Mechanical ventilation in acute respiratory distress syndrome: The open lung revisited

Hypertonic treatment of acute respiratory distress syndrome

Many viral infections, including the COVID-19 infection, are associated with the hindrance of blood oxygenation due to the accumulation of fluid, inflammatory cells, and cell debris in the lung alveoli. This condition is similar to Acute Respiratory Distress Syndrome (ARDS). Mechanical positive-pressure ventilation is often used to treat this condition, even though it might collapse pulmonary capillaries, trapping red blood cells and lowering the lung's functional capillary density. We posit that the hyperosmotic-hyperoncotic infusion should be explored as a supportive treatment for ARDS. As a first step in verifying the feasibility of this ARDS treatment, we model the dynamics of alveolar fluid extraction by osmotic effects. These are induced by increasing blood plasma osmotic pressure in response to the increase of blood NaCl concentration. Our analysis of fluid drainage from a plasma-filled pulmonary alveolus, in response to the intravenous infusion of 100 ml of 1.28 molar NaCl solution, shows that alveoli empty of fluid in approximately 15 min. These modeling results are in accordance with available experimental and clinical data; no new data were collected. They are used to calculate the temporal change of blood oxygenation, as oxygen diffusion hindrance decreases upon absorption of the alveolar fluid into the pulmonary circulation. Our study suggests the extraordinary speed with which beneficial effects of the proposed ARDS treatment are obtained and highlight its practicality, cost-efficiency, and avoidance of side effects of mechanical origin.

Optimal positive end-expiratory pressure reduces right ventricular dysfunction in COVID-19 patients on venovenous extracorporeal membrane oxygenation: A retrospective single-center study

While mechanical ventilation practices on venovenous extracorporeal membrane oxygenation (VV ECMO) are variable, most institutions utilize a lung rest strategy utilizing relatively low positive end-expiratory pressure (PEEP). The effect of PEEP titration using esophageal manometry during VV ECMO on pulmonary and cardiac function is unknown. This was a retrospective study of 69 patients initiated on VV ECMO between March 2020 through November 2021. Patients underwent standard PEEP (typically 10 cm H₂O) or optimal PEEP (PEEP titrated to an end-expiratory transpulmonary pressure 0-3 cm H₂O) throughout the ECMO run. The optimal PEEP strategy had higher levels of applied PEEP (17.9 vs. 10.8 cm H₂O on day 2 of ECMO), decreased incidence of hemodynamically significant RV dysfunction (4.55% vs. 44.0%, p = 0.0001), and higher survival to decannulation (72.7% vs. 44.0%, p = 0.022). Survival to discharge did not reach statistical significance (27% vs. 11%, p = 0.211). In univariate logistic regression analysis, optimal PEEP was associated with less hemodynamically significant RV dysfunction with an odds ratio (OR) of 0.06 (95% confidence interval [CI] = 0.01-0.27, p = 0.0008) and increased survival to decannulation with an OR of 3.39 (95% CI 1.23-9.79), p = 0.02), though other confounding factors may have contributed.

Extracorporeal membrane oxygenation (ECMO) and beyond in near fatal asthma: A comprehensive review

The treatment of choice in severe asthma exacerbations with respiratory failure includes ventilatory support, both invasive and/or non-invasive, along with different kinds of asthma medication. Of note, the rate of mortality of patients with asthma has decreased substantially in recent years mainly due to significant advances in pharmacological treatment and other management strategies. However, the risk of death in patients with severe asthma who require invasive mechanical ventilation has been estimated between 6.5% and 10.3%. When conventional measures fail, rescue strategies, such as extracorporeal membrane oxygenation (ECMO) or extracorporeal CO2 removal (ECCO2R) may need to be implemented. While ECMO does not constitute a definitive treatment per se, it can minimize further ventilator associated lung injury (VALI) and can enable diagnostic-therapeutic maneuvers that cannot be performed without ECMO such as bronchoscopy and transfer for diagnostic imaging. Asthma is one of the diseases that is associated with excellent outcomes for patients with refractory respiratory failure requiring ECMO support, as shown by the Extracorporeal Life Support Organization (ELSO) registry. Moreover, in such situations, the use of ECCO2R for rescue has been described and utilized in both children and adults and is more widely spread in different hospitals than ECMO. In this article, we aim to review the evidence for the usefulness of extracorporeal respiratory support measures in the management of severe asthma exacerbations that lead to respiratory failure.

