Patient self-inflicted lung injury: implications for acute hypoxemic respiratory failure and ARDS patients on non-invasive support

Impact of neonatal noninvasive resuscitation strategies on lung mechanics, tracheal pressure, and tidal volume in preterm lambs

This study investigated the relationship between three respiratory support approaches on lung volume recruitment during the first 2 h of postnatal life in preterm lambs. We estimated changes in lung aeration, measuring respiratory resistance and reactance by oscillometry at 5 Hz. We also measured intratracheal pressure in subsets of lambs. The first main finding is that sustained inflation (SI) applied noninvasively (Mask SI; n = 7) or invasively [endotracheal tube (ETT) SI; n = 6] led to similar rapid lung volume recruitment (∼6 min). In contrast, Mask continuous positive airway pressure (CPAP) without SI (n = 6) resuscitation took longer (∼30-45 min) to reach similar lung volume recruitment. The second main finding is that, in the first 15 min of postnatal life, the Mask CPAP without SI group closed their larynx during custom ventilator-driven expiration, leading to intratracheal positive end-expiratory pressure of ∼17 cmH2O (instead of 8 cmH2O provided by the ventilator). In contrast, the Mask SI group used the larynx to limit inspiratory pressure to ∼26 cmH2O (instead of 30 cmH2O provided by the ventilator). These different responses affected tidal volume, being larger in the Mask CPAP without SI group [8.4 mL/kg; 6.7-9.3 interquartile range (IQR)] compared to the Mask SI (5.0 mL/kg; 4.4-5.2 IQR) and ETT SI groups (3.3 mL/kg; 2.6-3.7 IQR). Distinct physiological responses suggest that spontaneous respiratory activity of the larynx of preterm lambs at birth can uncouple pressure applied by the ventilator to that applied to the lung, leading to unpredictable lung pressure and tidal volume delivery independently from the ventilator settings.NEW & NOTEWORTHY We compared invasive and noninvasive resuscitation on lambs at birth, including or not sustained inflation (SI). Lung volume recruitment was faster in those receiving SI. During noninvasive resuscitation, larynx modulation reduced tracheal pressure from that applied to the mask in lambs receiving SI, while it led to increased auto-positive end-expiratory pressure and very large tidal volumes in lambs not receiving SI. Our results highlight the need for individualizing pressures and monitoring tidal volumes during resuscitation at birth.

A comparison study of temporal trends of SARS-CoV2 RNAemia and biomarkers to predict success and failure of high flow oxygen therapy among patients with moderate to severe COVID-19

Optimal timing for intubating patients with coronavirus disease 2019 (COVID-19) has been debated throughout the pandemic. Early use of high-flow nasal cannula (HFNC) can help reduce the need for intubation, but delay can result in poorer outcomes. This study examines trends in laboratory parameters and serum severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA levels of patients with COVID-19 in relation to HFNC failure. Patients requiring HFNC within three days of hospitalization between July 1 and September 30, 2021 were enrolled. The primary outcome was HFNC failure (early failure ≤Day 3; late failure ≥Day 4), defined as transfer to intensive care just before/after intubation or in-hospital death. We examined changes in laboratory markers and SARS-CoV2-RNAemia on Days 1, 4, and 7, together with demographic data, oxygenation status, and therapeutic agents. We conducted a univariate logistic regression with the explanatory variables defined as 10% change rate in each laboratory marker from Day 1 to 4. We utilized the log-rank test to assess the differences in HFNC failure rates, stratified based on the presence of SARS-CoV2 RNAemia. Among 122 patients, 17 (13.9%) experienced HFNC failure (early: n = 6, late: n = 11). Seventy-five patients (61.5%) showed an initial SpO2/FiO2 ratio ≤243, equivalent to PaO2/FiO2 ratio ≤200, and the initial SpO2/FiO2 ratio was significantly lower in the failure group (184 vs. 218, p = 0.018). Among the laboratory markers, a 10% increase from Day 1 to 4 of lactate dehydrogenase (LDH) and interleukin (IL)-6 was associated with late failure (Odds ratio [OR]: 1.42, 95% confidence interval [CI]: 1.09-1.89 and OR: 1.04, 95%CI: 1.00-1.19, respectively). Furthermore, in patients with persistent RNAemia on Day 4 or 7, the risk of late HFNC failure was significantly higher (Log-rank test, p<0.01). In conclusion, upward trends in LDH and IL-6 levels and the persistent RNAemia even after treatment were associated with HFNC failure.

The respiratory oxygenation index for identifying the risk of orotracheal intubation in COVID-19 patients receiving high-flow nasal cannula oxygen

OBJECTIVE

To assess whether the respiratory oxygenation index (ROX index) measured after the start of high-flow nasal cannula oxygen therapy can help identify the need for intubation in patients with acute respiratory failure due to coronavirus disease 2019.

METHODS

This retrospective, observational, multicenter study was conducted at the intensive care units of six Brazilian hospitals from March to December 2020. The primary outcome was the need for intubation up to 7 days after starting the high-flow nasal cannula.

RESULTS

A total of 444 patients were included in the study, and 261 (58.7%) were subjected to intubation. An analysis of the area under the receiver operating characteristic curve (AUROC) showed that the ability to discriminate between successful and failed high-flow nasal cannula oxygen therapy within 7 days was greater for the ROX index measured at 24 hours (AUROC 0.80; 95%CI 0.76 - 0.84). The median interval between high-flow nasal cannula initiation and intubation was 24 hours (24 - 72), and the most accurate predictor of intubation obtained before 24 hours was the ROX index measured at 12 hours (AUROC 0.75; 95%CI 0.70 - 0.79). Kaplan-Meier curves revealed a greater probability of intubation within 7 days in patients with a ROX index ≤ 5.54 at 12 hours (hazard ratio 3.07; 95%CI 2.24 - 4.20) and ≤ 5.96 at 24 hours (hazard ratio 5.15; 95%CI 3.65 - 7.27).

CONCLUSION

The ROX index can aid in the early identification of patients with acute respiratory failure due to COVID-19 who will progress to the failure of high-flow nasal cannula supportive therapy and the need for intubation.

High vs Low PEEP in Patients With ARDS Exhibiting Intense Inspiratory Effort During Assisted Ventilation: A Randomized Crossover Trial

BACKGROUND

Positive end-expiratory pressure (PEEP) can potentially modulate inspiratory effort (ΔPes), which is the major determinant of self-inflicted lung injury.

RESEARCH QUESTION

Does high PEEP reduce ΔPes in patients with moderate-to-severe ARDS on assisted ventilation?

STUDY DESIGN AND METHODS

Sixteen patients with Pao2/Fio2 ≤ 200 mm Hg and ΔPes ≥ 10 cm H2O underwent a randomized sequence of four ventilator settings: PEEP = 5 cm H2O or PEEP = 15 cm H2O + synchronous (pressure support ventilation [PSV]) or asynchronous (pressure-controlled intermittent mandatory ventilation [PC-IMV]) inspiratory assistance. ΔPes and respiratory system, lung, and chest wall mechanics were assessed with esophageal manometry and occlusions. PEEP-induced alveolar recruitment and overinflation, lung dynamic strain, and tidal volume distribution were assessed with electrical impedance tomography.

RESULTS

ΔPes was not systematically different at high vs low PEEP (pressure support ventilation: median, 20 cm H2O; interquartile range (IQR), 15-24 cm H2O vs median, 15 cm H2O; IQR, 13-23 cm H2O; P = .24; pressure-controlled intermittent mandatory ventilation: median, 20; IQR, 18-23 vs median, 19; IQR, 17-25; P = .67, respectively). Similarly, respiratory system and transpulmonary driving pressures, tidal volume, lung/chest wall mechanics, and pendelluft extent were not different between study phases. High PEEP resulted in lower or higher ΔPes, respiratory system driving pressure, and transpulmonary driving pressure according to whether this increased or decreased respiratory system compliance (r = -0.85, P < .001; r = -0.75, P < .001; r = -0.80, P < .001, respectively). PEEP-induced changes in respiratory system compliance were driven by its lung component and were dependent on the extent of PEEP-induced alveolar overinflation (r = -0.66, P = .006). High PEEP caused variable recruitment and systematic redistribution of tidal volume toward dorsal lung regions, thereby reducing dynamic strain in ventral areas (pressure support ventilation: median, 0.49; IQR, 0.37-0.83 vs median, 0.96; IQR, 0.62-1.56; P = .003; pressure-controlled intermittent mandatory ventilation: median, 0.65; IQR, 0.42-1.31 vs median, 1.14; IQR, 0.79-1.52; P = .002). All results were consistent during synchronous and asynchronous inspiratory assistance.

INTERPRETATION

The impact of high PEEP on ΔPes and lung stress is interindividually variable according to different effects on the respiratory system and lung compliance resulting from alveolar overinflation. High PEEP may help mitigate the risk of self-inflicted lung injury solely if it increases lung/respiratory system compliance.

TRIAL REGISTRATION

ClinicalTrials.gov; No.: NCT04241874; URL: www.

CLINICALTRIALS

gov.

High-Flow Nasal Cannula Versus Noninvasive Ventilation as Initial Treatment in Acute Hypoxia: A Propensity Score-Matched Study

IMPORTANCE

Patients presenting to the emergency department (ED) with hypoxemia often have mixed or uncertain causes of respiratory failure. The optimal treatment for such patients is unclear. Both high-flow nasal cannula (HFNC) and noninvasive ventilation (NIV) are used.

OBJECTIVES

We sought to compare the effectiveness of initial treatment with HFNC versus NIV for acute hypoxemic respiratory failure.

