Burn Injury Exacerbates Hemodynamic and Metabolic Responses in Rats with Polymicrobial Sepsis

Burn-Induced Local and Systemic Immune Response: Systematic Review and Meta-Analysis of Animal Studies

As burn injuries are often followed by a derailed immune response and excessive inflammation, a thorough understanding of the occurring reactions is key to prevent secondary complications. This systematic review, that includes 247 animal studies, shows the post-burn response of 14 different immune cell types involved in immediate and long-term effects, in both wound tissue and circulation. Peripheral blood neutrophil and monocyte numbers increased directly after burns, whereas thrombocyte numbers increased near the end of the first week. Lymphocyte numbers, however, were decreased for at least two weeks. In burn wound tissue, neutrophil and macrophage numbers accumulated during the first three weeks. Burns also altered cellular functions as we found increased migratory potential of leukocytes, impaired antibacterial activity of neutrophils and enhanced inflammatory mediator production by macrophages. Neutrophil surges were positively associated with burn size and were highest in rats. Altogether, this comprehensive overview of the temporal immune cell dynamics shows that unlike normal wound healing, burn injury induces a long-lasting inflammatory response. It provides a fundamental research basis to improve experimental set-ups, burn care and outcome.

A case series of concomitant burn and COVID-19

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Heightened inflammation and acute lung injury in major burn and COVID-19.

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Baseline comorbidities and possible worsening consequence.

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Medical management in concomitant burn and SARS-CoV-2 infection.

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Multidisciplinary approaches to manage coexisting diseases.

Background

The recently emerged severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) disease (COVID-19) has become a human pandemic. Heightened inflammation, vascular hyperpermeability, acute lung injury, coagulopathy, and cardiovascular abnormalities are among the SARS-CoV-2 infection-related complications. Major burn is also associated with metabolic derangements, vascular leak, and hemodynamic instability. Burn patients are at high risk for infections and developing sepsis. COVID-19 in burn victims might worsen the clinical outcome and make their medical management challenging.

Result

Here, we present four cases of concomitant burn and COVID-19 with different degrees of complications. They had no (three out of four) or multiple (one out of four) baseline comorbidities and all were admitted to hospital for further management. Three out of four cases demonstrated acute respiratory failure and were intubated (no longer than 7 days). It seems that one of them had COVID-19 on arrival, the other apparently contracted at outside hospital, and the last two infected during the index hospitalization.

Conclusion

Concomitant severe burn and COVID-19 might complicate the clinical presentation and hospital course. Such combination was associated with poor outcome in a case with baseline comorbidities, beyond what was expected from the severity of burn injury. However, a more comprehensive study with larger sample size is required to make a valid conclusion. With an ongoing COVID-19 global pandemic, SARS-CoV-2 infection might be a concurrent disease with other illnesses or traumas such as burn. This dictate multidisciplinary approaches to risk stratify, screen, assess, and manage coexisting diseases. Additionally, appropriate preparations and careful precautions need to be executed in burn units to prevent COVID-19 exposure and transmission to limit potential adverse outcomes.

Predictors of Early Onset Multiple Organ Dysfunction in Major Burn Patients with Ventilator Support: Experience from A Mass Casualty Explosion

Organ dysfunction is common in patients with major burns and associated with poor outcomes. The risk factors for early onset multiple organ dysfunction syndrome (MODS) in major burn patients with invasive ventilator support has rarely been evaluated before. In this study, major burn patients with invasive ventilator support from 499 victims suffered in a mass casualty color dust explosion were retrospectively enrolled. The development of early MODS that occurred within 5 days after burn injury was determined and the risk factors associated with early MODS were analyzed. A total of 88 patients from five medical centers were included. Their mean total body surface area (TBSA) was 60.9 ± 15.8%, and 45 (51.1%) patients had early MODS. Hematologic failure was the most common organ failure (68.6%), followed by respiratory failure (48.9%). Independent clinical factors associated with early MODS included TBSA ≥55% (OR: 3.83; 95% CI: 1.29-11.37) and serum albumin level <2.1 g/dL upon admission (OR: 3.43; 95% CI: 1.01-11.57). Patients with early MODS had prolonged ventilator dependence and longer ICU admission than those without early MODS. Our results showed that early MODS in major burn patients with invasive ventilator support is very common and can be predicted early on admission.

