The role of acute hypercapnia on mortality and short-term physiology in patients mechanically ventilated for ARDS: a systematic review and meta-analysis

Partial pressure of carbon dioxide/pH interaction and its association with mortality among patients mechanically ventilated in the emergency department

OBJECTIVES

There is currently conflicting data as to the effects of hypercapnia on clinical outcomes among mechanically ventilated patients in the emergency department (ED). These conflicting results may be explained by the degree of acidosis. We sought to test the hypothesis that hypercapnia is associated with increased in-hospital mortality and decreased ventilator-free days at lower pH, but associated with decreased in-hospital mortality and increased ventilator-free days at higher pH, among patients requiring mechanical ventilation in the emergency department (ED).

METHODS

Secondary analysis of patient level data from prior clinical trials and cohort studies that enrolled adult patients who required mechanical ventilation in the ED. Patients who had a documented blood gas while on mechanical ventilation in the ED were included in these analyses. The primary outcome was in-hospital mortality, and secondary outcome was ventilator-free days. Mixed-effects logistic, linear, and survival-time regression models were used to test if pH modified the association between partial pressure of carbon dioxide (pCO2) and outcome measures.

RESULTS

Of the 2348 subjects included, the median [interquartile range (IQR)] pCO2 was 43 (35-54) and pH was 7.31 (7.22-7.39). Overall, in-hospital mortality was 27%. We found pH modified the association between pCO2 and outcomes, with higher pCO2 associated with increased probability of in-hospital mortality when pH is below 7.00, and decreased probability of in-hospital mortality when pH is above 7.10. These results remained consistent across multiple sensitivity and subgroup analyses. A similar relationship was found with ventilator-free days.

CONCLUSIONS

Higher pCO2 is associated with decreased mortality and greater ventilator-free days when pH is >7.10; however, it is associated with increased mortality and fewer ventilator-free days when the pH is below 7.00. Targeting pCO2 based on pH in the ED may be a potential intervention target for future clinical trials to improve clinical outcomes.

Refractory cor pulmonale under extracorporeal membrane oxygenation for acute respiratory distress syndrome: the role of conversion to veno-pulmonary arterial assist-a case series

Introduction

Pulmonary vascular dysfunction during severe acute respiratory distress syndrome (ARDS) may lead to right ventricle (RV) dysfunction and acute cor pulmonale (ACP). The occurrence/persistence of ACP despite conventional extracorporeal membrane oxygenation (ECMO) is a challenging situation. We explored the usefulness of a specific dual-lumen cannula that bypasses the RV, and on which a veno-pulmonary arterial assist (V-P ECMO) was mounted, in ARDS patients.

Methods

We report a case-series of ARDS patients put on conventional veno-arterial or veno-venous ECMO and presented refractory ACP as an indication for a reconfiguration to V-P ECMO using the ProtekDuo cannula. The primary endpoint was the mitigation of RV and pulmonary vascular dysfunction as assessed by the change in end-diastolic RV/left ventricle (LV) surface ratio.

Results

Six patients had their conventional ECMO reconfigured to V-P ECMO to treat refractory ACP. There was a decrease in end-diastolic RV/LV surface ratio, as well as end-systolic LV eccentricity index, and lactatemia immediately after V-P ECMO initiation. The resolution of refractory ACP was immediately achieved in four of our six (66%) patients. The V-P ECMO was weaned after a median of 26 [8-93] days after implantation. All but one patient were discharged home. We detected one case of severe hemolysis with V-P ECMO and two suspected cases of right-sided infective endocarditis.

Conclusion

V-P ECMO is useful to mitigate RV overload and to improve hemodynamics in case of refractory ACP despite conventional ECMO.

Effects on mechanical power of different devices used for inhaled sedation in a bench model of protective ventilation in ICU

BACKGROUND

Inhaled sedation during invasive mechanical ventilation in patients with acute respiratory distress syndrome (ARDS) has received increasing attention. However, inhaled sedation devices increase dead-space ventilation and an undesirable effect is the increase in minute ventilation needed to maintain CO2 removal. A consequence of raising minute ventilation is an increase in mechanical power (MP) that can promote lung injury. However, the effect of inhaled sedation devices on MP remains unknown.

