Long-term outcomes of survivors with influenza A H1N1 virus-induced severe pneumonia and ARDS: a single-center prospective cohort study.

Introduction: Systematic evaluation of long-term outcomes in survivors of H1N1 is still lacking. This study aimed to characterize long-term outcomes of severe H1N1-induced pneumonia and acute respiratory distress syndrome (ARDS). Method: This was a single-center, prospective, cohort study. Survivors were followed up for four times after discharge from intensive care unit (ICU) by lung high-resolution computed tomography (HRCT), pulmonary function assessment, 6-minute walk test (6MWT), and SF-36 instrument. Result: A total of 60 survivors of H1N1-induced pneumonia and ARDS were followed up for four times. The carbon monoxide at single breath (DLCO) of predicted values and the 6MWT results didn't continue improving after 3 months. Health-related quality of life didn't change during the 12 months after ICU discharge. Reticulation or interlobular septal thickening on HRCT did not begin to improve significantly until the 12-month follow-up. The DLCO of predicted values showed negative correlation with the severity degree of primary disease and reticulation or interlobular septal thickening, and a positive correlation with physical functioning. The DLCO of predicted values and reticulation or interlobular septal thickening both correlated with the highest tidal volume during mechanical ventilation. Levels of fibrogenic cytokines had a positive correlation with reticulation or interlobular septal thickening. Conclusion: The improvements in pulmonary function and exercise capacity, imaging, and health-related quality of life had different time phase and impact on each other during 12 months of follow-up. Long-term outcomes of pulmonary fibrosis might be related to the lung injury and excessive lung fibroproliferation at the early stage during ICU admission.

[The value of point-of-care ultrasound in the diagnosis and management of acute respiratory distress syndrome].

Acute respiratory distress syndrome (ARDS) continues to cause significant morbidity and mortality worldwide. However, there are currently no corresponding specific medications. Lung, right heart, and diaphragm protective therapy is the cornerstone of ARDS management. Non-invasive, radiation-free, and transportation-free point-of-care ultrasound enables for real-time dynamic evaluation of the lung, right heart, and diaphragm. It is an essential tool for the diagnosis, monitoring, and clinical decision-making of ARDS patients. However, ultrasound has several limitations, and its clinical application must be carefully evaluated in conjunction with clinical symptoms and other monitoring techniques. Further research is needed to determine whether clinical decision-making based on point-of-care ultrasound examination can improve the prognosis of ARDS patients.

[Relationship between the lung ultrasound and the clinical severity of the patient with seasonal flu]. / Lien entre l'aspect échographique du poumon et la sévérité́ clinique du patient atteint d'une grippe saisonnière.

INTRODUCTION: The seasonal flu is a very important reason for consultation every winter. Symptoms can quickly progress to severe pneumonia. Currently, few tools exist to assess the clinical severity of patients. The aim of this study is to demonstrate the role of lung ultrasound as a marker of severity in patients with influenza. METHODS: 79 patients who arrived at the emergency department with flu-like symptoms were included. A pulmonary ultrasound looking for an interstitial syndrome or consolidation was performed. The qSOFA, the SOFA, the saturation, the PaO2/FiO2 ratio, the oxygen needs, the destination of the patient made it possible to establish the seriousness of the pathology of the patient. Ultrasound was then compared to these different tools. RESULTS: The more the ultrasound became pathological, the more we observed a proportion of qSOFA (p = 0.001) and pathological SOFA (p = 0.009). Most patients with acute respiratory distress syndrome have pathological ultrasound (p < 0.001). The average admission saturation is 89.2 % in the "pathological ultrasound" group compared to 95.8 % in the "normal ultrasound" group (p < 0.001). Patients who required invasive therapies had pathological ultrasound (p < 0.001). Of the 28 patients with pathological ultrasound, 24 required hospitalization (p < 0.001). CONCLUSION: Lung ultrasound is a major asset for assessing the severity of the patient with seasonal flu. In addition, ultrasound allows better monitoring of the patient by being able to influence the destination of the latter towards a return home or monitoring in intensive care.

