FiftyYears ofResearch inARDS. Spontaneous Breathing during Mechanical Ventilation. Risks, Mechanisms, and Management

Mechanical ventilation in septic shock

PURPOSE OF REVIEW

The aim of this study was to review the most recent literature on mechanical ventilation strategies in patients with septic shock.

RECENT FINDINGS

Indirect clinical trial evidence has refined the use of neuromuscular blocking agents, positive end-expiratory pressure (PEEP) and recruitment manoeuvres in septic shock patients with acute respiratory distress syndrome. Weaning strategies and devices have also been recently evaluated. The role of lung protective ventilation in patients with healthy lungs, while recognized, still needs to be further refined. The possible detrimental effects of spontaneous breathing in patients who develop acute respiratory distress syndrome is increasingly recognized, but clinical trial evidence is still lacking to confirm this hypothesis. A new concept of lung and diaphragm protective is emerging in the critical care literature, but its application will need a complex intervention implementation approach to allow adequate scrutiny of this concept and uptake by clinicians.

SUMMARY

Many advances in the management of the mechanically ventilated patient with sepsis and septic shock have occurred in recent years, but clinical trial evidence is still necessary to translate new hypotheses to the bedside and find the right balance between benefits and risks of these new strategies.

Spontaneous Versus Controlled Mechanical Ventilation in Patients with Acute Respiratory Distress Syndrome

Purpose of Review

To review clinical evidence on whether or not to allow mechanically ventilated patients with acute respiratory distress syndrome (ARDS) to breathe spontaneously.

Recent Findings

Observational data (LUNG SAFE study) indicate that mechanical ventilation allowing for spontaneous breathing (SB) is associated with more ventilator-free days and a shorter stay in the intensive care unit without any effect on hospital mortality. A paediatric trial, comparing airway pressure release ventilation (APRV) and low-tidal volume ventilation, showed an increase in mortality in the APRV group. Conversely, in an unpublished trial comparing SB and controlled ventilation (NCT01862016), the authors concluded that SB is feasible but did not improve outcomes in ARDS patients.

Summary

A paucity of clinical trial data continues to prevent firm guidance on if or when to allow SB during mechanical ventilation in patients with ARDS. No published large randomised controlled trial exists to inform practice about the benefits and harms of either mode.

Functional pathophysiology of SARS-CoV-2-induced acute lung injury and clinical implications

The worldwide pandemic caused by the SARS-CoV-2 virus has resulted in over 84,407,000 cases, with over 1,800,000 deaths when this paper was submitted, with comorbidities such as gender, race, age, body mass, diabetes, and hypertension greatly exacerbating mortality. This review will analyze the rapidly increasing knowledge of COVID-19-induced lung pathophysiology. Although controversial, the acute respiratory distress syndrome (ARDS) associated with COVID-19 (CARDS) seems to present as two distinct phenotypes: type L and type H. The "L" refers to low elastance, ventilation/perfusion ratio, lung weight, and recruitability, and the "H" refers to high pulmonary elastance, shunt, edema, and recruitability. However, the LUNG-SAFE (Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure) and ESICM (European Society of Intensive Care Medicine) Trials Groups have shown that ∼13% of the mechanically ventilated non-COVID-19 ARDS patients have the type-L phenotype. Other studies have shown that CARDS and ARDS respiratory mechanics overlap and that standard ventilation strategies apply to these patients. The mechanisms causing alterations in pulmonary perfusion could be caused by some combination of 1) renin-angiotensin system dysregulation, 2) thrombosis caused by loss of endothelial barrier, 3) endothelial dysfunction causing loss of hypoxic pulmonary vasoconstriction perfusion control, and 4) hyperperfusion of collapsed lung tissue that has been directly measured and supported by a computational model. A flowchart has been constructed highlighting the need for personalized and adaptive ventilation strategies, such as the time-controlled adaptive ventilation method, to set and adjust the airway pressure release ventilation mode, which recently was shown to be effective at improving oxygenation and reducing inspiratory fraction of oxygen, vasopressors, and sedation in patients with COVID-19.

Inspiratory Efforts, Positive End-Expiratory Pressure, and External Resistances Influence Intraparenchymal Gas Redistribution in Mechanically Ventilated Injured Lungs

Background

Potentially harmful lung overstretch can follow intraparenchymal gas redistribution during mechanical ventilation. We hypothesized that inspiratory efforts characterizing spontaneous breathing, positive end-expiratory pressure (PEEP), and high inspiratory resistances influence inspiratory intraparenchymal gas redistribution.

Methods

This was an experimental study conducted on a swine model of mild acute respiratory distress syndrome. Dynamic computed tomography and respiratory mechanics were simultaneously acquired at different PEEP levels and external resistances, during both spontaneous breathing and controlled mechanical ventilation. Images were collected at two cranial-caudal levels. Delta-volume images (ΔVOLs) were obtained subtracting pairs of consecutive inspiratory images. The first three ΔVOLs, acquired for each analyzed breath, were used for the analysis of inspiratory pendelluft defined as intraparenchymal gas redistribution before the start of inspiratory flow at the airway opening. The following ΔVOLs were used for the analysis of gas redistribution during ongoing inspiratory flow at the airway opening.

Results

During the first flow-independent phase of inspiration, the pendelluft of gas was observed only during spontaneous breathing and along the cranial-to-caudal and nondependent-to-dependent directions. The pendelluft was reduced by high PEEP (p < 0.04 comparing PEEP 15 and PEEP 0 cm H₂O) and low external resistances (p < 0.04 comparing high and low external resistance). During the flow-dependent phase of inspiration, two patterns were identified: (1) gas displacing characterized by large gas redistribution areas; (2) gas scattering characterized by small, numerous areas of gas redistribution. Gas displacing was observed at low PEEP, high external resistances, and it characterized controlled mechanical ventilation (p < 0.01, comparing high and low PEEP during controlled mechanical ventilation).

Conclusions

Low PEEP and high external resistances favored inspiratory pendelluft. During the flow-dependent phase of the inspiration, controlled mechanical ventilation and low PEEP and high external resistances favored larger phenomena of intraparenchymal gas redistribution (gas displacing) endangering lung stability.

Noninvasive ventilation in critically ill very old patients with pneumonia: A multicenter retrospective cohort study

Background

Very old patients (≥ 80 years-old, VOP) are increasingly admitted to intensive care units (ICUs). Community-acquired pneumonia (CAP) is a common reason for admission and the best strategy of support for respiratory failure in this scenario is not fully known. We evaluated whether noninvasive ventilation (NIV) would be beneficial compared to invasive mechanical ventilation (IMV) regarding hospital mortality.

Methods

Multicenter cohort study of VOPs admitted with CAP in need of IMV or NIV to 11 Brazilian ICUs from 2009 through 2012. We used logistic regression models to evaluate the association between the initial ventilatory strategy (NIV vs. IMV) and hospital mortality adjusting for confounding factors. We evaluated effect modification with interaction terms in pre-specified sub-groups.

Results

Of 369 VOPs admitted for CAP with respiratory failure, 232 (63%) received NIV and 137 (37%) received IMV as initial ventilatory strategy. IMV patients were sicker at baseline (median SOFA 8 vs. 4). Hospital mortality was 114/232 (49%) for NIV and 90/137 (66%) for IMV. For the comparison NIV vs. IMV (reference), the crude odds ratio (OR) was 0.50 (95% CI, 0.33–0.78, p = 0.002). This association was largely confounded by antecedent characteristics and non-respiratory SOFA (_adjOR = 0.70, 95% CI, 0.41–1.20, p = 0.196). The fully adjusted model, additionally including P_ao₂/F_io₂ ratio, pH and P_aco₂, yielded an _adjOR of 0.81 (95% CI, 0.46–1.41, p = 0.452). There was no strong evidence of effect modification among relevant subgroups, such as P_ao₂/F_io₂ ratio ≤ 150 (p = 0.30), acute respiratory acidosis (p = 0.42) and non-respiratory SOFA ≥ 4 (p = 0.53).

