High Frequency Oxygen Therapy
HFNC provides warm, humidified oxygen up to 60 liters per minute through nasal prongs or cannula for delivery to patients. The oxygen/air blender enables precise titration of FiO2 independent of patient inspiratory flow rate, minimizing room air entrainment.
HFNC appears to reduce dyspnea intensity and work of breathing for adults with various underlying conditions, as well as decreasing respiratory support escalation needs compared to conventional therapy.
Improved Oxygenation
HFNC stands out from traditional oxygen delivery devices by providing warmed, humidified gas at flows up to 60 LPM with oxygen concentrations reaching 100%, giving clinicians greater precision when tailoring oxygen delivery for individual patients.
Studies on HFNC have demonstrated its effectiveness at improving oxygenation. Unfortunately, variations in inclusion criteria, device flow rates, FiO2 settings, duration and therapy duration make comparisons challenging and some studies used surrogate endpoints such as PaO2/FiO2 as opposed to clinically meaningful outcomes such as mortality or intubations for their analysis.
HFNC may contribute to oxygenation benefits by alveolar recruitment. A study on healthy subjects demonstrated this by showing how HFNC increased end-expiratory lung impedance and pressure, thus increasing oxygen recruitment into each alveolus. Improvement was more marked for supine than for prone lung, consistent with other interventions that target this mechanism of improvement.
Studies have demonstrated that HFNC improves oxygenation for patients with hypoxemic respiratory failure, without needing more intensive forms of therapy such as noninvasive ventilation (NIV) or mechanical ventilator support. One small study demonstrated this fact by employing HFNC on high risk intubation patients where its use significantly reduced episodes of severe desaturation during intubation procedures and shortened ICU stay times significantly.
Recent research comparing the pre-oxygenation efficacy of HFNC with NIV for patients undergoing bronchoscopy found that the former significantly enhanced oxygenation prior to laryngoscopy and prevented severe desaturations and hypoxemia during laryngoscopy procedures; additionally, its users experienced less discomfort than those receiving NIV.
Studies comparing high frequency noise cancellation (HFNC) therapy to standard oxygen therapy in cardiac surgery patients have also demonstrated its benefits, with one finding HFNC reduced the need for postoperative day 3 oxygen support escalation due to reduced respiratory drive; another study randomly assigned 340 cardiac surgery patients either 45 liters per minute of HFNC or 2-4 liters per minute conventional oxygen; both approaches yielded similar SpO2/FiO2 results.
Reduced Work of Breathing
High flow nasal prongs (HFNP) deliver heated and humidified medical gases at flows up to 60 liters per minute, producing physiological benefits beneficial in treating some forms of respiratory distress. Humidified oxygen delivery increases functional residual capacity, improves mucociliary clearance of secretions and lowers work of breathing; additionally it generates positive airway pressure which may recruit alveoli and lessen the need for noninvasive ventilation (NIV) or intubation.
High flow non-invasive ventilation creates an anatomical oxygen reservoir within the nasopharynx and oropharynx which reduces dead space. When oxygen is recycled back into upper airways through normal tidal volumes, CO2 retention occurs as a result, leading to ventilation-perfusion mismatch and increased CO2 retention in lungs. With high flow oxygen delivery systems like HFNC delivering volumes far exceeding respiratory metabolic demand volumes allowing improved gas exchange, reduced rebreathing CO2, and increased oxygen uptake.
Due to an increase in oxygen delivery, tidal volume (VT) remains constant while PaCO2 decreases with increasing HFNC flow. Therefore, this treatment could serve as an effective alternative to face mask therapy for patients unable to tolerate higher tidal volumes with conventional oxygen delivery methods.
Studies have demonstrated that high frequency nasal cannula (HFNC) can create positive expiratory pressures in the nasopharynx with mouth closed; however, its intensity varies with flow and patient posture and body habitus – this may prove difficult for infants who cannot comfortably tolerate HFNC as their oxygen therapy must increase accordingly.
Animal studies demonstrate that high frequency nasal cannula (HFNC) increases oxygenation while simultaneously decreasing breathing effort compared with conventional face mask oxygen delivery. Furthermore, HFNC is better tolerated than NIV and may provide a viable alternative for patients who do not meet criteria for more intensive therapy such as intubation. While more extensive clinical research needs to be completed to fully determine its full impact, this form of oxygen therapy should certainly be included as part of clinician’s therapeutic toolbox and considered when treating patients who do not meet criteria for more intensive therapy.