INTRODUCTION: La grippe saisonnière représente chaque hiver un motif de consultation très important. La symptomatologie peut rapidement évoluer vers une pneumonie sévère. Actuellement, peu d'outils existent pour évaluer la sévérité clinique des patients. Le but de cette étude est de démontrer le rôle de l'échographie pulmonaire comme marqueur de sévérité́ chez les patients atteints d'une grippe. Méthodes : L'étude a comporté 79 patients arrivés aux urgences pour grippe. Une échographie pulmonaire a été réalisée à la recherche d'un syndrome interstitiel ou d'une consolidation. Le qSOFA, le SOFA, la saturation, le rapport PaO2/FiO2, les besoins en oxygène, la destination du patient ont permis d'établir la gravité de la pathologie du patient. L'échographie a alors été comparée à ces différents outils. Résultats : Plus l'échographie devient pathologique, plus on observe une proportion de qSOFA (p = 0,001) et de SOFA pathologiques (p = 0,009). La majorité́ des patients ayant un syndrome de détresse respiratoire aiguë ont une échographie pathologique (p < 0,001). La moyenne des saturations d'admission est de 89,2 % dans le groupe «échographie pathologique¼ contre 95,8 % dans le groupe «échographie normale¼ (p < 0,001). Les patients ayant eu recours à des thérapies invasives ont une échographie pathologique (p < 0,001). Sur les 28 patients ayant une échographie pathologique, 24 ont nécessité́ une hospitalisation (p < 0,001). CONCLUSION: L'échographie pulmonaire est un atout majeur pour l'évaluation de la sévérité du patient atteint d'une grippe saisonnière. De plus, l'échographie permet une meilleure surveillance du patient en pouvant influencer la destination de celui-ci vers un retour à̀ domicile ou une surveillance aux soins intensifs.

Regional pulmonary perfusion, blood volume, and their relationship change in experimental early ARDS.

Regional pulmonary perfusion (Q) has been investigated using blood volume (Fb) imaging as an easier-to-measure surrogate. However, it is unclear if changing pulmonary conditions could affect their relationship. We hypothesized that vascular changes in early acute respiratory distress syndrome (ARDS) affect Q and Fb differently. Five sheep were anesthetized and received lung protective mechanical ventilation for 20 h while endotoxin was continuously infused. Using dynamic 18F-FDG and 13NN Positron Emission Tomography (PET), regional Fb and Q were analysed in 30 regions of interest (ROIs) and normalized by tissue content (Fbn and Qn, respectively). After 20 h, the lung injury showed characteristics of early ARDS, including gas exchange and lung mechanics. PET images of Fbn and Qn showed substantial differences between baseline and lung injury. Lung injury caused a significant change in the Fbn-Qn relationship compared to baseline (p < 0.001). The best models at baseline and lung injury were Fbn = 0.32 + 0.690Qn and Fbn = 1.684Qn-0.538Qn2, respectively. Endotoxine-associated early ARDS changed the relationship between Fb and Q, shifting from linear to curvilinear. Effects of endotoxin exposure on the vasoactive blood flow regulation were most likely the key factor for this change limiting the quantitative accuracy of Fb imaging as a surrogate for regional Q.

Macklin Effect: From Pathophysiology to Clinical Implication.

Air leak syndromes (such as pneumomediastinum, pneumothorax, or subcutaneous emphysema) are frequent complications of acute respiratory distress syndrome (ARDS). Unfortunately, the development of air leaks is associated with worse outcomes. In addition, it has been hypothesized that the development of pneumomediastinum could be a marker of disease severity in patients with respiratory failure receiving noninvasive respiratory support or assisted ventilation. The so-called Macklin effect (or pulmonary interstitial emphysema) is the air dissection of the lung bronchovascular tree from peripheral to central airways following injury to distal alveoli. Ultimately, the progression of the Macklin effect leads to the development of pneumomediastinum, subcutaneous emphysema, or pneumothorax. The Macklin effect is identifiable on a chest computed tomography (CT) scan. The Macklin effect could be an accurate predictor of barotrauma in patients with ARDS (sensitivity = 89.2% [95% CI: 74.6-96.9]; specificity = 95.6% [95% CI: 90.6-98.4]), and may be a marker of disease severity. Accordingly, the detection of the Macklin effect on a chest CT scan could be used to select which patients with ARDS might benefit from different treatment algorithms, including advanced respiratory monitoring, early intubation, or, potentially, the institution of early extracorporeal support with or without invasive ventilation. In this video, the authors summarize the pathophysiology and potential clinical significance and applications of the Macklin effect in patients with acute respiratory failure.

