Clearance of expired air in the upper airways, reduces rebreathing of gas high in CO2 and depleted of O2, resulting in an increase in alveolar ventilation.
Watch the effect in action! (45 seconds)
This video depicts clearance of a radioactive tracer from upper airway model using a Gamma camera imaging superimposed on a CT scan. Flow rates were 15, 30 and 45 L/min. In this experiment you can see that as flow rate increases so does clearance.
NHF creates breath and flow-dependent pressure, making inspiration
easier and promoting slow, deep breathing on expiration,
thereby increasing alveolar ventilation.
Watch the effect in action (33 seconds)
Corley et al. 2011 showed once Optiflow NHF therapy is commenced in patients post-cardiac, there is a significant increase in areas of lung aeration.
This change reflects enhanced lung volume and tidal volume.
The researchers determined a strong correlation between airway pressure (Paw) and end-expiratory lung impedance (EELI). Paw increased by 3.0 cmH20 and EELI increased by 25.6%. EELI is a surrogate for end expiratory lung volume.
~ Corley et al. Br J Anaesth. 2011.
Humidity enables the comfortable delivery of high flows. Optimized humidity emulates the natural balance of heat and moisture that occurs normally in healthy lungs and may help to maintain physiological stability in compromised airways.
Watch the effect of low humidity in action!
The experiment portrayed in the video was conducted on two ovine tracheal samples exposed at 100% relative humidity (left panel) and the other at 90% relative humidity (right panel) for 15 minutes.
As the clip starts, tiny beating cilia are flickering in the background. Then, debris in the mucus of the right image becomes stationary. The dark spots moving quickly across the left image showed debris being cleared by effective mucociliary transport.
After just an hour at the lower humidity, the mucosa has completely dried out.
Respiratory support delivered via a mask poses challenges for clinicians and patients. NHF therapy is delivered via a cannula. Better patient comfort may promote improved compliance.
Clinical evidence suggests that use of Optiflow NHF therapy provides improved comfort compared to conventional oxygen delivery devices1,2. A study in JAMA3 found significantly reduced skin breakdown and noted a lower nurse workload with Optiflow NHF therapy than with Bi-level non-invasive ventilation. Patients are able to eat, drink and sleep with the Optiflow interface and can talk with their caregivers and families.
Providing oxygen via NHF therapy can give you some confidence in the accurate delivery of blended, humidified oxygen.
In the example illustrated, the maximum oxygen flow from the face mask (in the left pane) is limited to approximately 10 L/min which is not sufficient to meet the patient’s peak inspiratory demand of 50 L/min. To compensate for this deficit, 40 L/min of room air will be entrained for every breath, which will dilute the oxygen and deliver a variable (sometimes unknown) FiO2.
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