Ventilation with lower tidal volumes versus traditional tidal volumes in adults for acute lung injury and acute respiratory distress syndrome

Comparison of mortality and outcomes of four respiratory viruses in the intensive care unit: a multicenter retrospective study

This retrospective study aimed to compare the mortality and burden of respiratory syncytial virus (RSV group), SARS-CoV-2 (COVID-19 group), non-H1N1 (Seasonal influenza group) and H1N1 influenza (H1N1 group) in adult patients admitted to intensive care unit (ICU) with respiratory failure. A total of 807 patients were included. Mortality was compared between the four following groups: RSV, COVID-19, seasonal influenza, and H1N1 groups. Patients in the RSV group had significantly more comorbidities than the other patients. At admission, patients in the COVID-19 group were significantly less severe than the others according to the simplified acute physiology score-2 (SAPS-II) and sepsis-related organ failure assessment (SOFA) scores. Using competing risk regression, COVID-19 (sHR = 1.61; 95% CI 1.10; 2.36) and H1N1 (sHR = 1.87; 95% CI 1.20; 2.93) were associated with a statistically significant higher mortality while seasonal influenza was not (sHR = 0.93; 95% CI 0.65; 1.31), when compared to RSV. Despite occurring in more severe patients, RSV and seasonal influenza group appear to be associated with a more favorable outcome than COVID-19 and H1N1 groups.

A computational evaluation of FDA medicines’ ability to inhibit hypoxia-inducible factor prolyl hydroxylase-2 (PHD-2) for acute respiratory distress syndrome

COVID-19 infection is associated with a significant fatality rate in individuals suffering from severe acute respiratory distress syndrome (ARDS). Among the several possibilities, inhibition of hypoxia-inducible factor prolyl hydroxylase-2 or prolyl hydroxylase domain-containing protein 2 (PHD2) in a hypoxia-independent way is a prospective therapeutic target for the treatment of ARDS. Vadadustat, Roxadustat, Daprodustat, Desidustat, and Enarudustat are the available clinical trial inhibitors. This study is proposed to focus on the repurposing of FDA-approved drugs as effective PHD2 inhibitors. This computational study utilises e-pharmacophore hypothesis generation from the native ligand–protein complex (PDB ID: 5OX6) based on XP visualiser information. The hypothesis containing five essential features (AAANR) was incorporated for FDA database screening, followed by Glide XP molecular docking and Prime MM-GBSA binding free energy calculations. Top scored ligands were investigated and Fenbufen was identified as an effective PHD-2 inhibitor by comparing with the native co-crystal ligand (Vadadustat). The manual lead optimisation of the Fenbufen structure was adopted to improve inhibitory potency, by increasing the binding affinity and protein–ligand stability. The newly designed compounds B and C showed additional binding interactions, excellent docking scores, binding free energy, and an acceptable range of ADME properties. Also, Fenbufen and compound C owned preferable protein–ligand stability during MD simulation when compared with the co-crystallised clinical trial ligand. Based on our findings, we deduce that Fenbufen can be proposed as an effective repurposable candidate as its structural modification showed a remarkable improvement in PHD2 inhibition.

Clinical Profile of Patients with Severe Acute Respiratory Syndrome Coronavirus 2 Infection Developing Pulmonary Barotrauma on Mechanical Ventilation

Background

There is limited information on clinical profile and outcomes of patients on mechanical ventilation (MV) who developed pulmonary barotrauma (PBT) in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Patients and methods

In a retrospective observational study, all SARS-CoV-2 pneumonia patients admitted from March 28, 2020, to August 31, 2020, at Sir HN Reliance Foundation Hospital and Research Center and Seven Hills Hospital (Reliance Facility), Mumbai, India, of 18 years and above on MV and developed PBT, were included.

Results

A total of 14 SARS-CoV-2 patients of 45 on MV (31.0%) developed PBT of 1,029 hospitalized. All patients were male and divided as per admission into PaO₂/FiO₂ (P/F) ≤100 (median 80) and P/F >100 (median 222) group. Pneumothorax developed in seven and six cases of P/F ≤100 and P/F >100 groups, respectively. Three patients in each group developed subcutaneous emphysema, while four developed pneumomediastinum in P/F >100 group. Twelve patients (7, P/F ≤100, and 5, P/F >100) were on invasive, while two (P/F >100) were on noninvasive MV. The mean P/F on the day of PBT was reduced by 27.5 and 65.3%, while peak inspiratory pressure was elevated with a median of 36 and 28 cm H₂O in P/F ≤100 and P/F >100 groups, respectively. The median highest tidal volume (420 mL), positive-end expiratory pressure (8 vs 6 cm H₂O) on the day of PBT, and length of hospital stay (11 vs 25 days) did not differ between two groups. Survival was 28.6% (4/14).

Conclusion

SARS-CoV-2 patients requiring MV with PBT had poor outcomes. Clinicians should be vigilant about the diagnosis of PBT.