DESIGN SETTING AND PARTICIPANTS

We conducted a retrospective cohort study of patients with acute hypoxemic respiratory failure treated with HFNC or NIV within 24 hours of arrival to the University of Michigan adult ED from January 2018 to December 2022. We matched patients 1:1 using a propensity score for odds of receiving NIV.

MAIN OUTCOMES AND MEASURES

The primary outcome was major adverse pulmonary events (28-d mortality, ventilator-free days, noninvasive respiratory support hours) calculated using a win ratio.

RESULTS

A total of 1154 patients were included. Seven hundred twenty-six (62.9%) received HFNC and 428 (37.1%) received NIV. We propensity score matched 668 of 1154 (57.9%) patients. Patients on NIV versus HFNC had lower 28-day mortality (16.5% vs. 23.4%, p = 0.033) and required noninvasive treatment for fewer hours (median 7.5 vs. 13.5, p < 0.001), but had no difference in ventilator-free days (median [interquartile range]: 28 [26, 28] vs. 28 [10.5, 28], p = 0.199). Win ratio for composite major adverse pulmonary events favored NIV (1.38; 95% CI, 1.15-1.65; p < 0.001).

CONCLUSIONS AND RELEVANCE

In this observational study of patients with acute hypoxemic respiratory failure, initial treatment with NIV compared with HFNC was associated with lower mortality and fewer composite major pulmonary adverse events calculated using a win ratio. These findings underscore the need for randomized controlled trials to further understand the impact of noninvasive respiratory support strategies.

Severe Community-Acquired Pneumonia: Noninvasive Mechanical Ventilation, Intubation, and HFNT

Severe acute respiratory failure (ARF) is a major issue in patients with severe community-acquired pneumonia (CAP). Standard oxygen therapy is the first-line therapy for ARF in the less severe cases. However, respiratory supports may be delivered in more severe clinical condition. In cases with life-threatening ARF, invasive mechanical ventilation (IMV) will be required. Noninvasive strategies such as high-flow nasal therapy (HFNT) or noninvasive ventilation (NIV) by either face mask or helmet might cover the gap between standard oxygen and IMV. The objective of all the supporting measures for ARF is to gain time for the antimicrobial treatment to cure the pneumonia. There is uncertainty regarding which patients with severe CAP are most likely to benefit from each noninvasive support strategy. HFNT may be the first-line approach in the majority of patients. While NIV may be relatively contraindicated in patients with excessive secretions, facial hair/structure resulting in air leaks or poor compliance, NIV may be preferable in those with increased work of breathing, respiratory muscle fatigue, and congestive heart failure, in which the positive pressure of NIV may positively impact hemodynamics. A trial of NIV might be considered for select patients with hypoxemic ARF if there are no contraindications, with close monitoring by an experienced clinical team who can intubate patients promptly if they deteriorate. In such cases, individual clinician judgement is key to choose NIV, interface, and settings. Due to the paucity of studies addressing IMV in this population, the protective mechanical ventilation strategies recommended by guidelines for acute respiratory distress syndrome can be reasonably applied in patients with severe CAP.

Diagnosis and Management of Acute Respiratory Failure

Acute hypoxemic respiratory failure is defined by Pao2 less than 60 mm Hg or SaO2 less than 88% and may result from V/Q mismatch, shunt, hypoventilation, diffusion limitation, or low inspired oxygen tension. Acute hypercapnic respiratory failure is defined by Paco2 ≥ 45 mm Hg and pH less than 7.35 and may result from alveolar hypoventilation, increased fraction of dead space, or increased production of carbon dioxide. Early diagnostic maneuvers, such as measurement of SpO2 and arterial blood gas, can differentiate the type of respiratory failure and guide next steps in evaluation and management.

Incidence of noninvasive ventilation failure and mortality in patients with acute respiratory distress syndrome: a systematic review and proportion meta-analysis

BACKGROUND

Noninvasive ventilation (NIV) is commonly used in patients with acute respiratory distress syndrome (ARDS). However, the incidence and distribution of treatment failure are unclear.

METHODS

A comprehensive online search was conducted to select potentially eligible studies with reports of the rate of NIV failure in patients with ARDS. A manual search was also performed to identify additional studies. Data were extracted to calculate the pooled incidences of NIV failure and mortality. Based on oxygenation, the severity of the disease was classified as mild, moderate, or severe ARDS. Based on etiologies, ARDS was defined as being of pulmonary origin or extrapulmonary origin.

RESULTS

We enrolled 90 studies in this meta-analysis, involving 98 study arms. The pooled incidence of NIV failure was 48% (n = 5847, 95% confidence interval [CI]: 43-52%). The pooled incidence of ICU mortality was 29% (n = 2363, 95%CI: 22-36%), and that of hospital mortality was 33% (n = 2927, 95%CI: 27-40%). In patients with mild, moderate, and severe ARDS, the pooled incidence of NIV failure was 30% (n = 819, 95%CI: 21-39%), 51% (n = 1332, 95%CI: 43-60%), and 71% (n = 525, 95%CI: 62-79%), respectively. In patients with pulmonary ARDS, it was 45% (n = 2687, 95%CI: 39-51%). However, it was 30% (n = 802, 95%CI: 21-38%) in those with extrapulmonary ARDS. In patients with immunosuppression, the incidence of NIV failure was 62% (n = 806, 95%CI: 50-74%). However, it was 46% (n = 5041, 95%CI: 41-50%) in those without immunosuppression.

CONCLUSIONS

Nearly half of patients with ARDS experience NIV failure. The incidence of NIV failure increases with increasing ARDS severity. Pulmonary ARDS seems to have a higher rate of NIV failure than extrapulmonary ARDS. ARDS patients with immunosuppression have the highest rate of NIV failure.

Comparison between high-flow nasal cannula and conventional oxygen therapy in COVID-19 patients: a systematic review and meta-analysis

BACKGROUND

High-flow nasal cannula (HFNC) and conventional oxygen therapy (COT) are important respiratory support strategies for acute hypoxemic respiratory failure (AHRF) in coronavirus disease 2019 (COVID-19) patients. However, the results are conflicting for the risk of intubation with HFNC as compared to COT.

OBJECTIVES

We systematically synthesized the outcomes of HFNC relative to COT in COVID-19 patients with AHRF and evaluated these outcomes in relevant subpopulations.

DESIGN

This study was designed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

DATA SOURCES AND METHODS

We searched PubMed, EMBASE, Web of Science, Scopus, ClinicalTrials.gov, medRxiv, BioRxiv, and the Cochrane Central Register of Controlled Trials for randomized controlled trials and observational studies that compared the efficacy of HFNC with COT in patients with COVID-19-related AHRF. Primary outcomes were intubation rate and mortality rate. Secondary outcomes were the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2), respiratory rate, hospital length of stay, intensive care unit (ICU) length of stay, and days free from invasive mechanical ventilation.

RESULTS

In total, 20 studies with 5732 patients were included. We found a decreased risk of requiring intubation in HFNC compared to COT [odds ratio (OR) = 0.61, 95% confidence interval (CI): 0.46-0.82, p = 0.0009, I2 = 75%]. Similarly, we found HFNC was associated with lower risk of intubation rate compared to COT in the subgroup of patients with baseline PaO2/FiO2 < 200 mmHg (OR = 0.69, 95% CI: 0.55-0.86, p = 0.0007, I2 = 45%), and who were in ICU settings at enrollment (OR = 0.57, 95% CI: 0.38-0.85, p = 0.005, I2 = 80%). HFNC was associated with an improvement of PaO2/FiO2 and respiratory rate compared to COT. The use of HFNC compared to COT did not reduce the mortality rate, days free from invasive mechanical ventilation, hospital length of stay, or ICU length of stay.

CONCLUSION

Compared to COT, HFNC may decrease the need for tracheal intubation in patients with COVID-19-related AHRF, particularly among patients with baseline PaO2/FiO2 < 200 mmHg and those in ICU settings.

TRIAL REGISTRATION

This systematic review and meta-analysis protocol was prospectively registered with PROSPERO (no. CRD42022339072).

Comparison of Noninvasive Mechanical Ventilation With High-Flow Nasal Cannula, Face-Mask, and Helmet in Hypoxemic Respiratory Failure in Patients With COVID-19: A Randomized Controlled Trial

OBJECTIVES

For COVID-19-related respiratory failure, noninvasive respiratory assistance via a high-flow nasal cannula (HFNC), helmet, and face-mask noninvasive ventilation is used. However, which of these options is most effective is yet to be determined. This study aimed to compare the three techniques of noninvasive respiratory support and to determine the superior technique.

DESIGN

A randomized control trial with permuted block randomization of nine cases per block for each parallel, open-labeled arm.

SETTING AND PATIENTS

Adult patients with COVID-19 with a Pa o2 /F io2 ratio of less than 300, admitted between February 4, 2021, and August 9, 2021, to three tertiary centers in Oman, were studied.

INTERVENTIONS

This study included three interventions: HFNC ( n = 47), helmet continuous positive airway pressure (CPAP; n = 52), and face-mask CPAP ( n = 52).

MEASUREMENTS AND MAIN RESULTS

The endotracheal intubation rate and mortality at 28 and 90 days were measured as the primary and secondary outcomes, respectively. Of the 159 randomized patients, 151 were analyzed. The median age was 52 years, and 74% were men. The endotracheal intubation rates were 44%, 45%, and 46% ( p = 0.99), and the median intubation times were 7.0, 5.5, and 4.5 days ( p = 0.11) in the HFNC, face-mask CPAP, and helmet CPAP, respectively. In comparison to face-mask CPAP, the relative risk of intubation was 0.97 (95% CI, 0.63-1.49) for HFNC and 1.0 (95% CI 0.66-1.51) for helmet CPAP. The mortality rates were 23%, 32%, and 38% at 28 days ( p = 0.24) and 43%, 38%, and 40% ( p = 0.89) at 90 days for HFNC, face-mask CPAP, and helmet CPAP, respectively. The trial was stopped prematurely because of a decline in cases.