Conclusions

NIV was not associated with lower hospital mortality when compared to IMV in critically ill VOP admitted with CAP, but there was no strong signal of harm from its use. The main confounders of this association were both the severity of respiratory dysfunction and of extra-respiratory organ failures.

Esophageal Manometry

The estimation of pleural pressure with esophageal manometry has been used for decades, and it has been a fertile area of physiology research in healthy subject as well as during mechanical ventilation in patients with lung injury. However, its scarce adoption in clinical practice takes its roots from the (false) ideas that it requires expertise with years of training, that the values obtained are not reliable due to technical challenges or discrepant methods of calculation, and that measurement of esophageal pressure has not proved to benefit patient outcomes. Despites these criticisms, esophageal manometry could contribute to better monitoring, optimization, and personalization of mechanical ventilation from the acute initial phase to the weaning period. This review aims to provide a comprehensive but comprehensible guide addressing the technical aspects of esophageal catheter use, its application in different clinical situations and conditions, and an update on the state of the art with recent studies on this topic and on remaining questions and ways for improvement.

Prevent deterioration and long-term ventilation: intensive care following thoracic surgery

PURPOSE OF REVIEW

Patients with indication for lung surgery besides the pulmonary pathology often suffer from independent comorbidities affecting several other organ systems. Preventing patients from harmful complications due to decompensation of underlying organ insufficiencies perioperatively is pivotal. This review draws attention to the peri- and postoperative responsibility of the anaesthetist and intensivist to prevent patients undergoing lung surgery deterioration.

RECENT FINDINGS

During the last decades we had to accept that 'traditional' intensive care medicine implying deep sedation, controlled ventilation, liberal fluid therapy, and broad-spectrum antimicrobial therapy because of several side-effects resulted in prolongation of hospital length of stay and a decline in quality of life. Modern therapy therefore should focus on the convalescence of the patient and earliest possible reintegration in the 'life-before.' Avoidance of sedative and anticholinergic drugs, early extubation, prophylactic noninvasive ventilation and high-flow nasal oxygen therapy, early mobilization, well-adjusted fluid balance and reasonable use of antibiotics are the keystones of success.

SUMMARY

A perioperative interprofessional approach and a change in paradigms are the prerequisites to improve outcome and provide treatment for elder and comorbid patients with an indication for thoracic surgery.

High-flow Oxygen Therapy via Tracheostomy to Liberate COVID-19-induced ARDS from Invasive Ventilation: A Case Series

Lung involvement with differing phenotypes characterizes COVID-19-induced acute respiratory distress syndrome (CARDS). The liberation of these patients from mechanical ventilation has been challenging. Excessive stress and strain following increased respiratory efforts spiral their vulnerable lung tissue into ventilator-induced lung injury vortex. The use of high-flow oxygen therapy via tracheostomy (HFOTTracheal)eases weaning process. As a safe option for both the patient and the healthcare workers, HFOTTracheal was successfully employed to wean two CARDS patients from the mechanical ventilator. How to cite this article: Vadi S, Phadtare S, Shetty K. High-flow Oxygen Therapy via Tracheostomy to Liberate COVID-19-induced ARDS from Invasive Ventilation: A Case Series. Indian J Crit Care Med 2021;25(6):724-728.

Evolving targets for sedation during mechanical ventilation

PURPOSES OF REVIEW

Critically ill patients frequently require mechanical ventilation as part of their care. Administration of analgesia and sedation to ensure patient comfort and facilitate mechanical ventilation must be balanced against the known negative consequences of excessive sedation. The present review focuses on the current evidence for sedation management during mechanical ventilation, including choice of sedatives, sedation strategies, and special considerations for acute respiratory distress syndrome (ARDS).

RECENT FINDINGS

The Society of Critical Care Medicine recently published their updated clinical practice guidelines for analgesia, agitation, sedation, delirium, immobility, and sleep in adult patients in the ICU. Deep sedation, especially early in the course of mechanical ventilation, is associated with prolonged time to liberation from mechanical ventilation, longer ICU stays, longer hospital stays, and increased mortality. Dexmedetomidine may prevent ICU delirium when administered nocturnally at low doses; however, it was not shown to improve mortality when used as the primary sedative early in the course of mechanical ventilation, though the majority of patients in the informing study failed to achieve the prescribed light level of sedation. In a follow up to the ACURASYS trial, deep sedation with neuromuscular blockade did not result in improved mortality compared to light sedation in patients with severe ARDS.

SUMMARY

Light sedation should be targeted early in the course of mechanical ventilation utilizing daily interruptions of sedation and/or nursing protocol-based algorithms, even in severe ARDS.

NAVA and PAV+ for lung and diaphragm protection

PURPOSE OF REVIEW

Complications of mechanical ventilation, such as ventilator-induced lung injury (VILI) and ventilator-induced diaphragmatic dysfunction (VIDD), adversely affect the outcome of critically ill patients. Although mostly studied during control ventilation, it is increasingly appreciated that VILI and VIDD also occur during assisted ventilation. Hence, current research focuses on identifying ways to monitor and deliver protective ventilation in assisted modes. This review describes the operating principles of proportional modes of assist, their implications for lung and diaphragm protective ventilation, and the supporting clinical data.

RECENT FINDINGS

Proportional modes of assist, proportional assist ventilation, PAV, and neurally adjusted ventilatory assist, NAVA, deliver a pressure assist that is proportional to the patient's effort, enabling ventilation to be better controlled by the patient's brain. This control underlies the potential of proportional modes to avoid over-assist and under-assist, improve patient--ventilator interaction, and provide protective ventilation. Indeed, in clinical studies, proportional modes have been associated with reduced asynchronies, enhanced diaphragmatic recovery, and limitation of excessive tidal volume. Additionally, proportional modes facilitate better monitoring of the delivery of protective assisted ventilation.

SUMMARY

Physiological rationale and clinical data suggest a potential role for proportional modes of assist in providing and monitoring lung and diaphragm protective ventilation.

Continuous assessment of neuro-ventilatory drive during 12 h of pressure support ventilation in critically ill patients

Introduction

Pressure support ventilation (PSV) should allow spontaneous breathing with a “normal” neuro-ventilatory drive. Low neuro-ventilatory drive puts the patient at risk of diaphragmatic atrophy while high neuro-ventilatory drive may causes dyspnea and patient self-inflicted lung injury. We continuously assessed for 12 h the electrical activity of the diaphragm (EAdi), a close surrogate of neuro-ventilatory drive, during PSV. Our aim was to document the EAdi trend and the occurrence of periods of “Low” and/or “High” neuro-ventilatory drive during clinical application of PSV.

Method

In 16 critically ill patients ventilated in the PSV mode for clinical reasons, inspiratory peak EAdi peak (EAdi_PEAK), pressure time product of the trans-diaphragmatic pressure per breath and per minute (PTP_DI/b and PTP_DI/min, respectively), breathing pattern and major asynchronies were continuously monitored for 12 h (from 8 a.m. to 8 p.m.). We identified breaths with “Normal” (EAdi_PEAK 5–15 μV), “Low” (EAdi_PEAK < 5 μV) and “High” (EAdi_PEAK > 15 μV) neuro-ventilatory drive.

Results

Within all the analyzed breaths (177.117), the neuro-ventilatory drive, as expressed by the EAdi_PEAK, was “Low” in 50.116 breath (28%), “Normal” in 88.419 breaths (50%) and “High” in 38.582 breaths (22%). The average times spent in “Low”, “Normal” and “High” class were 1.37, 3.67 and 0.55 h, respectively (p < 0.0001), with wide variations among patients. Eleven patients remained in the “Low” neuro-ventilatory drive class for more than 1 h, median 6.1 [3.9–8.5] h and 6 in the “High” neuro-ventilatory drive class, median 3.4 [2.2–7.8] h. The asynchrony index was significantly higher in the “Low” neuro-ventilatory class, mainly because of a higher number of missed efforts.

