelet-activating factor and prostaglandins), studies of use of corticosteroids at low doses late in sepsis, and studies of administration of high doses of a nonspecific nitric oxide synthase inhibitor to decrease nitric oxide production in septic shock. The three trials of agents designed to limit host proinflammatory mediators showed minimal beneficial effects, results that are similar to those of the approximately 20 previous trials of similar agents. Low-dose corticosteroid therapy reversed shock and showed nonsignificant trends towards improvements in survival rates. In contrast, high doses of corticosteroids given early in sepsis have shown harmful effects in clinical sepsis trials. Finally, inhibition of nitric oxide production was lethal, indicating that high doses of nonspecific inhibitors of nitric oxide production are contraindicated in septic shock.

Increasing the efficacy of anti-inflammatory agents used in the treatment of sepsis

Excessive production of inflammatory mediators during invasive infection plays a key role in the pathogenesis of septic shock. In an attempt to improve survival of patients with this lethal syndrome, agents were developed to selectively inhibit mediators in this inflammatory response. Despite promising preclinical results, several different mediator-specific anti-inflammatory agents failed to demonstrate significant benefit in patients. There was, however, a significant difference in mortality between preclinical and clinical trials. The median control mortality in preclinical trials, performed almost uniformly in highly lethal sepsis models, was 88%. In clinical trials however, the median control mortality rate was much lower, at 41%. A recent meta-regression analysis of these preclinical and clinical trials in combination with prospective confirmatory studies demonstrated that risk of death as assessed by control group mortality rate significantly altered the treatment effect of these agents in both humans and animals. While anti-inflammatory agents were very beneficial in groups with high control mortality rates, they were ineffective or harmful in groups with low control mortality rates. Thus, variation in the risk of death due to sepsis provides a basis for the marked difference in the efficacy of these anti-inflammatory agents in preclinical and clinical trials over the last decade. In contrast to mediator-specific anti-inflammatory agents, glucocorticoids and activated protein C have recently demonstrated significant beneficial effects in individual clinical trials. However, glucocorticoids were studied only in patients with vasopressor-dependent septic shock, which is associated with a high control mortality rate (i.e. 61%) similar to the level at which mediator-specific agents would have been expected to be markedly beneficial. Furthermore, consistent with earlier findings for mediator-specific anti-inflammatory agents, analysis of the activated protein C study also demonstrated a relationship between risk of death and effect of treatment. Developing better methods to define high-risk septic populations for treatment with anti-inflammatory agents will increase the efficacy of this therapeutic approach and minimize its potential for harm.

Acute G-CSF therapy is not protective during lethal E. coli sepsis

We investigated whether decreases in circulating polymorphonuclear neutrophils (PMN) during lethal Escherichia coli (E. coli) sepsis in canines are related to insufficient host granulocyte colony-stimulating factor (G-CSF). Two-year-old purpose-bred beagles had intraperitoneal E. coli-infected or -noninfected fibrin clots surgically placed. By 10 to 12 h following clot, both infected survivors and nonsurvivors had marked increases (P = 0.001) in serum G-CSF levels (mean peak G-CSF ng/ml +/- SE, 1,931 +/- 364 and 2,779 +/- 681, respectively) compared with noninfected controls (134 +/- 79), which decreased at 24 to 48 h. Despite increases in G-CSF, infected clot placement caused delayed (P = 0.06) increases in PMN (mean +/- SE change from baseline in cells x 10(3)/mm(3) at 24 and 48 h) in survivors (+3.9 +/- 3.9 and +13.8 +/- 3.6) compared with noninfected controls (+13.1 +/- 2.8 and +9.1 +/- 2.5). Furthermore, infected nonsurvivors had decreases in PMN (-1.4 +/- 1.0 and -1.1 +/- 2.3, P = 0.006 compared with the other groups). We next investigated whether administration of G-CSF immediately after clot placement and continued for 96 h to produce more rapid and prolonged high levels of G-CSF after infection would alter PMN levels. Although G-CSF caused large increases in PMN compared with control protein from 2 to 48 h following clot in noninfected controls, it caused much smaller increases in infected survivors and decreases in infected nonsurvivors (P = 0.03 for the ordered effect of G-CSF comparing the three groups). Thus insufficient host G-CSF is unlikely the cause of decreased circulating PMN in this canine model of sepsis. Other factors associated with sepsis either alone or in combination with G-CSF itself may reduce increases or cause decreases in circulating PMN.

Anti-inflammatory therapies in sepsis and septic shock

Despite advances in supportive care, the morbidity and mortality rate resulting from sepsis and septic shock remain high (30 - 50%). A central hypothesis driving sepsis research in recent years is that this syndrome is the result of excessive inflammation. Therapies designed to inhibit the inflammatory response were first shown to be markedly beneficial in animal models of sepsis and then tested in numerous clinical trials involving thousands of patients. Three broad anti-inflammatory strategies have been investigated. First, glucocorticoids in high doses administered at the onset of sepsis were studied. This approach proved unsuccessful. More recently, however, glucocorticoids in lower doses have been found to have a beneficial effect in patients with septic shock. Whether the mechanism of this treatment benefit is through inhibition of inflammation, or by counteracting a relative steroid refractoriness occurring during sepsis, remains unknown. The next focus of research were agents active against the endotoxin molecule. However, as with the experience with glucocorticoids, this approach lacked a consistent pattern of efficacy. It is unclear if this lack of efficacy is the result of endotoxin being a poor therapeutic target, or from testing agents which lacked the appropriate biological activity. Most recently, clinical trials in sepsis have focused on inhibiting specific host pro-inflammatory mediators (e.g., TNF, interleukins). While individual trials of inhibitors of these pro-inflammatory mediators failed to show a convincing benefit, pooling the results of these trials suggest that this approach has a marginal effect, supporting a role for excessive inflammation in sepsis. An unanswered question is reconcilling the very favourable effects obtained with anti-inflammatory treatments in animal models with the marginal results in humans. Further clinical and laboratory research is needed and may provide insight into more effective ways to use the anti-inflammatory agents already tested, or to investigate other potentially more effective anti-inflammatory agents in this syndrome.

ICAM-1 and CD11b inhibition worsen outcome in rats with E. coli pneumonia

We investigated whether inhibiting an endothelial adhesion molecule [intracellular adhesion molecule 1 (ICAM-1)] would alter outcome and lung injury in a similar fashion to inhibition of a leukocyte adhesion molecule (integrin CD11b) in a rat model of gram-negative pneumonia. Inhibition of ICAM-1 with monoclonal antibody (MAb) 1A29 (1 mg/kg sc or 0.2 or 2 mg/kg iv, q 12 h x 3) or of CD11b with MAb 1B6 (1 mg/kg sc, q 12 h x 3) were compared against similarly administered placebo proteins in rats challenged with intrabronchial Escherichia coli. After challenge, all animals were treated with antibiotics. ICAM-1 MAb (6 mg/kg, iv, total dose) increased mortality vs. control (P = 0.03). CD11b MAb (3 mg/kg, sc, total dose) did not significantly (P = 0.16) increase mortality rates, but this was not in a range of probability to exclude a harmful effect. All other doses of MAb had no significant effect on survival rates. ICAM-1 and CD11b MAbs had significantly different effects on the time course of lung injury, circulating white cells and lymphocytes, and lung lavage white cells and neutrophils (P = 0.04-0.003). CD11b MAb decreased, whereas ICAM-1 MAb increased these measures compared with control from 6 to 12 h after E. coli. However, from 144 to 168 h after E. coli both MAbs increased these measures compared with control rats but to a greater level with CD11b MAb. Thus both ICAM-1 and CD11b appear to be necessary for survival during E. coli pneumonia. Although these adhesion molecules may participate differently in early lung injury, with CD11b increasing and ICAM-1 decreasing inflammation and injury, both are important for the resolution of later injury. During gram-negative pneumonia the protective roles of ICAM-1 and CD11b may make their therapeutic inhibition difficult.