Quantifying heterogeneity in an animal model of acute respiratory distress syndrome, a comparison of inspired sinewave technique to computed tomography.

The inspired sinewave technique (IST) is a non-invasive method to measure lung heterogeneity indices (including both uneven ventilation and perfusion or heterogeneity), which reveal multiple conditions of the lung and lung injury. To evaluate the reproducibility and predicted clinical outcomes of IST heterogeneity values, a comparison with a quantitative lung computed tomography (CT) scan is performed. Six anaesthetised pigs were studied after surfactant depletion by saline-lavage. Paired measurements of lung heterogeneity were then taken with both the IST and CT. Lung heterogeneity measured by the IST was calculated by (a) the ratio of tracer gas outputs measured at oscillation periods of 180 s and 60 s, and (b) by the standard deviation of the modelled log-normal distribution of ventilations and perfusions in the simulation lung. In the CT images, lungs were manually segmented and divided into different regions according to voxel density. A quantitative CT method to calculate the heterogeneity (the Cressoni method) was applied. The IST and CT show good Pearson correlation coefficients in lung heterogeneity measurements (ventilation: 0.71, and perfusion, 0.60, p < 0.001). Within individual animals, the coefficients of determination average ventilation (R2 = 0.53) and perfusion (R2 = 0.68) heterogeneity. Strong concordance rates of 98% in ventilation and 89% when the heterogeneity changes were reported in pairs measured by CT scanning and IST methods. This quantitative method to identify heterogeneity has the potential to replicate CT lung heterogeneity, and to aid individualised care in ARDS.

Inspiratory-expiratory variation of pleural line thickness in neonates with and without acute respiratory failure.

BACKGROUND: There are relatively few data about the ultrasound evaluation of pleural line in patients with respiratory failure. We measured the pleural line thickness during different phases of the respiratory cycle in neonates with and without acute respiratory failure as we hypothesized that this can significantly change. METHODS: Prospective, observational, cohort study performed in an academic tertiary neonatal intensive care unit recruiting neonates with transient tachypnoea of the neonate (TTN), respiratory distress syndrome (RDS) or neonatal acute respiratory distress syndrome (NARDS). Neonates with no lung disease (NLD) were also recruited as controls. Pleural line thickness was measured with high-frequency ultrasound at end-inspiration and end-expiration by two different raters. RESULTS: Pleural line thickness was slightly but significantly higher at end-expiration (0.53 [0.43-0.63] mm) than at end-inspiration (0.5 [0.4-0.6] mm; p = 0.001) for the whole population. End-inspiratory (NLD: 0.45 [0.38-0.53], TTN: 0.49 [0.43-0.59], RDS: 0.53 [0.41-0.62], NARDS: 0.6 [0.5-0.7] mm) and -expiratory (NLD: 0.47 [0.42-0.56], TTN: 0.48 [0.43-0.61], RDS: 0.53 [0.46-0.65], NARDS: 0.61 [0.54-0.72] mm) thickness were significantly different (overall p = 0.021 for both), between the groups although the absolute differences were small. The inter-rater agreement was optimal (ICC: 0.95 (0.94-0.96)). Coefficient of variation was 2.8% and 2.5% for end-inspiratory and end-expiratory measurements, respectively. These findings provide normative data of pleural line thickness for the most common forms of neonatal acute respiratory failure and are useful to design future studies to investigate possible clinical applications.

Lung ultrasound score and in-hospital mortality of adults with acute respiratory distress syndrome: a meta-analysis.

