Peter C. Minneci

Hemolysis-associated endothelial dysfunction mediated by accelerated NO inactivation by decompartmentalized oxyhemoglobin.

During intravascular hemolysis in human disease, vasomotor tone and organ perfusion may be impaired by the increased reactivity of cell-free plasma hemoglobin (Hb) with NO. We experimentally produced acute intravascular hemolysis in a canine model in order to test the hypothesis that low levels of decompartmentalized or cell-free plasma Hb will severely reduce NO bioavailability and produce vasomotor instability. Importantly, in this model the total intravascular Hb level is unchanged; only the compartmentalization of Hb within the erythrocyte membrane is disrupted. Using a full-factorial design, we demonstrate that free water-induced intravascular hemolysis produces dose-dependent systemic vasoconstriction and impairs renal function. We find that these physiologic changes are secondary to the stoichiometric oxidation of endogenous NO by cell-free plasma oxyhemoglobin. In this model, 80 ppm of inhaled NO gas oxidized 85-90% of plasma oxyhemoglobin to methemoglobin, thereby inhibiting endogenous NO scavenging by cell-free Hb. As a result, the vasoconstriction caused by acute hemolysis was attenuated and the responsiveness to systemically infused NO donors was restored. These observations confirm that the acute toxicity of intravascular hemolysis occurs secondarily to the accelerated dioxygenation reaction of plasma oxyhemoglobin with endothelium-derived NO to form bioinactive nitrate. These biochemical and physiological studies demonstrate a major role for the intact erythrocyte in NO homeostasis and provide mechanistic support for the existence of a human syndrome of hemolysis-associated NO dysregulation, which may contribute to the vasculopathy of hereditary, acquired, and iatrogenic hemolytic states.

Bundled care for septic shock: An analysis of clinical trials

Context: Sepsis bundles have been developed to improve patient outcomes by combining component therapies. Valid bundles require effective components with additive benefits. Proponents encourage evaluation of bundles, both as a whole and based on the performance of each component. Objective: Assess the association between outcome and the utilization of component therapies in studies of sepsis bundles. Data Source: Database searches (January 1980 to July 2008) of PubMed, Embase, and the Cochrane Library, using the terms sepsis, bundles, guidelines, and early goal directed therapy. Data Extraction: Inclusion required comparison of septic adults who received bundled care vs. nonprotocolized care. Survival and use rates for individual interventions were abstracted. Main Results: Eight unblinded trials, one randomized and seven with historical controls, were identified. Sepsis bundles were associated with a consistent (I2 = 0%, p = .87) and significant increase in survival (odds ratio, 1.91; 95% confidence interval, 1.49–2.45; p < .0001). For all studies reporting such data, there were consistent (I2 = 0%, p ≥ .64) decreases in time to antibiotics, and increases in the appropriateness of antibiotics (p ≤ .0002 for both). In contrast, significant heterogeneity was seen across trials for all other treatments (antibiotic use within a specified time period; administration of fluids, vasopressors, inotropes, and packed red blood cells titrated to hemodynamic goals; corticosteroids and human recombinant activated protein C use) (all I2 ≥ 67%, p < .002). Except for antibiotics, sepsis bundle components are still being investigated for efficacy in randomized controlled trials. Conclusion: Bundle use was associated with consistent and significant improvement in survival and antibiotic use. Use of other bundle components changed heterogeneously across studies, making their impact on survival uncertain. However, this analysis should be interpreted cautiously as these studies were unblinded, and only one was randomized.

Randomization in clinical trials of titrated therapies: unintended consequences of using fixed treatment protocols.

