Heated Humidified High-Flow Nasal Oxygen in Adults: Mechanisms of Action and Clinical Implications

Ventilatory support after extubation in critically ill patients

The periextubation period represents a crucial moment in the management of critically ill patients. Extubation failure, defined as the need for reintubation within 2-7 days after a planned extubation, is associated with prolonged mechanical ventilation, increased incidence of ventilator-associated pneumonia, longer intensive care unit and hospital stays, and increased mortality. Conventional oxygen therapy is commonly used after extubation. Additional methods of non-invasive respiratory support, such as non-invasive ventilation and high-flow nasal therapy, can be used to avoid reintubation. The aim of this Review is to describe the pathophysiological mechanisms of postextubation respiratory failure and the available techniques and strategies of respiratory support to avoid reintubation. We summarise and discuss the available evidence supporting the use of these strategies to achieve a tailored therapy for an individual patient at the bedside.

Aeration changes induced by high flow nasal cannula are more homogeneous than those generated by non-invasive ventilation in healthy subjects

BACKGROUND

Non-invasive mechanical ventilation (NIV) is a standard respiratory support technique used in intensive care units. High-Flow Nasal Cannula (HFNC) has emerged as an alternative, but further evidence is needed. The lung aeration and diaphragm changes achieved with these two strategies in healthy subjects have not been compared to date.

METHODS

Twenty healthy subjects were recruited. Ten were ventilated with NIV and ten underwent HFNC. Lung impedance and diaphragmatic ultrasound measurements were performed before and after 30 min of respiratory support. The Mar-index was defined as the ratio of the diaphragm excursion-time index to the respiratory rate.

RESULTS

Both groups showed significant decreases in respiratory rate (NIV: 14.4 (4.1) vs 10.4 (1.6), p = 0.009; HFNC: 13.6 (4.3) vs 7.9 (1.5) bpm, p = 0.002) and significant increases in the end-expiratory lung impedance (EELI) (NIV: 66,348(10,761) vs. 73,697 (6858), p = 0.005; HFNC: 66,252 (9793) vs 69,869 (9135), p = 0.012). NIV subjects showed a significant increase in non-dependent silent spaces (4.13 (2.25) vs 5.81 (1.49)%, p = 0.037) while the increase was more homogeneous with HFNC. The variation in EELI tended to be higher in NIV than in HFNC (8137.08 (6152.04) vs 3616.94 (3623.03), p = 0.077). The Mar-index was higher in HFNC group (13.15 vs 5.27 cm-sec²/bpm, p = 0.02).

CONCLUSIONS

NIV and HFNC increased EELI in healthy subjects, suggesting an increase in the functional residual capacity. The EELI increase may be higher in NIV, but HFNC produced a more homogeneous change in lung ventilation. HFNC group has a higher MAR-index that could reflect a different ventilatory system adaptation.

High-flow oxygen therapy for treating re-expansion pulmonary edema

Re-expansion pulmonary edema (REPE) is a lethal complication, which usually occurs after rapid re-expansion of a collapsed lung following chest tube insertion. As REPE can induce respiratory failure, mechanical ventilation is necessary in some cases. However, ventilator therapy can worsen ventilation perfusion mismatch at the initial stage of the treatment procedure, and increases the risk of fatality. To resolve this problem, it is advisable to maintain spontaneous breathing without using a mechanical ventilator. A high-flow nasal cannula can supply a high concentration of oxygen while maintaining spontaneous breathing in patients with dyspnea, which has recently emerged as an alternative to ventilators. We introduced a high-flow nasal cannula to treat REPE instead of a mechanical ventilator and successfully treated a patient with severe REPE.

Correlation of high flow nasal cannula outlet area with gas clearance and pressure in adult upper airway replicas

BACKGROUND

Primary benefits of high flow nasal cannula therapy include washout of carbon dioxide rich exhaled gas and increased airway pressures during tidal breathing. This work reports on the influence of high flow nasal cannula outlet area on upper airways gas clearance and tracheal pressures using measurements in five realistic adult nose-throat airway replicas.

METHODS

Two commercial high flow nasal cannulas and one generic nasal cannula of varying size were compared. 100% oxygen was supplied via cannulas at flow rates ranging from 30 to 90l/min to replicas originally filled with air, and oxygen concentrations at the larynx and trachea were compared over time. Additionally, and separately, replicas were connected to a mechanical lung simulator to simulate tidal breathing while undergoing high flow nasal cannula therapy, with tracheal pressure-time waveforms recorded.

FINDINGS

Faster gas clearance corresponded with higher flow rates (P<0.001), and with smaller cannula outlet area (P<0.001). Observed pressures were in approximate agreement with limited available in-vivo data in the literature. Between 0 and 60L/min cannula flow rates, tracheal positive end expiratory pressures increase was greater with the smallest cannula (∆P_PEEP=785SD(185) Pa) compared to the largest cannula (∆P_PEEP=380SD(120)Pa). Regression analysis indicates that positive end expiratory pressure is proportional to the square of flow velocities exiting the cannula and nares (R²=0.906).

INTERPRETATION

Since increased pressure and clearance rate have been associated with improved clinical outcomes in previous studies, our results suggest that smaller cannula outlet area may be preferable.

High-flow nasal cannula oxygenation utilization in respiratory failure

High flow nasal cannula (HFNC) represents a new oxygenation system to be used in the treatment of respiratory emergencies. During HFNC therapy, the active humidification and air heating system allow the patient to tolerate higher flows by favouring physiologic mucociliary clearance and improving fluidity of respiratory secretions. Following this, FiO₂ values are more stable and reliable, by reducing losses and minimizing ambient air entrainment. Several clinical trials in acute respiratory failure patients have suggested lower rate of invasive mechanical ventilation, improved comfort and enhanced survival by early HFNC utilization in comparison with conventional oxygen therapy (COT) or non-invasive ventilation (NIV). This review aims to summarize the main evidences on the use of HFNC in the acute setting and its major indications.

Ultrasound Assessment of Respiratory Workload With High-Flow Nasal Oxygen Versus Other Noninvasive Methods After Chest Surgery

OBJECTIVE

To compare the respiratory workload using the diaphragm thickening fraction (DTf) determined by sonography during high-flow nasal oxygen (HFNO), standard oxygen therapy (SOT), and noninvasive bilevel positive airway pressure support (BIPAP) in patients with acute respiratory failure (ARF) after cardiothoracic surgery.

DESIGN

Prospective controlled clinical trial.

SETTING

A French 23-bed cardiothoracic surgical intensive care unit.

PARTICIPANTS

Nonintubated patients with ARF after cardiothoracic surgery or while awaiting lung transplantation.

