Effectiveness of nasal highflow in hypercapnic COPD patients is flow and leakage dependent

Nasal High-Flow (NHF) Improves Ventilation in Patients with Interstitial Lung Disease (ILD)-A Physiological Study

INTRODUCTION

Acute hypercapnic respiratory failure has a poor prognosis in patients with interstitial lung disease (ILD). Recent data demonstrated a positive effect of nasal high-flow (NHF) in patients with acute hypoxemic respiratory failure. Preliminary data also show benefits in several hypercapnic chronic lung diseases.

OBJECTIVES

The aim of this study was to characterize flow-dependent changes in mean airway pressure, breathing volumes, and breathing frequency and decreases in PCO2.

METHODS

Mean airway pressure was measured in the nasopharyngeal space. To evaluate breathing volumes, a polysomnographic device was used (16 patients). All subjects received 20, 30, 40, and 50 L/min and-to illustrate the effects-nCPAP and nBiPAP. Capillary blood gas analyses were performed in 25 hypercapnic ILD subjects before and 5 h after the use of NHF. Additionally, comfort and dyspnea during the use of NHF were surveyed.

RESULTS

NHF resulted in a small flow-dependent increase in mean airway pressure. Tidal volume was unchanged and breathing rate decreased. The calculated minute volume decreased by 20 and 30 L/min NHF breathing. In spite of this fact, hypercapnia decreased at a flow rate of 24 L/min. Additionally, an improvement in dyspnea was observed.

CONCLUSIONS

NHF leads to a reduction in paCO2. This is most likely achieved by a washout of the respiratory tract and a reduction in functional dead space. NHF enhances the effectiveness of breathing in ILD patients by the reduction in respiratory rate. In summary, NHF works as an effective ventilatory support device in hypercapnic ILD patients.

The effects of flow settings during high-flow nasal cannula support for adult subjects: a systematic review

BACKGROUND

During high-flow nasal cannula (HFNC) therapy, flow plays a crucial role in the physiological effects. However, there is no consensus on the initial flow settings and subsequent titration. Thus, we aimed to systematically synthesize the effects of flows during HFNC treatment.

METHODS

In this systematic review, two investigators independently searched PubMed, Embase, Web of Science, Scopus, and Cochrane for in vitro and in vivo studies investigating the effects of flows in HFNC treatment published in English before July 10, 2022. We excluded studies that investigated the pediatric population (< 18 years) or used only one flow. Two investigators independently extracted the data and assessed the risk of bias. The study protocol was prospectively registered with PROSPERO, CRD42022345419.

RESULTS

In total, 32,543 studies were identified, and 44 were included. In vitro studies evaluated the effects of flow settings on the fraction of inspired oxygen (F_IO₂), positive end-expiratory pressure, and carbon dioxide (CO₂) washout. These effects are flow-dependent and are maximized when the flow exceeds the patient peak inspiratory flow, which varies between patients and disease conditions. In vivo studies report that higher flows result in improved oxygenation and dead space washout and can reduce work of breathing. Higher flows also lead to alveolar overdistention in non-dependent lung regions and patient discomfort. The impact of flows on different patients is largely heterogeneous.

INTERPRETATION

Individualizing flow settings during HFNC treatment is necessary, and titrating flow based on clinical findings like oxygenation, respiratory rates, ROX index, and patient comfort is a pragmatic way forward.

Asymmetrical nasal high flow ventilation improves clearance of CO2 from the anatomical dead space and increases positive airway pressure

Positive airway pressure that dynamically changes with breathing, and clearance of anatomical dead space are the key mechanisms of noninvasive respiratory support with nasal high flow (NHF). Pressure mainly depends on flow rate and nare occlusion. The hypothesis is that an increase in asymmetrical occlusion of the nares leads to an improvement in dead-space clearance resulting in a reduction in re-breathing. Clearance was investigated with volumetric capnography in an adult upper-airway model, which was ventilated by a lung simulator with entrained carbon dioxide (CO₂) at respiratory rates (RR) of 15-45 min^-1 and at 18 min^-1 with chronic obstructive pulmonary disease (COPD) breathing patterns. Clearance was assessed at NHF of 20-60 L/min with a symmetrical interface (SI) and an asymmetrical interface (AI). CO₂ kinetics visualized by infrared spectroscopy and mathematical modeling were used to study the mechanisms of clearance. At a higher RR (35 min^-1) and NHF of 60 L/min, clearance in the upper airway was significantly higher with the AI when compared with the SI (29.64 ± 9.96%, P < 0.001), as opposed to at a lower RR (15 min^-1) (1.40 ± 6.25%, P > 0.05), (means ± SD). With COPD breathing, clearance by NHF was reduced but significantly improved with the AI by 45.93% relative to the SI at NHF 20 L/min (P < 0.0001). The maximum pressure achieved with the AI was 6.6 cmH₂O and NHF was 60 L/min at the end of expiration. Pressure differences between nasal cavities led to the reverse flow observed in the optical model. Asymmetrical NHF increases dead-space clearance by reverse flow through the choanae and accelerates purging of expired gas via the less occluded nare.NEW & NOTEWORTHY The asymmetrical interface generated reverse flow in the nasal cavities and across the choana, which led to unidirectional purging of expired gas from the upper airways. This accelerated the clearance of anatomical dead space and reduced re-breathing while increased resistance to flow resulted in higher positive end-expiratory pressure (PEEP). These findings are relevant to patients with elevated respiratory rates or with expiratory flow limitations where dead-space clearance by NHF can be substantially reduced.

Comparison of high-flow nasal cannula and conventional oxygen therapy for high-risk patients during bronchoscopy examination: protocol for a randomized controlled trial

INTRODUCTION

High-flow nasal cannula (HFNC) has been proven to improve oxygenation and avoid intubation in hypoxemic patients. It has also been utilized during endoscopy examination to reduce the incidence of hypoxia. However, little is known about the effects of HFNC versus conventional oxygen therapy (COT) on oxygenation during bronchoscopy examination via nasal route; particularly, no study has compared the use of HFNC with that of COT at similar F_IO₂ for patients who have high-risk factors of desaturation during bronchoscopy examination.

METHODS AND ANALYSIS

This randomized controlled trial will be implemented in four academic centers in China. Patients who have high-risk factors including hypoxemia, hypercapnia, morbid obesity, and narrow airway will be enrolled to use HFNC or COT during bronchoscopy examination. In the HFNC group, the initial gas flow will be set at 50 L/min with a fraction of inspired oxygen (F_IO₂) at 0.45, if the patient tolerates, the flow can be increased to 60L/min at most, while in the COT group, oxygen flow will be set at 6 L/min via a conventional nasal cannula. After 5 min pre-oxygenation, the bronchoscope will be inserted via the nasal route. Vital signs, oxygenation (SpO₂), and transcutaneous CO₂ (PtCO₂) will be continuously monitored. The primary outcome is the incidence of hypoxemia, defined as SpO₂ < 90% for 10 s during bronchoscopy examination, and secondary outcomes include the need for treatment escalation and adverse events.