Conclusions

We observed wide variations in EAdi amplitude and unevenly distributed “Low” and “High” neuro ventilatory drive periods during 12 h of PSV in critically ill patients. Further studies are needed to assess the possible clinical implications of our physiological findings.

RAC1 nitration at Y32 IS involved in the endothelial barrier disruption associated with lipopolysaccharide-mediated acute lung injury

Acute lung injury (ALI), a devastating illness induced by systemic inflammation e.g., sepsis or local lung inflammation e.g., COVID-19 mediated severe pneumonia, has an unacceptably high mortality and has no effective therapy. ALI is associated with increased pulmonary microvascular hyperpermeability and alveolar flooding. The small Rho GTPases, RhoA and Rac1 are central regulators of vascular permeability through cytoskeleton rearrangements. RhoA and Rac1 have opposing functional outcome: RhoA induces an endothelial contractile phenotype and barrier disruption, while Rac1 stabilizes endothelial junctions and increases barrier integrity. In ALI, RhoA activity is increased while Rac1 activity is reduced. We have shown that the activation of RhoA in lipopolysaccharide (LPS)-mediated ALI, is dependent, at least in part, on a single nitration event at tyrosine (Y)³⁴. Thus, the purpose of this study was to determine if the inhibition of Rac1 is also dependent on its nitration. Our data show that Rac1 inhibition by LPS is associated with its nitration that mass spectrometry identified as Y³², within the switch I region adjacent to the nucleotide-binding site. Using a molecular modeling approach, we designed a nitration shielding peptide for Rac1, designated NipR2 (nitration inhibitor peptide for the Rho GTPases 2), which attenuated the LPS-induced nitration of Rac1 at Y³², preserves Rac1 activity and attenuates the LPS-mediated disruption of the endothelial barrier in human lung microvascular endothelial cells (HLMVEC). Using a murine model of ALI induced by intratracheal installation of LPS we found that NipR2 successfully prevented Rac1 nitration and Rac1 inhibition, and more importantly attenuated pulmonary inflammation, reduced lung injury and prevented the loss of lung function. Together, our data identify a new post-translational mechanism of Rac1 inhibition through its nitration at Y³². As NipR2 also reduces sepsis induced ALI in the mouse lung, we conclude that Rac1 nitration is a therapeutic target in ALI.

•

Endotoxin exposure induces site specific nitration of Rac1 at Y³² via peroxynitrite stress.

•

Rac1 nitration at Y³² leads to persistent Rac GTPase inhibition and endothelial barrier disruption.

•

Novel Rac1 nitration shielding peptide, NipR2 blocks Rac1 nitration and rescues endotoxin induced lung inflammation.

•

NipR2 is potentially an effective therapy for sepsis induced lung injury by targeting Rac1 Y³² nitration.

Lung- and Diaphragm-Protective Ventilation

Mechanical ventilation can cause acute diaphragm atrophy and injury, and this is associated with poor clinical outcomes. Although the importance and impact of lung-protective ventilation is widely appreciated and well established, the concept of diaphragm-protective ventilation has recently emerged as a potential complementary therapeutic strategy. This Perspective, developed from discussions at a meeting of international experts convened by PLUG (the Pleural Pressure Working Group) of the European Society of Intensive Care Medicine, outlines a conceptual framework for an integrated lung- and diaphragm-protective approach to mechanical ventilation on the basis of growing evidence about mechanisms of injury. We propose targets for diaphragm protection based on respiratory effort and patient-ventilator synchrony. The potential for conflict between diaphragm protection and lung protection under certain conditions is discussed; we emphasize that when conflicts arise, lung protection must be prioritized over diaphragm protection. Monitoring respiratory effort is essential to concomitantly protect both the diaphragm and the lung during mechanical ventilation. To implement lung- and diaphragm-protective ventilation, new approaches to monitoring, to setting the ventilator, and to titrating sedation will be required. Adjunctive interventions, including extracorporeal life support techniques, phrenic nerve stimulation, and clinical decision-support systems, may also play an important role in selected patients in the future. Evaluating the clinical impact of this new paradigm will be challenging, owing to the complexity of the intervention. The concept of lung- and diaphragm-protective ventilation presents a new opportunity to potentially improve clinical outcomes for critically ill patients.

Early Inspiratory Effort Assessment by Esophageal Manometry Predicts Noninvasive Ventilation Outcome in De Novo Respiratory Failure. A Pilot Study

Rationale: The role of inspiratory effort still has to be determined as a potential predictor of noninvasive mechanical ventilation (NIV) failure in acute hypoxic de novo respiratory failure.Objectives: To explore the hypothesis that inspiratory effort might be a major determinant of NIV failure in these patients.Methods: Thirty consecutive patients with acute hypoxic de novo respiratory failure admitted to a single center and candidates for a 24-hour NIV trial were enrolled. Clinical features, tidal change in esophageal pressure (ΔPes), tidal change in dynamic transpulmonary pressure (ΔPl), expiratory Vt, and respiratory rate were recorded on admission and 2-4 to 12-24 hours after NIV start and were tested for correlation with outcomes.Measurements and Main Results: ΔPes and ΔPes/ΔPl ratio were significantly lower 2 hours after NIV start in patients who successfully completed the NIV trial (n = 18) compared with those who needed endotracheal intubation (n = 12) (median [interquartile range], 11 [8-15] cm H₂O vs. 31.5 [30-36] cm H₂O; P < 0.0001), whereas other variables differed later. ΔPes was not related to other predictors of NIV failure at baseline. NIV-induced reduction in ΔPes of 10 cm H₂O or more after 2 hours of treatment was strongly associated with avoidance of intubation and represented the most accurate predictor of treatment success (odds ratio, 15; 95% confidence interval, 2.8-110; P = 0.001 and area under the curve, 0.97; 95% confidence interval, 0.91-1; P < 0.0001).Conclusions: The magnitude of inspiratory effort relief as assessed by ΔPes variation within the first 2 hours of NIV was an early and accurate predictor of NIV outcome at 24 hours.Clinical trial registered with www.clinicaltrials.gov (NCT03826797).

Myorelaxants in ARDS patients

Neuromuscular blocking agents (NMBAs) inhibit patient-initiated active breath and the risk of high tidal volumes and consequent high transpulmonary pressure swings, and minimize patient/ ventilator asynchrony in acute respiratory distress syndrome (ARDS). Minimization of volutrauma and ventilator-induced lung injury (VILI) results in a lower incidence of barotrauma, improved oxygenation and a decrease in circulating proinflammatory markers. Recent randomized clinical trials did not reveal harmful muscular effects during a short course of NMBAs. The use of NMBAs should be considered during the early phase of severe ARDS for patients to facilitate lung protective ventilation or prone positioning only after optimising mechanical ventilation and sedation. The use of NMBAs should be integrated in a global strategy including the reduction of tidal volume, the rational use of PEEP, prone positioning and the use of a ventilatory mode allowing spontaneous ventilation as soon as possible. Partial neuromuscular blockade should be evaluated in future trials.

Neuromuscular blocking agents in acute respiratory distress syndrome: updated systematic review and meta-analysis of randomized trials

Purpose

Existing clinical practice guidelines support the use of neuromuscular blocking agents (NMBA) in acute respiratory distress syndrome (ARDS); however, a recent large randomized clinical trial (RCT) has questioned this practice. Therefore, we updated a previous systematic review to determine the efficacy and safety of NMBAs in ARDS.