INTERVENTIONS

HFNO (50 L/min), SOT via a standard facemask, and BIPAP (pressure support, 4 cmH₂O; positive end-expiratory pressure [PEEP], 4 cmH₂O), with F_IO₂ kept constant were successively applied and compared. With BIPAP, pressure support or PEEP increments up to 8 cmH₂O were compared with baseline settings. Each measurement was made after stable breathing for 5 minutes.

MEASUREMENTS AND MAIN RESULTS

Fifty patients aged 60.0 ± 12.2 years were enrolled, including 14 (28%) with obesity. Mean PaO₂/F_IO₂ was 153 ± 55 mmHg. DTf was lower with HFNO and BIPAP than with SOT (respectively 21.2% ± 15.1% v 30.9% ± 21.1% and 17.8% ± 19.1% v 30.9% ± 21.1%, p < 0.001) and was not different with HFNO versus BIPAP (p = 0.22). With BIPAP, increasing pressure support to 8 cmH₂O decreased DTf (21.0% ± 14.3% v 28.8% ± 19.8%, p = 0.009), whereas increasing PEEP to 8 cmH₂O did not (25.2% ± 17.2% v 28.8% ± 19.8%, p = 0.79). Tidal volume increased to 10.6 ± 3.4 mL/kg with 8 cmH₂O pressure support v 8.8 ± 2.7 mL/kg with 4 cmH₂O pressure support (p < 0.001).

CONCLUSION

HFNO provides a comparable respiratory workload decrease compared with BIPAP at lower levels of pressure support and PEEP compared with SOT. Increasing BIPAP pressure support may provide higher levels of assistance but carries a risk of overdistension.

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.

Aerosol drug delivery to the lungs during nasal high flow therapy: an in vitro study

Background

Aerosol delivery through a nasal high flow (NHF) system is attractive for clinicians as it allows for simultaneous administration of oxygen and inhalable drugs. However, delivering a fine particle fraction (FPF, particle wt. fraction < 5.0 μm) of drugs into the lungs has been very challenging, with highest value of only 8%. Here, we aim to develop an efficient nose-to-lung delivery system capable of delivering improved quantities (FPF > 16%) of dry powder aerosols to the lungs via an NHF system.

Methods

We evaluated the FPF of spray-dried mannitol with leucine with a next generation impactor connected to a nasopharyngeal outlet of an adult nasal airway replica. In addition, we investigated the influence of different dispersion (20–30 L/min) and inspiratory (20–40 L/min) flow rates, on FPF.

Results

We found an FPF of 32% with dispersion flow rate at 25 L/min and inspiratory flow rate at 40 L/min. The lowest FPF (21%) obtained was at the dispersion flow rate at 30 L/min and inspiratory flow rate at 30 L/min. A higher inspiratory flow rate was generally associated with a higher FPF. The nasal cannula accounted for most loss of aerosols.

Conclusions

In conclusion, delivering a third of inhalable powder to the lungs is possible in vitro through an NHF system using a low dispersion airflow and a highly dispersible powder. Our results may lay the foundation for clinical evaluation of powder aerosol delivery to the lungs during NHF therapy in humans.

A New Promising Treatment Strategy for Carbon Monoxide Poisoning: High Flow Nasal Cannula Oxygen Therapy

Background

High-flow nasal cannula (HFNC) is an alternative to conventional normobaric oxygen therapy (NBO) for hypoxemic patients. Since nothing is known about its effect on carbon monoxide (CO) poisoning, we hypothesized that HFNC might be a useful device in the treatment of CO poisoning victims.

Material/Methods

We retrospectively reviewed the medical records of patients who were admitted consecutively to the emergency department with CO intoxication. Patients were divided into 2 groups: patients treated with HFNC and patients treated with conventional face mask (CFM). Demographic data, pretreatment, and control (after 1 hour) arterial blood gas analyses values of the patients were evaluated.

Results

Sixty-eight patients (mean age 35.8±18.7 years) were included in this study. NBO was given via HFNC to 38 patients (55.9%), and via CFM to 30 patients (44.1%). The demographic characteristics and pretreatment values of carboxy-hemoglobin (COHb) were similar in the 2 groups. The mean COHb value of the HFNC group at the first hour was found significantly lower than the CFM group: 9.5±4.7 and 12.0±5.1, respectively (P=0.041). Improvement of COHb level was significantly higher in the HFNC group compared to the CFM group: 12.5±4.5 versus 6.7±3.7, respectively (P=0.001).

Conclusions

HFNC was superior than CFM in alleviating COHb levels in the victims of CO poisoning. We believe that using HFNC will increase patient comfort by shortening the duration of treatment in emergency department settings, especially in patients who have mild clinical findings of CO poisoning.

Non-Invasive Positive airway Pressure thErapy to Reduce Postoperative Lung complications following Upper abdominal Surgery (NIPPER PLUS): protocol for a single-centre, pilot, randomised controlled trial

INTRODUCTION

Postoperative pulmonary complications (PPCs) are a common serious complication following upper abdominal surgery leading to significant consequences including increased mortality, hospital costs and prolonged hospitalisation. The primary objective of this study is to detect whether there is a possible signal towards PPC reduction with the use of additional intermittent non-invasive ventilation (NIV) compared with continuous high-flow nasal oxygen therapy alone following high-risk elective upper abdominal surgery. Secondary objectives are to measure feasibility of: (1) trial conduct and design and (2) physiotherapy-led NIV and a high-flow nasal oxygen therapy protocol, safety of NIV and to provide preliminary costs of care information of NIV and high-flow nasal oxygen therapy.

METHODS AND ANALYSIS

This is a single-centre, parallel group, assessor blinded, pilot, randomised trial, with 130 high-risk upper abdominal surgery patients randomly assigned via concealed allocation to either (1) usual care of continuous high-flow nasal oxygen therapy for 48 hours following extubation or (2) usual care plus five additional 30 min physiotherapy-led NIV sessions within the first two postoperative days. Both groups receive standardised preoperative physiotherapy and postoperative early ambulation. No additional respiratory physiotherapy is provided to either group. Outcome measures will assess incidence of PPC within the first 14 postoperative days, recruitment ability, physiotherapy-led NIV and high-flow nasal oxygen therapy protocol adherence, adverse events relating to NIV delivery and costs of providing a physiotherapy-led NIV and a high-flow nasal oxygen therapy service following upper abdominal surgery.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from the relevant institution and results will be published to inform future multicentre trials.

TRIAL REGISTRATION NUMBER

ACTRN12617000269336; Pre-results.