DISCUSSION

Hypoxia is a common complication of bronchoscopy, our study attempted to demonstrate that HFNC may reduce the probability of hypoxia during bronchoscopy in high-risk patients. The results will be disseminated through peer-reviewed journals and national and international conferences.

TRIAL REGISTRATION

http://www.chictr.org.cn/ : ChiCTR2100055038. Registered on 31 December 2021.

Home High-Flow Nasal Cannula Oxygen Therapy for Stable Hypercapnic COPD: A Randomized Clinical Trial

Rationale: The long-term effects of using a high-flow nasal cannula for chronic hypercapnic respiratory failure caused by chronic obstructive pulmonary disease remain unclear. Objectives: To assess whether long-term high-flow nasal cannula use reduces the number of exacerbations and improves other physiological parameters in patients with chronic hypercapnic respiratory failure caused by chronic obstructive pulmonary disease. Methods: We enrolled 104 participants (aged ⩾40 yr) with daytime hypercapnia (Global Initiative for Chronic Obstructive Lung Disease stages 2-4) receiving long-term oxygen therapy (⩾16 h/d for ⩾1 mo) and randomly assigned them to high-flow nasal cannula/long-term oxygen therapy and long-term oxygen therapy groups. The primary endpoint was the moderate or severe exacerbation rate. We compared changes from baseline in arterial blood gas values, peripheral oxygen saturation, pulmonary function, health-related quality-of-life scores, and the 6-minute-walk test. Measurements and Main Results: High-flow nasal cannula use significantly reduced the rate of moderate/severe exacerbations (unadjusted mean count 1.0 vs. 2.5, a ratio of the adjusted mean count between groups [95% confidence interval] of 2.85 [1.48-5.47]) and prolonged the duration without moderate or severe exacerbations. The median time to first moderate or severe exacerbation in the long-term oxygen therapy group was 25 (14.1-47.4) weeks; this was not reached in the high-flow nasal cannula/long-term oxygen therapy group. High-flow nasal cannula use significantly improved health-related quality of life scores, peripheral oxygen saturation, and specific pulmonary function parameters. No safety concerns were identified. Conclusions: A high-flow nasal cannula is a reasonable therapeutic option for patients with stable hypercapnic chronic obstructive pulmonary disease and a history of exacerbations. Clinical trial registered with www.umin/ac.jp (UMIN000028581) and www.clinicaltrials.gov (NCT03282019).

An Analysis of the Effect of Noninvasive Positive Pressure Ventilation on Patients with Respiratory Failure Complicated by Diabetes Mellitus

Objective

To observe the clinical effectiveness of noninvasive positive pressure ventilation in patients with respiratory failure complicated by diabetes.

Methods

From May 2021 to May 2022, 90 patients with respiratory failure complicated by diabetes treated in our hospital were recruited and randomly assigned to receive either medication (control group) or noninvasive positive pressure ventilation (study group), with 45 patients in each group. The clinical endpoint was therapeutic outcomes.

Results

Noninvasive positive pressure ventilation resulted in significantly lower Self-Rating Anxiety Scale (SAS) and Self-Rating Depression Scale (SDS) scores versus medications (P < 0.05). Patients with noninvasive positive pressure ventilation showed better pulmonary function indices versus those with medications (P > 0.05). There was no significant difference in arterial oxygen (PaO₂), carbon dioxide partial pressure (PaCO₂), and arterial oxygen pressure/inspired fraction of O₂ (PaO₂/FiO₂) between the two groups prior to the intervention (P > 0.05). However, patients in the study group had significantly elevated PaO₂ and PaO₂/FiO₂ and lower PaCO₂ levels than those in the control group (P < 0.05). Following the intervention, noninvasive positive pressure ventilation resulted in significantly lower inflammatory factor levels versus medications (P > 0.05). After the intervention, markedly better glucose control was observed in the study group versus the control group (P < 0.05). The incidence of complications in the control group was 2.38%, which was significantly lower than that of the control group (16.67) (P < 0.05).

Conclusion

Noninvasive positive pressure ventilation effectively suppresses the inflammatory response, improves the blood gas analysis index, and eliminates the negative emotions of patients, thereby maintaining hemodynamic stability and improving clinical efficacy with a better safety profile. Further studies are recommended prior to clinical promotion.

Efficacy of Nasal High-Flow Oxygen Therapy in Chronic Obstructive Pulmonary Disease Patients in Long-Term Oxygen and Nocturnal Non-Invasive Ventilation during Exercise Training

High-flow oxygen therapy (HFOT) improves gas exchange and dead space washout and reduces the level of work required for breathing. This study aimed to evaluate pulmonary rehabilitation (PR) combined with HFOT in COPD patients treated with nocturnal non-invasive ventilation (NIV) and long-term oxygen therapy (LTOT). In particular, we sought to discover whether the addition of HFOT during exercise training could improve patients’ performance, mainly with regard to their Six-Minute Walking Test (6MWT) outcomes, and reduce the exacerbation rates, periods of rehospitalization or need to resort to unscheduled visits. Thirty-one COPD subjects (13 female) who used nocturnal NIV were included in a randomized controlled trial and allocated to one of two groups: the experimental group (EG), with 15 subjects, subjected to PR with HFOT; and the control group (CG), with 16 subjects, subjected to PR without HFOT. The primary outcome of the study was the observation of changes in the 6MWT. The secondary outcome of the study was related to the rate of exacerbation and hospitalization. Data were collected at baseline and after one, two and three cycles of cycle-ergometer exercise training performed in 20 supervised sessions of 40 min thrice per week, with a washout period of 3 months between each rehabilitation cycle. Statistical significance was not found for the 6MWT distance (W = 0.974; p = 0.672) at the last follow-up, but statistical significance was found for the Borg scale in regard to dyspnea (W = 2.50; p < 0.001) and fatigue (W = 2.00; p < 0.001). HFOT may offer a positive option for dyspnea-affected COPD patients in the context of LTOT and nocturnal NIV.

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.

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 versus conventional oxygen therapy in acute COPD exacerbation with mild hypercapnia: a multicenter randomized controlled trial

Background

High-flow nasal cannula (HFNC) can improve ventilatory function in patients with acute COPD exacerbation. However, its effect on clinical outcomes remains uncertain.