METHODS

We conducted a bench study to assess and compare the effects of three devices delivering inhaled sevoflurane currently available in ICU (AnaConDa-50 mL (ANA-50), AnaConDa-100 mL (ANA-100), and MIRUS) on MP by using a test lung model set with three compliances (20, 40, and 60 mL/cmH2O). We simulated lung-protective ventilation using a low tidal volume and two levels of positive end-expiratory pressure (5 and 15 cmH2O) under ambient temperature and dry conditions. Following the insertion of the devices, either the respiratory rate or tidal volume was increased in 15%-steps until end-tidal CO2 (EtCO2) returned to the baseline value. MP was calculated at baseline and after EtCO2 correction using a simplified equation.

RESULTS

Following device insertion, the EtCO2 increase was significantly greater with MIRUS (+ 78 ± 13%) and ANA-100 (+ 100 ± 11%) than with ANA-50 (+ 49 ± 7%). After normalizing EtCO2 by adjusting minute ventilation, MP significantly increased by more than 50% with all inhaled sedation devices compared to controls. The lowest increase in MP was observed with ANA-50 (p < 0.05 versus ANA-100 and MIRUS). The Costa index, another parameter assessing the mechanical energy delivered to the lungs, calculated as driving pressure × 4 + respiratory rate, significantly increased by more than 20% in all experimental conditions. Additional experiments performed under body temperature, ambient pressure, and gas saturated with water vapor conditions, confirmed the main results with an increase in MP > 50% with all devices after normalizing EtCO2 by adjusting minute ventilation.

CONCLUSION

Inhaled sedation devices substantially increased MP in this bench model of protective ventilation, which might limit their benefits in ARDS.

Intraoperative partial pressure of arterial carbon dioxide levels and adverse outcomes in patients undergoing lung transplantation

OBJECTIVE

Patients undergoing lung transplantation (LTx) often experience abnormal hypercapnia or hypocapnia. This study aimed to investigate the association between intraoperative PaCO2 and postoperative adverse outcomes in patients undergoing LTx.

METHODS

We retrospectively reviewed the medical records of 151 patients undergoing LTx. Patients' demographics, perioperative clinical factors, and pre- and intraoperative PaCO2 data after reperfusion were collected and analyzed. Based on the PaCO2 levels, patients were classified into three groups: hypocapnia (≤35 mmHg), normocapnia (35.1-55 mmHg), and hypercapnia (>55 mmHg). Univariate and multivariable logistic regressions were used to identify independent risk factors for postoperative composite adverse events and in-hospital mortality.

RESULTS

Intraoperative hypercapnia occurred in 69 (45.7%) patients, and hypocapnia in 17 (11.2%). Patients with intraoperative PaCO2 of 35.1-45 mmHg showed a lower incidence of composite adverse events (53.3%) and mortality (6.2%) (P < 0.001). There was no significant difference in composite adverse events and mortality among preoperative PaCO2 groups (P > 0.05). Compared with intraoperative PaCO2 at 35.1-45 mmHg, the risk of composite adverse events in hypercapnia group increased: the adjusted OR was 3.07 (95% confidence interval [CI]: 1.36-6.94; P = 0.007). The risk of death was significantly higher in hypocapnia group than normocapnia group, the adjusted OR was 7.69 (95% CI: 1.68-35.24; P = 0.009). Over ascending ranges of PaCO2, PaCO2 at 55.1-65 mmHg had the strongest association with composite adverse events, the adjusted OR was 6.40 (95% CI: 1.18-34.65; P = 0.031).

CONCLUSION

These results demonstrate that intraoperative hypercapnia independently predicts postoperative adverse outcomes in patients undergoing LTx. Intraoperative hypocapnia shows predictive value for postoperative in-hospital mortality in LTx.

