Respiratory mechanics in patients with acute respiratory distress syndrome

Previous Coronavirus Disease-2019 Infection and Lung Mechanics in Surgical Patients: A Hospital Registry Study

BACKGROUND

Long-term pulmonary complications have been reported after a coronavirus disease-2019 (COVID-19). We hypothesized that a history of COVID-19 is associated with a measurable decrease in baseline respiratory system compliance in patients undergoing general anesthesia.

METHODS

In this hospital registry study, we included adult patients undergoing general anesthesia between January 2020 and March 2022 at a tertiary health care network in Massachusetts. We excluded patients with an American Society of Anesthesiologists physical status >IV, laryngoscopic surgeries, and patients who arrived intubated. The primary exposure was a history of COVID-19. The primary outcome was baseline respiratory system compliance (mL/cmH2O). Effects of severity of infection, surges (Alpha1, Alpha2, Delta, and Omicron), patient demographics, and time between infection and assessment of compliance were investigated.

RESULTS

A total of 19,921 patients were included. Approximately 1386 (7.0%) patients had a history of COVID-19. A history of COVID-19 at any time before surgery was associated with a measurably lower baseline respiratory system compliance (ratio of meansadj = 0.96; 95% confidence interval [CI], 0.94-0.97; P < .001; adjusted compliance difference: -1.6 mL/cmH2O). The association was more pronounced in patients with a severe form of COVID-19 (ratio of meansadj = 0.95; 95% CI, 0.90-0.99; P = .02, adjusted compliance difference: -2 mL/cmH2O). Alpha1, Alpha2, and Delta surges, but not Omicron, led to a lower baseline respiratory system compliance (P < .001, P = .02, and P < .001). The Delta surge effect was magnified in Hispanic ethnicity (P-for-interaction = 0.003; ratio of meansadj = 0.83; 95% CI, 0.74-0.93; P = .001; adjusted compliance difference: -4.6 mL/cmH2O).

CONCLUSIONS

A history of COVID-19 infection during Alpha1, Alpha2, and Delta surges was associated with a measurably lower baseline respiratory system compliance.

Analysis of Survival Modification by Furosemide Use in a Cohort of Hospitalized COVID-19 Patients with Severe or Critical Disease in Mexico: Due to Its Chemical Structure, Furosemide Is More than Just a Diuretic

In the ongoing fight against Coronavirus Disease 2019 (COVID-19), researchers are exploring potential treatments to improve outcomes, especially in severe cases. This includes investigating the repurposing of existing medications, such as furosemide, which is widely available. This study aimed to evaluate the impact of furosemide on mortality rates among COVID-19 patients with severe or critical illness. We assessed a cohort of 515 hospitalized adults who experienced a high mortality rate of 43.9%. Using a multivariate analysis with adjusted risk ratios (AdRRs), factors like smoking (AdRR 2.48, 95% CI 1.53-4.01, p < 0.001), a high Pneumonia Severity Index (PSI) score (AdRR 7.89, 95% CI 5.82-10.70, p < 0.001), mechanical ventilation (AdRR 23.12, 95% CI 17.28-30.92, p < 0.001), neutrophilia (AdRR 2.12, 95% CI 1.52-2.95, p < 0.001), and an elevated neutrophil-to-lymphocyte ratio (NLR) (AdRR 2.39, 95% CI 1.72-3.32, p < 0.001) were found to increase mortality risk. In contrast, vaccination and furosemide use were associated with reduced mortality risk (AdRR 0.58, p = 0.001 and 0.60, p = 0.008; respectively). Furosemide showed a pronounced survival benefit in patients with less severe disease (PSI < 120) and those not on hemodialysis, with mortality rates significantly lower in furosemide users (3.7% vs. 25.7%). A Kaplan-Meier analysis confirmed longer survival and better oxygenation levels in patients treated with furosemide. Furthermore, a Structure-Activity Relationship analysis revealed that furosemide's sulfonamide groups may interact with cytokine sites such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), potentially explaining its beneficial effects in COVID-19 management. These findings suggest that furosemide could be a beneficial treatment option in certain COVID-19 patient groups, enhancing survival and improving oxygenation.

Tidal volume selection in volume-controlled ventilation guided by driving pressure versus actual body weight in healthy anesthetized and mechanically ventilated dogs: A randomized crossover trial

OBJECTIVE

To compare static compliance of the respiratory system (CstRS) and the ratio of partial pressure of end-tidal to arterial carbon dioxide (Pe'CO2/PaCO2), in healthy dogs using two approaches for tidal volume (VT) selection during volume-controlled ventilation: body mass based and driving pressure (ΔPaw) guided.

STUDY DESIGN

Randomized, nonblinded, crossover, clinical trial.

ANIMALS

A total of 19 client-owned dogs anesthetized for castration and ovariohysterectomy.

METHODS

After a stable 10 minute baseline, each dog was mechanically ventilated with a VT selection strategy, randomized to a constant VT of 15 mL kg-1 of actual body mass (VTBW) or ΔPaw-guided VT (VTΔP) of 7-8 cmH2O. Both strategies used an inspiratory time of 1 second, 20% end-inspiratory pause, 4 cmH2O positive end-expiratory pressure and fraction of inspired oxygen of 0.4. Respiratory frequency was adjusted to maintain Pe'CO2 between 35 and 40 mmHg. Respiratory mechanics, arterial blood gases and Pe'CO2/PaCO2 were assessed. Continuous variables are presented as mean ± SD or median (interquartile range; quartiles 1-3), depending on distribution, and compared with Wilcoxon signed-rank tests.

