The lung and the brain: a dangerous cross-talk

Therapeutic role of gut microbiota in lung injury-related cognitive impairment

Lung injury can lead to specific neurocognitive dysfunction, and the "triple-hit" phenomenon may be the key theoretical mechanism for the progressive impairment of lung injury-related cognitive impairment. The lung and brain can communicate biologically through immune regulation pathway, hypoxic pathway, neural circuit, mitochondrial dysfunction, and microbial influence, which is called the "lung-brain axis." The gut microbiota is a highly complex community of microorganisms that reside in the gut and communicate with the lung via the "gut-lung axis." The dysregulation of gut microbiota may lead to the migration of pathogenic bacteria to the lung, and directly or indirectly regulate the lung immune response through their metabolites, which may cause or aggravate lung injury. The gut microbiota and the brain interact through the "gut-brain axis." The gut microbiota can influence and regulate cognitive function and behavior of the brain through neural pathway mechanisms, immune regulation pathway and hypothalamic-pituitary-adrenal (HPA) axis regulation. Based on the gut microbiota regulation mechanism of the "gut-lung axis" and "gut-brain axis," combined with the mechanisms of cognitive impairment caused by lung injury, we proposed the "triple-hit" hypothesis. It states that the pathophysiological changes of lung injury trigger a series of events such as immune disorder, inflammatory responses, and microbiota changes, which activate the "lung-gut axis," thus forming a "triple-hit" that leads to the development or deterioration of cognitive impairment. This hypothesis provides a more comprehensive framework for studying and understanding brain dysfunction in the context of lung injury. This review proposes the existence of an interactive tandem network for information exchange among the gut, lung, and brain, referred to as the "gut-lung-brain axis." It further explores the potential mechanism of lung injury-related cognitive impairment caused by multiple interactions of gut microbiota in the "gut-lung-brain axis." We found that there are many numerous pathophysiological factors that influence the interaction within the "gut-lung-brain axis." The impact of gut microbiota on cognitive functions related to lung injury may be mediated through mechanisms such as the "triple-hit" hypothesis, direct translocation of microbes and their metabolites, hypoxic pathway, immune modulation, vagal nerve activity, and the HPA axis regulation, among others. As the research deepens, based on the "triple-hit" hypothesis of lung injury, it is further discovered that gut microbial therapy can significantly change the pathogenesis of the inflammatory process on the "gut-lung-brain axis." It can also relieve lung injury and therapeutically modulate brain function and behavior. This perspective provides a new idea for the follow-up treatment of lung injury-related cognitive impairment caused by dysregulation of gut microbiota.

Annexin A5 derived from lung alleviates brain damage after ischemic stroke

Ischemic stroke is a leading cause of disability and death worldwide. It is now accepted that brain interacts bidirectionally with other organs after brain diseases. However, factors that might mediate crosstalk between brain and other organs are still less reported. Here we reported that plasma level of Annexin A5, not Annexin A1 or A2, was upregulated in stroke patients when compared to controls. In normal mice, the highest level of Annexin A5 were detected in lung tissues compared with other major organs and lowest level in brain. Moreover, Annexin A5 was increased in brain and decreased in lung after stroke in mice when compared to sham group. Fluorescence in situ hybridization (FISH) assay indicated that Annexin A5 could penetrate the blood-brain barrier (BBB). Treatment with Annexin A5 recombinant protein reduced the infarct volumes and improved neurological function after stroke in mice, while administration of anti-Annexin A5 increased the infarct sizes and aggravated neurological function. In a proof-of-concept analysis, patients with both ischemic stroke and lung diseases had a lower plasma Annexin A5 level than those with only ischemic stroke. Furthermore, Annexin A5 level in bronchoalveolar lavage fluid (BALF) was lower in patients with severe chronic obstructive pulmonary disease (COPD) when compared with those at a less severe grade of COPD, and level of Annexin A5 was positively correlated with forced expiratory volume in 1 s/prediction (FEV1pred) and PaO2. Our results suggest that Annexin A5 could alleviate infarct area and improve general neurological performance post cerebral ischemia. Increased Annexin A5 may derive from lung tissue and permeate across BBB to provide a neuroprotective function. Therefore, Annexin A5 may potentially serve as a therapeutic candidate for defending against IS-induced brain injury.

Protective effects of paeonol against cognitive impairment in lung diseases

Pulmonary inflammation may lead to neuroinflammation resulting in neurological dysfunction, and it is associated with a variety of acute and chronic lung diseases. Paeonol is a herbal phenolic compound with anti-inflammatory and anti-oxidative properties. The aim of this study is to understand the beneficial effects of paeonol on cognitive impairment, pulmonary inflammation and its underlying mechanisms. Pulmonary inflammation-associated cognitive deficit was observed in TNFα-stimulated mice, and paeonol mitigated the cognitive impairment by reducing the expressions of interleukin (IL)-1β, IL-6, and NOD-like receptor family pyrin domain-containing 3 (NLRP3) in hippocampus. Moreover, elevated plasma miR-34c-5p in lung-inflamed mice was also reduced by paeonol. Pulmonary inflammation induced by intratracheal instillation of TNFα in mice resulted in immune cells infiltration in bronchoalveolar lavage fluid, pulmonary edema, and acute fibrosis, and these inflammatory responses were alleviated by paeonol orally. In MH-S alveolar macrophages, tumor necrosis factor (TNF) α- and phorbol myristate acetate (PMA)-induced inflammasome activation was ameliorated by paeonol. In addition, the expressions of antioxidants were elevated by paeonol, and reactive oxygen species production was reduced. In this study, paeonol demonstrates protective effects against cognitive deficits and pulmonary inflammation by exerting anti-inflammatory and anti-oxidative properties, suggesting a powerful benefit as a potential therapeutic agent.

Immune regulation of the gut-brain axis and lung-brain axis involved in ischemic stroke

Local ischemia often causes a series of inflammatory reactions when both brain immune cells and the peripheral immune response are activated. In the human body, the gut and lung are regarded as the key reactional targets that are initiated by brain ischemic attacks. Mucosal microorganisms play an important role in immune regulation and metabolism and affect blood-brain barrier permeability. In addition to the relationship between peripheral organs and central areas and the intestine and lung also interact among each other. Here, we review the molecular and cellular immune mechanisms involved in the pathways of inflammation across the gut-brain axis and lung-brain axis. We found that abnormal intestinal flora, the intestinal microenvironment, lung infection, chronic diseases, and mechanical ventilation can worsen the outcome of ischemic stroke. This review also introduces the influence of the brain on the gut and lungs after stroke, highlighting the bidirectional feedback effect among the gut, lungs, and brain.