CONCLUSIONS

This exploratory trial found no difference in intubation rate and mortality among the three intervention groups for the COVID-19 patients with hypoxemic respiratory failure; however, more evidence is needed to confirm these findings as the trial was aborted prematurely.

Ventilatory associated barotrauma in COVID-19 patients: A multicenter observational case control study (COVI-MIX-study)

BACKGROUND

The risk of barotrauma associated with different types of ventilatory support is unclear in COVID-19 patients. The primary aim of this study was to evaluate the effect of the different respiratory support strategies on barotrauma occurrence; we also sought to determine the frequency of barotrauma and the clinical characteristics of the patients who experienced this complication.

METHODS

This multicentre retrospective case-control study from 1 March 2020 to 28 February 2021 included COVID-19 patients who experienced barotrauma during hospital stay. They were matched with controls in a 1:1 ratio for the same admission period in the same ward of treatment. Univariable and multivariable logistic regression (OR) were performed to explore which factors were associated with barotrauma and in-hospital death.

RESULTS

We included 200 cases and 200 controls. Invasive mechanical ventilation was used in 39.3% of patients in the barotrauma group, and in 20.1% of controls (p<0.001). Receiving non-invasive ventilation (C-PAP/PSV) instead of conventional oxygen therapy (COT) increased the risk of barotrauma (OR 5.04, 95% CI 2.30 - 11.08, p<0.001), similarly for invasive mechanical ventilation (OR 6.24, 95% CI 2.86-13.60, p<0.001). High Flow Nasal Oxygen (HFNO), compared with COT, did not significantly increase the risk of barotrauma. Barotrauma frequency occurred in 1.00% [95% CI 0.88-1.16] of patients; these were older (p=0.022) and more frequently immunosuppressed (p=0.013). Barotrauma was shown to be an independent risk for death (OR 5.32, 95% CI 2.82-10.03, p<0.001).

CONCLUSIONS

C-PAP/PSV compared with COT or HFNO increased the risk of barotrauma; otherwise HFNO did not. Barotrauma was recorded in 1.00% of patients, affecting mainly patients with more severe COVID-19 disease. Barotrauma was independently associated with mortality.

TRIAL REGISTRATION

this case-control study was prospectively registered in clinicaltrial.gov as NCT04897152 (on 21 May 2021).

Inspiratory Effort and Respiratory Mechanics in Patients with Acute Exacerbation of Idiopathic Pulmonary fibrosis: A Preliminary Matched Control Study

BACKGROUND

Patients with acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) may experience severe acute respiratory failure, even requiring ventilatory assistance. Physiological data on lung mechanics during these events are lacking.

METHODS

Patients with AE-IPF admitted to Respiratory Intensive Care Unit to receive non-invasive ventilation (NIV) were retrospectively analyzed. Esophageal pressure swing (ΔPes) and respiratory mechanics before and after 2 hours of NIV were collected as primary outcome. The correlation between positive end-expiratory pressure (PEEP) levels and changes of in dynamic compliance (dynCRS) and PaO2/FiO2 ratio was assessed. Further, an exploratory comparison with a historical cohort of ARDS patients matched 1:1 by age, sequential organ failure assessment score, body mass index and PaO2/FiO2 level was performed.

RESULTS

At baseline, AE-IPF patients presented a high respiratory drive activation with ΔPes = 27 (21-34) cmH2O, respiratory rate (RR) = 34 (30-39) bpm and minute ventilation (VE) = 21 (20-26) L/min. Two hours after NIV application, ΔPes, RR and VE values showed a significant reduction (16 [14-24] cmH2O, p<0.0001, 27 [25-30] bpm, p=0.001, and 18 [17-20] L/min, p=0.003, respectively) while no significant change was found in dynamic transpulmonary pressure, expiratory tidal volume (Vte), dynCRS and dynamic mechanical power. PEEP levels negatively correlated with PaO2/FiO2 ratio and dynCRS (r=-0.67, p=0.03 and r=-0.27, p=0.4, respectively). When compared to AE-IPF, ARDS patients presented lower baseline ΔPes, RR, VE and dynamic mechanical power. Differently from AE-IPF, in ARDS both Vte and dynCRS increased significantly following NIV (p=0.01 and p=0.004 respectively) with PEEP levels directly associated with PaO2/FiO2 ratio and dynCRS (r=0.24, p=0.5 and r=0.65, p=0.04, respectively).

CONCLUSIONS

In this study, patients with AE-IPF showed a high inspiratory effort, whose intensity was reduced by NIV application without a significant improvement in respiratory mechanics. In an exploratory analysis, AE-IPF patients showed a different mechanical behavior under spontaneous unassisted and assisted breathing compared with ARDS patients of similar severity.

Ten Issues for Updating in Community-Acquired Pneumonia: An Expert Review

Community-acquired pneumonia represents the third-highest cause of mortality in industrialized countries and the first due to infection. Although guidelines for the approach to this infection model are widely implemented in international health schemes, information continually emerges that generates controversy or requires updating its management. This paper reviews the most important issues in the approach to this process, such as an aetiologic update using new molecular platforms or imaging techniques, including the diagnostic stewardship in different clinical settings. It also reviews both the Intensive Care Unit admission criteria and those of clinical stability to discharge. An update in antibiotic, in oxygen, or steroidal therapy is presented. It also analyzes the management out-of-hospital in CAP requiring hospitalization, the main factors for readmission, and an approach to therapeutic failure or rescue. Finally, the main strategies for prevention and vaccination in both immunocompetent and immunocompromised hosts are reviewed.

The Association between Non-Invasive Ventilation and the Rate of Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) has significant effects on patient outcomes, including prolonging the duration of both mechanical ventilation and stay in the intensive care unit (ICU). The aim of this study was to assess the association between non-invasive ventilation/oxygenation (NIVO) prior to intubation and the rate of subsequent VAP. This was a multicenter retrospective cohort study of adult patients who were admitted to the medical ICU from three tertiary care academic centers in three distinct regions. NIVO was defined as continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP), or high-flow nasal cannula (HFNC) for any duration during the hospitalization prior to intubation. The primary outcome variable was VAP association with NIVO. A total of 17,302 patients were included. VAP developed in 2.6% of the patients (444/17,302), 2.3% (285/12,518) of patients among those who did not have NIVO, 1.6% (30/1879) of patients who had CPAP, 2.5% (17/690) of patients who had HFNC, 8.1% (16/197) of patients who had BiPAP, and 4.8% (96/2018) of patients who had a combination of NIVO types. Compared to those who did not have NIVO, VAP was more likely to develop among those who had BiPAP (adj OR 3.11, 95% CI 1.80-5.37, p < 0.001) or a combination of NIVO types (adj OR 1.91, 95% CI 1.49-2.44, p < 0.001) after adjusting for patient demographics and comorbidities. The use of BiPAP or a combination of NIVO types significantly increases the odds of developing VAP once receiving IMV.

Diaphragm excursions as proxy for tidal volume during spontaneous breathing in invasively ventilated ICU patients

There is a need to monitor tidal volume in critically ill patients with acute respiratory failure, given its relation with adverse clinical outcome. However, quantification of tidal volume in non-intubated patients is challenging. In this proof-of-concept study, we evaluated whether ultrasound measurements of diaphragm excursion could be a valid surrogate for tidal volume in patients with respiratory failure. Diaphragm excursions and tidal volumes were simultaneously measured in invasively ventilated patients (N = 21) and healthy volunteers (N = 20). Linear mixed models were used to estimate the ratio between tidal volume and diaphragm excursion. The tidal volume-diaphragm excursion ratio was 201 mL/cm in ICU patients [95% confidence interval (CI) 161-240 mL/cm], and 361 (294-428) mL/cm in healthy volunteers. An excellent association was shown within participants (R2 = 0.96 in ICU patients, R2 = 0.90 in healthy volunteers). However, the differences between observed tidal volume and tidal volume as predicted by the linear mixed models were considerable: the 95% limits of agreement in Bland-Altman plots were ± 91 mL in ICU patients and ± 396 mL in healthy volunteers. Likewise, the variability in tidal volume estimation between participants was large. This study shows that diaphragm excursions measured with ultrasound correlate with tidal volume, yet quantification of absolute tidal volume from diaphragm excursion is unreliable.

High-flow nasal cannula vs non-invasive ventilation in acute hypoxia: Propensity score matched study

RATIONALE

The optimal treatment for early hypoxemic respiratory failure is unclear, and both high-flow nasal cannula and non-invasive ventilation are used. Determining clinically relevant outcomes for evaluating non-invasive respiratory support modalities remains a challenge.

OBJECTIVES

To compare the effectiveness of initial treatment with high-flow nasal cannula versus non-invasive ventilation for acute hypoxemic respiratory failure.

METHODS

We conducted a retrospective cohort study of patients with acute hypoxemic respiratory failure treated with high-flow nasal cannula or non-invasive ventilation within 24 hours of Emergency Department arrival (1/2018-12/2022). We matched patients 1:1 using a propensity score for odds of receiving non-invasive ventilation. The primary outcome was major adverse pulmonary events (28-day mortality, ventilator-free days, non-invasive respiratory support hours) calculated using a Win Ratio.