RESULTS

The VT was significantly higher in dogs ventilated with VTΔP than with VTBW strategy (17.20 ± 4.04 versus 15.03 ± 0.60 mL kg-1, p = 0.036). CstRS was significantly higher with VTΔP than with VTBW strategy [2.47 (1.86-2.86) versus 2.25 (1.79-2.58) mL cmH2O-1 kg-1, p = 0.011]. There were no differences in Pe'CO2/PaCO2 between VTΔP and VTBW strategies (0.94 ± 0.06 versus 0.92 ± 0.06, p = 0.094). No discernible difference in ΔPaw was noted between the strategies.

CONCLUSIONS AND CLINICAL RELEVANCE

While no apparent difference was observed in the Pe'CO2/PaCO2 between the VT selection strategies employed, CstRS significantly increased during the VTΔP approach. A future trial should explore if VTΔP improves perioperative gas exchange and prevents lung damage.

Estimation of inspiratory effort using airway occlusion maneuvers in ventilated children: a secondary analysis of an ongoing randomized trial testing a lung and diaphragm protective ventilation strategy

BACKGROUND

Monitoring respiratory effort in ventilated patients is important to balance lung and diaphragm protection. Esophageal manometry remains the gold standard for monitoring respiratory effort but is invasive and requires expertise for its measurement and interpretation. Airway pressures during occlusion maneuvers may provide an alternative, although pediatric data are limited. We sought to determine the correlation between change in esophageal pressure during tidal breathing (∆Pes) and airway pressure measured during three airway occlusion maneuvers: (1) expiratory occlusion pressure (Pocc), (2) airway occlusion pressure (P0.1), and (3) respiratory muscle pressure index (PMI) in children. We also sought to explore pediatric threshold values for these pressures to detect excessive or insufficient respiratory effort.

METHODS

Secondary analysis of physiologic data from children between 1 month and 18 years of age with acute respiratory distress syndrome enrolled in an ongoing randomized clinical trial testing a lung and diaphragm protective ventilation strategy (REDvent, R01HL124666). ∆Pes, Pocc, P0.1, and PMI were measured. Repeated measure correlations were used to investigate correlation coefficients between ∆Pes and the three measures, and linear regression equations were generated to identify potential therapeutic thresholds.

RESULTS

There were 653 inspiratory and 713 expiratory holds from 97 patients. Pocc had the strongest correlation with ∆Pes (r = 0.68), followed by PMI (r = 0.60) and P0.1 (r = 0.42). ∆Pes could be reliably estimated using the regression equation ∆Pes = 0.66 [Formula: see text] Pocc (R2 = 0.82), with Pocc cut-points having high specificity and moderate sensitivity to detect respective ∆Pes thresholds for high and low respiratory effort. There were minimal differences in the relationship between Pocc and ∆Pes based on age (infant, child, adolescent) or mode of ventilation (SIMV versus Pressure Support), although these differences were more apparent with P0.1 and PMI.

CONCLUSIONS

Airway occlusion maneuvers may be appropriate alternatives to esophageal pressure measurement to estimate the inspiratory effort in children, and Pocc represents the most promising target.

TRIAL REGISTRATION

NCT03266016; August 23, 2017.

Reliability of Respiratory System Compliance Calculation During Assisted Mechanical Ventilation: A Retrospective Study

OBJECTIVES

To compare respiratory system compliance (C rs ) calculation during controlled mechanical ventilation (MV) and, subsequently, during assisted MV.

DESIGN

This is a single-center, retrospective, observational study.

SETTING

This study was conducted on patients admitted to Neuro-ICU of Niguarda Hospital (tertiary referral hospital).

PATIENTS

We analyzed every patient greater than or equal to 18 years old having a C rs measurement in controlled and in assisted MV within 60 minutes. Plateau pressure (P plat ) was considered reliable if it was deemed visually stable for at least 2 seconds.

INTERVENTIONS

Inspiratory pause was incorporated to detect P plat in controlled and assisted MV. Calculation of C rs and driving pressure were achieved.

MEASUREMENTS AND MAIN RESULTS

A total of 101 patients were studied. An acceptable agreement was found (Bland-Altman plot bias -3.9, level of agreement upper 21.6, lower -29.6). C rs in assisted MV was 64.1 (52.6-79.3) and in controlled MV it was 61.2 (50-71.2) mL/cm H 2o ( p = 0.006). No statistical difference was found in C rs (assisted vs controlled MV) when peak pressure was lower than P plat nor when peak pressure was higher than P plat .

CONCLUSIONS

A P plat visually stable for at least 2 seconds leads to reliable C rs calculation during assisted MV.

Protective effect of β-glucan on Poly(I:C)-induced acute lung injury/inflammation: Therapeutic implications of viral infections in the respiratory system

AIMS

Acute lung inflammation, particularly acute respiratory distress syndrome (ARDS), is caused by a variety of pathogens including bacteria and viruses. β-Glucans have been reported to possess both anti-inflammatory and immunomodulatory properties. The current study evaluated the therapeutic effect of β-glucans on polyinosinic:polycytidylic acid (Poly(I:C)) induced lung inflammation in both hamster and mice models.

MAIN METHODS

Poly(I:C)-induced ALI/inflammation models were developed in hamsters (2.5 mg/kg) and mice (2 mg/kg) by delivering the Poly(I:C) intratracheally, and followed with and without β-glucan administration. After treatment, lung mechanics were assessed and lung tissues were isolated and analyzed for mRNA/protein expression, and histopathological examinations.