G-CSF during Escherichia coli versus Staphylococcus aureus pneumonia in rats has fundamentally different and opposite effects

We investigated if bacteria type alters outcome with prophylactic granulocyte colony stimulating factor (G-CSF) therapy during pneumonia. Rats received G-CSF or placebo daily for 6 d and after the third dose were intrabronchially inoculated with either Escherichia coli or Staphylococcus aureus. Without G-CSF, E. coli and S. aureus produced similar (p = NS) mortality rates (36 versus 38%) and serial changes in mean circulating neutrophil counts (CNC), but differing mean (+/- SE) tumor necrosis factor (TNF) levels (E. coli, 259 +/- 104 versus S. aureus, 51 +/- 17 pg/ml, p = 0.01). G-CSF prior to bacteria increased mean CNC more than six times compared with placebo (p = 0.001). However, with G-CSF in the first 6 h after E. coli, there was a greater than 20-fold decrease in mean (+/- SE) CNC (x 10(3)/ mm3) to below placebo (0.5 +/- 0.1 versus 0.8 +/- 0.1), whereas with G-CSF after S. aureus, there was only a fivefold decrease in mean CNC and CNC were greater than placebo (1.8 +/- 0.2 versus 0.8 +/- 0.1) (E. coli versus S. aureus decrease in CNC with G-CSF, p = 0.001). With E. coli, G-CSF worsened oxygenation and increased bacteremia and mortality, whereas with S. aureus, G-CSF improved oxygenation and decreased bacteremia and mortality (G-CSF therapy, E. coli versus S. aureus, p = 0.03, 0.05, and 0.001, respectively). Thus, during S. aureus pneumonia with low TNF levels, G-CSF increased CNC and bacterial clearance, resulting in less pulmonary injury and decreased death. During E. coli pneumonia with high TNF levels, G-CSF paradoxically decreased CNC, resulting in impaired bacterial clearance and worsened pulmonary injury and death. Bacterial species and the associated inflammatory mediator response can alter outcome with prophylactic G-CSF therapy during pneumonia.

Increasing doses of pentoxifylline as a continuous infusion in canine septic shock

We investigated effects of pentoxifylline during septic shock. Two-year-old (10-12 kg), purpose-bred beagles were infected i.p. with Escherichia coli 0111:B4 (1.2-1.5 x 10(9) colony-forming units per kilogram b.wt.) in a fibrin clot and then immediately treated with one of five doses of pentoxifylline (0.5-20 mg. kg-1. h-1 i.v.) as a 36-h continuous infusion or placebo. All animals received antibiotics and fluid resuscitation. Pentoxifylline levels increased in a dose-dependent manner during (p =.001) and were undetectable 12 h after stopping the infusion. During infusion of pentoxifylline at all doses, there were increases (p =.003), and once the infusion was stopped, there were decreases (p =.049) in endotoxin levels compared with controls. After clot implantation, at all pentoxifylline doses there was a significant increase in tumor necrosis factor levels, compared with controls (p =.025). The relative risk of death was significantly increased with pentoxifylline therapy in a dose-dependent fashion (20 >/= 10 >/= 5.0 >/= 1.0 >/= 0.5 mg. kg-1, p =.008). One hypothesis consistent with these data is that high pentoxifylline levels slowed endotoxin clearance, resulting in high levels of endotoxemia and increased proinflammatory mediator release and death. Pentoxifylline, used as a long-term continuous infusion as is commonly done clinically, can be harmful during Gram-negative septic shock.

Effects of L-NMMA and fluid loading on TNF-induced cardiovascular dysfunction in dogs

We investigated the effects of N(omega)-monomethyl-L-arginine (L-NMMA) and fluid loading on tumor necrosis factor (TNF)-induced cardiovascular dysfunction in awake dogs. L-NMMA (40 mg x kg(-1) given intravenously over a period of 10 min, and followed by dosing at 40 mg x kg(-1) x h(-1) for 6 h) and TNF (20 or 45 microg x kg(-1) given intravenously for 20 min), given alone or in combination, significantly decreased stroke volume, cardiac index, oxygen delivery, and left-ventricular (LV) function plots over a period of 6 h. Of note was that the cardiac-depressant effects of TNF and L-NMMA given together were significantly less than additive. Thus, the combination was beneficial (or significantly less harmful to cardiac performance than expected), possibly because L-NMMA augmented cardiac preload as shown by significant increases in both pulmonary capillary wedge pressure (PCWP) and central venous pressure (CVP). Fluid challenges at 6 h (Ringer's solution at 80 ml x kg(-1) given over a period of 30 min) also significantly increased PCWP and CVP, and abolished the beneficial preload effect of L-NMMA on cardiac performance. Thus, after fluid loading, the cardiac-depressant effects of TNF and L-NMMA given together became equal to the sum of those produced by TNF and L-NMMA given separately. Although L-NMMA significantly decreased serum nitrite/nitrate levels, TNF did not increase these end products of nitric oxide (NO) production relative to controls. Therefore, after preload abnormalities were eliminated with fluid loading, L-NMMA had no beneficial effect on TNF-induced cardiac depression, and TNF did not increase end products of NO production. These findings are not consistent with NO being the mechanism of TNF-induced acute cardiac depression.

Response of the septic vasculature to prolonged vasopressor therapy with N(omega)-monomethyl-L-arginine and epinephrine in canines

OBJECTIVE

To investigate the effect of blocking nitric oxide production on cardiovascular function and survival in canine septic shock treated with or without a conventional vasopressor.

DESIGN

Randomized, controlled trial.

SETTING

An animal research laboratory at the National Institutes of Health.

SUBJECTS

Sixty purpose-bred beagles.

INTERVENTIONS

Fibrin clots containing Escherichia coli were surgically placed into the peritoneal cavity. N(omega)-monomethyl-L-arginine (L-NMMA) 10 mg/kg followed by 0.5, 1.0, or 4.0 mg/kg/hr), epinephrine (1 microg/kg/min), both, or neither were infused for 24 hrs beginning 6 hrs after the onset of infection. All animals received fluid and antibiotic therapy.