MEASUREMENTS AND MAIN RESULTS

1,265 patients met inclusion criteria. 795 (62.8%) received high-flow oxygen and 470 (37.2%) received non-invasive ventilation. We propensity score matched 736/1,265 (58.2%) patients. There was no difference between non-invasive ventilation vs high-flow nasal cannula in 28-day mortality (17.7% vs 23.1%, p=0.08) or ventilator-free days (median [Interquartile Range]: 28 [25, 28] vs 28 [13, 28], p=0.50), but patients on non-invasive ventilation required treatment for fewer hours (median 7 vs 13, p< 0.001). Win Ratio for composite major adverse pulmonary events favored non-invasive ventilation (1.26, 95%CI 1.06-1.49, p< 0.001).

CONCLUSIONS

In this observational study of patients with acute hypoxemic respiratory failure, initial treatment with non-invasive ventilation was superior to high-flow nasal cannula for major pulmonary adverse events. Evaluation of composite outcomes is important in the assessment of respiratory support modalities.

Predictors of Failure of Noninvasive Ventilation in Critically Ill Children

Noninvasive ventilation (NIV) is a common modality employed to treat acute respiratory failure. Most data guiding its use is extrapolated from adult studies. We sought to identify clinical predictors associated with failure of NIV, defined as requiring intubation. This single-center retrospective observational study included children admitted to pediatric intensive care unit (PICU) between July 2014 and June 2016 treated with NIV, excluding postextubation. A total of 148 patients was included. Twenty-seven (18%) failed NIV. There was no difference between the two groups with regard to age, gender, comorbidities, or etiology of acute respiratory failure. Those that failed had higher admission pediatric risk of mortality ( p  = 0.01) and pediatric logistic organ dysfunction ( p  = 0.002) scores and higher fraction of inspired oxygen (FiO 2 ; p  = 0.009) at NIV initiation. Failure was associated with lack of improvement in tachypnea. At 6 hours of NIV, the failure group had worsening tachypnea with a median increase in respiratory rate of 8%, while the success group had a median reduction of 18% ( p  = 0.06). Multivariable Cox's proportional hazard models revealed FiO 2 at initiation and worsening respiratory rate at 1- and 6-hour significant risks for failure of NIV. Failure was associated with a significantly longer PICU length of stay (success [2.8 days interquartile range (IQR): 1.7, 5.5] vs. failure [10.6 days IQR: 5.6, 13.2], p  < 0.001). NIV can be successfully employed to treat acute respiratory failure in pediatric patients. There should be heightened concern for NIV failure in hypoxemic patients whose tachypnea is unresponsive to NIV. A trend toward improvement should be closely monitored.

Acute Airway Compromise Due to Spontaneous Pneumomediastinum in COVID-19 Infection and Subsequent Rapid Formation of Pulmonary Subpleural Bullae: A Case Report

Spontaneous pneumomediastinum (SPM), an increasingly documented complication of COVID-19 infection, usually presents with retrosternal chest pain and dyspnea but can present atypically. In this case, an exceptionally rare presentation could have led to inappropriate management and a poor outcome. Here, a previously healthy 41-year-old Afro-Caribbean male non-smoker presents with acute airway compromise due to SPM. Conservative management proved effective, with anxiolysis to mitigate patient self-induced lung injury (PSILI) and oxygen supplementation via a non-rebreather mask to increase the resolution rate till the patient stabilized over the following days. The sequelae of the lung insult were noted in subsequent imaging, showing the formation of many subpleural bullae. Our case demonstrates the need for a high index of suspicion for pneumomediastinum among teams caring for COVID-19 cases. It also highlights the potential need for follow-up for further research on pulmonary sequelae.

Days spent on non-invasive ventilation support: can it determine when to initiate VV- ECMO? Observational study in a cohort of Covid-19 patients

BACKGROUND

The study evaluates the impact of the time between commencing non-invasive ventilation (NIV) support and initiation of venovenous extracorporeal membrane oxygenation (VV-ECMO) in a cohort of critically ill patients with coronavirus disease 2019 (COVID-19) associated acute respiratory distress syndrome (ARDS).

METHODS

Prospective observational study design in an intensive Care Unit (ICU) of a tertiary hospital in Barcelona (Spain). All patients requiring VV-ECMO support due to COVID-19 associated ARDS between March 2020 and January 2022 were analysed. Survival outcome was determined at 90 days after VV-ECMO initiation. Demographic data, comorbidities at ICU admission, RESP (respiratory ECMO survival prediction) score, antiviral and immunomodulatory treatments received, inflammatory biomarkers, the need for vasopressors, the thromboprophylaxis regimen received, and respiratory parameters including the length of intubation previous to ECMO and the length of each NIV support (high-flow nasal cannula, continuous positive airway pressure and bi-level positive airway pressure), were also collated in order to assess risk factors for day-90 mortality. The effect of the time lapse between NIV support and VV-ECMO on survival was evaluated using logistic regression and adjusting the association with all factors that were significant in the univariate analysis.

RESULTS

Seventy-two patients finally received VV-ECMO support. At 90 days after commencing VV-ECMO 35 patients (48%) had died and 37 patients (52%) were alive. Multivariable analysis showed that at VV-ECMO initiation, age (p = 0.02), lactate (p = 0.001), and days from initiation of NIV support to starting VV-ECMO (p = 0.04) were all associated with day-90 mortality.

CONCLUSIONS

In our small cohort of VV-ECMO patients with COVID-19 associated ARDS, the time spent between initiation of NIV support and VV-ECMO (together with age and lactate) appeared to be a better predictor of mortality than the time between intubation and VV-ECMO.

Acute dyspnea in the emergency department: a clinical review

Acute dyspnea represents one of the most frequent symptoms leading to emergency room evaluation. Its significant prognostic value warrants a careful evaluation. The differential diagnosis of dyspnea is complex due to the lack of specificity and the loose association between its intensity and the severity of the underlying pathological condition. The initial assessment of dyspnea calls for prompt diagnostic evaluation and identification of optimal monitoring strategy and provides information useful to allocate the patient to the most appropriate setting of care. In recent years, accumulating evidence indicated that lung ultrasound, along with echocardiography, represents the first rapid and non-invasive line of assessment that accurately differentiates heart, lung or extra-pulmonary involvement in patients with dyspnea. Moreover, non-invasive respiratory support modalities such as high-flow nasal oxygen and continuous positive airway pressure have aroused major clinical interest, in light of their efficacy and practicality to treat patients with dyspnea requiring ventilatory support, without using invasive mechanical ventilation. This clinical review is focused on the pathophysiology of acute dyspnea, on its clinical presentation and evaluation, including ultrasound-based diagnostic workup, and on available non-invasive modalities of respiratory support that may be required in patients with acute dyspnea secondary or associated with respiratory failure.

Personalized Respiratory Support in ARDS: A Physiology-to-Bedside Review

Acute respiratory distress syndrome (ARDS) is a leading cause of disability and mortality worldwide, and while no specific etiologic interventions have been shown to improve outcomes, noninvasive and invasive respiratory support strategies are life-saving interventions that allow time for lung recovery. However, the inappropriate management of these strategies, which neglects the unique features of respiratory, lung, and chest wall mechanics may result in disease progression, such as patient self-inflicted lung injury during spontaneous breathing or by ventilator-induced lung injury during invasive mechanical ventilation. ARDS characteristics are highly heterogeneous; therefore, a physiology-based approach is strongly advocated to titrate the delivery and management of respiratory support strategies to match patient characteristics and needs to limit ARDS progression. Several tools have been implemented in clinical practice to aid the clinician in identifying the ARDS sub-phenotypes based on physiological peculiarities (inspiratory effort, respiratory mechanics, and recruitability), thus allowing for the appropriate application of personalized supportive care. In this narrative review, we provide an overview of noninvasive and invasive respiratory support strategies, as well as discuss how identifying ARDS sub-phenotypes in daily practice can help clinicians to deliver personalized respiratory support and potentially improve patient outcomes.

Assessment of Inspiratory Effort in Spontaneously Breathing COVID-19 ARDS Patients Undergoing Helmet CPAP: A Comparison between Esophageal, Transdiaphragmatic and Central Venous Pressure Swing

INTRODUCTION

The clinical features of COVID-19 are highly variable. It has been speculated that the progression across COVID-19 may be triggered by excessive inspiratory drive activation. The aim of the present study was to assess whether the tidal swing in central venous pressure (ΔCVP) is a reliable estimate of inspiratory effort.

METHODS

Thirty critically ill patients with COVID-19 ARDS underwent a PEEP trial (0-5-10 cmH₂O) during helmet CPAP. Esophageal (ΔPes) and transdiaphragmatic (ΔPdi) pressure swings were measured as indices of inspiratory effort. ΔCVP was assessed via a standard venous catheter. A low and a high inspiratory effort were defined as ΔPes ≤ 10 and  >15 cmH2O, respectively.

RESULTS

During the PEEP trial, no significant changes in ΔPes (11 [6-16] vs. 11 [7-15] vs. 12 [8-16] cmH2O, p = 0.652) and in ΔCVP (12 [7-17] vs. 11.5 [7-16] vs. 11.5 [8-15] cmH2O, p = 0.918) were detected. ΔCVP was significantly associated with ΔPes (marginal R² 0.87, p < 0.001). ΔCVP recognized both low (AUC-ROC curve 0.89 [0.84-0.96]) and high inspiratory efforts (AUC-ROC curve 0.98 [0.96-1]).

CONCLUSIONS

ΔCVP is an easily available a reliable surrogate of ΔPes and can detect a low or a high inspiratory effort. This study provides a useful bedside tool to monitor the inspiratory effort of spontaneously breathing COVID-19 patients.