Incidence and Outcomes of Acute Respiratory Distress Syndrome in Brain-Injured Patients Receiving Invasive Ventilation: A Secondary Analysis of the ENIO Study

Background: Acute respiratory distress syndrome (ARDS) is an important pulmonary complication in brain-injured patients receiving invasive mechanical ventilation (IMV). We aimed to evaluate the incidence and association between ARDS and clinical outcomes in patients with different forms of acute brain injury requiring IMV in the intensive care unit (ICU). Methods: This was a preplanned secondary analysis of a prospective, multicenter, international cohort study (NCT03400904). We included brain-injured patients receiving IMV for ≥ 24 h. ARDS was the main exposure of interest and was identified during index ICU admission using the Berlin definition. We examined the incidence and adjusted association of ARDS with ICU mortality, ICU length of stay, duration of IMV, and extubation failure. Outcomes were evaluated using mixed-effect logistic regression and cause-specific Cox proportional hazards models. Results: 1492 patients from 67 hospitals and 16 countries were included in the analysis, of whom 137 individuals developed ARDS (9.2% of overall cohort). Across countries, the median ARDS incidence was 5.1% (interquartile range [IQR] 0-10; range 0-27.3). ARDS was associated with increased ICU mortality (adjusted odds ratio (OR) 2.66; 95% confidence interval [CI], 1.29-5.48), longer ICU length of stay (adjusted hazard ratio [HR] 0.59; 95% CI, 0.48-0.73), and longer duration of IMV (adjusted HR 0.54; 95% CI, 0.44-0.67). The association between ARDS and extubation failure approached statistical significance (adjusted HR 1.48; 95% CI 0.99-2.21). Higher ARDS severity was associated with incrementally longer ICU length of stay and longer cumulative duration of IMV. Findings remained robust in a sensitivity analysis evaluating the magnitude of unmeasured confounding. Conclusions: In this cohort of acutely brain-injured patients, the incidence of ARDS was similar to that reported in other mixed cohorts of critically ill patients. Development of ARDS was associated with worse outcomes.

Future directions in ventilator-induced lung injury associated cognitive impairment: a new sight

Mechanical ventilation is a widely used short-term life support technique, but an accompanying adverse consequence can be pulmonary damage which is called ventilator-induced lung injury (VILI). Mechanical ventilation can potentially affect the central nervous system and lead to long-term cognitive impairment. In recent years, many studies revealed that VILI, as a common lung injury, may be involved in the central pathogenesis of cognitive impairment by inducing hypoxia, inflammation, and changes in neural pathways. In addition, VILI has received attention in affecting the treatment of cognitive impairment and provides new insights into individualized therapy. The combination of lung protective ventilation and drug therapy can overcome the inevitable problems of poor prognosis from a new perspective. In this review, we summarized VILI and non-VILI factors as risk factors for cognitive impairment and concluded the latest mechanisms. Moreover, we retrospectively explored the role of improving VILI in cognitive impairment treatment. This work contributes to a better understanding of the pathogenesis of VILI-induced cognitive impairment and may provide future direction for the treatment and prognosis of cognitive impairment.

Pressure-support compared with pressure-controlled ventilation mitigates lung and brain injury in experimental acute ischemic stroke in rats

BACKGROUND

We aimed to evaluate the pulmonary and cerebral effects of low-tidal volume ventilation in pressure-support (PSV) and pressure-controlled (PCV) modes at two PEEP levels in acute ischemic stroke (AIS).

METHODS

In this randomized experimental study, AIS was induced by thermocoagulation in 30 healthy male Wistar rats. After 24 h, AIS animals were randomly assigned to PSV or PCV with VT = 6 mL/kg and PEEP = 2 cmH2O (PSV-PEEP2 and PCV-PEEP2) or PEEP = 5 cmH2O (PSV-PEEP5 and PCV-PEEP5) for 2 h. Lung mechanics, arterial blood gases, and echocardiography were evaluated before and after the experiment. Lungs and brain tissue were removed for histologic and molecular biology analysis. The primary endpoint was diffuse alveolar damage (DAD) score; secondary endpoints included brain histology and brain and lung molecular biology markers.

RESULTS

In lungs, DAD was lower with PSV-PEEP5 than PCV-PEEP5 (p < 0.001); interleukin (IL)-1β was lower with PSV-PEEP2 than PCV-PEEP2 (p = 0.016) and PSV-PEEP5 than PCV-PEEP5 (p = 0.046); zonula occludens-1 (ZO-1) was lower in PCV-PEEP5 than PCV-PEEP2 (p = 0.042). In brain, necrosis, hemorrhage, neuropil edema, and CD45 + microglia were lower in PSV than PCV animals at PEEP = 2 cmH2O (p = 0.036, p = 0.025, p = 0.018, p = 0.011, respectively) and PEEP = 5 cmH2O (p = 0.003, p = 0.003, p = 0.007, p = 0.003, respectively); IL-1β was lower while ZO-1 was higher in PSV-PEEP2 than PCV-PEEP2 (p = 0.009, p = 0.007, respectively), suggesting blood-brain barrier integrity. Claudin-5 was higher in PSV-PEEP2 than PSV-PEEP5 (p = 0.036).

CONCLUSION

In experimental AIS, PSV compared with PCV reduced lung and brain injury. Lung ZO-1 reduced in PCV with PEEP = 2 versus PEEP = 5 cmH2O, while brain claudin-5 increased in PSV with PEEP = 2 versus PEEP = 5 cmH2O.

n-3 Polyunsaturated Fatty Acids Modulate LPS-Induced ARDS and the Lung-Brain Axis of Communication in Wild-Type versus Fat-1 Mice Genetically Modified for Leukotriene B4 Receptor 1 or Chemerin Receptor 23 Knockout

Specialized pro-resolving mediators (SPMs) and especially Resolvin E1 (RvE1) can actively terminate inflammation and promote healing during lung diseases such as acute respiratory distress syndrome (ARDS). Although ARDS primarily affects the lung, many ARDS patients also develop neurocognitive impairments. To investigate the connection between the lung and brain during ARDS and the therapeutic potential of SPMs and its derivatives, fat-1 mice were crossbred with RvE1 receptor knockout mice. ARDS was induced in these mice by intratracheal application of lipopolysaccharide (LPS, 10 µg). Mice were sacrificed at 0 h, 4 h, 24 h, 72 h, and 120 h post inflammation, and effects on the lung, liver, and brain were assessed by RT-PCR, multiplex, immunohistochemistry, Western blot, and LC-MS/MS. Protein and mRNA analyses of the lung, liver, and hypothalamus revealed LPS-induced lung inflammation increased inflammatory signaling in the hypothalamus despite low signaling in the periphery. Neutrophil recruitment in different brain structures was determined by immunohistochemical staining. Overall, we showed that immune cell trafficking to the brain contributed to immune-to-brain communication during ARDS rather than cytokines. Deficiency in RvE1 receptors and enhanced omega-3 polyunsaturated fatty acid levels (fat-1 mice) affect lung-brain interaction during ARDS by altering profiles of several inflammatory and lipid mediators and glial activity markers.

Factors associated with acute respiratory distress syndrome in brain-injured patients: A systematic review and meta-analysis

PURPOSE

Acute respiratory distress syndrome (ARDS) is common in patients with acute brain injury admitted to the ICU. We aimed to identify factors associated with ARDS in this population.

