Protecting lungs during spontaneous breathing: what can we do?

Incidence and outcomes following pulmonary barotrauma in COVID-19 ventilated and non-ventilated patients with acute respiratory failure: A retrospective study

Background and Objectives

: Alveolar rupture following increased transalveolar pressure on positive pressure ventilation is associated with pulmonary barotrauma (PB). The spectrum varies from pneumothorax, pneumomediastinum, pneumopericardium, pneumoperitoneum, retro-pneumoperitoneum and subcutaneous emphysema. We studied the incidence of PB and their clinical characteristics in patients with coronavirus disease 19 (COVID-19)-associated acute respiratory failure.

Methods

Patients aged >18 years with COVID-19-associated acute respiratory distress syndrome were included in the study. We recorded demographics (age, gender, comorbidities), severity scores (APACHE II on admission, SOFA on the day of barotrauma), type of PB and outcomes at discharge from the hospital. Patient characteristics are descriptively reported. Survival analysis was done using Kaplan-Meier survival tests after classifying by various factors. Survival was compared using the log-rank test.

Results

Thirty-five patients experienced PB. Eighty per cent of patients in this cohort were males with mean age of 55.89 years. The commonest comorbidities were diabetes mellitus and hypertension. Twelve spontaneously breathing patients developed barotrauma. Eight patients experienced sequential events. In all, 18 patients required insertion of pigtail catheters. The median survival time in patients was 37 days (95% CI: 25-49 days). The overall survival rate was 34.3%. Mean serum ferritin levels were six times upper limit of normal in deceased, reflecting the severity of lung involvement.

Conclusion

A high incidence of PB was noted following severe acute respiratory syndrome coronavirus (SARS CoV-2) infection even in the non-ventilated patients, a consequence of SARS CoV-2 effects on the pulmonary parenchyma causing widespread lung injury.

Low tidal volume ventilation is associated with mortality in COVID-19 patients-Insights from the PRoVENT-COVID study

Purpose

Low tidal volume ventilation (LTVV) is associated with mortality in patients with acute respiratory distress syndrome. We investigated the association of LTVV with mortality in COVID-19 patients.

Methods

Secondary analysis of a national observational study in COVID-19 patients in the first wave of the pandemic. We compared COVID-19 patients that received LTVV, defined as controlled ventilation with a median tidal volume ≤ 6 mL/kg predicted body weight over the first 4 calendar days of ventilation, with patients that did not receive LTVV. The primary endpoint was 28-day mortality. In addition, we identified factors associated with use of LTVV.

Results

Of 903 patients, 294 (32.5%) received LTVV. Disease severity scores and ARDS classification was not different between the two patient groups. The primary endpoint, 28-day mortality, was met in 68 out of 294 patients (23.1%) that received LTVV versus in 193 out of 609 patients (31.7%) that did not receive LTVV (P < 0.001). LTVV was independently associated with 28-day mortality (HR, 0.68 (0.45 to 0.95); P = 0.025). Age, height, the initial tidal volume and continuous muscle paralysis was independently associated with use of LTVV.

Conclusions

In this cohort of invasively ventilated COVID-19 patients, approximately a third of patients received LTVV. Use of LTVV was independently associated with reduced 28-day mortality. The initial tidal volume and continuous muscle paralysis were potentially modifiable factors associated with use of LTVV. These findings are important as they could help clinicians to recognize patients who are at risk of not receiving LTVV.

Noninvasive respiratory support and patient self-inflicted lung injury in COVID-19: a narrative review

COVID-19 pneumonia is associated with hypoxaemic respiratory failure, ranging from mild to severe. Because of the worldwide shortage of ICU beds, a relatively high number of patients with respiratory failure are receiving prolonged noninvasive respiratory support, even when their clinical status would have required invasive mechanical ventilation. There are few experimental and clinical data reporting that vigorous breathing effort during spontaneous ventilation can worsen lung injury and cause a phenomenon that has been termed patient self-inflicted lung injury (P-SILI). The aim of this narrative review is to provide an overview of P-SILI pathophysiology and the role of noninvasive respiratory support in COVID-19 pneumonia. Respiratory mechanics, vascular compromise, viscoelastic properties, lung inhomogeneity, work of breathing, and oesophageal pressure swings are discussed. The concept of P-SILI has been widely investigated in recent years, but controversies persist regarding its mechanisms. To minimise the risk of P-SILI, intensivists should better understand its underlying pathophysiology to optimise the type of noninvasive respiratory support provided to patients with COVID-19 pneumonia, and decide on the optimal timing of intubation for these patients.