KEY FINDINGS

Poly(I:C) administration, caused a significant elevation of inflammatory marker's expression in lung tissues and showed abnormal lung mechanics in mice and hamsters. Interestingly, treatment with β-glucan significantly (p < 0.001) reversed the Poly(I:C)-induced inflammatory events and inflammatory markers expression in both mRNA (IL-6, IL-1β, TNF-α, CCL2 and CCL7) and protein levels (TNF-α, CD68, myeloperoxidase, neutrophil elastase, MUC-5Ac and iNOS). Lung functional assays revealed that β-glucan treatment significantly improved lung mechanics. Histopathological analysis showed that β-glucan treatment significantly attenuated the Poly(I:C) induced inflammatory cell infiltration, injury and goblet cell population in lung tissues. Consistent with these findings, β-glucan treatment markedly reduced the number of neutrophils and macrophages in lung tissues. Our findings further demonstrated that β-glucan could reduce inflammation by suppressing the MAPK pathway.

SIGNIFICANCE

These results suggested that β-glucan may attenuate the pathogenic effects of Poly(I:C)-induced ALI/ARDS via modulating the MAPK pathway, indicating β-glucan as a possible therapeutic agent for the treatment of viral-pulmonary inflammation/injury.

Exogenous surfactant reduces inflammation and redox imbalance in rats under prone or supine mechanical ventilation

Mechanical ventilation (MV) is a lifesaving therapy for patients with acute or chronic respiratory failure. Despite, it can also cause lung injury by inducing or worsening inflammatory responses and oxidative stress. Several clinical approaches have protective effects on the lungs, including the prone position and exogenous surfactant; however, few studies have evaluated the association between the two strategies, especially in individuals without previous lung injury. We tested the hypothesis that the effects of the homogenization in lung aeration caused by the prone position in association with the anti-inflammatory properties of exogenous surfactant pre-treatment could have a cumulative protective effect against ventilator-induced lung injury. Therefore, Wistar rats were divided into four experimental groups: Mechanical Ventilation in Supine Position (MVSP), Mechanical Ventilation in Prone position (MVPP), Mechanical Ventilation in Supine Position + surfactant (MVSPS), and Mechanical Ventilation in Prone Position + Surfactant (MVPPS). The intranasal instillation of a porcine surfactant (Curosurf®) was performed in the animals of MVSPS and MVPPS 1 h before the MV, all the rats were subjected to MV for 1 h. The prone position in association with surfactant decreased mRNA expression levels of pro-inflammatory cytokines in ventilated animals compared to the supine position; in addition, the NfκB was lower in MVPP, MVSPS and MVPPS when compared to MVSP. However, it had no effects on oxidative stress caused by MV. Pre-treatment with exogenous surfactant was more efficient in promoting lung protection than the prone position, as it also reduced oxidative damage in the lung parenchyma. Nevertheless, the surfactant did not cause additional improvements in most parameters that were also improved by the prone position. Our results indicate that the pre-treatment with exogenous surfactant, regardless of the position adopted in mechanical ventilation, preserves the original lung histoarchitecture, reduces redox imbalance, and reduces acute inflammatory responses caused by mechanical ventilation in healthy adult Wistar rats.

Ferrostatin-1 alleviates ventilator-induced lung injury by inhibiting ferroptosis

Ventilator-induced lung injury (VILI) has become an increasingly common complication in the clinic concerning mechanical ventilation. Previous research showed that VILI is the result of a response to cascade inflammation; however, the inflammatory mechanism involved remains unclear. As a newly recognized form of cell death, ferroptosis can release damage-related molecules (DAMPs) to trigger and amplify the inflammatory response and is involved in several inflammatory diseases. The present study aimed to investigate a previously unrecognized role of ferroptosis in VILI. A mouse model of VILI and a model of cyclic stretching (CS)-induced lung epithelial cell injury were established. Mice and cells were pretreated with ferrostain-1, an inhibitor of ferroptosis. Lung tissue and cells were then harvested to determine lung injury, inflammatory responses, indicators and protein expression associated with ferroptosis. Compared to the control group, mice subjected to high tidal volumes (HTV) for 4 h showed more severe pulmonary edema and inflammation and the activation of ferroptosis. Ferrostain-1 significantly ameliorated histological injury and inflammation in the VILI mouse and alleviated CS-induced lung epithelial cell injury. Mechanistically, ferrostain-1 markedly limited the activation of ferroptosis and recovered functionality of the SLC7A11/GPX4 axis both in vitro and in vivo, thus demonstrating its potential as a novel therapeutic target for VILI.

An in silico approach to understanding the interaction between cardiovascular and pulmonary lymphatic dysfunction

The lung is extremely sensitive to interstitial fluid balance, yet the role of pulmonary lymphatics in lung fluid homeostasis and its interaction with cardiovascular pressures is poorly understood. In health, there is a fine balance between fluid extravasated from the pulmonary capillaries into the interstitium and the return of fluid to the circulation via the lymphatic vessels. This balance is maintained by an extremely interdependent system governed by pressures in the fluids (air and blood) and tissue (interstitium), lung motion during breathing, and the permeability of the tissues. Chronic elevation in left atrial pressure (LAP) due to left heart disease increases the capillary blood pressure. The consequent fluid accumulation in the delicate lung tissue increases its weight, decreases its compliance, and impairs gas exchange. This interdependent system is difficult, if not impossible, to study experimentally. Computational modeling provides a unique perspective to analyze fluid movement in the cardiopulmonary vasculature in health and disease. We have developed an initial in silico model of pulmonary lymphatic function using an anatomically structured model to represent ventilation and perfusion and underlying biophysical laws governing fluid transfer at the interstitium. This novel model was tested against increased LAP and noncardiogenic effects (increased permeability). The model returned physiologically reasonable values for all applications, predicting pulmonary edema when LAP reached 25 mmHg and with increased permeability.NEW & NOTEWORTHY This model presents a novel approach to understanding the interaction between cardiac dysfunction and pulmonary lymphatic function, using anatomically structured models and biophysical equations to estimate regional variation in fluid transport from blood to interstitial and lymphatic flux. This fluid transport model brings together advanced models of ventilation, perfusion, and lung mechanics to produce a detailed model of fluid transport in health and various altered pathological conditions.