How to cite this article

Kargirwar KV, Rathod D, Kumar V, Patel M, Shah M, Choudhury H, et al. Clinical Profile of Patients with Severe Acute Respiratory Syndrome Coronavirus 2 Infection Developing Pulmonary Barotrauma on Mechanical Ventilation. Indian J Crit Care Med 2022;26(5):613–618.

COVID-19 with severe acute respiratory distress in a pregnant woman leading to preterm caesarean section: A case report

We report the case of a 25-year-old pregnant woman, parity one, at 34 + 2 weeks of gestation, with a body mass index of 41 kg/m2 but no other comorbidities. There was a family history of COVID-19 among her one-year-old son, husband, brother, father and mother. She was admitted with chest pain and a nasopharyngeal swap positive for COVID-19. Due to the severity of the infection, a multidisciplinary team of anaesthesiologists, intensivists, obstetricians, neonatologists, and infectious disease specialists recommended delivery by caesarean section at 35 + 0 weeks of gestation, with combined spinal and epidural anaesthesia. Three days after delivery, the patient developed severe acute respiratory distress syndrome (ARDS) and was intubated for 25 days. The neonate was observed in the neonatal intensive care unit and no vertical transmission occurred. This case highlights the importance of the timing of delivery, the need for extended postpartum observation and a beneficial effect of inhaled nitric oxide after delivery for women with COVID-19.

Clinical, molecular, and epidemiological characterization of the SARS-CoV-2 virus and the Coronavirus Disease 2019 (COVID-19), a comprehensive literature review

Coronaviruses are an extensive family of viruses that can cause disease in both animals and humans. The current classification of coronaviruses recognizes 39 species in 27 subgenera that belong to the family Coronaviridae. From those, at least 7 coronaviruses are known to cause respiratory infections in humans. Four of these viruses can cause common cold-like symptoms. Those that infect animals can evolve and become infectious to humans. Three recent examples of these viral jumps include SARS CoV, MERS-CoV and SARS CoV-2 virus. They are responsible for causing severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS) and the most recently discovered coronavirus disease during 2019 (COVID-19). COVID-19, a respiratory disease caused by the SARS-CoV-2 virus, was declared a pandemic by the World Health Organization (WHO) on 11 March 2020. The rapid spread of the disease has taken the scientific and medical community by surprise. Latest figures from 20 May 2020 show more than 5 million people had been infected with the virus, causing more than 330,000 deaths in over 210 countries worldwide. The large amount of information received daily relating to COVID-19 is so abundant and dynamic that medical staff, health authorities, academics and the media are not able to keep up with this new pandemic. In order to offer a clear insight of the extensive literature available, we have conducted a comprehensive literature review of the SARS CoV-2 Virus and the Coronavirus Diseases 2019 (COVID-19).

Assessment of spontaneous breathing during pressure controlled ventilation with superimposed spontaneous breathing using respiratory flow signal analysis

Integrating spontaneous breathing into mechanical ventilation (MV) can speed up liberation from it and reduce its invasiveness. On the other hand, inadequate and asynchronous spontaneous breathing has the potential to aggravate lung injury. During use of airway-pressure-release-ventilation (APRV), the assisted breaths are difficult to measure. We developed an algorithm to differentiate the breaths in a setting of lung injury in spontaneously breathing ewes. We hypothesized that differentiation of breaths into spontaneous, mechanical and assisted is feasible using a specially developed for this purpose algorithm. Ventilation parameters were recorded by software that integrated ventilator output variables. The flow signal, measured by the EVITA® XL (Lübeck, Germany), was measured every 2 ms by a custom Java-based computerized algorithm (Breath-Sep). By integrating the flow signal, tidal volume (V_T) of each breath was calculated. By using the flow curve the algorithm separated the different breaths and numbered them for each time point. Breaths were separated into mechanical, assisted and spontaneous. Bland Altman analysis was used to compare parameters. Comparing the values calculated by Breath-Sep with the data from the EVITA® using Bland-Altman analyses showed a mean bias of - 2.85% and 95% limits of agreement from - 25.76 to 20.06% for MV_total. For respiratory rate (RR) RR_set a bias of 0.84% with a SD of 1.21% and 95% limits of agreement from - 1.53 to 3.21% were found. In the cluster analysis of the 25th highest breaths of each group RR_total was higher using the EVITA®. In the mechanical subgroup the values for RR_spont and MV_spont the EVITA® showed higher values compared to Breath-Sep. We developed a computerized method for respiratory flow-curve based differentiation of breathing cycle components during mechanical ventilation with superimposed spontaneous breathing. Further studies in humans and optimizing of this technique is necessary to allow for real-time use at the bedside.

Hypercapnia attenuates ventilator-induced lung injury through vagus nerve activation

Purpose:

To investigate the role of vagus nerve activation in the protective effects of hypercapnia in ventilator-induced lung injury (VILI) rats.

Methods:

Male Sprague-Dawley rats were randomized to either high-tidal volume or low-tidal volume ventilation (control) and monitored for 4h. The high-tidal volume group was further divided into either a vagotomy or sham-operated group and each surgery group was further divided into two subgroups: normocapnia and hypercapnia. Injuries were assessed hourly through hemodynamics, respiratory mechanics and gas exchange. Protein concentration, cell count and cytokines (TNF-α and IL-8) in bronchoalveolar lavage fluid (BALF), lung wet-to-dry weight and pathological changes were examined. Vagus nerve activity was recorded for 1h.