Objective:Clinical trial designs that randomize patients to fixed treatment regimens may disrupt preexisting relationships between illness severity and level of therapy. The practice misalignments created by such designs may have unintended effects on trial results and safety. Methods:To illustrate this problem, the Transfusion Requirements in Critical Care (TRICC) trial and the Acute Respiratory Distress Syndrome Network low tidal volume (ARMA) trial were analyzed. Results:Publications before TRICC indicated that clinicians used higher transfusion thresholds in patients with ischemic heart disease compared with younger, healthier patients (p = .001). The trial, however, randomized patients (n = 838) to liberal (10 g/dL hemoglobin) or restrictive (7 g/dL) transfusion thresholds. Thirty-day mortality was different and opposite in the liberal compared with the restrictive arm depending on presence (21 vs. 26%) or absence (25 vs. 16%) of ischemic heart disease (p = .03). At baseline in ARMA, consistent with prior publications, physicians set ventilator volumes lower in patients with high airway pressures and poor compliance (8.4–10.6 mL/kg interquartile range) than patients with less severe abnormalities (9.6–12 mL/kg) (p = .0001). In the trial, however, patients (n = 861) were randomized to low (6 mL/kg) or high (12 mL/kg) tidal volumes. In patients with low compliance (<0.6 mL/kg), 28-day mortality was higher when tidal volumes were raised rather than lowered (42 vs. 29%), but this effect was reversed in patients with higher compliance (21 vs. 37%; p = .003). Conclusions:In TRICC and ARMA, randomization to fixed treatment regimens disrupted preexisting relationships between illness severity and therapy level. This created noncomparable subgroups in both study arms that received care different and opposite from titrated care, that is, practice misalignments. These subgroups reduced the interpretability and safety of each trial. Characterizing current practice, incorporating current practice controls, and using alternative trial designs to minimize practice misalignments should improve trial safety and interpretability.

Mechanical ventilation in ARDS: One size does not fit all.

In this issue of Critical Care Medicine, Dr. Kallet and colleagues (1) report a significant improvement in mortality in patients with adult respiratory distress syndrome (ARDS) and acute lung injury (ALI) who received lung protective ventilation based on the recommendations of the ARDS Network trial

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.

Nitrite reductase activity of hemoglobin as a systemic nitric oxide generator mechanism to detoxify plasma hemoglobin produced during hemolysis

Hemoglobin (Hb) potently inactivates the nitric oxide (NO) radical via a dioxygenation reaction forming nitrate (NO(3)(-)). This inactivation produces endothelial dysfunction during hemolytic conditions and may contribute to the vascular complications of Hb-based blood substitutes. Hb also functions as a nitrite (NO(2)(-)) reductase, converting nitrite into NO as it deoxygenates. We hypothesized that during intravascular hemolysis, nitrite infusions would limit the vasoconstrictive properties of plasma Hb. In a canine model of low- and high-intensity hypotonic intravascular hemolysis, we characterized hemodynamic responses to nitrite infusions. Hemolysis increased systemic and pulmonary arterial pressures and systemic vascular resistance. Hemolysis also inhibited NO-dependent pulmonary and systemic vasodilation by the NO donor sodium nitroprusside. Compared with nitroprusside, nitrite demonstrated unique effects by not only inhibiting hemolysis-associated vasoconstriction but also by potentiating vasodilation at plasma Hb concentrations of <25 muM. We also observed an interaction between plasma Hb levels and nitrite to augment nitroprusside-induced vasodilation of the pulmonary and systemic circulation. This nitrite reductase activity of Hb in vivo was recapitulated in vitro using a mitochondrial NO sensor system. Nitrite infusions may promote NO generation from Hb while maintaining oxygen delivery; this effect could be harnessed to treat hemolytic conditions and to detoxify Hb-based blood substitutes.

Mortality increases with recurrent episodes of nonaccidental trauma in children

BACKGROUND Nonaccidental trauma (NAT) is a leading cause of childhood traumatic injury and death. Our objectives were to compare the mortality rates of children who experience recurrent episodes of NAT (rNAT) with children who experience a single episode of NAT and to identify factors associated with rNAT and increased mortality from rNAT. METHODS Patients of NAT and rNAT in the Ohio State Trauma Registry were identified by matching date of birth, race, and sex between records of patients younger than 16 years between 2000 and 2010 with an DRG International Classification of Diseases—9th Rev. e-code for child abuse (E967–E967.9). Statistical comparisons were made using Fisher’s exact and Wilcoxon rank-sum tests. RESULTS A total of 1,572 patients of NAT were identified, with 53 patients meeting criteria for rNAT. Compared with patients with single-episode NAT, patients with rNAT were more commonly male (66% vs. 52%, p = 0.05), were white (83% vs. 65%, p = 0.02), were evaluated at a pediatric trauma center (87% vs. 69%, p = 0.008), and had higher mortality (24.5% vs. 9.9%, p = 0.002). Compared with rNAT patients who did not die, those who died with rNAT had a longer interval from initial episode to second episode (median [interquartile range], 527 days [83–1,099] vs. 166 days [52–502]; p = 0.07) and were older during their second episode (1 year [<6 months to 3 years] vs. <6 months [<6 months to 1 year]; p = 0.06). At initial presentation, lower-extremity fractures (p = 0.09) and liver injuries (p = 0.06) were reported more commonly in nonsurvivors of rNAT. CONCLUSION Mortality is significantly higher in children who experience rNAT. Therefore, it is critically important to effectively intervene with appropriate resources and follow-up after a child’s initial episode of NAT to prevent a future catastrophic episode. LEVEL OF EVIDENCE Prognostic/epidemiologic study, level IV.