Fundamental concepts and the latest evidence for esophageal pressure monitoring

Transpulmonary pressure is an essential physiologic concept as it reflects the true pressure across the alveoli, and is a more precise marker for lung stress. To calculate transpulmonary pressure, one needs an estimate of both alveolar pressure and pleural pressure. Airway pressure during conditions of no flow is the most widely accepted surrogate for alveolar pressure, while esophageal pressure remains the most widely measured surrogate marker for pleural pressure. This review will cover important concepts and clinical applications for esophageal manometry, with a particular focus on how to use the information from esophageal manometry to adjust or titrate ventilator support. The most widely used method for measuring esophageal pressure uses an esophageal balloon catheter, although these measurements can be affected by the volume of air in the balloon. Therefore, when using balloon catheters, it is important to calibrate the balloon to ensure the most appropriate volume of air, and we discuss several methods which have been proposed for balloon calibration. In addition, esophageal balloon catheters only estimate the pleural pressure over a certain area within the thoracic cavity, which has resulted in a debate regarding how to interpret these measurements. We discuss both direct and elastance-based methods to estimate transpulmonary pressure, and how they may be applied for clinical practice. Finally, we discuss a number of applications for esophageal manometry and review many of the clinical studies published to date which have used esophageal pressure. These include the use of esophageal pressure to assess lung and chest wall compliance individually which can provide individualized information for patients with acute respiratory failure in terms of setting PEEP, or limiting inspiratory pressure. In addition, esophageal pressure has been used to estimate effort of breathing which has application for ventilator weaning, detection of upper airway obstruction after extubation, and detection of patient and mechanical ventilator asynchrony.

Long-term outcome of COVID-19 patients treated with helmet noninvasive ventilation vs. high-flow nasal oxygen: a randomized trial

BACKGROUND

Long-term outcomes of patients treated with helmet noninvasive ventilation (NIV) are unknown: safety concerns regarding the risk of patient self-inflicted lung injury and delayed intubation exist when NIV is applied in hypoxemic patients. We assessed the 6-month outcome of patients who received helmet NIV or high-flow nasal oxygen for COVID-19 hypoxemic respiratory failure.

METHODS

In this prespecified analysis of a randomized trial of helmet NIV versus high-flow nasal oxygen (HENIVOT), clinical status, physical performance (6-min-walking-test and 30-s chair stand test), respiratory function and quality of life (EuroQoL five dimensions five levels questionnaire, EuroQoL VAS, SF36 and Post-Traumatic Stress Disorder Checklist for the DSM) were evaluated 6 months after the enrollment.

RESULTS

Among 80 patients who were alive, 71 (89%) completed the follow-up: 35 had received helmet NIV, 36 high-flow oxygen. There was no inter-group difference in any item concerning vital signs (N = 4), physical performance (N = 18), respiratory function (N = 27), quality of life (N = 21) and laboratory tests (N = 15). Arthralgia was significantly lower in the helmet group (16% vs. 55%, p = 0.002). Fifty-two percent of patients in helmet group vs. 63% of patients in high-flow group had diffusing capacity of the lungs for carbon monoxide < 80% of predicted (p = 0.44); 13% vs. 22% had forced vital capacity < 80% of predicted (p = 0.51). Both groups reported similar degree of pain (p = 0.81) and anxiety (p = 0.81) at the EQ-5D-5L test; the EQ-VAS score was similar in the two groups (p = 0.27). Compared to patients who successfully avoided invasive mechanical ventilation (54/71, 76%), intubated patients (17/71, 24%) had significantly worse pulmonary function (median diffusing capacity of the lungs for carbon monoxide 66% [Interquartile range: 47-77] of predicted vs. 80% [71-88], p = 0.005) and decreased quality of life (EQ-VAS: 70 [53-70] vs. 80 [70-83], p = 0.01).

CONCLUSIONS

In patients with COVID-19 hypoxemic respiratory failure, treatment with helmet NIV or high-flow oxygen yielded similar quality of life and functional outcome at 6 months. The need for invasive mechanical ventilation was associated with worse outcomes. These data indicate that helmet NIV, as applied in the HENIVOT trial, can be safely used in hypoxemic patients. Trial registration Registered on clinicaltrials.gov NCT04502576 on August 6, 2020.

The COVID-19 Driving Force: How It Shaped the Evidence of Non-Invasive Respiratory Support

During the COVID-19 pandemic, the use of non-invasive respiratory support (NIRS) became crucial in treating patients with acute hypoxemic respiratory failure. Despite the fear of viral aerosolization, non-invasive respiratory support has gained attention as a way to alleviate ICU overcrowding and reduce the risks associated with intubation. The COVID-19 pandemic has led to an unprecedented increased demand for research, resulting in numerous publications on observational studies, clinical trials, reviews, and meta-analyses in the past three years. This comprehensive narrative overview describes the physiological rationale, pre-COVID-19 evidence, and results of observational studies and randomized control trials regarding the use of high-flow nasal oxygen, non-invasive mechanical ventilation, and continuous positive airway pressure in adult patients with COVID-19 and associated acute hypoxemic respiratory failure. The review also highlights the significance of guidelines and recommendations provided by international societies and the need for further well-designed research to determine the optimal use of NIRS in treating this population.

Optimal machine learning methods for prediction of high-flow nasal cannula outcomes using image features from electrical impedance tomography

BACKGROUND

High-flow nasal cannula (HNFC) is able to provide ventilation support for patients with hypoxic respiratory failure. Early prediction of HFNC outcome is warranted, since failure of HFNC might delay intubation and increase mortality rate. Existing methods require a relatively long period to identify the failure (approximately 12 h) and electrical impedance tomography (EIT) may help identify the patient's respiratory drive during HFNC.

OBJECTIVES

This study aimed to investigate a proper machine-learning model to predict HFNC outcomes promptly by EIT image features.

METHODS

The Z-score standardization method was adopted to normalize the samples from 43 patients who underwent HFNC and six EIT features were selected as model input variables through the random forest feature selection method. Machine-learning methods including discriminant, ensembles, k-nearest neighbour (KNN), artificial neural network (ANN), support vector machine (SVM), AdaBoost, xgboost, logistic, random forest, bernoulli bayes, gaussian bayes and gradient-boosted decision trees (GBDT) were used to build prediction models with the original data and balanced data proceeded by the synthetic minority oversampling technique.

RESULTS

Prior to data balancing, an extremely low specificity (less than 33.33%) as well as a high accuracy in the validation data set were observed in all the methods. After data balancing, the specificity of KNN, xgboost, random forest, GBDT, bernoulli bayes and AdaBoost significantly reduced (p<0.05) while the area under curve did not improve considerably (p>0.05); and the accuracy and recall decreased significantly (p<0.05).

CONCLUSIONS

The xgboost method showed better overall performance for balanced EIT image features, which may be considered as the ideal machine learning method for early prediction of HFNC outcomes.

Respective Effects of Helmet Pressure Support, Continuous Positive Airway Pressure, and Nasal High-Flow in Hypoxemic Respiratory Failure: A Randomized Crossover Clinical Trial

Rationale: The respective effects of positive end-expiratory pressure (PEEP) and pressure support delivered through the helmet interface in patients with hypoxemia need to be better understood. Objectives: To assess the respective effects of helmet pressure support (noninvasive ventilation [NIV]) and continuous positive airway pressure (CPAP) compared with high-flow nasal oxygen (HFNO) on effort to breathe, lung inflation, and gas exchange in patients with hypoxemia (PaO2/FiO2 ⩽ 200). Methods: Fifteen patients underwent 1-hour phases (constant FiO2) of HFNO (60 L/min), helmet NIV (PEEP = 14 cm H2O, pressure support = 12 cm H2O), and CPAP (PEEP = 14 cm H2O) in randomized sequence. Measurements and Main Results: Inspiratory esophageal (ΔPES) and transpulmonary pressure (ΔPL) swings were used as surrogates for inspiratory effort and lung distension, respectively. Tidal Volume (Vt) and end-expiratory lung volume were assessed with electrical impedance tomography. ΔPES was lower during NIV versus CPAP and HFNO (median [interquartile range], 5 [3-9] cm H2O vs. 13 [10-19] cm H2O vs. 10 [8-13] cm H2O; P = 0.001 and P = 0.01). ΔPL was not statistically different between treatments. PaO2/FiO2 ratio was significantly higher during NIV and CPAP versus HFNO (166 [136-215] and 175 [158-281] vs. 120 [107-149]; P = 0.002 and P = 0.001). NIV and CPAP similarly increased Vt versus HFNO (mean change, 70% [95% confidence interval (CI), 17-122%], P = 0.02; 93% [95% CI, 30-155%], P = 0.002) and end-expiratory lung volume (mean change, 198% [95% CI, 67-330%], P = 0.001; 263% [95% CI, 121-407%], P = 0.001), mostly due to increased aeration/ventilation in dorsal lung regions. During HFNO, 14 of 15 patients had pendelluft involving >10% of Vt; pendelluft was mitigated by CPAP and further by NIV. Conclusions: Compared with HFNO, helmet NIV, but not CPAP, reduced ΔPES. CPAP and NIV similarly increased oxygenation, end-expiratory lung volume, and Vt, without affecting ΔPL. NIV, and to a lesser extent CPAP, mitigated pendelluft. Clinical trial registered with clinicaltrials.gov (NCT04241861).