BACKGROUND: Lung ultrasound (LUS) score could quantitatively reflect the lung aeration, which has been well applied in critically ill patients. The aim of the systematic review and meta-analysis was to evaluate the association between LUS score at admission and the risk of in-hospital mortality of adults with acute respiratory distress syndrome (ARDS). METHODS: Toachieve the objective of this meta-analysis, we conducted a thorough search of PubMed, Embase, Cochrane Library, and the Web of Science to identify relevant observational studies with longitudinal follow-up. We employed random-effects models to combine the outcomes, considering the potential influence of heterogeneity. RESULTS: Thirteen cohort studies with 1,022 hospitalized patients with ARDS were included. Among them, 343 patients (33.6%) died during hospitalization. The pooled results suggested that the LUS score at admission was higher in non-survivors as compared to survivors (standardized mean difference = 0.73, 95% confidence interval [CI]: 0.55 to 0.91, p < 0.001; I2 = 25%). Moreover, a high LUS score at admission was associated with a higher risk of in-hospital mortality of patients with ARDS (risk ratio: 1.44, 95% CI: 1.14 to 1.81, p = 0.002; I2 = 46%). Subgroup analyses showed consistent results in studies with LUS score analyzed with 12 or 16 lung regions, and in studies reporting mortality during ICU or within 1-month hospitalization. CONCLUSION: Our findings suggest that a high LUS score at admission may be associated with a high risk of in-hospital mortality of patients with ARDS.

A novel tree shrew model of lipopolysaccharide-induced acute respiratory distress syndrome.

INTRODUCTION: Acute respiratory distress syndrome (ARDS) is a leading cause of respiratory failure, with substantial attributable morbidity and mortality. The small animal models that are currently used for ARDS do not fully manifest all of the pathological hallmarks of human patients, which hampers both the studies of disease mechanism and drug development. OBJECTIVES: To examine whether the phenotypic changes of primate-like tree shrews in response to a one-hit lipopolysaccharides (LPS) injury resemble human ARDS features. METHODS: LPS was administered to tree shrews through intratracheal instillation; then, the animals underwent CT or PET/CT imaging to examine the changes in the structure and function of the whole lung. The lung histology was analyzed by H&E staining and immunohistochemical staining of inflammatory cells. RESULTS: Results demonstrated that tree shrews exhibited an average survival time of 3-5 days after LPS insult, as well as an obvious symptom of dyspnea before death. The ratios of PaO2 to FiO2 (P/F ratio) were close to those of moderate ARDS in humans. CT imaging showed that the scope of the lung injury in tree shrews after LPS treatment were extensive. PET/CT imaging with 18F-FDG displayed an obvious inflammatory infiltration. Histological analysis detected the formation of a hyaline membrane, which is usually present in human ARDS. CONCLUSION: This study established a lung injury model with a primate-like small animal model and confirmed that they have similar features to human ARDS, which might provide a valuable tool for translational research.

Causes of Hypoxemia in COVID-19 Acute Respiratory Distress Syndrome: A Combined Multiple Inert Gas Elimination Technique and Dual-energy Computed Tomography Study.