Gastric Aspiration and Ventilator-Induced Model of Acute Respiratory Distress Syndrome in Swine

INTRODUCTION

Mainstays of current treatment for acute respiratory distress syndrome (ARDS) focus on supportive care and rely on intrinsic organ recovery. Animal models of ARDS are often limited by systemic injury. We hypothesize that superimposing gastric aspiration and ventilator-induced injury will induce a lung-specific injury model of severe ARDS.

MATERIALS AND METHODS

Adult swine (n = 8) were subject to a 12 h injury development period followed by 24 h of post-injury monitoring. Lung injury was induced with gastric secretions (3 cc/kg body weight/lung, pH 1-2) instilled to bilateral mainstem bronchi under direct bronchoscopic vision. Ventilator settings within the injury period contradicted baseline settings using high tidal volumes and low positive end-expiratory pressure. Baseline settings were restored following the injury period. Arterial oxygenation and lung compliance were monitored.

RESULTS

At 12 h, PaO2/FiO2 ratio and static and dynamic compliance were significantly reduced from baseline (P < 0.05). During the postinjury period, animals showed no signs of recovery in PaO2/FiO2 ratio and lung compliance. Lung edema (wet/dry weight ratio) of injured lungs was significantly elevated versus noninjured lungs (8.5 ± 1.7 versus 5.6 ± 0.3, P = 0.009). Expression of proinflammatory cytokines IL-6 and IL-8 were significantly elevated in injured lungs (P < 0.05).

CONCLUSIONS

Twelve hours of high tidal volume and low positive end-expiratory pressure in conjunction with low-pH gastric content instillation produces significant acute lung injury in swine. This large animal model may be useful for testing severe ARDS treatment strategies.

Correlation between serum surfactant protein-D level with respiratory compliance and acute respiratory distress syndrome in critically ill COVID-19 Patients: A retrospective observational study

Background

Acute respiratory distress syndrome (ARDS) is one of the manifestations of severe coronavirus disease 2019 (COVID-19) with low respiratory compliance and poor oxygenation as main characteristics and mortality rate of 50%-94%. Surfactants, including surfactant protein D (SP-D), have a role in maintaining respiratory compliance. This study aimed to analyze the relationship between serum SP-D levels with respiratory compliance and ARDS in patients with critically ill COVID-19 pneumonia.

Methods

This study was a cross-sectional study. Subjects were adult reverse transcription-polymerase chain reaction-confirmed COVID-19 patients who had ARDS treated with invasive mechanical ventilation. All data were obtained from medical records. Statistical analysis was done using Spearman test, Mann-Whitney test, and receiver operating characteristic curve.

Results

Serum level of SP-D was significantly correlated with static respiratory compliance (P = 0.009; correlation coefficient [rs] = 0.467). Serum SP-D levels correlated with ARDS severity (P < 0.001). SP-D levels had a very strong diagnostic value for ARDS severity, with an optimal cutoff value of 44.24 ng/mL (sensitivity 92.3%; specificity 94.1%). ARDS severity also correlated significantly with respiratory compliance (P = 0.005; correlation coefficient 0.496).

Conclusion

Higher serum SP-D levels were associated with lower respiratory compliance, ARDS severity, and may be utilized diagnostically to identify patients with severe ARDS.

Lung function improves after delayed treatment with CNP-miR146a following acute lung injury

Acute respiratory distress syndrome (ARDS) is a highly morbid pulmonary disease characterized by hypoxic respiratory failure. Its pathogenesis is characterized by unrestrained oxidative stress and inflammation, with long-term sequelae of pulmonary fibrosis and diminished lung function. Unfortunately, prior therapeutic ARDS trials have failed and therapy is limited to supportive measures. Free radical scavenging cerium oxide nanoparticles (CNP) conjugated to the anti-inflammatory microRNA-146a (miR146a), termed CNP-miR146a, have been shown to prevent acute lung injury in a pre-clinical model. In this study, we evaluated the potential of delayed treatment with CNP-miR146a at three or seven days after injury to rescue the lung from acute injury. We found that intratracheal CNP-miR146a administered three days after injury lowers pulmonary leukocyte infiltration, reduce inflammation and oxidative stress, lower pro-fibrotic gene expression and collagen deposition in the lung, and ultimately improve pulmonary function.

A research update: Significance of cytokine storm and diaphragm in COVID-19

Emerging research on severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) shows that it is spreading to multiple organs in addition to the respiratory system. Though the SARS-CoV2 enters the human body by binding to ACE2 receptors on pulmonary alveolar cells, recent studies indicate that it is spreading to the central nervous system, cardiac and skeletal muscles leading to various pathological conditions in these organs. In particular, the effects of SARS-CoV-2 on triggering the cytokine storm and its consequential effects on skeletal muscles has generated a lot of discussion. The effects of this virus on muscular function especially in susceptible elderly populations is still being explored. However, its effects on diaphragm, a respiratory muscle which plays an important role in determining lung capacity are not completely explored. Currently, as new evidence on using lung ultrasounds to confirm COVID-19 diagnosis is gaining traction, it is necessary to explore the role of diaphragm in treating COVID-19 patients. This article will review the effects of cytokine storm triggered by the SARS-CoV-2 and its resultant effects on skeletal muscle with a specific focus on the diaphragm in order to identify knowledge gaps in effectively treating COVID-19 patients, especially those who are on a mechanical ventilator.