Comparison of the efficacy and comfort of high-flow nasal cannula with different initial flow settings in patients with acute hypoxemic respiratory failure: a systematic review and network meta-analysis

BACKGROUND

High-flow nasal cannula (HFNC) has been proven effective in improving patients with acute hypoxemic respiratory failure (AHRF), but a discussion of its use for initial flow settings still need to be provided. We aimed to compare the effectiveness and comfort evaluation of HFNC with different initial flow settings in patients with AHRF.

METHODS

Studies published by October 10, 2022, were searched exhaustively in PubMed, Embase, Web of Science, Cochrane Library (CENTRAL), and the China National Knowledge Infrastructure (CNKI) database. Network meta-analysis (NMA) was performed with STATA 17.0 and R software (version 4.2.1). A Bayesian framework was applied for this NMA. Comparisons of competing models based on the deviance information criterion (DIC) were used to select the best model for NMA. The primary outcome is the intubation at day 28. Secondary outcomes included short-term and long-term mortality, comfort score, length of ICU or hospital stay, and 24-h PaO₂/FiO₂.

RESULTS

This NMA included 23 randomized controlled trials (RCTs) with 5774 patients. With NIV as the control, the HFNC_high group was significantly associated with lower intubation rates (odds ratio [OR] 0.72 95% credible interval [CrI] 0.56 to 0.93; moderate quality evidence) and short-term mortality (OR 0.81 95% CrI 0.69 to 0.96; moderate quality evidence). Using HFNC_Moderate (Mod) group (mean difference [MD] - 1.98 95% CrI -3.98 to 0.01; very low quality evidence) as a comparator, the HFNC_Low group had a slight advantage in comfort scores but no statistically significant difference. Of all possible interventions, the HFNC_High group had the highest probability of being the best in reducing intubation rates (73.04%), short-term (82.74%) and long-term mortality (67.08%). While surface under the cumulative ranking curve value (SUCRA) indicated that the HFNC_Low group had the highest probability of being the best in terms of comfort scores.

CONCLUSIONS

The high initial flow settings (50-60 L/min) performed better in decreasing the occurrence of intubation and mortality, albeit with poor comfort scores. Treatment of HFNC for AHRF patients ought to be initiated from moderate flow rates (30-40 L/min), and individualized flow settings can make HFNC more sensible in clinical practice.

An observational study on the timing of intubation and outcome in COVID-19 ARDS patients who were treated with high flow nasal oxygen prior to invasive mechanical ventilation: A time series analysis (InOutHFNO trial)

Background and Aims

Prolonged high flow nasal oxygen (HFNO) application might delay intubation and increase mortality in acute hypoxemic respiratory failure (AHRF) patients. Intubation in coronavirus disease 2019 (COVID-19) AHRF (CAHRF) patients 24 to 48 hours after HFNO initiation has been associated with increased mortality in previous studies. This cut-off period is variable in previous studies. A time series analysis could reflect more robust data on outcome in relation to HFNO duration before intubation in CAHRF.

Methods

A retrospective study was conducted at 30-bedded ICU of a tertiary care teaching hospital from July 2020 to August 2021. The study cohort comprised 116 patients who required HFNO and were subsequently intubated following HFNO failure. A time series analysis of patient outcomes on each day of HFNO application prior to invasive mechanical ventilation (IMV) was done.

Results

ICU and hospital mortality was 67.2%. Beyond day 4 of HFNO application, there was a trend towards increased risk-adjusted ICU and hospital mortality for each day delay in intubation of CAHRF patients on HFNO [OR 2.718; 95% CI 0.957-7.721; P 0.061]. This trend was maintained till day 8 of HFNO application, after which there was 100% mortality. Taking day four as a cut-off in the timeline of HFNO application, we have observed an absolute mortality benefit of 15% with early intubation despite a higher APACHE-IV score than the late intubation group.

Conclusion

IMV beyond the 4^th day of HFNO initiation in CAHRF patients increases mortality.

Hypocapnia as a predictor of the need for non-invasive mechanical ventilation in subjects with SARS-CoV-2 related pneumonia

Background: SARS-CoV-2 related pneumonia is characterized by moderate-to severe hypoxemia often associated with hypocapnia the prognostic role of which is poorely documented. Aims: evaluate if hypocapnia can predict the need for non-invasive mechanical ventilation (NIMV) in this setting. Materials and methods: we prospectively studied 52 subjects with moderate-severe SARS-CoV-2 related pneumonia. All the following data were collected at admission to the Emergency Department and processed by univariate and multivariate analysis: clinical and laboratory data, blood gas analysis in room air and lung ultrasound. Results: 33/52 subjects (63,4%) underwent NIMV. At univariate analysis PaCO2 was inversely associated to the need for NIMV (OR 0,82, CI 95% 0,689-0,976, p .025). At multivariate analysis PaCO2 predicted the need for NIMV independently from age, gender, number of comorbidities, d-dimer, CRP, PaO2 and LUS SCORE (OR 0,838, CI 95% 0,710-0,988, p .035). Conclusions: our data suggest that hypocapnia could be an early predictor of clinical worsening in these patients independently from other known predictors of unfavourable outcome, reflecting the occurrence of a deep and frequent respiratory pattern possibly related to the generation of excessive transpulmonary pressure swings leading to a self-induced lung injury (P-SILI). Further studies are needed for validating these data on greater populations.

Resource utilization and preparedness within the COVID-19 pandemic in Tunisian medical intensive care units: A nationwide retrospective multicentre observational study

BACKGROUND

The worldwide SARS-CoV-2 pandemic represents the most recent global healthcare crisis. While all healthcare systems suffered facing the immense burden of critically-ill COVID-19 patients, the levels of preparedness and adaptability differed highly between countries.

AIM

to describe resource mobilization throughout the COVID-19 waves in Tunisian University Medical Intensive Care Units (MICUs) and to identify discrepancies in preparedness between the provided and required resource.

METHODS

This is a longitudinal retrospective multicentre observational study conducted between March 2020 and May 2022 analyzing data from eight University MICUs. Data were collected at baseline and at each bed expansion period in relation to the nation's four COVID-19 waves. Data collected included epidemiological, organizational and management trends and outcomes of COVID-19 and non-COVID-19 admissions.

RESULTS

MICU-beds increased from 66 to a maximum of 117 beds. This was possible thanks to equipping pre-existing non-functional MICU beds (n = 20) and creating surge ICU-beds in medical wards (n = 24). MICU nurses increased from 53 to 200 of which 99 non-ICU nurses, by deployment from other departments and temporary recruitment. The nurse-to-MICU-bed ratio increased from 1:1 to around 1·8:1. Only 55% of beds were single rooms, 80% were equipped with ICU ventilators. These MICUs managed to admit a total of 3368 critically-ill patients (15% of hospital admissions). 33·2% of COVID-19-related intra-hospital deaths occurred within the MICUs.

CONCLUSION

Despite a substantial increase in resource mobilization during the COVID-19 pandemic, the current study identified significant persisting discrepancies between supplied and required resource, at least partially explaining the poor overall prognosis of critically-ill COVID-19 patients.

Delayed mechanical ventilation with prolonged high-flow nasal cannula exposure time as a risk factor for mortality in acute respiratory distress syndrome due to SARS-CoV-2

In a high proportion of patients, infection by COVID-19 progresses to acute respiratory distress syndrome (ARDS), requiring invasive mechanical ventilation (IMV) and admission to an intensive care unit (ICU). Other devices, such as a high-flow nasal cannula (HFNC), have been alternatives to IMV in settings with limited resources. This study evaluates whether HFNC exposure time prior to IMV is associated with mortality. This observational, analytical study was conducted on a historical cohort of adults with ARDS due to SARS-CoV-2 who were exposed to HFNC and subsequently underwent IMV. Univariate and multivariate logistic regression was used to analyze the impact of HFNC exposure time on mortality, controlling for multiple potential confounders. Of 325 patients with ARDS, 41 received treatment with HFNC for more than 48 h before IMV initiation. These patients had a higher mortality rate (43.9% vs. 27.1%, p: 0.027) than those using HFNC < 48 h. Univariate analysis evidenced an association between mortality and HFNC ≥ 48 h (OR 2.16. 95% CI 1.087-4.287. p: 0.028). Such an association persisted in the multivariable analysis (OR 2.21. 95% CI 1.013-4.808. p: 0.046) after controlling for age, sex, comorbidities, basal severity of infection, and complications. This study also identified a significant increase in mortality after 36 h in HFNC (46.3%, p: 0.003). In patients with ARDS due to COVID-19, HFNC exposure ≥ 48 h prior to IMV is a factor associated with mortality after controlling multiple confounders. Physiological mechanisms for such an association are need to be defined.

Oxygenation thresholds for invasive ventilation in hypoxemic respiratory failure: a target trial emulation in two cohorts

BACKGROUND

The optimal thresholds for the initiation of invasive ventilation in patients with hypoxemic respiratory failure are unknown. Using the saturation-to-inspired oxygen ratio (SF), we compared lower versus higher hypoxemia severity thresholds for initiating invasive ventilation.

METHODS

This target trial emulation included patients from the Medical Information Mart for Intensive Care (MIMIC-IV, 2008-2019) and the Amsterdam University Medical Centers (AmsterdamUMCdb, 2003-2016) databases admitted to intensive care and receiving inspired oxygen fraction ≥ 0.4 via non-rebreather mask, noninvasive ventilation, or high-flow nasal cannula. We compared the effect of using invasive ventilation initiation thresholds of SF < 110, < 98, and < 88 on 28-day mortality. MIMIC-IV was used for the primary analysis and AmsterdamUMCdb for the secondary analysis. We obtained posterior means and 95% credible intervals (CrI) with nonparametric Bayesian G-computation.