Methods

This randomized controlled trial was conducted from July 2017 to December 2020 in 16 tertiary hospitals in China. Patients with acute COPD exacerbation with mild hypercapnia (pH ≥ 7.35 and arterial partial pressure of carbon dioxide > 45 mmHg) were randomly assigned to either HFNC or conventional oxygen therapy. The primary outcome was the proportion of patients who met the criteria for intubation during hospitalization. Secondary outcomes included treatment failure (intolerance and need for non-invasive or invasive ventilation), length of hospital stay, hospital cost, mortality, and readmission at day 90.

Results

Among 337 randomized patients (median age, 70.0 years; 280 men [83.1%]; median pH 7.399; arterial partial pressure of carbon dioxide 51 mmHg), 330 completed the trial. 4/158 patients on HFNC and 1/172 patient on conventional oxygen therapy met the criteria for intubation (P = 0.198). Patients progressed to NPPV in both groups were comparable (15 [9.5%] in the HFNC group vs. 22 [12.8%] in the conventional oxygen therapy group; P = 0.343). Compared with conventional oxygen therapy, HFNC yielded a significantly longer median length of hospital stay (9.0 [interquartile range, 7.0–13.0] vs. 8.0 [interquartile range, 7.0–11.0] days) and a higher median hospital cost (approximately $2298 [interquartile range, $1613–$3782] vs. $2005 [interquartile range, $1439–$2968]). There were no significant differences in other secondary outcomes between groups.

Conclusions

In this multi-center randomized controlled study, HFNC compared to conventional oxygen therapy did not reduce need for intubation among acute COPD exacerbation patients with mild hypercapnia. The future studies should focus on patients with acute COPD exacerbation with respiratory acidosis (pH < 7.35). However, because the primary outcome rate was well below expected, the study was underpowered to show a meaningful difference between the two treatment groups.

Trial registration: NCT03003559. Registered on December 28, 2016.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03973-7.

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.

Nasal pressure swings as the measure of inspiratory effort in spontaneously breathing patients with de novo acute respiratory failure

Background

Excessive inspiratory effort could translate into self-inflicted lung injury, thus worsening clinical outcomes of spontaneously breathing patients with acute respiratory failure (ARF). Although esophageal manometry is a reliable method to estimate the magnitude of inspiratory effort, procedural issues significantly limit its use in daily clinical practice. The aim of this study is to describe the correlation between esophageal pressure swings (ΔP_es) and nasal (ΔP_nos) as a potential measure of inspiratory effort in spontaneously breathing patients with de novo ARF.

Methods

From January 1, 2021, to September 1, 2021, 61 consecutive patients with ARF (83.6% related to COVID-19) admitted to the Respiratory Intensive Care Unit (RICU) of the University Hospital of Modena (Italy) and candidate to escalation of non-invasive respiratory support (NRS) were enrolled. Clinical features and tidal changes in esophageal and nasal pressure were recorded on admission and 24 h after starting NRS. Correlation between ΔP_es and ΔP_nos served as primary outcome. The effect of ΔP_nos measurements on respiratory rate and ΔP_es was also assessed.

Results

ΔP_es and ΔP_nos were strongly correlated at admission (R² = 0.88, p < 0.001) and 24 h apart (R² = 0.94, p < 0.001). The nasal plug insertion and the mouth closure required for ΔP_nos measurement did not result in significant change of respiratory rate and ΔP_es. The correlation between measures at 24 h remained significant even after splitting the study population according to the type of NRS (high-flow nasal cannulas [R² = 0.79, p < 0.001] or non-invasive ventilation [R² = 0.95, p < 0.001]).

Conclusions

In a cohort of patients with ARF, nasal pressure swings did not alter respiratory mechanics in the short term and were highly correlated with esophageal pressure swings during spontaneous tidal breathing. ΔP_nos might warrant further investigation as a measure of inspiratory effort in patients with ARF.

Trial registration: NCT03826797. Registered October 2016.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03938-w.

Nasal high-flow compared to non-invasive ventilation in treatment of acute acidotic hypercapnic exacerbation of chronic obstructive pulmonary disease-protocol for a randomized controlled noninferiority trial (ELVIS)

Background

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) have a major negative impact on health status, rates of hospitalization, readmission, disease progression and mortality. Non-invasive ventilation (NIV) is the standard therapy for hypercapnic acidotic respiratory failure in AECOPD. Despite its beneficial effects, NIV is often poorly tolerated (11–34 % failure rate). An increasing number of studies have documented a beneficial effect of nasal high-flow (NHF) in acute hypercapnia. We designed a prospective, randomized, multi-centre, open label, non-inferiority trial to compare treatment failure in nasal NHF vs NIV in patients with acidotic hypercapnic AECOPD.

Methods

The study will be conducted in about 35 sites in Germany. Patients with hypercapnic AECOPD with respiratory acidosis (pH < 7.35) will be randomized 1:1 to NIV or NHF. The primary outcome is the combined endpoint of intubation, treatment failure or death at 72 h. The switch from one to the other device marks a device failure but acts as a rescue treatment in absence of intubation criteria. A sample size of 720 was calculated to have 80% power for showing that NHF is non-inferior to NIV with a margin of 8 percentage points. Linear regression will be used for the confirmatory analysis.

Discussion

If NHF is shown to be non-inferior to NIV in acidotic hypercapnic AECOPD, it could become an important alternative treatment.

Trial registration

ClinicalTrials.gov, NCT04881409, Registered on May 11, 2021

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-021-05978-z.

β Agonist Delivery by High-Flow Nasal Cannula During COPD Exacerbation: A Prospective Physiological Study

BACKGROUND

Whereas high-flow nasal cannula (HFNC) oxygen therapy is increasingly used in patients with exacerbation of COPD, the effectiveness of β ₂ agonist nebulization through HFNC has been poorly assessed. We hypothesized that salbutamol vibrating-mesh nebulization through HFNC improves pulmonary function tests in subjects with COPD.

METHODS

We conducted a physiological crossover study including subjects admitted to the ICU for severe exacerbation of COPD. After subject improvement allowing a 3-h washout period without bronchodilator, pulmonary function tests were performed while breathing through HFNC alone and after salbutamol vibrating-mesh nebulization through HFNC. The primary end point consisted in the changes in FEV₁ before and after salbutamol nebulization. Secondary end points included the changes in FVC, peak expiratory flow (PEF), airway resistance, and clinical parameters.

RESULTS

Among the 15 subjects included, mean (SD) FEV₁ significantly increased after salbutamol nebulization from 931 mL (383) to 1,019 (432), mean difference +87 mL (95% CI 30-145) (P = .006). Similarly, FVC and PEF significantly increased, +174 mL (95% CI 66-282) (P = .004) and +0.3 L/min (95% CI 0-0.6) (P = .037), respectively. Airway resistances and breathing frequency did not significantly differ, whereas heart rate significantly increased after nebulization.