The Neutrophil-to-Lymphocyte Ratio is Associated with the Requirement and the Duration of Invasive Mechanical Ventilation in Acute Respiratory Distress Syndrome Patients: A Retrospective Study

Background

Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality and most ARDS patients require ventilatory support. Applying appropriate ventilation strategies based on patients' individual situations has a direct impact upon patients' outcome. The neutrophil-to-lymphocyte ratio (NLR) has been shown to predict the early requirement of invasive mechanical ventilation (IMV) in patients with coronavirus disease 2019 (COVID-19). Our study aimed to investigate the relationship between baseline NLR and IMV in ARDS.

Methods

A retrospective study was performed on patients who were diagnosed with ARDS using the Berlin definition and admitted to the First Affiliated Hospital of Soochow University from 2017 to 2022. Clinical data within 24 h after the ARDS diagnosis were collected from the medical record system. Based on the ventilation strategies during hospitalization, patients were divided into three groups and their clinical characteristics were compared. Furthermore, logistic regression analysis was used to screen the independent risk factors for IMV. STROBE checklist was used for this manuscript.

Results

520 ARDS patients were included and the median NLR value in IMV group was significantly higher than that of other groups (P < 0.001). NLR was significantly associated with the requirement of IMV in ARDS patients (OR, 1.042; 95% CI, 1.025–1.060; P < 0.001), other independent risk factors included PaO₂/FiO₂, Hb, lactate, and use of vasoactive drugs (all P < 0.05). Moreover, we found that the duration of IMV was longer in patients with high NLR (8[IQR, 3–13], 10[IQR, 6–16], respectively, P=0.025).

Conclusions

Our results revealed that high baseline NLR level was significantly correlated with an increased risk of IMV in patients with ARDS. Furthermore, higher NLR was associated with prolonged duration of IMV in patients with ARDS.

High versus low positive end-expiratory pressure (PEEP) levels for mechanically ventilated adult patients with acute lung injury and acute respiratory distress syndrome

BACKGROUND

In patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), mortality remains high. These patients require mechanical ventilation, which has been associated with ventilator-induced lung injury. High levels of positive end-expiratory pressure (PEEP) could reduce this condition and improve patient survival. This is an updated version of the review first published in 2013.

OBJECTIVES

To assess the benefits and harms of high versus low levels of PEEP in adults with ALI and ARDS.

SEARCH METHODS

For our previous review, we searched databases from inception until 2013. For this updated review, we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, LILACS, and the Web of Science from inception until May 2020. We also searched for ongoing trials (www.trialscentral.org; www.clinicaltrial.gov; www.controlled-trials.com), and we screened the reference lists of included studies.

SELECTION CRITERIA

We included randomised controlled trials that compared high versus low levels of PEEP in ALI and ARDS participants who were intubated and mechanically ventilated in intensive care for at least 24 hours.

DATA COLLECTION AND ANALYSIS

Two review authors assessed risk of bias and extracted data independently. We contacted investigators to identify additional published and unpublished studies. We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included four new studies (1343 participants) in this review update. In total, we included 10 studies (3851 participants). We found evidence of risk of bias in six studies, and the remaining studies fulfilled all criteria for low risk of bias. In eight studies (3703 participants), a comparison was made between high and low levels of PEEP, with the same tidal volume in both groups. In the remaining two studies (148 participants), the tidal volume was different between high- and low-level groups. In the main analysis, we assessed mortality occurring before hospital discharge only in studies that compared high versus low PEEP, with the same tidal volume in both groups. Evidence suggests that high PEEP may result in little to no difference in mortality compared to low PEEP (risk ratio (RR) 0.97, 95% confidence interval (CI) 0.90 to 1.04; I² = 15%; 7 studies, 3640 participants; moderate-certainty evidence). In addition, high PEEP may result in little to no difference in barotrauma (RR 1.00, 95% CI 0.64 to 1.57; I² = 63%; 9 studies, 3791 participants; low-certainty evidence). High PEEP may improve oxygenation in patients up to the first and third days of mechanical ventilation (first day: mean difference (MD) 51.03, 95% CI 35.86 to 66.20; I² = 85%; 6 studies, 2594 participants; low-certainty evidence; third day: MD 50.32, 95% CI 34.92 to 65.72; I² = 83%; 6 studies, 2309 participants; low-certainty evidence) and probably improves oxygenation up to the seventh day (MD 28.52, 95% CI 20.82 to 36.21; I² = 0%; 5 studies, 1611 participants; moderate-certainty evidence). Evidence suggests that high PEEP results in little to no difference in the number of ventilator-free days (MD 0.45, 95% CI -2.02 to 2.92; I² = 81%; 3 studies, 1654 participants; low-certainty evidence). Available data were insufficient to pool the evidence for length of stay in the intensive care unit.

