Physician anesthesiologist at Stanford at Associated Anesthesiologists Medical Group
Richard Novak, MD is a Stanford physician board certified in anesthesiology and internal medicine.Dr. Novak is an Adjunct Clinical Professor in the Department of Anesthesiology, Perioperative and Pain Medicine at Stanford University, the Medical Director at Waverley Surgery Center in Palo Alto, California, and a member of the Associated Anesthesiologists Medical Group in Palo Alto, California.
Latest posts by THE ANESTHESIA CONSULTANT (see all)

At the 2023 American Society of Anesthesiologists meeting in San Francisco, I walked by a booth advertising High Flow Nasal Oxygen. The product was called Optiflow. I asked the representative to educate me. She began by opening a package containing an Optiflow nasal cannula, and she strapped it around my head and into my nostrils. Within one minute she started a flow of 40 liters per minute of humidified, warmed 100% oxygen into my nose. I felt a slight sensation of moving air, but because the flow was humidified and warm, I felt no caustic insult of gas blasting through my nose and upper airway. I was—in a word—flabbergasted. The capacity to deliver this much oxygen to a non-intubated patient is a marked advance in anesthesia care.

HFNO was originally used in neonatal and pediatric ICUs to oxygenate acute hypoxemic respiratory failure patients without utilizing an endotracheal tube. Its use expanded to adult ICUs. The ability to deliver 60 to 70 liters per minute of oxygen via the nose enabled physicians to delay or avoid intubating ICU patients with hypoxemia. HFNO is delivered via nasal prongs which are larger than conventional nasal cannula prongs, and at higher flow rates than are generally applied during conventional oxygen therapy. Inspired oxygen/air is heated to 37 °C, and is humidified to 100% relative humidity.

A typical nasal oxygen cannula is limited to supplying 6 liters per minute of oxygen, which is approximately equivalent to delivering 45% oxygen. Using a typical nasal oxygen cannula at a flow higher than 6 liters will cause a patient significant irritation and drying of the nasal mucosa.  By humidifying and heating the oxygen inflow, HFNO can deliver 100% oxygen at a flow rate of up to 60 liters per minute via heated tubing and wide-bore nasal prongs.



Optiflow Airvo 2 high-flow nasal oxygen device: (1) wire-heated circuit tubing; (2) hot plate-heated humidification chamber system; (3) nasal cannula; (4) oxygen inlet port; (5) sterile water supply.


One day after attending the ASA meeting in San Francisco, I heard an in-person lecture in Palo Alto, California by Professor Anil Patel from the Royal National Throat, Nose and Ear Hospital in London. Dr. Patel has been a pioneer in bringing HFNO/THRIVE from the ICU into the operating room. Dr. Patel is the author of a seminal THRIVE (Transnasal Humidified Rapid-Insufflation Ventilatory Exchange ) study, in which he wrote that THRIVE “has the potential to transform the practice of anesthesia by changing the nature of securing a definitive airway in emergency and difficult intubations from a pressured stop–start process to a smooth and unhurried undertaking.

Patel’s landmark 2015 publication “Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE): a physiological method of increasing apnea time in patients with difficult airways” demonstrated that High Flow Nasal Oxygen (HFNO), or THRIVE, “combines the benefits of ‘classical’ apneic oxygenation with continuous positive airway pressure and gaseous exchange through flow-dependent dead space flushing. We extended the apnea times of 25 patients with difficult airways who were undergoing general anesthesia for hypopharyngeal or laryngotracheal surgery. This was achieved through continuous delivery of transnasal high-flow humidified oxygen, initially to provide pre-oxygenation, and continuing as post-oxygenation during intravenous induction of anesthesia and neuromuscular blockade until a definitive airway was secured. Apnea time commenced at administration of neuromuscular blockade and ended with commencement of jet ventilation, positive-pressure ventilation or recommencement of spontaneous ventilation. During this time, upper airway patency was maintained with jaw-thrust. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) was used in 15 males and 10 females. Mean (SD [range]) age at treatment was 49 (15 [25–81]) years. The median (IQR [range]) Mallampati grade was 3 (2–3 [2–4]), and direct laryngoscopy grade was 3 (3–3 [2–4]). There were 12 obese patients and nine patients were stridulous. The median apnea time was 14 (9–19 [5–65]) minutes. No patient experienced arterial desaturation < 90%.(bold emphasis added by me.)

Figure 2 from this study shows the stability of O2 saturation during the prolonged apnea:

Figure 3 from this study shows the stability of end-tidal CO2 levels during the prolonged apnea, with an average rate of carbon dioxide rise of only 1.1 mm Hg per minute.

HFNO can generate a low level of positive pressure in the upper airway, directly proportional to the high gas flow delivered, probably improving oxygenation by PEEP (positive end-expiratory pressure). This PEEP effect improves alveolar recruitment, and might also improve gas exchange.

