Physiologic Effects of High-Flow Nasal Cannula in Acute Hypoxemic Respiratory Failure

An expanded definition of acute respiratory distress syndrome: Challenging the status quo

Although the Berlin definition of acute respiratory distress syndrome (ARDS), 2012 has been widely used in clinical practice, issues have occasionally been raised regarding various criteria since it was proposed. High-flow nasal oxygen (HFNO) is widely used for effective respiratory support in acute respiratory failure. As patients who do not require ventilation but meet the Berlin criteria have similar characteristics to those with ARDS, the definition of ARDS may be broadened to include patients receiving HFNO. As the PaO₂/FiO₂ under-recognizes the diagnosis of ARDS, a SpO₂/FiO₂ value of ≤315 may be considered instead of a PaO₂/FiO₂ value of ≤300 for diagnosing the condition in resource-constrained settings. In this context, patients with severe COVID-19 always meet other criteria for ARDS except for 7-day acute onset. Therefore, the timeframe for the onset of ARDS may be extended to up to 14 days. An expanded definition of ARDS may allow early identification of patients with less severe diseases and facilitate testing and application of new therapies in patients with a high risk of poor outcomes. Here, we discuss the major controversies regarding the extension of the ARDS definition with a view to improving clinical implementation and patient outcomes.

High-flow nasal cannula: Evaluation of the perceptions of various performance aspects among Chinese clinical staff and establishment of a multidimensional clinical evaluation system

Objective

In order to facilitate education for clinical users, performance aspects of the high-flow nasal cannula (HFNC) devices were evaluated in the present study. A multidimensional HFNC clinical evaluation system was established accordingly.

Materials and Methods

Clinical staff from Chinese hospitals were invited to participate in an online questionnaire survey. The questionnaire was mainly about the accuracy of temperature, flow rate, and oxygen concentration of HFNC, as well as its humidification capacity. We also investigated how the clinical staff of different professions made decisions on HFNC evaluation indicators. Based on the results of the questionnaire survey of clinicians with rich experience in using HFNC, the relative weights of temperature accuracy, flow velocity accuracy, oxygen concentration accuracy, and humidification ability of HFNC equipment were calculated by the AHP to establish a clinical evaluation system. Four kinds of common HFNC devices were tested and evaluated, and the clinical performance of the four kinds of HFNC devices was evaluated by the new scoring system.

Results

A total of 356 clinicians participated in and completed the questionnaire survey. To ensure the reliability of the HFNC evaluation system, we only adopted the questionnaire results of clinicians with rich experience in using HFNCs. Data from 247 questionnaires (80 doctors, 105 nurses, and 62 respiratory therapists [RTs]) were analyzed. A total of 174 participants used HFNC more than once a week; 88.71% of RTs used HFNC ≥ 1 score daily, 62.86% of nurses used HFNC ≥ 1 score daily, and 66.25% of doctors used HFNC ≥ 1 daily. There was no significant difference in the frequency of use between doctors and nurses. Finally, the relative weights of temperature accuracy (0.088), humidification capacity (0.206), flow velocity accuracy (0.311), and oxygen concentration accuracy (0.395) in the HFNC clinical evaluation system were obtained. The relative weights of clinicians with different occupations and the frequency of HFNC use were obtained. After testing four kinds of HFNC devices through the evaluation system, it was found that the four kinds of HFNC devices have different advantages in different clinical performances, and AiRVO₂ has excellent performance with regard to temperature accuracy and humidification ability. HF-75A and NeoHiF-i7 are good at ensuring the stability of oxygen concentration and the accuracy of the flow velocity of the transported gas, while OH-80S is relatively stable in all aspects.

Conclusion

The clinical evaluation system of HFNC is based on the weight of the experience of clinical personnel with different medical backgrounds. Although the existing practitioners have different educational backgrounds (academic qualifications, majors), our evaluation system can enhance clinical staff’s awareness of HFNC and further optimize the clinical use of HFNC.

Neutrophil Membrane-Coated Therapeutic Liposomes for Targeted Treatment in Acute Lung Injury

Acute lung injury (ALI) is one of the most common comorbidities associated with sepsis and can lead to acute respiratory distress syndrome. Intense inflammatory response due to excessive activation and uncontrolled infiltration of neutrophils are the central processes in the development of sepsis-induced ALI. In this study, a biomimetic nanoplatform that is a neutrophil membrane-coated liposome-loaded acidic fibroblast growth factor (aFGF@NMLs), which can selectively target the inflamed lung and effectively alleviate sepsis-induced ALI via inflammation suppression, was constructed. In vitro findings revealed that aFGF@NMLs has pro-inflammatory cytokine binding capabilities and can promote cellular uptake, substantially attenuate inflammatory responses, and enhance cellular antioxidant capacity. The in vivo results show that aFGF@NMLs can specifically accumulate in injured lungs in ALI mice after intravenous injection, thereby reducing the secretion of pro-inflammatory cytokines, inhibiting pulmonary cell apoptosis, and promoting lung function recovery. In conclusion, aFGF@NMLs demonstrated anti-inflammatory effects, mitigated the progression of ALI, and contributed to the disease prognosis. This research offers an innovative strategy and concept for the clinical treatment of diseases related to pulmonary inflammation.

Nasal pillow noninvasive ventilation versus high-flow nasal therapy after extubation in surgical intensive care patients: A propensity-matched cohort study

Objective

To evaluate the tolerability and efficacy of nasal pillow-noninvasive ventilation (NP-NIV) compared with high-flow nasal therapy (HFNT) in postsurgical patients.

Methods

This propensity score-matched retrospective study enrolled postoperative patients that received NP-NIV (NP-NIV group) or HFNT (HFNT group) in the intensive care unit. Data were collected from their medical records and the tolerability and respiratory status before and after extubation were compared between the two groups.

Results

The study enrolled 83 patients in the NP-NIV group and 27 patients in the HFNT group. After propensity score matching, there were 19 patients in each group. After matching, there were no significant differences in the baseline demographic and clinical characteristics before extubation. The tolerability was similar in both groups. When the NP-NIV group was compared with the HFNT group, the respiratory rate was significantly lower (median 16 [interquartile range, 14–17] versus median 19 [interquartile range, 18–26], respectively) and the partial pressure of arterial oxygen/fraction of inspired oxygen ratio was significantly higher (median 205 [174–256] versus median 155 [130–192], respectively) at 1 h after extubation.

Conclusion

NP-NIV was equally well tolerated and provided better respiratory support than HFNT in postsurgical patients.

Expert opinion document: "Electrical impedance tomography: applications from the intensive care unit and beyond"

Mechanical ventilation is a life-saving technology, but it can also inadvertently induce lung injury and increase morbidity and mortality. Currently, there is no easy method of assessing the impact that ventilator settings have on the degree of lung inssflation. Computed tomography (CT), the gold standard for visually monitoring lung function, can provide detailed regional information of the lung. Unfortunately, it necessitates moving critically ill patients to a special diagnostic room and involves exposure to radiation. A technique introduced in the 1980s, electrical impedance tomography (EIT) can non-invasively provide similar monitoring of lung function. However, while CT provides information on the air content, EIT monitors ventilation-related changes of lung volume and changes of end expiratory lung volume (EELV). Over the past several decades, EIT has moved from the research lab to commercially available devices that are used at the bedside. Being complementary to well-established radiological techniques and conventional pulmonary monitoring, EIT can be used to continuously visualize the lung function at the bedside and to instantly assess the effects of therapeutic maneuvers on regional ventilation distribution. EIT provides a means of visualizing the regional distribution of ventilation and changes of lung volume. This ability is particularly useful when therapy changes are intended to achieve a more homogenous gas distribution in mechanically ventilated patients. Besides the unique information provided by EIT, its convenience and safety contribute to the increasing perception expressed by various authors that EIT has the potential to be used as a valuable tool for optimizing PEEP and other ventilator settings, either in the operative room and in the intensive care unit. The effects of various therapeutic interventions and applications on ventilation distribution have already been assessed with the help of EIT, and this document gives an overview of the literature that has been published in this context.

Prediction of high-flow nasal cannula outcomes at the early phase using the modified respiratory rate oxygenation index

BACKGROUND

This study was designed to explore the early predictive value of the respiratory rate oxygenation (ROX) index modified by PaO₂ (mROX) in high-flow nasal cannula (HFNC) therapy in patients with acute hypoxemia respiratory failure (AHRF).