CONCLUSIONS

In subjects with severe exacerbation of COPD, salbutamol vibrating-mesh nebulization through HFNC induced a significant bronchodilator effect with volume and flow improvement.

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.

Noninvasive Tidal Volume Measurements, Using a Time-of-Flight Camera, Under High-Flow Nasal Cannula-A Physiological Evaluation, in Healthy Volunteers

OBJECTIVES

The mechanisms of high-flow nasal cannula are still debated but may be mediated by the generation of low positive end-expiratory pressure and a washout of the airway dead space. The aims of this study were to assess the effects of high-flow nasal cannula on tidal volume using a noninvasive method using a time-of-flight camera, under various conditions.

DESIGN

A physiologic evaluation in healthy volunteers.

SETTING

An university hospital ICU.

SUBJECTS

Ten healthy volunteers were included in a physiologic study (CamOpt study, ClinicalTrials.gov identifier: NCT04096183).

INTERVENTIONS

All volunteers were submitted to 12 different conditions (i.e., gas flow [baseline = 0; 30-60 L/min]; mouth [open/closed]; respiratory rate [baseline; baseline + 10 breaths/min]). Tidal volume measurements were performed every minute, during a 6-minute recording period. In all combinations, reference respiratory rate was measured by using chronometric evaluation, over a 30-second period (RRREF), and by using the time-of-flight camera (RRTOF).

MEASUREMENTS AND MAIN RESULTS

Tidal volume increased while increasing gas flow whatever the respiratory rate and mouth condition (p < 0.001). Similar results were observed whatever the experimental conditions (p < 0.01), except one (baseline respiratory rate + 10 breaths/min and mouth closed). Tidal volume increased while decreasing respiratory rate (p < 0.001) and mouth closing (p < 0.05). Proportion of tidal volume greater than 10, 15, and 20 mL/kg changed while increasing the flow. RRTOF was in agreement with RRREF (intraclass correlation coefficient, 0.96), with a low mean bias (0.55 breaths/min) and acceptable deviation.

CONCLUSIONS

Time-of-flight enables to detect tidal volume changes under various conditions of high-flow nasal cannula application. Tidal volume increased significantly while increasing gas flow and mouth closing. Such technique might be useful to monitor the risk of patient self-inflicted lung injury or under assistance.

Cost-Effectiveness of Domiciliary High Flow Nasal Cannula Treatment in COPD Patients with Chronic Respiratory Failure

PURPOSE

To evaluate the cost-effectiveness of long-term domiciliary high flow nasal cannula (HFNC) treatment in COPD patients with chronic respiratory failure.

PATIENTS AND METHODS

A cohort of 200 COPD patients were equally randomized into usual care ± HFNC and followed for 12 months. The outcome of the analysis was the incremental cost per quality-adjusted life-year (QALY) gained, and the analysis was conducted from a healthcare sector perspective. Data on the patients' health-related quality of life (HRQoL), gathered throughout the trial using the St. George's Respiratory Questionnaire (SGRQ), was converted into EQ-5D-3L health state utility values. Costs were estimated using Danish registers and valued in British pounds (£) at price level 2019. Scenario analyses and probabilistic sensitivity analyses were conducted to assess the uncertainty of the results.

RESULTS

The adjusted mean difference in QALYs between the HFNC group and the control group was 0.059 (95% CI: 0.017; 0.101), and the adjusted mean difference in total costs was £212 (95% CI: -1572; 1995). The analysis resulted in an incremental cost-effectiveness ratio (ICER) of £3605 per QALY gained. At threshold values of £20.000-30.000 per QALY gained, the intervention had an 83-92% probability of being cost-effective. The scenario analyses all revealed ICERs below the set threshold value and demonstrated the robustness of the main result.

CONCLUSION

This is the first cost-effectiveness study on domiciliary HFNC in Europe. The findings demonstrate that long-term domiciliary HFNC treatment is very likely to be a cost-effective addition to usual care for COPD patients with chronic respiratory failure. The results must be interpreted in light of the uncertainty associated with the indirect estimation of health state utilities.

High flow nasal oxygen for acute type two respiratory failure: a systematic review

Background: Acute type two respiratory failure (AT2RF) is characterized by high carbon dioxide levels (PaCO 2 >6kPa). Non-invasive ventilation (NIV), the current standard of care, has a high failure rate. High flow nasal therapy (HFNT) has potential additional benefits such as CO 2 clearance, the ability to communicate and comfort. The primary aim of this systematic review is to determine whether HFNT in AT2RF improves 1) PaCO 2, 2) clinical and patient-centred outcomes and 3) to assess potential harms. Methods: We searched EMBASE, MEDLINE and CENTRAL  (January 1999-January 2021). Randomised controlled trials (RCTs) and cohort studies comparing HFNT with low flow nasal oxygen (LFO) or NIV were included. Two authors independently assessed studies for eligibility, data extraction and risk of bias. We used Cochrane risk of bias tool for RCTs and Ottawa-Newcastle scale for cohort studies. Results: From 727 publications reviewed, four RCTs and one cohort study (n=425) were included. In three trials of HFNT vs NIV, comparing PaCO 2 (kPa) at last follow-up time point, there was a significant reduction at four hours (1 RCT; HFNT median 6.7, IQR 5.6 - 7.7 vs NIV median 7.6, IQR 6.3 - 9.3) and no significant difference at  24-hours or five days. Comparing HFNT with LFO, there was no significant difference at 30-minutes. There was no difference in intubation or mortality. Conclusions: This review identified a small number of studies with low to very low certainty of evidence. A reduction of PaCO 2 at an early time point of four hours post-intervention was demonstrated in one small RCT. Significant limitations of the included studies were lack of adequately powered outcomes and clinically relevant time-points and small sample size. Accordingly, systematic review cannot recommend the use of HFNT as the initial management strategy for AT2RF and trials adequately powered to detect clinical and patient-relevant outcomes are urgently warranted.