Modification of Respiratory Drive and Lung Stress by Level of Support Pressure and ECMO Sweep Gas Flow in Patients With Severe COVID-19-Associated Acute Respiratory Distress Syndrome: an Exploratory Retrospective Analysis

OBJECTIVES

Patients with severe acute respiratory distress syndrome (ARDS) often exhibit an unusually strong respiratory drive, which predisposes them to effort-induced lung injury. Careful titration of support pressure via the ventilator and carbon dioxide removal via extracorporeal membrane oxygenation (ECMO) may attenuate respiratory drive and lung stress.

DESIGN

A retrospective cohort study.

SETTING

At a single center, a university hospital.

PARTICIPANTS

Ten patients with severe COVID-19-associated ARDS (CARDS) on venovenous ECMO therapy.

INTERVENTIONS

Assessment of the effect of titrated support pressure and titrated ECMO sweep gas flow on respiratory drive and lung stress in spontaneously breathing patients during ECMO therapy.

MEASUREMENTS AND MAIN RESULTS

Airway occlusion pressure (P0.1) and the total swing of the transpulmonary pressure were determined as surrogate parameters of respiratory drive and lung stress. Ventilator-mediated elevation of support pressure decreased P0.1 but increased transpulmonary driving pressure, airway pressure, tidal volume, and end-inspiratory transpulmonary occlusion pressure. The increase in ECMO sweep gas flow lowered P0.1, transpulmonary pressures, tidal volume, and respiratory frequency linearly.

CONCLUSIONS

In patients with CARDS on pressure support ventilation, even moderate support pressure may lead to overassistance during assisted ventilation, which is only reflected by advanced monitoring of respiratory mechanics. Modifying carbon dioxide removal via the extracorporeal system profoundly affects respiratory effort and mechanics. Spontaneously breathing patients with CARDS may benefit from consequent carbon dioxide removal.

Cardiovascular changes induced by targeted mild hypercapnia after out of hospital cardiac arrest. A sub-study of the TAME cardiac arrest trial

AIM

Hypercapnia may elicit detrimental haemodynamic effects in critically ill patients. We aimed to investigate the consequences of targeted mild hypercapnia versus targeted normocapnia on pulmonary vascular resistance and right ventricular function in patients resuscitated from out-of-hospital cardiac arrest (OHCA).

METHODS

Pre-planned, single-centre, prospective, sub-study of the Targeted Therapeutic Mild Hypercapnia After Resuscitated Cardiac Arrest (TAME) trial. Patients were randomised to mild hypercapnia (PaCO2 = 6.7-7.3 kPa) or normocapnia (PaCO2 = 4.7-6.0 kPa) for 24 hours. Haemodynamic assessment was performed with right heart catheterisation and serial blood-gas analyses every4th hour for 48 hours.

RESULTS

We studied 84 patients. Mean pH was 7.24 (95% CI 7.22-7.30) and 7.32 (95% CI 7.31-7.34) with hypercapnia and normocapnia, respectively (P-group < 0.001). Pulmonary vascular resistance index (PVRI), pulmonary artery pulsatility index, and right atrial pressure did not differ between groups (P-group > 0.05). Mean cardiac index was higher with mild hypercapnia (P-group < 0.001): 2.0 (95% CI 1.85-2.1) vs 1.6 (95% CI 1.52-1.76) L/min/m2. Systemic vascular resistance index was 2579 dyne-sec/cm-5/ m2 (95% CI 2356-2830) with hypercapnia, and 3249 dyne-sec/cm-5/ m2 (95% CI 2930-3368) with normocapnia (P-group < 0.001). Stroke volumes (P-group = 0.013) and mixed venous oxygen saturation (P-group < 0.001) were higher in the hypercapnic group.

CONCLUSION

In resuscitated OHCA patients, targeting mild hypercapnia did not increase PVRI or worsen right ventricular function compared to normocapnia. Mild hypercapnia comparatively improved cardiac performance and mixed venous oxygen saturation.