Inhibition of IP3R/Ca2+ Dysregulation Protects Mice From Ventilator-Induced Lung Injury via Endoplasmic Reticulum and Mitochondrial Pathways

Rationale

Disruption of intracellular calcium (Ca2+) homeostasis is implicated in inflammatory responses. Here we investigated endoplasmic reticulum (ER) Ca2+ efflux through the Inositol 1,4,5-trisphosphate receptor (IP3R) as a potential mechanism of inflammatory pathophysiology in a ventilator-induced lung injury (VILI) mouse model.

Methods

C57BL/6 mice were exposed to mechanical ventilation using high tidal volume (HTV). Mice were pretreated with the IP3R agonist carbachol, IP3R inhibitor 2-aminoethoxydiphenyl borate (2-APB) or the Ca2+ chelator BAPTA-AM. Lung tissues and bronchoalveolar lavage fluid (BALF) were collected to measure Ca2+ concentrations, inflammatory responses and mRNA/protein expression associated with ER stress, NLRP3 inflammasome activation and inflammation. Analyses were conducted in concert with cultured murine lung cell lines.

Results

Lungs from mice subjected to HTV displayed upregulated IP3R expression in ER and mitochondrial-associated-membranes (MAMs), with enhanced formation of MAMs. Moreover, HTV disrupted Ca2+ homeostasis, with increased flux from the ER to the cytoplasm and mitochondria. Administration of carbachol aggravated HTV-induced lung injury and inflammation while pretreatment with 2-APB or BAPTA-AM largely prevented these effects. HTV activated the IRE1α and PERK arms of the ER stress signaling response and induced mitochondrial dysfunction-NLRP3 inflammasome activation in an IP3R-dependent manner. Similarly, disruption of IP3R/Ca2+ in MLE12 and RAW264.7 cells using carbachol lead to inflammatory responses, and stimulated ER stress and mitochondrial dysfunction.

Conclusion

Increase in IP3R-mediated Ca2+ release is involved in the inflammatory pathophysiology of VILI via ER stress and mitochondrial dysfunction. Antagonizing IP3R/Ca2+ and/or maintaining Ca2+ homeostasis in lung tissue represents a prospective treatment approach for VILI.

Respiratory Mechanics in a Cohort of Critically Ill Subjects With COVID-19 Infection

BACKGROUND

Patients with coronavirus disease 2019 (COVID-19) often develop acute hypoxemic respiratory failure and receive invasive mechanical ventilation. Much remains unknown about their respiratory mechanics, including the trajectories of pulmonary compliance and [Formula: see text]/[Formula: see text], the prognostic value of these parameters, and the effects of prone positioning. We described respiratory mechanics among subjects with COVID-19 who were intubated during the first month of hospitalization.

METHODS

We included patients with COVID-19 who were mechanically ventilated between February and May 2020. Daily values of pulmonary compliance, [Formula: see text], [Formula: see text], and the use of prone positioning were abstracted from electronic medical records. The trends were analyzed separately over days 1-10 and days 1-35 of intubation, stratified by prone positioning use, survival, and initial [Formula: see text]/[Formula: see text].

RESULTS

Among 49 subjects on mechanical ventilation day 1, the mean compliance was 41 mL/cm H₂O, decreasing to 25 mL/cm H₂O by day 14, the median duration of mechanical ventilation. In contrast, the [Formula: see text]/[Formula: see text] on day 1 was similar to day 14. The overall mean compliance was greater among the non-survivors versus the survivors (27 mL/cm H₂O vs 24 mL/cm H₂O; P = .005), whereas [Formula: see text]/[Formula: see text] was higher among the survivors versus the non-survivors over days 1-10 (159 mm Hg vs 138 mm Hg; P = .002) and days 1-35 (175 mm Hg vs 153 mm Hg; P < .001). The subjects who underwent early prone positioning had lower compliance during days 1-10 (27 mL/cm H₂O vs 33 mL/cm H₂O; P < .001) and lower [Formula: see text]/[Formula: see text] values over days 1-10 (139.9 mm Hg vs 167.4 mm Hg; P < .001) versus those who did not undergo prone positioning. After day 21 of hospitalization, the average compliance of the subjects who had early prone positioning surpassed that of the subjects who did not have prone positioning.

CONCLUSIONS

Respiratory mechanics of the subjects with COVID-19 who were on mechanical ventilation were characterized by persistently low respiratory system compliance and [Formula: see text]/[Formula: see text], similar to ARDS due to other etiologies. The [Formula: see text]/[Formula: see text] was more tightly associated with mortality than with compliance.

Dysregulated plasma lipid mediator profiles in critically ill COVID-19 patients

Coronavirus disease (COVID)-19, as a result of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection, has been the direct cause of over 2.2 million deaths worldwide. A timely coordinated host-immune response represents the leading driver for restraining SARS-CoV-2 infection. Indeed, several studies have described dysregulated immunity as the crucial determinant for critical illness and the failure of viral control. Improved understanding and management of COVID-19 could greatly reduce the mortality and morbidity caused by SARS-CoV-2. One aspect of the immune response that has to date been understudied is whether lipid mediator production is dysregulated in critically ill patients. In the present study, plasma from COVID-19 patients with either severe disease and those that were critically ill was collected and lipid mediator profiles were determined using liquid chromatography tandem mass spectrometry. Results from these studies indicated that plasma concentrations of both pro-inflammatory and pro-resolving lipid mediator were reduced in critically ill patients when compared with those with severe disease. Furthermore, plasma concentrations of a select group of mediators that included the specialized pro-resolving mediators (SPM) Resolvin (Rv) D1 and RvE4 were diagnostic of disease severity. Interestingly, peripheral blood SPM concentrations were also linked with outcome in critically ill patients, where we observed reduced overall concentrations of these mediators in those patients that did not survive. Together the present findings establish a link between plasma lipid mediators and disease severity in patients with COVID-19 and indicate that plasma SPM concentrations may be linked with survival in these patients.