Results:

Compared to the control group, injurious ventilation resulted in a decrease in PaO₂/FiO₂ and greater lung static compliance, MPO activity, enhanced BALF cytokines, protein concentration, cell count, and histology injury score. Conversely, hypercapnia significantly improved VILI by decreasing the above injury parameters. However, vagotomy abolished the protective effect of hypercapnia on VILI. In addition, hypercapnia enhanced efferent vagus nerve activity compared to normocapnia.

Conclusion:

These results indicate that the vagus nerve plays an important role in mediating the anti-inflammatory effect of hypercapnia on VILI.

A pragmatic approach to intravenous anaesthetics and electroencephalographic endpoints for the treatment of refractory and super-refractory status epilepticus in critical care

Status epilepticus is a common neurological emergency, with overall mortality around 20%. Over half of cases are first time presentations of seizures. The pathological process by which spontaneous seizures are generated arises from an imbalance in excitatory and inhibitory neuronal networks, which if unchecked, can result in alterations in intracellular signalling pathways and electrolyte shifts, which bring about changes in the blood brain barrier, neuronal cell death and eventually cerebral atrophy. This narrative review focusses on the treatment of status epilepticus in adults. Anaesthetic agents interrupt neuronal activity by enhancing inhibitory or decreasing excitatory transmission, primarily via GABA and NMDA receptors. Intravenous anaesthetic agents are commonly used as second or third line drugs in the treatment of refractory status epilepticus, but the optimal timing and choice of anaesthetic drug has not yet been established by high quality evidence. Titration of antiepileptic and anaesthetic drugs in critically ill patients presents a particular challenge, due to alterations in drug absorbtion and metabolism as well as changes in drug distrubution, which arise from fluid shifts and altered protein binding. Furthermore, side effects associated with prolonged infusions of anaesthetic drugs can lead to multi-organ dysfunction and a need for critical care support. Electroencelography can identify patterns of burst suppression, which may be a target to guide weaning of intravenous therapy. Continuous elctroencephalography has the potential to directly impact clinical care, but despite its utility, major barriers exist which have limited its widespread use in clinical practice. A flow chart outlining the timing and dosage of anaesthetic agents used at our institution is provided.

Altered blood levels of vitamin D, cathelicidin and parathyroid hormone in patients with sepsis-a pilot study

It has been recognised that vitamin D (VitD) has a potential role in the regulation of inflammation and protection from infection. In a prospective clinical observational pilot study, we investigated the serum levels of 25-hydroxyvitamin-D3 (25(OH)D3), 1,25-hydroxyvitamin-D3 (1,25(OH)2D3), parathyroid hormone (PTH), and cathelicidin in intensive care unit (ICU) patients with or without systemic inflammatory response syndrome (SIRS). We included 32 patients with SIRS (septic patients), 16 ICU patients without SIRS, and 16 healthy controls. To substantiate the findings of the clinical study, we stimulated monocyte-derived macrophages with microbial patterns and analysed the impact of VitD on release of cytokines and antimicrobial activity. We found that patients with or without SIRS had relatively low levels of 25(OH)D3 and 1,25(OH)2D3. Patients with sepsis had significantly lower levels of 25(OH)D3 as compared to ICU control patients and healthy controls (10.53 ± 11.3 µg/l versus 16.46 ± 12.58 µg/l versus 24.04 ± 12.07 µg/l); the same was true for 1,25(OH)2D3. Serum levels of PTH and cathelicidin were significantly increased in sepsis patients, as compared to the other groups. In vitro, VitD significantly decreased the release of pro-inflammatory cytokines from macrophages and increased the antimicrobial activity of the cells. We concluded that patients with sepsis have significantly lower VitD levels. In vitro, VitD modulates inflammation and increases the antibacterial activity of innate immune cells. These findings suggest that VitD insufficiency is mechanistically related to increased susceptibility to SIRS and sepsis.

Focused cardiac ultrasound in the early resuscitation of severe sepsis and septic shock: a prospective pilot study

PURPOSE

Point-of-care ultrasonography has been increasingly used in the care of critically ill patients; however, reports on its use during active resuscitation are limited. The aim of this study was to investigate the true impact of focused cardiac ultrasound (FCU) during the management of sepsis with early (6-h) resuscitation.

METHODS

A prospective pilot observational study was conducted at an academic medical center from March 2011 through July 2012. Patients undergoing resuscitation for severe sepsis or septic shock were prospectively enrolled at medical and combined medical-surgical intensive care units. Patients underwent a 10-min FCU examination when echocardiography was not part of their care plan. FCU was performed by sonographers and interpreted by cardiologists to minimize risks of inadequate image acquisition and misinterpretation. Intensivists completed surveys on their diagnostic and therapeutic plans before and after receiving FCU information.