METHOD

Seventy-five patients with AHRF treated with HFNC were retrospectively reviewed. Respiratory parameters at baseline and 2 h after HFNC initiation were analyzed. The predictive value of the ROX (ratio of pulse oximetry/FIO₂ to respiratory rate) and mROX (ratio of arterial oxygen /FIO₂ to respiratory rate) indices with two variations by adding heart rate to each index (ROX-HR and mROX-HR) was evaluated.

RESULTS

HFNC therapy failed in 24 patients, who had significantly higher intensive care unit (ICU) mortality and longer ICU stay. Both the ROX and mROX indices at 2 h after HFNC initiation can predict the risk of intubation after HFNC. Two hours after HFNC initiation, the mROX index had a higher area under the receiver operating characteristic curve (AUROC) for predicting HFNC success than the ROX index. Besides, baseline mROX index of greater than 7.1 showed a specificity of 100% for HFNC success.

CONCLUSION

The mROX index may be a suitable predictor of HFNC therapy outcomes at the early phase in patients with AHRF.

Effects of non-invasive respiratory supports on inspiratory effort in moderate-severe COVID-19 patients. A randomized physiological study

RATIONALE AND OBJECTIVE

Various forms of Non-invasive respiratory support (NRS) have been used during COVID-19, to treat Hypoxemic Acute Respiratory Failure (HARF), but it has been suggested that the occurrence of strenuous inspiratory efforts may cause Self Induced Lung Injury(P-SILI). The aim of this investigation was to record esophageal pressure, when starting NRS application, so as to better understand the potential risk of the patients in terms of P-SILI and ventilator induced lung injury (VILI).

METHODS AND MEASUREMENTS

21 patients with early de-novo respiratory failure due to COVID-19, underwent three 30 min trials applied in random order: high-flow nasal cannula (HFNC), continuous positive airway pressure (CPAP), and non-invasive ventilation (NIV). After each trial, standard oxygen therapy was reinstituted using a Venturi mask (VM). 15 patients accepted a nasogastric tube placement. Esophageal Pressure (ΔPes) and dynamic transpulmonary driving pressure (ΔPLDyn), together with the breathing pattern using a bioelectrical impedance monitor were recorded. Arterial blood gases were collected in all patients.

MAIN RESULTS

No statistically significant differences in breathing pattern and PaCO₂ were found. PaO₂/FiO₂ ratio improved significantly during NIV and CPAP vs VM. NIV was the only NRS to reduce significantly ΔPes vs. VM (-10,2 ±5 cmH20 vs -3,9 ±3,4). No differences were found in ΔPLDyn between NRS (10,2±5; 9,9±3,8; 7,6±4,3; 8,8±3,6 during VM, HFNC, CPAP and NIV respectively). Minute ventilation (Ve) was directly dependent on the patient's inspiratory effort, irrespective of the NRS applied. 14% of patients were intubated, none of them showing a reduction in ΔPes during NRS.

CONCLUSIONS

In the early phase of HARF due to COVID-19, the inspiratory effort may not be markedly elevated and the application of NIV and CPAP ameliorates oxygenation vs VM. NIV was superior in reducing ΔPes, maintaining ΔPLDyn within a range of potential safety.

Electrical Impedance Tomography in Acute Respiratory Distress Syndrome Management

OBJECTIVE

To describe, through a narrative review, the physiologic principles underlying electrical impedance tomography, and its potential applications in managing acute respiratory distress syndrome (ARDS). To address the current evidence supporting its use in different clinical scenarios along the ARDS management continuum.

DATA SOURCES

We performed an online search in Pubmed to review articles. We searched MEDLINE, Cochrane Central Register, and clinicaltrials.gov for controlled trials databases.

STUDY SELECTION

Selected publications included case series, pilot-physiologic studies, observational cohorts, and randomized controlled trials. To describe the rationale underlying physiologic principles, we included experimental studies.

DATA EXTRACTION

Data from relevant publications were reviewed, analyzed, and its content summarized.

DATA SYNTHESIS

Electrical impedance tomography is an imaging technique that has aided in understanding the mechanisms underlying multiple interventions used in ARDS management. It has the potential to monitor and predict the response to prone positioning, aid in the dosage of flow rate in high-flow nasal cannula, and guide the titration of positive-end expiratory pressure during invasive mechanical ventilation. The latter has been demonstrated to improve physiologic and mechanical parameters correlating with lung recruitment. Similarly, its use in detecting pneumothorax and harmful patient-ventilator interactions such as pendelluft has been proven effective. Nonetheless, its impact on clinically meaningful outcomes remains to be determined.

CONCLUSIONS

Electrical impedance tomography is a potential tool for the individualized management of ARDS throughout its different stages. Clinical trials should aim to determine whether a specific approach can improve clinical outcomes in ARDS management.

Die neue internationale Sepsis-Leitlinie der Surviving Sepsis Campaign 2021

The new Surviving Sepsis Campaign (SSC) guideline was substantially revised in 2021. These updated recommendations are intended to guide intensivists in providing adequate care to adult patients with sepsis or septic shock. In particular, the current SSC guideline emphasizes early recognition and stringent management in the first hours after the onset of sepsis. In particular, the implementation of acute interventions should help to improve the chances of survival of sepsis patients.This article summarizes the most important recommendations for acute therapy and presents them as a comparative overview to the previous SSC guideline and the German S3 guideline. This should allow the reader to adopt the knowledge from the new guideline into clinical practice as quickly as possible in order to improve the quality of treatment of patients with sepsis or septic shock.

High flow nasal cannula oxygen therapy: P-SILI or not P-SILI?

We would like to thank A.S. Saini and co-workers for their interest and their valuable and constructive comments concerning our study [1]. We have shown that, assessed by pulmonary electrical impedance tomography (EIT), high-flow nasal cannula (HFNC) oxygen therapy and noninvasive ventilation (NIV) could generate comparable alveolar recruitment, but NIV generated larger lung volumes. This increase in lung volumes with NIV could be involved in alveolar lesions worsening, induced by the patient's spontaneous ventilation or “patient self-inflicted lung injury” (P-SILI) [2]. However, A.S. Saini and co-workers argue that HFNC could also generate P-SILI and describe the main pathophysiological determinants involved in this deleterious effect. If one can accept this potential risk with HFNC and share the arguments proposed by A.S. Saini and co-workers concerning its mechanisms, we nevertheless wish to make a few additional comments.

The risk of P-SILI with HFNC is controversial and may be less than with NIV. Some physiological mechanisms of the protective effect of HFNC are hypoxaemia correction, reduction of inspiratory efforts and homogeneity of lung volume distribution.https://bit.ly/3skOEKX

High Flow Nasal Cannula compared to Continuous Positive Airway Pressure: a bench and physiological study

High-flow nasal cannula (HFNC) is extensively used for acute respiratory failure. However, questions remain regarding its physiological effects. We explored 1) whether HFNC produced similar effects to continuous positive airway pressure (CPAP); 2) possible explanations of respiratory rate changes; 3) the effects of mouth opening. Two studies were conducted: a bench study using a manikin's head with lungs connected to a breathing simulator while delivering HFNC flow rates from 0 to 60L/min; a physiological cross-over study in 10 healthy volunteers receiving HFNC (20 to 60L/min) with the mouth open or closed and CPAP 4cmH2O delivered through face-mask. Nasopharyngeal and esophageal pressures were measured; tidal volume and flow were estimated using calibrated electrical impedance tomography. In the bench study, nasopharyngeal pressure at end-expiration reached 4cmH2O with HFNC at 60L/min, while tidal volume decreased with increasing flow. In volunteers with HFNC at 60L/min, nasopharyngeal pressure reached 6.8cmH2O with mouth closed and 0.8cmH2O with mouth open; p<0.001. When increasing HFNC flow, respiratory rate decreased by lengthening expiratory time, tidal volume did not change, and effort decreased (pressure-time product of the respiratory muscles); at 40L/min, effort was equivalent between CPAP and HFNC40L/min and became lower at 60L/min (p=0.045). During HFNC with mouth closed, and not during CPAP, resistance to breathing was increased, mostly during expiration. In conclusion, mouth closure during HFNC induces a positive nasopharyngeal pressure proportional to flow rate and an increase in expiratory resistance that might explain the prolonged expiration and reduction in respiratory rate and effort, and contribute to physiological benefits.

