1.  H. Arthur Sadhanandham Medical ICU. CMC. Vellore .

2.  Hypoxia is the most dangerous condition which requires immediate intervention.  Initially, Hypoxemic respiratory failure was managed by administration of supplemental oxygen through different devices.  Though there were several limitations in these conventional methods, they did not feel any severe adverse clinical consequences because the delivered oxygen flow was sufficient to correct Hypoxemia.  Initial focus was essentially correcting the Hypoxemia.

3.  Low flow or Variable performance devices are the ones which provide O 2 at flow rates that are lower than patient’s inspiratory demands which gives rise to the possibilities for room air to entrain especially when the total ventilation exceeds the O 2 reservoir. Therefore the final delivered FiO 2 depends on the ventilatory demands of the patient, size of the O 2 reservoir and the entrainment of room air.  High flow or Fixed performance devices are the ones which are set to deliver the gas at flow rates that exceed the patient’s peak inspiratoty flow thus the entrainment of room air also is fixed thereby ensuring the desired and fixed FiO 2.

5.  Poor Tolerance because of insufficient humidification  Difficulty in heating the oxygen flow delivered through mask and cannula.  The maximum possible flow that could be delivered through these devices was < 15 L/min.  The patients who are in respiratory distress may require more flow …. 30 liters and above/ minute where as these devices could not give > 15 L/min. This used to cause flow starvation.  The FiO2 usually would not be accurate and could not be ascertained.

6.  Insufficient humidification, flow starvation and accurate FiO 2 had become a challenge.  To overcome these three important problems, a technique namely High Flow Nasal Cannula Oxygen Therapy ( HFNC) was introduced.  This High flow Therapy was added with heated humidification which had reduced the damage to the linings of the air way.  Humidified high flow nasal cannula oxygen therapy thus came into being.

8.  The blender that is used enables to give FiO 2 ranging from 0.21 to 1.0 (21% to 100% ).  Moisturized Gases are given to the patients after the gases are passed through an heated humidifier which contains sterile distilled water.  Single limb and nasal cannula with larger diameter is used primarily to prevent heat loss and condensation.  Through the above measures, accurate FiO 2 is ensured. Humidification is taken care of and flow starvation is overcome with high flow.

9.  Tolerance and comfort levels are better  High flow prevents flow starvation  Generates continuous positive airway pressure which also helps in creating a low level positive end expiratory pressure that improves oxygenation and an increased Functional residual capacity  Washes out the dead space at nasopharyngeal region  Ensures desired and accurate FiO2.  Because of all of the above, it is believed that the pulmonary defense mechanisms are restored.

10.  Tolerance and Comfort: Conventional mask, dry gas and cold air cause mask discomfort, eye irritation, pressure/ allergy sores, oral/nasal dryness, and aspiration. But High Flow method ensures optimally humidified and heated gas and more flow for better tolerance and greater comfort. Constant high flow indirectly helps alveolar recruitment.  Establishes certain amount of PEEP: Employing continuous high flow of gas with positive pressure establishes certain amount low level PEEP though variable, prevents alveolar collapse.

11.  Washing out dead space at nasopharyngeal region: Delivering high flow gas directly into the nasopharynx washes out CO 2, reduces CO 2 re breathing and enhances oxygenation. The continuous high flow also reduces nasopharyngeal resistance.  Ensures desired and accurate FiO 2 : As we use the blender and with high flow, desired and accurate FiO 2 is ensured whereas in low flow method mixing of atmospheric air will be at a greater level.

12.  As of now, high flow devices are more commonly used in pediatric and neonatal set ups. With regard to the adult cases, it is not popular because studies done so far had shown no difference in the final out come.

13. CONCLUSIONS OF CERTAIN STUDIES:  The precise role of high flow nasal cannulae in the management and prevention of hypoxia is controversial  Failure of HFNC might cause delayed intubation and worse clinical outcomes in patients with respiratory failure (Kang et al, 2015)

14. Contd……  The FLORALI study, a small multicentre, open – label trial found that in patients with acute hypoxaemic respiratory failure and without hypercapnia, treatment with high – flow nasal oxygen, standard face mask oxygen, or non - invasive ventilation did not result in a significantly different with regard to intubation rates. There was a significant difference in favor of high – flow nasal oxygen in 90 days mortality (Frat et al, 2015: FLIRALI study).  Only mortality was postponed.

15. Contd ….  Pre-oxgenation and apnoeic oxygenation Compared to HFFM (high flow face mask), HFNC as a pre-oxygenation device did not reduce the lowest level of desaturation in an RCT (Vour’ch et al, 2015 – PREOXYFLOW trail)  A case series of 25 patients with difficult airways undergoing general anaesthesia for hypopharyngeal or laryngotracheal surgery had mean apnoea times of 14 minutes without desaturaion (i.e. SaO2 > 90%) (Pateal et al, 2015; THRIVE study)

16.  High Flow Oxygen Therapy is certainly a method which gives greater comfort and better tolerance to the patients.  High Flow Oxygen Therapy facilitates humidification which is certainly an added advantage to the patient with regard to the reduction in the damage to the linings of the airway and better mucociliary clearance  High Flow Oxygen ensures better control of FiO 2 Which enables the doctors to titrate the O 2 concentration effectively BUT IT’S EFFICACY IN ADULTS IS YET TO BE ESTABLISHED.

17.  Roca O, Riera J et al. High – flow oxygen therapy in acute respiratory failure. Repir Care 2010, 55: 408 – 13  Sztrymf B, Messika J, Bertrand et al. Beneficial effects of humidified high flow nasaloxygen in critical care patients: a prospective pilot study: Intensive Care Med; 1780 – 6  Ricard JD. High flow nasal oxygen in acute respiratory failure. Minerva Anestesiol. 2012; 78: 836 – 41  WardJJ. High –Flow oxygenadministrationby nasal cannula for adult and perinatal patients. Respir. Care 2013; 58: 98 – 122.  Groves N, Tobin A. High flow nasal oxygen generates positive airway pressure in adult volunteers. Aust.Crt.Care 2007; 20:126 - 31  Parke R, McGuinness S et al. Nasal high – flow therapy delivers low level positive airway pressure. Br.J. Anaesth. 2009; 103: 886 - 90