The Pathophysiology and Dangers of Silent Hypoxemia in COVID-19 Lung Injury

The ongoing coronavirus disease (COVID-19) pandemic has been unprecedented on many levels, not least of which are the challenges in understanding the pathophysiology of these new critically ill patients. One widely reported phenomenon is that of a profoundly hypoxemic patient with minimal to no dyspnea out of proportion to the extent of radiographic abnormality and change in lung compliance. This apparently unique presentation, sometimes called "happy hypoxemia or hypoxia" but better described as "silent hypoxemia," has led to the speculation of underlying pathophysiological differences between COVID-19 lung injury and acute respiratory distress syndrome (ARDS) from other causes. We explore three proposed distinctive features of COVID-19 that likely bear on the genesis of silent hypoxemia, including differences in lung compliance, pulmonary vascular responses to hypoxia, and nervous system sensing and response to hypoxemia. In the context of known principles of respiratory physiology and neurobiology, we discuss whether these particular findings are due to direct viral effects or, equally plausible, are within the spectrum of typical ARDS pathophysiology and the wide range of hypoxic ventilatory and pulmonary vascular responses and dyspnea perception in healthy people. Comparisons between lung injury patterns in COVID-19 and other causes of ARDS are clouded by the extent and severity of this pandemic, which may underlie the description of "new" phenotypes, although our ability to confirm these phenotypes by more invasive and longitudinal studies is limited. However, given the uncertainty about anything unique in the pathophysiology of COVID-19 lung injury, there are no compelling pathophysiological reasons at present to support a therapeutic approach for these patients that is different from the proven standards of care in ARDS.

Pulmonary Barotrauma in COVID-19 Patients With ARDS on Invasive and Non-Invasive Positive Pressure Ventilation

BACKGROUND

We experienced a high incidence of pulmonary barotrauma among patients with coronavirus disease-2019 (COVID-19) associated acute respiratory distress syndrome (ARDS) at our institution. In current study, we sought to evaluate the incidence, clinical outcomes, and characteristics of barotrauma among COVID-19 patients receiving invasive and non-invasive positive pressure ventilation.

METHODOLOGY

This retrospective cohort study included adult patients diagnosed with COVID-19 pneumonia and requiring oxygen support or positive airway pressure for ARDS who presented to our tertiary-care center from March through November, 2020.

RESULTS

A total of 353 patients met our inclusion criteria, of which 232 patients who required heated high-flow nasal cannula, continuous or bilevel positive airway pressure were assigned to non-invasive group. The remaining 121 patients required invasive mechanical ventilation and were assigned to invasive group. Of the total 353 patients, 32 patients (65.6% males) with a mean age of 63 ± 11 years developed barotrauma in the form of subcutaneous emphysema, pneumothorax, or pneumomediastinum. The incidence of barotrauma was 4.74% (11/232) and 17.35% (21/121) in the non-invasive group and invasive group, respectively. The median length of hospital stay was 22 (15.7 -33.0) days with an overall mortality of 62.5% (n = 20).

CONCLUSIONS

Patients with COVID-19 ARDS have a high incidence of barotrauma. Pulmonary barotrauma should be considered in patients with COVID-19 pneumonia who exhibit worsening of their respiratory disease as it is likely associated with a high mortality risk. Utilizing lung-protective ventilation strategies may reduce the risk of barotrauma.

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.

Driving pressure during proportional assist ventilation: an observational study

Background

During passive mechanical ventilation, the driving pressure of the respiratory system is an important mediator of ventilator-induced lung injury. Monitoring of driving pressure during assisted ventilation, similar to controlled ventilation, could be a tool to identify patients at risk of ventilator-induced lung injury. The aim of this study was to describe driving pressure over time and to identify whether and when high driving pressure occurs in critically ill patients during assisted ventilation.

Methods

Sixty-two patients fulfilling criteria for assisted ventilation were prospectively studied. Patients were included when the treating physician selected proportional assist ventilation (PAV+), a mode that estimates respiratory system compliance. In these patients, continuous recordings of all ventilator parameters were obtained for up to 72 h. Driving pressure was calculated as tidal volume-to-respiratory system compliance ratio. The distribution of driving pressure and tidal volume values over time was examined, and periods of sustained high driving pressure (≥ 15 cmH₂O) and of stable compliance were identified and analyzed.

Results

The analysis included 3200 h of ventilation, consisting of 8.8 million samples. For most (95%) of the time, driving pressure was < 15 cmH₂O and tidal volume < 11 mL/kg (of ideal body weight). In most patients, high driving pressure was observed for short periods of time (median 2.5 min). Prolonged periods of high driving pressure were observed in five patients (8%). During the 661 periods of stable compliance, high driving pressure combined with a tidal volume ≥ 8 mL/kg was observed only in 11 cases (1.6%) pertaining to four patients. High driving pressure occurred almost exclusively when respiratory system compliance was low, and compliance above 30 mL/cmH₂O excluded the presence of high driving pressure with 90% sensitivity and specificity.

Conclusions

In critically ill patients fulfilling criteria for assisted ventilation, and ventilated in PAV+ mode, sustained high driving pressure occurred in a small, yet not negligible number of patients. The presence of sustained high driving pressure was not associated with high tidal volume, but occurred almost exclusively when compliance was below 30 mL/cmH₂O.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0477-4) contains supplementary material, which is available to authorized users.