High-flow nasal cannula improves respiratory impedance evaluated by impulse oscillometry in chronic obstructive pulmonary disease patients: a randomised controlled trial

Non-pharmacological treatment with high-flow nasal cannula (HFNC) may play a vital role in treatment of patients with chronic obstructive pulmonary disease (COPD). To evaluate the efficacy of HFNC, impulse oscillation system (IOS) is a new noninvasive technique in measuring the impedance of different portions of lungs. It shows higher sensitivity in contrast to conventional pulmonary function tests (PFT). However, whether IOS is an appropriate technique to evaluate the efficacy of HFNC in improving the impedance of small airways or peripheral lung in patients with COPD is still unclear. We enrolled 26 stable COPD participants randomised into two groups receiving HFNC or nasal cannula (NC) for 10 min followed by a 4-week washout period and crossover alternatively. IOS was used to detect the difference of respiratory impedance after HFNC or NC interventions. IOS parameters, PFT results, transcutaneous partial pressure of carbon dioxide, peripheral oxygen saturation, body temperature, respiratory rate, pulse rate, and blood pressure at the time of pre-HFNC, post-HFNC, pre-NC, and post-NC, were collected and analysed using SPSS (version 25.0, IBM, Armonk, NY, USA). The IOS measurement indicated that HFNC significantly improved R5, R5% predicted, R5–R20, X5-predicted, and Fres compared with NC, whereas no significant difference was observed through the PFT measurement. The beneficial effect of HFNC in improving small airway resistance and peripheral lung reactance compared with that of NC in patients with stable COPD was confirmed through IOS measurement.

Trial registration: ClinicalTrials.gov NCT05130112 22/11/2021.

Higher mortality and intubation rate in COVID-19 patients treated with noninvasive ventilation compared with high-flow oxygen or CPAP

The effectiveness of noninvasive respiratory support in severe COVID-19 patients is still controversial. We aimed to compare the outcome of patients with COVID-19 pneumonia and hypoxemic respiratory failure treated with high-flow oxygen administered via nasal cannula (HFNC), continuous positive airway pressure (CPAP) or noninvasive ventilation (NIV), initiated outside the intensive care unit (ICU) in 10 university hospitals in Catalonia, Spain. We recruited 367 consecutive patients aged ≥ 18 years who were treated with HFNC (155, 42.2%), CPAP (133, 36.2%) or NIV (79, 21.5%). The main outcome was intubation or death at 28 days after respiratory support initiation. After adjusting for relevant covariates and taking patients treated with HFNC as reference, treatment with NIV showed a higher risk of intubation or death (hazard ratio 2.01; 95% confidence interval 1.32–3.08), while treatment with CPAP did not show differences (0.97; 0.63–1.50). In the context of the pandemic and outside the intensive care unit setting, noninvasive ventilation for the treatment of moderate to severe hypoxemic acute respiratory failure secondary to COVID-19 resulted in higher mortality or intubation rate at 28 days than high-flow oxygen or CPAP. This finding may help physicians to choose the best noninvasive respiratory support treatment in these patients.

Clinicaltrials.gov identifier: NCT04668196.

Closed-loop oxygen control improves oxygen therapy in acute hypoxemic respiratory failure patients under high flow nasal oxygen: a randomized cross-over study (the HILOOP study)

Background

We aimed to assess the efficacy of a closed-loop oxygen control in critically ill patients with moderate to severe acute hypoxemic respiratory failure (AHRF) treated with high flow nasal oxygen (HFNO).

Methods

In this single-centre, single-blinded, randomized crossover study, adult patients with moderate to severe AHRF who were treated with HFNO (flow rate ≥ 40 L/min with FiO₂ ≥ 0.30) were randomly assigned to start with a 4-h period of closed-loop oxygen control or 4-h period of manual oxygen titration, after which each patient was switched to the alternate therapy. The primary outcome was the percentage of time spent in the individualized optimal SpO₂ range.

Results

Forty-five patients were included. Patients spent more time in the optimal SpO₂ range with closed-loop oxygen control compared with manual titrations of oxygen (96.5 [93.5 to 98.9] % vs. 89 [77.4 to 95.9] %; p < 0.0001) (difference estimate, 10.4 (95% confidence interval 5.2 to 17.2). Patients spent less time in the suboptimal range during closed-loop oxygen control, both above and below the cut-offs of the optimal SpO₂ range, and less time above the suboptimal range. Fewer number of manual adjustments per hour were needed with closed-loop oxygen control. The number of events of SpO₂ < 88% and < 85% were not significantly different between groups.

Conclusions

Closed-loop oxygen control improves oxygen administration in patients with moderate-to-severe AHRF treated with HFNO, increasing the percentage of time in the optimal oxygenation range and decreasing the workload of healthcare personnel. These results are especially relevant in a context of limited oxygen supply and high medical demand, such as the COVID-19 pandemic.

Trial registration The HILOOP study was registered at www.clinicaltrials.gov under the identifier NCT04965844.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03970-w.

Noninvasive Oxygenation in Patients with Acute Respiratory Failure: Current Perspectives

Purpose of Review

High-flow nasal oxygen and noninvasive ventilation are two alternative strategies to standard oxygen in the management of acute respiratory failure.

Discussion

Although high-flow nasal oxygen has gained major popularity in ICUs due to its simplicity of application, good comfort for patients, efficiency in improving oxygenation and promising results in patients with acute hypoxemic respiratory failure, further large clinical trials are needed to confirm its superiority over standard oxygen. Non-invasive ventilation may have deleterious effects, especially in patients exerting strong inspiratory efforts, and no current recommendations support its use in this setting. Protective non-invasive ventilation using higher levels of positive-end expiratory pressure, more prolonged sessions and other interfaces such as the helmet may have beneficial physiological effects leading to it being proposed as alternative to high-flow nasal oxygen in acute hypoxemic respiratory failure. By contrast, non-invasive ventilation is the first-line strategy of oxygenation in patients with acute exacerbation of chronic lung disease, while high-flow nasal oxygen could be an alternative to non-invasive ventilation after partial reversal of respiratory acidosis. Questions remain about the target populations and non-invasive oxygen strategy representing the best alternative to standard oxygen in acute hypoxemic respiratory failure. As concerns acute on-chronic-respiratory failure, the place of high-flow nasal oxygen remains to be evaluated.

Comparison of the effectiveness of high-flow nasal oxygen vs. standard facemask oxygenation for pre- and apneic oxygenation during anesthesia induction: a systematic review and meta-analysis

BACKGROUND

In recent years, high flow nasal oxygen (HFNO) has been widely used in clinic, especially in perioperative period. Many studies have discussed the role of HFNO in pre- and apneic oxygenation, but their results are controversial. Our study aimed to examine the effectiveness of HFNO in pre- and apneic oxygenation by a meta-analysis of RCTs.

METHODS

EMBASE, PUBMED, and COCHRANE LIBRARY databases were searched from inception to July 2021 for relevant randomized controlled trails (RCTs) on the effectiveness of HFNO versus standard facemask ventilation (FMV) in pre- and apenic oxygenation. Studies involving one of the following six indicators: (1) Arterial oxygen partial pressure (PaO2), (2) End expiratory oxygen concentration (EtO2), (3) Safe apnoea time, (4) Minimum pulse oxygen saturation (SpO2min), (5) Oxygenation (O2) desaturation, (6) End expiratory carbon dioxide (EtCO2) or Arterial carbon dioxide partial pressure(PaCO2) were included. Due to the source of clinical heterogeneity in the observed indicators in this study, we adopt random-effects model for analysis, and express it as the mean difference (MD) or risk ratio (RR) with a confidence interval of 95% (95%CI). We conducted a risk assessment of bias for eligible studies and assessed the overall quality of evidence for each outcome.

RESULTS

Fourteen RCTs and 1012 participants were finally included. We found the PaO2 was higher in HFNO group than FMV group with a MD (95% CI) of 57.38 mmHg (25.65 to 89.10; p = 0.0004) after preoxygenation and the safe apnoea time was significantly longer with a MD (95% CI) of 86.93 s (44.35 to 129.51; p < 0.0001) during anesthesia induction. There were no significant statistical difference in the minimum SpO2, CO2 accumulation, EtO2 and O2 desaturation rate during anesthesia induction between the two groups.

CONCLUSIONS

This systematic review and meta-analysis suggests that HFNO should be considered as an oxygenation tool for patients during anesthesia induction. Compared with FMV, continuous use of HFNO during anesthesia induction can significantly improve oxygenation and prolong safe apnoea time in surgical patients.