RESULTS

Of the 30 patients enrolled, 18 (60%) were male and the median age was 61 years [interquartile range (IQR) 50-71 years]. Median central venous oxygen saturation and lactate levels were 59.6% (IQR 53.1-66.2%) and 2.7 mmol/L (IQR 1.2-4.1 mmol/L), respectively. Clinical assessment by intensivists before FCU commonly failed to correctly estimate ventricular function; specifically, left ventricular in 12 patients [40%, 95% confidence interval (CI) 25-58%] and right ventricular function in 15 patients (50%, 95% CI 33-67%). Intensivists' therapeutic plans changed in eight cases (27%, 95% CI 14-44%) after FCU information became available. The most common changes were fluid management and imaging tests. Intensivists' confidence in their therapeutic plans improved for 11 patients (37%, 95% CI 22-55%).

CONCLUSION

FCU is a valuable examination tool during early resuscitation of severe sepsis and septic shock.

Uncoupling Protein 2 Increases Susceptibility to Lipopolysaccharide-Induced Acute Lung Injury in Mice

Uncoupling protein 2 (UCP2) is upregulated in patients with systemic inflammation and infection, but its functional role is unclear. We up- or downregulated UCP2 expression using UCP2 recombinant adenovirus or the UCP2 inhibitor, genipin, in lungs of mice, and investigated the mechanisms of UCP2 in ALI. UCP2 overexpression in mouse lungs increased LPS-induced pathological changes, lung permeability, lung inflammation, and lowered survival rates. Furthermore, ATP levels and mitochondrial membrane potential were decreased, while reactive oxygen species production was increased. Additionally, mitogen-activated protein kinases (MAPKs) activity was elevated, which increased the sensitivity to LPS-induced apoptosis and inflammation. LPS-induced apoptosis and release of inflammatory factors were alleviated by pretreatment of the Jun N-terminal kinase (JNK) inhibitor SP600125 or the p38 MAPK inhibitor SB203580, but not by the extracellular signal-regulated kinase (ERK) inhibitor PD98059 in UCP2-overexpressing mice. On the other hand, LPS-induced alveolar epithelial cell death and inflammation were attenuated by genipin. In conclusion, UCP2 increased susceptibility to LPS-induced cell death and pulmonary inflammation, most likely via ATP depletion and activation of MAPK signaling following ALI in mice.

Hexa-acylated LPS-lipid A deploys the appropriate level of fibrin to confer protection through MyD88

OBJECTIVES

Fibrin has been demonstrated to function protectively against pathogens in our previous studies, but we observed that a very high level of fibrin played a negative role during infection. We performed this research to address the complication.

METHODS

After infection, mice were monitored daily and harvested on day 4. The fibrin levels within the tissue samples were quantified by Western-blot. The in situ assay was used to detect plasminogen activators, protein C-ase and prothrombinase activation. PT-PCR was used to test coagulation factors expression.

RESULTS

Mice treated with Coumadin showed that the protection correlates with fibrin levels. By interacting with Toll-like receptor 4, the hexa-acylated lipopolysaccharide, although not the tetra-acylated lipopolysaccharide, activates coagulation and regulates plasminogen activator inhibitor 1, thrombin activatable fibrinolysis inhibitor and thrombomodulin expression through myeloid differentiation factor 88, leading to plasminogen activators, protein C-ase and prothrombinase activation and fibrin formation. Because of the regulation, fibrin formation was controlled to deposit appropriate levels and confer protection.

CONCLUSIONS

We demonstrated that the appropriate level of fibrin formation was deployed by hexa-acylated LPS-lipid A through myeloid differentiation factor 88 to confer protection.

Impact of serum biomarkers and clinical factors on intensive care unit mortality and 6-month outcome in relatively healthy patients with severe pneumonia and acute respiratory distress syndrome

Objectives. This study aimed to identify the independent biomarkers and clinical factors that could predict ICU mortality and 6-month outcomes in relatively healthy patients with severe pneumonia and acute respiratory distress syndrome (ARDS). Patients and Methods. We prospectively enrolled patients with severe pneumonia-related ARDS that required mechanical ventilation. Patients were excluded if they were unable to take care of themselves. Several biomarkers and clinical factors were evaluated prospectively on day 1 and day 3 after ICU admission. All biomarkers and clinical factors were collected for analysis. Results. 56 patients were enrolled in this study. We determined that the initial appropriate antibiotics use was an independent clinical factor and day 1 high-mobility group protein B1 (HMGB1) concentration was an independent biomarker for ICU mortality. Interestingly, we also found that a low day 1 albumin level was an independent biomarker for predicting patient life dependence 6 months after a pneumonia event. Conclusion. Patients with severe pneumonia and ARDS requiring mechanical ventilation experience high rates of ICU mortality or disability, even if they were quite healthy before. Initial appropriate antibiotics use and day 1 level of HMGB1 were independent factors for predicting ICU mortality. Day 1 albumin level was predictive of 6-month patient life dependence.