Progress of clinical practice on the management of burn-associated pain: Lessons from animal models

Opioid-based analgesics provide the mainstay for attenuating burn pain, but they have a myriad of side effects including respiratory depression, nausea, impaired gastrointestinal motility, sedation, dependence, physiologic tolerance, and opioid-induced hyperalgesia. To test and develop novel analgesics, validated burn-relevant animal models of pain are indispensable. Herein we review such animal models, which are mostly limited to rodent models of burn-induced, inflammatory, and neuropathic pain. The latter two are pain syndromes that provide insight into the pain caused by systemic pro-inflammatory cytokines and direct injury to nerves (e.g., after severe burn), respectively. To date, no single animal model optimally mimics the complex pathophysiology and pain that a human burn patient experiences. No currently available burn-pain model examines effects of pharmacological intervention on wound healing. As cornerstones of pain and wound healing, pro-inflammatory mediators may be utilized for insight into both processes. Moreover, common clinical concerns such as systemic inflammatory response syndrome and multiple organ dysfunction remain unaddressed. For development of analgesics, these aberrations can significantly alter the potential efficacy and/or adverse effects of a prescribed analgesic following burn trauma. We therefore suggest that a multi-model strategy would be the most clinically relevant when evaluating novel analgesics for use in burn patients.

Cardiovascular Dysfunction Following Burn Injury: What We Have Learned from Rat and Mouse Models

Severe burn profoundly affects organs both proximal and distal to the actual burn site. Cardiovascular dysfunction is a well-documented phenomenon that increases morbidity and mortality following a massive thermal trauma. Beginning immediately post-burn, during the ebb phase, cardiac function is severely depressed. By 48 h post-injury, cardiac function rebounds and the post-burn myocardium becomes tachycardic and hyperinflammatory. While current clinical trials are investigating a variety of drugs targeted at reducing aspects of the post-burn hypermetabolic response such as heart rate and cardiac work, there is still a paucity of knowledge regarding the underlying mechanisms that induce cardiac dysfunction in the severely burned. There are many animal models of burn injury, from rodents, to sheep or swine, but the majority of burn related cardiovascular investigations have occurred in rat and mouse models. This literature review consolidates the data supporting the prevalent role that β-adrenergic receptors play in mediating post-burn cardiac dysfunction and the idea that pharmacological modulation of this receptor family is a viable therapeutic target for resolving burn-induced cardiac deficits.

Role of non-muscle myosin light chain kinase in neutrophil-mediated intestinal barrier dysfunction during thermal injury

Neutrophils and non-muscle myosin light chain kinase (nmMLCK) have been implicated in intestinal microvascular leakage and mucosal hyperpermeability in inflammation and trauma. The aim of this study was to characterize the role of nmMLCK in neutrophil-dependent gut barrier dysfunction following thermal injury, a common form of trauma that typically induces inflammation in multiple organs. Histopathological examination of the small intestine in mice after a full-thickness burn revealed morphological evidence of mucosa inflammation characterized by neutrophil infiltration into the lamina propria, epithelial contraction, and narrow villi with blunt brush borders and loss of goblet cells. Compared with their wild-type counterparts, nmMLCK mice displayed diminished morphological abnormalities. Likewise, intravital microscopic studies showed significant leukocyte adhesion in intestinal microvessels after burn, a response that was blunted in the absence of nmMLCK. Functionally, thermal injury significantly increased the gut lumen-to-blood transport of fluorescein isothiocyanate-dextran (4 kd), and this hyperpermeability was attenuated by either neutrophil depletion or nmMLCK deficiency. Consistent with the in vivo observations, in vitro assays with Caco-2 epithelial cell monolayers revealed a decrease in transcellular electric resistance coupled with myosin light chain phosphorylation, actomyosin ring condensation, and claudin-1 internalization upon stimulation with fMLP (N-formyl-methionyl-leucyl-phenylalanine)-activated neutrophils. Pretreatment of the cells with the MLCK inhibitor ML-7 prevented the tight junction responses. Taken together, the results suggest that nmMLCK plays an important role in neutrophil-dependent intestinal barrier dysfunction during inflammatory injury.