High-flow nasal cannula for respiratory failure in adult patients

The high-flow nasal cannula (HFNC) has been recently used in several clinical settings for oxygenation in adults. In particular, the advantages of HFNC compared with low-flow oxygen systems or non-invasive ventilation include enhanced comfort, increased humidification of secretions to facilitate expectoration, washout of nasopharyngeal dead space to improve the efficiency of ventilation, provision of a small positive end-inspiratory pressure effect, and fixed and rapid delivery of an accurate fraction of inspired oxygen (FiO₂) by minimizing the entrainment of room air. HFNC has been successfully used in critically ill patients with several conditions, such as hypoxemic respiratory failure, hypercapneic respiratory failure (exacerbation of chronic obstructive lung disease), post-extubation respiratory failure, pre-intubation oxygenation, and others. However, the indications are not absolute, and much of the proven benefit remains subjective and physiologic. This review discusses the practical application and clinical uses of HFNC in adults, including its unique respiratory physiologic effects, device settings, and clinical indications.

Treatment of acute respiratory failure: high-flow nasal cannula

Background: High-flow nasal cannulas (HFNCs) have recently been used for several conditions, such as hypoxemic respiratory failure, hypercapnic respiratory failure, post-extubation respiratory failure, and preintubation oxygenation, in critically ill patients.Current Concepts: The advantages of HFNC compared with those of low-flow oxygen systems or noninvasive ventilation include enhanced comfort, increased humidification of secretions to facilitate expectoration, washout of the nasopharyngeal dead space to improve ventilation efficiency, provisioning for low positive end-inspiratory pressure effect, and fixed and rapid delivery of accurate fraction of inspired oxygen by minimizing the entrainment of room air. However, the indications are not absolute, with much of the proven benefit being subjective and physiologic.Discussion and Conclusion: The goal of this review is to discuss the practical application and clinical uses of HFNCs in patients with acute respiratory failure, highlighting its unique respiratory and physiologic effects, device settings, and clinical indications.

High flow nasal catheter therapy versus non-invasive positive pressure ventilation in acute respiratory failure (RENOVATE trial): protocol and statistical analysis plan

Background: The best way to offer non-invasive respiratory support across several aetiologies of acute respiratory failure (ARF) is presently unclear. Both high flow nasal catheter (HFNC) therapy and non-invasive positive pressure ventilation (NIPPV) may improve outcomes in critically ill patients by avoiding the need for invasive mechanical ventilation (IMV). Objective: Describe the details of the protocol and statistical analysis plan designed to test whether HFNC therapy is non-inferior or even superior to NIPPV in patients with ARF due to different aetiologies. Methods: RENOVATE is a multicentre adaptive randomised controlled trial that is recruiting patients from adult emergency departments, wards and intensive care units (ICUs). It takes advantage of an adaptive Bayesian framework to assess the effectiveness of HFNC therapy versus NIPPV in four subgroups of ARF (hypoxaemic non-immunocompromised, hypoxaemic immunocompromised, chronic obstructive pulmonary disease exacerbations, and acute cardiogenic pulmonary oedema). The study will report the posterior probabilities of non-inferiority, superiority or futility for the comparison between HFNC therapy and NIPPV. The study assumes neutral priors and the final sample size is not fixed. The final sample size will be determined by a priori determined stopping rules for non-inferiority, superiority and futility for each subgroup or by reaching the maximum of 2000 patients. Outcomes: The primary endpoint is endotracheal intubation or death within 7 days. Secondary outcomes are 28-day and 90-day mortality, and ICU-free and IMV-free days in the first 28 days. Results and conclusions: RENOVATE is designed to provide evidence on whether HFNC therapy improves, compared with NIPPV, important patient-centred outcomes in different aetiologies of ARF. Here, we describe the rationale, design and status of the trial. Trial registration:ClinicalTrials.gov NCT03643939.

Validation of an Electronic Phenotyping Algorithm for Patients With Acute Respiratory Failure

Acute respiratory failure is a common reason for ICU admission and imposes significant strain on patients and the healthcare system. Noninvasive positive-pressure ventilation and high-flow nasal oxygen are increasingly used as an alternative to invasive mechanical ventilation to treat acute respiratory failure. As such, there is a need to accurately cohort patients using large, routinely collected, clinical data to better understand utilization patterns and patient outcomes. The primary objective of this retrospective observational study was to externally validate our computable phenotyping algorithm for patients with acute respiratory failure requiring various sequences of respiratory support in real-world data from a large healthcare delivery network.

Comparison of high-flow nasal oxygen therapy and noninvasive ventilation in COVID-19 patients: a systematic review and meta-analysis

Background

Acute respiratory failure (ARF) is a major adverse event commonly encountered in severe coronavirus disease 2019 (COVID-19). Although noninvasive mechanical ventilation (NIV) has long been used in the management of ARF, it has several adverse events which may cause patient discomfort and lead to treatment complication. Recently, high-flow nasal cannula (HFNC) has the potential to be an alternative for NIV in adults with ARF, including COVID-19 patients. The objective was to investigate the efficacy of HFNC compared to NIV in COVID-19 patients.

Methods

This meta-analysis was reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria. Literature search was carried out in electronic databases for relevant articles published prior to June 2021. The protocol used in this study has been registered in International Prospective Register of Systematic Reviews (CRD42020225186).

Results

Although the success rate of NIV is higher compared to HFNC (odds ratio [OR], 0.39; 95% confidence interval [CI], 0.16–0.97; P=0.04), this study showed that the mortality in the NIV group is also significantly higher compared to HFNC group (OR, 0.49; 95% CI, 0.39–0.63; P<0.001). Moreover, this study also demonstrated that there was no significant difference in intubation rates between the two groups (OR, 1.35; 95% CI, 0.86–2.11; P=0.19).

Conclusions

Patients treated with HFNC showed better outcomes compared to NIV for ARF due to COVID-19. Therefore, HFNC should be considered prior to NIV in COVID-19-associated ARF. However, further studies with larger sample sizes are still needed to better elucidate the benefit of HFNC in COVID-19 patients.

Non-invasive oxygenation support in acutely hypoxemic COVID-19 patients admitted to the ICU: a multicenter observational retrospective study

Background

Non-invasive oxygenation strategies have a prominent role in the treatment of acute hypoxemic respiratory failure during the coronavirus disease 2019 (COVID-19). While the efficacy of these therapies has been studied in hospitalized patients with COVID-19, the clinical outcomes associated with oxygen masks, high-flow oxygen therapy by nasal cannula and non-invasive mechanical ventilation in critically ill intensive care unit (ICU) patients remain unclear.

Methods

In this retrospective study, we used the best of nine covariate balancing algorithms on all baseline covariates in critically ill COVID-19 patients supported with > 10 L of supplemental oxygen at one of the 26 participating ICUs in Catalonia, Spain, between March 14 and April 15, 2020.

Results

Of the 1093 non-invasively oxygenated patients at ICU admission treated with one of the three stand-alone non-invasive oxygenation strategies, 897 (82%) required endotracheal intubation and 310 (28%) died during the ICU stay. High-flow oxygen therapy by nasal cannula (n = 439) and non-invasive mechanical ventilation (n = 101) were associated with a lower rate of endotracheal intubation (70% and 88%, respectively) than oxygen masks (n = 553 and 91% intubated), p < 0.001. Compared to oxygen masks, high-flow oxygen therapy by nasal cannula was associated with lower ICU mortality (hazard ratio 0.75 [95% CI 0.58–0.98), and the hazard ratio for ICU mortality was 1.21 [95% CI 0.80–1.83] for non-invasive mechanical ventilation.

Conclusion

In critically ill COVID-19 ICU patients and, in the absence of conclusive data, high-flow oxygen therapy by nasal cannula may be the approach of choice as the primary non-invasive oxygenation support strategy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03905-5.

Noninvasive respiratory support for acute respiratory failure due to COVID-19

PURPOSE OF REVIEW

Noninvasive respiratory support has been widely applied during the COVID-19 pandemic. We provide a narrative review on the benefits and possible harms of noninvasive respiratory support for COVID-19 respiratory failure.

RECENT FINDINGS

Maintenance of spontaneous breathing by means of noninvasive respiratory support in hypoxemic patients with vigorous spontaneous effort carries the risk of patient self-induced lung injury: the benefit of averting intubation in successful patients should be balanced with the harms of a worse outcome in patients who are intubated after failing a trial of noninvasive support.The risk of noninvasive treatment failure is greater in patients with the most severe oxygenation impairment (PaO2/FiO2 < 200 mmHg).High-flow nasal oxygen (HFNO) is the most widely applied intervention in COVID-19 patients with hypoxemic respiratory failure. Also, noninvasive ventilation (NIV) and continuous positive airway pressure delivered with different interfaces have been used with variable success rates. A single randomized trial showed lower need for intubation in patients receiving helmet NIV with specific settings, compared to HFNO alone.Prone positioning is recommended for moderate-to-severe acute respiratory distress syndrome patients on invasive ventilation. Awake prone position has been frequently applied in COVID-19 patients: one randomized trial showed improved oxygenation and lower intubation rate in patients receiving 6-h sessions of awake prone positioning, as compared to conventional management.