AUTHORS' CONCLUSIONS

Moderate-certainty evidence shows that high levels compared to low levels of PEEP do not reduce mortality before hospital discharge. Low-certainty evidence suggests that high levels of PEEP result in little to no difference in the risk of barotrauma. Low-certainty evidence also suggests that high levels of PEEP improve oxygenation up to the first and third days of mechanical ventilation, and moderate-certainty evidence indicates that high levels of PEEP improve oxygenation up to the seventh day of mechanical ventilation. As in our previous review, we found clinical heterogeneity - mainly within participant characteristics and methods of titrating PEEP - that does not allow us to draw definitive conclusions regarding the use of high levels of PEEP in patients with ALI and ARDS. Further studies should aim to determine the appropriate method of using high levels of PEEP and the advantages and disadvantages associated with high levels of PEEP in different ARDS and ALI patient populations.

Case Report: Severe ARDS in a Pediatric Hematopoietic Stem-Cell Transplantation Recipient Caused by Disseminated Toxoplasmosis

Toxoplasma gondii infection is a severe complication of hematopoietic stem-cell transplantation (HSCT) recipients that can remain unnoticed without a high clinical suspicion. We present the case of a 6-year-old patient with acute lymphoblastic leukemia and HSCT recipient who was admitted to the Pediatric Intensive Care Unit (PICU) on post-transplantation day +39 with fever, hypotension, severe respiratory distress and appearance of a lumbar subcutaneous node. She developed severe Acute Respiratory Distress Syndrome (ARDS) and underwent endotracheal intubation and early mechanical ventilation. Subsequently, she required prone ventilation, inhaled nitric oxide therapy and high-frequency oscillatory ventilation (HFOV). An etiologic study was performed, being blood, urine, bronchoalveolar lavage and biopsy of the subcutaneous node positive for Toxoplasma gondii by Polymerase Chain Reaction (PCR). Diagnosis of disseminated toxoplasmosis was established and treatment with pyrimethamine, sulfadiazine and folinic acid started. The patient showed clinical improvement, allowing weaning of mechanical ventilation and transfer to the hospitalization ward after 40 days in the PICU. It is important to consider toxoplasmosis infection in immunocompromised patients with sepsis and, in cases of severe respiratory distress, early mechanical ventilation should be started using the open lung approach. In Toxoplasma IgG positive patients, close monitoring and appropriate anti-infectious prophylaxis is needed after HSCT.

Effect of lung recruitment on blood gas index, hemodynamics, lung compliance, and rehabilitation index in children with acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a common pediatric disease, with an increasing mortality rate in recent years. This study aims to explore the effects of lung recruitment on blood gas indexes, hemodynamics, lung compliance, and rehabilitation index in children with ARDS.

METHODS

Seventy children with ARDS admitted to our hospital from December 2017 to December 2018 were selected as the study subjects, and were divided into a study group (35 cases, treated with lung recruitment strategy) and a control group (35 cases, treated with routine therapy). The changes of blood gas indexes, such as partial pressure of oxygen (PO₂), partial pressure of carbon dioxide (PCO₂), and partial pressure of oxygen/fraction of inspired oxygen (PO₂/FiO₂) levels, as well as hemodynamic indexes, including cardiac output (CO), heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), were compared before and after treatment in the two groups.

RESULTS

Results showed that the difference in blood gas indexes between the two groups was statistically significant after treatment (P<0.05), and that the levels of PaO₂, PaCO₂, pondus Hydrogenii (pH), and PO₂/FiO₂ in the study group were all higher compared to the control group (P<0.05). The hemodynamic indexes showed that CO was significantly different between the two groups (P<0.05), but HR, MAP, and CVP were not (P>0.05). The lung compliance values of the two groups continued to increase at different time points after treatment (P<0.05), and the lung compliance of the study group was higher than that of the control group immediately after recruitment, as well as at 10 and 60 min of lung recruitment (P<0.05). In addition, the ventilator use, ICU stay, and hospital stay times of the study group were shorter than those in the control group (P<0.05), and the mortality rate of the study group was lower than that of the control group (P>0.05).