MEASUREMENTS AND MAIN RESULTS

Serum nitric oxide metabolites, nitrite and nitrate, increased with infection (p = .024) and decreased with L-NMMA (p = .004, all doses combined). Myocardial nitric oxide synthase activity was ranked as follows: nonsurvivors > survivors > noninfected controls (p < .01). Other tissues examined showed the same pattern. L-NMMA produced sustained increases in systemic vascular resistance index and mean arterial pressure 9 and 24 hrs after the onset of infection (p < or = .04). Left ventricular ejection fraction was depressed by septic shock (p = .01) and further decreased by L-NMMA (p = .02). However, control and L-NMMA cardiac index values were similar (p > .4), perhaps because L-NMMA increased pulmonary artery occlusion pressure (p = .02). From 9 to 24 hrs, epinephrine, in the absence or presence of L-NMMA, blunted recovery of cardiac index (p < .02) and had a diminishing vasopressor effect (p = .05). Neither L-NMMA nor epinephrine, individually or combined, significantly altered survival rates at the doses investigated (p > or = .69).

CONCLUSIONS

The tested doses showed that nitric oxide production was inhibited by L-NMMA in canine septic shock, but mortality and myocardial depression were unaffected. These results suggest that if L-NMMA has a beneficial effect on survival rates in septic shock, it is small.

Cardiopulmonary effects of inhaled nitric oxide in normal dogs and during E. coli pneumonia and sepsis

We investigated the effect of inhaled nitric oxide (NO) at increasing fractional inspired O2 concentrations (FIO2) on hemodynamic and pulmonary function during Escherichia coli pneumonia. Thirty-eight conscious, spontaneously breathing, tracheotomized 2-yr-old beagles had intrabronchial inoculation with either 0.75 or 1.5 x 10(10) colony-forming units/kg of E. coli 0111:B4 (infected) or 0.9% saline (noninfected) in one or four pulmonary lobes. We found that neither the severity nor distribution (lobar vs. diffuse) of bacterial pneumonia altered the effects of NO. However, in infected animals, with increasing FIO2 (0.08, 0.21, 0.50, and 0.85), NO (80 parts/million) progressively increased arterial PO2 [-0.3 +/- 0.6, 3 +/- 1, 13 +/- 4, 10 +/- 9 (mean +/- SE) Torr, respectively] and decreased the mean arterial-alveolar O2 gradient (0.5 +/- 0.3, 4 +/- 2, -8 +/- 7, -10 +/- 9 Torr, respectively). In contrast, in noninfected animals, the effect of NO was significantly different and opposite; NO progressively decreased mean PO2 with increasing FIO2 (2 +/- 1, -5 +/- 3, -2 +/- 3, and -12 +/- 5 Torr, respectively; P < 0.05 compared with infected animals) and increased mean arterial-alveolar O2 gradient (0.3 +/- 0.04, 2 +/- 2, 1 +/- 3, 11 +/- 5 Torr; P < 0.05 compared with infected animals). In normal and infected animals alike, only at FIO2 < or = 0.21 did NO significantly lower mean pulmonary artery pressure, pulmonary artery occlusion pressure, and pulmonary vascular resistance index (all P < 0.01). However, inhaled NO had no significant effect on increases in mean pulmonary artery pressure associated with bacterial pneumonia. Thus, during bacterial pneumonia, inhaled NO had only modest effects on oxygenation dependent on high FIO2 and did not affect sepsis-induced pulmonary hypertension. These data do not support a role for inhaled NO in bacterial pneumonia. Further studies are necessary to determine whether, in combination with ventilatory support, NO may have more pronounced effects.

rG-CSF reduces endotoxemia and improves survival during E. coli pneumonia

We investigated the effects of recombinant granulocyte colony-stimulating factor (rG-CSF) during canine bacterial pneumonia. Beagles with chronic tracheostomies received daily subcutaneous rG-CSF (5 micrograms/kg body wt) or placebo for 14 days, beginning 9 days before intrabronchial inoculation with E. coli. Animals received antibiotics and fluid support; a subset received humidified oxygen (fractional inspired O2 0.40). Compared with controls, rG-CSF increased circulating neutrophil counts (57.4 vs. 11.0 x 10(3)/mm3, day 1 after infection; P = 0.0001), decreased plasma endotoxin (7.5 vs. 1.1 EU/ml at 8 h; P < 0.01) and serum tumor necrosis factor-alpha (3,402 vs. 729 pg/ml at 2 h; P = 0.01) levels, and prolonged survival (relative risk of death = 0.45, 95% confidence interval 0.21-0.97; P = 0.038). Also, rG-CSF attenuated sepsis-associated myocardial dysfunction (P < 0.001). rG-CSF had no effect on pulmonary function or on blood and lung bacteria counts (all P = not significant). Other animals challenged with endotoxin (4 mg/kg i.v.) after similar treatment with rG-CSF had lower serum endotoxin levels (7.62 vs. 5.81 log EU/ml at 6 h; P < 0.01) and less cardiovascular dysfunction (P < 0.05 to < 0.002) but similar tumor necrosis factor-alpha levels (P = not significant) compared with controls. Thus prophylactic rG-CSF sufficient to increase circulating neutrophils during bacterial pneumonia may improve cardiovascular function and survival by mechanisms that in part enhance the clearance of bacterial toxins but do not improve lung function.

Tyrphostin AG 556 improves survival and reduces multiorgan failure in canine Escherichia coli peritonitis

Tyrosine kinase-dependent cell signaling is postulated to be a pivotal control point in inflammatory responses initiated by bacterial products and TNF. Using a canine model of gram-negative septic shock, we investigated the effect of tyrosine kinase inhibitors (tyrphostins) on survival. Animals were infected intraperitoneally with Escherichia coli 0111: B4, and then, in a randomized, blinded fashion, were treated immediately with one of two tyrphostins, AG 556 (n = 40) or AG 126 (n = 10), or with control (n = 50), and followed for 28 d or until death. All animals received supplemental oxygen, fluids, and antibiotics. Tyrphostin AG 556 improved survival times when compared to controls (P = 0.05). During the first 48 h after infection, AG 556 also improved mean arterial pressure, left ventricular ejection fraction, cardiac output, oxygen delivery, and alveolar-arterial oxygen gradient compared to controls (all P < or = 0.05). These improvements in organ injury were significantly predictive of survival. Treatment with AG 556 had no effect on clearance of endotoxin or bacteria from the blood (both P = NS); however, AG 556 did significantly lower serum TNF levels (P = 0.03). These data are consistent with the conclusion that AG 556 prevented cytokine-induced multiorgan failure and death during septic shock by inhibiting cell-signaling pathways without impairing host defenses as determined by clearance of bacteria and endotoxin.