BACKGROUND: Despite the fervent scientific effort, a state-of-the art assessment of the different causes of hypoxemia (shunt, ventilation-perfusion mismatch, and diffusion limitation) in COVID-19 acute respiratory distress syndrome (ARDS) is currently lacking. In this study, the authors hypothesized a multifactorial genesis of hypoxemia and aimed to measure the relative contribution of each of the different mechanism and their relationship with the distribution of tissue and blood within the lung. METHODS: In this cross-sectional study, the authors prospectively enrolled 10 patients with COVID-19 ARDS who had been intubated for less than 7 days. The multiple inert gas elimination technique (MIGET) and a dual-energy computed tomography (DECT) were performed and quantitatively analyzed for both tissue and blood volume. Variables related to the respiratory mechanics and invasive hemodynamics (PiCCO [Getinge, Sweden]) were also recorded. RESULTS: The sample (51 ± 15 yr; Pao2/Fio2, 172 ± 86 mmHg) had a mortality of 50%. The MIGET showed a shunt of 25 ± 16% and a dead space of 53 ± 11%. Ventilation and perfusion were mismatched (LogSD, Q, 0.86 ± 0.33). Unexpectedly, evidence of diffusion limitation or postpulmonary shunting was also found. In the well aerated regions, the blood volume was in excess compared to the tissue, while the opposite happened in the atelectasis. Shunt was proportional to the blood volume of the atelectasis (R2 = 0.70, P = 0.003). V˙A/Q˙T mismatch was correlated with the blood volume of the poorly aerated tissue (R2 = 0.54, P = 0.016). The overperfusion coefficient was related to Pao2/Fio2 (R2 = 0.66, P = 0.002), excess tissue mass (R2 = 0.84, P < 0.001), and Etco2/Paco2 (R2 = 0.63, P = 0.004). CONCLUSIONS: These data support the hypothesis of a highly multifactorial genesis of hypoxemia. Moreover, recent evidence from post-mortem studies (i.e., opening of intrapulmonary bronchopulmonary anastomosis) may explain the findings regarding the postpulmonary shunting. The hyperperfusion might be related to the disease severity.

Use of Lung Ultrasound in the New Definitions of Acute Respiratory Distress Syndrome Increases the Occurrence Rate of Acute Respiratory Distress Syndrome.

OBJECTIVES: To assess the effect of incorporating bilateral abnormalities as detected by lung ultrasound (LUS) in the Kigali modification and the New Global definition of acute respiratory distress syndrome (ARDS) on the occurrence rate of ARDS. DESIGN: Post hoc analysis of a previously published prospective cohort study. SETTING: An academic mixed medical-surgical ICU. PATIENTS: The original study included critically ill adults with any opacity on chest radiography in whom subsequent LUS was performed. Patients with ARDS according to the Berlin definition, COVID-19 patients and patients with major thorax trauma were excluded. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: LUS was performed within 24 hours of chest radiography and the presence of unilateral and bilateral abnormalities on LUS and chest radiograph (opacities) was scored. Subsequently, the Kigali modification and the New Global definition of ARDS were applied by two independent researchers on the patients with newly found bilateral opacities. Of 120 patients, 116 were included in this post hoc analysis. Thirty-three patients had bilateral opacities on LUS and unilateral opacities on chest radiograph. Fourteen of these patients had ARDS according to the Kigali modification and 12 had ARDS according to the New Global definition. The detected LUS patterns were significantly different between patients with and without ARDS ( p = 0.004). An A-profile with a positive PosteroLateral Alveolar and/or Pleural Syndrome was most prevalent in patients without ARDS, whereas heterogeneous and mixed A, B, and C patterns were most prevalent in patients with ARDS. CONCLUSION: The addition of bilateral abnormalities as detected by LUS to the Kigali modification and the New Global definition increases the occurrence rate of the ARDS. The nomenclature for LUS needs to be better defined as LUS patterns differ between patients with and without ARDS. Incorporating well-defined LUS criteria can increase specificity and sensitivity of new ARDS definitions.

Preload Responsiveness in Patients With Acute Respiratory Distress Syndrome Managed With Extracorporeal Membrane Oxygenation.

A restrictive fluid strategy is recommended in patients with acute respiratory distress syndrome (ARDS) managed with venovenous extracorporeal membrane oxygenation (VV ECMO). However, there are no established predictors for preload responsiveness in these patients. In 20 ARDS patients managed with VV ECMO, transesophageal echocardiography was used to repeatedly evaluate dynamic parameters of the left (velocity and stroke volume variation) and right ventricular outflow tract (velocity [respiratory variations of the maximal Doppler velocity in the truncus pulmonalis {ΔV max TP}] and velocity time integral [respiratory variation of the velocity time integral measured in the truncus pulmonalis {ΔVTI_TP}] variation in the truncus pulmonalis), the diameter variation in the superior and inferior vena cava and stroke volume variation measured by pulse contour analysis (SVV_PCA). Patients were categorized as responders and nonresponders according to an increase in stroke volume measured by echocardiography during a Passive Leg Raise Test with a cutoff value ≥10%. The final analysis includes 86 measurements. Predictive values for preload responsiveness were found for ΔV max TP (area under the curve [AUC] of 0.64), ΔVTI_TP (AUC 0.67), and SVV_PCA (AUC 0.74). In conclusion, SVV_PCA and, to a lesser extent, ΔV max TP and ΔVTI_TP are the most accurate parameters to predict preload responsiveness in ARDS patients managed with VV ECMO. Transesophageal echocardiography offers no advantages over pulse contour analysis for predicting preload responsiveness and provides only intermittent monitoring and assessment.