SUMMARY

Noninvasive respiratory support and awake prone position are tools possibly capable of averting endotracheal intubation in COVID-19 patients; carefully monitoring during any treatment is warranted to avoid delays in endotracheal intubation, especially in patients with PaO2/FiO2 < 200 mmHg.

Effect of respiratory rate and size of cannula on pressure and dead-space clearance during nasal high flow in patients with COPD and acute respiratory failure

Nasal high flow (NHF) is an efficient oxygenation tool for the treatment of respiratory failure. The study investigated the effect of breathing pattern on positive airway pressure and dead-space clearance by NHF. The breathing cycle during NHF was characterized in 26 patients with acute respiratory failure (ARF) and stable COPD and after mechanical ventilation (post-MV) via tracheostomy where also pressure was measured in the trachea. Dead-space clearance was measured in airway models during different breathing patterns. NHF reduced the respiratory rate (RR) and T_I/T_E through prolonging the T_E; the T_I/T_E ranged between ≤0.5 observed in the COPD patients and ∼1.0 in the ARF patients. NHF via a standard medium-sized cannula interface generated a low-level expiratory pressure proportional to NHF rate and breathing flow; the median generated positive end-expiratory pressure was only 1.71 cmH₂O at NHF 45 L/min. The dilution and purging of expired gas from a nasal cavity model were observed to occur at the end of expiration as expiratory flow slowed and the dynamic pressure decreased. The higher RR with shorter end-expiratory period resulted in reduced dead-space clearance by NHF; 20 L/min cleared 43 ± 2 mL at RR 15 min⁻¹ vs. 9 ± 5 mL at RR 45 min⁻¹, P < 0.001, which was increased at higher NHF rate. At lower RR, the clearance was similar between NHF rates 20 and 60 L/min. Higher NHF rates elevate positive airway pressure, and at the increased RR can improve the clearance. This may enhance gas exchange and lead to a reduction in the work of breathing.

NEW & NOTEWORTHY During nasal high flow (NHF) an increased breathing frequency, which is commonly observed in acute respiratory failure, can lead to decreased dead-space clearance. Higher NHF rates increase the clearance and reduce the rebreathing which may eventually lower the respiratory rate and the work of breathing. Monitoring of the respiratory rate could be an important indicator of not only the respiratory function but also the NHF rate selection and the therapy efficacy.

Non-invasive Respiratory Support in COVID-19: A Narrative Review

Acute respiratory failure secondary to COVID-19 pneumonia may require a variety of non-pharmacological strategies in addition to oxygen therapy to avoid endotracheal intubation. The response to all these strategies, which include high nasal flow, continuous positive pressure, non-invasive ventilation, or even prone positioning in awake patients, can be highly variable depending on the predominant phenotypic involvement. Deciding when to replace conventional oxygen therapy with non-invasive respiratory support, which to choose, the role of combined methods, definitions, and attitudes toward treatment failure, and improved case improvement procedures are directly relevant clinical questions for the daily care of critically ill COVID-19 patients. The experience accumulated after more than a year of the pandemic should lead to developing recommendations that give answers to all these questions.

Impact of exposure time in awake prone positioning on clinical outcomes of patients with COVID-19-related acute respiratory failure treated with high-flow nasal oxygen: a multicenter cohort study

Background

In patients with COVID-19-related acute respiratory failure (ARF), awake prone positioning (AW-PP) reduces the need for intubation in patients treated with high-flow nasal oxygen (HFNO). However, the effects of different exposure times on clinical outcomes remain unclear. We evaluated the effect of AW-PP on the risk of endotracheal intubation and in-hospital mortality in patients with COVID-19-related ARF treated with HFNO and analyzed the effects of different exposure times to AW-PP.

Methods

This multicenter prospective cohort study in six ICUs of 6 centers in Argentine consecutively included patients > 18 years of age with confirmed COVID-19-related ARF requiring HFNO from June 2020 to January 2021. In the primary analysis, the main exposure was awake prone positioning for at least 6 h/day, compared to non-prone positioning (NON-PP). In the sensitivity analysis, exposure was based on the number of hours receiving AW-PP. Inverse probability weighting–propensity score (IPW-PS) was used to adjust the conditional probability of treatment assignment. The primary outcome was endotracheal intubation (ETI); and the secondary outcome was hospital mortality.

Results

During the study period, 580 patients were screened and 335 were included; 187 (56%) tolerated AW-PP for [median (p25–75)] 12 (9–16) h/day and 148 (44%) served as controls. The IPW–propensity analysis showed standardized differences < 0.1 in all the variables assessed. After adjusting for other confounders, the OR (95% CI) for ETI in the AW-PP group was 0.36 (0.2–0.7), with a progressive reduction in OR as the exposure to AW-PP increased. The adjusted OR (95% CI) for hospital mortality in the AW-PP group ≥ 6 h/day was 0.47 (0.19–1.31). The exposure to prone positioning ≥ 8 h/d resulted in a further reduction in OR [0.37 (0.17–0.8)].

Conclusion

In the study population, AW-PP for ≥ 6 h/day reduced the risk of endotracheal intubation, and exposure ≥ 8 h/d reduced the risk of hospital mortality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03881-2.

Expanding the utility of the ROX index among patients with acute hypoxemic respiratory failure

BACKGROUND

Delaying intubation in patients who fail high-flow nasal cannula (HFNC) may result in increased mortality. The ROX index has been validated to predict HFNC failure among pneumonia patients with acute hypoxemic respiratory failure (AHRF), but little information is available for non-pneumonia causes. In this study, we validate the ROX index among AHRF patients due to both pneumonia or non-pneumonia causes, focusing on early prediction.

METHODS

This was a retrospective observational study in eight Singapore intensive care units from 1 January 2015 to 30 September 2017. All patients >18 years who were treated with HFNC for AHRF were eligible and recruited. Clinical parameters and arterial blood gas values at HFNC initiation and one hour were recorded. HFNC failure was defined as requiring intubation post-HFNC initiation.

RESULTS

HFNC was used in 483 patients with 185 (38.3%) failing HFNC. Among pneumonia patients, the ROX index was most discriminatory in pneumonia patients one hour after HFNC initiation [AUC 0.71 (95% CI 0.64-0.79)], with a threshold value of <6.06 at one hour predicting HFNC failure (sensitivity 51%, specificity 80%, positive predictive value 61%, negative predictive value 73%). The discriminatory power remained moderate among pneumonia patients upon HFNC initiation [AUC 0.65 (95% CI 0.57-0.72)], non-pneumonia patients at HFNC initiation [AUC 0.62 (95% CI 0.55-0.69)] and one hour later [AUC 0.63 (95% CI 0.56-0.70)].

CONCLUSION

The ROX index demonstrated moderate discriminatory power among patients with either pneumonia or non-pneumonia-related AHRF at HFNC initiation and one hour later.

The physiological underpinnings of life-saving respiratory support

Treatment of respiratory failure has improved dramatically since the polio epidemic in the 1950s with the use of invasive techniques for respiratory support: mechanical ventilation and extracorporeal respiratory support. However, respiratory support is only a supportive therapy, designed to "buy time" while the disease causing respiratory failure abates. It ensures viable gas exchange and prevents cardiorespiratory collapse in the context of excessive loads. Because the use of invasive modalities of respiratory support is also associated with substantial harm, it remains the responsibility of the clinician to minimize such hazards. Direct iatrogenic consequences of mechanical ventilation include the risk to the lung (ventilator-induced lung injury) and the diaphragm (ventilator-induced diaphragm dysfunction and other forms of myotrauma). Adverse consequences on hemodynamics can also be significant. Indirect consequences (e.g., immobilization, sleep disruption) can have devastating long-term effects. Increasing awareness and understanding of these mechanisms of injury has led to a change in the philosophy of care with a shift from aiming to normalize gases toward minimizing harm. Lung (and more recently also diaphragm) protective ventilation strategies include the use of extracorporeal respiratory support when the risk of ventilation becomes excessive. This review provides an overview of the historical background of respiratory support, pathophysiology of respiratory failure and rationale for respiratory support, iatrogenic consequences from mechanical ventilation, specifics of the implementation of mechanical ventilation, and role of extracorporeal respiratory support. It highlights the need for appropriate monitoring to estimate risks and to individualize ventilation and sedation to provide safe respiratory support to each patient.