Activated protein C in sepsis: emerging insights regarding its mechanism of action and clinical effectiveness

Purpose of review Dysregulation of endogenous coagulant and anticoagulant systems is now believed to play an important role in the pathogenesis of sepsis and septic shock. Reductions in host activated protein C levels and resultant microvascular thrombosis provided a basis for the use of recombinant human activated protein C in sepsis. Although controversial, the findings from an initial phase III trial testing this agent resulted in its approval for use in patients with severe sepsis and high risk of death. This review highlights emerging insights into the biology of protein C and activated protein C in sepsis, summarizes additional analysis growing out of the phase III trial testing recombinant human activated protein C, and assesses the cost-effectiveness that the clinical use of the agent has had thus far. Recent findings Binding of activated protein C to the endothelial cell protein C receptor is recognized to result in a growing number of actions including increased activity of activated protein C itself and inhibition of both nuclear factor-κB, a central regulator in the host inflammatory response, and apoptosis. Additional analysis of the original phase III trial testing recombinant human activated protein C appears to emphasize one of the US Food and Drug Administrations original concerns regarding an association between severity of sepsis and this agents effects. Postmarketing analysis and growing experience with other anticoagulant agents and corticosteroids in sepsis raise questions regarding the ultimate cost-effectiveness of activated protein C. Summary The protein C pathway is important both to coagulant and inflammatory pathways during sepsis. Based on emerging investigations, its actions appear to be increasingly complex ones. Despite potentially promising results in an initial phase III trial, the role of recombinant human activated protein C in the treatment of septic patients must continue to be evaluated.

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.

Antithrombotic therapies for sepsis: A need for more studies*

I n this issue of Critical Care Medicine, Dr. Wiedermann and colleagues (1) performed a retrospective analysis of the phase III Kybersept trial and demonstrated a beneficial effect of antithrombin (AT) III in the subgroup of patients with a moderate risk of death (40–70% mortality rate) (2). However, over the past 2 decades, beneficial effects of new sepsis therapies identified by such subgroup analysis have not been confirmed in subsequent clinical trials (3). To maximize predictive ability, subgroup analysis of clinical trials should include all patients enrolled in the trial and should test whether treatment effects are altered by important variables. In addition, p values should be corrected for those factors tested that could potentially alter the treatment effect of an agent. Finally, findings should be consistent with known pathophysiologic mechanisms. The analysis by Dr. Wiedermann and colleagues does not meet these requirements. However, their report represents an intriguing application of a previous hypothesis by Knaus and Wagner (4). They postulated that treatments which alter the host inflammatory response, such as AT III, should be beneficial in septic patients with intermediate mortality rates but not the extremes (4). These therapies would have no effect in very low risk patients because host responses are appropriate and of limited harm, and they would be ineffective in very high risk patients because the overall likelihood of death is so great that no treatment would be beneficial. To further test this hypothesis for AT III, we examined the clinical sepsis trials of AT III and two other antithrombotic agents: recombinant human activated protein C (rhAPC) and tissue factor pathway inhibitor (TFPI, Table 1) (2, 5, 6). Examining these three agents separately and combined, we attempted to provide insights into how these agents act as a class, to improve our understanding of the similarities and differences in these agents, and to potentially identify factors that alter their efficacy. This analysis explores additional data not available in prior review of these agents (7).