High flow nasal oxygen for acute type two respiratory failure: a systematic review

Background: Acute type two respiratory failure (AT2RF) is characterized by high carbon dioxide levels (PaCO 2 >6kPa). Non-invasive ventilation (NIV), the current standard of care, has a high failure rate. High flow nasal therapy (HFNT) has potential additional benefits such as CO 2 clearance, the ability to communicate and comfort. The primary aim of this systematic review is to determine whether HFNT in AT2RF improves 1) PaCO 2, 2) clinical and patient-centred outcomes and 3) to assess potential harms. Methods: We searched EMBASE, MEDLINE and CENTRAL  (January 1999-January 2021). Randomised controlled trials (RCTs) and cohort studies comparing HFNT with low flow nasal oxygen (LFO) or NIV were included. Two authors independently assessed studies for eligibility, data extraction and risk of bias. We used Cochrane risk of bias tool for RCTs and Ottawa-Newcastle scale for cohort studies. Results: From 727 publications reviewed, four RCTs and one cohort study (n=425) were included. In three trials of HFNT vs NIV, comparing PaCO 2 (kPa) at last follow-up time point, there was a significant reduction at four hours (1 RCT; HFNT median 6.7, IQR 5.6 - 7.7 vs NIV median 7.6, IQR 6.3 - 9.3) and no significant difference at  24-hours or five days. Comparing HFNT with LFO, there was no significant difference at 30-minutes. There was no difference in intubation or mortality. Conclusions: This review identified a small number of studies with low to very low certainty of evidence. A reduction of PaCO 2 at an early time point of four hours post-intervention was demonstrated in one small RCT. Significant limitations of the included studies were lack of adequately powered outcomes and clinically relevant time-points and small sample size. Accordingly, systematic review cannot recommend the use of HFNT as the initial management strategy for AT2RF and trials adequately powered to detect clinical and patient-relevant outcomes are urgently warranted.

Safety and efficacy of high flow nasal cannula therapy in acute hypercapnic respiratory failure - a retrospective audit

BACKGROUND

While the role of high flow nasal cannulae (HFNC) in the management of respiratory failure continues to expand, few studies describe its use in acute hypercapnic respiratory failure.

AIMS

In this retrospective study we assessed the safety and efficacy of HFNC for treatment of acute hypercapnic respiratory failure.

METHODS

Admissions with acute hypercapnic respiratory failure to a thoracic medicine unit at a tertiary centre between January and August 2018 were included if treated with either HFNC or non-invasive ventilation (NIV). The primary outcome was post-treatment change in arterial pCO₂ . Demographics, comorbidities, length of stay, readmission rate and mortality were also collected.

RESULTS

64 patients were identified, comprising 69 presentations grouped according to initial treatment: HFNC (n=24) or NIV (n=45). Patients in the NIV group had more severe blood gas derangement. In both groups, mean arterial pCO₂ improved significantly (-10 (95% CI: -14 to -6) mmHg) from baseline with no evidence of a differential effect between groups. Six (25%) patients were transitioned from HFNC to NIV, of whom 3 had comorbid obesity and 2 had sleep disordered breathing. No significant differences in hospital length of stay, 30-day readmission rate or 90-day mortality were observed.

CONCLUSIONS

HFNC may be a reasonable initial treatment for patients with mild acute hypercapnic respiratory failure who do not have comorbid obesity or sleep disordered breathing. Prospective study may help identify clinical factors or phenotypes predictive of success with this treatment modality. This article is protected by copyright. All rights reserved.

Acute Responses to Oxygen Delivery via High Flow Nasal Cannula in Patients with Severe Chronic Obstructive Pulmonary Disease-HFNC and Severe COPD

Differences in oxygen delivery methods to treat hypoxemia have the potential to worsen CO₂ retention in chronic obstructive lung disease (COPD). Oxygen administration using high flow nasal cannula (HFNC) has multiple physiological benefits in treating respiratory failure including reductions in PaCO₂ in a flow-dependent manner. We hypothesized that patients with COPD would develop worsening hypercapnia if oxygen fraction was increased without increasing flow rate. We evaluated the acute response to HFNC in subjects with severe COPD when flow remained constant and inspired oxygen was increased. In total, 11 subjects with severe COPD (FEV1 < 50%) on supplemental oxygen with baseline normocapnia (PaCO₂ < 45 mm Hg; n = 5) and hypercapnia (PaCO₂ ≥ 45 mm Hg; n = 6) were studied. Arterial blood gas responses were studied at three timepoints: Baseline, HFNC at a flow rate of 30 L/min at resting oxygen supplementation for 1 h, and FiO₂ 30% above baseline with the same flow rate for the next hour. The primary endpoint was the change in PaCO₂ from baseline. No significant changes in PaCO₂ were noted in response to HFNC applied at baseline FiO₂ in the normocapnic and hypercapnic group. At HFNC with FiO₂ 30% above baseline, the normocapnic group did not show a change in PaCO₂ (baseline: 38.9 ± 1.8 mm Hg; HFNC at higher FiO₂: 38.8 ± 3.1 mm Hg; p = 0.93), but the hypercapnic group demonstrated significant increase in PaCO₂ (baseline: 58.2 ± 9.3 mm Hg; HFNC at higher FiO₂: 63.3 ± 10.9 mm Hg; p = 0.025). We observed worsening hypercapnia in severe COPD patients and baseline hypercapnia who received increased oxygen fraction when flow remained constant. These data show the need for careful titration of oxygen therapy in COPD patients, particularly those with baseline hypercapnia when flow rate is unchanged.

Development in PaCO2 over 12 months in patients with COPD with persistent hypercapnic respiratory failure treated with high-flow nasal cannula-post-hoc analysis from a randomised controlled trial

Introduction

Persistent hypercapnic failure in chronic obstructive pulmonary disease (COPD) is associated with poor prognosis. Long-term home non-invasive ventilation is recommended for patients with PaCO₂ >7.0 kPa. Domiciliary high-flow nasal cannula (HFNC) reduces PaCO₂ in short-term studies. This post-hoc analysis examines the effect of HFNC on PaCO₂ levels, exacerbations and admissions in patients with COPD with persistent hypercapnic and hypoxic failures.

Methods

The original trial included 74 long-term oxygen-treated patients (31 HFNC treated/43 controls) with persistent hypercapnic failure (PaCO₂ >6 kPa) who completed the 12-month study period. Baseline data included age, sex, blood gases, exacerbations and hospital admissions in the previous year. Data on blood gases were also recorded at 6 and 12 months for all patients. In addition, acute changes in blood gases after 30 min of HFNC use at site visits were examined, as were exacerbations and hospital admissions during study.

Results

Patients were comparable at baseline. After 12 months there was a 1.3% decrease in PaCO₂ in patients using HFNC and a 7% increase in controls before HFNC use on site (p=0.003). After 30 min of HFNC at visits PaCO₂ changed significantly, with comparable reductions, at 0, 6 and 12 months, including for controls who tried HFNC at study end (p<0.001). The exacerbation rate increased, compared with 12 months prestudy, by 2.2/year for controls (p<0.001) and 0.15/year for HFNC-treated patients (p=0.661). Hospital admission rates increased in the control group,+0.3/year from prestudy (p=0.180), And decreased by 0.67/year (p=0.013)for HFNC-treated patients.

Conclusion

This post-hoc analysis indicates that HFNC stabilises patients with COPD with persistent hypoxic and hypercapnic failures, in terms of PaCO₂, exacerbations and number of hospitalisations, whereas those not receiving HFNC worsened. This suggests that HFNC is a possible treatment for patients with persistent hypercapnic COPD.