Methods

We searched MEDLINE, EMBASE (October 2012 to July 2019), the Cochrane (Central) database, and clinical trial registries (ClinicalTrials.gov, ISRCTN Register, and WHO ICTRP) for RCTs comparing the effects of NMBA as a continuous infusion versus placebo or no NMBA infusion (but allowing intermittent NMBA boluses) on patient-important outcomes for adults with ARDS. Two independent reviewers assessed the methodologic quality of the primary studies and abstracted data.

Results

Seven RCTs, including four new RCTs, met eligibility criteria for this review. These trials enrolled 1598 patients with moderate to severe ARDS at centers in the USA, France, and China. All trials assessed short-term continuous infusions of cisatracurium or vecuronium. The pooled estimate for mortality outcomes showed significant statistical heterogeneity, which was only explained by a subgroup analysis by depth of sedation in the control arm. A continuous NMBA infusion did not improve mortality when compared to a light sedation strategy with no NMBA infusion (relative risk [RR] 0.99; 95% CI 0.86–1.15; moderate certainty; P = 0.93). On the other hand, continuous NMBA infusion reduced mortality when compared to deep sedation with as needed NMBA boluses (RR 0.71; 95% CI 0.57–0.89; low certainty; P = 0.003). Continuous NMBA infusion reduced the rate of barotrauma (RR 0.55; 95% CI 0.35–0.85, moderate certainty; P = 0.008) across eligible trials, but the effect on ventilator-free days, duration of mechanical ventilation, and ICU-acquired weakness was uncertain.

Conclusions

Inconsistency in study methods and findings precluded the pooling of all trials for mortality. In a pre-planned sensitivity analysis, the impact of NMBA infusion on mortality depends on the strategy used in the control arm, showing reduced mortality when compared to deep sedation, but no effect on mortality when compared to lighter sedation. In both situations, a continuous NMBA infusion may reduce the risk of barotrauma, but the effects on other patient-important outcomes remain unclear. Future research, including an individual patient data meta-analysis, could help clarify some of the observed findings in this updated systematic review.

Ventilator dyssynchrony - Detection, pathophysiology, and clinical relevance: A Narrative review

Mortality associated with the acute respiratory distress syndrome remains unacceptably high due in part to ventilator-induced lung injury (VILI). Ventilator dyssynchrony is defined as the inappropriate timing and delivery of a mechanical breath in response to patient effort and may cause VILI. Such deleterious patient–ventilator interactions have recently been termed patient self-inflicted lung injury. This narrative review outlines the detection and frequency of several different types of ventilator dyssynchrony, delineates the different mechanisms by which ventilator dyssynchrony may propagate VILI, and reviews the potential clinical impact of ventilator dyssynchrony. Until recently, identifying ventilator dyssynchrony required the manual interpretation of ventilator pressure and flow waveforms. However, computerized interpretation of ventilator waive forms can detect ventilator dyssynchrony with an area under the receiver operating curve of >0.80. Using such algorithms, ventilator dyssynchrony occurs in 3%–34% of all breaths, depending on the patient population. Moreover, two types of ventilator dyssynchrony, double-triggered and flow-limited breaths, are associated with the more frequent delivery of large tidal volumes >10 mL/kg when compared with synchronous breaths (54% [95% confidence interval (CI), 47%–61%] and 11% [95% CI, 7%–15%]) compared with 0.9% (95% CI, 0.0%–1.9%), suggesting a role in propagating VILI. Finally, a recent study associated frequent dyssynchrony-defined as >10% of all breaths-with an increase in hospital mortality (67 vs. 23%, P = 0.04). However, the clinical significance of ventilator dyssynchrony remains an area of active investigation and more research is needed to guide optimal ventilator dyssynchrony management.

Volatile Isoflurane in Critically Ill Coronavirus Disease 2019 Patients-A Case Series and Systematic Review

OBJECTIVES

The ongoing coronavirus pandemic is challenging, especially in severely affected patients who require intubation and sedation. Although the potential benefits of sedation with volatile anesthetics in coronavirus disease 2019 patients are currently being discussed, the use of isoflurane in patients with coronavirus disease 2019-induced acute respiratory distress syndrome has not yet been reported.

DESIGN

We performed a retrospective analysis of critically ill patients with hypoxemic respiratory failure requiring mechanical ventilation.

SETTING

The study was conducted with patients admitted between April 4 and May 15, 2020 to our ICU.

PATIENTS

We included five patients who were previously diagnosed with severe acute respiratory syndrome coronavirus 2 infection.

INTERVENTION

Even with high doses of several IV sedatives, the targeted level of sedation could not be achieved. Therefore, the sedation regimen was switched to inhalational isoflurane. Clinical data were recorded using a patient data management system. We recorded demographical data, laboratory results, ventilation variables, sedative dosages, sedation level, prone positioning, duration of volatile sedation and outcomes.

MEASUREMENTS & MAIN RESULTS

Mean age (four men, one women) was 53.0 (± 12.7) years. The mean duration of isoflurane sedation was 103.2 (± 66.2) hours. Our data demonstrate a substantial improvement in the oxygenation ratio when using isoflurane sedation. Deep sedation as assessed by the Richmond Agitation and Sedation Scale was rapidly and closely controlled in all patients, and the subsequent discontinuation of IV sedation was possible within the first 30 minutes. No adverse events were detected.

CONCLUSIONS

Our findings demonstrate the feasibility of isoflurane sedation in five patients suffering from severe coronavirus disease 2019 infection. Volatile isoflurane was able to achieve the required deep sedation and reduced the need for IV sedation.

Analogy between classical Yoga/Zen breathing and modern clinical respiratory therapy

Anesthesiologists and intensivists are modern-day professionals who provide appropriate respiratory care, vital for patient survival. Recently, anesthesiologists have increasingly focused their attention on the type of spontaneous breathing made by non-intubated patients with pulmonary disease cared for in an intensive care unit, and also patients with chronic pain receiving cognitive behavioral therapy. Prior to our modern understanding of respiratory physiology, Zen meditators recognized that breathing has a significant impact on a person’s mental state and general physical well-being. Examples of this knowledge regarding respiration include the beneficial effects of deep inhalation and slow exhalation on anxiety and general wellness. The classical literature has noted many suggestions for breathing and its psycho-physical effects. In the present review, we examine the effect of classical breathing methods and find an analogy between typical Yoga/Zen breathing and modern clinical respiratory therapy. Evidence is increasing about historical breathing and related meditation techniques that may be effective in modern clinical practice, especially in the field of anesthesiology, such as in improving respiratory function and reducing chronic pain. Clarification of the detailed mechanisms involved is anticipated.

A physiological approach to understand the role of respiratory effort in the progression of lung injury in SARS-CoV-2 infection

Deterioration of lung function during the first week of COVID-19 has been observed when patients remain with insufficient respiratory support. Patient self-inflicted lung injury (P-SILI) is theorized as the responsible, but there is not robust experimental and clinical data to support it. Given the limited understanding of P-SILI, we describe the physiological basis of P-SILI and we show experimental data to comprehend the role of regional strain and heterogeneity in lung injury due to increased work of breathing.

In addition, we discuss the current approach to respiratory support for COVID-19 under this point of view.

Detection of strong inspiratory efforts from the analysis of central venous pressure swings: a preliminary clinical study

BACKGROUND

Swings of central venous pressure (ΔCVP) may reflect those of pleural and esophageal (ΔPES) pressure and, therefore, the strength of inspiration. Strong inspiratory efforts can produce some harm. Herein we preliminarily assessed the diagnostic accuracy of ΔCVP for strong inspiratory efforts in critically-ill subjects breathing spontaneously.

METHODS

We measured ΔCVP and ΔPES in 48 critically-ill subjects breathing spontaneously with zero end-expiratory pressure (ZEEP) or 10 cmH<inf>2</inf>O of continuous positive airway pressure (CPAP). The overall diagnostic accuracy of ΔCVP for strong inspiratory efforts (arbitrarily defined as ΔPES >8 mmHg) was described as the area under the receiver operating characteristic (ROC) curve, with 0.50 indicating random guess. The agreement between ΔCVP and ΔPES was assessed with the Bland-Altman analysis.

