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Stefanie J. LaJuett
RVT, VTS (ECC)
Stefanie earned her AAS degree in veterinary technology from Medaille College in 2006 and her veterinary technician specialist (VTS) credential in emergency and critical care (ECC) in 2013. She has worked in the intensive care unit (ICU) of the North Carolina State University College of Veterinary Medicine since 2007 and has served as an interim supervisor, lead technician, and trainer. She has served on the AVECCT nursing standards committee as well as successfully mentored several other veterinary nurses/technicians in obtaining their VTS (ECC). She has also spoken at several conferences and has been the technician program chair for the North Carolina Veterinary Conference for the past 5 years. Her particular interests include technician training and education, wildlife rehabilitation, ventilator patient management, and advanced catheterization.Read Articles Written by Stefanie J. LaJuett
RVT, VTS (ECC)
Lynne obtained a BA degree in anthropology from the University of Massachusetts, Amherst, before becoming certified as a veterinary technician in 2004. She joined the ICU team at NC State Veterinary Teaching Hospital in 2013 and obtained her VTS (ECC) in 2016. Lynne has also served as a co-chair of the technician program for the North Carolina Veterinary Conference for the past 4 years. Lynne has worked in general practice, emergency medicine, ophthalmology, and zoo medicine, but is happiest managing critical cases and learning from the amazing doctors and fellow veterinary nurses at NC State.Read Articles Written by Lynne Babineau
For emergency patients presenting with respiratory distress who do not respond adequately to conventional oxygen therapy, high-flow oxygen therapy (HFOT) offers a middle-ground option before using mechanical ventilation. The purpose of this article is to review how HFOT compares with conventional oxygen therapy and mechanical ventilation, indications and contraindications, and guidelines for sedation protocols, nasal prong application techniques, and patient monitoring.
- High-flow oxygen therapy is not a replacement for mechanical ventilation.
- Oxygen toxicity can occur in patients maintained at 100% Fıo2 in as little as 24 hours.
- The nasal prong cannula diameter must be carefully measured to be sure it does not exceed approximately 50% of the diameter of the nares.
- The curvature of the nasal prongs should always point downward to prevent trauma to the mucous membranes and properly direct oxygen flow.
- When placing nasal prongs, nasoesophageal and nasogastric tubes may be left in place.
Respiratory distress is one of the most common presenting emergencies in veterinary medicine. Until recently, therapies were limited to medical management, conventional oxygen therapy, and mechanical ventilation. Conventional oxygen therapies are relatively simple, involving oxygen cages, nasal oxygen cannulas, or flow-by oxygen. Mechanical ventilation is less commonly available because it is expensive and requires extensive training.
Approximately 6 years ago, high-flow oxygen therapy (HFOT) became available as a bridge between conventional oxygen therapies and mechanical ventilation in the veterinary setting.1 HFOT has been used in human medicine for at least 20 years, primarily for neonates with respiratory compromise. Applications of this therapy in veterinary medicine have proven promising.2
What is High-Flow Oxygen Therapy?
HFOT is the administration of warm, humidified oxygen via nasal prongs, using a commercially available unit (FIGURE 1). It allows the delivery of higher flow rates of oxygen (4 to 60 L/min with some devices). The flow rate is set to meet or exceed the inspiratory flow demand of the patient (the speed at which the patient inhales). In normal mesocephalic dogs, the average flow demand is approximately 500 to 1000 mL/sec.3 Brachycephalic dogs may have lower flow demands due to naturally occurring airway obstructions. When a critically ill patient is experiencing respiratory distress, the flow demands are considerably higher owing to increased work of breathing, as well as the metabolic demands of illness.
How Does HFOT Compare to Conventional Oxygen Therapy?
Flow-by oxygen, oxygen cages, and nasal oxygen cannulas are often sufficient for initial support. One or more of these therapies is readily available in most clinical settings.
Flow-by oxygen therapy is a temporary solution. It requires 1-on-1 nursing care and can often feel like the room is receiving more oxygen support than the patient. While easily accessible and very inexpensive, it is not feasible for long-term support.
