Morphological Differences between Patient Self-inflicted and Ventilator-induced Lung Injury: An Experimental Study

Spontaneous breathing-induced lung injury in mechanically ventilated patients

PURPOSE OF REVIEW

Recent experimental and clinical studies have suggested that spontaneous effort can potentially injure the lungs. This review summarizes the harmful effects of spontaneous breathing on the lungs during mechanical ventilation in ARDS and suggests potential strategies to minimize spontaneous breathing-induced lung injury.

RECENT FINDINGS

Recent clinical and experimental studies have shown that vigorous spontaneous breathing during mechanical ventilation can potentially injure the lungs due to high transpulmonary pressure, the Pendelluft phenomenon, increased pulmonary perfusion, and patient-ventilator asynchrony. A definitive approach to minimize spontaneous breathing-induced lung injury is the systemic use of neuromuscular blocking agents; however, there is a risk of muscle atrophy. Alternatively, partial paralysis, bilateral phrenic nerve blockade, and sedatives may be useful for decreasing force generation from the diaphragm while maintaining muscle function. A higher positive end-expiratory pressure (PEEP) and prone positioning may reduce force generation from the diaphragm by decreasing neuromechanical efficiency.

SUMMARY

Several potential strategies, including neuromuscular blockade, partial paralysis, phrenic nerve blockade, sedatives, PEEP, and prone positioning, could be useful to minimize spontaneous breathing-induced lung injury.

Bedside Assessment of the Respiratory System During Invasive Mechanical Ventilation

Assessing the respiratory system of a patient receiving mechanical ventilation is complex. We provide an overview of an approach at the bedside underpinned by physiology. We discuss the importance of distinguishing between extensive and intensive ventilatory variables. We outline methods to evaluate both passive patients and those making spontaneous respiratory efforts during assisted ventilation. We believe a comprehensive assessment can influence setting mechanical ventilatory support to achieve lung and diaphragm protective ventilation.

The protective effect of carbamazepine on acute lung injury induced by hemorrhagic shock and resuscitation in rats

Hemorrhagic shock and resuscitation (HSR) enhances the risk of acute lung injury (ALI). This study investigated the protective effect of carbamazepine (CBZ) on HSR-induced ALI in rats. Male Sprague-Dawley rats were allocated into five distinct groups through randomization: control (SHAM), saline + HSR (HSR), CBZ + HSR (CBZ/HSR), dimethyl sulfoxide (DMSO) + HSR (DMSO/HSR), and CBZ + chloroquine (CQ) + HSR (CBZ/CQ/HSR). Subsequently, HSR models were established. To detect tissue damage, we measured lung histological changes, lung injury scores, and wet/dry weight ratios. We measured neutrophil counts as well as assessed the expression of inflammatory factors using RT-PCR to determine the inflammatory response. We detected autophagy-related proteins LC3II/LC3I, P62, Beclin-1, and Atg12-Atg5 using western blotting. Pretreatment with CBZ improved histopathological changes in the lungs and reduced lung injury scores. The CBZ pretreatment group exhibited significantly reduced lung wet/dry weight ratio, neutrophil aggregation and number, and inflammation factor (TNF-α and iNOS) expression. CBZ changed the expression levels of autophagy-related proteins (LC3II/LC3I, beclin-1, Atg12-Atg5, and P62), suggesting autophagy activation. However, after injecting CQ, an autophagy inhibitor, the beneficial effects of CBZ were reversed. Taken together, CBZ pretreatment improved HSR-induced ALI by suppressing inflammation, at least in part, through activating autophagy. Thus, our study offers a novel perspective for treating HSR-induced ALI.

Resistive spontaneous breathing exacerbated lipopolysaccharide-induced lung injury in mice

Background

Spontaneous respiratory mechanical force interacted with the primary lung injury and aggravated the progression of ARDS clinically. But the exact role and involved mechanism of it in the pathogenesis of ARDS animal model remained obscure.

Aim

This study was to investigate the effect of spontaneous respiratory mechanical force on lung injury of ARDS in mice.

Methods

Female C57BL/6 mice were subjected to resistive spontaneous breathing (RSB) by tracheal banding after 4-6 h of intranasal inhalation of LPS. Pulmonary function was examined by Buxco system, partial pressures of oxygen and carbon dioxide (PO2 and PCO2) were measured by a blood gas analyzer, and lung pathological changes were analyzed with hematoxylin and eosin staining. The levels of inflammatory markers were quantified by ELISA, total protein assay, and FACS analysis. The expression levels of mechanosensitive ion channels were detected by qRT-PCR and immunohistochemistry.