METHODS

We searched MEDLINE, Embase, Cochrane Central, Scopus, and Web of Science from inception to January 14, 2022. Three reviewers independently screened articles and selected English-language studies reporting risk factors for ARDS in brain-injured adult patients. Data were extracted on ARDS incidence, adjusted and unadjusted risk factors, and clinical outcomes. Risk of bias was reported using the Quality in Prognostic Studies tool. Certainty of evidence was assessed using GRADE.

RESULTS

We selected 23 studies involving 6,961,284 patients with acute brain injury. The pooled cumulative incidence of ARDS after brain injury was 17.0% (95%CI 10.7-25.8). In adjusted analysis, factors associated with ARDS included sepsis (odds ratio (OR) 4.38, 95%CI 2.37-8.10; high certainty), history of hypertension (OR 3.11, 95%CI 2.31-4.19; high certainty), pneumonia (OR 2.69, 95%CI 2.35-3.10; high certainty), acute kidney injury (OR 1.44, 95%CI 1.30-1.59; moderate certainty), admission hypoxemia (OR 1.67, 95%CI 1.29-2.17; moderate certainty), male sex (OR 1.30, 95%CI 1.06-1.58; moderate certainty), and chronic obstructive pulmonary disease (OR 1.27, 95%CI 1.13-1.44; moderate certainty). Development of ARDS was independently associated with increased odds of in-hospital mortality (OR 3.12, 95% CI 1.39-7.00).

CONCLUSIONS

Multiple risk factors are associated with ARDS in brain-injured patients. These findings could be used to develop prognostic models for ARDS or as prognostic enrichment strategies for patient enrolment in future clinical trials.

Diaphragmatic ultrasound can help evaluate pulmonary dysfunction in patients with stroke

Objective

Pulmonary dysfunction after stroke is increasingly gaining attention from clinical and rehabilitation specialists. However, owing to cognitive and motor dysfunction in patients with stroke, determining the pulmonary function of these patients remains challenging. The present study aimed to devise a simple method for an early evaluation of pulmonary dysfunction in patients with stroke.

Methods

Overall, 41 patients with stroke in the recovery period (stroke group) and 22 matched healthy controls (control group) were included in the study. We first collected data regarding baseline characteristics for all participants. Furthermore, the participants with stroke were examined using additional scales, such as the National Institutes of Health Stroke Scale (NIHSS), Fugl-Meyer assessment scale (FMA), and modified Barthel Index (MBI). Subsequently, we examined the participants with simple pulmonary function detection and diaphragm ultrasound (B-mode). Ultrasound indices calculated were as follows: the thickness of the diaphragm under the position of functional residual capacity (TdiFRC), the thickness of the diaphragm under the position of forced vital capacity (TdiFVC), thickness fraction, and diaphragmatic mobility. Finally, we compared and analyzed all data to identify group differences, the correlation between pulmonary function and diaphragmatic ultrasound indices, and the correlation between pulmonary function and assessment scale scores in patients with stroke, respectively.

Results

Compared with the control group, patients in the stroke group exhibited lower values for indices of pulmonary and diaphragmatic function (p < 0.001), except for TdiFRC (p > 0.05). The majority of the patients with stroke had restrictive ventilatory dysfunction, as indicated by a significantly higher incidence ratio (36 in 41 patients) than that in the control group (0 in 22 patients) (p < 0.001). Moreover, significant correlations were found between pulmonary function and diaphragmatic ultrasound indices (p < 0.05), with the strongest correlation between TdiFVC and pulmonary indices. In the stroke group, pulmonary function indices were negatively correlated with the NIHSS scores (p < 0.001) and positively correlated with the FMA scores (p < 0.001). No (p > 0.05) or weak (p < 0.05) correlation was found between pulmonary function indices and the MBI scores.

Conclusion

We found that patients with stroke had pulmonary dysfunction even in the recovery period. Diaphragmatic ultrasound can be used as a simple and effective tool for detecting pulmonary dysfunction in patients with stroke, with TdiFVC being the most effective index.

MILD TRAUMATIC BRAIN INJURY ATTENUATES PNEUMONIA-INDUCED LUNG INJURY BY MODULATIONS OF ALVEOLAR MACROPHAGE BACTERICIDAL ACTIVITY AND M1 POLARIZATION

ABSTRACT

Traumatic brain injury is one of the main causes of death and disability worldwide, and results in multisystem complications. However, the mechanism of mild traumatic brain injury (MTBI) on lung injury remains unclear. In this study, we used a murine model of MTBI and pneumonia ( Pseudomonas aeruginosa ;) to explore the relationship between these conditions and the underlying mechanism. Methods: Mice (n = 104) were divided into control, MTBI, pneumonia, and MTBI + pneumonia groups. MTBI was induced by the weight-drop method. Pneumonia was induced by intratracheal injection with P. aeruginosa Xen5 strain. Animals were killed 24 h after bacterial challenging. Histological, cellular, and molecular indices of brain and lung injury were assessed using various methods. Results: Mice in both the MTBI and pneumonia groups had more Fluoro-Jade C-positive neurons than did the controls ( P < 0.01), but mice in the MTBI + pneumonia group had fewer Fluoro-Jade C-positive cells than did the pneumonia group ( P < 0.01). The MTBI + pneumonia mice showed decreased bacterial load ( P < 0.05), reduced lung injury score and pulmonary permeability ( P < 0.01), less inflammatory cells, and lower levels of proinflammatory cytokines (TNF-α and IL-1β; P < 0.01) when compared with the pneumonia group. Molecular analysis indicated lower levels of phosphorylated nuclear factor-κB in the lung of MTBI + pneumonia mice compared with the pneumonia group ( P < 0.01). Furthermore, alveolar macrophages from MTBI mice exhibited enhanced bactericidal capacity compared with those from controls ( P < 0.01). Moreover, MTBI + pneumonia mice exhibited less CD86-positive M1 macrophages compared with the pneumonia group ( P < 0.01). Conclusions: MTBI attenuates pneumonia-induced acute lung injury through the modulation of alveolar macrophage bactericidal capacity and M1 polarization in bacterial pneumonia model.

Management of the Potential Lung Donor

The use of donor management protocols has significantly improved recovery rates; however, the inherent instability of lungs after death results in low utilization rates of potential donor lungs. Donor lungs are susceptible to direct trauma, aspiration, neurogenic edema, ventilator-associated barotrauma, and ventilator-associated pneumonia. After irreversible brain injury and determination of futility of care, the goal of medical management of the donor shifts to maintaining hemodynamic stability and maximizing the likelihood of successful organ recovery.

Monocyte Signature Associated with Herpes Simplex Virus Reactivation and Neurological Recovery After Brain Injury

RATIONALE

Brain injury induces systemic immunosuppression increasing the risk of viral reactivations and altering neurological recovery.

OBJECTIVES

To determine if systemic immune alterations and lung replication of Herpesviridae are associated and can help predict outcomes after brain injury.

METHODS

We collected peripheral blood mononuclear cells in severely brain-injured patients requiring invasive mechanical ventilation. We systematically searched for respiratory Herpes Simplex Virus (HSV) replications in tracheal aspirates. We also performed CHiP-sequencing, RNA-sequencing and in vitro functional assays of monocytes and CD4 T cells collected on day 1 to characterize immune response to severe acute brain injury. The primary outcome was the Glasgow outcome scale Extended (GOS-E) at 6 months.