Carbon dioxide and MAPK signalling: towards therapy for inflammation

Inflammation, although necessary to fight infections, becomes a threat when it exceeds the capability of the immune system to control it. In addition, inflammation is a cause and/or symptom of many different disorders, including metabolic, neurodegenerative, autoimmune and cardiovascular diseases. Comorbidities and advanced age are typical predictors of more severe cases of seasonal viral infection, with COVID-19 a clear example. The primary importance of mitogen-activated protein kinases (MAPKs) in the course of COVID-19 is evident in the mechanisms by which cells are infected with SARS-CoV-2; the cytokine storm that profoundly worsens a patient's condition; the pathogenesis of diseases, such as diabetes, obesity, and hypertension, that contribute to a worsened prognosis; and post-COVID-19 complications, such as brain fog and thrombosis. An increasing number of reports have revealed that MAPKs are regulated by carbon dioxide (CO2); hence, we reviewed the literature to identify associations between CO2 and MAPKs and possible therapeutic benefits resulting from the elevation of CO2 levels. CO2 regulates key processes leading to and resulting from inflammation, and the therapeutic effects of CO2 (or bicarbonate, HCO3-) have been documented in all of the abovementioned comorbidities and complications of COVID-19 in which MAPKs play roles. The overlapping MAPK and CO2 signalling pathways in the contexts of allergy, apoptosis and cell survival, pulmonary oedema (alveolar fluid resorption), and mechanical ventilation-induced responses in lungs and related to mitochondria are also discussed. Video Abstract.

A framework of transient hypercapnia to achieve an increased cerebral blood flow induced by nasal breathing during aerobic exercise

During exercise, cerebral blood flow (CBF) is expected to only increase to a maximal volume up to a moderate intensity aerobic effort, suggesting that CBF is expected to decline past 70 % of a maximal aerobic effort. Increasing CBF during exercise permits an increased cerebral metabolic activity that stimulates neuroplasticity and other key processes of cerebral adaptations that ultimately improve cognitive health. Recent work has focused on utilizing gas-induced exposure to intermittent hypoxia during aerobic exercise to maximize the improvements in cognitive function compared to those seen under normoxic conditions. However, it is postulated that exercising by isolating breathing only to the nasal route may provide a similar effect by stimulating a transient hypercapnic condition that is non-gas dependent. Because nasal breathing prevents hyperventilation during exercise, it promotes an increase in the partial arterial pressure of CO2. The rise in systemic CO2 stimulates hypercapnia and permits the upregulation of hypoxia-related genes. In addition, the rise in systemic CO2 stimulates cerebral vasodilation, promoting a greater increase in CBF than seen during normoxic conditions. While more research is warranted, nasal breathing might also promote benefits related to improved sleep, greater immunity, and body fat loss. Altogether, this narrative review presents a theoretical framework by which exercise-induced hypercapnia by utilizing nasal breathing during moderate-intensity aerobic exercise may promote greater health adaptations and cognitive improvements than utilizing oronasal breathing.

Extracorporeal Carbon Dioxide Removal With the Hemolung in Patients With Acute Respiratory Failure: A Multicenter Retrospective Cohort Study

OBJECTIVES

Extracorporeal carbon dioxide removal (ECCO 2 R) devices are effective in reducing hypercapnia and mechanical ventilation support but have not been shown to reduce mortality. This may be due to case selection, device performance, familiarity, or the management. The objective of this study is to investigate the effectiveness and safety of a single ECCO 2 R device (Hemolung) in patients with acute respiratory failure and identify variables associated with survival that could help case selection in clinical practice as well as future research.

DESIGN

Multicenter, multinational, retrospective review.

SETTING

Data from the Hemolung Registry between April 2013 and June 2021, where 57 ICUs contributed deidentified data.

PATIENTS

Patients with acute respiratory failure treated with the Hemolung. The characteristics of patients who survived to ICU discharge were compared with those who died. Multivariable logistical regression analysis was used to identify variables associated with ICU survival.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of the 159 patients included, 65 (41%) survived to ICU discharge. The survival was highest in status asthmaticus (86%), followed by acute respiratory distress syndrome (ARDS) (52%) and COVID-19 ARDS (31%). All patients had a significant reduction in Pa co2 and improvement in pH with reduction in mechanical ventilation support. Patients who died were older, had a lower Pa o2 :F io2 (P/F) and higher use of adjunctive therapies. There was no difference in the complications between patients who survived to those who died. Multivariable regression analysis showed non-COVID-19 ARDS, age less than 65 years, and P/F at initiation of ECCO 2 R to be independently associated with survival to ICU discharge (P/F 100-200 vs <100: odds ratio, 6.57; 95% CI, 2.03-21.33).