Hypercapnia in the critically ill: insights from the bench to the bedside

Carbon dioxide (CO2) has long been considered, at best, a waste by-product of metabolism, and at worst, a toxic molecule with serious health consequences if physiological concentration is dysregulated. However, clinical observations have revealed that 'permissive' hypercapnia, the deliberate allowance of respiratory produced CO2 to remain in the patient, can have anti-inflammatory effects that may be beneficial in certain circumstances. In parallel, studies at the cell level have demonstrated the profound effect of CO2 on multiple diverse signalling pathways, be it the effect from CO2 itself specifically or from the associated acidosis it generates. At the whole organism level, it now appears likely that there are many biological sensing systems designed to respond to CO2 concentration and tailor respiratory and other responses to atmospheric or local levels. Animal models have been widely employed to study the changes in CO2 levels in various disease states and also to what extent permissive or even directly delivered CO2 can affect patient outcome. These findings have been advanced to the bedside at the same time that further clinical observations have been elucidated at the cell and animal level. Here we present a synopsis of the current understanding of how CO2 affects mammalian biological systems, with a particular emphasis on inflammatory pathways and diseases such as lung specific or systemic sepsis. We also explore some future directions and possibilities, such as direct control of blood CO2 levels, that could lead to improved clinical care in the future.

Direction and Magnitude of Change in Plateau From Peak Pressure During Inspiratory Holds Can Identify the Degree of Spontaneous Effort and Elastic Workload in Ventilated Patients

OBJECTIVES

Inspiratory holds with measures of airway pressure to estimate driving pressure (elastic work) are often limited to patients without respiratory effort. We sought to evaluate if measures of airway pressure during inspiratory holds could be used for patients with spontaneous respiratory effort during mechanical ventilation to estimate the degree of spontaneous effort and elastic work.

DESIGN

We compared the direction and degree of change in airway pressure during inspiratory holds versus esophageal pressure through secondary analysis of physiologic data.

SETTING

ICUs at Children's Hospital Los Angeles.

PATIENTS

Children with pediatric acute respiratory distress syndrome with evidence of spontaneous respiration while on pressure control or pressure support ventilation.

INTERVENTIONS

Inspiratory hold maneuvers.

MEASUREMENTS AND MAIN RESULTS

From airway pressure, we defined "plateau - peak pressure" as Pmusc, index, which was divided into three categories for analysis (< -1 ["negative"], between -1 and 1 ["neutral"], and > 1 cm H2O ["positive"]). A total of 30 children (age 36.8 mo [16.1-70.3 mo]) from 65 study days, comprising 118 inspiratory holds were included. Pmusc, index was "negative" in 29 cases, was "neutral" in 17 cases, and was "positive" in 72 cases. As Pmusc, index went from negative to neutral to positive, there was larger negative deflection in esophageal pressure -5.0 (-8.2 to 1.9), -5.9 (-7.6 to 4.3), and -10.7 (-18.1 to 7.9) cm H2O (p < 0.0001), respectively. There was a correlation between max negative esophageal pressure and Pmusc, index (r = -0.52), and when Pmusc, index was greater than or equal to 7 cm H2O, the max negative esophageal pressure was greater than 10 cm H2O. There was a stronger correlation between Pmusc, index and markers of elastic work from esophageal pressure (r = 0.84).

CONCLUSIONS

The magnitude of plateau minus peak pressure during an inspiratory hold is correlated with the degree of inspiratory effort, particularly for those with high elastic work. It may be useful to identify patients with excessively high effort or high driving pressure.

Management of critically ill patients with COVID-19: suggestions and instructions from the coordination of intensive care units of Lombardy

With 63,098 confirmed cases on 17 April 2020 and 11,384 deaths, Lombardy has been the most affected region in Italy by coronavirus disease 2019 (COVID-19). To cope with this emergency, the COVID-19 Lombardy intensive care units (ICU) network was created. The network identified the need of defining a list of clinical recommendations to standardize treatment of patients with COVID-19 admitted to Intensive Care Unit (ICU). Three core topics were identified: 1) rational use of intensive care resources; 2) ventilation strategies; 3) non-ventilatory interventions. Identification of patients who may benefit from ICU treatment is challenging. Clinicians should consider baseline performance and frailty status and they should adopt disease-specific staging tools. Continuous positive airway pressure, mainly delivered through a helmet as elective method, should be considered as initial treatment for all patients with respiratory failure associated with COVID-19. In case of persisting dyspnea and/or desaturation despite 4-6 hours of noninvasive ventilation, endotracheal intubation and invasive mechanical ventilation should be considered. In the early phase, muscle relaxant use and volume-controlled ventilation is recommended. Prone position should be performed in patients with PaO<inf>2</inf>/FiO<inf>2</inf>≤100 mmHg. For patients admitted to ICU with COVID-19 interstitial pneumonia, we do not recommend empiric antibiotic therapy for community-acquired pneumonia. Consultation of an infectious disease specialist is suggested before start of any antiviral therapy. In conclusion, the COVID-19 Lombardy ICU Network identified a list of best practice statements supported by the available evidence and clinical experience or identified as panel members expert opinions for the management of critically ill patients with COVID-19.