High-flow oxygen therapy in tracheostomized patients at high risk of weaning failure

Purpose

High-flow oxygen therapy delivered through nasal cannulae improves oxygenation and decreases work of breathing in critically ill patients. Little is known of the physiological effects of high-flow oxygen therapy applied to the tracheostomy cannula (T-HF). In this study, we compared the effects of T-HF or conventional low-flow oxygen therapy (conventional O₂) on neuro-ventilatory drive, work of breathing, respiratory rate (RR) and gas exchange, in a mixed population of tracheostomized patients at high risk of weaning failure.

Methods

This was a single-center, unblinded, cross-over study on fourteen patients. After disconnection from the ventilator, each patient received two 1-h periods of T-HF (T-HF1 and T-HF2) alternated with 1 h of conventional O₂. The inspiratory oxygen fraction was titrated to achieve an arterial O₂ saturation target of 94–98% (88–92% in COPD patients). We recorded neuro-ventilatory drive (electrical diaphragmatic activity, EAdi), work of breathing (inspiratory muscular pressure–time product per breath and per minute, PTP_musc/b and PTP_musc/min, respectively) respiratory rate and arterial blood gases.

Results

The EAdi_peak remained unchanged (mean ± SD) in the T-HF1, conventional O₂ and T-HF2 study periods (8.8 ± 4.3 μV vs 8.9 ± 4.8 μV vs 9.0 ± 4.1 μV, respectively, p = 0.99). Similarly, PTP_musc/b and PTP_musc/min, RR and gas exchange remained unchanged.

Conclusions

In tracheostomized patients at high risk of weaning failure from mechanical ventilation, T-HF did not improve neuro-ventilatory drive, work of breathing, respiratory rate and gas exchange compared with conventional O₂ after disconnection from the ventilator. The present findings might suggest that physiological effects of high-flow therapy through tracheostomy substantially differ from nasal high flow.

Management of Chronic Respiratory Failure in Interstitial Lung Diseases: Overview and Clinical Insights

Interstitial lung diseases (ILDs) may be complicated by chronic respiratory failure (CRF), especially in the advanced stages. Aim of this narrative review is to evaluate the current evidence in management of CRF in ILDs. Many physiological mechanisms underlie CRF in ILDs, including lung restriction, ventilation/perfusion mismatch, impaired diffusion capacity and pulmonary vascular damage. Intermittent exertional hypoxemia is often the initial sign of CRF, evolving, as ILD progresses, into continuous hypoxemia. In the majority of the cases, the development of CRF is secondary to the worsening of the underlying disease; however, associated comorbidities may also play a role. When managing CRF in ILDs, the need for pulmonary rehabilitation, the referral to lung transplant centers and palliative care should be assessed and, if necessary, promptly offered. Long-term oxygen therapy is commonly prescribed in case of resting or exertional hypoxemia with the purpose to decrease dyspnea and improve exercise tolerance. High-Flow Nasal Cannula oxygen therapy may be used as an alternative to conventional oxygen therapy for ILD patients with severe hypoxemia requiring both high flows and high oxygen concentrations. Non-Invasive Ventilation may be used in the chronic setting for palliation of end-stage ILD patients, although the evidence to support this application is very limited.

New modalities for non-invasive positive pressure ventilation: A review article

Efficiency of non-invasive positive pressure ventilation in the treatment of respiratory failure has been shown in many published studies. In this review article, we introduced new modalities of non-invasive ventilation (NIV), clinical settings in which NIV can be used and a practical summary of the latest official guidelines published by the European Respiratory Clinical Practice. Clinical trials and review articles in four databases up to 25 February 2018 about new modalities of non-invasive positive pressure ventilation were reviewed. Commonly used modalities for treatment of respiratory failure include: CPAP (continuous positive airway pressure) and BiPAP (bilevel positive airway pressure) or NIPSV (noninvasive pressure support ventilation). The limitations of the BiPAP method are the trigger and cycle asynchrony, inadequate volume delivery and increased respiratory rate. Newer methods, such as adaptive servo-ventilation, have been developed to treat central and complex sleep apnea and the NAVA (neutrally adjusted ventilatory assist) to improve the trigger and cycle asynchrony. In the proportional assist ventilation, unlike the pressure support ventilation, with increased patient effort (flow) the tidal volume increases and it prevents the increase in the respiratory rate and respiratory distress. High-flow nasal cannula is a non-invasive technique that does not provide respiratory support, but provides a mixture of oxygen to the patient. The use of non-invasive pursed-lip breathing ventilation in chronic obstructive pulmonary disease (COPD) patients reduces dyspnea (decreases respiratory rate) and increases blood oxygen saturation. New modalities of NIV improve patient comfort and patient-ventilator interactions, and are recommended in patients with respiratory failure.

Nasal high-flow bronchodilator nebulization: a randomized cross-over study

Background

There is an absence of controlled clinical data showing bronchodilation effectiveness after nebulization via nasal high-flow therapy circuits.

Results

Twenty-five patients with reversible airflow obstruction received, in a randomized order: (1) 2.5 mg albuterol delivered via a jet nebulizer with a facial mask; (2) 2.5 mg albuterol delivered via a vibrating mesh nebulizer placed downstream of a nasal high-flow humidification chamber (30 L/min and 37 °C); and (3) nasal high-flow therapy without nebulization. All three conditions induced significant individual increases in forced expiratory volume in one second (FEV₁) compared to baseline. The median change was similar after facial mask nebulization [+ 350 mL (+ 180; + 550); + 18% (+ 8; + 30)] and nasal high flow with nebulization [+ 330 mL (+ 140; + 390); + 16% (+ 5; + 24)], p = 0.11. However, it was significantly lower after nasal high-flow therapy without nebulization [+ 50 mL (− 10; + 220); + 3% (− 1; + 8)], p = 0.0009. FEV₁ increases after facial mask and nasal high-flow nebulization as well as residual volume decreases were well correlated (p < 0.0001 and p = 0.01). Both techniques showed good agreement in terms of airflow obstruction reversibility (kappa 0.60).

Conclusion

Albuterol vibrating mesh nebulization within a nasal high-flow circuit induces similar bronchodilation to standard facial mask jet nebulization. Beyond pharmacological bronchodilation, nasal high flow by itself may induce small but significant bronchodilation.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0473-8) contains supplementary material, which is available to authorized users.

SponTaneous Respiration using IntraVEnous anaesthesia and Hi-flow nasal oxygen (STRIVE Hi) maintains oxygenation and airway patency during management of the obstructed airway: an observational study

Background. High-flow nasal oxygen (HFNO) has been shown to benefit oxygenation, ventilation and upper airway patency in a range of clinical scenarios, however its use in spontaneously breathing patients during general anaesthesia has not been described. Spontaneous respiration using i.v. anaesthesia is the primary technique used at our institution for tubeless airway surgery. We hypothesized that the addition of HFNO would increase our margin of safety, particularly during management of an obstructed airway.