Apolipoprotein A-I mimetic peptide treatment inhibits inflammatory responses and improves survival in septic rats

Systemic inflammation induces a multiple organ dysfunction syndrome that contributes to morbidity and mortality in septic patients. Since increasing plasma apolipoprotein A-I (apoA-I) and HDL may reduce the complications of sepsis, we tested the hypothesis that the apoA-I mimetic peptide 4F confers similar protective effects in rats undergoing cecal ligation and puncture (CLP) injury. Male Sprague-Dawley rats were randomized to undergo CLP or sham surgery. IL-6 levels were significantly elevated in plasma by 6 h after CLP surgery compared with shams. In subsequent studies, CLP rats were further subdivided to receive vehicle or 4F (10 mg/kg) by intraperitoneal injection, 6 h after sepsis induction. Sham-operated rats received saline. Echocardiographic studies showed a reduction in left ventricular end-diastolic volume, stroke volume, and cardiac output (CO) 24 h after CLP surgery. These changes were associated with reduced blood volume and left ventricular filling pressure. 4F treatment improved blood volume status, increased CO, and reduced plasma IL-6 in CLP rats. Total cholesterol (TC) and HDL were 79 +/- 5 and 61 +/- 4 mg/dl, respectively, in sham rats. TC was significantly reduced in CLP rats (54 +/- 3 mg/dl) due to a reduction in HDL (26 +/- 3 mg/dl). 4F administration to CLP rats attenuated the reduction in TC (69 +/- 4 mg/dl) and HDL (41 +/- 3 mg/dl) and prevented sepsis-induced changes in HDL protein composition. Increased plasma HDL in 4F-treated CLP rats was associated with an improvement in CO and reduced mortality. It is proposed that protective effects of 4F are related to its ability to prevent the sepsis-induced reduction in plasma HDL.

Long-term immunosuppression in burned patients assessed by in vitro neutrophil oxidative burst (Phagoburst®)

OBJECTIVE

To assess the duration and magnitude of immunosuppression induced by burns as measured by the neutrophil oxidative burst in vitro.

DESIGN

Prospective exploratory cohort study.

SETTING

Tertiary referral unit, University Hospital, Linkoping, Sweden (National Burn Unit). PATIENTS AND HEALTHY VOLUNTEERS (CONTROLS): Twenty-eight subjects consecutively admitted to the Burn Unit. The mean total burn surface area (TBSA%) was 36 (range 13-87) and mean age 44 years (range 14-89). Patients' data were collected prospectively in the burn unit, which also included sequential organ failure assessment (SOFA) score.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

To assess the changes in the oxidative capacity of neutrophils after the burn, blood samples for the Phagoburst analysis were taken on admission and at least once every second week for the duration of stay in hospital and thereafter monthly up to 12 months after the burn. Neutrophils were stimulated in vitro by Escherichia coli, phorbol 12-phorbol myristate 13-acetate (PMA), and peptide N-formyl-Met-Leu-Phe (fMLP). Oxidative burst was measured by flow cytometry. Oxidative capacity of the neutrophils decreased similarly for all three stimulants: there was a pathological decrease shortly after admission, with the lowest value occurring between days 7 and 10, followed by a gradual recovery during the ensuing months. Full recovery (to the values of the controls) was seen first 3.5 months after the burn. Using multiple regression, we found that only age and time since the burn significantly (p<0.05) affected the oxidative burst. White cell count (WCC) and C-reactive protein (CRP) values returned to reference ranges long before the oxidative burst.

CONCLUSIONS

This study provides evidence that immunosuppression in those injured by burns, as assessed by the in vitro oxidative burst of neutrophils, remains long after the event of the burn (up to 3.5 months after burn). Absence of correlations to TBSA%, FTB%, blood transfusion, opiates provided, and multiple organ failure score and laboratory infection variables together with the finding that decreased oxidative burst was uniform after the injury, suggesting that this immunosuppression is primarily due to the general metabolic response rather than recurring infections.