Pumpless extracorporeal CO(2) removal restores normocapnia and is associated with less regional perfusion in experimental acute lung injury

BACKGROUND

Lung protective ventilation may lead to hypoventilation with subsequent hypercapnic acidosis (HA). If HA cannot be tolerated or occurs despite increasing respiratory rate or buffering, extracorporeal CO2-removal using a percutaneous extracorporeal lung assist (pECLA) is an option. We hypothesised that compensation of HA using pECLA impairs regional perfusion. To test this hypothesis we determined organ blood flows in a lung-injury model with combined hypercapnic and metabolic acidosis.

METHODS

After induction of lung injury using hydrochloric acid (HCl) aspiration and metabolic acidosis by intravenous HCl infusion in nine pigs, an arterial-venous pECLA device was inserted. In randomised order, four treatments were tested: pECLA shunt (1) with and (2) without HA, and clamped pECLA shunt (3) with and (4) without HA. Regional blood flows were measured with the coloured microsphere technique.

RESULTS

HA resulted in higher perfusion in adrenal glands, spleen and parts of splanchnic area (P < 0.05) compared with normocapnia. During CO2-removal with pECLA, regional perfusion decreased to levels comparable with those without pECLA and normocapnia. Cardiac output (CO) increased during HA without a pECLA shunt and was highest during HA with a pECLA shunt compared with normocapnia. During CO2-removal with pECLA, this variable decreased but stayed higher than during normocapnia with clamped pECLA shunt (P < 0.05).

CONCLUSION

In our lung-injury model, HA was associated with increased systemic and regional blood flow in several organs. pECLA provides effective CO2 removal, requiring a higher CO for perfusion of the pECLA device without improvement of regional organ perfusion.

Advances in monitoring and management of pediatric acute lung injury

This article focuses on the respiratory management and monitoring of pediatric acute lung injury (ALI) as a specific cause for respiratory failure. Definitive, randomized, controlled trials in pediatrics to guide optimal ventilatory management are few. The only adjunct therapy that has been proved to improve clinical outcome is low tidal volume ventilation, but only in adult patients. Careful monitoring of the patient's respiratory status with airway graphic analysis and capnography can be helpful. Definitive data are needed in the pediatric population to assist in the care of infants, children, and adolescents with ALI to improve survival and functional outcome.

Lung protective ventilation strategy for the acute respiratory distress syndrome

BACKGROUND

Patients with acute respiratory distress syndrome and acute lung injury require mechanical ventilatory support. Acute respiratory distress syndrome and acute lung injury are further complicated by ventilator-induced lung injury. Lung protective ventilation strategies may lead to improved survival. This systematic review is an update of a Cochrane review originally published in 2003 and updated in 2007.

OBJECTIVES

To assess the effects of ventilation with lower tidal volume on morbidity and mortality in patients aged 16 years or older affected by acute respiratory distress syndrome and acute lung injury. A secondary objective was to determine whether the comparison between low and conventional tidal volume was different if a plateau airway pressure of greater than 30 to 35 cm H20 was used.

SEARCH METHODS

In our previous 2007 updated review, we searched databases from inception until 2006. In this third updated review, we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL and the Web of Science from 2006 to September 2012. We also updated our search of databases of ongoing research and of reference lists from 2006 to September 2012.

SELECTION CRITERIA

We included randomized controlled trials comparing ventilation using either a lower tidal volume (Vt) or low airway driving pressure (plateau pressure 30 cm H2O or less), resulting in a tidal volume of 7 ml/kg or less, versus ventilation that used Vt in the range of 10 to 15 ml/kg in adults (16 years old or older) with acute respiratory distress syndrome and acute lung injury.

DATA COLLECTION AND ANALYSIS

We independently assessed trial quality and extracted data. Wherever appropriate, results were pooled. We applied fixed-effect and random-effects models.

MAIN RESULTS

We did not find any new study which were eligible for inclusion in this update. The total number of studies remained unchanged, six trials involving 1297 patients. Five trials had a low risk of bias. One trial had an unclear risk of bias. Mortality at day 28 was significantly reduced by lung-protective ventilation with a relative risk (RR) of 0.74 (95% confidence interval (CI) 0.61 to 0.88); hospital mortality was reduced with a RR of 0.80 (95% CI 0.69 to 0.92). Overall mortality was not significantly different if a plateau pressure less than or equal to 31 cm H2O in the control group was used (RR 1.13, 95% CI 0.88 to 1.45). There was insufficient evidence for morbidity and long-term outcomes.

AUTHORS' CONCLUSIONS

Clinical heterogeneity, such as different lengths of follow up and higher plateau pressure in control arms in two trials, makes the interpretation of the combined results difficult. Mortality was significantly reduced at day 28 and at the end of the hospital stay. The effects on long-term mortality are unknown, although the possibility of a clinically relevant benefit cannot be excluded. Ventilation with lower tidal volumes is becoming a routine strategy of treatment of acute respiratory distress syndrome and acute lung injury, stopping investigators from carrying out additional trials.