High-Flow Nasal Cannula in Hypercapnic Respiratory Failure: A Systematic Review and Meta-Analysis

Background

Although the efficacy and safety of high-flow nasal cannula (HFNC) in hypoxemic respiratory failure are widely recognized, it is yet unclear whether HFNC can effectively reduce the intubation rate and mortality in hypercapnic respiratory failure. We performed a systematic review and meta-analysis to assess the safety and efficiency of HFNC in these patients.

Methods

A systematic search of PubMed, Embase, and Cochrane Library (CENTRAL) was carried out. Two reviewers independently screened all references according to the inclusion criteria. We used the Cochrane risk-of-bias tool and the Newcastle–Ottawa Quality Assessment Scale to assess the quality of randomized controlled trials (RCTs) and cohort studies, respectively. Data from eligible trials were extracted for the meta-analysis.

Results

Eight studies with a total of 621 participants were included (six RCTs and two cohort studies). Our analysis showed that HFNC is noninferior to noninvasive ventilation (NIV) with respect to intubation rate in both RCTs (OR = 0.92, 95% CI: 0.45–1.88) and cohort studies (OR = 0.94, 95% CI: 0.55–1.62). Similarly, the analysis of cohort studies showed no difference in reducing mortality rates (OR = 0.96, 95% CI: 0.42–2.20). Based on RCTs, NIV seemed more effective in reducing mortality (OR = 1.33, 95% CI: 0.68–2.60), but the intertreatment difference was not statistically significant. Furthermore, no significant differences were found between HFNC and NIV relating to change of blood gas analysis or respiratory rate (MD = −0.75, 95% CI: −2.6 to 1.09). Likewise, no significant intergroup differences were found with regard to intensive care unit stay (SMD = −0.07, 95% CI: 0.26 to 0.11). Due to a physiological friendly interface and variation, HFNC showed a significant advantage over NIV in patients' comfort and complication of therapy.

Conclusion

Despite the limitations noted, HFNC may be an effective and safe alternative to prevent endotracheal intubation and mortality when NIV is unsuitable in mild-to-moderate hypercapnia. Further high-quality studies are needed to validate these findings.

Tolerability and Safety of High-Flow Nasal Therapy in Patients Hospitalized with an Exacerbation of COPD

BACKGROUND

The effect of high-flow nasal therapy (HFNT) in individuals with an exacerbation of chronic obstructive pulmonary disease (COPD) and hypercapnia is not well studied. We assessed patient tolerance and impact of air-gas therapy delivered by humidified HFNT (20-35 L/min) on gas exchange in hypercapnic COPD patients during hospitalization for COPD exacerbation. We hypothesized that HFNT use would be safe and well tolerated in individuals hospitalized for COPD exacerbation regardless of the degree of hypercapnia.

METHODS

Patients hospitalized for a COPD exacerbation were included if they were hypercapnic (arterial partial pressure of carbon dioxide [PaCO2] > 45 mmHg), ≥ 10 pack-year history, and agreed to treatment with HFNT, along with daily arterial blood gas (ABG) samples and bedside spirometry. They were placed on a HFNT system following admission for at least 3 days with an air-gas blend to maintain a flow rate between 20-35 L/min and fraction of inspired oxygen (FiO2) titrated to keep oxygen saturation (SaO2) values > 90%. Patient tolerance of HFNT and evidence of clinical deterioration as defined by worsening hypoxia or hypercapnia was the primary endpoint.

RESULTS

Ten consecutive patients participated in the study. The patients had frequent prior exacerbations, were hypercapnic, dyspneic, and gas trapped. Participants received an air-gas flow rate (median [interquartile range (IQR)] 25 (IQR 20-30) L/min and FiO2 of 30 (IQR 30-30) %. There was no increase in PaCO2- levels (p = 0.26) or dyspnea (Borg scale, p= 0.52) while using HFNT. No patient discontinued HFNT, had further decompensation, required non-invasive ventilation or intubation during the study period.

CONCLUSION

In a pilot study, patients experiencing a severe COPD exacerbation were able to tolerate continuous HFNT safely regardless of degree of hypercapnia.

Use of nasal high flow oxygen during acute respiratory failure

Nasal high flow (NHF) has gained popularity among intensivists to manage patients with acute respiratory failure. An important literature has accompanied this evolution. In this review, an international panel of experts assessed potential benefits of NHF in different areas of acute respiratory failure management. Analyses of the physiological effects of NHF indicate flow-dependent improvement in various respiratory function parameters. These beneficial effects allow some patients with severe acute hypoxemic respiratory failure to avoid intubation and improve their outcome. They require close monitoring to not delay intubation. Such a delay may worsen outcome. The ROX index may help clinicians decide when to intubate. In immunocompromised patients, NHF reduces the need for intubation but does not impact mortality. Beneficial physiological effects of NHF have also been reported in patients with chronic respiratory failure, suggesting a possible indication in acute hypercapnic respiratory failure. When intubation is required, NHF can be used to pre-oxygenate patients either alone or in combination with non-invasive ventilation (NIV). Similarly, NHF reduces reintubation alone in low-risk patients and in combination with NIV in high-risk patients. NHF may be used in the emergency department in patients who would not be offered intubation and can be better tolerated than NIV.

The ventilatory effect of high velocity nasal insufflation compared to non-invasive positive-pressure ventilation in the treatment of hypercapneic respiratory failure: A subgroup analysis

PURPOSE

Oxygen delivery by high flow nasal cannula (HFNC) is effective in providing respiratory support. HFNC has utility in clearing the extra-thoracic dead space, making it potentially beneficial in the treatment of hypercapnic respiratory failure. This study compares high velocity nasal insufflation (HVNI), a form of HFNC, to non-invasive positive pressure ventilation (NIPPV) in their abilities to provide ventilatory support for patients with hypercapnic respiratory failure.

METHODS

This is a pre-defined subgroup analysis from a larger randomized clinical trial of Emergency Department (ED) patients with respiratory failure requiring NIPPV support. Patients were randomized to HVNI or NIPPV. Subgroup selection was done for patients with discharge diagnoses of acute hypercapnic respiratory failure or acute exacerbation of chronic obstructive pulmonary disease. The primary outcomes were change in pCO₂ and pH over time. Secondary outcomes were treatment failure and intubation rate.

RESULTS

65 patients with hypercapnic respiratory failure were compared. 34 were randomized to HVNI and 31 to NIPPV. The therapeutic impact on PCO₂ and pH over time was similar in each group. The intubation rate was 5.9% in the HVNI group and 16.1% in the NIPPV group (p = 0.244). The rate of treatment failure was 23.5% in the HVNI group and 25.8% in the NIPPV group (p = 1.0).