RESULTS

We studied 3,357 patients in the primary analysis. For invasive ventilation initiation thresholds SF < 110, SF < 98, and SF < 88, the predicted 28-day probabilities of invasive ventilation were 72%, 47%, and 19%. Predicted 28-day mortality was lowest with threshold SF < 110 (22.2%, CrI 19.2 to 25.0), compared to SF < 98 (absolute risk increase 1.6%, CrI 0.6 to 2.6) or SF < 88 (absolute risk increase 3.5%, CrI 1.4 to 5.4). In the secondary analysis (1,279 patients), the predicted 28-day probability of invasive ventilation was 50% for initiation threshold SF < 110, 28% for SF < 98, and 19% for SF < 88. In contrast with the primary analysis, predicted mortality was highest with threshold SF < 110 (14.6%, CrI 7.7 to 22.3), compared to SF < 98 (absolute risk decrease 0.5%, CrI 0.0 to 0.9) or SF < 88 (absolute risk decrease 1.9%, CrI 0.9 to 2.8).

CONCLUSION

Initiating invasive ventilation at lower hypoxemia severity will increase the rate of invasive ventilation, but this can either increase or decrease the expected mortality, with the direction of effect likely depending on baseline mortality risk and clinical context.

How long is too long: A retrospective study evaluating the impact of the duration of noninvasive oxygenation support strategies (high flow nasal cannula & BiPAP) on mortality in invasive mechanically ventilated patients with COVID-19

BACKGROUND/AIM

We investigated the association of noninvasive oxygenation support [high flow nasal cannula (HFNC) and BiPAP], timing of invasive mechanical ventilation (IMV), and inpatient mortality among patients hospitalized with COVID-19.

METHODS

Retrospective chart review study of patients hospitalized with COVID-19 (ICD-10 code U07.1) and received IMV from March 2020-October 2021. Charlson comorbidity index (CCI) was calculated; Obesity defined as body mass index (BMI) ≥ 30 kg/m2; morbid obesity was BMI ≥ 40 kg/m2. Clinical parameters/vital signs recorded at time of admission.

RESULTS

709 COVID-19 patients underwent IMV, predominantly admitted from March-May 2020 (45%), average age 62±15 years, 67% male, 37% Hispanic, and 9% from group living settings. 44% had obesity, 11% had morbid obesity, 55% had type II diabetes, 75% had hypertension, and average CCI was 3.65 (SD = 3.11). Crude mortality rate was 56%. Close linear association of age with inpatient-mortality risk was found [OR (95% CI) = 1.35 (1.27-1.44) per 5 years, p<0.0001)]. Patients who died after IMV received noninvasive oxygenation support significantly longer: 5.3 (8.0) vs. 2.7 (SD 4.6) days; longer use was also independently associated with a higher risk of inpatient-mortality: OR = 3.1 (1.8-5.4) for 3-7 days, 7.2 (3.8-13.7) for ≥8 days (reference: 1-2 days) (p<0.0001). The association magnitude varied between age groups: 3-7 days duration (ref: 1-2 days), OR = 4.8 (1.9-12.1) in ≥65 years old vs. 2.1 (1.0-4.6) in <65 years old. Higher mortality risk was associated with higher CCI in patients ≥65 (P = 0.0082); among younger patients, obesity (OR = 1.8 (1.0-3.2) or morbid obesity (OR = 2.8;1.4-5.9) (p<0.05) were associated. No mortality association was found for sex or race.

CONCLUSION

Time spent on noninvasive oxygenation support [as defined by high flow nasal cannula (HFNC) and BiPAP] prior to IMV increased mortality risk. Research for the generalizability of our findings to other respiratory failure patient populations is needed.

Advantages and drawbacks of helmet noninvasive support in acute respiratory failure

INTRODUCTION

Non-invasive ventilation (NIV) represents an effective strategy for managing acute respiratory failure. Facemask NIV is strongly recommended in acute exacerbation of chronic obstructive pulmonary disease (AECOPD) with hypercapnia and acute cardiogenic pulmonary edema (ACPE). Its role in managing acute hypoxemic respiratory failure (AHRF) remains a debated issue. NIV and continuous positive airway pressure (CPAP) delivered through the helmet are recently receiving growing interest for AHRF management.

AREAS COVERED

In this narrative review, we discuss the clinical applications of helmet support compared to the other available noninvasive strategies in the different phenotypes of acute respiratory failure.

EXPERT OPINION

Helmets enable the use of high positive end-expiratory pressure, which may protect from self-inflicted lung injury: in AHRF, the possible superiority of helmet support over other noninvasive strategies in terms of clinical outcome has been hypothesized in a network metanalysis and a randomized trial, but has not been confirmed by other investigations and warrants confirmation. In AECOPD patients, helmet efficacy may be inferior to that of face masks, and its use prompts caution due to the risk of CO₂ rebreathing. Helmet support can be safely applied in hypoxemic patients with ACPE, with no advantages over facemasks.

Incidence and Outcome of Pneumomediastinum in Non-ICU Hospitalized COVID-19 Patients

OBJECTIVES

Pneumomediastinum (PNM) is a rare complication of mechanical ventilation, but its reported occurrence in patients with acute respiratory distress syndrome secondary to COVID-19 is significant. The objective is to determine the incidence, risk factors, and outcome of PNM in non-ICU hospitalized patients with severe-to-critical COVID-19 pneumonia.

DESIGN

Retrospective observational study.

SETTING

Population-based, single-setting, tertiary-care level COVID treatment center.

PATIENTS

Individuals hospitalized with a diagnosis of COVID-19 pneumonia and severe to critical illness were included. Those hospitalized without respiratory failure, observed for less than 24 hours, or admitted from an ICU were excluded.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All patients underwent a complete clinical assessment and chest CT scan, and were followed up from hospitalization to discharge or death. The outcome was the number of cases of PNM, defined as the presence of free air in the mediastinal tissues diagnosed by chest CT scan, in non-ICU hospitalized patients and the subsequent risk of intubation and mortality. PNM occurred in 48 out of 331 participants. The incidence was 14.5% (95% CI, 10.9-18.8%). A CT-Scan Severity score greater than 15 was positively associated with PNM (odds ratio [OR], 4.09; p = 0.002) and was observed in 35.2% of the participants (95% CI, 26.2-44.9%). Noninvasive ventilation was also positively associated with PNM (OR, 4.46; p = 0.005), but there was no positive association with airway pressures. Fifty patients (15%) were intubated, and 88 (27%) died. Both the risk for intubation and mortality were higher in patients with PNM, with a hazard ratio of 3.72 ( p < 0.001) and 3.27 ( p < 0.001), respectively.

CONCLUSIONS

Non-ICU hospitalized patients with COVID-19 have a high incidence of PNM, increasing the risk for intubation and mortality three- to four-fold, particularly in those with extensive lung damage. These findings help define the risk and outcome of PNM in severe-to-critical COVID-19 pneumonia in a non-ICU setting.

Finding Cost-effective Solutions: Need of the Hour

How to cite this article: Patil VP, Rajput A. Finding Cost-effective Solutions: Need of the Hour. Indian J Crit Care Med 2022;26(11):1163-1164.

Role of Platelets in Acute Lung Injury After Extracorporeal Circulation in Cardiac Surgery Patients: A Systemic Review

In vitro circulation (cardiopulmonary bypass, CPB) has been widely used in heart surgery. In the past, it was believed that the reduction of platelet count and impaired platelet function during cardiac surgery were the main causes of acute lung injury (ALI). ALI is a life-threatening clinical syndrome in critically ill patients due to an uncontrolled systemic inflammatory response resulting from direct injury to the lung or indirect injury in the setting of a systemic process. Platelets have an emerging and incompletely understood role in a myriad of ALI after extracorporeal circulation in cardiac surgery patients. An electronic literature search was performed using Pubmed, Scopus and Cinahl investigating ALI, pathogenesis, and role of platelets, treatment and management for ALI patients. Many studies have shown that in vitro circulation is a nonphysiological process that can lead to a decrease in the number of platelets and impaired platelet function, as well as varying degrees of lung damage. The relationship between the effects of in vitro circulation on platelets and acute lung injury is still controversial. This review article discusses the role of platelets in lung injury after cardiopulmonary bypass and resent development in the management of ALI.

Role of prognostic scores in predicting in-hospital mortality and failure of non-invasive ventilation in adults with COVID-19

We tested the prognostic performance of different scores for the identification of subjects with acute respiratory failure by COVID-19, at risk of in-hospital mortality and NIV failure. We conducted a retrospective study, in the Medical High-Dependency Unit of the University-Hospital Careggi. We included all subjects with COVID-19 and ARF requiring non-invasive ventilation (NIV) between March 2020 and January 2021. Clinical parameters, the HACOR score (Heart rate, Acidosis, Consciousness, Oxygenation, Respiratory Rate) and ROX index ((SpO2/FiO2)/respiratory rate) were collected 3 (-3) and 1 day (-1) before the NIV initiation, the first day of treatment (Day0) and after 1 (+1), 2 (+2), 5 (+5), 8 (+8) and 11 (+11) of treatment. The primary outcomes were in-hospital mortality and NIV failure. We included 135 subjects, mean age 69±13 years, 69% male. Patients, who needed mechanical ventilation, showed a higher HACOR score (Day0: 6 [5-7] vs 6 [6-7], p=.057; Day+2: 6 [6-6] vs 6 [4-6], p=.013) and a lower ROX index (Day0: 4.2±2.3 vs 5.1±2.3, p=.055; Day+2: 4.4±1.2.vs 5.5±1.3, p=.001) than those with successful NIV. An HACOR score >5 was more frequent among nonsurvivors (Day0: 82% vs 58%; Day2: 82% vs 48%, all p<0.01) and it was associated with in-hospital mortality (Day0: RR 5.88, 95%CI 2.01-17.22; Day2: RR 4.33, 95%CI 1.64-11.41) independent to age and Charlson index. In conclusion, in subjects treated with NIV for ARF caused by COVID19, respiratory parameters collected after the beginning of NIV allowed to identify those at risk of an adverse outcome. An HACOR score >5 was independently associated with increased mortality rate.