CONCLUSIONS

Significant improvement in hypercapnic acidosis along with reduction in ventilation supports was noted within 4 hours of initiating ECCO 2 R. Non-COVID-19 ARDS, age, and P/F at commencement of ECCO 2 R were independently associated with survival.

PaCO2 trajectories in mechanically ventilated patients with COVID-19: A population-based cohort study

OBJECTIVE

To identify PaCO2 trajectories and assess their associations with mortality in critically ill patients with coronavirus disease 2019 (COVID-19) during the first and second waves of the pandemic in Denmark.

DESIGN

A population-based cohort study with retrospective data collection.

PATIENTS

All COVID-19 patients were treated in eight intensive care units (ICUs) in the Capital Region of Copenhagen, Denmark, between March 1, 2020 and March 31, 2021.

MEASUREMENTS

Data from the electronic health records were extracted, and latent class analyses were computed based on up to the first 3 weeks of mechanical ventilation to depict trajectories of PaCO2 levels. Multivariable Cox regression analyses were used to calculate adjusted hazard ratios (aHRs) for Simplified Acute Physiology Score 3, sex and age with 95% confidence intervals (CIs) for death according to PaCO2 trajectories.

MAIN RESULTS

In latent class trajectory models, including 25,318 PaCO2 measurements from 244 patients, three PaCO2 latent class trajectories were identified: a low isocapnic (Class I; n = 130), a high isocapnic (Class II; n = 80), as well as a progressively hypercapnic (Class III; n = 34) trajectory. Mortality was higher in Class II [aHR: 2.16 {1.26-3.68}] and Class III [aHR: 2.97 {1.63-5.40}]) compared to Class I (reference).

CONCLUSION

Latent class analysis of arterial blood gases in mechanically ventilated COVID-19 patients identified distinct PaCO2 trajectories, which were independently associated with mortality.

Mechanical Ventilation during ECMO: Best Practices

Adults and children who require extracorporeal membrane oxygenation for respiratory failure remain at risk for ongoing lung injury if ventilator management is not optimized. This review serves as a guide to assist the bedside clinician in ventilator titration for patients on extracorporeal membrane oxygenation, with a focus on lung-protective strategies. Existing data and guidelines for extracorporeal membrane oxygenation ventilator management are reviewed, including non-conventional ventilation modes and adjunct therapies.

Impact of Arterial CO2 Retention in Patients With Moderate or Severe ARDS

BACKGROUND

Lung-protective ventilation (reduced tidal volume and limited plateau pressure) may lead to CO2 retention. Data about the impact of hypercapnia in patients with ARDS are scarce and conflicting.

METHODS

We performed a non-interventional cohort study with subjects with ARDS admitted from 2006 to 2021 and with PaO2 /FIO2 ≤ 150 mm Hg. We examined the association between severe hypercapnia (PaCO2 ≥ 50 mm Hg) on the first 5 days after the diagnosis of ARDS and death in ICU for 930 subjects. All the subjects received lung-protective ventilation.

RESULTS

Severe hypercapnia was noted in 552 subjects (59%) on the first day of ARDS (day 1); 323/930 (34.7%) died in the ICU. Severe hypercapnia on day 1 was associated with mortality in the unadjusted (odds ratio 1.54, 95% CI 1.16-1.63; P = .003) and adjusted (odds ratio 1.47, 95% CI 1.08-2.43; P = .004) models. In the Bayesian analysis, the posterior probability that severe hypercapnia was associated with ICU death was > 90% in 4 different priors, including a septic prior for this association. Sustained severe hypercapnia on day 5, defined as severe hypercapnia present from day 1 to day 5, was noted in 93 subjects (12%). After propensity score matching, severe hypercapnia on day 5 remained associated with ICU mortality (odds ratio 1.73, 95% CI 1.02-2.97; P = .047).