Effects of high-flow nasal cannula with oxygen on self-paced exercise performance in COPD: A randomized cross-over trial

INTRODUCTION

Studies have demonstrated that noninvasive ventilation improves exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). The role of heated humidified high-flow nasal cannula (HFNC) therapy in patients with COPD on self-paced exercise performance remains unclear. Therefore, the purpose of the present study was to determine whether HFNC-aided supplemental oxygen during a 6-minute walk test (6MWT) would change self-paced exercise performance and cardiopulmonary outcomes in patients with stable COPD.

METHODS

A single-site, cross-over trial was conducted in a pulmonary rehabilitation outpatient department. This study enrolled 30 stable COPD patients without disability. The participants with and without HFNC performed 6MWTs on 2 consecutive days. Outcomes were the distance walked in the 6MWT, physiological, and cardiopulmonary parameters.

RESULTS

Those performing HFNC-aided walking exhibited a longer walking distance than those performing unaided walking. The mean difference in meters walked between the HFNC-aided and unaided walking scenarios was 27.3 ± 35.6 m (95% CI: 14.4-40.5 m). The energy expenditure index was significantly lower when walking was aided by HHHNFC rather than unaided (median: 1.21 beats/m walked vs median: 1.37 beats/m walked, P < .001). However, there were no differences in transcutaneous carbon dioxide tension between HHHNFC and non-HHHNFC patients.

CONCLUSION

Walking distance and arterial oxygen saturation improved in stable COPD patients receiving HFNC with additional oxygen support. However, HFNC did not affect transcutaneous carbon dioxide tension and the self-reported dyspnea score during the walking test. The present study demonstrated the feasibility and safety of using HFNC in self-paced exercise.

TRIAL REGISTRATION

NCT03863821.

High-flow oxygen therapy versus noninvasive ventilation: a randomised physiological crossover study of alveolar recruitment in acute respiratory failure

High-flow nasal cannula (HFNC) oxygen therapy has recently shown clinical benefits in hypoxaemic acute respiratory failure (ARF) patients, while the value of noninvasive ventilation (NIV) remains debated. The primary end-point was to compare alveolar recruitment using global end-expiratory electrical lung impedance (EELI) between HFNC and NIV. Secondary end-points compared regional EELI, lung volumes (global and regional tidal volume variation (V_T)), respiratory parameters, haemodynamic tolerance, dyspnoea and patient comfort between HFNC and NIV, relative to face mask (FM).

A prospective randomised crossover physiological study was conducted in patients with hypoxaemic ARF due to pneumonia. They received alternately HFNC, NIV and FM.

16 patients were included. Global EELI was 4083 with NIV and 2921 with HFNC (p=0.4). Compared to FM, NIV and HFNC significantly increased global EELI by 1810.5 (95% CI 857–2646) and 826 (95% CI 399.5–2361), respectively. Global and regional V_T increased significantly with NIV compared to HFNC or FM, but not between HFNC and FM. NIV yielded a significantly higher pulse oxygen saturation/inspired oxygen fraction ratio compared to HFNC (p=0.03). No significant difference was observed between HFNC, NIV and FM for dyspnoea. Patient comfort score with FM was not significantly different than with HFNC (p=0.1), but was lower with NIV (p=0.001).

This study suggests a potential benefit of HFNC and NIV on alveolar recruitment in patients with hypoxaemic ARF. In contrast with HFNC, NIV increased lung volumes, which may contribute to overdistension and its potentially deleterious effect in these patients.

This study found a potential benefit of HFNC and NIV on alveolar recruitment in patients with hypoxaemic ARF, but NIV also increases lung volumes, which may give rise to overdistension, reinforcing the concept of patient self-inflicted lung injuryhttps://bit.ly/3iRcZDJ

Benefits and risks of noninvasive oxygenation strategy in COVID-19: a multicenter, prospective cohort study (COVID-ICU) in 137 hospitals

Rational

To evaluate the respective impact of standard oxygen, high-flow nasal cannula (HFNC) and noninvasive ventilation (NIV) on oxygenation failure rate and mortality in COVID-19 patients admitted to intensive care units (ICUs).

Methods

Multicenter, prospective cohort study (COVID-ICU) in 137 hospitals in France, Belgium, and Switzerland. Demographic, clinical, respiratory support, oxygenation failure, and survival data were collected. Oxygenation failure was defined as either intubation or death in the ICU without intubation. Variables independently associated with oxygenation failure and Day-90 mortality were assessed using multivariate logistic regression.

Results

From February 25 to May 4, 2020, 4754 patients were admitted in ICU. Of these, 1491 patients were not intubated on the day of ICU admission and received standard oxygen therapy (51%), HFNC (38%), or NIV (11%) (P < 0.001). Oxygenation failure occurred in 739 (50%) patients (678 intubation and 61 death). For standard oxygen, HFNC, and NIV, oxygenation failure rate was 49%, 48%, and 60% (P < 0.001). By multivariate analysis, HFNC (odds ratio [OR] 0.60, 95% confidence interval [CI] 0.36–0.99, P = 0.013) but not NIV (OR 1.57, 95% CI 0.78–3.21) was associated with a reduction in oxygenation failure). Overall 90-day mortality was 21%. By multivariable analysis, HFNC was not associated with a change in mortality (OR 0.90, 95% CI 0.61–1.33), while NIV was associated with increased mortality (OR 2.75, 95% CI 1.79–4.21, P < 0.001).

Conclusion

In patients with COVID-19, HFNC was associated with a reduction in oxygenation failure without improvement in 90-day mortality, whereas NIV was associated with a higher mortality in these patients. Randomized controlled trials are needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03784-2.

Effect of High-Flow Oxygen Therapy vs Conventional Oxygen Therapy on Invasive Mechanical Ventilation and Clinical Recovery in Patients With Severe COVID-19: A Randomized Clinical Trial

IMPORTANCE

The effect of high-flow oxygen therapy vs conventional oxygen therapy has not been established in the setting of severe COVID-19.

OBJECTIVE

To determine the effect of high-flow oxygen therapy through a nasal cannula compared with conventional oxygen therapy on need for endotracheal intubation and clinical recovery in severe COVID-19.

DESIGN, SETTING, AND PARTICIPANTS

Randomized, open-label clinical trial conducted in emergency and intensive care units in 3 hospitals in Colombia. A total of 220 adults with respiratory distress and a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen of less than 200 due to COVID-19 were randomized from August 2020 to January 2021, with last follow-up on February 10, 2021.

INTERVENTIONS

Patients were randomly assigned to receive high-flow oxygen through a nasal cannula (n = 109) or conventional oxygen therapy (n = 111).

MAIN OUTCOMES AND MEASURES

The co-primary outcomes were need for intubation and time to clinical recovery until day 28 as assessed by a 7-category ordinal scale (range, 1-7, with higher scores indicating a worse condition). Effects of treatments were calculated with a Cox proportional hazards model adjusted for hypoxemia severity, age, and comorbidities.

RESULTS

Among 220 randomized patients, 199 were included in the analysis (median age, 60 years; n = 65 women [32.7%]). Intubation occurred in 34 (34.3%) randomized to high-flow oxygen therapy and in 51 (51.0%) randomized to conventional oxygen therapy (hazard ratio, 0.62; 95% CI, 0.39-0.96; P = .03). The median time to clinical recovery within 28 days was 11 (IQR, 9-14) days in patients randomized to high-flow oxygen therapy vs 14 (IQR, 11-19) days in those randomized to conventional oxygen therapy (hazard ratio, 1.39; 95% CI, 1.00-1.92; P = .047). Suspected bacterial pneumonia occurred in 13 patients (13.1%) randomized to high-flow oxygen and in 17 (17.0%) of those randomized to conventional oxygen therapy, while bacteremia was detected in 7 (7.1%) vs 11 (11.0%), respectively.

CONCLUSIONS AND RELEVANCE

Among patients with severe COVID-19, use of high-flow oxygen through a nasal cannula significantly decreased need for mechanical ventilation support and time to clinical recovery compared with conventional low-flow oxygen therapy.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04609462.

Effect of High-Flow Oxygen Therapy vs Conventional Oxygen Therapy on Invasive Mechanical Ventilation and Clinical Recovery in Patients With Severe COVID-19: A Randomized Clinical Trial

IMPORTANCE

The effect of high-flow oxygen therapy vs conventional oxygen therapy has not been established in the setting of severe COVID-19.

OBJECTIVE

To determine the effect of high-flow oxygen therapy through a nasal cannula compared with conventional oxygen therapy on need for endotracheal intubation and clinical recovery in severe COVID-19.