CONCLUSIONS

The lung recruitment strategy has a significant therapeutic effect on children with ARDS. It can effectively improve blood and gas function and lung compliance, and has a positive effect on the hemodynamic stability of children with ARDS.

Outcomes of ventilatory asynchrony in patients with inspiratory effort

Objective

To identify the relationship of patient-ventilator asynchrony with the level of sedation and hemogasometric and clinical results.

Methods

This was a prospective study of 122 patients admitted to the intensive care unit who underwent > 24 hours of invasive mechanical ventilation with inspiratory effort. In the first 7 days of ventilation, patient-ventilator asynchrony was evaluated daily for 30 minutes. Severe patient-ventilator asynchrony was defined as an asynchrony index > 10%.

Results

A total of 339,652 respiratory cycles were evaluated in 504 observations. The mean asynchrony index was 37.8% (standard deviation 14.1 - 61.5%). The prevalence of severe patient-ventilator asynchrony was 46.6%. The most frequent patient-ventilator asynchronies were ineffective trigger (13.3%), autotrigger (15.3%), insufficient flow (13.5%), and delayed cycling (13.7%). Severe patient-ventilator asynchrony was related to the level of sedation (ineffective trigger: p = 0.020; insufficient flow: p = 0.016; premature cycling: p = 0.023) and the use of midazolam (p = 0.020). Severe patient-ventilator asynchrony was also associated with hemogasometric changes. The persistence of severe patient-ventilator asynchrony was an independent risk factor for failure of the spontaneous breathing test, ventilation time, ventilator-associated pneumonia, organ dysfunction, mortality in the intensive care unit, and length of stay in the intensive care unit.

Conclusion

Patient-ventilator asynchrony is a frequent disorder in critically ill patients with inspiratory effort. The patient’s interaction with the ventilator should be optimized to improve hemogasometric parameters and clinical results. Further studies are required to confirm these results.

ROS Signaling in the Pathogenesis of Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS)

The generation of reactive oxygen species (ROS) plays an important role for the maintenance of cellular processes and functions in the body. However, the excessive generation of oxygen radicals under pathological conditions such as acute lung injury (ALI) and its most severe form acute respiratory distress syndrome (ARDS) leads to increased endothelial permeability. Within this hallmark of ALI and ARDS, vascular microvessels lose their junctional integrity and show increased myosin contractions that promote the migration of polymorphonuclear leukocytes (PMNs) and the transition of solutes and fluids in the alveolar lumen. These processes all have a redox component, and this chapter focuses on the role played by ROS during the development of ALI/ARDS. We discuss the origins of ROS within the cell, cellular defense mechanisms against oxidative damage, the role of ROS in the development of endothelial permeability, and potential therapies targeted at oxidative stress.

Anti-inflammatory effect of dexmedetomidine combined with hypothermia on acute respiratory distress syndrome in rats

BACKGROUND

To investigate the protective effect of combination of dexmedetomidine and hypothermia on lipopolysaccharide (LPS) induced acute respiratory distress syndrome in rats.

METHODS

Fifty male Wistar rats were randomly divided into five groups, with 10 rats in each group. The acute respiratory distress syndrome model was reproduced by LPS injected into the right external jugular vein (L group); only saline was injected into the right external jugular vein for control group (C group). In hypothermia group (T group), the body temperature was lowered to 32.5°C-33.0°C after 1 h of LPS injection, and 10 rats were sacrificed at 8 h. Group dexmedetomidine (D group) and dexmedetomidine combined with hypothermia group (DT group) received intraperitoneal dexmedetomidine 30 min before LPS was injected. The arterial blood gas was determined in all the groups before and 8 h after instillation of saline or LPS, and the oxygenation index (PaO₂/FiO₂) was calculated. The pro-inflammatory cytokines TNF-alpha (TNF-α) and interleukin- 6 (IL-6) levels were determined by enzyme-linked immunosorbent assay. The expression of inflammatory signaling proteins in bronchial alveolar lavage fluid was determined by Western blot.

RESULTS

Compared with group L, TNF-α and IL-6 levels in serum of rats were significantly lower (P < 0.05), the expression of toll-like receptors 4 and phosphorylated c-Jun N-terminal kinase was significantly lower (P < 0.05), and the p-Akt level was significantly higher (P < 0.05). Moreover, the dexmedetomidine combined with hypothermia treated was superior to the single method.

CONCLUSIONS

The combination of dexmedetomidine and hypothermia could alleviate acute lung injury in rats.