Anti-inflammatory effects of ellagic acid on acute lung injury induced by acid in mice

Acute lung injury (ALI) is characterized by alveolar edema and uncontrolled neutrophil migration to the lung, and no specific therapy is still available. Ellagic acid, a compound present in several fruits and medicinal plants, has shown anti-inflammatory activity in several experimental disease models. We used the nonlethal acid aspiration model of ALI in mice to determine whether preventive or therapeutic administration of ellagic acid (10 mg/kg; oral route) could interfere with the development or establishment of ALI inflammation. Dexamethasone (1 mg/kg; subcutaneous route) was used as a positive control. In both preventive and therapeutic treatments, ellagic acid reduced the vascular permeability changes and neutrophil recruitment to the bronchoalveolar lavage fluid (BALF) and to lung compared to the vehicle. In addition, the ellagic acid accelerated the resolution for lung neutrophilia. Moreover, ellagic acid reduced the COX-2-induced exacerbation of inflammation. These results were similar to the dexamethasone. However, while the anti-inflammatory effects of dexamethasone treatment were due to the reduced activation of NF-κB and AP-1, the ellagic acid treatment led to reduced BALF levels of IL-6 and increased levels of IL-10. In addition, dexamethasone treatment reduced IL-1β. Together, these findings identify ellagic acid as a potential therapeutic agent for ALI-associated inflammation.

Clinical effectiveness and safety of permissive hypercapnia

Experimental and clinical data indicate that ventilator strategies with permissive hypercapnia may reduce lung injury by a variety of mechanisms. Seven randomized controlled trials in preterm neonates suggest that permissive hypercapnia started early, before the initiation of mechanical ventilation (in conjunction with continuous positive airway pressure), followed by prolonged permissive hypercapnia if mechanical ventilation is needed is an alternative to early ventilation and surfactant. Permissive hypercapnia may improve pulmonary outcomes and survival.

Accuracy of stroke volume variation in predicting fluid responsiveness: a systematic review and meta-analysis

PURPOSE

Stroke volume variation (SVV) appears to be a good predictor of fluid responsiveness in critically ill patients. However, a wide range of its predictive values has been reported in recent years. We therefore undertook a systematic review and meta-analysis of clinical trials that investigated the diagnostic value of SVV in predicting fluid responsiveness.

METHODS

Clinical investigations were identified from several sources, including MEDLINE, EMBASE, WANFANG, and CENTRAL. Original articles investigating the diagnostic value of SVV in predicting fluid responsiveness were considered to be eligible. Participants included critically ill patients in the intensive care unit (ICU) or operating room (OR) who require hemodynamic monitoring.

RESULTS

A total of 568 patients from 23 studies were included in our final analysis. Baseline SVV was correlated to fluid responsiveness with a pooled correlation coefficient of 0.718. Across all settings, we found a diagnostic odds ratio of 18.4 for SVV to predict fluid responsiveness at a sensitivity of 0.81 and specificity of 0.80. The SVV was of diagnostic value for fluid responsiveness in OR or ICU patients monitored with the PiCCO or the FloTrac/Vigileo system, and in patients ventilated with tidal volume greater than 8 ml/kg.

CONCLUSIONS

SVV is of diagnostic value in predicting fluid responsiveness in various settings.

Complement 3 is involved with ventilator-induced lung injury

Humoral molecules can trigger injury on mechanically stressed and damaged tissue. We have studied the role of complement 3 (C3) in a mouse model of ventilator-induced lung injury (VILI). Compared with sham-treated wild type (WT) mice, ventilated WT mice have reduced total bronchoalveolar lavage (BAL) cells; and elevated activities of thrombin and matrix metalloproteinases (MMPs), such as gelatinase/collagenase in the BAL fluid. In contrast, these parameters in ventilated C3 null mice are not significantly different from sham-treated WT and C3 null mice. In mechanically ventilated mice, thrombin activity and MMPs are lower in C3 null mice than in WT mice and are inversely correlated with total single BAL cells. C3 activation is associated with MMP activation in vitro. Pretreatment of WT mice with humanized cobra venom factor, which inactivates C3, reduces C3 deposition in the lung and increases total BAL cells in VILI. We propose that C3 is involved with VILI and inhibition of complement activation may be a potential therapeutic strategy.

Respiratory care

PURPOSE OF THE REVIEW

Neurosurgical patients frequently develop respiratory complications, adversely affecting neurologic outcome and survival. The review summarizes current literature and management of respiratory complications associated with brain injury.

MAJOR FINDINGS

Respiratory complications are commonly associated with traumatic brain injury and subarachnoid haemorrhage. Lung-protective ventilation with reduced tidal volumes improves outcome in acute lung injury, and should be applied to neurosurgical patients in the absence of increased intracranial pressure. Weaning from the mechanical ventilation should be initiated as soon as possible, although the role of neurological status in the weaning process is not clear. Prevention of pneumonia and aspiration improves survival. In patients with difficult weaning, early bedside percutaneous tracheostomy should be considered.

FURTHER INVESTIGATIONS

Further studies are warranted to elucidate an optimal oxygenation and ventilation in brain-injured patients, weaning strategies, predictors of the failed weaning and extubation, respiratory support in patients with difficulties to wean, and early tracheostomy.

