Use of dornase alfa in the paediatric intensive care unit: current literature and a national cross-sectional survey.

OBJECTIVES: Airway mucus obstruction is a major challenge in children admitted to the paediatric intensive care unit (PICU). We aimed to evaluate the evidence and contemporary use of the mucolytic medication dornase alfa for non-cystic fibrosis conditions in the PICU. METHODS: (1) We performed a systematic review with searches in PubMed, EMBASE, and the Cochrane Library. Study selection: for quality assessment and data synthesis, we included only randomised controlled trials (RCTs) that compared dornase alfa to standard care or placebo in critically-ill paediatric patients (<18 years of age) in the PICU. However, non-randomised controlled studies and case series are also discussed. Data extraction: data were extracted independently by multiple reviewers using data extraction forms. The primary outcome was duration of mechanical ventilation. Data synthesis: The GRADE approach was used for quality assessment. No meta-analysis could be performed. (2) A national cross-sectional survey among all seven PICUs in the Netherlands was also performed. RESULTS: The systematic review yielded only one RCT, comparing dornase alfa with normal saline in children after cardiac surgery. In this study, dornase alfa led to a reduction in duration of mechanical ventilation by approximately 1 day (36% reduction). In addition, we found nine retrospective observational and case studies. The survey revealed high current use of dornase alfa in Dutch PICUs: 42% of the respondents reported prescribing dornase alfa at least once every week. Only 4% of the respondents reported having access to a local PICU dornase alfa protocol. CONCLUSIONS: The off-label use of dornase alfa in the PICU is frequent without strong evidence or local protocols, highlighting the need for further research on the effectiveness of this mucolytic agent.

Age-dependent differences in pulmonary host responses in ARDS: a prospective observational cohort study.

BACKGROUND: Results from preclinical studies suggest that age-dependent differences in host defense and the pulmonary renin-angiotensin system (RAS) are responsible for observed differences in epidemiology of acute respiratory distress syndrome (ARDS) between children and adults. The present study compares biomarkers of host defense and RAS in bronchoalveolar lavage (BAL) fluid from neonates, children, adults, and older adults with ARDS. METHODS: In this prospective observational study, we enrolled mechanical ventilated ARDS patients categorized into four age groups: 20 neonates (< 28 days corrected postnatal age), 29 children (28 days-18 years), 26 adults (18-65 years), and 17 older adults (> 65 years of age). All patients underwent a nondirected BAL within 72 h after intubation. Activities of the two main enzymes of RAS, angiotensin converting enzyme (ACE) and ACE2, and levels of biomarkers of inflammation, endothelial activation, and epithelial damage were determined in BAL fluid. RESULTS: Levels of myeloperoxidase, interleukin (IL)-6, IL-10, and p-selectin were higher with increasing age, whereas intercellular adhesion molecule-1 was higher in neonates. No differences in activity of ACE and ACE2 were seen between the four age groups. CONCLUSIONS: Age-dependent differences in the levels of biomarkers in lungs of ARDS patients are present. Especially, higher levels of markers involved in the neutrophil response were found with increasing age. In contrast to preclinical studies, age is not associated with changes in the pulmonary RAS.

Local dornase alfa treatment reduces NETs-induced airway obstruction during severe RSV infection.

Respiratory syncytial virus (RSV) infection is characterised by airway obstruction with mucus plugs, containing DNA networks in the form of neutrophil extracellular traps (NETs). We investigated the effect of dornase alfa on histopathological NETs-induced airway obstruction and viral load in an age-relevant calf model of severe bovine RSV disease. As compared with the control animals, dornase alfa treatment resulted in a strong reduction of NETs-induced airway obstruction. Viral load in the lower respiratory tract was not different between the two groups. We conclude that NETs form a relevant target for treatment of airway obstruction in severe RSV disease.

Neutrophil subset responses in infants with severe viral respiratory infection.

Neutrophils are the predominant inflammatory cells recruited to the respiratory tract as part of the innate immune response to viral infections. Recent reports indicate the existence of distinct functional neutrophil subsets in the circulatory compartment of adults, following severe inflammatory conditions. Here, we evaluated the occurrence of neutrophil subsets in blood and broncho-alveolar lavage fluid during severe viral respiratory infection in infants based on CD16/CD62L expression. We show that during the course of severe respiratory infection infants may develop four heterogeneous neutrophil subsets in blood (mature, immature, progenitor, and suppressive neutrophils), each with distinct activation states. However, while isolated viral respiratory infection was characterized by a relative absence of suppressive neutrophils in both blood and lungs, only patients with bacterial co-infection were shown to produce suppressive neutrophils. These data suggest the occurrence of distinct and unique neutrophil subset responses during severe viral and (secondary) bacterial respiratory infection in infants.

Pneumovirus-Induced Lung Disease in Mice Is Independent of Neutrophil-Driven Inflammation.