DESIGN, SETTING, AND PARTICIPANTS

Randomized, open-label clinical trial conducted in emergency and intensive care units in 3 hospitals in Colombia. A total of 220 adults with respiratory distress and a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen of less than 200 due to COVID-19 were randomized from August 2020 to January 2021, with last follow-up on February 10, 2021.

INTERVENTIONS

Patients were randomly assigned to receive high-flow oxygen through a nasal cannula (n = 109) or conventional oxygen therapy (n = 111).

MAIN OUTCOMES AND MEASURES

The co-primary outcomes were need for intubation and time to clinical recovery until day 28 as assessed by a 7-category ordinal scale (range, 1-7, with higher scores indicating a worse condition). Effects of treatments were calculated with a Cox proportional hazards model adjusted for hypoxemia severity, age, and comorbidities.

RESULTS

Among 220 randomized patients, 199 were included in the analysis (median age, 60 years; n = 65 women [32.7%]). Intubation occurred in 34 (34.3%) randomized to high-flow oxygen therapy and in 51 (51.0%) randomized to conventional oxygen therapy (hazard ratio, 0.62; 95% CI, 0.39-0.96; P = .03). The median time to clinical recovery within 28 days was 11 (IQR, 9-14) days in patients randomized to high-flow oxygen therapy vs 14 (IQR, 11-19) days in those randomized to conventional oxygen therapy (hazard ratio, 1.39; 95% CI, 1.00-1.92; P = .047). Suspected bacterial pneumonia occurred in 13 patients (13.1%) randomized to high-flow oxygen and in 17 (17.0%) of those randomized to conventional oxygen therapy, while bacteremia was detected in 7 (7.1%) vs 11 (11.0%), respectively.

CONCLUSIONS AND RELEVANCE

Among patients with severe COVID-19, use of high-flow oxygen through a nasal cannula significantly decreased need for mechanical ventilation support and time to clinical recovery compared with conventional low-flow oxygen therapy.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04609462.

High-flow nasal cannula in children with asthma exacerbation: A review of current evidence

Asthma is the commonest obstructive airway disease and the leading cause of morbidity in children. In the pediatric population, acute exacerbations of asthma are a frequent cause of presentations and hospital admissions. An acute asthma exacerbation is potentially life-threatening; it is predominantly treated using conventional oxygen therapy with bronchodilators and systemic corticosteroids. The treatment of those who do not respond to conventional therapy is escalated to noninvasive positive pressure ventilation (NIPPV) before invasive ventilation. Although NIPPV has demonstrated benefits and safety, it still has limitations such as treatment intolerance caused mainly by discomfort and complications. High-flow oxygen therapy administered through a nasal cannula (HFNC) provides respiratory support with adequate airway humidity and has demonstrated safety and benefits in clinical practice. In the present review, we discuss HFNC and variations in HFNC use, focusing on its feasibility and current evidence of using it on children with asthma exacerbations.

Respiratory Drive in Patients with Sepsis and Septic Shock: Modulation by High-flow Nasal Cannula

BACKGROUND

Experimental and pilot clinical data suggest that spontaneously breathing patients with sepsis and septic shock may present increased respiratory drive and effort, even in the absence of pulmonary infection. The study hypothesis was that respiratory drive and effort may be increased in septic patients and correlated with extrapulmonary determinant and that high-flow nasal cannula may modulate drive and effort.

METHODS

Twenty-five nonintubated patients with extrapulmonary sepsis or septic shock were enrolled. Each patient underwent three consecutive steps: low-flow oxygen at baseline, high-flow nasal cannula, and then low-flow oxygen again. Arterial blood gases, esophageal pressure, and electrical impedance tomography data were recorded toward the end of each step. Respiratory effort was measured as the negative swing of esophageal pressure (ΔPes); drive was quantified as the change in esophageal pressure during the first 500 ms from start of inspiration (P0.5). Dynamic lung compliance was calculated as the tidal volume measured by electrical impedance tomography, divided by ΔPes. The results are presented as medians [25th to 75th percentile].

RESULTS

Thirteen patients (52%) were in septic shock. The Sequential Organ Failure Assessment score was 5 [4 to 9]. During low-flow oxygen at baseline, respiratory drive and effort were elevated and significantly correlated with arterial lactate (r = 0.46, P = 0.034) and inversely with dynamic lung compliance (r = -0.735, P < 0.001). Noninvasive support by high-flow nasal cannula induced a significant decrease of respiratory drive (P0.5: 6.0 [4.4 to 9.0] vs. 4.3 [3.5 to 6.6] vs. 6.6 [4.9 to 10.7] cm H2O, P < 0.001) and effort (ΔPes: 8.0 [6.0 to 11.5] vs. 5.5 [4.5 to 8.0] vs. 7.5 [6.0 to 12.6] cm H2O, P < 0.001). Oxygenation and arterial carbon dioxide levels remained stable during all study phases.

CONCLUSIONS

Patients with sepsis and septic shock of extrapulmonary origin present elevated respiratory drive and effort, which can be effectively reduced by high-flow nasal cannula.

EDITOR’S PERSPECTIVE

Enabling Longitudinal Respiration Monitoring Using Vapor-Coated Conducting Textiles

Wearable sensors allow for portable, long-term health monitoring in natural environments. Recently, there has been an increase in demand for technology that can reliably monitor respiration, which can be indicative of cardiac diseases, asthma, and infection by respiratory viruses. However, to date, the most reliable respiration monitoring system involves a tightly worn chest belt that is not conducive to longitudinal monitoring. Herein, we report that accurate respiration monitoring can be effected using a fabric-based humidity sensor mounted within a face mask. Our humidity sensor is created using cotton fabrics coated with a persistently p-doped conjugated polymer, poly(3,4-ethylenedioxythiophene):chloride (PEDOT-Cl), using a previously reported chemical vapor deposition process. The vapor-deposited polymer coating displays a stable, rapid, and reversible change in conductivity with an increase in local humidity, such as the humidity changes experienced within a face mask as the wearer breathes. Thus, when integrated into a face mask, the PEDOT-Cl-coated cotton humidity sensor is able to transduce breaths into an electrical signal. The humidity sensor-incorporated face mask is able to differentiate between deep and shallow breathing, as well as breathing versus talking. The sensor-incorporated face mask platform also functions both while walking and sitting, providing equally high signal quality in both indoor and outdoor contexts. Additionally, we show that the face mask can be worn for long periods of time with a negligible decline in the signal quality.

Optimizing high-flow nasal cannula flow settings in adult hypoxemic patients based on peak inspiratory flow during tidal breathing

Background

Optimal flow settings during high-flow nasal cannula (HFNC) therapy are unknown. We investigated the optimal flow settings during HFNC therapy based on breathing pattern and tidal inspiratory flows in patients with acute hypoxemic respiratory failure (AHRF).

Methods

We conducted a prospective clinical study in adult hypoxemic patients treated by HFNC with a fraction of inspired oxygen (F_IO₂) ≥ 0.4. Patient’s peak tidal inspiratory flow (PTIF) was measured and HFNC flows were set to match individual PTIF and then increased by 10 L/min every 5–10 min up to 60 L/min. F_IO₂ was titrated to maintain pulse oximetry (SpO₂) of 90–97%. SpO₂/F_IO₂, respiratory rate (RR), ROX index [(SpO₂/F_IO₂)/RR], and patient comfort were recorded after 5–10 min on each setting. We also conducted an in vitro study to explore the relationship between the HFNC flows and the tracheal F_IO₂, peak inspiratory and expiratory pressures.

Results

Forty-nine patients aged 58.0 (SD 14.1) years were enrolled. At enrollment, HFNC flow was set at 45 (38, 50) L/min, with an F_IO₂ at 0.62 (0.16) to obtain an SpO₂/F_IO₂ of 160 (40). Mean PTIF was 34 (9) L/min. An increase in HFNC flows up to two times of the individual patient’s PTIF, incrementally improved oxygenation but the ROX index plateaued with HFNC flows of 1.34–1.67 times the individual PTIF. In the in vitro study, when the HFNC flow was set higher than PTIF, tracheal peak inspiratory and expiratory pressures increased as HFNC flow increased but the F_IO₂ did not change.

Conclusion

Mean PTIF values in most patients with AHRF were between 30 and 40 L/min. We observed improvement in oxygenation with HFNC flows set above patient PTIF. Thus, a pragmatic approach to set optimal flows in patients with AHRF would be to initiate HFNC flow at 40 L/min and titrate the flow based on improvement in ROX index and patient tolerance.

Trial registration: ClinicalTrials.gov (NCT03738345). Registered on November 13th, 2018. https://clinicaltrials.gov/ct2/show/NCT03738345?term=NCT03738345&draw=2&rank=1

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-021-00949-8.