Serial measures of total body oxygen consumption in an awake canine model of septic shock

We examined serial changes in total body oxygen consumption (Vo2) in a permanently tracheotomized canine sepsis model. On Day 0, beagles had an Escherichia coli-infected (septic) or sterile (control) clot surgically placed in the peritoneum. During the 21-d study, 10 of the 16 septic animals and none of the six control animals died (p = 0.02). After clot placement septic versus control animals had decreased mean arterial blood pressure (mm Hg; Day 1: 106 versus 128, p = 0.055; Day 2: 95 versus 125, p = 0.004, respectively) and left ventricular ejection fraction (Day 1: 0.44 versus 0.69, p = 0.0006; Day 2: 0.33 versus 0.57, p = 0.0001, respectively). Despite significant lethality and cardiovascular dysfunction, in the septic group on Days 1 and 2, septic versus control animals had no significant differences in mean metabolic cart measured (Vo2DIR, ml/kg/min; Day 1: 11.9 versus 12.4, p = 0.81; Day 2: 14.2 versus 13.5, p = 0.72, respectively) and intravascular catheter calculated (Vo2INDIR, ml/kg/min; Day 1: 11.2 versus 11.2, p = 0.99; Day 2: 12.8 versus 15.4, p = 0.49, respectively). On Day 1 in septic and control animals, volume infusion produced increases (p < 0.001) in oxygen delivery (Do2). In septic and control animals these changes in Do2 were similar and were associated with similar increases in Vo2DIR (p = 0.001), and Vo2INDIR (p = 0.001). In fact, at all time points studied (baseline, Day 1, 2, and 21), both before and after volume infusion, levels of Do2, Vo2DIR, and Vo2INDIR did not differ between septic and control animals, nor did they differ between septic survivors and nonsurvivors. Because levels of Vo2DIR and Vo2INDIR were similar in both groups, we pooled data from septic and control animals. Throughout the study, Vo2 showed a moderate association with Vo2INDIR (r = 0.55, p = 0.003), but mean Vo2DIR was lower at baseline (p = 0.001) and on Day 21 (p = 0.07) and greater on Day 2 (p < 0.01). In summary, our techniques, which detected small changes in both Vo2DIR and Vo2INDIR occurring with volume infusion, did not demonstrate differences in these parameters comparing control and septic animals. These results in euvolemic septic animals suggest that total body Vo2 may not reflect pathogenetic mechanisms during sepsis and septic shock. Furthermore, these results suggest that although the level of total body Vo2 may reflect the effects of therapeutic interventions such as volume loading, it should not itself serve as a therapeutic target.

Controlled trials of rG-CSF and CD11b-directed MAb during hyperoxia and E. coli pneumonia in rats

We studied the effects of inhibiting and augmenting neutrophil function by using an immunocompetent rat model of infectious and hyperoxic lung injury. After intrabronchial Escherichia coli challenge at all fractional inspired O2 (FIO2) values studied (FIO2 = 0.21, 0.60, and 0.95) and after lethal O2 exposure alone (FIO2 = 0.90), lung injury, as measured by histological and physiological changes, was reduced by a CD11b/CD18-directed monoclonal antibody (MAb 1B6, P < 0.05 vs. controls) but was increased by recombinant granulocyte colony-stimulating factor (rG-CSF; P < 0.05 vs. control; MAb 1B6 vs. rG-CSF, P < 0.004). Pulmonary neutrophil counts were reduced by MAb 1B6 (P < 0.04) and increased by rG-CSF (P < 0.0004) compared with control animals. However, despite antibiotics, MAb 1B6 and rG-CSF both significantly increased the relative risk of death, independent of O2 concentration, during E. coli pneumonia (1.74 [symbol: see text] 1.20 and 2.39 [symbol: see text] 1.19, respectively, each P < 0.01). During lethal hyperoxia, MAb 1B6 increased the relative risk of death (1.76 [symbol: see text] 1.28, P < 0.16), whereas rG-CSF had no effect on survival (0.97 [symbol: see text] 1.28, P = 0.89). Thus inhibition of neutrophil function attenuated and enhancement worsened lung injury in response to infectious and hyperoxic challenges, supporting a pathophysiological role of the neutrophil in these processes. However, it is problematic that MAb 1B6 therapy, despite preventing lung damage, ultimately worsened host defenses and survival. Furthermore, rG-CSF also adversely affected survival during infectious lung injury, demonstrating the inherent risks of inhibiting or augmenting neutrophil function in an immunocompetent host during infection.

Role of endotoxemia in cardiovascular dysfunction and lethality: virulent and nonvirulent Escherichia coli challenges in a canine model of septic shock

We investigated whether the severity of septic shock is determined by virulence factors associated with or the levels of endotoxemia produced by two Escherichia coli strains. Canines were challenged intraperitoneally with an E. coli strain (O6:H1:K2) that has virulence factors associated with human disease or with an equal dose of a nonvirulent strain (O86:H8) that lacks these factors. Both strains were administered in viable, heat-killed, and purified endotoxin forms. Median survival times with the virulent strain compared with the nonvirulent strain were shorter with viable bacteria (5 x 10(10) CFU/kg) (144 h versus > 672 h; Wilcoxon, P = 0.03), longer with heat-killed bacteria (5 x 10(9) CFU/kg) ( > 676 h versus 26 h; P = 0.03), and similar with purified endotoxin (15 mg/kg) (28 h versus 48 h; P = 0.71). However, whether the challenge contained viable bacteria, heat-killed bacteria, or purified endotoxin, the virulent strain produced less endotoxemia (P = 0.001). Hence, the changing outcomes with differing forms of the two strains cannot be attributed solely to endotoxin levels. The viable virulent strain caused less endotoxemia but more harm, and this does not appear to be explained by a more potent endotoxin or other heat-stable component. This study suggests that circulating endotoxin levels per se are less important in the outcome of septic shock than virulence factors associated with E. coli strains. Furthermore, the data call into question the significance of the endotoxin concentration in the blood in predicting the severity of shock and the lethality of gram-negative infections.

Differential hemodynamic effects of L-NMMA in endotoxemic and normal dogs

We studied the differential hemodynamic effects of N omega-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide (NO) synthesis, in normal and endotoxemic dogs and examined its activity across the venous, pulmonary, and systemic circulations. Survival was used to determine therapeutic efficacy. In both normal and endotoxemic animals, L-NMMA similarly increased systemic (P = 0.01) and pulmonary (P = 0.047) vascular resistance, marginally increased mean arterial pressure (P = 0.07), and decreased oxygen delivery (P = 0.01) compared with normal saline. In contrast, the effect of L-NMMA on mean pulmonary arterial pressure, central venous pressure, and pulmonary capillary wedge pressure was different in endotoxemic than in normal animals (P < 0.05), but this differential effect occurred > 6 h after endotoxin challenge. L-NMMA (1-10 mg.kg-1.h-1) did not significantly increase survival rates or times in endotoxemic animals, but the highest dose decreased survival times (P < 0.05). Thus the effect of L-NMMA was similar on the systemic arterial circulation in endotoxemic dogs compared with normal dogs but was increased in the venous and pulmonary vascular beds after endotoxin, suggesting that the induction of NO production was greater in low-resistance vessels. We were unable to show that nonselective inhibition of NO production was beneficial in endotoxemic dogs.

Continuous arteriovenous hemofiltration does not improve survival in a canine model of septic shock

BACKGROUND

We examined whether or not continuous arteriovenous hemofiltration (CAVH), in the absence of renal failure, would improve either hemodynamic abnormalities or survival in a canine model of septic shock.