COVID-19-related organ dysfunction and management strategies on the intensive care unit: a narrative review

The coronavirus disease 2019 (COVID-19) pandemic has resulted in a significant surge of critically ill patients and an unprecedented demand on intensive care services. The rapidly evolving understanding of pathogenesis, limited disease specific evidence, and demand-resource imbalances have posed significant challenges for intensive care clinicians. COVID-19 is a complex multisystem inflammatory vasculopathy with a significant mortality implication for those admitted to intensive care. Institutional strategic preparation and meticulous intensive care support are essential to maximising outcomes during the pandemic. The significant mortality variation observed between institutions and internationally, despite a single aetiology and uniform presentation, highlights the potential influence of management strategies on outcome. Given that optimal organ support and adjunctive therapies for COVID-19 have not yet been well defined by trial-based outcomes, strategies are predicated on existing literature and experiential learning. This review outlines the relevant pathophysiology and management strategies for critically ill patients with COVID-19, and shares some of the collective learning accumulated in a high volume severe respiratory failure centre in London.

Fluctuations of driving pressure during mechanical ventilation indicates elevated central venous pressure and poor outcomes

Inappropriate mechanical ventilation may induce hemodynamic alterations through cardiopulmonary interactions. The aim of this study was to explore the relationship between airway pressure and central venous pressure during the first 72 h of mechanical ventilation and its relevance to patient outcomes. We conducted a retrospective study of the Department of Critical Care Medicine of Peking Union Medical College Hospital and a secondary analysis of the MIMIC-III clinical database. The relationship between the ranges of driving pressure and central venous pressure during the first 72 h and their associations with prognosis were investigated. Data from 2790 patients were analyzed. Wide range of driving airway pressure (odds ratio, 1.0681; 95% CI, 1.0415-1.0953; p < 0.0001) were independently associated with mortality, ventilator-free time, intensive care unit and hospital length of stay. Furthermore, wide range of driving pressure and elevated central venous pressure exhibited a close correlation. The area under receiver operating characteristic demonstrated that range of driving pressure and central venous pressure were measured at 0.689 (95% CI, 0.670-0.707) and 0.681 (95% CI, 0.662-0.699), respectively. Patients with high ranges of driving pressure and elevated central venous pressure had worse outcomes. Post hoc tests showed significant differences in 28-day survival rates (log-rank (Mantel-Cox), 184.7; p < 0.001). In conclusion, during the first 72 h of mechanical ventilation, patients with hypoxia with fluctuating driving airway pressure have elevated central venous pressure and worse outcomes.

Emodin Inhibits Lipopolysaccharide-Induced Inflammation by Activating Autophagy in RAW 264.7 Cells

OBJECTIVE

To investigate the effects of emodin on inflammation and autophagy in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages and reveal its underlying mechanism.

METHODS

3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay was conducted to find the appropriate dose for emodin. RAW264.7 cells pretreated with different concentrations (0-50 μmol/L) of emodin or vehicle for 2 h prior to exposure to LPS for 16 h. Cell morphology was examined and propidium iodide staining was used to examine cell cycle. Expressions of inflammation-related proteins [nuclear factor-kappaB (NF-κ B) and I-kappaB (I κ B)α] and autophagy-related proteins [light chain (LC)3, P62/sequestosome 1, mammalian target of rapamycin (mTOR), and p-mTOR] were examined using Western blot analysis. Expression of inflammation-related cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 were detected by enzyme-linked immunosorbent assay. Autophagy was examined with LC3B fluorescence intensity and aggregation. The effect of emodin on autophagy was conducted with an autophagy inhibitor, 3-methyladenine (3-MA).

RESULTS

The expression of NF-κ B in LPS-induced cells was significantly increased (P<0.01) and simultaneously I κ B α decreased compared with the normal cell (P<0.05). The expressions of TNF-α, IL-β, and IL-6 proteins in the LPS-induced RAW264.7 cells were significantly higher than in the normal cell (P<0.05 or P<0.01). LPS increased the percentage of cells in the G₀/G₁ phase, which was recovered by emodin at different doses (12.5, 25, and 50μ mol/L, P<0.05 or P<0.01). The medium-dose (25 μ ml/L) emodin decreased the expressions of NF-κ B, P62 and p-mTOR (P<0.01) and increased I κ B α expression, LC3B II/I ratio as well as LC3B fluorescence intensity (P<0.05 or P<0.01). Meanwhile, the enhanced autophagic effects of emodin, such as the increment of LC3B II/ratio and the decrement of P62 expression, were suppressed by autophagy inhibitor 3-MA.

CONCLUSION

Emodin could inhibit inflammation of mice RAW264.7 macrophages induced by LPS, possibly through activating autophagy.

Airway pressure morphology and respiratory muscle activity during end-inspiratory occlusions in pressure support ventilation

Background

The driving pressure of the respiratory system is a valuable indicator of global lung stress during passive mechanical ventilation. Monitoring lung stress in assisted ventilation is indispensable, but achieving passive conditions in spontaneously breathing patients to measure driving pressure is challenging. The accuracy of the morphology of airway pressure (Paw) during end-inspiratory occlusion to assure passive conditions during pressure support ventilation has not been examined.

Methods

Retrospective analysis of end-inspiratory occlusions obtained from critically ill patients during pressure support ventilation. Flow, airway, esophageal, gastric, and transdiaphragmatic pressures were analyzed. The rise of gastric pressure during occlusion with a constant/decreasing transdiaphragmatic pressure was used to identify and quantify the expiratory muscle activity. The Paw during occlusion was classified in three patterns, based on the differences at three pre-defined points after occlusion (0.3, 1, and 2 s): a “passive-like” decrease followed by plateau, a pattern with “clear plateau,” and an “irregular rise” pattern, which included all cases of late or continuous increase, with or without plateau.