CONCLUSION

HVNI may provide ventilatory support similar to NIPPV in patients presenting with acute hypercapnic respiratory failure, but further study is needed to corroborate these findings.

High-Flow Oxygen Therapy Concepts: Time to Standardize Nomenclature and Avoid Confusion

High-flow nasal oxygen systems are rapidly being adopted as an initial noninvasive treatment for acute respiratory failure. However, the term "high-flow nasal cannula" is nonspecific and leads to imprecise communication between physicians, respiratory therapists, and nurses with the potential for patient harm. In this viewpoint and a brief review of the technology, we argue for a change in nomenclature in order to reduce the chance for future clinical, administrative, and research misunderstanding surrounding high-flow nasal oxygen systems.

High-Flow Nasal Cannula: A Promising Oxygen Therapy for Patients with Severe Bronchial Asthma Complicated with Respiratory Failure

Severe bronchial asthma complicated with respiratory failure, a common critical illness in respiratory medicine, may be life-threatening. High-flow nasal cannula (HFNC) is a novel oxygen therapy technique developed in recent years. HFNC was applied in this study for treating adult patients with severe bronchial asthma complicated with respiratory failure. Its efficacy was analyzed comparatively to conventional oxygen therapy (COT). HFNC and COT were randomly performed based on conventional treatment. The HFNC group was similar to COT-treated patients in terms of response rate, with no significant difference in efficacy between the two groups. In patients with bronchial asthma, effectively increased PO₂ and reduced PCO₂ were observed after treatment in both groups. However, HFNC was more efficient than COT in elevating PO₂ in patients with severe bronchial asthma complicated with respiratory failure, while no statistically significant difference in PCO₂ reduction was found between the two groups. Heart rate (HR) and respiratory rate (RR) between the two groups on admission (0 h) and at 2, 8, 24, and 48 h after admission were compared. Both indicators significantly decreased with time. No significant differences in HR and RR were found between the groups at 0, 2, and 8 h after admission. However, these indicators were significantly lower in the HFNC group compared with the COT group at 24 and 48 h after admission. HFNC could significantly elevate PO₂ and reduce HR and RR. Thus, it is a promising option for patients with severe bronchial asthma complicated with respiratory failure.

Nasal High Flow Use in COPD Patients with Hypercapnic Respiratory Failure: Treatment Algorithm & Review of the Literature

Nasal high flow (NHF) therapy has recently gained attention as a new respiratory support system and is increasingly being utilized in every day clinical practice. Recent studies suggest that it may also be effective in patients with hypercapnia and suggest NHF as a possible alternative for patients who cannot tolerate standard noninvasive ventilation. The present review discusses the mechanisms of action that make NHF potentially suitable for chronic obstructive pulmonary disease (COPD) patients and evaluates the current evidence of NHF use for treatment of stable hypercapnic COPD patients as well as acute hypercapnic exacerbation of COPD. An algorithm is also proposed for the clinical application of NHF in patients with acute hypercapnic exacerbation of COPD, based on current literature.

Effects of high-flow nasal cannula in patients with persistent hypercapnia after an acute COPD exacerbation: a prospective pilot study

BACKGROUND

Persistent hypercapnia after COPD exacerbation is associated with excess mortality and early rehospitalization. High Flow Nasal cannula (HFNC), may be theoretically an alternative to long-term noninvasive ventilation (NIV), since physiological studies have shown a reduction in PaCO2 level after few hours of treatment. In this clinical study we assessed the acceptability of HFNC and its effectiveness in reducing the level of PaCO₂ in patients recovering from an Acute Hypercapnic Respiratory Failure (AHRF) episode. We also hypothesized that the response in CO₂ clearance is dependent on baseline level of hypercapnia.

METHODS

Fifty COPD patients recovering from an acute exacerbation and with persistent hypercapnia, despite having attained a stable pH (i.e. pH > 7,35 and PaCO₂ > 45 mmHg on 3 consecutive measurements), were enrolled and treated with HFNC for at least 8 h/day and during the nighttime RESULTS: HFNC was well tolerated with a global tolerance score of 4.0 ± 0.9. When patients were separated into groups with or without COPD/OSA overlap syndrome, the "pure" COPD patients showed a statistically significant response in terms of PaCO₂ decrease (p = 0.044). In addition, the subset of patients with a lower pH at enrolment were those who responded best in terms of CO₂ clearance (score test for trend of odds, p = 0.0038).

CONCLUSIONS

HFNC is able to significantly decrease the level of PaCO₂ after 72 h only in "pure" COPD patients, recovering from AHRF. No effects in terms of CO2 reduction were found in those with overlap syndrome. The present findings will help guide selection of the best target population and allow a sample size calculation for future long-term randomized control trials of HFNC vs NIV.

TRIAL REGISTRATION

This study is registered with www. clinicaltrials.gov with identifier number NCT03759457.

Dose Response to Transnasal Pulmonary Administration of Bronchodilator Aerosols via Nasal High-Flow Therapy in Adults with Stable Chronic Obstructive Pulmonary Disease and Asthma

BACKGROUND

There has been increasing interest in transnasal pulmonary aerosol administration, but the dose-response relationship has not been reported.

OBJECTIVES

To determine the accumulative bronchodilator dose at which patients with stable mild-to-moderate asthma and chronic obstructive pulmonary disease (COPD) achieve similar spirometry responses before and after bronchodilator tests using albuterol via a metered dose inhaler with a valved holding chamber (MDI + VHC).

METHOD

Adult patients who met ATS/ERS criteria for bronchodilator responses in pulmonary function laboratory were recruited and consented to participate. After a washout period, patients received escalating doubling dosages (0.5, 1, 2, and 4 mg) of albuterol in a total volume of 2 mL delivered by vibrating mesh nebulizer via a nasal cannula at 37°C with a flow rate of 15-20 L/min using a Venturi air entrainment device. Spirometry was measured at baseline and after each dose. Titration was stopped when an additional forced expiratory volume in 1 second (FEV1) improvement was <5%.

RESULTS

42 patients (16 males) with stable mild-to-moderate asthma (n = 29) and COPD (n = 13) were enrolled. FEV1 increment after a cumulative dose of 1.5 mg of albuterol via nasal cannula at 15-20 L/min was similar to 4 actuations of MDI + VHC (0.34 ± 0.18 vs. 0.34 ± 0.12 L, p = 0.878). Using ATS/ERS criteria of the bronchodilator test, 33.3% (14/42) and 69% (29/42) of patients responded to 0.5 and 1.5 mg of albuterol, respectively.