Methods. A retrospective observational study was conducted using a SponTaneous Respiration using IntraVEnous anaesthesia and High-flow nasal oxygen (STRIVE Hi) technique to manage 30 adult patients undergoing elective laryngotracheal surgery.

Results. Twenty-six patients (87%) presented with significant airway and/or respiratory compromise (16 were stridulous, 10 were dyspnoeic). No episodes of apnoea or complete airway obstruction occurred during the induction of anaesthesia using STRIVE Hi. The median [IQR (range)] lowest oxygen saturation during the induction period was 100 [99–100 (97–100)] %. The median [IQR (range)] overall duration of spontaneous ventilation was 44 [40–49.5 (18–100)] min. The median [IQR (range)] end-tidal carbon dioxide (ETCO₂) level at the end of the spontaneous ventilation period was 6.8 [6.4–7.1 (4.8–8.9)] kPa. The mean rate of increase in ETCO₂ was 0.03 kPa min⁻¹.

Conclusions. STRIVE Hi succeeded in preserving adequate oxygen saturation, end-tidal carbon dioxide and airway patency. We suggest that the upper and lower airway benefits attributed to HFNO, are ideally suited to a spontaneous respiration induction, increasing its margin of safety. STRIVE Hi is a modern alternative to the traditional inhalation induction.

Facilitating Airway Surgery in a Morbidly Obese Patient Using Transnasal Humidified Rapid Insufflation Ventilatory Exchange (THRIVE)

Transnasal Humidified Rapid Insufflation Ventilatory Exchange (THRIVE) is a relatively new noninvasive oxygenation technique with a broad range of applications. It is used in the treatment of type one respiratory failure, as a preoxygenation tool, as a rescue and temporising measure in difficult airways, and as step-down oxygen therapy in patients after extubation. Its use has also been described in laryngeal surgeries, but they mainly involved normal-weight subjects or were used as a bridging oxygenation therapy before definitive airway is secured. The major benefits of using THRIVE in obese subjects undergoing laryngeal surgery include a tubeless and uninterrupted surgical field. This advantage is especially crucial in obese patients as they tend to have limited oropharyngeal space, rendering a shared airway technically challenging for surgeons. However, concerns of potential difficult airway and shorter safe apnoeic time in the obese population limit its use. In this case, we report its use as the sole oxygenation strategy in a morbidly obese patient undergoing airway surgery. Our experience suggests that THRIVE can provide a conducive operating field and adequate oxygenation in short apnoeic laryngeal procedures in the obese population, without causing excessive hypercarbia.

High flow nasal cannula in the emergency department: indications, safety and effectiveness

INTRODUCTION

Heated humidified high flow nasal cannula therapy (HHHFNCT) is emerging as a popular non-invasive mode of respiratory support in adults and children. In recent years, its use has extended beyond the intensive care unit to other clinical areas. This review aims to explore the mechanism of action, indications, safety, and effectiveness of HHHFNCT use in the Emergency Department (ED).

AREAS COVERED

The mechanism of action of HHHFNCT, as well as its use in adult and pediatric ED will be discussed in this review.

EXPERT COMMENTARY

While there exists increasing enthusiasm in the use of HHHFNCT in the ED, constant monitoring of the patients and an experienced assessment of their response to treatment are critical and may require additional manpower deployment, which may be challenging, in the busy ED environment. Our experience with the use of HHHFNCT in children is still growing. Continual research in this area remains crucial in helping us better understand the patient types and conditions managed in ED that would most benefit from this device.

High flow nasal therapy in perioperative medicine: from operating room to general ward

BACKGROUND

High flow nasal therapy (HFNT) is a technique in which humidified and heated gas is delivered to the airways through the nose via small nasal prongs at flows that are higher than the rates generally applied during conventional oxygen therapy. The delivered high flow rates combine mixtures of air and oxygen and enable different inspired oxygen fractions ranging from 0.21 to 1. HFNT is increasingly used in critically ill adult patients, especially hypoxemic patients in different clinical settings.

MAIN BODY

Noninvasive ventilation delivers positive pressure (end-expiratory and inspiratory pressures or continuous positive airway pressure) via different external interfaces. In contrast, HFNT produces different physiological effects that are only partially linked to the generation of expiratory positive airway pressure. HFNT and noninvasive ventilation (NIV) are interesting non-invasive supports in perioperative medicine. HFNT exhibits some advantages compared to NIV because HFNT is easier to apply and requires a lower nursing workload. Tolerance of HFNT remains a matter of intense debate, and it may be related to selected parameters. Patients receiving HFNT and their respiratory patterns should be closely monitored to avoid delays in intubation despite correct oxygenation parameters.

CONCLUSION

HFNT seems to be an interesting noninvasive support in perioperative medicine. The present review provides anesthesiologists with an overview of current evidence and practical advice on the application of HFNT in perioperative medicine in adult patients.

High-flow nasal therapy vs standard oxygen during breaks off noninvasive ventilation for acute respiratory failure: A pilot randomized controlled trial

PURPOSE

To assess the role of high-flow nasal therapy (HFNT) compared to standard oxygen (SO) as complementary therapy to non-invasive ventilation (NIV).

METHODS

Multicenter trial including patients (n = 54) anticipated to receive NIV for ≥24 h due to acute or acute-on-chronic respiratory failure. Subjects were randomized (1:1) to SO or HFNT during breaks off NIV. Primary outcome was total time on and off NIV. Secondary outcomes were comfort and dyspnea, respiratory rate (RR), oxygen saturation (S_pO₂), tolerance and side effects.

RESULTS

Total time per patient on NIV (1315 vs 1441 min) and breaks (1362 vs 1196 min), and mean duration of each break (520 vs 370 min) were similar in the HFNT and SO arms (p > .05). Comfort score was higher on HFNT than on SO (8.3 ± 2.7 vs 6.9 ± 2.3, p = .001). Dyspnea, RR and S_pO₂ were similar in the two arms, but the increase in RR and dyspnea seen with SO during breaks did not occur with HFNT.

CONCLUSION

Compared to SO, HFNT did not reduce time on NIV. However, it was more comfortable and the increase in RR and dyspnea seen with SO did not occur with HFNT. Therefore, HFNT could be a suitable alternative to SO during breaks off NIV.

Effect of high-flow nasal cannula oxygen therapy vs conventional oxygen therapy on adult postcardiothoracic operation: A meta-analysis

INTRODUCTION

The effect of high-flow nasal cannula (HFNC) on adult post cardiothoracic operation remains controversial. We conducted a meta-analysis of randomized controlled trials to evaluate the effect of HFNC and conventional oxygen therapy (COT) on postcardiothoracic surgery.

