Nasal high flow confers benefits that conventional oxygen therapies cannot. It's a significantly more sophisticated form of respiratory support, including dynamic, positive airway pressure, and reduction of dead space.
The airway hydration resulting from heating and humidifying the air is critical to facilitating comfortable treatment but is equally valuable in preserving mucociliary function.
As with any treatment, patient comfort is a significant factor. One of the standout features of NHF is the level of respiratory support that can be achieved without the downsides of a mask.
Below is an overview of how each mechanism contributes to the therapy, with some cool videos showing the effects in action.
Clearance of expired air in the upper airways reduces rebreathing of gas high in CO2 and depleted O2, increasing alveolar ventilation.
How dead space clearance improves oxygenation with just room air.
Watch this effect in action
This video depicts the clearance of a radioactive tracer from an upper airway model using Gamma camera imaging superimposed on a CT scan.
Flow rates were 15, 30, and 45 L/min.
In this experiment, as the flow rate increases, so does clearance.1
This effect is flow dependent2
NHF creates breath and flow-dependent pressure, making inspiration
easier and promoting slow, deep breathing on expiration,
thereby increasing alveolar ventilation.
How pressure creates slower, deeper, more regular breathing.
Corley et al. 20114 demonstrated a significant increase in lung aeration once therapy starts.
This change reflects enhanced lung volume and tidal volume.
This effect is flow-dependent
Increases approximately 0.5 - 1 cmH2O per 10 L/min3,5-6
Mean airway pressure (for illustrative purposes only)
It's different from CPAP pressure!
Humidity enables the comfortable delivery of high flows of gas. Optimized humidity emulates the natural balance of heat and moisture in healthy lungs and may promote physiological stability in compromised airways.
Watch this effect in action.
Watch the effect of low humidity under a microscope (1 min - turn audio on)
As the clip starts, you can see cilia beating. The dark spots moving across the left panel are debris (possibly bacteria) removed by effective mucociliary transport.
Conversely, debris in the right low-humidity panel stops as cilia slow, the effect of low humidity. After just an hour at 90% RH, the mucosa has dried out.
Do you need a refresher on how MCT works - watch this cool animation!
Respiratory support delivered via a mask poses challenges for clinicians and patients.
NHF delivered via a cannula promotes patient comfort and may improve compliance.
Clinical evidence suggests that Optiflow NHF therapy provides better comfort than conventional oxygen delivery devices.10,11
Patients can eat, drink and sleep with the Optiflow interface and can more easily communicate with clinicians and families than with a mask.
Additionally, a study in JAMA12 found significantly reduced skin breakdown and noted a lower nurse workload with Optiflow NHF therapy compared with Bi-level ventilation.
Oxygen delivered via conventional oxygen therapy (COT) is 'bone' dry. Delivering oxygen via NHF therapy allows for oxygen to be optimally humidified eliminating the issues associated with exposure of the vulnerable upper airway to dry gas.
Additionally delivering oxygen via NHF gives you confidence in the accurate delivery of blended oxygen.
The advantage of NHF for oxygen delivery - is reducing oxygen dilution.
In the example illustrated, the maximum oxygen flow from the face mask (in the left panel) is limited to 10 L/min, which is insufficient to meet the patient’s peak inspiratory demand of 50 L/min.
The patient will draw in/entrain 40 L/min of room air to compensate, diluting the 100% oxygen delivered via the face mask.
Conversely, in the right panel, NHF therapy can meet the patient’s total inspiratory demand of 50 L/min without the need for dilution of oxygen - this gives confidence in the delivery of a specified FiO2.
Why using NHF gives you confidence in the oxygen fraction you are delivering.
With conventional oxygen, inspiratory flow is variable, so the oxygen fraction delivered is variable.
In contrast with NHF, you may be able to meet or exceed peak inspiratory flow, reducing or eliminating dilution from room air.
Although an NHF device can deliver high oxygen levels (up to 100% O2), it’s not specifically an oxygen delivery device. NHF can be, and is, often used without supplemental oxygen, i.e., with room air – 21% O2.
Conventional oxygen therapy via a low-flow cannula and most styles of oxygen face masks are limited to lower flow rates (up to 10 L/min) partly because the gas is cold and dry, making tolerability a significant issue.
These lower flow rates also limit FiO2 delivery and accuracy and aren’t high enough to offer the benefits of dead-space washout and positive airway pressure.
Typically, “high flow” refers to flow rates above 15 L/min of a fully humidified air and oxygen mix. These higher flow rates enable mechanisms that cold, dry oxygen alone cannot provide.
See the table below for a comparison of standard COT devices and NHF.