Results

The airway resistance (Raw) was increased and the tidal volume (TV) was decreased remarkedly in RSB group. RSB treatment did not affect PO2, PCO2, pathology and inflammation levels of lung in mice. The Raw increased and ventilatory indicators decreased in RSB + ARDS compared to ARDS significantly. Besides, RSB treatment deteriorated the changes of PO2, PCO2 and level of lactic acid induced by LPS. Meanwhile, RSB significantly promoted LPS-induced pulmonary histopathological injury, and elevated the levels of IL-1β, IL-6, TNF-α and total proteins, increased neutrophils infiltration. The expression level of Piezo1 in RSB + ARDS group was remarkably reduced compared to ARDS group and consistent with the severity of pulmonary damage.

Conclusion

RSB exacerbated LPS-induced ARDS hypoxemia and hypercapnia, inflammation and damage. The mechanosensitive protein Piezo1 expression decreased and may play an important role in the process.

Association between mechanical ventilation parameters and mortality in children with respiratory failure on ECMO: a systematic review and meta-analysis

Background

In refractory respiratory failure (RF), extracorporeal membrane oxygenation (ECMO) is a salvage therapy that seeks to reduce lung injury induced by mechanical ventilation. The parameters of optimal mechanical ventilation in children during ECMO are not known. Pulmonary ventilatory management during this therapy may impact mortality. The objective of this study was to evaluate the association between ventilatory parameters in children during ECMO therapy and in-hospital mortality.

Methods

A systematic search of PubMed/MEDLINE, Embase, Cochrane, and Google Scholar from January 2013 until May 2022 (PROSPERO 450744), including studies in children with ECMO-supported RF assessing mechanical ventilation parameters, was conducted. Risk of bias was assessed using the Newcastle-Ottawa scale; heterogeneity, with absence <25% and high >75%, was assessed using I2. Sensitivity and subgroup analyses using the Mantel-Haenszel random-effects model were performed to explore the impact of methodological quality on effect size.

Results

Six studies were included. The median age was 3.4 years (IQR: 3.2-4.2). Survival in the 28-day studies was 69%. Mechanical ventilation parameters associated with higher mortality were a very low tidal volume ventilation (<4 ml/kg; OR: 4.70; 95% CI: 2.91-7.59; p < 0.01; I2: 38%), high plateau pressure (mean Dif: -0.70 95% CI: -0.18, -0.22; p < 0.01), and high driving pressure (mean Dif: -0.96 95% CI: -1.83, -0.09: p = 0.03). The inspired fraction of oxygen (p = 0.09) and end-expiratory pressure (p = 0.69) were not associated with higher mortality. Patients who survived had less multiple organ failure (p < 0.01).

Conclusion

The mechanical ventilation variables associated with higher mortality in children with ECMO-supported respiratory failure are high plateau pressures, high driving pressure and very low tidal volume ventilation. No association between mortality and other parameters of the mechanical ventilator, such as the inspired fraction of oxygen or end-expiratory pressure, was found.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023450744, PROSPERO 2023 (CRD42023450744).

Endotracheal tube, by the venturi effect, reduces the efficacy of increasing inlet pressure in improving pendelluft

In mechanically ventilated severe acute respiratory distress syndrome patients, spontaneous inspiratory effort generates more negative pressure in the dorsal lung than in the ventral lung. The airflow caused by this pressure difference is called pendelluft, which is a possible mechanisms of patient self-inflicted lung injury. This study aimed to use computer simulation to understand how the endotracheal tube and insufficient ventilatory support contribute to pendelluft. We established two models. In the invasive model, an endotracheal tube was connected to the tracheobronchial tree with 34 outlets grouped into six locations: the right and left upper, lower, and middle lobes. In the non-invasive model, the upper airway, including the glottis, was connected to the tracheobronchial tree. To recreate the inspiratory effort of acute respiratory distress syndrome patients, the lower lobe pressure was set at -13 cmH2O, while the upper and middle lobe pressure was set at -6.4 cmH2O. The inlet pressure was set from 10 to 30 cmH2O to recreate ventilatory support. Using the finite volume method, the total flow rates through each model and toward each lobe were calculated. The invasive model had half the total flow rate of the non-invasive model (1.92 L/s versus 3.73 L/s under 10 cmH2O, respectively). More pendelluft (gas flow into the model from the outlets) was observed in the invasive model than in the non-invasive model. The inlet pressure increase from 10 to 30 cmH2O decreased pendelluft by 11% and 29% in the invasive and non-invasive models, respectively. In the invasive model, a faster jet flowed from the tip of the endotracheal tube toward the lower lobes, consequently entraining gas from the upper and middle lobes. Increasing ventilatory support intensifies the jet from the endotracheal tube, causing a venturi effect at the bifurcation in the tracheobronchial tree. Clinically acceptable ventilatory support cannot completely prevent pendelluft.