Structural Brain Injury on Brain Magnetic Resonance Imaging in Acute Respiratory Distress Syndrome.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is an acute inflammatory respiratory failure condition that may be associated with brain injury. We aimed to describe the types of structural brain injuries detected by brain magnetic resonance imaging (MRI) among patients with ARDS. METHODS: We retrospectively reviewed and collected data on brain injuries as detected by brain MRI during index hospitalization of all patients with ARDS at a single tertiary center in the United States from January 2010 to October 2018 (pre-COVID era). Structural brain injuries were classified as cerebral ischemia (ischemic infarct and hypoxic-ischemic brain injury) or cerebral hemorrhage (intraparenchymal hemorrhage, cerebral microbleeds, subarachnoid hemorrhage, and subdural hematoma). Descriptive statistics were conducted. RESULTS: Of the 678 patients with ARDS, 66 (9.7%) underwent brain MRI during their ARDS illness. The most common indication for brain MRI was encephalopathy (45.4%), and the median time from hospital admission to MRI was 10 days (interquartile range 4-17). Of 66 patients, 29 (44%) had MRI evidence of brain injury, including cerebral ischemia in 33% (22 of 66) and cerebral hemorrhage in 21% (14 of 66). Among those with cerebral ischemia, common findings were bilateral globus pallidus infarcts (n = 7, 32%), multifocal infarcts (n = 5, 23%), and diffuse hypoxic-ischemic brain injury (n = 3, 14%). Of those with cerebral hemorrhage, common findings were cerebral microbleeds (n = 12, 86%) and intraparenchymal hemorrhage (n = 2, 14%). Patients with ARDS with cerebral hemorrhage had significantly greater use of rescue therapies, including prone positioning (28.6% vs. 5.8%, p = 0.03), inhaled vasodilator (35.7% vs. 11.5%, p = 0.046), and recruitment maneuver (14.3% vs. 0%, p = 0.04). CONCLUSIONS: Structural brain injury was not uncommon among selected patients with ARDS who underwent brain MRI. The majority of brain injuries seen were bilateral globus pallidus infarcts and cerebral microbleeds.

Lung ultrasound score for monitoring the withdrawal of extracorporeal membrane oxygenation on neonatal acute respiratory distress syndrome.

BACKGROUND: Extracorporeal membrane oxygenation (ECMO) is considered an efficient and life-saving treatment for neonatal severe acute respiratory distress syndrome (ARDS). Bedside lung ultrasound (LUS) is an attractive and feasible method for evaluating neonatal ARDS. OBJECTIVE: To evaluate the value of LUS score at veno-arterial (V-A) ECMO withdrawal in neonatal patients with severe acute ARDS. METHODS: A retrospective preliminary study was conducted in our cardiac intensive care unit from June 2021 to June 2022. Eight severe ARDS neonates who received V-A ECMO were enroled in this study. LUS was measured daily during ECMO and when weaning off ECMO. The relationships between the LUS score and ECMO parameters (blood flow and the sweep gas of FiO2) were assessed. RESULTS: (1) There was a significant improvement in LUS score by ECMO treatment. And, various diagnostic signs of lung ultrasound were detected during ECMO, including pulmonary edema (7 neonates) and lung consolidation (4 neonates), followed by pleural effusion (1 neonate) and bilateral white lung (1 neonate). (2) A total of 12 trials for weaning off ECMO were carried out, of which four failed, but all eight neonates finally succeeded in passing the weaning trial. LUS score of 21 or less was defined as a cut-off value for predicting ECMO weaning success. During ECMO treatment, LUS score was positively correlated with ECMO blood flow (r = 0.866, P < 0.05). CONCLUSIONS: LUS can be used to evaluate the various lung diagnostic signs in ARDS neonatal patients during ECMO treatment, and the LUS score under ECMO treatment decreases over time. The reduction in LUS score is associated with lower ECMO blood flow. LUS score is regarded as a predictor of ECMO weaning success.