Reduced Intubation Risk
Intubation can be a high-risk procedure in patients with severe hypoxemia, and complications have occurred up to 40% of the time [49]. It is therefore vitally important that they are well pre-oxygenated prior to intubation; HFNC provides an effective means of pre-oxygenation as it does not interfere with laryngoscopy and nasal cannula delivery.
Utilization of HFNC to prevent intubation has been associated with reduced reintubation episodes, shorter ICU stays and an improvement in survival for intensive care unit (ICU) patients. Furthermore, using HFNC does not increase their risk for comorbidities or death in ICU patients.
HFNC has also been used for providing apneic oxygenation during tracheal intubation in patients with severe respiratory failure, and recent animal research demonstrated its ability to significantly delay severe desaturation during intubation compared with traditional face mask oxygen delivery methods.
A recent randomized controlled trial has demonstrated the benefits of high frequency noninvasive ventilation (HFNC) on ICU patients at lower risk, including less need for noninvasive positive pressure ventilation (NIPPV) and re-intubation; increased secretion clearance; reduced antibiotic need in those suffering sepsis; as well as decreased need for hospital readmission.
Another randomized controlled trial has demonstrated that early introduction of high-flow nasal cannulae (HFNC) therapy among ICU patients with hypoxemia was linked with decreased intubation rates and shorter hospital stays. 322 ICU patients with pre-extubation ROX index scores of 40 were randomly allocated either 20 L/min of HFNC therapy or conventional oxygen (1-5 L/min).
In another randomized trial, 30 LPM of HFNC was compared with NIV for use in intensive care unit patients meeting low-risk intubation criteria, and 49% versus 19% with NIV were able to avoid re-intubation without complications.
HFNC has also been proven to reduce re-intubation among lung transplant recipients and to improve survival, according to this study. Immunocompromised transplant recipients were randomly assigned either HFNC or conventional oxygen as a control treatment; with HFNC showing 29% less re-intubations compared with 45% in the control group and consequently better lung function, oxygenation, lower mortality rates and greater ventilator-free days at 90-day mortality reduction versus conventional oxygen alone.
More Comfortable
High frequency oxygen therapy has emerged as a non-invasive oxygenation support modality that has broad clinical application in the perioperative setting. It improves oxygenation, reduces WOB, enhances patient comfort, and extends the safe-apnoea window compared with conventional low-flow oxygen interfaces. It is a preferred oxygenation strategy during critical perioperative phases including pre-oxygenation and induction of general anesthesia, management of the anticipated or unanticipated difficult airway, sedation for endoscopic and upper airway procedures, tubeless microlaryngeal surgery, emergence and extubation. Furthermore, it is a superior oxygenation support modality in high-risk patients and special populations such as the obese, pregnant and pediatric population.
A key advantage of HFNC is its effective humidification and warming. This helps to clear secretions, decreases atelectasis, and prevents airway surface dehydration. This leads to enhanced patient tolerance and comfort compared with the use of conventional oxygenation interfaces such as face masks. It also enables more accurate delivery of oxygen to the target tissues while avoiding pulmonary hyperinflation and carbon dioxide desaturation.
Several studies have demonstrated superior oxygenation and patient tolerance with HFNC over low-flow oxygen delivered via face masks. A recent randomized trial of obese parturients undergoing cesarean delivery found that 3 min of HFNC significantly improved arterial PaO2 and lengthened the safe-apnoea period compared with face mask (FM) oxygenation, without altering minimum SpO2/EtCO2, nadir SpO2, or intubation success (51).
Another important clinical benefit of HFNC is its ability to sustain oxygenation during invasive procedures. In a study of pediatric patients requiring bronchoscopy, HFNC reduced moderate and severe desaturation episodes and procedure interruptions compared to low-flow oxygen (52). A similar finding was reported in a randomized trial of children undergoing glottic dilation for stenosis by bronchoscopy. HFNC maintained oxygenation, preserved respiratory stability and extended the safe-apnoea time compared with conventional oxygenation (61).
Despite these impressive benefits, HFNC should not be considered as a substitute for mechanical ventilation in severe hypoxaemic respiratory failure. However, it may be appropriate for patients with mild hypoxaemia or in whom there is a contraindication to the use of PEEP or a contraindication to nasal cannulas. Furthermore, it should be reserved for patients who cannot tolerate tracheal intubation and/or who require long periods of noninvasive oxygenation.