CONCLUSIONS

Severe hypercapnia was associated with mortality in subjects with ARDS who received lung-protective ventilation. Our results deserve further evaluation of the strategies and treatments that aim to control CO2 retention.

The use of mean circulatory filling pressure analogue for monitoring hemodynamic coherence: A post-hoc analysis of the SPARSE data and proof-of-concept study

BACKGROUND

Dissociation between macrocirculation and microcirculation is often observed in surgical patients.

OBJECTIVE

To test the hypothesis that the analogue of mean circulatory filling pressure (Pmca) can monitor hemodynamic coherence during major non-cardiac surgery.

METHODS

In this post-hoc analysis and proof-of-concept study, we used the central venous pressure (CVP), mean arterial pressure (MAP), and cardiac output (CO) to calculate Pmca. Efficiency of the heart (Eh), arterial resistance (Rart), effective arterial elastance (Ea), venous compartment resistance (Rven), oxygen delivery (DO2), and oxygen extraction ratio (O2ER) were also calculated. Sublingual microcirculation was assessed using SDF + imaging, and the De Backer score, Consensus Proportion of Perfused Vessels (Consensus PPV), and Consensus PPV (small) were determined.

RESULTS

Thirteen patients were included, with a median age of 66 years. Median Pmca was 16 (14.9-18) mmHg and was positively associated with CO [p <  0.001; a 1 mmHg increase in Pmca increases CO by 0.73 L  min - 1 (p <  0.001)], Eh (p <  0.001), Rart (p = 0.01), Ea (p = 0.03), Rven (p = 0.005), DO2 (p = 0.03), and O2ER (p = 0.02). A significant correlation was observed between Pmca and Consensus PPV (p = 0.02), but not with De Backer Score (p = 0.34) or Consensus PPV (small) (p = 0.1).

CONCLUSION

Significant associations exist between Pmca and several hemodynamic and metabolic variables including Consensus PPV. Adequately powered studies should determine whether Pmca can provide real-time information on hemodynamic coherence.

Dead space ventilation-related indices: bedside tools to evaluate the ventilation and perfusion relationship in patients with acute respiratory distress syndrome

Cumulative evidence has demonstrated that the ventilatory ratio closely correlates with mortality in acute respiratory distress syndrome (ARDS), and a primary feature in coronavirus disease 2019 (COVID-19)-ARDS is increased dead space that has been reported recently. Thus, new attention has been given to this group of dead space ventilation-related indices, such as physiological dead space fraction, ventilatory ratio, and end-tidal-to-arterial PCO₂ ratio, which, albeit distinctive, are all global indices with which to assess the relationship between ventilation and perfusion. These parameters have already been applied to positive end expiratory pressure titration, prediction of responses to the prone position and the field of extracorporeal life support for patients suffering from ARDS. Dead space ventilation-related indices remain hampered by several deflects; notwithstanding, for this catastrophic syndrome, they may facilitate better stratifications and identifications of subphenotypes, thereby providing therapy tailored to individual needs.

Risk Factors of AKI in Acute Respiratory Distress Syndrome: A Time-Dependent Competing Risk Analysis on Severe COVID-19 Patients

Introduction

Acute kidney injury (AKI) is frequently observed in patients with COVID-19 admitted to intensive care units (ICUs). Observational studies suggest that cardiovascular comorbidities and mechanical ventilation (MV) are the most important risk factors for AKI. However, no studies have investigated the renal impact of longitudinal covariates such as drug treatments, biological variations, and/or MV parameters.

Methods

We performed a monocentric, prospective, longitudinal analysis to identify the dynamic risk factors for AKI in ICU patients with severe COVID-19.