Feasibility of Prone Positioning for Brain-injured Patients with Severe Acute Respiratory Distress Syndrome: A Systematic Review and Pilot Study (ProBrain).

BACKGROUND: Prone position is a key component to treat hypoxemia in patients with severe acute respiratory distress syndrome. However, most studies evaluating it exclude patients with brain injuries without any medical evidence. METHODS: This study includes a systematic review to determine whether brain-injured patients were excluded in studies evaluating prone position on acute respiratory distress syndrome; a prospective study including consecutive brain-injured patients needing prone position. The primary endpoint was the evaluation of cerebral blood flow using transcranial Doppler after prone positioning. Secondary outcomes were intracranial pressure, cerebral perfusion pressure, and tissue oxygen pressure. RESULTS: From 8,183 citations retrieved, 120 studies were included in the systematic review. Among them, 90 studies excluded brain-injured patients (75%) without any justification, 16 included brain-injured patients (4 randomized, 7 nonrandomized studies, 5 retrospective), and 14 did not retrieve brain-injured data. Eleven patients were included in the authors' pilot study. No reduction of cerebral blood flow surrogates was observed during prone positioning, with diastolic speed values (mean ± SD) ranging from 37.7 ± 16.2 cm/s to 45.2 ± 19.3 cm/s for the right side (P = 0.897) and 39.6 ± 18.2 cm/s to 46.5 ± 21.3 cm/s for the left side (P = 0.569), and pulsatility index ranging from 1.14 ± 0.31 to 1.0 ± 0.32 for the right side (P = 0.145) and 1.14 ± 0.31 to 1.02 ± 0.2 for the left side (P = 0.564) before and during prone position. CONCLUSIONS: Brain-injured patients are largely excluded from studies evaluating prone position in acute respiratory distress syndrome. However, cerebral blood flow seems not to be altered considering increasing of mean arterial pressure during the session. Systematic exclusion of brain-injured patients appears to be unfounded, and prone position, while at risk in brain-injured patients, should be evaluated on these patients to review recommendations, considering close monitoring of neurologic and hemodynamic parameters.

Setting positive end-expiratory pressure: lung and diaphragm ultrasound.

PURPOSE OF REVIEW: The purpose of this review is to summarize the role of lung ultrasound and diaphragm ultrasound in guiding ventilator settings with an emphasis on positive end-expiratory pressure (PEEP). Recent advances for using ultrasound to assess the effects of PEEP on the lungs and diaphragm are discussed. RECENT FINDINGS: Lung ultrasound can accurately diagnose the cause of acute respiratory failure, including acute respiratory distress syndrome and can identify focal and nonfocal lung morphology in these patients. This is essential in determining optimal ventilator strategy and PEEP level. Assessment of the effect of PEEP on lung recruitment using lung ultrasound is promising, especially in the perioperative setting. Diaphragm ultrasound can monitor the effects of PEEP on the diaphragm, but this needs further validation. In patients with an acute exacerbation of chronic obstructive pulmonary disease, diaphragm ultrasound can be used to predict noninvasive ventilation failure. Lung and diaphragm ultrasound can be used to predict weaning outcome and accurately diagnose the cause of weaning failure. SUMMARY: Lung and diaphragm ultrasound are useful for diagnosing the cause of respiratory failure and subsequently setting the ventilator including PEEP. Effects of PEEP on lung and diaphragm can be monitored using ultrasound.

Electrical Impedance Tomography to Monitor Hypoxemic Respiratory Failure.

