High-flow nasal cannula—protocol for initiation, titration and weaning

patient selection for HFNC therapy Avoid in

 Hemodynamically unstable patients
o Moderate/severe bronchiolitis o pneumonia o postextubation state  emergent intubation situations
o Acute asthma excerbation o DNR o Postoperative cardiac  Upper airway abnormalities

Initial settings
 Gas temperature: 34-37° C
 Fio2: 40-60% (adjust to achieve Target Spo2 as per condition)
 Flow: start with 1 L/kg for first 10 kg and 0.5 L/kg afterwards
 Any signs of impending respiratory
failure at any stage
Monitor HR, RR, Signs of work of breathing, Spo2, Consciousness  severe respiratory acidosis (PaCO2 >60)
 Fio2 >60%

Respiratory distress improved No improvement or worsening in WOB, SpO2 and respiratory distress
Clinical parameter target
Heart rate ↓ by about 20%
Respiratory rate ↓ by about 20% increase Flow first (up to 2L/kg for first 10 kg then 0.5 L/kg afterward)
Work of breathing Improved
Oxygen saturation Wean Fio2 to 40% within 2 hour

Continue monitoring Improved No improvement/worsening

HFNC Failure

MY PICUparameters
Respiratory NOTES stable PICU Journey 1
for 24-48 h HFNC successful Escalation of respiratory support to NIV/invasive ventilation

Wean Fio2 first to 30-40%

Wean flow by 0.5 L/kg every 4-6 h Continue monitoring
Or
Children <10 kg Children >10 kg
Decrease flow in Decrease flow in
increments of 1 L/min Q4–6 increments of 1 L/min If any signs of worsening respiratory Weaning tolerated well
hourly based on the clinical Q4–6 hourly based on
parameters the clinical parameters distress, go back to previous setting
Then change to low-flow No need for low flow and try weaning later
nasal cannula at 1–2 L/min weaning

Flow < 0.5 L/kg/min, Spo2 >92%

with a FIO2 < 40%

HFNC Discontinued, Considerstart oxygen therapy (nasal cannula/simple mask/venturi mask)

may be weaned to room air if no oxygen requirement

Continue monitoring
Humidified High-flow nasal cannulae (HHFNC) are: small, tapered cannulae that are used to deliver
heated, humidified high-flow air and blended oxygen.
 HFNC may deliver positive end expiratory pressure.
 They are usually less than 1cm long and should occlude less than 50% of the area of nares

THE PRINCIPLE BEHIND HFNC

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  Unlike atmospheric air, oxygen is a dry gas and prolonged administration of it can cause dryness and irritation
of mucus membranes.
 The airway mucosa alone is unable to transfer sufficient heat and humidity at supraphysiologic flow rates.
 The bubble humidifier commonly used with nasal cannula cannot provide adequate humidification for gas flows
>3–5 L/min.
 Hence, it is essential to humidify and heat the air-oxygen mixture prior to delivery for higher flow rates.

MECHANISM OF ACTION OF HFNC:

MY PICU NOTES PICU Journey 2

Figure 1. Mechanisms of action of high flow nasal cannula (HFNC) in acute hypoxemic respiratory failure. HFNC exerts a range of important and
interdependent physiological effects on a variety of factors that may determine clinical outcomes for patients with acute respiratory failure. VILI = ventilatorinduced
lung injury; V/Q = ventilation/perfusion; WOB = work of breathing. Illustration by Jacqueline Schaffer.

COMPONENTS OF HFNC SYSTEM:

• Source of pressurized oxygen and air regulated by a flowmeter and blender
• Sterile water reservoir attached to a heater humidifier
• Insulated and/or heated circuit that maintains temperature and relative humidity
• Nonocclusive cannula interface.
Common commercially available HFNC equipment are:
Airvo 2 (Fischer and Paykel, New Zealand) and Precision Flow system (Vapotherm Inc, Exeter, United States).

Suggested mechanisms for the reduction in work of breathing and improvement in efficiency of ventilation by HFNC
include:
• Reduces work of breathing:
High flow of gas mixture decreases the work of breathing by reduction in the inspiratory resistance associated with the
nasopharynx
• Reduction in energy expenditure:

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Adequate humidification reduces the evaporative losses from the mucosa of the airway and thereby the metabolic
work for gas conditioning
• Improvement in lung compliance and mucociliary function by supplying adequately warmed and humidified gas.
Bronchoconstriction associated with airway cooling is also reduced
• Washout of nasopharyngeal dead space leading to improved alveolar ventilation:
The nasal passages and oropharynx are continuously flushed and replenished, resulting in better removal of exhaled
gas, reduction in rebreathing and increased clearance of carbon dioxide.
HFNC needs to remain an “open system” for this mechanism to operate, nasal cannula should not cover more than
half the diameter of the nostril and mouth need not be closed
• Provides distending pressure:
HFNC systems provide some positive airway pressure and the variable and unpredictable nature of this pressure is a
matter of concern.
The amount of pressure delivered may depend on the flow, size of the patient, and the fit of the nasal cannula.
In a study, HFNC therapy at rates of 2 L/kg/ min in infants with viral bronchiolitis, generated mean pharyngeal
pressures of more than or equal to 4 cmH2O. Pressure increases linearly with the flow and decreases with age and size
of the patient.

ADVERSE EFFECTS OF HFNC THERAPY

Skin irritation caused by cannula interface is significantly lower compared to CPAP.
Other adverse effects reported include:
• Abdominal distension:
- This may limit its application in children with intra-abdominal pathology.
- Children on HFNC need to be monitored for aerophagia and orogastric tube should be kept open if distension develops
• Air leaks:
- Unpredictable rise in positive airways pressure could be the possible contributory factor.
- Properly sized cannula that allows for some gas leak needs to be ensured.
MY PICU NOTES PICU Journey 3
FEEDING CHILDREN ON HFNC
HFNC responders who had significant and sustained clinical improvement of their respiratory distress can be given
feeds, regardless of the HFNC flow rate.
It is better to withhold enteral nutrition in patients who continue to struggle and are at risk of aspiration or requiring
escalation of support.

AEROSOL THERAPY DURING HFNC

Children receiving HFNC support may also benefit from aerosol therapy, depending upon the disease process.
Easiest option to deliver aerosolized medications to patients on HFNC is to remove the cannula and administer aerosolized therapy
via traditionally used interfaces like nebulizer mask.
But few patients may decompensate if nasal cannula is discontinued even for a short period.
Aerosol administration through HFNC circuit is an interesting option. Although the use of aerosol administration
via HFNC using mesh nebulizers in the circuit has been described, the efficiency of the therapy and aerosol particle
delivery is controversial. Flow rate more than 3 L/min, smaller cannula sizes and nebulizer position after humidifier are
factors found to result in poor aerosol delivery.
Few in vitro studies have shown that heliox increases the efficiency of aerosol delivery compared to oxygen. Hence, the available
options for aerosol delivery through the HFNC circuit are to either decrease the flow rate to less than or equal to 3 L/min during
aerosol therapy or delivering aerosol through HFNC and heliox at flow rates more than 3 L/min, in patients who can tolerate a
lower FiO2.
However, it is still unclear whether the use of heliox can produce a clinically significant aerosol particle delivery at flows >3 L/min.

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