Widespread adoption of HFNO as routine therapy in the operating room is still lacking. The main textbook in our specialty, Miller’s Anesthesia, 9th Edition, describes the use of THRIVE for difficult intubations, but their coverage is limited to one paragraph in a chapter on Adult Airway Management, in a section describing Apneic Oxygenation, out of the 3112 pages in the publication.

Many clinicians are simply not aware the technology exists or that it is available.  I believe many smaller hospitals and outpatient facilities such as ambulatory surgery centers do not own the required equipment. The cost of using HFNO exceeds the cost of standard nasal cannulae, but  the cost is not prohibitive. One Optiflow oxygenation+humidification unit made by F & P Healthcare sells for about $1500. The disposable nasal tubing apparatus for one patient sells for about $35.

Important uses of HFNO in perioperative medicine will include : a) keeping a difficult airway patient oxygenated while the anesthesia provider is performing intubation or airway procedures; and b) keeping morbidly obese patients or patients with hypoxemic cardiopulmonary disease oxygenated for brief procedures without needing to place an endotracheal tube or a laryngeal mask airway (LMA).

Let’s look at two demonstrative examples:

High Flow Nasal Oxygen utilized during difficult intubation


  • A 53-year-old patient with a difficult airway presents for general anesthesia for bariatric surgery. The patient weighs 350 pounds, stands 5 feet 8 inches tall, and has a Body Mass Index of 53, classifying him as super morbidly obese. His airway exam shows a thick neck (circumference 42 cm, or 16.5 inches), a small mouth, a Mallampati 4 classification, and limited neck extension. You apply HFNO with 100% oxygen at 60 liters per minute, and continue this for 10 minutes prior to inducing anesthesia with propofol and rocuronium. Once the patient is unconscious, you attempt intubation with a Glidescope, and have difficulty visualizing the vocal cords. A colleague assists you by advancing an endotracheal tube threaded over a fiberoptic laryngoscope, while you hold the Glidescope in place. After 14 minutes of apnea time, your colleague is able to advance the fiberoptic scope into the trachea and slide the endotracheal tube past the vocal cords. During all this time the patient was apneic but remained well oxygenated with a saturation nadir of 97% because of the HFNO.
  • A 40-year-old patient presents for an upper GI endoscopy under intravenous sedation. The patient weighs 275 pounds and stands 5 feet 5 inches tall, for a BMI = 45. His airway exam is Mallampati 2. His abdomen is protuberant, and you’re concerned this morbidly obese patient will become hypoxemic under propofol sedation. You connect the patient to HFNO with 100% oxygen at 60 liters per minute for 5 minutes, and then position the patient in the lateral position, left side down. His oxygen saturation is 100%, and you begin a propofol infusion. The patient’s breathing becomes shallower as he loses consciousness, but his oxygen saturation remains 100% as the GI doctor inserts the endoscope into her mouth and completes the procedure. Once the gastroenterologist is finished, you turn off the propofol, the patient awakens, and you bring him to the Post Anesthesia Care Unit where he is stable until discharge.

Upper GI Endoscopy with Optiflow High Flow Nasal Oxygen


Currently the American Society of Anesthesiologists (ASA) Difficult Airway Algorithm states, “Recommend supplemental oxygen administration before initiating and throughout difficult airway management, including the extubation process.” There is no specific mention of High Flow Nasal Oxygen (HFNO) or Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE), but the most effective way to administer supplemental oxygen during difficult airway management, without interfering with efforts to manage the airway, is High Flow Nasal Oxygen (HFNO) or Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE).

I believe a statement that High Flow Nasal Oxygen (HFNO) or Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) is a standard of care in perioperative airway management is, in all likelihood, coming in the very near future. The benefit/risk ration of utilizing High Flow Nasal Oxygen (HFNO) or Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) is very high.

I’d suggest you contact a manufacturer of High Flow Nasal Oxygen (HFNO) equipment such as the Optiflow unit,  and look into obtaining this useful adjunct for your facilities.

Disclaimer: I have no financial ties to the manufacturers of Optiflow, nor do I have any financial incentive for recommending their product. I simply want safer care for patients everywhere.




The most popular posts for laypeople on The Anesthesia Consultant include: How Long Will It Take To Wake Up From General Anesthesia? Why Did Take Me So Long To Wake From General Anesthesia? Will I Have a Breathing Tube During Anesthesia? What Are the Common Anesthesia Medications? How Safe is Anesthesia in the 21st Century? Will I Be Nauseated After General Anesthesia? What Are the Anesthesia Risks For Children?

The most popular posts for anesthesia professionals on The Anesthesia Consultant  include: 10 Trends for the Future of Anesthesia Should You Cancel Anesthesia for a Potassium Level of 3.6? 12 Important Things to Know as You Near the End of Your Anesthesia Training Should You Cancel Surgery For a Blood Pressure = 170/99? Advice For Passing the Anesthesia Oral Board Exams What Personal Characteristics are Necessary to Become a Successful Anesthesiologist?