MEASUREMENTS AND MAIN RESULTS

In 344 severe brain-injured patients, lung HSV reactivations were observed in 39% of patients seropositive for HSV, and independently associated with poor neurological recovery at six months (hazard ratio 1.90, 95%CI 1.08-3.57). WGNA analyses of the transcriptomic response of monocytes to brain injury defined a module of 721 genes, including PD-L1 and CD80, enriched for the binding DNA motif of the transcriptional factor Zeb2, and whose ontogenic analyses revealed decreased interferon--mediated and anti-viral response signaling pathways. This monocyte signature was preserved in a validation cohort and predicted the neurological outcome at 6 months with good accuracy (AUC 0.786, 95%CI 0.593-0.978).

CONCLUSIONS

A specific monocyte signature is associated with HSV reactivation and predicts recovery after brain injury. The alterations of the immune control of Herpesviridae replication are understudied and represent a novel therapeutic target.

Lung-brain 'cross-talk': systemic propagation of cytokines in the ARDS via the bloodstream using a blood transfusion model does not influence cerebral inflammatory response in pigs

Background

Interorgan cross-talk describes the phenomenon in which a primarily injured organ causes secondary damage to a distant organ. This cross-talk is well known between the lung and brain. One theory suggests that the release and systemic distribution of cytokines via the bloodstream from the primarily affected organ sets in motion proinflammatory cascades in distant organs. In this study, we analysed the role of the systemic distribution of cytokines via the bloodstream in a porcine ARDS model for organ cross-talk and possible inflammatory changes in the brain.

Methods

After approval of the State and Institutional Animal Care Committee, acute respiratory distress syndrome (ARDS) induction with oleic acid injection was performed in seven animals. Eight hours after ARDS induction, blood (35-40 ml kg^-1) was taken from these seven 'ARDS donor' pigs. The collected 'ARDS donor' blood was transfused into seven healthy 'ARDS-recipient' pigs. Three animals served as a control group, and blood from these animals was transfused into three healthy pigs after an appropriate ventilation period. All animals were monitored for 8 h using advanced cardiorespiratory monitoring. Postmortem assessment included cerebral (hippocampal and cortex) mediators of early inflammatory response (IL-6, TNF-alpha, iNOS, sLCN-2), wet-to-dry ratio and lung histology. TNF-alpha serum concentration was measured in all groups.

Results

ARDS was successfully induced in the 'ARDS donor' group, and serum TNF-alpha levels were elevated compared with the 'ARDS-recipient' group. In the 'ARDS-recipient' group, neither significant ARDS alterations nor upregulation of inflammatory mediators in the brain tissue were detected after high-volume random allogenic 'ARDS-blood' transfusion. The role of the systemic distribution of inflammatory cytokines from one affected organ to another could not be confirmed in this study.

Comparative effects of dexmedetomidine and propofol on brain and lung damage in experimental acute ischemic stroke

Acute ischemic stroke is associated with pulmonary complications, and often dexmedetomidine and propofol are used to decrease cerebral metabolic rate. However, it is unknown the immunomodulatory actions of dexmedetomidine and propofol on brain and lungs during acute ischemic stroke. The effects of dexmedetomidine and propofol were compared on perilesional brain tissue and lung damage after acute ischemic stroke in rats. Further, the mean amount of both sedatives was directly evaluated on alveolar macrophages and lung endothelial cells primarily extracted 24-h after acute ischemic stroke. In twenty-five Wistar rats, ischemic stroke was induced and after 24-h treated with sodium thiopental (STROKE), dexmedetomidine and propofol. Dexmedetomidine, compared to STROKE, reduced diffuse alveolar damage score [median(interquartile range); 12(7.8–15.3) vs. 19.5(18–24), p = 0.007)], bronchoconstriction index [2.28(2.08–2.36) vs. 2.64(2.53–2.77), p = 0.006], and TNF-α expression (p = 0.0003), while propofol increased VCAM-1 expression compared to STROKE (p = 0.0004). In perilesional brain tissue, dexmedetomidine, compared to STROKE, decreased TNF-α (p = 0.010), while propofol increased VCAM-1 compared to STROKE (p = 0.024). In alveolar macrophages and endothelial cells, dexmedetomidine decreased IL-6 and IL-1β compared to STROKE (p = 0.002, and p = 0.040, respectively), and reduced IL-1β compared to propofol (p = 0.014). Dexmedetomidine, but not propofol, induced brain and lung protection in experimental acute ischemic stroke.

Brain-lung interactions and mechanical ventilation in patients with isolated brain injury

During the last decade, experimental and clinical studies have demonstrated that isolated acute brain injury (ABI) may cause severe dysfunction of peripheral extracranial organs and systems. Of all potential target organs and systems, the lung appears to be the most vulnerable to damage after brain injury (BI). The pathophysiology of these brain–lung interactions are complex and involve neurogenic pulmonary oedema, inflammation, neurodegeneration, neurotransmitters, immune suppression and dysfunction of the autonomic system. The systemic effects of inflammatory mediators in patients with BI create a systemic inflammatory environment that makes extracranial organs vulnerable to secondary procedures that enhance inflammation, such as mechanical ventilation (MV), surgery and infections. Indeed, previous studies have shown that in the presence of a systemic inflammatory environment, specific neurointensive care interventions—such as MV—may significantly contribute to the development of lung injury, regardless of the underlying mechanisms. Although current knowledge supports protective ventilation in patients with BI, it must be born in mind that ABI-related lung injury has distinct mechanisms that involve complex interactions between the brain and lungs. In this context, the role of extracerebral pathophysiology, especially in the lungs, has often been overlooked, as most physicians focus on intracranial injury and cerebral dysfunction. The present review aims to fill this gap by describing the pathophysiology of complications due to lung injuries in patients with a single ABI, and discusses the possible impact of MV in neurocritical care patients with normal lungs.

Ischaemic stroke-induced distal organ damage: pathophysiology and new therapeutic strategies

Acute ischaemic stroke is associated with a high risk of non-neurological complications, which include respiratory failure, cardiovascular dysfunction, kidney and liver injury, and altered immune and endocrine function. The aim of this manuscript is to provide an overview of the main forms of stroke-induced distal organ damage, providing new pathophysiological insights and recommendations for clinical management.Non-neurological complications of stroke can affect outcomes, with potential for serious short-term and long-term consequences. Many of these complications can be prevented; when prevention is not feasible, early detection and proper management can still be effective in mitigating their adverse impact. The general care of stroke survivors entails not only treatment in the acute setting but also prevention of secondary complications that might hinder functional recovery. Acute ischaemic stroke triggers a cascade of events-including local and systemic activation of the immune system-which results in a number of systemic consequences and, ultimately, may cause organ failure. Understanding the pathophysiology and clinical relevance of non-neurological complications is a crucial component in the proper treatment of patients with acute stroke.Little evidence-based data is available to guide management of these complications. There is a clear need for improved surveillance and specific interventions for the prevention, early diagnosis, and proper management of non-neurological complications during the acute phase of ischaemic stroke, which should reduce morbidity and mortality.