Physiological Responses and Perceived Comfort to High Flow Nasal Cannula Therapy in Awake Adults: Effects of Flow Magnitude and Temperature

Clinical use of heated, high flow nasal cannula (HFNC) for non-invasive respiratory support is increasing and may have a therapeutic role in stabilizing the upper airway in obstructive sleep apnea (OSA). However, physiological mechanisms by which HFNC therapy may improve upper-airway function and effects of different temperature modes are unclear. Accordingly, this study aimed to determine effects of incremental flows and temperature modes (heated and non-heated) of HFNC on upper airway muscle activity (genioglossus), pharyngeal airway pressure, breathing parameters and perceived comfort. Six participants (2 females, aged 35±14 years) were studied during wakefulness in supine position and received HFNC at variable flows (0-60 L/min) during heated (37ºC) and non-heated (21ºC) modes. Breathing parameters via calibrated Respitrace inductance bands (chest and abdomen), upper-airway pressures via airway transducers, and genioglossus muscle activity via intra-muscular bipolar fine wire electrodes were measured. Comfort levels during HFNC were quantified using a visual analogue scale. Increasing HFNC flows did not increase genioglossus muscle activation despite increased negative epiglottic pressure swings (p=0.009). HFNC provided ~7cmH₂O positive airway pressure at 60 L/min in non-heated and heated modes. In addition, increasing the magnitude of HFNC flow reduced breathing frequency (p=0.045), increased expiratory time (p=0.040), increased peak inspiratory flow (p=0.002), and increased discomfort (p=0.004). Greater discomfort occurred at higher flows in non-heated versus heated mode (p=0.034). These findings provide novel insight into key physiological changes that occur with HFNC for respiratory support and indicate the primary mechanism for improved upper-airway stability is positive airway pressure, not increased pharyngeal muscle activity.

ERS Clinical Practice Guidelines: High-flow nasal cannula in acute respiratory failure

BACKGROUND

High-flow nasal cannula (HFNC) has become a frequently used non-invasive form of respiratory support in acute settings, however evidence supporting its use has only recently emerged. These guidelines provide evidence-based recommendations for the use of HFNC alongside other noninvasive forms of respiratory support in adults with acute respiratory failure (ARF).

MATERIALS AND METHODOLOGY

The European Respiratory Society Task Force panel included expert clinicians and methodologists in pulmonology and intensive care medicine. The Task Force used the GRADE (Grading of Recommendations, Assessment, Development, and Evaluations) methods to summarize evidence and develop clinical recommendations for the use of HFNC alongside conventional oxygen therapy (COT) and non-invasive ventilation (NIV) for the management of adults in acute settings with ARF.

RESULTS

The Task Force developed 8 conditional recommendations, suggesting using: 1) HFNC over COT in hypoxemic ARF, 2) HFNC over NIV in hypoxemic ARF, 3)HFNC over COT during breaks from NIV, 4) either HFNC or COT in post-operative patients at low risk of pulmonary complications, 5) either HFNC or NIV in post-operative patients at high risk of pulmonary complications, 6) HFNC over COT in non-surgical patients at low risk of extubation failure, 7) NIV over HFNC for patients at high risk of extubation failure unless there are relative or absolute contraindications to NIV, 8) trialling NIV prior to use of HFNC in patients with chronic obstructive pulmonary disease (COPD) and hypercapnic ARF.

CONCLUSIONS

HFNC is a valuable intervention in adults with ARF. These conditional recommendations can assist clinicians in choosing the most appropriate form of non-invasive respiratory support to provide to patients in different acute settings.

First Attempt at Using Electrical Impedance Tomography to Predict High Flow Nasal Cannula Therapy Outcomes at an Early Phase

Objective: Spatial and temporal ventilation distributions in patients with acute respiratory failure during high flow nasal cannula (HFNC) therapy were previously studied with electrical impedance tomography (EIT). The aim of the study was to explore the possibility of predicting HFNC failure based on various EIT-derived parameters.

Methods: High flow nasal cannula failure was defined reintubation within 48 h after HFNC. EIT was performed with the patients spontaneously breathing in the supine position at the start of HFNC. EIT-based indices (comprising the global inhomogeneity index, center of ventilation, ventilation delay, rapid shallow breathing index, minute volume, and inspiration to expiration time) were explored and evaluated at three time points (prior to HFNC, T1; 30 min after HFNC started, T2; and 1 h after, T3).

Results: A total of 46 subjects were included in the final analysis. Eleven subjects had failed HFNC. The time to failure was 27.8 ± 12.4 h. The ROX index (defined as SpO₂/FiO₂/respiratory rate) for HFNC success patients was 8.3 ± 2.7 and for HFNC failure patients, 6.2 ± 1.8 (p = 0.23). None of the investigated EIT-based parameters showed significant differences between subjects with HFNC failure and success. Further subgroup analysis indicated that a significant difference in ventilation inhomogeneity was found between ARDS and non-ARDS [0.54 (0.37) vs. 0.46 (0.28) as evaluated with GI, p < 0.01]. Ventilation homogeneity significantly improved in ARDS after 60-min HFNC treatment [0.59 (0.20) vs 0.57 (0.19), T1 vs. T3, p < 0.05].

Conclusion: Spatial and temporal ventilation distributions were slightly but insignificantly different between the HFNC success and failure groups. HFNC failure could not be predicted by changes in EIT temporal and spatial indexes of ventilation distribution within the first hour. Further studies are required to predict the outcomes of HFNC.

ROX index as predictor of high flow nasal cannula therapy success in acute respiratory failure due to SARS-CoV-2

Background

High-Flow Nasal Cannula (HFNC) therapy is useful treatment in patients with acute respiratory failure (ARF). The ROX index (ratio of pulse oximetry/fraction of inspired oxygen to respiratory rate) has been evaluated to predict success of HFNC in patients with pneumonia.

Objective

The aim of this study was to determine whether the ROX Index could predict HFNC therapy success in patients with ARF due to SARS-CoV-2 pneumonia.

Methods

An observational, prospective study was performed including patients admitted with ARF secondary to SARS-CoV-2 pneumonia who met criteria for HFNC therapy initiation. Demographic, radiological, laboratory and clinical course data were collected. The ROX index was calculated at 1 h, 6 h, 12 h and 24 h after starting HFNC.

Results

In total 85 patients were included (age, 64.51 + 11.78 years; male, 69.4%). HFNC failed in 47 (55.3%) patients, of whom 45 (97.8%) were initially managed with noninvasive ventilation (NIV). ROX index at 24 h was the best predictor of HFNC success (AUC 0.826, 95%CI 0.593–1.00, p = 0.015) with a cut-off point of 5.35 (S 0.91, Sp 0.79, PPV 0.92, NPP 0.79). In multivariate logistic regression analysis ROX index at 24 h proved the best predictor of HFNC success.

Conclusions

ROX index at 24 h with a cut-off point of 5.35 predicts HFNC success in patients with SARS-Cov-2-induced ARF.

Bronchoscopy during COVID-19 pandemic, ventilatory strategies and procedure measures

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has changed bronchoscopy practices worldwide. Bronchoscopy is a high-risk aerosol-generating procedure with a potential for direct SARS-CoV-2 exposure and hospital-acquired infection. Current guidelines about personal protective equipment and environment considerations represent key competencies to minimize droplets dispersion and reduce the risk of transmission. Different measures should be put in field based on setting, patient's clinical characteristics, urgency and indications of bronchoscopy. The use of this technique in SARS-CoV-2 patients is reported primarily for removal of airway plugs and for obtaining microbiological culture samples. In mechanically ventilated patients with SARS-CoV-2, bronchoscopy is commonly used to manage complications such as hemoptysis, atelectasis or lung collapse when prone positioning, physiotherapy or recruitment maneuvers have failed. Further indications are represented by assistance during percutaneous tracheostomy. Continuous positive airway pressure, non-invasive ventilation support and high flow nasal cannula oxygen are frequently used in patient affected by Coronavirus Disease-2019 (COVID-19): management of patients' airways and ventilation strategies differs from bronchoscopy indications, patient's clinical status and in course or required ventilatory support. Sedation is usually administered by the pulmonologist (performing the bronchoscopy) or by the anesthetist depending on the complexity of the procedure and the level of sedation required. Finally, elective bronchoscopy for diagnostic indications during COVID-19 pandemic should be carried on respecting rigid standards which allow to minimize potential viral transmission, independently from patient's COVID-19 status. This narrative review aims to evaluate the indications, procedural measures and ventilatory strategies of bronchoscopy performed in different settings during COVID-19 pandemic.