Pattern of inspiratory gas delivery affects CO2 elimination in health and after acute lung injury

OBJECTIVE

To avoid ventilator induced lung injury, tidal volume should be low in acute lung injury (ALI). Reducing dead space may be useful, for example by using a pattern of inspiration that prolongs the time available for gas distribution and diffusion within the respiratory zone, the mean distribution time (MDT). A study was conducted to investigate how MDT affects CO2 elimination in pigs at health and after ALI.

DESIGN AND SETTING

Randomised crossover study in the animal laboratory of Lund University Biomedical Center.

SUBJECTS AND INTERVENTION

Healthy pigs and pigs with ALI, caused by surfactant perturbation and lung-damaging ventilation were ventilated with a computer-controlled ventilator. With this device each breath could be tailored with respect to insufflation time and pause time (TI and TP) as well as flow shape (square, increasing or decreasing flow).

MEASUREMENTS AND RESULTS

The single-breath test for CO2 allowed analysis of the volume of expired CO2 and the volume of CO2 re-inspired from Y-piece and tubes. With a long MDT caused by long TI or TP, the expired volume of CO2 increased markedly in accordance with the MDT concept in both healthy and ALI pigs. High initial inspiratory flow caused by a short TI or decreasing flow increased the re-inspired volume of CO2. Arterial CO2 increased during a longer period of short MDT and decreased again when MDT was prolonged.

CONCLUSIONS

CO2 elimination can be enhanced by a pattern of ventilation that prolongs MDT. Positive effects of prolonged MDT caused by short TI and decreasing flow were attenuated by high initial inspiratory flow.

Lung protective ventilation strategy for the acute respiratory distress syndrome

BACKGROUND

Patients with acute respiratory distress syndrome and acute lung injury require mechanical ventilatory support. Acute respiratory distress syndrome and acute lung injury are further complicated by ventilator-induced lung injury. Lung-protective ventilation strategies may lead to improved survival.

OBJECTIVES

To assess the effects of ventilation with lower tidal volume on morbidity and mortality in patients aged 16 years or older affected by acute respiratory distress syndrome and acute lung injury. A secondary objective was to determine whether the comparison between low and conventional tidal volume was different if a plateau airway pressure of greater than 30 to 35 cm H20 was used.

SEARCH STRATEGY

In our original review, we searched databases from inception until 2003. In this updated review, we searched The Cochrane Central Register of Controlled Trials (CENTRAL), (The Cochrane Library 2006, Issue 3). We updated our search of MEDLINE, EMBASE, CINAHL and the Web of Science from 2003 to 2006. We also updated our search of intensive care journals and conference proceedings; databases of ongoing research, reference lists and 'grey literature' from 2003 to 2006.

SELECTION CRITERIA

We included randomized controlled trials comparing ventilation using either lower tidal volume (Vt) or low airway driving pressure (plateau pressure 30 cm H2O or less), resulting in tidal volume of 7 ml/kg or less versus ventilation that uses Vt in the range of 10 to 15 ml/kg, in adults (16 years old or older).

DATA COLLECTION AND ANALYSIS

We independently assessed trial quality and extracted data. Wherever appropriate, results were pooled. We applied fixed- and random-effects models.

MAIN RESULTS

We found one new study in this update for a total of six trials, involving 1297 patients, which were eligible for inclusion. Mortality at day 28 was significantly reduced by lung-protective ventilation: relative risk (RR) 0.74 (95% confidence interval (CI) 0.61 to 0.88); hospital mortality was reduced: RR 0.80 (95% CI 0.69 to 0.92); overall mortality was not significantly different if a plateau pressure less than or equal to 31 cm H2O in control group was used: RR 1.13 (95% CI 0.88 to 1.45). There was insufficient evidence about morbidity and long term outcomes.

AUTHORS' CONCLUSIONS

Clinical heterogeneity, such as different lengths of follow up and higher plateau pressure in control arms in two trials, make the interpretation of the combined results difficult. Mortality is significantly reduced at day 28 and at the end of hospital stay. The effects on long-term mortality are unknown, although the possibility of a clinically relevant benefit cannot be excluded.

Basic ventilator management: lung protective strategies

Acute respiratory failure is manifested clinically as a patient with variable degrees of respiratory distress, but characteristically an abnormal arterial blood partial pressure of oxygen or carbon dioxide. The application of mechanical ventilation in this setting can be life-saving. An emerging body of clinical and basic research, however, has highlighted the potential adverse effects of positive pressure ventilation. Clinicians involved with the care of critically ill patients must recognize and seek to prevent these complications using lung-protective ventilation strategies. This article discusses the basic concepts of mechanical ventilation, reviews the categories of ventilator-associated lung injury, and discusses current strategies for the recognition and prevention of these adverse effects in the application of mechanical ventilation.