The human pneumovirus respiratory syncytial virus (RSV) is the most common pathogen causing lower respiratory tract disease in young children worldwide. A hallmark of severe human RSV infection is the strong neutrophil recruitment to the airways and lungs. Massive neutrophil activation has been proven detrimental in numerous diseases, yet in RSV the contribution of neutrophils to disease severity, and thereby, the relevance of targeting them, is largely unknown. To determine the relevance of potential neutrophil targeting therapies, we implemented antibody-mediated neutrophil depletion in a mouse pneumonia virus of mice (PVM) model. PVM is a host specific murine pneumovirus closely related to human RSV, which reproduces many of the features of RSV infection, such as high viral replication and neutrophil recruitment. Clinical disease and markers of lung inflammation and injury were studied in PVM-infected mice treated with either depleting or isotype control antibodies. To confirm our results we performed all experiments in two mice strains: C57Bl6 and BALBc mice. Neutrophil depletion in blood and lungs was efficient throughout the disease. Remarkably, in both mouse strains we found no difference in clinical disease severity between neutrophil-depleted and control arms. In line with this observation, we found no differences between groups in histopathological lung injury and lung viral loads. In conclusion, our study shows that in mice neutrophil recruitment to the lungs does not affect disease outcome or viral clearance during severe PVM infection. As such, this model does not support the notion that neutrophils play a key role in mouse pneumovirus disease.

Transfusion of 35-Day Stored RBCs in the Presence of Endotoxemia Does Not Result in Lung Injury in Humans.

OBJECTIVE: Transfusion-related acute lung injury is the leading cause of transfusion-related mortality. Preclinical studies have shown that aged RBCs can induce transfusion-related acute lung injury in the presence of a "first hit" (e.g., sepsis). Clinical studies, however, show conflicting results on this matter. We tested whether maximally stored RBCs are able to induce lung injury in the presence of a "first hit" in humans (Dutch Trial Register: NTR4455). DESIGN: Open-label, randomized controlled trial. PATIENTS: Healthy male volunteers. INTERVENTIONS: Eighteen healthy male volunteers donated one unit of autologous RBCs 2 or 35 days before the experiment. The experiment was started by infusion of 2 ng/kg lipopolysaccharide ("first hit"). After 2 hours, volunteers received normal saline (n = 6), 2-day stored transfusion (n = 6), or 35-day stored transfusion (n = 6) ("second hit"). Blood was sampled hourly. Six hours after transfusion, the diffusion capacity of the lungs for carbon monoxide was tested and volunteers underwent spirometry, chest x-ray study, and a bronchoalveolar lavage. MEASUREMENTS AND MAIN RESULTS: All volunteers fulfilled sepsis criteria after lipopolysaccharide injection. The stored blood transfusion did not result in significant changes in either hemodynamic or respiratory variables compared with the control groups. Furthermore, chest x-rays, lung function, and PaO2/FIO2 ratios did not differ between groups. Transfusion of stored autologous RBCs did not result in an increased level of protein in the lungs or neutrophil influx. CONCLUSIONS: Transfusion of 35-day stored autologous RBCs in the presence of endotoxemia does not result in lung injury in humans.

Neutrophil extracellular traps cause airway obstruction during respiratory syncytial virus disease.

Human respiratory syncytial virus (RSV) is the most important cause of severe lower respiratory tract disease (LRTD) in young children worldwide. Extensive neutrophil accumulation in the lungs and occlusion of small airways by DNA-rich mucus plugs are characteristic features of severe RSV-LRTD. Activated neutrophils can release neutrophil extracellular traps (NETs), extracellular networks of DNA covered with antimicrobial proteins, as part of the first-line defence against pathogens. NETs can trap and eliminate microbes; however, abundant NET formation may also contribute to airway occlusion. In this study, we investigated whether NETs are induced by RSV and explored their potential anti-viral effect in vitro. Second, we studied NET formation in vivo during severe RSV-LRTD in infants and bovine RSV-LRTD in calves, by examining bronchoalveolar lavage fluid and lung tissue sections, respectively. NETs were visualized in lung cytology and tissue samples by DNA and immunostaining, using antibodies against citrullinated histone H3, elastase and myeloperoxidase. RSV was able to induce NET formation by human neutrophils in vitro. Furthermore, NETs were able to capture RSV, thereby precluding binding of viral particles to target cells and preventing infection. Evidence for the formation of NETs in the airways and lungs was confirmed in children with severe RSV-LRTD. Detailed histopathological examination of calves with RSV-LRTD showed extensive NET formation in dense plugs occluding the airways, either with or without captured viral antigen. Together, these results suggest that, although NETs trap viral particles, their exaggerated formation during severe RSV-LRTD contributes to airway obstruction.

Lung-protective mechanical ventilation does not protect against acute kidney injury in patients without lung injury at onset of mechanical ventilation.

INTRODUCTION: Preclinical and clinical studies suggest that mechanical ventilation contributes to the development of acute kidney injury (AKI), particularly in the setting of lung-injurious ventilator strategies. OBJECTIVE: To determine whether ventilator settings in critically ill patients without acute lung injury (ALI) at onset of mechanical ventilation affect the development of AKI. DESIGN, SETTING, AND PATIENTS: Secondary analysis of a randomized controlled trial (N = 150), comparing conventional tidal volume (V(T), 10 mL/kg) with low tidal volume (V(T), 6 mL/kg) mechanical ventilation in critically ill patients without ALI at randomization. During the first 5 days of mechanical ventilation, the RIFLE class was determined daily, whereas neutrophil gelatinase-associated lipocalin and cystatin C levels were measured in plasma collected on days 0, 2, and 4. RESULTS: Eighty-six patients had no AKI at inclusion, and 18 patients (21%) subsequently developed AKI, but without significant difference between ventilation strategies. (Cumulative hazard, 0.26 vs 0.23; P = .88.) The courses of neutrophil gelatinase-associated lipocalin and cystatin C plasma levels did not differ significantly between randomization groups. CONCLUSION: In the present study in critically patients without ALI at onset of mechanical ventilation, lower tidal volume ventilation did not reduce the development or worsening of AKI compared with conventional tidal volume ventilation.