STUDY DESIGN

Escherichia coli 0111, as an intraperitoneal clot, was surgically implanted into 21 one- to two-year-old purpose-bred beagles. The dogs were randomized to no CAVH (control group, n = 7), sham CAVH (extracorporeal circulation without hemofiltration, n = 7), or true CAVH (hemofiltration with removal of 600 mL/hour of ultrafiltrate, n = 7). Hemofiltration began one hour after clot implantation and continued for six hours. All dogs received antibiotics and had serial hemodynamic and laboratory evaluations.

RESULTS

During the first seven hours of the study, all dogs displayed a progressive, significant decrease in mean arterial pressure, cardiac index, left ventricular ejection fraction, and serum pH (all p < 0.05). Two of seven dogs in the control group, one of seven dogs in the sham CAVH group, and one of seven dogs in the true CAVH group survived seven days after clot implantation. True CAVH, which included fluid replacement with lactated Ringer's solution, significantly increased serum lactate and decreased serum bicarbonate levels after six hours (both p < 0.05). However, pH did not differ between the three treatment groups (p > 0.20). Continuous arteriovenous hemofiltration therapy had no significant effect on cardiovascular abnormalities or survival.

CONCLUSIONS

The results of this study suggest that CAVH would be unlikely to provide benefit to patients with gram-negative septic shock, in the absence of renal failure.

Therapeutic trial of reconstituted human high-density lipoprotein in a canine model of gram-negative septic shock

In a controlled, randomized trial, the authors investigated the effects of reconstituted human high-density lipoprotein (R-HDL) on survival, endotoxemia, cytokine production and pathophysiologic and metabolic events in an animal model of gram-negative septic shock. At 0.5, 8 and 16 hr after implantation of a clot infected with Escherichia coli, canines received intravenous R-HDL (n = 13), control lipid (n = 7) or human serum albumin (HSA, n = 7) divided into three doses (0.3, 0.1 and 0.1 g/kg, respectively) at an hourly rate of 0.1 g/kg. All animals were treated with antibiotics and fluids. Animals treated with R-HDL had lower levels of circulating endotoxin and tumor necrosis factor and a smaller decrease in white blood cell counts than did animals treated with lipids and HSA (all P < .05). The survival times of lipid- and HSA-treated animals were similar (P = .3) and were significantly greater than those of R-HDL-treated animals (P = .02). During the first 6 hr after clot implantation, R-HDL-treated animals had significantly greater abnormalities in liver function test findings compared with lipid- and HSA-treated animals (all P < .05). For the first 24 hr, R-HDL-treated animals had significant increases in HDL levels; however, there were no significant relationships between these levels and the constituents of HDL (apolipoprotein AI and phosphatidylcholine) or liver function abnormalities and survival times (all r < .2, P > .3). In normal animals, administration of R-HDL (in similar doses) caused transient elevation of liver enzymes; in animals given sterile clot i.p., R-HDL caused seizures.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic effects of dopamine, norepinephrine, and fluids in a dog model of sepsis

To study how sepsis affects hemodynamic responses to catecholamines and fluids, either Escherichia coli-infected (septic, n = 8) or sterile (controls, n = 6) fibrin clots were implanted intraperitoneally into 2-yr-old beagles. Hemodynamics were measured at each of four doses of dopamine (0, 5, 10, and 20 micrograms.kg-1.min-1) and norepinephrine (0, 10, 20, and 40 micrograms.min-1), before and after infusion of fluid (Ringer 40 ml.kg-1). Septic animals had lower mean arterial pressure (MAP, P = 0.04), stroke volume index (SVI, P = 0.0001), and left ventricular (LV) ejection fraction (LVEF) (P = 0.0001) than controls. During this time, increasing doses of dopamine and norepinephrine produced corresponding increases (P < 0.001) in LVEF, SVI, and MAP. However, during sepsis, the ability of dopamine to increase MAP diminished, while its ability to increase LVEF and SVI was maintained. Conversely, the ability of norepinephrine to increase LVEF and SVI diminished, but its ability to increase MAP was maintained. During sepsis, fluids alone increased (P < 0.05) MAP, LVEF, SVI, and cardiac index (CI). Fluids with catecholamines also significantly increased (P < 0.05) MAP with only minimal increases in LVEF, SVI, and CI. These data demonstrate that during sepsis without catecholamines, fluids improve cardiac performance and systemic pressures, but with catecholamines, fluids have minimal effects on cardiac performance and augment MAP. Furthermore, during sepsis dopamine is more effective than norepinephrine in increasing LV performance, but norepinephrine is more effective than dopamine in increasing systemic pressures.

New strategies for combatting sepsis: the magic bullets missed the mark ... but the search continues

Despite the high expectations of scientists and industry, multiple clinical trials of anti-endotoxin- and anti-cytokine-based therapies for sepsis have failed to demonstrate benefit. Indeed, in some cases, the agents used were actually harmful to patients. In retrospect, perhaps the therapeutic premises on which these therapies were based were flawed. In the future, a better understanding of sepsis should lead to the development of accurate laboratory and clinical predictors that will identify when, and which, patients can benefit from a given therapy. Much has been learned from the efforts of industry and academia and, hopefully, the search for new therapies for this lethal syndrome will continue.

Cardiopulmonary effects of granulocyte colony-stimulating factor in a canine model of bacterial sepsis

We investigated the effects of recombinant granulocyte colony-stimulating factor (G-CSF) in a canine model of septic shock. Awake 2-yr-old beagles were studied before and after intraperitoneal placement of an Escherichia coli-infected clot. Nine days before and until 3 days after clot placement, animals received daily high-dose (G-CSF (5 microgram/kg body wt; n = 17), low-dose G-CSF (0.1 microgram/kg body wt; n = 17), or a control protein (5 micrograms/kg body wt; n = 20). Survival rate was greater (P < 0.04, Wilcoxon test) in the high-dose G-CSF group (14/17) than in the low-dose G-CSF (10/17) and control (12/20) groups. High-dose G-CSF improved cardiovascular function, as evidenced by increased left ventricular ejection fraction (day 1 after clot; P < 0.001) and mean arterial pressure (day 2; P < 0.02) compared with low-dose G-CSF and control groups. High-dose G-CSF increased (P < 0.001) mean peripheral neutrophils before (-3 days) and after (2 h to 4 days) clot and produced a more rapid (P < 0.001) rise (day 2) and fall (day 4) in mean alveolar neutrophil numbers compared with the low-dose G-CSF and control groups. High-dose G-CSF decreased mean serum endotoxin (2-8 h; P < 0.002) and tumor necrosis factor (2 h; P < 0.02) levels and lowered blood bacteria counts (2-6 h; P < 0.04) compared with the low-dose G-CSF and control groups. Thus, in this canine model, G-CSF sufficient to increase peripheral neutrophils before and during peritonitis and septic shock enhances host defense, reduces cytokine (tumor necrosis factor) levels, and improves cardiovascular function and survival.

Selected treatment strategies for septic shock based on proposed mechanisms of pathogenesis

PURPOSE

To review selected new therapies for septic shock designed to inhibit bacterial toxins or endogenous mediators of inflammation.

DATA SOURCES

Scientific journals, scientific meeting proceedings, and Food and Drug Administration advisory committee proceedings.

STUDY SELECTION AND EXTRACTION

Preclinical and clinical data from trials using core-directed antiendotoxin antibodies and anticytokine therapies for sepsis and studies in animal models of sepsis from our laboratory.