METHODS

A search was conducted in Embase, MEDLINE, Ovid, and Cochrane databases until December, 2017 for all the controlled study to compare HFNC with COT in adult postcardiothoracic surgery. Two authors extracted data and assessed the quality of each study independently. The meta-analysis was performed by using RevMan 5.3. The primary outcome was the rate of escalation of respiratory support rate and pulmonary complications; secondary outcome included the length of intensive care unit (ICU) stay and length of hospital stay and the rate of intubation.

RESULTS

Four studies that involved 649 patients were included in the analysis. No significant heterogeneity was found in outcome measures. Compared with COT, HFNC were associated with a significant reduction in the escalation of respiratory support (odds ratio [OR] = 0.44, 95% confidence interval [CI] = 0.29-0.66, P < .001) and pulmonary complications (OR = 0.28, 95% CI = 0.13-0.6, P = .001). There were no significant differences in the reintubation rate (OR = 0.33, 95% CI = 0.02-5.39, P = .43), length of ICU stay (weighted mean difference = 0.11; 95% CI = -0.44 -0.26, P = .14) or length of hospital stay (weighted mean difference = -0.15, 95% CI = -0.46 -0.17, P = .36) between the 2 groups. No severe complications were reported in either group.

CONCLUSION

The HFNC could reduce respiratory support and pulmonary complications, and it could be safely administered for adult postcardiothoracic surgery. Further large-scale, randomized, and controlled trials are needed to update this finding.

Positive Pressure Ventilation in the Cardiac Intensive Care Unit

Contemporary cardiac intensive care units (CICUs) provide care for an aging and increasingly complex patient population. The medical complexity of this population is partly driven by an increased proportion of patients with respiratory failure needing noninvasive or invasive positive pressure ventilation (PPV). PPV often plays an important role in the management of patients with cardiogenic pulmonary edema, cardiogenic shock, or cardiac arrest, and those undergoing mechanical circulatory support. Noninvasive PPV, when appropriately applied to selected patients, may reduce the need for invasive mechanical PPV and improve survival. Invasive PPV can be lifesaving, but has both favorable and unfavorable interactions with left and right ventricular physiology and carries a risk of complications that influence CICU mortality. Effective implementation of PPV requires an understanding of the underlying cardiac and pulmonary pathophysiology. Cardiologists who practice in the CICU should be proficient with the indications, appropriate selection, potential cardiopulmonary interactions, and complications of PPV.

Comparison of high flow nasal cannula oxygen and conventional oxygen therapy on ventilatory support duration during acute-on-chronic respiratory failure: study protocol of a multicentre, randomised, controlled trial. The 'HIGH-FLOW ACRF' study

INTRODUCTION

This study protocol describes a trial designed to investigate whether high-flow heated and humidified nasal oxygen (HFHO) therapy in patients with hypercapnic acute respiratory failure (ARF) reduces the need of non-invasive ventilation (NIV).

METHODS AND ANALYSIS

This is an open-label, superiority, international, parallel-group, multicentre randomised controlled two-arm trial, with an internal feasibility pilot phase. 242 patients with hypercapnic ARF requiring NIV admitted to an intensive care unit, an intermediate care or a respiratory care unit will be randomised in a 1:1 ratio to receive HFHO or standard oxygen in between NIV sessions. Randomisation will be centralised and stratified by centre and pH at admission (pH ≤7.25 or >7.25). The primary outcome will be the number of ventilator-free days (VFDs) and alive at day 28 postrandomisation. The secondary outcomes will encompass parameters related to the VFDs, comfort and tolerance variables, hospital length of stay and mortality. VFDs at 28 days postrandomisation will be compared between the two groups by Wilcoxon-Mann-Whitney two-sample rank-sum test in the intention-to-treat population. A sensitivity analysis will be conducted in the population of patients for whom the criteria of switching from NIV to spontaneous breathing, or conversely, are not strictly verified.

ETHICS AND DISSEMINATION

The protocol has been approved by the Comité de Protection des Personnes (CPP) Sud-Ouest & Outre-Mer IV (ref CPP17-049a/2017-A01830-53) and will be carried out in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. A trial steering committee will oversee the progress of the study. Findings will be disseminated through national and international scientific conferences, and publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT03406572.

High-flow nasal cannula oxygen therapy decreases postextubation neuroventilatory drive and work of breathing in patients with chronic obstructive pulmonary disease

BACKGROUND

The physiological effects of high-flow nasal cannula O₂ therapy (HFNC) have been evaluated mainly in patients with hypoxemic respiratory failure. In this study, we compared the effects of HFNC and conventional low-flow O₂ therapy on the neuroventilatory drive and work of breathing postextubation in patients with a background of chronic obstructive pulmonary disease (COPD) who had received mechanical ventilation for hypercapnic respiratory failure.

METHODS

This was a single center, unblinded, cross-over study on 14 postextubation COPD patients who were recovering from an episode of acute hypercapnic respiratory failure of various etiologies. After extubation, each patient received two 1-h periods of HFNC (HFNC1 and HFNC2) alternated with 1 h of conventional low-flow O₂ therapy via a face mask. The inspiratory fraction of oxygen was titrated to achieve an arterial O₂ saturation target of 88-92%. Gas exchange, breathing pattern, neuroventilatory drive (electrical diaphragmatic activity (EAdi)) and work of breathing (inspiratory trans-diaphragmatic pressure-time product per minute (PTP_DI/min)) were recorded.

RESULTS

EAdi peak increased from a mean (±SD) of 15.4 ± 6.4 to 23.6 ± 10.5 μV switching from HFNC1 to conventional O₂, and then returned to 15.2 ± 6.4 μV during HFNC2 (conventional O₂: p < 0.05 versus HFNC1 and HFNC2). Similarly, the PTP_DI/min increased from 135 ± 60 to 211 ± 70 cmH₂O/s/min, and then decreased again during HFNC2 to 132 ± 56 (conventional O₂: p < 0.05 versus HFNC1 and HFNC2).

CONCLUSIONS

In patients with COPD, the application of HFNC postextubation significantly decreased the neuroventilatory drive and work of breathing compared with conventional O₂ therapy.