RESULTS

ΔCVP recognized strong inspiratory efforts with an area under the ROC curve of 0.95 (95% confidence intervals, 0.85-0.99) with ZEEP and 0.89 (0.76-0.96) with CPAP, both significantly larger than 0.50 (P<0.001). With the best cut-off value around 8 mmHg, the diagnostic accuracy of ΔCVP was 0.92 (0.80-0.98) with ZEEP and 0.94 (0.83-0.99) with CPAP. With ZEEP, the median difference between ΔCVP and ΔPES (bias) was -0.2 mmHg, and the 95% limits of agreement (LoA) were -3.9 and +5.5 mmHg. With CPAP, bias was -0.1 mmHg, and 95%-LoA were -5.8 and +4.5 mmHg. In both cases, ΔCVP correlated with ΔPES (r<inf>s</inf> 0.81 and 0.67; P<0.001 for both).

CONCLUSIONS

In critically-ill subjects breathing spontaneously, ΔCVP recognized strong inspiratory efforts with acceptable accuracy. Even so, it sometimes largely differed from ∆PES.

ECMO管理を要した重症COVID–19市中肺炎に対して腹臥位療法やステロイドの全身投与により軽快した2例(Two cases of severe coronavirus disease 2019 community–acquired pneumonia successfully treated with extracorporeal membrane oxygenation and prone positioning and systemic corticosteroid therapy)

The first case was that of a 58–year–old man diagnosed with coronavirus disease 2019 (COVID–19) pneumonia after 7 days of fever. Favipiravir was administered on admission; however, the patient’s respiratory status worsened with high fever. On day 2 of admission, after tracheal intubation, maintaining oxygenation was difficult after initiating mechanical ventilation, and extracorporeal membrane oxygenation (ECMO) was initiated. On day 5, prone positioning and corticosteroid therapy were started. The patient was weaned from ECMO on day 9 and from ventilator support on day 11. On day 27, he was discharged ambulatory. The second case was that of a 44–year–old man who complained of dyspnea after 12 days of fever. After tracheal intubation, he was diagnosed with COVID–19 pneumonia. Favipiravir was administered on admission; nevertheless, the patient’s respiratory status worsened gradually with high fever. On day 4 of admission, ECMO and corticosteroid therapy were initiated. On day 5, prone positioning was started. The patient was weaned from ECMO on day 12 and from ventilator support on day 15. On day 30, he was discharged ambulatory. The aggravation of COVID–19 pneumonia may be associated with excessive inflammation; therefore, some patients were effectively treated with corticosteroid therapy.

COVID-19-associated acute respiratory distress syndrome: is a different approach to management warranted?

The COVID-19 pandemic has seen a surge of patients with acute respiratory distress syndrome (ARDS) in intensive care units across the globe. As experience of managing patients with COVID-19-associated ARDS has grown, so too have efforts to classify patients according to respiratory system mechanics, with a view to optimising ventilatory management. Personalised lung-protective mechanical ventilation reduces mortality and has become the mainstay of treatment in ARDS. In this Viewpoint, we address ventilatory strategies in the context of recent discussions on phenotypic heterogeneity in patients with COVID-19-associated ARDS. Although early reports suggested that COVID-19-associated ARDS has distinctive features that set it apart from historical ARDS, emerging evidence indicates that the respiratory system mechanics of patients with ARDS, with or without COVID-19, are broadly similar. In the absence of evidence to support a shift away from the current paradigm of ventilatory management, we strongly recommend adherence to evidence-based management, informed by bedside physiology, as resources permit.

Protective ventilation from ICU to operating room: state of art and new horizons

The prevention of ventilator-associated lung injury (VALI) and postoperative pulmonary complications (PPC) is of paramount importance for improving outcomes both in the operating room and in the intensive care unit (ICU). Protective respiratory support includes a wide spectrum of interventions to decrease pulmonary stress-strain injuries. The motto 'low tidal volume for all' should become routine, both during major surgery and in the ICU, while application of a high positive end-expiratory pressure (PEEP) strategy and of alveolar recruitment maneuvers requires a personalized approach and requires further investigation. Patient self-inflicted lung injury is an important type of VALI, which should be diagnosed and mitigated at the early stage, during restoration of spontaneous breathing. This narrative review highlights the strategies used for protective positive pressure ventilation. The emerging concepts of damaging energy and power, as well as pathways to personalization of the respiratory settings, are discussed in detail. In the future, individualized approaches to protective ventilation may involve multiple respiratory settings extending beyond low tidal volume and PEEP, implemented in parallel with quantifying the risk of VALI and PPC.

Physiological Comparison of High-Flow Nasal Cannula and Helmet Noninvasive Ventilation in Acute Hypoxemic Respiratory Failure

Rationale: High-flow nasal cannula (HFNC) and helmet noninvasive ventilation (NIV) are used for the management of acute hypoxemic respiratory failure.Objectives: Physiological comparison of HFNC and helmet NIV in patients with hypoxemia.Methods: Fifteen patients with hypoxemia with Pa_O2/Fi_O2 < 200 mm Hg received helmet NIV (positive end-expiratory pressure ≥ 10 cm H₂O, pressure support = 10-15 cm H₂O) and HFNC (50 L/min) in randomized crossover order. Arterial blood gases, dyspnea, and comfort were recorded. Inspiratory effort was estimated by esophageal pressure (Pes) swings. Pes-simplified pressure-time product and transpulmonary pressure swings were measured.Measurements and Main Results: As compared with HFNC, helmet NIV increased Pa_O2/Fi_O2 (median [interquartile range]: 255 mm Hg [140-299] vs. 138 [101-172]; P = 0.001) and lowered inspiratory effort (7 cm H₂O [4-11] vs. 15 [8-19]; P = 0.001) in all patients. Inspiratory effort reduction by NIV was linearly related to inspiratory effort during HFNC (r = 0.84; P < 0.001). Helmet NIV reduced respiratory rate (24 breaths/min [23-31] vs. 29 [26-32]; P = 0.027), Pes-simplified pressure-time product (93 cm H₂O ⋅ s ⋅ min^-1 [43-138] vs. 200 [168-335]; P = 0.001), and dyspnea (visual analog scale 3 [2-5] vs. 8 [6-9]; P = 0.002), without affecting Pa_CO2 (P = 0.80) and comfort (P = 0.50). In the overall cohort, transpulmonary pressure swings were not different between treatments (NIV = 18 cm H₂O [14-21] vs. HFNC = 15 [8-19]; P = 0.11), but patients exhibiting lower inspiratory effort on HFNC experienced increases in transpulmonary pressure swings with helmet NIV. Higher transpulmonary pressure swings during NIV were associated with subsequent need for intubation.Conclusions: As compared with HFNC in hypoxemic respiratory failure, helmet NIV improves oxygenation, reduces dyspnea, inspiratory effort, and simplified pressure-time product, with similar transpulmonary pressure swings, Pa_CO2, and comfort.