Results

Seventy-seven patients were included in our study (median age: 63 [interquartile range, IQR: 53-73] years; 58 (75%) men). Acute kidney injury was detected in 28 (36.3%) patients and occurred at a median time of 3 [IQR: 2-6] days after ICU admission. Multivariate Cox cause-specific time-dependent analysis identified a history of hypertension (cause-specific hazard (CSH) = 2.46 [95% confidence interval, CI: 1.04-5.84]; P = .04), a high hemodynamic Sequential Organ Failure Assessment score (CSH = 1.63 [95% CI: 1.23-2.16]; P < .001), and elevated Paco₂ (CSH = 1.2 [95%CI: 1.04-1.39] per 5 mm Hg increase in Pco₂; P = .02) as independent risk factors for AKI. Concerning the MV parameters, positive end-expiratory pressure (CSH = 1.11 [95% CI: 1.01-1.23] per 1 cm H₂O increase; P = .04) and the use of neuromuscular blockade (CSH = 2.96 [95% CI: 1.22-7.18]; P = .02) were associated with renal outcome only in univariate analysis but not after adjustment.

Conclusion

Acute kidney injury is frequent in patients with severe COVID-19 and is associated with a history of hypertension, the presence of hemodynamic failure, and increased Pco₂. Further studies are necessary to evaluate the impact of hypercapnia on increasing the effects of ischemia, particularly in the most at-risk vascular situations.

Rhamnetin, a Natural Flavonoid, Ameliorates Organ Damage in a Mouse Model of Carbapenem-Resistant Acinetobacter baumannii-Induced Sepsis

In sepsis, the persistence of uncontrolled inflammatory response of infected host cells eventually leads to severe lung and organ failure and, ultimately, death. Carbapenem-resistant Acinetobacter baumannii (CRAB), causative bacteria of sepsis and lung failure in acute cases, belongs to a group of critical pathogens that cannot be eradicated using the currently available antibiotics. This underlines the necessity of developing new modes of therapeutics that can control sepsis at the initial stages. In this study, we investigated the anti-inflammatory activities in vitro and in vivo and the antiseptic effects of rhamnetin, a naturally occurring flavonoid. We found that among its isoforms, the potency of rhamnetin was less explored but rhamnetin possessed superior anti-inflammatory activity with least cytotoxicity. Rhamnetin showed significant anti-inflammatory effects in lipopolysaccharide-, CRAB-, and Escherichia coli (E. coli)-stimulated mouse macrophages by inhibiting the release of interleukin-6 and nitric oxide. In a mouse model of sepsis infected with clinically isolated CRAB or E. coli, rhamnetin significantly reduced the bacterial burden in the organs. In addition, normalized pro-inflammatory cytokine levels in lung lysates and histological analysis of lung tissue indicated alleviation of lung damage. This study implies that a potent natural product such as rhamnetin could be a future therapeutic for treating carbapenem-resistant gram-negative sepsis.

Study to Explore the Association of the Renin-Angiotensin System and Right Ventricular Function in Mechanically Ventilated Patients

Background: Right ventricular (RV) dysfunction is associated with pulmonary vasoconstriction in mechanically ventilated patients. Enhancing the activity of angiotensin-converting enzyme 2 (ACE2), a key enzyme of the renin-angiotensin system (RAS), using recombinant human ACE2 (rhACE2) could alleviate RAS-mediated vasoconstriction and vascular remodeling. Methods: This prospective observational study investigated the association between concentrations of RAS peptides (Ang II or Ang(1–7)) and markers of RV function, as assessed by echocardiography (ratio of RV to left ventricular end-diastolic area, interventricular septal motion, and pulmonary arterial systolic pressure (PASP)). Results: Fifty-seven mechanically ventilated patients were enrolled. Incidence rates of acute cor pulmonale (ACP) and pulmonary circulatory dysfunction (PCD) were consistent with previous studies. In the 45 evaluable participants, no notable or consistent changes in RAS peptides concentration were observed over the observation period, and there was no correlation between Ang II concentration and either PASP or RV size. The model of the predicted posterior distributions for the pre- and post-dose values of Ang II demonstrated no change in the likelihood of PCD after hypothetical dosing with rhACE2, thus meeting the futility criteria. Similar results were observed with the other RAS peptides evaluated. Conclusions: Pre-defined success criteria for an association between PCD and the plasma RAS peptides were not met in the mechanically ventilated unselected patients.