Hypoxemic respiratory failure is one of the leading causes of mortality in intensive care. Frequent assessment of individual physiological characteristics and delivery of personalized mechanical ventilation (MV) settings is a constant challenge for clinicians caring for these patients. Electrical impedance tomography (EIT) is a radiation-free bedside monitoring device that is able to assess regional lung ventilation and changes in aeration. With real-time tomographic functional images of the lungs obtained through a thoracic belt, clinicians can visualize and estimate the distribution of ventilation at different ventilation settings or following procedures such as prone positioning. Several studies have evaluated the performance of EIT to monitor the effects of different MV settings in patients with acute respiratory distress syndrome, allowing more personalized MV. For instance, EIT could help clinicians find the positive end-expiratory pressure that represents a compromise between recruitment and overdistension and assess the effect of prone positioning on ventilation distribution. The clinical impact of the personalization of MV remains to be explored. Despite inherent limitations such as limited spatial resolution, EIT also offers a unique noninvasive bedside assessment of regional ventilation changes in the ICU. This technology offers the possibility of a continuous, operator-free diagnosis and real-time detection of common problems during MV. This review provides an overview of the functioning of EIT, its main indices, and its performance in monitoring patients with acute respiratory failure. Future perspectives for use in intensive care are also addressed.

Dynamic relative regional lung strain estimated by computed tomography and electrical impedance tomography in ARDS patients.

BACKGROUND: In the acute distress respiratory syndrome (ARDS), specific lung regions can be exposed to excessive strain due to heterogeneous disease, gravity-dependent lung collapse and injurious mechanical ventilation. Computed tomography (CT) is the gold standard for regional strain assessment. An alternative tool could be the electrical impedance tomography (EIT). We aimed to determine whether EIT-based methods can predict the dynamic relative regional strain (DRRS) between two levels of end-expiratory pressure (PEEP) in gravity-non-dependent and dependent lung regions. METHODS: Fourteen ARDS patients underwent CT and EIT acquisitions (at end-inspiratory and end-expiratory) at two levels of PEEP: a low-PEEP based on ARDS-net strategy and a high-PEEP titrated according to EIT. Three EIT-based methods for DRRS were compared to relative CT-based strain: (1) the change of the ratio between EIT ventilation and end-expiratory lung impedance in arbitrary units ([ΔZAU low-PEEP/EELIAU low-PEEP]/[ΔZAU high-PEEP/EELIAU high-PEEP]), (2) the change of ΔZ/EELI ratio calibrated to mL ([ΔZml low-PEEP/EELIml low-PEEP]/[ΔZml high-PEEP/EELIml high-PEEP]) using CT data, and (3) the relative change of ∆ZAU (∆ZAU low-PEEP/∆ZAU high-PEEP). We performed linear regressions analysis and calculated bias and limits of agreement to assess the performance of DRRS by EIT in comparison with CT. RESULTS: The DRRS assessed by (ΔZml low-PEEP/EELIml low-PEEP)/(ΔZml high-PEEP/EELIml high-PEEP) and ∆ZAU low-PEEP/∆ZAU high-PEEP showed good relationship and agreement with the CT method (R2 of 0.9050 and 0.8679, respectively, in non-dependent region; R2 of 0.8373 and 0.6588, respectively, in dependent region; biases ranging from - 0.11 to 0.51 and limits of agreement ranging from - 0.73 to 1.16 for both methods and lung regions). Conversely, DRRS based on EELIAU ([ΔZAU low-PEEP/EELIAU low-PEEP]/[ΔZAU high-PEEP/EELIAU high-PEEP]) exhibited a weak negative relationship and poor agreement with the CT method for both non-dependent and dependent regions (R2 ~ 0.3; bias of 3.11 and 2.08, and limits of agreement of - 2.13 to 8.34 and from - 1.49 to 5.64, respectively). CONCLUSION: Changes in DRRS during a PEEP trial in ARDS patients could be monitored using EIT, based on changes in ΔZmL/EELIml and ∆ZAU. The relative change ∆ZAU offers the advantage of not requiring CT data for calibration.