Pharmacological utility of melatonin in the treatment of septic shock: experimental and clinical evidence

Sepsis is a major cause of mortality in critically ill patients and develops as a result of the host response to infection. In recent years, important advances have been made in understanding the pathophysiology and treatment of sepsis. Mitochondria play a central role in the intracellular events associated with inflammation and septic shock. One of the current hypotheses for the molecular mechanisms of sepsis is that the enhanced nitric oxide (NO) production by mitochondrial nitric oxide synthase (mtNOS) leads to excessive peroxynitrite (ONOO-) production and protein nitration, impairing mitochondrial function. Despite the advances in understanding of its pathophysiology, therapy for septic shock remains largely symptomatic and supportive. Melatonin has well documented protective effects against the symptoms of severe sepsis/shock in both animals and in humans; its use for this condition significantly improves survival. Melatonin administration counteracts mtNOS induction and respiratory chain failure, restores cellular and mitochondrial redox status, and reduces proinflammatory cytokines. Melatonin clearly prevents multiple organ failure, circulatory failure, and mitochondrial damage in experimental sepsis, and reduces lipid peroxidation, indices of inflammation and mortality in septic human newborns. Considering these effects of melatonin and its virtual absence of toxicity, the use of melatonin (along with conventional therapy) to preserve mitochondrial bioenergetics as well as to limit inflammatory responses and oxidative damage should be seriously considered as a treatment option in both septic newborn and adult patients. This review summarizes the data that provides a rationale for using melatonin in septic shock patients.

Meta-analysis: Methods, strengths, weaknesses, and political uses

The general methodology, strengths and weaknesses, and political uses of meta-analysis are examined. As a systematic study of all studies that have been conducted to answer a specific question or hypothesis, meta-analysis is strong in revealing structural flaws and sources of bias in primary research and in posing promising research questions for future study. It cannot exceed, however, the limits of what is reported by primary researchers. Meta-analysis is particularly challenged to quantify the size of a common effect of treatment across reported trials because of (1) the clinical diversity of the trials and (2) the myriad of potential differences among patients with varying characteristics within the trials. Without access to the original data of reported trials, meta-analysis cannot overcome the bias of underpowered trials toward overstatement of the size of main treatment effects, nor the tendency for such trials to falsely conclude there were no statistically significant adverse events. Although severely compromised by ghost-written or honorary-authored reports of primary research, meta-analysis can make use of its methods to focus on the conflicts of interest and likely sources of bias of such research and make known what precautions should be taken by would-be consumers. Examples show how meta-analysis has clarified thinking about the off-label use of selective serotonin reuptake inhibitors for treating child and adolescent depression, use of low-tidal volume respirator assistance for acute lung injury and acute respiratory distress syndrome patients, and the long-term use of COX-2 inhibitors for relieving arthritic pain. Recommendations are made for Congressional action.

Study protocol: The Improving Care of Acute Lung Injury Patients (ICAP) study

INTRODUCTION

The short-term mortality benefit of lower tidal volume ventilation (LTVV) for patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) has been demonstrated in a large, multi-center randomized trial. However, the impact of LTVV and other critical care therapies on the longer-term outcomes of ALI/ARDS survivors remains uncertain. The Improving Care of ALI Patients (ICAP) study is a multi-site, prospective cohort study that aims to evaluate the longer-term outcomes of ALI/ARDS survivors with a particular focus on the effect of LTVV and other critical care therapies.

METHODS

Consecutive mechanically ventilated ALI/ARDS patients from 11 intensive care units (ICUs) at four hospitals in the city of Baltimore, MD, USA, will be enrolled in a prospective cohort study. Exposures (patient-based, clinical management, and ICU organizational) will be comprehensively collected both at baseline and throughout patients' ICU stay. Outcomes, including mortality, organ impairment, functional status, and quality of life, will be assessed with the use of standardized surveys and testing at 3, 6, 12, and 24 months after ALI/ARDS diagnosis. A multi-faceted retention strategy will be used to minimize participant loss to follow-up.

RESULTS

On the basis of the historical incidence of ALI/ARDS at the study sites, we expect to enroll 520 patients over two years. This projected sample size is more than double that of any published study of long-term outcomes in ALI/ARDS survivors, providing 86% power to detect a relative mortality hazard of 0.70 in patients receiving higher versus lower exposure to LTVV. The projected sample size also provides sufficient power to evaluate the association between a variety of other exposure and outcome variables, including quality of life.

CONCLUSION

The ICAP study is a novel, prospective cohort study that will build on previous critical care research to improve our understanding of the longer-term impact of ALI/ARDS, LTVV and other aspects of critical care management. Given the paucity of information about the impact of interventions on long-term outcomes for survivors of critical illness, this study can provide important information to inform clinical practice.

Methods to prevent ventilator-associated lung injury: a summary

Mechanical ventilation can cause ventilator-associated lung injury (VALI). This may manifest itself in various forms such as pneumothorax or, at the most extreme level, multi-system organ failure. The exact mechanisms by which the injury occurs are not known but appear to involve the conversion of mechanical stimulation of alveolar membranes into intracellular signalling, with subsequent upregulation of inflammatory mediators that produce the damage. This has been termed biotrauma. Furthermore, disruption of alveolar-capillary membranes may allow the release of these mediators into the systemic circulation that underpins the systemic inflammatory response syndrome. Various protective ventilatory strategies may be employed in order to reduce the lung damage and shall be discussed in this paper.