Severe acute respiratory syndrome coronavirus 2 may be an underappreciated pathogen of the central nervous system

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a highly contagious respiratory disease referred to as COVID-19. However, emerging evidence indicates that a small but growing number of COVID-19 patients also manifest neurological symptoms, suggesting that SARS-CoV-2 may infect the nervous system under some circumstances. SARS-CoV-2 primarily enters the body through the epithelial lining of the respiratory and gastrointestinal tracts, but under certain conditions this pleiotropic virus may also infect peripheral nerves and gain entry into the central nervous system (CNS). The brain is shielded by various anatomical and physiological barriers, most notably the blood-brain barrier (BBB) which functions to prevent harmful substances, including pathogens and pro-inflammatory mediators, from entering the brain. The BBB is composed of highly specialized endothelial cells, pericytes, mast cells and astrocytes that form the neurovascular unit, which regulates BBB permeability and maintains the integrity of the CNS. In this review, potential routes of viral entry and the possible mechanisms utilized by SARS-CoV-2 to penetrate the CNS, either by disrupting the BBB or infecting the peripheral nerves and using the neuronal network to initiate neuroinflammation, are briefly discussed. Furthermore, the long-term effects of SARS-CoV-2 infection on the brain and in the progression of neurodegenerative diseases known to be associated with other human coronaviruses are considered. Although the mechanisms of SARS-CoV-2 entry into the CNS and neurovirulence are currently unknown, the potential pathways described here might pave the way for future research in this area and enable the development of better therapeutic strategies.

A Canadian perspective on severe acute respiratory syndrome coronavirus 2 infection and treatment: how prevalent underlying inflammatory disease contributes to pathogenesis

The coronavirus disease 2019 (COVID-19), a serious respiratory illness caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has emerged as a global pandemic. Canada reported its first case of COVID-19 on the 25th January 2020. By March 2020, the virus had spread within Canadian communities reaching the most frail and vulnerable elderly population in long-term care facilities. The majority of cases were reported in the provinces of Quebec, Ontario, Alberta, and British Columbia, and the highest mortality was seen among individuals aged 65 years or older. Canada has the highest prevalence and incidence rates of several chronic inflammatory diseases, such as multiple sclerosis, inflammatory bowel disease, and Parkinson's disease. Many elderly Canadians also live with comorbid medical illnesses, such as hypertension, diabetes, cardiovascular disease, and chronic lung disease, and are more likely to suffer from severe COVID-19 with a poor prognosis. It is becoming increasingly evident that underlying inflammatory disease contributes to the pathogenesis of SARS-CoV-2. Here, we review the mechanisms behind SARS-CoV-2 infection, and the host inflammatory responses that lead to resolution or progression to severe COVID-19 disease. Furthermore, we discuss the landscape of COVID-19 therapeutics that are currently in development in Canada.

Neurological consequences of COVID-19: what have we learned and where do we go from here?

The coronavirus disease-19 (COVID-19) pandemic is an unprecedented worldwide health crisis. COVID-19 is caused by SARS-CoV-2, a highly infectious pathogen that is genetically similar to SARS-CoV. Similar to other recent coronavirus outbreaks, including SARS and MERS, SARS-CoV-2 infected patients typically present with fever, dry cough, fatigue, and lower respiratory system dysfunction, including high rates of pneumonia and acute respiratory distress syndrome (ARDS); however, a rapidly accumulating set of clinical studies revealed atypical symptoms of COVID-19 that involve neurological signs, including headaches, anosmia, nausea, dysgeusia, damage to respiratory centers, and cerebral infarction. These unexpected findings may provide important clues regarding the pathological sequela of SARS-CoV-2 infection. Moreover, no efficacious therapies or vaccines are currently available, complicating the clinical management of COVID-19 patients and emphasizing the public health need for controlled, hypothesis-driven experimental studies to provide a framework for therapeutic development. In this mini-review, we summarize the current body of literature regarding the central nervous system (CNS) effects of SARS-CoV-2 and discuss several potential targets for therapeutic development to reduce neurological consequences in COVID-19 patients.

Mechanical ventilation in neurocritical care setting: A clinical approach

Neuropatients often require invasive mechanical ventilation (MV). Ideal ventilator settings and respiratory targets in neuro patients are unclear. Current knowledge suggests maintaining protective tidal volumes of 6-8 ml/kg of predicted body weight in neuropatients. This approach may reduce the rate of pulmonary complications, although it cannot be easily applied in a neuro setting due to the need for special care to minimize the risk of secondary brain damage. Additionally, the weaning process from MV is particularly challenging in these patients who cannot control the brain respiratory patterns and protect airways from aspiration. Indeed, extubation failure in neuropatients is very high, while tracheostomy is needed in one-third of the patients. The aim of this manuscript is to review and describe the current management of invasive MV, weaning, and tracheostomy for the main four subpopulations of neuro patients: traumatic brain injury, acute ischemic stroke, subarachnoid hemorrhage, and intracerebral hemorrhage.

Neurological Manifestations of Severe SARS-CoV-2 Infection: Potential Mechanisms and Implications of Individualized Mechanical Ventilation Settings

In December 2019, an outbreak of illness caused by a novel coronavirus (2019-nCoV, subsequently renamed SARS-CoV-2) was reported in Wuhan, China. Coronavirus disease 2019 (COVID-19) quickly spread worldwide to become a pandemic. Typical manifestations of COVID-19 include fever, dry cough, fatigue, and respiratory distress. In addition, both the central and peripheral nervous system can be affected by SARS-CoV-2 infection. These neurological changes may be caused by viral neurotropism, by a hyperinflammatory and hypercoagulative state, or even by mechanical ventilation-associated impairment. Hypoxia, endothelial cell damage, and the different impacts of different ventilatory strategies may all lead to increased stress and strain, potentially exacerbating the inflammatory response and leading to a complex interaction between the lungs and the brain. To date, no studies have taken into consideration the possible secondary effect of mechanical ventilation on brain recovery and outcomes. The aim of our review is to provide an updated overview of the potential pathogenic mechanisms of neurological manifestations in COVID-19, discuss the physiological issues related to brain-lung interactions, and propose strategies for optimization of respiratory support in critically ill patients with SARS-CoV-2 pneumonia.