High flow nasal oxygen after bariatric surgery (OXYBAR), prophylactic post-operative high flow nasal oxygen versus conventional oxygen therapy in obese patients undergoing bariatric surgery: study protocol for a randomised controlled pilot trial

BACKGROUND

The incidence of obesity is increasing worldwide. In selected individuals, bariatric surgery may offer a means of achieving long-term weight loss, improved health, and healthcare cost reduction. Physiological changes that occur because of obesity and general anaesthesia predispose to respiratory complications following bariatric surgery. The aim of this study is to determine whether post-operative high flow nasal oxygen therapy (HFNO2) improves respiratory function and reduces the incidence of post-operative pulmonary complications (PPCs) in comparison to conventional oxygen therapy in these patients.

METHOD

The OXYBAR study is a prospective, un-blinded, single centre, randomised, controlled pilot study. Patients with body mass index (BMI) > 30 kg/m2, undergoing laparoscopic bariatric surgery, will be randomised to receive either standard low flow oxygen therapy or HFNO2 in the post-operative period. The primary outcome measure is the change in end expiratory lung impedance (∆EELI) as measured by electrical impedance tomography (EIT). Secondary outcome measures include change in tidal volume (∆Vt), partial arterial pressure of oxygen/fraction of inspired oxygen (PaO2/FiO2) ratio, incidence of PPCs, hospital length of stay and measures of patient comfort.

DISCUSSION

We hypothesise that the post-operative administration of HFNO2 will increase EELI and therefore end expiratory lung volume (EELV) in obese patients. To our knowledge this is the first trial designed to assess the effects of HFNO2 on EELV in this population. We anticipate that data collected during this pilot study will inform a larger multicentre trial.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (ANZCTR), ACTRN12617000694314 . Registered on 15 May 2017.

Accuracy of Administrative Codes for Distinguishing Positive Pressure Ventilation From High-Flow Nasal Cannula

OBJECTIVES

Noninvasive positive pressure ventilation (NIPPV) is increasingly used in critically ill pediatric patients, despite limited data on safety and efficacy. Administrative data may be a good resource for observational studies. Therefore, we sought to assess the performance of the International Classification of Diseases, Ninth Revision procedure code for NIPPV.

METHODS

Patients admitted to the PICU requiring NIPPV or heated high-flow nasal cannula (HHFNC) over the 11-month study period were identified from the Virtual PICU System database. The gold standard was manual review of the electronic health record to verify the use of NIPPV or HHFNC among the cohort. The presence or absence of a NIPPV procedure code was determined by using administrative data. Test characteristics with 95% confidence intervals (CIs) were generated, comparing administrative data with the gold standard.

RESULTS

Among the cohort (n = 562), the majority were younger than 5 years, and the most common primary diagnosis was bronchiolitis. Most (82%) required NIPPV, whereas 18% required only HHFNC. The NIPPV code had a sensitivity of 91.1% (95% CI: 88.2%-93.6%) and a specificity of 57.6% (95% CI: 47.2%-67.5%), with a positive likelihood ratio of 2.15 (95% CI: 1.70-2.71) and negative likelihood ratio of 0.15 (95% CI: 0.11-0.22).

CONCLUSIONS

Among our critically ill pediatric cohort, NIPPV procedure codes had high sensitivity but only moderate specificity. On the basis of our study results, there is a risk of misclassification, specifically failure to identify children who require NIPPV, when using administrative data to study the use of NIPPV in this population.

Management of acute respiratory failure in interstitial lung diseases: overview and clinical insights

Background

Interstitial lung diseases (ILDs) are a heterogeneous group of diseases characterized by widespread fibrotic and inflammatory abnormalities of the lung. Respiratory failure is a common complication in advanced stages or following acute worsening of the underlying disease. Aim of this review is to evaluate the current evidence in determining the best management of acute respiratory failure (ARF) in ILDs.

Methods

A literature search was performed in the Medline/PubMed and EMBASE databases to identify studies that investigated the management of ARF in ILDs (the last search was conducted on November 2017).

Results

In managing ARF, it is important to establish an adequate diagnostic and therapeutic management depending on whether the patient has an underlying known chronic ILD or ARF is presenting in an unknown or de novo ILD. In the first case both primary causes, such as acute exacerbations of the disease, and secondary causes, including concomitant pulmonary infections, fluid overload and pulmonary embolism need to be investigated. In the second case, a diagnostic work-up that includes investigations in regards to ILD etiology, such as autoimmune screening and bronchoalveolar lavage, should be performed, and possible concomitant causes of ARF have to be ruled out.

Oxygen supplementation and ventilatory support need to be titrated according to the severity of ARF and patients’ therapeutic options. High-Flow Nasal oxygen might potentially be an alternative to conventional oxygen therapy in patients requiring both high flows and high oxygen concentrations to correct hypoxemia and control dyspnea, however the evidence is still scarce. Neither Non-Invasive Ventilation (NIV) nor Invasive Mechanical Ventilation (IMV) seem to change the poor outcomes associated to advanced stages of ILDs. However, in selected patients, such as those with less severe ARF, a NIV trial might help in the early recognition of NIV-responder patients, who may present a better short-term prognosis. More invasive techniques, including IMV and Extracorporeal Membrane Oxygenation, should be limited to patients listed for lung transplant or with reversible causes of ARF.

Conclusions

Despite the overall poor prognosis of ARF in ILDs, a personalized approach may positively influence patients’ management, possibly leading to improved outcomes. However, further studies are warranted.

Early experience with high-flow nasal oxygen therapy (HFNOT) in pediatric endoscopic airway surgery

OBJECTIVE

Reporting our institutional experience with high-flow nasal oxygen therapy (HFNOT), a recently-introduced technique, for endoscopic airway approaches.

METHODS

Prospective collection of data of children (<16 years) undergoing endoscopic between January 2016 and August 2017 at a tertiary referral university hospital.

RESULTS

HFNOT was used in 6 children who underwent 14 procedures for different forms and causes of upper airway obstruction of various origins. No intraoperative complications; related to oxygenation were observed, and the surgical procedures could be carried out as; initially planned.

CONCLUSIONS

We found that HFNOT is an effective and safe technique with a variety of potential applications in the field of endoscopic pediatric airway surgery.

Pilot Clinical Trial of High-Flow Oxygen Therapy in Children with Asthma in the Emergency Service

OBJECTIVES

To assess the efficacy of high-flow nasal cannula (HFNC) oxygen therapy and safety in children with asthma and moderate respiratory failure in the emergency department (ED).

STUDY DESIGN

This was a prospective randomized pilot trial of children (aged 1-14 years) presenting to a tertiary academic pediatric ED with moderate-to-severe asthma exacerbations between September 2012 and December 2015. Patients with a pulmonary score (PS) ≥6 or oxygen saturation <94% with a face mask despite initial treatment (salbutamol/ipratropium bromide and corticosteroids) were randomized to HFNC or to conventional oxygen therapy. Pharmacologic treatment was at the discretion of attending physicians. The primary outcome was a decrease in PS ≥2 in the first 2 hours. Secondary outcomes included disposition, length of stay, and need for additional therapies.