Monitoring Patient Respiratory Effort During Mechanical Ventilation: Lung and Diaphragm-Protective Ventilation

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2020. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2020. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Mechanical Ventilation Management during Extracorporeal Membrane Oxygenation for Acute Respiratory Distress Syndrome. An International Multicenter Prospective Cohort

Rationale: Current practices regarding mechanical ventilation in patients treated with extracorporeal membrane oxygenation (ECMO) for acute respiratory distress syndrome are unknown.Objectives: To report current practices regarding mechanical ventilation in patients treated with ECMO for severe acute respiratory distress syndrome (ARDS) and their association with 6-month outcomes.Methods: This was an international, multicenter, prospective cohort study of patients undergoing ECMO for ARDS during a 1-year period in 23 international ICUs.Measurements and Main Results: We collected demographics, daily pre- and per-ECMO mechanical ventilation settings and use of adjunctive therapies, ICU, and 6-month outcome data for 350 patients (mean ± SD pre-ECMO Pa_O2/Fi_O2 71 ± 34 mm Hg). Pre-ECMO use of prone positioning and neuromuscular blockers were 26% and 62%, respectively. Vt (6.4 ± 2.0 vs. 3.7 ± 2.0 ml/kg), plateau pressure (32 ± 7 vs. 24 ± 7 cm H₂O), driving pressure (20 ± 7 vs. 14 ± 4 cm H₂O), respiratory rate (26 ± 8 vs. 14 ± 6 breaths/min), and mechanical power (26.1 ± 12.7 vs. 6.6 ± 4.8 J/min) were markedly reduced after ECMO initiation. Six-month survival was 61%. No association was found between ventilator settings during the first 2 days of ECMO and survival in multivariable analysis. A time-varying Cox model retained older age, higher fluid balance, higher lactate, and more need for renal-replacement therapy along the ECMO course as being independently associated with 6-month mortality. A higher Vt and lower driving pressure (likely markers of static compliance improvement) across the ECMO course were also associated with better outcomes.Conclusions: Ultraprotective lung ventilation on ECMO was largely adopted across medium- to high-case volume ECMO centers. In contrast with previous observations, mechanical ventilation settings during ECMO did not impact patients' prognosis in this context.

A Physiologically Informed Strategy to Effectively Open, Stabilize, and Protect the Acutely Injured Lung

Acute respiratory distress syndrome (ARDS) causes a heterogeneous lung injury and remains a serious medical problem, with one of the only treatments being supportive care in the form of mechanical ventilation. It is very difficult, however, to mechanically ventilate the heterogeneously damaged lung without causing secondary ventilator-induced lung injury (VILI). The acutely injured lung becomes time and pressure dependent, meaning that it takes more time and pressure to open the lung, and it recollapses more quickly and at higher pressure. Current protective ventilation strategies, ARDSnet low tidal volume (LVt) and the open lung approach (OLA), have been unsuccessful at further reducing ARDS mortality. We postulate that this is because the LVt strategy is constrained to ventilating a lung with a heterogeneous mix of normal and focalized injured tissue, and the OLA, although designed to fully open and stabilize the lung, is often unsuccessful at doing so. In this review we analyzed the pathophysiology of ARDS that renders the lung susceptible to VILI. We also analyzed the alterations in alveolar and alveolar duct mechanics that occur in the acutely injured lung and discussed how these alterations are a key mechanism driving VILI. Our analysis suggests that the time component of each mechanical breath, at both inspiration and expiration, is critical to normalize alveolar mechanics and protect the lung from VILI. Animal studies and a meta-analysis have suggested that the time-controlled adaptive ventilation (TCAV) method, using the airway pressure release ventilation mode, eliminates the constraints of ventilating a lung with heterogeneous injury, since it is highly effective at opening and stabilizing the time- and pressure-dependent lung. In animal studies it has been shown that by “casting open” the acutely injured lung with TCAV we can (1) reestablish normal expiratory lung volume as assessed by direct observation of subpleural alveoli; (2) return normal parenchymal microanatomical structural support, known as alveolar interdependence and parenchymal tethering, as assessed by morphometric analysis of lung histology; (3) facilitate regeneration of normal surfactant function measured as increases in surfactant proteins A and B; and (4) significantly increase lung compliance, which reduces the pathologic impact of driving pressure and mechanical power at any given tidal volume.

Impact of spontaneous breathing during mechanical ventilation in acute respiratory distress syndrome

PURPOSE OF REVIEW

Facilitating spontaneous breathing has been traditionally recommended during mechanical ventilation in acute respiratory distress syndrome (ARDS). However, early, short-term use of neuromuscular blockade appears to improve survival, and spontaneous effort has been shown to potentiate lung injury in animal and clinical studies. The purpose of this review is to describe the beneficial and deleterious effects of spontaneous breathing in ARDS, explain potential mechanisms for harm, and provide contemporary suggestions for clinical management.

RECENT FINDINGS

Gentle spontaneous effort can improve lung function and prevent diaphragm atrophy. However, accumulating evidence indicates that spontaneous effort may cause or worsen lung and diaphragm injury, especially if the ARDS is severe or spontaneous effort is vigorous. Recently, such effort-dependent lung injury has been termed patient self-inflicted lung injury (P-SILI). Finally, several approaches to minimize P-SILI while maintaining some diaphragm activity (e.g. partial neuromuscular blockade, high PEEP) appear promising.

SUMMARY

We update and summarize the role of spontaneous breathing during mechanical ventilation in ARDS, which can be beneficial or deleterious, depending on the strength of spontaneous activity and severity of lung injury. Future studies are needed to determine ventilator strategies that minimize injury but maintaining some diaphragm activity.

Real-time effects of PEEP and tidal volume on regional ventilation and perfusion in experimental lung injury

BACKGROUND

Real-time bedside information on regional ventilation and perfusion during mechanical ventilation (MV) may help to elucidate the physiological and pathophysiological effects of MV settings in healthy and injured lungs. We aimed to study the effects of positive end-expiratory pressure (PEEP) and tidal volume (V_T) on the distributions of regional ventilation and perfusion by electrical impedance tomography (EIT) in healthy and injured lungs.

METHODS

One-hit acute lung injury model was established in 6 piglets by repeated lung lavages (injured group). Four ventilated piglets served as the control group. A randomized sequence of any possible combination of three V_T (7, 10, and 15 ml/kg) and four levels of PEEP (5, 8, 10, and 12 cmH₂O) was performed in all animals. Ventilation and perfusion distributions were computed by EIT within three regions-of-interest (ROIs): nondependent, middle, dependent. A mixed design with one between-subjects factor (group: intervention or control), and two within-subjects factors (PEEP and V_T) was used, with a three-way mixed analysis of variance (ANOVA).

RESULTS

Two-way interactions between PEEP and group, and V_T and group, were observed for the dependent ROI (p = 0.035 and 0.012, respectively), indicating that the increase in the dependent ROI ventilation was greater at higher PEEP and V_T in the injured group than in the control group. A two-way interaction between PEEP and V_T was observed for perfusion distribution in each ROI: nondependent (p = 0.030), middle (p = 0.006), and dependent (p = 0.001); no interaction was observed between injured and control groups.

CONCLUSIONS

Large PEEP and V_T levels were associated with greater pulmonary ventilation of the dependent lung region in experimental lung injury, whereas they affected pulmonary perfusion of all lung regions both in the control and in the experimental lung injury groups.

The Control of Breathing During Mechanical Ventilation

On mechanical ventilation, the lungs is subjected to the action of 2 pumps with independent control systems. The patient's control system responds to actions of the ventilator via programmed mechanisms that alter respiratory output in response to lung volume changes; blood gas tensions; and, in conscious patients, to ventilator-induced changes that are different from those expected by the patient's control system. By contrast, the ventilator responds to the patient's actions according to operational characteristics of the specific ventilator mode. That patient and ventilator responses are not coordinated results in complex breathing patterns that may adversely affect the clinical outcome.

Airway pressure release ventilation in children

PURPOSE OF REVIEW

In patients with acute respiratory distress syndrome (ARDS), airway pressure release ventilation (APRV) has been purported to have several physiological benefits. This review synthesizes recent research evaluating APRV mode and provides perspectives on the utility of this mode in children with ARDS.

RECENT FINDINGS

Two single-center clinical trials on APRV, one adult and one pediatric, have been published this year. These two trials have not only elicited editorials and letters that highlight some of their strengths and weaknesses but also rekindled debate on several aspects of APRV. Despite their contradicting results, both trials provide significant insights into APRV strategies that work and those that may not. This review places the newer evidence in the context of existing literature and provides a comprehensive analysis of APRV use in children.

