Airway obstruction and bacterial invasion in autopsy tissue of pediatric burn victims

Effects of nebulized adipose-derived mesenchymal stem cells on acute lung injury following smoke inhalation in sheep

INTRODUCTION

Treatment of ARDS caused by smoke inhalation is challenging with no specific therapies available. The aim of this study was to test the efficacy of nebulized adipose-derived mesenchymal stem cells (ASCs) in a well-characterized, clinically relevant ovine model of smoke inhalation injury.

MATERIAL AND METHODS

Fourteen female Merino sheep were surgically instrumented 5-7 days prior to study. After induction of acute lung injury (ALI) by cooled cotton smoke insufflation into the lungs (under anesthesia and analgesia), sheep were placed on a mechanical ventilator for 48 hrs and monitored for cardiopulmonary hemodynamics in a conscious state. ASCs were isolated from ovine adipose tissue. Sheep were randomly allocated to two groups after smoke injury: 1) ASCs group (n = 6): 10 million ASCs were nebulized into the airway at 1 hr post-injury; and 2) Control group (n = 8): Nebulized with saline into the airways at 1 hr post-injury. ASCs were labeled with green fluorescent protein (GFP) to trace cells within the lung. ASCs viability was determined in bronchoalveolar lavage fluid (BALF).

RESULTS

PaO2/FiO2 in the ASCs group was significantly higher than in the control group (p = 0.001) at 24 hrs. Oxygenation index: (mean airway pressure × FiO2/PaO2) was significantly lower in the ASCs group at 36 hr (p = 0.003). Pulmonary shunt fraction tended to be lower in the ASCs group as compared to the control group. GFP-labelled ASCs were found on the surface of trachea epithelium 48 hrs after injury. The viability of ASCs in BALF was significantly lower than those exposed to the control vehicle solution.

CONCLUSION

Nebulized ASCs moderately improved pulmonary function and delayed the onset of ARDS.

Introduction: The Multidisciplinary Team Approach to Burn Care

Since the first burn units were established following World War II, great advances in understanding and treating burn shock, smoke inhalation injury, pneumonia, and invasive burn wound infections, and in achieving early burn-wound closure, have greatly decreased postburn morbidity and mortality. These advances were the result of closely integrated multidisciplinary teams of clinicians and researchers. The team approach to burns is a model for success in the care of any challenging clinical problem.

Inhalation Injury in the Burned Patient

Inhalation injury causes a heterogeneous cascade of insults that increase morbidity and mortality among the burn population. Despite major advancements in burn care for the past several decades, there remains a significant burden of disease attributable to inhalation injury. For this reason, effort has been devoted to finding new therapeutic approaches to improve outcomes for patients who sustain inhalation injuries.The three major injury classes are the following: supraglottic, subglottic, and systemic. Treatment options for these three subtypes differ based on the pathophysiologic changes that each one elicits.Currently, no consensus exists for diagnosis or grading of the injury, and there are large variations in treatment worldwide, ranging from observation and conservative management to advanced therapies with nebulization of different pharmacologic agents.The main pathophysiologic change after a subglottic inhalation injury is an increase in the bronchial blood flow. An induced mucosal hyperemia leads to edema, increases mucus secretion and plasma transudation into the airways, disables the mucociliary escalator, and inactivates hypoxic vasocontriction. Collectively, these insults potentiate airway obstruction with casts formed from epithelial debris, fibrin clots, and inspissated mucus, resulting in impaired ventilation. Prompt bronchoscopic diagnosis and multimodal treatment improve outcomes. Despite the lack of globally accepted standard treatments, data exist to support the use of bronchoscopy and suctioning to remove debris, nebulized heparin for fibrin casts, nebulized N-acetylcysteine for mucus casts, and bronchodilators.Systemic effects of inhalation injury occur both indirectly from hypoxia or hypercapnia resulting from loss of pulmonary function and systemic effects of proinflammatory cytokines, as well as directly from metabolic poisons such as carbon monoxide and cyanide. Both present with nonspecific clinical symptoms including cardiovascular collapse. Carbon monoxide intoxication should be treated with oxygen and cyanide with hydroxocobalamin.Inhalation injury remains a great challenge for clinicians and an area of opportunity for scientists. Management of this concomitant injury lags behind other aspects of burn care. More clinical research is required to improve the outcome of inhalation injury.The goal of this review is to comprehensively summarize the diagnoses, treatment options, and current research.

Pathophysiology, research challenges, and clinical management of smoke inhalation injury

Smoke inhalation injury is a serious medical problem that increases morbidity and mortality after severe burns. However, relatively little attention has been paid to this devastating condition, and the bulk of research is limited to preclinical basic science studies. Moreover, no worldwide consensus criteria exist for its diagnosis, severity grading, and prognosis. Therapeutic approaches are highly variable depending on the country and burn centre or hospital. In this Series paper, we discuss understanding of the pathophysiology of smoke inhalation injury, the best evidence-based treatments, and challenges and future directions in diagnostics and management.

Integrity of airway epithelium in pediatric burn autopsies: Association with age and extent of burn injury

This study examines the structural integrity of the airway epithelium in autopsy tissues from pediatric burn subjects.

METHODS

A semi-quantitative score for the degree of airway epithelial integrity was made for seventy- two pediatric burn autopsies. Multivariate ordinal logistic regression was performed to identify relationships between epithelial integrity and conditions related to tissue fixation, time of death after injury, age, total body surface area burn (TBSA), extent of 3rd degree burn, presence of inhalation injury, ventilator days and pneumonia.

RESULTS

No significant difference in epithelial integrity scores was identified between burn only cases and those with inhalation injury. Significant correlations with bronchiolar epithelial integrity scores were identified for age, p=0.02, and percent 3rd degree burn, p=0.02. There was no significant relationship between epithelial integrity and time between death and autopsy, p>0.44.

CONCLUSIONS

Airway epithelial loss seen in autopsy tissue is not simply an artifact of tissue fixation. The degree of compromise correlates most strongly with age and degree of burn. Further studies are needed to identify physiological or critical care factors following burn injury that contribute to compromise in the structural and functional properties of the airway epithelium.