RESULTS OF DATA SYNTHESIS

Ten clinical trials using core-directed antiendotoxin antibodies produced inconsistent results and did not conclusively establish the safety or benefit of this approach. Both anti-interleukin-1 and anti-tumor necrosis factor (TNF) therapies have been beneficial in some animal models of sepsis but did not clearly improve survival in initial human trials, and one anti-TNF therapy actually produced harm. Neutrophils, another target for therapeutic intervention, protect the host from infection but may also contribute to the development of tissue injury during sepsis. In a canine model of septic shock, granulocyte colony-stimulating factor increased the number of circulating neutrophils and improved survival, but an anti-integrin (CD11/18) antibody that inhibits neutrophil function worsened outcome. Nitric oxide, a vasodilator produced by the host, causes hypotension during septic shock but may also protect the endothelium and maintain organ blood flow. In dogs challenged with endotoxin, the inhibition of nitric oxide production decreased cardiac index and did not improve survival.

CONCLUSIONS

No new therapy for sepsis has shown clinical efficacy. Perhaps more accurate clinical and laboratory predictors are needed to identify patients who may benefit from a given treatment strategy. On the other hand, the therapeutic premises may be flawed. Targeting a single microbial toxin such as endotoxin may not represent a viable strategy for treating a complex inflammatory response to diverse gram-negative bacteria. Similarly, the strategy of inhibiting the host inflammatory response may not be beneficial because immune cells and cytokines play both pathogenic and protective roles. Finally, our scientific knowledge of the complex timing of mediator release and balance during sepsis may be insufficient to develop successful therapeutic interventions for this syndrome.

The third component of complement protects against Escherichia coli endotoxin-induced shock and multiple organ failure

We investigated whether the third component of complement (C3) is involved in the pathophysiology of endotoxic shock, and if it is involved, whether it plays a protective role or whether it mediates shock and multiple organ failure. In a prospective, controlled investigation, six Brittany spaniels that were homozygous for a genetically determined deficiency of C3 (C3 deficient, < 0.003% of normal serum C3 levels) and six heterozygous littermates (controls, approximately 50% of mean normal serum C3 level) were given 2 mg/kg of reconstituted Escherichia coli 026:B6 acetone powder as a source of endotoxin, intravenously. All animals were given similar fluid and prophylactic antibiotic therapy, and had serial hemodynamic variables obtained. After E. coli endotoxin infusion, C3-deficient animals had higher peak levels of endotoxin and less of a rise in temperature than controls (P < 0.05). During the first 4 h after E. coli endotoxin infusion, C3-deficient animals had significantly greater decreases in mean central venous pressure and mean pulmonary artery pressure than controls (P < 0.02). During the first 48 h after E. coli endotoxin infusion, C3-deficient animals had significantly greater decreases in mean arterial pH, left ventricular ejection fraction, and mean pulmonary capillary wedge pressure, and greater increases in mean arterial lactate, arterial-alveolar O2 gradient, and transaminases (aspartate aminotransferase and alanine aminotransferase) than controls, (all P < 0.05). After E. coli endotoxin infusion, C3-deficient animals compared to controls had significantly less of a decrease in mean C5 levels (P < 0.01), but similar (P = NS) increases in circulating tumor necrosis factor levels, bronchoalveolar lavage neutrophils, and protein, and similar (P = NS) decreases in blood leukocytes and platelets. Two of six C3-deficient animals and two of six controls died. In summary, after intravenous infusion of E. coli endotoxin, canines with C3 deficiency have decreased endotoxin clearance and worse E. coli endotoxin-induced shock and organ damage. Thus, the third component of the complement system plays a beneficial role in the host defense against E. coli endotoxic shock.

A controlled trial of HA-1A in a canine model of gram-negative septic shock

OBJECTIVE

To investigate the therapeutic efficacy and microbiological and physiological effects of a human IgM monoclonal antibody (HA-1A) directed against the lipid A component of endotoxin in a canine model of sepsis that simulates the cardiovascular abnormalities of human septic shock.

DESIGN

Blinded, placebo-controlled 28-day trial.

INTERVENTIONS

Purpose-bred beagles were implanted with an intraperitoneal clot infected with Escherichia coli O111:B4. At clot placement, animals received HA-1A (10 mg.kg-1), control human IgM antibody (10 mg.kg-1), or control human serum albumin intravenously. All animals were given antibiotic and fluid therapy.

MEASURES

Survival and microbiological and physiological events.

RESULTS

Only two (15%) of 13 animals in the HA-1A group, compared with eight (57%) of 14 control animals (combined control human IgM antibody and control human serum albumin groups) (P = .05), survived 28 days. At 24 hours, the HA-1A group had lower mean arterial pressure (P = .04) and cardiac index (P = .004) and higher lactate levels (P = .05) compared with the combined-controls group. In addition, these parameters in the HA-1A group were significantly more predictive of death. The HA-1A and combined-controls groups had similar significant increases in the level of endotoxemia and bacteremia. Studies of toxic effects showed no harmful effects of control human IgM antibody in infected animals or HA-1A in non-infected animals.

CONCLUSION

In a canine model of E coli sepsis, HA-1A did not alter levels of bacteremia or endotoxemia and actually decreased survival. If these data are relevant to human septic shock, HA-1A therapy should be limited until the conditions under which this monoclonal antibody has beneficial or deleterious effects are more completely defined.

Plasma exchange does not improve survival in a canine model of human septic shock

Whether plasma exchange would improve survival in antibiotic-treated canines with septic shock was investigated. Escherichia coli O86H8 (1.4 X 10(10)) was surgically implanted as an intraperitoneal clot in 18 two-year-old (10-12 kg) purpose-bred beagles. Beginning 4 hours after surgery, all animals received cefoxitin and gentamicin for 5 days. Three treatment groups were defined: 1) a no apheresis, or control group, (n = 6); 2) a sham apheresis group, whose whole blood plasma was removed, separated, and then transfused (n = 6); and 3) a plasma exchange group from whom blood and plasma were removed and separated, to whom the blood was returned, and in whom infected plasma was replaced with compatible fresh-frozen canine plasma (n = 6). For the sham apheresis and plasma exchange groups, a commercial blood cell processor was used to separate 1.5 blood volumes of plasma at 5 and 24 hours after surgery. Serial radionuclide left ventricular ejection fractions and femoral and pulmonary arterial catheter hemodynamics were measured simultaneously in awake animals. All six animals in the plasma exchange group died. In both the sham and control groups, only one of six animals survived. Survival times were ordered (median in hours) (control [372 h] > sham apheresis [48 h] > plasma exchange [24 h] [p < 0.038]). Decreases in mean cardiac index and mean arterial pressure (from before apheresis to after) at 5 to 7 hours after surgery were ordered (plasma exchange > sham apheresis > control; p < 0.03). Thus, plasma exchange in this controlled trial of septic shock was associated with decreased survival and worsened hemodynamics.(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutic trial of lipid X in a canine model of septic shock

Three groups of dogs were given lipid X (0, 1, or 10 mg/kg) every 8 h for for seven doses, starting simultaneously with the intraperitoneal placement of Escherichia coli-containing fibrin clots. All animals developed bacteremia, hypotension, and a pattern of decreased left ventricular ejection fraction characteristic of septic shock (P = .01). Survival rates and survival times were not significantly different between treatment groups (P > .2). In a similar experiment, higher doses of lipid X resulted in a significantly decreased survival time compared with concurrent controls (P = .04). Animals receiving lipid X did not differ from controls in serial determinations of temperature, hemodynamic measurements, or laboratory parameters (except serum total protein). Although lipid X has antiendotoxin effects, no benefit could be demonstrated in this antibiotic-treated, gram-negative bacillary-infected model of septic shock. These data do not support a therapeutic role for lipid X in the treatment of gram-negative sepsis.