Results

Data from 40 patients and 227 occlusions were analyzed. Expiratory muscle activity during occlusion was identified in 79% of occlusions, and at all levels of assist. After classifying occlusions according to Paw pattern, expiratory muscle activity was identified in 52%, 67%, and 100% of cases of Paw of passive-like, clear plateau, or irregular rise pattern, respectively. The driving pressure was evaluated in the 133 occlusions having a passive-like or clear plateau pattern in Paw. An increase in gastric pressure was present in 46%, 62%, and 64% of cases at 0.3, 1, and 2 s, respectively, and it was greater than 2 cmH₂O, in 10%, 20%, and 15% of cases at 0.3, 1, and 2 s, respectively.

Conclusions

The pattern of Paw during an end-inspiratory occlusion in pressure support cannot assure the absence of expiratory muscle activity and accurate measurement of driving pressure. Yet, because driving pressure can only be overestimated due to expiratory muscle contraction, in everyday practice, a low driving pressure indicates an absence of global lung over-stretch. A measurement of high driving pressure should prompt further diagnostic workup, such as a measurement of esophageal pressure.

Influence of Positive End-Expiratory Pressure Titration on the Effects of Pronation in Acute Respiratory Distress Syndrome: A Comprehensive Experimental Study

Prone position can reduce mortality in acute respiratory distress syndrome (ARDS), but several studies found variable effects on oxygenation and lung mechanics. It is unclear whether different positive end-expiratory pressure (PEEP) titration techniques modify the effect of prone position. We tested, in an animal model of ARDS, if the PEEP titration method may influence the effect of prone position on oxygenation and lung protection. In a crossover study in 10 piglets with a two-hit injury ARDS model, we set the "best PEEP" according to the ARDS Network low-PEEP table (BP_ARDS) or targeting the lowest transpulmonary driving pressure (BP_DPL). We measured gas exchange, lung mechanics, aeration, ventilation, and perfusion with computed tomography (CT) and electrical impedance tomography in each position with both PEEP titration techniques. The primary endpoint was the PaO₂/FiO₂ ratio. Secondary outcomes were lung mechanics, regional distribution of ventilation, regional distribution of perfusion, and homogeneity of strain derived by CT scan. The PaO₂/FiO₂ ratio increased in prone position when PEEP was set with BP_ARDS [difference 54 (19-106) mmHg, p = 0.04] but not with BP_DPL [difference 17 (-24 to 68) mmHg, p = 0.99]. The transpulmonary driving pressure significantly decreased during prone position with both BP_ARDS [difference -0.9 (-1.5 to -0.9) cmH₂O, p = 0.009] and BP_DPL [difference -0.55 (-1.6 to -0.4) cmH₂O, p = 0.04]. Pronation homogenized lung regional strain and ventilation and redistributed the ventilation/perfusion ratio along the sternal-to-vertebral gradient. The PEEP titration technique influences the oxygenation response to prone position. However, the lung-protective effects of prone position could be independent of the PEEP titration strategy.

Driving Pressure Is Associated with Outcome during Assisted Ventilation in Acute Respiratory Distress Syndrome

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

Higher driving pressure during controlled mechanical ventilation is known to be associated with increased mortality in patients with acute respiratory distress syndrome.Whereas patients with acute respiratory distress syndrome are initially managed with controlled mechanical ventilation, as they improve, they are transitioned to assisted ventilation. Whether higher driving pressure assessed during pressure support (assisted) ventilation can be reliably assessed and whether higher driving pressure is associated with worse outcomes in patients with acute respiratory distress syndrome has not been well studied.

WHAT THIS ARTICLE TELLS US THAT IS NEW

This study shows that in the majority of adult patients with acute respiratory distress syndrome, both driving pressure and respiratory system compliance can be reliably measured during pressure support (assisted) ventilation.Higher driving pressure measured during pressure support (assisted) ventilation significantly associates with increased intensive care unit mortality, whereas peak inspiratory pressure does not.Lower respiratory system compliance also significantly associates with increased intensive care unit mortality.

BACKGROUND

Driving pressure, the difference between plateau pressure and positive end-expiratory pressure (PEEP), is closely associated with increased mortality in patients with acute respiratory distress syndrome (ARDS). Although this relationship has been demonstrated during controlled mechanical ventilation, plateau pressure is often not measured during spontaneous breathing because of concerns about validity. The objective of the present study is to verify whether driving pressure and respiratory system compliance are independently associated with increased mortality during assisted ventilation (i.e., pressure support ventilation).

METHODS

This is a retrospective cohort study conducted on 154 patients with ARDS in whom plateau pressure during the first three days of assisted ventilation was available. Associations between driving pressure, respiratory system compliance, and survival were assessed by univariable and multivariable analysis. In patients who underwent a computed tomography scan (n = 23) during the stage of assisted ventilation, the quantity of aerated lung was compared with respiratory system compliance measured on the same date.

RESULTS

In contrast to controlled mechanical ventilation, plateau pressure during assisted ventilation was higher than the sum of PEEP and pressure support (peak pressure). Driving pressure was higher (11 [9-14] vs. 10 [8-11] cm H2O; P = 0.004); compliance was lower (40 [30-50] vs. 51 [42-61] ml · cm H2O; P < 0.001); and peak pressure was similar, in nonsurvivors versus survivors. Lower respiratory system compliance (odds ratio, 0.92 [0.88-0.96]) and higher driving pressure (odds ratio, 1.34 [1.12-1.61]) were each independently associated with increased risk of death. Respiratory system compliance was correlated with the aerated lung volume (n = 23, r = 0.69, P < 0.0001).

CONCLUSIONS

In patients with ARDS, plateau pressure, driving pressure, and respiratory system compliance can be measured during assisted ventilation, and both higher driving pressure and lower compliance are associated with increased mortality.