RESULTS

We randomly allocated 62 children to receive either HFNC (n = 30) or standard oxygen therapy (n = 32). Baseline patient characteristics were similar in the 2 groups. At 2 hours after the start of therapy, PS had decreased by ≥2 points in 16 patients in the HFNC group (53%) compared with 9 controls (28%) (P = .01). Between-group differences in disposition, length of stay, and need for additional therapies were not significant. No side effects were reported.

CONCLUSION

HFNC appears to be superior to conventional oxygen therapy for reducing respiratory distress within the first 2 hours of treatment in children with moderate-to-severe asthma exacerbation refractory to first-line treatment. Further studies are needed to demonstrate its overall efficacy in the management of asthma and respiratory failure in the ED.

TRIAL REGISTRATION

EudraCT: 2012-001771-36.

Use of high-flow nasal cannula in obese patients receiving colonoscopy under intravenous propofol sedation: A case series

Intravenous sedation during colonoscopy has become the standard practice in the United States given its higher patient satisfaction and procedural quality. This practice is not free of side effects as a significant proportion of patients undergoing this procedure tend to have respiratory depression and desaturation events. Obesity, as it relates to higher levels of body mass index (BMI) has a positive correlation with the incidence of hypoxemia. During colonoscopy High flow nasal cannula (HFNC) may potentially improve oxygen performance in patients receiving colonoscopy under intravenous sedation. Here we present 3 cases of patients undergoing adjunctive oxygen therapy with HFNC during colonoscopy with intravenous sedation. We found patients to have lower number of desaturation events and were satisfied with their experience.

Clinical Characteristics Based on the New Criteria of Acute Exacerbation in Patients with Idiopathic Pulmonary Fibrosis

Objective

Idiopathic pulmonary fibrosis (IPF) is the most common parenchymal lung disease. Patients with IPF sometimes develop acute exacerbation (AE), which predicts a poor prognosis. To evaluate the predictors of 90-day mortality of AE in patients with IPF based on the new 2016 criteria.

Materials and Methods

Sixty-five patients with AE were studied retrospectively between January 2001 and December 2016 at Okinawa Chubu Hospital.

Results

The mean age of the patients was 74 years, with 40 (61.5%) men and 25 (38.5%) women. Among our cohort, 37 were current or ex-smokers, with a mean exposure of 32.4 pack-years. The mean grade of the modified Medical Research Council breathlessness scale was 2.8, and the mean duration of dyspnea prior to admission was 6.5 days. Clubbed fingernails were present in 29% of patients. Triggered AE occurred in 12 (18%) of patients. Patients with triggered AE had more extensive ground-glass opacity and higher consolidation scores than the idiopathic AE group (7.3 vs. 4.2, p=0.01). The triggered group had shorter survival than the idiopathic group (1.4 vs. 11.4 months, p=0.094). Serum lactate dehydrogenase (LDH), ΔLDH, and the ratio of partial pressure of oxygen to the fraction of inspiratory oxygen ratio were strong predictors of 90-day mortality. Hazard ratios were 1.003 (p=0.004), 1.004 (p=0.02), and 0.994 (p=0.010), respectively.

Conclusion

Compared with idiopathic AE, triggered AE in patients with IPF had more extensive infiltration and tended toward shorter survival. Serial trends of serum LDH >2 weeks can help predict prognosis of AE in patients with IPF.

Global and Regional Ventilation during High Flow Nasal Cannula in Patients with Hypoxia

Background

High flow nasal cannula (HFNC) is known to increase global ventilation volume in healthy subjects. We sought to investigate the effect of HFNC on global and regional ventilation patterns in patients with hypoxia.

Methods

Patients were randomized to receive one of two oxygen therapies in sequence: nasal cannula (NC) followed by HFNC or HFNC followed by NC. Global and regional ventilation was assessed using electric impedance tomography.

Results

Twenty-four patients participated. Global tidal variation (TV) in the lung was higher during HFNC (NC, 2,241 ± 1,381 arbitrary units (AU); HFNC, 2,543 ± 1,534 AU; P < 0.001). Regional TVs for four iso-gravitational quadrants of the lung were also all higher during HFNC than NC. The coefficient of variation for the four quadrants of the lung was 0.90 ± 0.61 during NC and 0.77 ± 0.48 during HFNC (P = 0.035). Within the four gravitational layers of the lung, regional TVs were higher in the two middle layers during HFNC when compared to NC. Regional TV values in the most ventral and dorsal layers of the lung were not higher during HFNC compared with NC. The coefficient of variation for the four gravitational layers of the lung were 1.00 ± 0.57 during NC and 0.97 ± 0.42 during HFNC (P = 0.574).

Conclusions

In patients with hypoxia, ventilation of iso-gravitational regions of the lung during HFNC was higher and more homogenized compared with NC. However, ventilation of gravitational layers increased only in the middle layers. (Clinical trials registration number: NCT02943863).

High-Velocity Nasal Insufflation in the Treatment of Respiratory Failure: A Randomized Clinical Trial

STUDY OBJECTIVE

We compare high-velocity nasal insufflation, a form of high-flow nasal cannula, with noninvasive positive-pressure ventilation in the treatment of undifferentiated respiratory failure with respect to therapy failure, as indicated by requirement for endotracheal intubation or cross over to the alternative therapy.

METHODS

This was a multicenter, randomized trial of adults presenting to the emergency department (ED) with respiratory failure requiring noninvasive positive-pressure ventilation. Patients were randomly assigned to high-velocity nasal insufflation (initial flow 35 L/min; temperature 35°C (95°F) to 37°C (98.6°F); FiO₂ 1.0) or noninvasive positive-pressure ventilation using an oronasal mask (inspiratory positive airway pressure 10 cm H₂O; expiratory positive airway pressure 5 cm H₂O). The primary outcome was therapy failure at 72 hours after enrollment. A subjective outcome of crossover was allowed as a risk mitigation to support deferment of informed consent. Noninferiority margins were set at 15 and 20 percentage points, respectively.

RESULTS

A total of 204 patients were enrolled and included in the analysis, randomized to high-velocity nasal insufflation (104) and noninvasive positive-pressure ventilation (100). The intubation rate (high-velocity nasal insufflation=7%; noninvasive positive-pressure ventilation=13%; risk difference=-6%; 95% confidence interval -14% to 2%) and any failure of the assigned arm (high-velocity nasal insufflation=26%; noninvasive positive-pressure ventilation=17%; risk difference 9%; confidence interval -2% to 20%) at 72 hours met noninferiority. The effect on PCO₂ over time was similar in the entire study population and in patients with baseline hypercapnia. Vital signs and blood gas analyses improved similarly over time. The primary limitation was the technical inability to blind the clinical team.