SUMMARY

There have been significant recent advancements in our understanding of the clinical utility of APRV in children with ARDS. The recent trial highlights the urgent need to evolve a consensus on definition of APRV and identify strategies that work. Pending further research, clinicians should avoid the use of a zero-PLOW Personalized-APRV strategy as a primary ventilation modality in children with moderate-severe ARDS.

A physiology-based mathematical model for the selection of appropriate ventilator controls for lung and diaphragm protection

Mechanical ventilation is used to sustain respiratory function in patients with acute respiratory failure. To aid clinicians in consistently selecting lung- and diaphragm-protective ventilation settings, a physiology-based decision support system is needed. To form the foundation of such a system, a comprehensive physiological model which captures the dynamics of ventilation has been developed. The Lung and Diaphragm Protective Ventilation (LDPV) model centers around respiratory drive and incorporates respiratory system mechanics, ventilator mechanics, and blood acid–base balance. The model uses patient-specific parameters as inputs and outputs predictions of a patient’s transpulmonary and esophageal driving pressures (outputs most clinically relevant to lung and diaphragm safety), as well as their blood pH, under various ventilator and sedation conditions. Model simulations and global optimization techniques were used to evaluate and characterize the model. The LDPV model is demonstrated to describe a CO₂ respiratory response that is comparable to what is found in literature. Sensitivity analysis of the model indicate that the ventilator and sedation settings incorporated in the model have a significant impact on the target output parameters. Finally, the model is seen to be able to provide robust predictions of esophageal pressure, transpulmonary pressure and blood pH for patient parameters with realistic variability. The LDPV model is a robust physiological model which produces outputs which directly target and reflect the risk of ventilator-induced lung and diaphragm injury. Ventilation and sedation parameters are seen to modulate the model outputs in accordance with what is currently known in literature.

Static and Dynamic Transpulmonary Driving Pressures Affect Lung and Diaphragm Injury during Pressure-controlled versus Pressure-support Ventilation in Experimental Mild Lung Injury in Rats

BACKGROUND

Pressure-support ventilation may worsen lung damage due to increased dynamic transpulmonary driving pressure. The authors hypothesized that, at the same tidal volume (VT) and dynamic transpulmonary driving pressure, pressure-support and pressure-controlled ventilation would yield comparable lung damage in mild lung injury.

METHODS

Male Wistar rats received endotoxin intratracheally and, after 24 h, were ventilated in pressure-support mode. Rats were then randomized to 2 h of pressure-controlled ventilation with VT, dynamic transpulmonary driving pressure, dynamic transpulmonary driving pressure, and inspiratory time similar to those of pressure-support ventilation. The primary outcome was the difference in dynamic transpulmonary driving pressure between pressure-support and pressure-controlled ventilation at similar VT; secondary outcomes were lung and diaphragm damage.

RESULTS

At VT = 6 ml/kg, dynamic transpulmonary driving pressure was higher in pressure-support than pressure-controlled ventilation (12.0 ± 2.2 vs. 8.0 ± 1.8 cm H2O), whereas static transpulmonary driving pressure did not differ (6.7 ± 0.6 vs. 7.0 ± 0.3 cm H2O). Diffuse alveolar damage score and gene expression of markers associated with lung inflammation (interleukin-6), alveolar-stretch (amphiregulin), epithelial cell damage (club cell protein 16), and fibrogenesis (metalloproteinase-9 and type III procollagen), as well as diaphragm inflammation (tumor necrosis factor-α) and proteolysis (muscle RING-finger-1) were comparable between groups. At similar dynamic transpulmonary driving pressure, as well as dynamic transpulmonary driving pressure and inspiratory time, pressure-controlled ventilation increased VT, static transpulmonary driving pressure, diffuse alveolar damage score, and gene expression of markers of lung inflammation, alveolar stretch, fibrogenesis, diaphragm inflammation, and proteolysis compared to pressure-support ventilation.

CONCLUSIONS

In the mild lung injury model use herein, at the same VT, pressure-support compared to pressure-controlled ventilation did not affect biologic markers. However, pressure-support ventilation was associated with a major difference between static and dynamic transpulmonary driving pressure; when the same dynamic transpulmonary driving pressure and inspiratory time were used for pressure-controlled ventilation, greater lung and diaphragm injury occurred compared to pressure-support ventilation.

Role of Neuromuscular Blocking Agents in Acute Respiratory Distress Syndrome: An Updated Meta-Analysis of Randomized Controlled Trials

Background

The therapeutic role of neuromuscular blocking agents (NMBA) in patients with acute respiratory distress syndrome (ARDS) remains controversial.

Methods

We systematically reviewed randomized controlled trials investigating the use of NMBA in ARDS patients from inception to July 2019. Relative risk (RR) was calculated for the incidence of barotrauma and mortality using the random-effect or fixed-effect model according to heterogeneity analysis.

Results

Data were combined from five randomized controlled trials that included 1,461 patients (724 in the NMBA group and 737 in the control group). Pooled analysis showed that NMBA infusion did not reduce 28-day mortality (RR = 0.72, 95% confidence interval (CI) 0.44 to 1.17, P=0.180, I-squared = 62.8%), but was associated with lower intensive care unit (ICU) mortality (RR = 0.60, 95% CI 0.41 to 0.88, P = 0.009, I-squared = 9.2%). In addition, the incidence of barotrauma was significantly lower in patients treated with NMBA (RR = 0.53, 95% CI 0.33 to 0.84, P = 0.007, I-squared = 0). However, infusion of NMBA might increase the risk of ICU-acquired weakness (RR = 1.34, 95% CI 0.97 to 1.84, P = 0.066, I-squared = 0).

Conclusion

Infusion of NMBA could reduce ICU mortality and the incidence of barotrauma. The risk of ICU-acquired weakness was higher in moderate-to-severe ARDS patients treated with NMBA. The real effects of NMBA need to be further evaluated and confirmed by a study with a stricter design.

Effects of Positive End-Expiratory Pressure and Spontaneous Breathing Activity on Regional Lung Inflammation in Experimental Acute Respiratory Distress Syndrome

OBJECTIVES

To determine the impact of positive end-expiratory pressure during mechanical ventilation with and without spontaneous breathing activity on regional lung inflammation in experimental nonsevere acute respiratory distress syndrome.

DESIGN

Laboratory investigation.

SETTING

University hospital research facility.

SUBJECTS

Twenty-four pigs (28.1-58.2 kg).

INTERVENTIONS

In anesthetized animals, intrapleural pressure sensors were placed thoracoscopically in ventral, dorsal, and caudal regions of the left hemithorax. Lung injury was induced with saline lung lavage followed by injurious ventilation in supine position. During airway pressure release ventilation with low tidal volumes, positive end-expiratory pressure was set 4 cm H2O above the level to reach a positive transpulmonary pressure in caudal regions at end-expiration (best-positive end-expiratory pressure). Animals were randomly assigned to one of four groups (n = 6/group; 12 hr): 1) no spontaneous breathing activity and positive end-expiratory pressure = best-positive end-expiratory pressure - 4 cm H2O, 2) no spontaneous breathing activity and positive end-expiratory pressure = best-positive end-expiratory pressure + 4 cm H2O, 3) spontaneous breathing activity and positive end-expiratory pressure = best-positive end-expiratory pressure + 4 cm H2O, 4) spontaneous breathing activity and positive end-expiratory pressure = best-positive end-expiratory pressure - 4 cm H2O.