Acute hemorrhage in dogs: construction and validation of models to quantify blood loss

We examined the ability of commonly used clinical parameters to quantify acute hemorrhage in dogs. Eight animals were bled 40 ml/kg body wt over 100 min. Ten hemodynamic and 20 blood laboratory parameters were obtained every 10 min to construct, with use of linear regression analysis, models that quantify blood loss. During model construction, the best indicator of quantity of hemorrhage was arterial base deficit [ABD; coefficient of variation (CV) 35%]. This model was more accurate (P < 0.05) than 27 others (CV range 43 to 63%) and similar to systolic (CV 40%) and mean (CV 40%) arterial pressures. In validation studies in 10 additional animals, our best models based on ABD and systolic and mean arterial pressures each unexpectedly showed a significant (P < 0.05) decrease in accuracy (CV 86, 57, and 60%, respectively) attributable to large baseline (before hemorrhage) variability among animals. To eliminate this variability, models based on changes from baseline measurements were investigated. The best predictor of change in blood volume was change in ABD (CV 27%). This model was significantly (P < 0.05) more accurate than any of 27 others (CV range 36 to 65%) and similar to change in venous base deficit and venous pH (each CV 31%). When validated, acid-base models such as ABD, venous pH, and arterial bicarbonate were the best predictors of volume change (CV range 28 to 40%). With the use of multivariate analysis, pairwise combinations of single parameter models (n = 465) improved prediction errors only minimally. In summary, most commonly used hemodynamic and blood indexes could not be validated as accurate measurements in quantifying hemorrhage. In contrast, changes in acid-base parameters were validated as moderately accurate predictors of blood volume changes and therefore may have utility in the assessment of patients with ongoing hemorrhage.

N omega-amino-L-arginine, an inhibitor of nitric oxide synthase, raises vascular resistance but increases mortality rates in awake canines challenged with endotoxin

Inhibitors of nitric oxide synthase (NOS) have been reported to increase mean arterial pressure in animal models of sepsis and recently have been given to patients in septic shock. However, controlled studies to determine the effects of these agents on cardiovascular function and survival in awake animal models of sepsis have not been reported. To examine the therapeutic potential of NOS inhibition in septic shock, we challenged canines with endotoxin (2 or 4 mg/kg i.v.) and treated them with either normal saline or N omega-amino-L-arginine (10 or 1 mg/kg/h), the most specific inhibitor available for the isoform of NOS implicated in septic shock. Endotoxemic animals treated with N omega-amino-L-arginine (n = 11) had higher systemic and pulmonary vascular resistance indices (SVRI and PVRI, p less than or equal to 0.033) and decreased heart rates (p = 0.009), cardiac indices (CI, p = 0.01), oxygen delivery indices (p = 0.027), and oxygen consumption indices (p = 0.046) compared with controls (n = 6). Moreover, N omega-amino-L-arginine increased mortality rates after endotoxin challenge (10 of 11 vs. 1 of 6 controls, p = 0.005). Administration of L-arginine did not improve survival or alter the cardiopulmonary effects of N omega-amino-L-arginine, which suggests that inhibition of NOS may not have been competitive. In normal animals, N omega-amino-L-arginine alone (n = 3) increased SVRI (p = 0.0008) and mean arterial pressure (p = 0.016), and decreased CI (p = 0.01) compared with saline-treated controls (n = 3), but, at the high dose, also produced neuromuscular rigidity and seizure-like activity that was not apparent in the endotoxemic model. Thus, the mortality rate from endotoxemia increased either because of NOS inhibition per se or because of properties unique to N omega-amino-L-arginine, or both.

Systemic hemodynamic abnormalities and vasopressor therapy in sepsis and septic shock

Septic shock, a distributive form of shock, is a common and lethal disease characterized by tachycardia, hypotension, normal or elevated cardiac index, and decreased systemic vascular resistance (SVR). For 2 to 4 days after onset of shock, the left ventricular ejection fraction (LVEF) is depressed; with adequate volume replacement, the left ventricle dilates and cardiac output (CO) is maintained or increased. In survivors, these abnormalities reverse to normal within 7 to 10 days. The myocardial depression found in patients with septic shock is not associated with global myocardial ischemia. In our animal model of sepsis, myocardial depression is not associated with impaired myocardial high-energy stores, or abnormal myocardial oxygen utilization. However, septic animals have histopathologic evidence of coronary nonocclusive microvascular damage and myocyte injury. The majority of human deaths caused by septic shock are related to the peripheral vascular dysfunction and multiorgan system failure that occurs over time. The pathophysiology of this disease is complex. Clinical and experimental evidence support the notion that myocardial depression, peripheral vascular abnormalities, and multiorgan dysfunction result from the combined effect of exogenous and endogenous mediators (eg, endotoxin, cytokines, and nitric oxide) released during septic shock. Although conventional therapy with fluids, vasopressors, and antibiotics is effective, the disease still has a high mortality rate. Studies investigating the effects of bacterial toxins and potentially harmful host mediators offer the greatest hope in finding new ways to eradicate this highly lethal disease.

Tumor necrosis factor challenges in canines: patterns of cardiovascular dysfunction

Three groups of conscious canines were given different intravenous doses of human recombinant tumor necrosis factor (TNF) over 1 h, and the resulting cardiovascular abnormalities were examined for 10 days. As TNF dose increased [0 (controls), 30, 60, and 120 micrograms/kg body wt], the number of deaths increased (P less than 0.025; 0 of 6, 1 of 8, 4 of 8, number of deaths in each group, respectively). In all three groups receiving TNF, the mean left ventricular ejection fraction (LVEF) at 2 h after infusion decreased (P less than 0.003) compared with controls. The group receiving the highest dose of TNF (120 micrograms/kg body wt) had the greatest decrease (P less than 0.05) in LVEF from 0 to 2 h. At 8 h, all three groups receiving TNF had similar LVEF. In these three groups, other multiple measures of LV function at 8 h showed significant and similar decreases in cardiac contractility compared with controls. From 24 to 240 h, however, the time required for cardiac performance (LVEF) to return to normal was dose dependent (30 less than 60 less than 120 micrograms/kg body wt; P less than 0.05). Canines receiving the lowest dose of TNF had near normal cardiac function (LVEF) at 24 h, whereas canines receiving the highest dose had persistent cardiac abnormalities at 240 h. Thus, at 8 h, the severity of cardiac dysfunction is independent of TNF dose, but the rate of onset and the duration of cardiac abnormality are markedly dependent of dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukocyte CD11b/18 antigen-directed monoclonal antibody improves early survival and decreases hypoxemia in dogs challenged with tumor necrosis factor