Mechanical ventilation in patients with acute ischaemic stroke: from pathophysiology to clinical practice

Most patients with ischaemic stroke are managed on the ward or in specialty stroke units, but a significant number requires higher-acuity care and, consequently, admission to the intensive care unit. Mechanical ventilation is frequently performed in these patients due to swallowing dysfunction and airway or respiratory system compromise. Experimental studies have focused on stroke-induced immunosuppression and brain-lung crosstalk, leading to increased pulmonary damage and inflammation, as well as reduced alveolar macrophage phagocytic capability, which may increase the risk of infection. Pulmonary complications, such as respiratory failure, pneumonia, pleural effusions, acute respiratory distress syndrome, lung oedema, and pulmonary embolism from venous thromboembolism, are common and found to be among the major causes of death in this group of patients. Furthermore, over the past two decades, tracheostomy use has increased among stroke patients, who can have unique indications for this procedure—depending on the location and type of stroke—when compared to the general population. However, the optimal mechanical ventilator strategy remains unclear in this population. Although a high tidal volume (V_T) strategy has been used for many years, the latest evidence suggests that a protective ventilatory strategy (V_T = 6–8 mL/kg predicted body weight, positive end-expiratory pressure and rescue recruitment manoeuvres) may also have a role in brain-damaged patients, including those with stroke. The aim of this narrative review is to explore the pathophysiology of brain-lung interactions after acute ischaemic stroke and the management of mechanical ventilation in these patients.

Infusion of HIV-1 Nef-expressing astrocytes into the rat hippocampus induces enteropathy and interstitial pneumonitis and increases blood-brain-barrier permeability

Even though HIV-1 replication can be suppressed by combination antiretroviral therapy (cART) inflammatory processes still occur, contributing to comorbidities. Comorbidities are attributed to variety of factors, including HIV-1 mediated inflammation. Several HIV-1 proteins mediate central nervous system (CNS) inflammation, including Nef. Nef is an early HIV-1 protein, toxic to neurons and glia and is sufficient to cause learning impairment similar to some deficits observed in HIV-1 associated neurocognitive disorders. To determine whether hippocampal Nef expression by astrocytes contributes to comorbidities, specifically peripheral inflammation, we infused Sprague Dawley rats with GFP- (control) or Nef-transfected astrocytes into the right hippocampus. Brain, lung, and ileum were collected postmortem for the measurement of inflammatory markers. Increased blood-brain-barrier permeability and serum IL-1β levels were detected in the Nef-treated rats. The lungs of Nef-treated rats demonstrated leukocyte infiltration, macrophage upregulation, and enhanced vascular permeability. Ileal tissue showed reactive follicular lymphoid hyperplasia, increased permeability and macrophage infiltration. The intracerebroventricular application of IL-1 receptor antagonist reduced infiltration of immune cells into ileum and lung, indicating the important role of IL-1β in mediating the spread of inflammation from the brain to other tissues. This suggests that localized expression of a single viral protein, HIV-1 Nef, can contribute to a broader inflammatory response by upregulation of IL-1β. Further, these results suggest that Nef contributes to the chronic inflammation seen in HIV patients, even in those whose viremia is controlled by cART.

Random allogeneic blood transfusion in pigs: characterisation of a novel experimental model

Background

Organ cross-talk describes interactions between a primary affected organ and a secondarily injured remote organ, particularly in lung-brain interactions. A common theory is the systemic distribution of inflammatory mediators that are released by the affected organ and transferred through the bloodstream. The present study characterises the baseline immunogenic effects of a novel experimental model of random allogeneic blood transfusion in pigs designed to analyse the role of the bloodstream in organ cross-talk.

Methods

After approval of the State and Institutional Animal Care Committee, 20 anesthetized pig were randomized in a donor and an acceptor (each n = 8): the acceptor animals each received high-volume whole blood transfusion from the donor (35–40 ml kg⁻¹). Four animals received balanced electrolyte solution instead of blood transfusion (control group; n = 4). Afterwards the animals underwent extended cardiorespiratory monitoring for eight hours. Post mortem assessment included pulmonary, cerebral and systemic mediators of early inflammatory response (IL-6, TNF-alpha, iNOS), wet to dry ratio, and lung histology.

Results

No adverse events or incompatibilities occurred during the blood transfusion procedures. Systemic cytokine levels and pulmonary function were unaffected. Lung histopathology scoring did not display relevant intergroup differences. Neither within the lung nor within the brain an up-regulation of inflammatory mediators was detected. High volume random allogeneic blood transfusion in pigs neither impaired pulmonary integrity nor induced systemic, lung, or brain inflammatory response.

Conclusion

This approach can represent a novel experimental model to characterize the blood-bound transmission in remote organ injury.

Effect of PEEP and I:E ratio on cerebral oxygenation in ARDS: an experimental study in anesthetized rabbit

Background

Although PEEP and inversed I:E ratio have been shown to improve gas exchange in ARDS, both can adversely affect systemic hemodynamics and cerebral perfusion. The goal of this study was to assess how changes in PEEP and I:E ratio affect systemic and cerebral oxygenation and perfusion in normal and injured lung.

Methods

Eight anesthetized Chinchilla-Bastard rabbits were ventilated at baseline with pressure-regulated volume control mode, V_T = 6 ml/kg, PEEP = 6 cmH₂O, FIO₂ = 0.4; respiratory rate set for ETCO₂ = 5.5%, and I:E = 1:2, 1:1 or 2:1 in random order. Ultrasonic carotid artery flow (CF), arterial (PaO₂), jugular venous blood gases and near infrared spectroscopic cerebral oxygenation (∆HBO₂) were recorded for each experimental condition. After induced lung injury, the animals were ventilated with PEEP = 9 followed by 6 cmH₂O.

Results

At baseline, inverse-ratio ventilation (IRV) significantly reduced cerebral oxygenation (∆O₂HB; − 27 at 1:2; − 15 at 1:1 vs. 0.27 μmol/L at 2:1; p < 0.05), due to a significant reduction in mean arterial pressure and CF without modifying gas exchange. In injured lung, IRV improved gas exchange but decreased cerebral perfusion without affecting brain oxygenation. The higher PEEP level, however, improved PaO₂ (67.5 ± 19.3 vs. 42.2 ± 8.4, p < 0.05), resulting in an improved ∆HBO₂ (− 13.8 ± 14.7 vs. –43.5 ± 21.3, p < 0.05), despite a drop in CF.

Conclusions

Our data suggest that unlike moderate PEEP, IRV is not effective in improving brain oxygenation in ARDS. In normal lung, IRV had a deleterious effect on brain oxygenation, which is relevant in anesthetized patients.

Electronic supplementary material

The online version of this article (10.1186/s12871-019-0782-y) contains supplementary material, which is available to authorized users.

Two hit induced acute lung injury impairs cognitive function in mice: A potential model to study cross talk between lung and brain

Acute lung injury (ALI), a pulmonary inflammatory disorder, is associated with high morbidity and mortality rates. Interestingly, ALI survivors have been reported for some neurocognitive deterioration at/after discharge. However, the molecular factors behind such extra pulmonary manifestation are not clearly known. The present work was designed to investigate lung-brain cross talk in experimental mice for deciphering primary molecular factors that may be involved in ALI-mediated cognitive impairment. ALI was induced in Balb/c mice by intra-tracheal administration of either 0.1 N HCl (2 ml/kg) or LPS (1 mg/kg) as single hits or both agents were administered successively to mimic the 'two hit' model. Interestingly two hit-mediated ALI resulted in exaggerated inflammatory response as reflected by increased pulmonary neutrophils and inflammatory factors (TNF-α/IL-1β/IL-6). Additionally, two hits resulted in delayed resolution of lung inflammation and was coupled with persistent decline in memory, as assessed by Morris water maze test. Further, two hits elevate serum levels of TNF-α/IL-1β which was associated with compromised blood brain barrier (BBB), as evident by decreased expression of occludin/claudin-5 and consequent Evans-blue extravasation in hippocampus 1 week post injury. Finally, dexamethasone protects against the two hit mediated cognitive impairment by lowering the pro-inflammatory factors (TNF-α/IL-1β) both in lungs and blood. Overall, we report for the first time that 'two hit' mediated ALI cause persistent cognitive impairment in mice partly via up-regulating systemic expression of TNF-α/IL-1β that may disrupt BBB and hence the model may be a useful tool to examine the lung-brain cross-talk at the molecular level for exploring newer therapeutics.