MEASUREMENTS AND MAIN RESULTS

Global lung inflammation assessed by specific [F]fluorodeoxyglucose uptake rate (median [25-75% percentiles], min) was decreased with higher compared with lower positive end-expiratory pressure both without spontaneous breathing activity (0.029 [0.027-0.030] vs 0.044 [0.041-0.065]; p = 0.004) and with spontaneous breathing activity (0.032 [0.028-0.043] vs 0.057 [0.042-0.075]; p = 0.016). Spontaneous breathing activity did not increase global lung inflammation. Lung inflammation in dorsal regions correlated with transpulmonary driving pressure from spontaneous breathing at lower (r = 0.850; p = 0.032) but not higher positive end-expiratory pressure (r = 0.018; p = 0.972). Higher positive end-expiratory pressure resulted in a more homogeneous distribution of aeration and regional transpulmonary pressures at end-expiration along the ventral-dorsal gradient, as well as a shift of the perfusion center toward dependent zones in the presence of spontaneous breathing activity.

CONCLUSIONS

In experimental mild-to-moderate acute respiratory distress syndrome, positive end-expiratory pressure levels that stabilize dependent lung regions reduce global lung inflammation during mechanical ventilation, independent from spontaneous breathing activity.

ERS International Congress, Madrid, 2019: highlights from the Respiratory Intensive Care Assembly

The Respiratory Intensive Care Assembly of the European Respiratory Society is delighted to present the highlights from the 2019 International Congress in Madrid, Spain. We have selected four sessions that discussed recent advances in a wide range of topics: from acute respiratory failure to cough augmentation in neuromuscular disorders and from extra-corporeal life support to difficult ventilator weaning. The subjects are summarised by early career members in close collaboration with the Assembly leadership. We aim to give the reader an update on the most important developments discussed at the conference. Each session is further summarised into a short list of take-home messages.

Impact of Altered Airway Pressure on Intracranial Pressure, Perfusion, and Oxygenation: A Narrative Review

OBJECTIVES

A narrative review of the pathophysiology linking altered airway pressure and intracranial pressure and cerebral oxygenation.

DATA SOURCES

Online search of PubMed and manual review of articles (laboratory and patient studies) of the altered airway pressure on intracranial pressure, cerebral perfusion, or cerebral oxygenation.

STUDY SELECTION

Randomized trials, observational and physiologic studies.

DATA EXTRACTION

Our group determined by consensus which resources would best inform this review.

DATA SYNTHESIS

In the normal brain, positive-pressure ventilation does not significantly alter intracranial pressure, cerebral oxygenation, or perfusion. In injured brains, the impact of airway pressure on intracranial pressure is variable and determined by several factors; a cerebral venous Starling resistor explains much of the variability. Negative-pressure ventilation can improve cerebral perfusion and oxygenation and reduce intracranial pressure in experimental models, but data are limited, and mechanisms and clinical benefit remain uncertain.

CONCLUSIONS

The effects of airway pressure and ventilation on cerebral perfusion and oxygenation are increasingly understood, especially in the setting of brain injury. In the face of competing mechanisms and priorities, multimodal monitoring and individualized titration will increasingly be required to optimize care.

Spontaneous Breathing in Early Acute Respiratory Distress Syndrome: Insights From the Large Observational Study to UNderstand the Global Impact of Severe Acute Respiratory FailurE Study

Supplemental Digital Content is available in the text.

Objectives:

To describe the characteristics and outcomes of patients with acute respiratory distress syndrome with or without spontaneous breathing and to investigate whether the effects of spontaneous breathing on outcome depend on acute respiratory distress syndrome severity.

Design:

Planned secondary analysis of a prospective, observational, multicentre cohort study.

Setting:

International sample of 459 ICUs from 50 countries.

Patients:

Patients with acute respiratory distress syndrome and at least 2 days of invasive mechanical ventilation and available data for the mode of mechanical ventilation and respiratory rate for the 2 first days.

Interventions:

Analysis of patients with and without spontaneous breathing, defined by the mode of mechanical ventilation and by actual respiratory rate compared with set respiratory rate during the first 48 hours of mechanical ventilation.

Measurements and Main Results:

Spontaneous breathing was present in 67% of patients with mild acute respiratory distress syndrome, 58% of patients with moderate acute respiratory distress syndrome, and 46% of patients with severe acute respiratory distress syndrome. Patients with spontaneous breathing were older and had lower acute respiratory distress syndrome severity, Sequential Organ Failure Assessment scores, ICU and hospital mortality, and were less likely to be diagnosed with acute respiratory distress syndrome by clinicians. In adjusted analysis, spontaneous breathing during the first 2 days was not associated with an effect on ICU or hospital mortality (33% vs 37%; odds ratio, 1.18 [0.92–1.51]; p = 0.19 and 37% vs 41%; odds ratio, 1.18 [0.93–1.50]; p = 0.196, respectively ). Spontaneous breathing was associated with increased ventilator-free days (13 [0–22] vs 8 [0–20]; p = 0.014) and shorter duration of ICU stay (11 [6–20] vs 12 [7–22]; p = 0.04).

Conclusions:

Spontaneous breathing is common in patients with acute respiratory distress syndrome during the first 48 hours of mechanical ventilation. Spontaneous breathing is not associated with worse outcomes and may hasten liberation from the ventilator and from ICU. Although these results support the use of spontaneous breathing in patients with acute respiratory distress syndrome independent of acute respiratory distress syndrome severity, the use of controlled ventilation indicates a bias toward use in patients with higher disease severity. In addition, because the lack of reliable data on inspiratory effort in our study, prospective studies incorporating the magnitude of inspiratory effort and adjusting for all potential severity confounders are required.

Physiological effects of high-flow oxygen in tracheostomized patients

Background

High-flow oxygen therapy via nasal cannula (HFOT_NASAL) increases airway pressure, ameliorates oxygenation and reduces work of breathing. High-flow oxygen can be delivered through tracheostomy (HFOT_TRACHEAL), but its physiological effects have not been systematically described. We conducted a cross-over study to elucidate the effects of increasing flow rates of HFOT_TRACHEAL on gas exchange, respiratory rate and endotracheal pressure and to compare lower airway pressure produced by HFOT_NASAL and HFOT_TRACHEAL.

Methods

Twenty-six tracheostomized patients underwent standard oxygen therapy through a conventional heat and moisture exchanger, and then HFOT_TRACHEAL through a heated humidifier, with gas flow set at 10, 30 and 50 L/min. Each step lasted 30 min; gas flow sequence during HFOT_TRACHEAL was randomized. In five patients, measurements were repeated during HFOT_TRACHEAL before tracheostomy decannulation and immediately after during HFOT_NASAL. In each step, arterial blood gases, respiratory rate, and tracheal pressure were measured.

Results

During HFOT_TRACHEAL, PaO₂/FiO₂ ratio and tracheal expiratory pressure slightly increased proportionally to gas flow. The mean [95% confidence interval] expiratory pressure raise induced by 10-L/min increase in flow was 0.2 [0.1–0.2] cmH₂O (ρ = 0.77, p < 0.001). Compared to standard oxygen, HFOT_TRACHEAL limited the negative inspiratory swing in tracheal pressure; at 50 L/min, but not with other settings, HFOT_TRACHEAL increased mean tracheal expiratory pressure by (mean difference [95% CI]) 0.4 [0.3–0.6] cmH₂O, peak tracheal expiratory pressure by 0.4 [0.2–0.6] cmH₂O, improved PaO₂/FiO₂ ratio by 40 [8–71] mmHg, and reduced respiratory rate by 1.9 [0.3–3.6] breaths/min without PaCO₂ changes. As compared to HFOT_TRACHEAL, HFOT_NASAL produced higher tracheal mean and peak expiratory pressure (at 50 L/min, mean difference [95% CI]: 3 [1–5] cmH₂O and 4 [1–7] cmH₂O, respectively).

Conclusions

As compared to standard oxygen, 50 L/min of HFOT_TRACHEAL are needed to improve oxygenation, reduce respiratory rate and provide small degree of positive airway expiratory pressure, which, however, is significantly lower than the one produced by HFOT_NASAL.