CONCLUSION

High-velocity nasal insufflation is noninferior to noninvasive positive-pressure ventilation for the treatment of undifferentiated respiratory failure in adult patients presenting to the ED.

Efficacy and Safety of Using High-Flow Nasal Oxygenation in Patients Undergoing Rapid Sequence Intubation

Objective

To assess the efficacy and safety of high-flow nasal oxygen (HFNO) therapy in patients undergoing rapid sequence intubation (RSI) for emergency abdominal surgery.

Methods

HFNO of 60 L.min^-1 at an inspiratory oxygen fraction of 1 was delivered 4 min before laryngoscopy and maintained until the patient was intubated, and correct intubation was verified by the appearance of the end-tidal CO₂ (EtCO₂) waveform. Transcutaneous oxygenation (SpO₂), heart rate and non-invasive mean arterial pressure were monitored at baseline (T0), after 4 min on HFNO (T1) and at the time of laryngoscopy (T2) and endotracheal intubation (ETI) (T3). An SpO₂ of <3% from baseline was recorded at any sampled time. The value of EtCO₂ at T3 was registered after two mechanical breaths. The apnoea time was defined as the time from the end of propofol injection to ETI. RSI was performed with propofol, fentanyl and rocuronium.

Results

Forty-five patients were enrolled. SpO₂ levels showed a statistically significant increase at T1, T2 and T3 compared with those at T0 (p<0.05); median SpO₂% (interquartile range) was 97% (range, 96%-99%) at T0, 99% (range, 99%-100%) at T1, 99% (range, 99%-100%) at T2 and 99% (range, 99%-100%) at T3. Minimal SpO₂ was 96%; no patient showed an SpO₂ of <3% from baseline; mean EtCO₂ at the time of ETI was 36±4 mmHg. Maximum apnoea time was 12 min.

Conclusion

HFNO is an effective and safe technique for pre-oxygenation in patients undergoing rapid sequence induction of general anaesthesia for emergency surgery.

The value of high-flow nasal cannula oxygen therapy after extubation in patients with acute respiratory failure

OBJECTIVE

To investigate the value of high-flow nasal cannula oxygen therapy after extubation in patients with acute respiratory failure.

METHODS

A single-center, prospective, randomized, controlled pilot trial was conducted between January 2013 and December 2014. Sixty enrolled patients were randomized immediately after extubation into either a high-flow nasal cannula group (n=30) or an air entrainment mask group (n=30) at a fixed inspired oxygen fraction (40%). The success rate of oxygen therapy, respiratory and hemodynamic parameters and subjective discomfort (using a visual analogue scale) were assessed at 24h after extubation.

RESULTS

The two groups were comparable at extubation. A total of 46 patients were successfully treated including 27 patients in the high-flow nasal cannula group and 19 patients in the air entrainment mask group. Compared to the air entrainment mask group, the success rate of oxygen therapy and the partial pressure of arterial oxygen were significantly higher and the respiratory rate was lower in the high-flow nasal cannula group. In addition, less discomfort related to interface displacement and airway dryness was observed in the high-flow nasal cannula group than in the air entrainment mask group.

CONCLUSIONS

At a fixed inspired oxygen fraction, the application of a high-flow nasal cannula after extubation achieves a higher success rate of oxygen therapy and less discomfort at 24h than an air entrainment mask in patients with acute respiratory failure.

Nitrous Oxide Inhalation Sedation Through a Nasal High-Flow System: The Possibility of a New Technique in Dental Sedation

High-flow nasal cannula (HFNC) systems are increasingly used for patients with both acute and chronic respiratory failure because of the clinical effectiveness and patient comfort associated with their use. Recently, HFNC has been used not only as a respiratory support device, but also as a drug delivery system. HFNC is designed to administer heated and humidified inspiratory oxygen flows (100% relative humidity at 37°C). Therefore, HFNC can provide high flows (up to 60 L/min) without discomfort. Moreover, HFNC improves oxygenation by exerting physiologic effects such as (a) dead-space washout and (b) moderate positive airway pressure. These characteristics and physiologic effects of HFNC may permit administration of high-flow nitrous oxide sedation while ensuring patient comfort and adequate sedative effect.

Powder aerosol delivery through nasal high-flow system: In vitro feasibility and influence of process conditions

We aimed to obtain fundamental information for potential pulmonary delivery of powder aerosols using a clinically-approved nasal high-flow system (AIRVO), with spray-dried mannitol (SD-Man) being a model powder. Compressed air exiting the AIRVO at set 'dispersion' air flow rates dispersed SD-Man loaded in an Osmohaler^® into a human nasal airway replica (NAR) coupled downstream to a Next Generation Impactor (NGI) running at specific 'inspiratory' flow rates. Increasing the dispersion flow rate from 30 to 60L/min increased powder deposition in the NAR from 50 to 70% of the emitted dose, while decreased the NGI deposition from 50 to 30% of the emitted dose. The inspiratory flow rate did not affect powder deposition in the NAR and NGI. In contrast, as the inspiratory flow rate was increased from 15 to 40L/min, powder recovery, emitted fraction, and fine particle fraction below 5μm (as aerosol performance indices) were increased from 90, 30 and 5% to 97, 45 and 8% of the loaded dose, respectively. The dispersion flow rate did not change the performance indices. Importantly, heating and humidification of dispersion airflow, loaded doses, and nasal cannula sizes did not greatly affect the aerosol characteristics.

Nasal high flow therapy: a novel treatment rather than a more expensive oxygen device

Nasal high flow is a promising novel oxygen delivery device, whose mechanisms of action offer some beneficial effects over conventional oxygen systems. The administration of a high flow of heated and humidified gas mixture promotes higher and more stable inspiratory oxygen fraction values, decreases anatomical dead space and generates a positive airway pressure that can reduce the work of breathing and enhance patient comfort and tolerance. Nasal high flow has been used as a prophylactic tool or as a treatment device mostly in patients with acute hypoxaemic respiratory failure, with the majority of studies showing positive results. Recently, its clinical indications have been expanded to post-extubated patients in intensive care or following surgery, for pre- and peri-oxygenation during intubation, during bronchoscopy, in immunocompromised patients and in patients with “do not intubate” status. In the present review, we differentiate studies that suggest an advantage (benefit) from other studies that do not suggest an advantage (no benefit) compared to conventional oxygen devices or noninvasive ventilation, and propose an algorithm in cases of nasal high flow application in patients with acute hypoxaemic respiratory failure of almost any cause.