Mechanisms involved in brain dysfunction in mechanically ventilated critically ill patients: implications and therapeutics

Critical illness may lead to significant long-term neurological morbidity and patients frequently develop neuropsychological disturbances including acute delirium or memory impairment after intensive care unit (ICU) discharge. Mechanical ventilation (MV) is a risk factor to the development of adverse neurocognitive outcomes. Patients undergoing MV for long periods present neurologic impairment with memory and cognitive alteration. Delirium is considered an acute form of brain dysfunction and its prevalence rises in mechanically ventilated patients. Delirium duration is an independent predictor of mortality, ventilation time, ICU length of stay and short- and long-term cognitive impairment in the ICU survivors. Although, neurocognitive sequelae tend to improve after hospital discharge, residual deficits persist even 6 years after ICU stay. ICU-related neurocognitive impairments occurred in many cognitive domains and are particularly pronounced with regard to memory, executive functions, attentional functions, and processing speed. These sequelae have an important impact on patients' lives and ICU survivors often require institutionalization and hospitalization. Experimental studies have served to explore the possible mechanisms or pathways involved in this lung to brain interaction. This communication can be mediated via a complex web of signaling events involving neural, inflammatory, immunologic and neuroendocrine pathways. MV can affect respiratory networks and the application of protective ventilation strategies is mandatory in order to prevent adverse effects. Therefore, strategies focused to minimize lung stretch may improve outcomes, avoiding failure of distal organ, including the brain. Long-term neurocognitive impairments experienced by critically ill survivors may be mitigated by early interventions, combining cognitive and physical therapies. Inpatient rehabilitation interventions in ICU promise to improve outcomes in critically ill patients. The cross-talk between lung and brain, involving specific pathways during critical illness deserves further efforts to evaluate, prevent and improve cognitive alterations after ICU admission, and highlights the crucial importance of tailoring MV to prevent adverse outcomes.

Erythropoietin mediates brain-vascular-kidney crosstalk and may be a treatment target for pulmonary and resistant essential hypertension

Organ crosstalk pathways represent the next frontier for target-mining in molecular medicine for existing syndromes. Pulmonary hypertension and resistant essential hypertension are syndromes that have been proven elusive in etiology, and frequently refractory to first-line management. Underlying crosstalk mechanisms, not yet considered in these treatments, may hinder outcomes or unlock novel treatments. This review focuses systematically on erythropoietin, a synthesizable molecule, as a mediator of brain-kidney crosstalk. Insights gained from this review will be applied to cardiovascular diseases in a clinician-directed fashion.

Toll-like receptor 4 knockout ameliorates neuroinflammation due to lung-brain interaction in mechanically ventilated mice

Toll-like receptor 4 (TLR4) is a crucial receptor in the innate immune system, and increasing evidence supports its role in inflammation, stress, and tissue injury, including injury to the lung and brain. We aimed to investigate the effects of TLR4 on neuroinflammation due to the lung-brain interaction in mechanically ventilated mice. Male wild-type (WT) C57BL/6 and TLR4 knockout (TLR4 KO) mice were divided into three groups: (1) control group (C): spontaneous breathing; (2) anesthesia group (A): spontaneous breathing under anesthesia; and (3) mechanical ventilation group (MV): 6h of MV under anesthesia. The behavioral responses of mice were tested with fear conditioning tests. The histological changes in the lung and brain were assessed using hematoxylin-eosin (HE) staining. The level of TLR4 mRNA in tissue was measured using reverse transcription-polymerase chain reaction (RT-PCR). The levels of inflammatory cytokines were measured with an enzyme-linked immunosorbent assay (ELISA). Microgliosis, astrocytosis, and the TLR4 immunoreactivity in the hippocampus were measured by double immunofluorescence. MV mice exhibited impaired cognition, and this impairment was less severe in TLR4 KO mice than in WT mice. In WT mice, MV increased TLR4 mRNA expression in the lung and brain. MV induced mild lung injury, which was prevented in TLR4 KO mice. MV mice exhibited increased levels of inflammatory cytokines, increased microglia and astrocyte activation. Microgliosis was alleviated in TLR4 KO mice. MV mice exhibited increased TLR4 immunoreactivity, which was expressed in microglia and astrocytes. These results demonstrate that TLR4 is involved in neuroinflammation due to the lung-brain interaction and that TLR4 KO ameliorates neuroinflammation due to lung-brain interaction after prolonged MV. In addition, Administration of a TLR4 antagonist (100μg/mice) to WT mice also significantly attenuated neuroinflammation of lung-brain interaction due to prolonged MV. TLR4 antagonism may be a new and novel approach for the treatment and management of neuroinflammation in long-term mechanically ventilated patients.

CD11d integrin blockade reduces the systemic inflammatory response syndrome after traumatic brain injury in rats

Traumatic CNS injury triggers a systemic inflammatory response syndrome (SIRS), in which circulating inflammatory cells invade body organs causing local inflammation and tissue damage. We have shown that the SIRS caused by spinal cord injury is greatly reduced by acute intravenous treatment with an antibody against the CD11d subunit of the CD11d/CD18 integrin expressed by neutrophils and monocyte/macrophages, a treatment that reduces their efflux from the circulation. Traumatic brain injury (TBI) is a frequently occurring injury after motor vehicle accidents, sporting and military injuries, and falls. Our studies have shown that the anti-CD11d treatment diminishes brain inflammation and oxidative injury after moderate or mild TBI, improving neurological outcomes. Accordingly, we examined the impact of this treatment on the SIRS triggered by TBI. The anti-CD11d treatment was given at 2h after a single moderate (2.5-3.0 atm) or 2 and 24h after each of three consecutive mild (1.0-1.5 atm) fluid percussion TBIs. Sham-injured, saline-treated rats served as controls. At 24h, 72 h, and 4 or 8 weeks after the single TBI and after the third of three TBIs, lungs of rats were examined histochemically, immunocytochemically and biochemically for downstream effects of SIRS including inflammation, tissue damage and expression of oxidative enzymes. Lung sections revealed that both the single moderate and repeated mild TBI caused alveolar disruption, thickening of inter-alveolar tissue, hemorrhage into the parenchyma and increased density of intra-and peri-alveolar macrophages. The anti-CD11d treatment decreased the intrapulmonary influx of neutrophils and the density of activated macrophages and the activity of myeloperoxidase after these TBIs. Moreover, Western blotting studies showed that the treatment decreased lung protein levels of oxidative enzymes gp91(phox), inducible nitric oxide synthase and cyclooxygenase-2, as well as the apoptotic pathway enzyme caspase-3 and levels of 4-hydroxynonenal-bound proteins (an indicator of lipid peroxidation). Decreased expression of the cytoprotective transcription factor Nrf2 reflected decreased lung oxidative stress. Anti-CD11d treatment also diminished the lung concentration of free radicals and tissue aldehydes. In conclusion, the substantial lung component of the SIRS after single or repeated TBIs is significantly decreased by a simple, minimally invasive and short-lasting anti-inflammatory treatment.

