High-Flow Nasal Cannula Therapy

Introduction:

Supplemental oxygen therapy is the first line of treatment in hypoxic conditions associated with respiratory failure. Additional oxygen therapy aims to provide adequate ventilation and oxygenation to facilitate breathing. High-flow cannula oxygen therapy is an effective and innovative therapy for respiratory failure. It is also called mini-continuous positive airway pressure, nasal high-flow, high-flow therapy, nasal high-flow ventilation, and transnasal insufflation.

What Are the Components of High-Flow Nasal Cannula Therapy?

High-flow cannula therapy has numerous advantages over conventional oxygen-delivering systems with better physiologic effects. It consists of components such as:

• An air blender.

• An active humidifier.

• Single heated circuit.

• Nasal cannula.

What Are the Advantageous Physiological Effects of High-Flow Cannula Therapy?

High-flow cannula therapy can provide adequately heated and humidified medical gas up to 60 liters per minute. The following are the advantages of high cannula therapy with numerous physiologic effects that include:

1) Positive End-Expiratory Pressure (Peep) Effect:

• Certain factors such as gender, body mass index, open or closed mouth, and position influence end-expiratory pressure.
• Few reports suggest that the positive pharyngeal pressure increases with the high flow nasal cannula therapy.
• With the mouth closed, pharyngeal pressure increases as flow increases.
• As the report suggests, the end-expiratory lung volume is evaluated using electrical lung impedance tomography. The end-expiratory lung volume is more significant with a high-flow nasal cannula when compared with low-flow oxygen therapy.
• This value is excellent in patients with higher body mass indexes.
• The end-expiratory lung volume is evaluated in different positions with lung impedance tomography. The value is increased in both the supine or prone position with a high-flow nasal cannula.
• With the mouth closed, the mean upper airway pressure increases with the increase in the gas flow delivery.

2) Anatomical Dead Space Reduction:

• The thoracoabdominal synchrony is evaluated using respiratory inductance plethysmography.
• The value of thoracoabdominal synchrony is better with a high-flow nasal cannula than with fast mask delivery.
• As the report suggests, the partial pressure of carbon dioxide decreases with the high flow nasal flow increases, which results in the greater escape of gas more effectively. This can suggest an adequate carbon dioxide washout with a high-flow nasal cannula.
• With the mouth position open and closed, the fraction of inspiratory oxygen is evaluated in healthy individuals.
• The fraction of inspiratory oxygen is higher with open-mouth breathing due to the reservoir function of the nose and the pharynx.
• With mouth-open breathing, it efficiently washes out carbon dioxide and provides a more extensive anatomic reservoir.
• During inhalation, the nasal oxygen entrained contributes to an increase in the fraction of inspiratory oxygen level.

3) Good Level of Humidification:

• The conventional oxygen devices which deliver unwarmed gas cause certain adverse effects such as nasal dryness, mask discomfort, eye irritation, oral dryness, nasal and eye traumas, aspiration, and gastric distension.
• The unwarmed or cold air in conventional therapy causes bronchoconstriction. An adequately conditioned gas has less effect on the physiologic response of the lungs.
• Conditioning of the gas reduces the work of breathing and constriction of airways. It increases mucociliary functions and helps in clearing nasal secretions resulting in better oxygenation and good ventilation. It is particularly indicated in patients with chronic obstructive pulmonary disease.
• Noninvasive ventilation delivers these medical gasses with increased flow, but the patient may present with oral dryness and discomfort with inadequate humidity.
• The humidity of gas delivered to oronasal masks during noninvasive ventilation is influenced by humidifier settings, and the amount of leakage varies among patients with equivalent humidifier settings.

4) Constant Fraction of Inspired Oxygen:

• The fraction of inspiratory oxygen is found to be higher during open-mouth breathing than in closed-mouth breathing.
• High inspiratory flow with exercise is associated with lower fixation of inspiratory oxygen due to increased air entrainment.

Why High-Flow Nasal Cannula Therapy Is Most Preferred Over Noninvasive Ventilation?

• The respiratory support is balanced with adequate alveolar ventilation.

• In order to maintain adequate alveolar ventilation, it is significant to expel carbon dioxide from the body.

• The alveolar ventilation is adequately maintained by manipulating minute ventilation during invasive or noninvasive ventilatory support.

• Noninvasive ventilation (NIV) helps in enhancing the inspiratory tidal volume (TV) and maintaining adequate alveolar ventilation. Therefore, this is the most preferred primary modality for respiratory support in patients with chronic obstructive lung disease.

• The main disadvantage of the noninvasive ventilation method is the poor mask tolerance in patients, which makes this inapplicable in some situations.

• High-flow nasal cannula oxygen therapy is used as an alternative means of respiratory support in the case of critically ill patients.

• The interface is the major difference between noninvasive ventilation and high-flow nasal cannula. The interfaces for noninvasive ventilation increase the anatomical dead space, but in a high-flow nasal cannula, it decreases the dead space. Therefore, by decreasing the dead space, high-flow cannula therapy improves alveolar ventilation in chronic obstructive pulmonary disease patients.

What Are the Principles of High-Flow Nasal Cannula?

• The air or oxygen blender allows an inspiratory fraction of oxygen (FIO2) from 0.21 to one in a flow of up to 60 liters per minute.

• The gas is then heated up and humidified with an active humidifier and delivered through the heated inspiratory circuit.

• The patient breathes adequately heated and humidified medical oxygen gas through the nasal cannulas in large diameters.

What Are the Contraindications of a High-Flow Nasal Cannula?

1) High-flow nasal cannula gains more attention and is applied to various diseases under a variety of conditions.

2) It is to be applied carefully or contraindicated in patients to whom noninvasive positive pressure ventilation (NPPV) is contraindicated.

3) Certain conditions which are contraindicated to noninvasive positive pressure ventilation are as follows:

• Conscious disorders.
• Airway obstruction.
• Facial injury and facial malformation.
• Risk of aspiration.
• A lot of sputum.
• Unstable hemodynamics.
• Respiratory arrest.

Conclusion:

High-flow nasal cannula therapy is an effective and valuable modality that can be used as an alternative method of respiratory support for critically ill patients. It is used in a wide variety of underlying diseases. Specific issues, such as criteria for timing the start of high flow nasal cannula and indications, need to be evaluated and resolved to attain effective results.