Positive Expiratory Pressure Oxygen Therapy for Respiratory Distress: A Single-arm Feasibility Trial

Background

Oxygen delivery devices with positive end-expiratory pressure (PEEP) valves have been described, but high inspiratory flows may lead to poor tolerance in tachypneic patients. Positive expiratory pressure oxygen therapy (PEP-OT) using an occlusive face mask, oxygen reservoir, and PEEP valve has not been evaluated in clinical settings.

Materials and methods

In a single-arm intervention trial, patients aged 19-55 years admitted with acute respiratory illness with oxygen support were enrolled. PEP-OT trial was given with PEEP of 5 and 7 cm of water over 45 minutes. Feasibility was assessed as uninterrupted completion of the PEP-OT trial. The effects of PEP-OT on cardiopulmonary physiology and adverse effects of therapy were recorded.

Results

Fifteen patients (6 males) were enrolled. Fourteen patients had pneumonia and one patient had pulmonary edema. Twelve patients (80%) completed the PEP-OT trial. There was significant improvement in respiratory rate (RR) and heart rate (HR) at the end of the 45-minute PEP-OT trial (p-values 0.048 and 0.003, respectively). There was a trend toward improved SpO₂ and perceived dyspnea. None of the patients developed desaturation, shock, or air leaks. Positive expiratory pressure oxygen therapy is a feasible oxygen therapy in patients with acute hypoxia.

Conclusion

Positive expiratory pressure oxygen therapy seems to be safe and has a positive impact on respiratory mechanics in parenchymal respiratory pathology.

How to cite this article

Dhochak N, Ray A, Soneja M, Wig N, Kabra SK, Lodha R. Positive Expiratory Pressure Oxygen Therapy for Respiratory Distress: A Single-arm Feasibility Trial. Indian J Crit Care Med 2022;26(11):1169-1174.

Non-invasive ventilation for acute hypoxemic respiratory failure, including COVID-19

Optimal initial non-invasive management of acute hypoxemic respiratory failure (AHRF), of both coronavirus disease 2019 (COVID-19) and non-COVID-19 etiologies, has been the subject of significant discussion. Avoidance of endotracheal intubation reduces related complications, but maintenance of spontaneous breathing with intense respiratory effort may increase risks of patients' self-inflicted lung injury, leading to delayed intubation and worse clinical outcomes. High-flow nasal oxygen is currently recommended as the optimal strategy for AHRF management for its simplicity and beneficial physiological effects. Non-invasive ventilation (NIV), delivered as either pressure support or continuous positive airway pressure via interfaces like face masks and helmets, can improve oxygenation and may be associated with reduced endotracheal intubation rates. However, treatment failure is common and associated with poor outcomes. Expertise and knowledge of the specific features of each interface are necessary to fully exploit their potential benefits and minimize risks. Strict clinical and physiological monitoring is necessary during any treatment to avoid delays in endotracheal intubation and protective ventilation. In this narrative review, we analyze the physiological benefits and risks of spontaneous breathing in AHRF, and the characteristics of tools for delivering NIV. The goal herein is to provide a contemporary, evidence-based overview of this highly relevant topic.

Helmet noninvasive support for acute hypoxemic respiratory failure: rationale, mechanism of action and bedside application

Introduction

Helmet noninvasive support may provide advantages over other noninvasive oxygenation strategies in the management of acute hypoxemic respiratory failure. In this narrative review based on a systematic search of the literature, we summarize the rationale, mechanism of action and technicalities for helmet support in hypoxemic patients.

Main results

In hypoxemic patients, helmet can facilitate noninvasive application of continuous positive-airway pressure or pressure-support ventilation via a hood interface that seals at the neck and is secured by straps under the arms. Helmet use requires specific settings. Continuous positive-airway pressure is delivered through a high-flow generator or a Venturi system connected to the inspiratory port of the interface, and a positive end-expiratory pressure valve place at the expiratory port of the helmet;  alternatively, pressure-support ventilation is delivered by connecting the helmet to a mechanical ventilator through a bi-tube circuit. The helmet interface allows continuous treatments with high positive end-expiratory pressure with good patient comfort. Preliminary data suggest that helmet noninvasive ventilation (NIV) may provide physiological benefits compared to other noninvasive oxygenation strategies (conventional oxygen, facemask NIV, high-flow nasal oxygen) in non-hypercapnic patients with moderate-to-severe hypoxemia (PaO₂/FiO₂ ≤ 200 mmHg), possibly because higher positive end-expiratory pressure (10–15 cmH₂O) can be applied for prolonged periods with good tolerability. This improves oxygenation, limits ventilator inhomogeneities, and may attenuate the potential harm of lung and diaphragm injury caused by vigorous inspiratory effort. The potential superiority of helmet support for reducing the risk of intubation has been hypothesized in small, pilot randomized trials and in a network metanalysis.

Conclusions

Helmet noninvasive support represents a promising tool for the initial management of patients with severe hypoxemic respiratory failure. Currently, the lack of confidence with this and technique and the absence of conclusive data regarding its efficacy render helmet use limited to specific settings, with expert and trained personnel. As per other noninvasive oxygenation strategies, careful clinical and physiological monitoring during the treatment is essential to early identify treatment failure and avoid delays in intubation.

The optimal management of the patient with COVID‐19 pneumonia: HFNC, NIV/CPAP or mechanical ventilation?

The recent pandemic has seen unprecedented demand for respiratory support of patients with COVID‐19 pneumonia, stretching services and clinicians. Yet despite the global numbers of patients treated, guidance is not clear on the correct choice of modality or the timing of escalation of therapy for an individual patient.This narrative review assesses the available literature on the best use of different modalities of respiratory support for an individual patient, and discusses benefits and risks of each, coupled with practical advice to improve outcomes. On current data, in an ideal context, it appears that as disease severity worsens, conventional oxygen therapy is not sufficient alone. In more severe disease, i.e. PaO2/FiO2 ratios below approximately 200, helmet‐CPAP (continuous positive airway pressure) (although not widely available) may be superior to high‐flow nasal cannula (HFNC) therapy or facemask non‐invasive ventilation (NIV)/CPAP, and that facemask NIV/CPAP may be superior to HFNC, but with noted important complications, including risk of pneumothoraces. In an ideal context, invasive mechanical ventilation should not be delayed where indicated and available. Vitally, the choice of respiratory support should not be prescriptive but contextualised to each setting, as supply and demand of resources vary markedly between institutions. Over time, institutions should develop clear policies to guide clinicians before demand exceeds supply, and should frequently review best practice as evidence matures.

Reply to: Effect of prone positioning without mechanical ventilation in COVID-19 patients with acute respiratory failure

We have read the letter by Yanfei Shen and co-workers, and appreciate their interest in our study of awake prone positioning (APP) in non-intubated patients with acute hypoxaemic respiratory failure (AHRF) due to coronavirus disease 2019 (COVID-19). We would like to add a few comments to their purposeful remarks.

Several questions on the efficacy of awake prone positioning for hypoxaemic respiratory failure remain unanswered. Research targeting those questions is needed. https://bit.ly/3xmbNPP

Application of High-Flow Nasal Cannula in COVID-19: A Narrative Review

Background: During the first wave of COVID-19, the large influx of severely ill patients led to insufficient availability of beds in intensive care units and a shortage of ventilators. The shortage of ventilators, high mortality of intubated patients, and high risk of infections among healthcare workers involved in intubation were the main factors that led to the prevalence of noninvasive respiratory support during the pandemic. The high-flow nasal cannula (HFNC) is a commonly used, popular form of noninvasive respiratory support. Due to its unique physiological effects, HFNC can provide a high fraction of humidified oxygen and is satisfactorily comfortable for patients with COVID-19. However, before the COVID-19 era, there was little evidence on the application of HFNC in patients with acute respiratory failure caused by viral infection. Aim: This narrative review provides an overview of recent studies on the use of HFNC in patients with COVID-19-related acute hypoxemic respiratory failure. The main topics discussed include the probability of successful use of HFNC in these patients, whether late intubation increases mortality, the availability of convenient and accurate monitoring tools, comparison of HFNC with other types of noninvasive respiratory support, whether HFNC combined with the prone position is more clinically useful, and strategies to further reduce the infection risk associated with HFNC. The implication of this study is to identify some of the limitations and research gaps of the current literature and to give some advice for future research.

Awake prone positioning for patients with COVID-19-induced acute hypoxemic respiratory failure

Whereas prone positioning of intubated patients suffering from acute respiratory distress syndrome represents the standard of care, proning non-intubated patients, so-called "awake prone positioning (APP)," has only recently gained popularity and undergone scientific evaluation. In this review, we summarize current evidence on physiological and clinical effects of APP on patients' centered outcomes, such as intubation and mortality, the safety of the technique, factors and predictors of success, practical issues for optimal implementation, and future areas of research. Current evidence supports using APP among patients suffering from acute hypoxemic respiratory failure due to COVID-19 and undergoing advanced respiratory support, such as high-flow nasal cannula, in an intensive care unit setting. Healthcare teams should aim to prone patients at least 8 h daily. Future research should focus on optimizing the tolerance of the technique and comprehensively evaluating benefits in other patient populations.