[Ventilation as a trigger for organ dysfunction and sepsis]

Both in the intensive care setting and during surgery, mechanical ventilation plays an important role in the treatment of critically ill patients with lung injury, but also in lung healthy patients. Mechanical ventilation is noncurative and is accompanied by various severe side effects. It is hypothesized that multiorgan failure can be induced by mechanical ventilation. Furthermore, there is evidence to suggest cross-talk between lungs and other organs. In particular, the activation of specific cells and cell programs in peripheral organs is an important step on the way to multiorgan failure. In addition to bidirectional connection between the lung and brain, nonprotective ventilation leads to cell apoptosis in the kidney and intestine and leads to an increase of biomarkers for organ dysfunction. It is believed that both inflammation mediators and pro-apoptotic factors are responsible for organ dysfunction.

Prolonged mechanical ventilation-induced neuroinflammation affects postoperative memory dysfunction in surgical mice

INTRODUCTION

Patients undergoing surgery frequently develop neuropsychological disturbances, including cognitive decline or memory impairment, and routine clinical procedures such as mechanical ventilation (MV) may affect acute-phase brain outcome. We aimed to investigate the effect of the prolonged MV on postoperative memory dysfunction in surgical mice.

METHODS

Male C57BL/6 mice were randomly divided into the following three groups: (1) The control group (group C) comprised anesthetized, unventilated animals; (2) the surgery group (subgroups S1h, S3h and S6h) was unventilated animals that underwent surgery under general anesthesia; and (3) the MV group (subgroups MV1h, MV3h and MV6h) was made up of animals under MV for 1 hour, 3 hours or 6 hours after surgery. Separate cohorts of animals were tested for memory function with fear conditioning tests or were killed at 6 hours, 1 day or 3 days postsurgery or post-MV to examine levels systemic and hippocampal interleukin (IL)-1β, IL-6 and tumor necrosis factor α (TNFα), and assessed synaptic structure and microglial activation. Nuclear factor κB (NF-κB) p65, cytochrome c, cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase (PARP) activation were analyzed by Western blotting.

RESULTS

The MV6h group showed increased CD11b-immunopositive cells, synapse degeneration, cytochrome c release, cleaved caspase-3 and cleaved PARP-1 activation after surgery, as well as a decrease in freezing time after surgery. At 6 hours and 1 day post-MV, MV6h increased NF-κB activation and levels of systemic and hippocampal IL-1β, IL-6 and TNFα after surgery.

CONCLUSIONS

Prolonged MV after surgery further aggravates cognitive decline that may stem from upregulation of hippocampal IL-1β, IL-6 and TNFα, partially via activation of gliocytes in the surgical mouse hippocampus.

The role of neuromuscular blockade in patients with traumatic brain injury: a systematic review

Management of Traumatic Brain Injury (TBI) focuses on controlling intracranial pressure (ICP), while other treatments, such as the use of neuromuscular blocking agents (NMBAs), need scientific evidence. We conducted a systematic review to investigate the usefulness of NMBAs in the context of TBI and/or increased ICP. We searched MEDLINE and EMBASE databases up to January 31st 2014, including both clinical and experimental findings. We found a total of 34 articles, of which 22 were prospective clinical trials. No systematic review/meta-analyses were found. Seven studies evaluated NMBA boluses in preventing stimulation-related ICP surges: paralysis was effective during tracheal suctioning and physiotherapy but not during bronchoscopy. Fourteen small studies (8 to 25 patients) assessed the effect of NMBA boluses on ICP. Two studies showed an ICP increase by succinylcholine and one found a decrease in ICP after atracurium. No ICP changes were observed in the other studies. One prospective study confirmed that discontinuing paralysis increases energy expenditure. Two retrospective studies investigated mortality/morbidity: one found that early paralysis (continued for >12 h) was not beneficial and potentially associated with extra-cranial complications, while the second demonstrated a correlation between continuous infusion of NMBA and time spent with ICP > 20 mmHg. Eight animal studies were also retrieved. In most studies, NMBA bolus was beneficial in controlling ICP, especially when performing stimulating procedures. However, retrospective evidence found potential harm by continuous NMBA infusion. In the context of TBI patients, we discuss the potentially positive effects of paralysis with its negative ones. Well-conducted randomized controlled trials and/or large pharmaco-epidemiologic studies are warranted.

High-frequency oscillatory ventilation with tracheal gas insufflation: the rescue strategy for brain-lung interaction

The occurrence of moderate to severe acute respiratory distress syndrome due to traumatic brain injury is not uncommon and is associated with an extremely high incidence of morbidity and mortality. Owing to the complex interaction between the lung and brain, protective ventilation for the lung with lower tidal volume and higher positive end-expiratory pressure with or without mild hypercapnia might be harmful for the brain, and maintaining normocapnia or mild hypocapnia by increasing tidal volume or respiratory rate (or both) with lower positive end-expiratory pressure levels for protecting the brain might lead to ventilator-induced lung injury. Balancing the end-point between lungs and brain becomes a challenging issue, and non-conventional modes of mechanical ventilation might play a role in the more difficult clinical cases. In this commentary, the authors discuss the rationale, based on the physiologic principle of targeting both vital organs, of applying high-frequency oscillation and tracheal gas insufflation in acute respiratory distress syndrome patients with traumatic brain injury.

Organ crosstalk during acute lung injury, acute respiratory distress syndrome, and mechanical ventilation

PURPOSE OF REVIEW

Multiple organ failure is the main cause of morbidity and mortality in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) patients. Moreover, survivors of both ALI and ARDS often show significant neurocognitive decline at discharge. These data suggest a deleterious organ crosstalk between lungs and distal organs. This article reviews the recent literature concerning the role of this organ crosstalk during ALI, ARDS, and mechanical ventilation, especially focusing on brain-lung communication.

RECENT FINDINGS

Numerous pulmonary and extrapulmonary disorders could predispose critically ill patients to ALI and ARDS. Mechanical ventilation, although a lifesaving intervention, could contribute by modulating the mechanisms involved in the pathophysiology of lung damage and their impact on remote organs. Emerging clinical and experimental evidence supports the hypothesis of a multidirectional organ crosstalk between lungs and distal organs.

SUMMARY

Organ crosstalk is an emerging area of research in lung disease in critically ill patients. The findings of these studies are clinically relevant and show the importance of an integrative approach in the management of critical patients. However, further studies are necessary to understand the complex interactions concurring in these pathologies.