CONCLUSIONS

With a nasal cannula at 15-20 L/min, transnasal pulmonary delivery of 1.5 mg albuterol resulted in similar bronchodilator response as 4 actuations of MDI + VHC.

Effectiveness of high-flow nasal oxygen therapy in management of acute hypoxemic and hypercapnic respiratory failure

Background

High-flow nasal oxygen therapy (HFNOT) therapy has been increasingly used in patients with acute hypoxemic (Type I) respiratory failure (RF). Meanwhile indications and clinical effectiveness of HFNOT in patients with hypercapnic (Type II) RF remain controversial. The aim of our study was to evaluate the outcomes of primary HFTNOT in patients with hypoxemic and hypercapnic RF.

Materials and methods

We conducted a retrospective observational study of patients diagnosed with severe community acquired pneumonia (CAP), who required HFNC oxygen therapy for hypoxemia. Primary end-point was intubation or escalation to NIV rate after HFNOT. The secondary endpoint was the 30-day mortality after an admission regardless of the cause.

Results

Analysis was conducted on all 51 (n = 51) patients. Of these, 32 (63%) were diagnosed with Type I RF and 19 (37%) with Type II RF. The partial pressure of arterial carbon dioxide (PaCO₂) in Type I RF patients was 34.05 mmHg at admission and decreased to 33.07 mmHg after 1 hour of HFNOT. In patients with Type II RF PaCO₂ decreased from 56.47 to 54.97 mmHg. In Type I RF successful outcome was achieved in 25 patients (78%) compared to 11 patients (58%) with Type II RF. Escalation was required in seven patients with Type I RF and eight patients in Type II group. There were no mortalities in our population group.

Conclusions

Our data suggest that HFNOT can be effectively used in Type I and Type II RF. Clinicians should be cautious identifying patients at risk of escalation. A larger population group study is needed to identify predictors of HFNOT failure.

Exhaled air dispersion during high-flow nasal cannula therapy versus CPAP via different masks

BACKGROUND

High-flow nasal cannula (HFNC) is an emerging therapy for respiratory failure but the extent of exhaled air dispersion during treatment is unknown. We examined exhaled air dispersion during HFNC therapy versus continuous positive airway pressure (CPAP) on a human patient simulator (HPS) in an isolation room with 16 air changes·h^-1.

METHODS

The HPS was programmed to represent different severity of lung injury. CPAP was delivered at 5-20 cmH₂O via nasal pillows (Respironics Nuance Pro Gel or ResMed Swift FX) or an oronasal mask (ResMed Quattro Air). HFNC, humidified to 37°C, was delivered at 10-60 L·min^-1 to the HPS. Exhaled airflow was marked with intrapulmonary smoke for visualisation and revealed by laser light-sheet. Normalised exhaled air concentration was estimated from the light scattered by the smoke particles. Significant exposure was defined when there was ≥20% normalised smoke concentration.

RESULTS

In the normal lung condition, mean±sd exhaled air dispersion, along the sagittal plane, increased from 186±34 to 264±27 mm and from 207±11 to 332±34 mm when CPAP was increased from 5 to 20 cmH₂O via Respironics and ResMed nasal pillows, respectively. Leakage from the oronasal mask was negligible. Mean±sd exhaled air distances increased from 65±15 to 172±33 mm when HFNC was increased from 10 to 60 L·min^-1. Air leakage to 620 mm occurred laterally when HFNC and the interface tube became loose.

CONCLUSION

Exhaled air dispersion during HFNC and CPAP via different interfaces is limited provided there is good mask interface fitting.

Comparison of high flow nasal cannula with noninvasive ventilation in chronic obstructive pulmonary disease patients with hypercapnia in preventing postextubation respiratory failure: A pilot randomized controlled trial

High flow nasal cannula (HFNC) has been shown to improve extubation outcomes in patients with hypoxemia, but the role of HFNC in weaning patients with chronic obstructive pulmonary disease (COPD) with hypercapnia from invasive ventilation is unclear. We compared the effects of HFNC to noninvasive ventilation (NIV) on postextubation vital signs and arterial blood gases (ABGs) among patients with COPD. Other outcomes included comfort scores, need for bronchoscopy, use of pulmonary medications, and chest physiotherapy. Forty-two COPD patients who had persistent hypercapnia at extubation were assigned randomly to receive HFNC (22) or NIV (20). Twenty patients in each group were enrolled for per-protocol analysis with regard to primary outcomes. Vital signs and ABGs before extubation were similar between groups. At 3 hr after extubation, pH in the NIV group was lower than HFNC group (7.42 ± 0.06 vs. 7.45 ± 0.05, p = 0.01). At 24 hr after extubation, patients' mean arterial pressure (82.97 ± 9.04 vs. 92.06 ± 11.11 mmHg, p = 0.05) and pH (7.42 ± 0.05 vs. 7.46 ± 0.03, p = 0.05) in the NIV group were lower than in the HFNC group. No significant differences were found at 48 hr after extubation. In the HFNC group, comfort scores were better (3.55 ± 2.01 vs. 5.15 ± 2.28, p = 0.02) and fewer patients needed bronchoscopy for secretion management within 48 hr after extubation (2/22 vs. 9/20, p = 0.03). HFNC is a potential alternative to NIV to wean hypercapnic COPD patients with regard to vital signs and ABGs, HFNC improved patients' comfort and secretion clearance.

Non-invasive ventilation or high-flow oxygen therapy: When to choose one over the other?

It has been found that high-flow oxygen therapy (HFOT) can reduce mortality of patients admitted to intensive care unit (ICU) for de novo acute respiratory failure (ARF) as compared to non-invasive ventilation (NIV). HFOT might therefore be considered as a first-line strategy of oxygenation in these patients. The beneficial effects of HFOT may be explained by its good tolerance and by physiological characteristics including delivery of high FiO₂ , positive end expiratory pressure (PEEP) effect and continuous dead space washout contributing to decreased work of breathing. In contrast, NIV should be used cautiously in patients with de novo ARF due to high tidal volumes promoted by pressure support and that may potentially worsen pre-existing lung injury. Although recent studies have reported no benefit and even deleterious effects of NIV in immunocompromised patients with ARF, the experts have recommended its use as a first-line strategy. In patients with acute-on-chronic respiratory failure and respiratory acidosis, it has been clearly shown that NIV is the best strategy of oxygenation. However, HFOT seems able to reverse respiratory acidosis and further studies are needed to evaluate whether HFOT could represent an alternative to standard oxygen. Although NIV is recommended to treat ARF in post-operative patients or to prevent post-extubation respiratory failure in ICU, recent large-scale randomized studies suggest that HFOT could be equivalent to NIV. While recent recommendations have been established from studies comparing NIV with standard oxygen, new studies are needed to compare NIV versus HFOT in order to better define the appropriate indications for both treatments.