This study examined the effect of monoclonal antibody (MAb) directed against leukocyte CD11b/18 glycoprotein complex (904MAb) on cardiopulmonary injury induced by tumor necrosis factor (TNF), and death. Eighteen 2-yr-old, purpose-bred beagles with chronic tracheostomies were challenged with TNF (60 micrograms/kg of body weight) intravenously. Nine of 18 animals were treated with 0.5 to 1.0 mg/kg of body weight 904MAb intravenously 45 min before and 12, 36, and 48 h after TNF infusion. Serial femoral and pulmonary arterial catheter hemodynamics, blood gas analysis, and radionuclide cineangiographic left ventricular ejection fractions (EF) were done before and after a fluid challenge. Serial bronchoalveolar lavages (BAL) with cell and protein analysis also were performed using the chronic tracheostomies. Compared with animals given TNF alone, animals treated with 904MAb did not differ in overall survival (TNF alone, 2/9; 904MAb, 3/9); however, the group of animals treated with 904MAb had significantly (p less than 0.01) fewer deaths within the first 30 h of TNF challenge. At 4 h after TNF challenge, all animals had significantly (p less than 0.05) reduced PaO2 after fluid challenge; however, animals given 904MAb (compared with animals given TNF alone) had significantly (p less than 0.05) smaller reductions in PaO2. Throughout the study, animals given 904MAb before TNF or TNF alone had similar changes in cardiac index, mean arterial pressure, EF, and BAL protein and neutrophil concentration. Thus, MAb directed against the leukocyte CD11b/18 glycoprotein complex prolonged survival and reduced the hypoxemia occurring after TNF challenge, but this antibody did not improve overall survival or cardiopulmonary function.(ABSTRACT TRUNCATED AT 250 WORDS)

TNF but not IL-1 in dogs causes lethal lung injury and multiple organ dysfunction similar to human sepsis

We compared the early and late pulmonary effects of human recombinant tumor necrosis factor (TNF) and interleukin 1 (IL-1) challenges in awake dogs with chronic tracheostomies. Serial blood gas analysis, bronchoalveolar lavage (BAL) with cell and protein analysis, intravascular catheter hemodynamics, and radionuclide left ventricular ejection fractions (LVEF) were determined before and after infusion of TNF (60 micrograms/kg body wt, n = 8), IL-1 (1,000 micrograms/kg body wt, n = 6), or heat-inactivated IL-1 (n = 6, controls). Controls given heat-inactivated IL-1 had no changes (P = NS) in any pulmonary parameter throughout the study. Animals given IL-1 had a transient increase (P less than 0.05) in BAL neutrophil concentration 1 day after infusion but no other changes (P = NS) in pulmonary function throughout the study. Animals given TNF had early (0-4 h) decreases (P less than 0.05) in arterial PO2, increases (P less than 0.05) in physiological shunt fraction and alveolar-to-arterial PO2 gradient, and a high mortality rate (50%). In TNF animals, volume challenges at 4 h were associated (P less than 0.05) with death and noncardiogenic pulmonary edema. In TNF survivors, hypoxemia persisted for 2-3 days and was associated with increases (P less than 0.05) in alveolar protein and neutrophil concentration on days 1 and 3, respectively, which in survivors returned to near normal over 6-21 days. Animals challenged with TNF and not IL-1 had reversible depression of LVEF similar in time course to abnormalities in arterial PO2. In this study, TNF (but not IL-1) challenges were lethal and produced acute pulmonary dysfunction sustained over days (reversible in survivors) that was similar to that seen in human septic shock. The ability of TNF to induce pulmonary injury similar to bacterial shock suggests that TNF is a key mediator of sepsis-induced lung injury. Furthermore, because TNF challenge induced both sustained pulmonary and cardiac injury, TNF may be a common pathway for the multiple organ dysfunction that occurs during septic shock.

Factors that determine the hemodynamic response to inhalation anesthetics

The hemodynamic response to inhalation anesthesia is influenced by three factors: 1) the specific drug, 2) the dose, and 3) individual characteristics of the subject. To investigate the importance of these factors on the cardiovascular response, we administered five doses [0, 0.5, 1.0, 1.5, and 2.0 minimum alveolar concentration (MAC)] of enflurane, halothane, and isoflurane to each of six dogs. Twelve hemodynamic variables were measured. For all variables, a change in the dose of each drug produced a consistent effect in each dog. Increases in dose resulted in significant decreases in seven variables [left ventricular ejection fraction, cardiac index (CI), stroke volume index (SVI), mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), left ventricular stroke work index (LVSWI), and heart rate (HR)] and a significant increase in one variable [central venous pressure (CVP)]. In contrast, the response of individual dogs to different drugs was not consistent. For seven variables [MAP, MPAP, LVSWI, CVP, pulmonary capillary wedge pressure (PCWP), end-diastolic volume index (EDVI), and end-systolic volume index (ESVI)], a significant difference in the responses of a dog to two drugs was greater than zero, whereas a significant difference in the response of at least one other dog to the same two drugs was less than zero (discordant dog-drug interactions). Thus, in contrast to the consistency of the cardiovascular response to changes in dose, the hemodynamic response to different drugs was inconsistent among dogs. We also studied the effect of fluid challenge on hemodynamic response at 1.5 or 2.0 MAC of the three drugs given to each dog.(ABSTRACT TRUNCATED AT 250 WORDS)

Pseudomonas aeruginosa compared with Escherichia coli produces less endotoxemia but more cardiovascular dysfunction and mortality in a canine model of septic shock

We investigated the effects of two different Gram-negative bacteria and radiation-induced leukopenia on endotoxemia, cardiovascular abnormalities, and mortality in a canine model of septic shock. Serial hemodynamics were measured in conscious dogs using radionuclide heart scans and thermodilution cardiac output catheters. Plasma endotoxin concentrations were determined with a chromogenic Limulus amebocyte lysate assay. Viable Pseudomonas aeruginosa or Escherichia coli implanted intraperitoneally produced concordant hemodynamic patterns of septic shock (p less than 0.01). Endotoxin concentrations were more than tenfold lower in dogs infected with P aeruginosa compared with E coli (p less than 0.0001). Despite lower endotoxin levels, P aeruginosa-infected dogs had a higher mortality (p less than 0.01), more severe hypotension (p less than 0.05), and greater depression of the left ventricular ejection fraction (p less than 0.05) than dogs with E coli sepsis. A nonlethal E coli challenge combined with leukopenia (induced by a nonlethal dose of radiation) resulted in a mortality of 60 percent (p less than 0.01) without greater cardiovascular dysfunction or higher endotoxin concentrations. These findings suggest that bacterial products other than endotoxin and host-related factors may be important contributors to the toxicity, cardiovascular instability, and mortality of Gram-negative septic shock. Quantitative determinations of plasma endotoxin are unlikely to correlate with the clinical severity of septicemia in heterogeneous patient populations infected with different Gram-negative organisms.