Oxygen cages take up a lot of space compared with other methods of support. They require frequent maintenance and routine soda lime changes, and the limited space can contribute to patient stress. While some oxygen cages come in larger sizes, patients often get overheated even with cooling support. Additionally, opening the cage door frequently to perform treatments may result in a decrease in oxygen levels inside the cage. Larger cages take longer to achieve adequate oxygen content, and flow-by is often needed to bridge the gap.
Oxygen delivered via conventional nasal cannulas is not heated and not sufficiently humidified, and the flow rates are limited (1 to 5 L/min). These flow rates are further diluted by room air (~21% oxygen) each time the patient inspires because mixing of gases leads to a less exact fraction of inspired oxygen (Fıo2).4 Furthermore, the lack of temperature regulation and humidification may result in damage to the nasal mucosa, airway constriction, and inflammation.2
High-Flow Oxygen Therapy
Compared with conventional oxygen therapies, HFOT has been shown to improve oxygenation in moderate to severe cases of hypoxemia.2,5 A patient is considered hypoxemic when the arterial partial pressure of oxygen (Pao2) is less than 80 mm Hg or the oxygen saturation (Spo2) is less than 95%.6 The heated and humidified oxygen is better tolerated by most patients and can be delivered at much higher flow rates. The patient also experiences less energy expenditure by not having to heat the oxygen gas on its own. The nasal prongs used in HFOT are usually well tolerated by most patients.
HFOT uses high rates of oxygen to flush out carbon dioxide from gas-conducting (versus gas-exchanging) areas of the upper airway and replacing it with oxygen-rich air.7 This allows for a more optimized Fıo2 to reach the alveoli and eliminates the mixing of gases. The resulting maintenance of increased pressure throughout the breathing cycle aids in the recruitment of alveoli, effectively acting similarly to PEEP (positive end-expiratory pressure) in ventilated patients.2,5 HFOT provides approximately 3 to 5 cm H2O of simulated PEEP, which increases resistance to exhalation and promotes retention of oxygen.
How Does HFOT Compare to Mechanical Ventilation?
It is important to remember that HFOT is not mechanical ventilation. There are no inspiratory pressure settings and no ability to set PEEP, respiratory rate, or volume, and it offers no additional monitoring (e.g., pressure-volume loops). Mechanical ventilation allows for full control of the airway and breathing cycle; however, it is very expensive, requires full-time care and monitoring by specially trained doctors and veterinary nurses, as well as the use of heavy sedation or anesthetics, and is not commonly available in most veterinary practices.
HFOT bridges the gap to mechanical ventilation, is less invasive than ventilation, and is generally more cost effective. For example, the unit used in the authors’ institution (DRE Volumax; Avante Animal Health, dreveterinary.com) employs a disposable cartridge that may be used for up to 30 days.8 Disposable single-use nasal prongs are relatively inexpensive, and the sterile water bags necessary are often readily available.
Indications and Contraindications For the Use of HFOT
HFOT is indicated for any patient in which conventional oxygen therapy has failed or where mechanical ventilation is unavailable, too costly, or detrimental to patient safety. It is also a great alternative when owners are unwilling to consider mechanical ventilation. HFOT has also been utilized in brachycephalic dogs immediately after extubation to aid in recovery from anesthesia.9
Early indicators of a poor response to HFOT may include persistently increased respiratory rate and effort, increased heart rate, ventricular premature contractions, orthopneic posturing, head bobbing, restlessness, “guppy” breathing, true dyspnea or signs of respiratory fatigue, and cyanosis.10 HFOT is not a replacement for mechanical ventilation. If Spo2 cannot be maintained above 93%, carbon dioxide cannot be maintained below 60 mm Hg, or the patient has clinical signs of respiratory fatigue, then intubation and mechanical ventilation are indicated.11
Exclusion criteria for HFOT may include chronic lung disease or severe hypercapnic respiratory failure. Patients requiring a chest tube should have one placed prior to using HFOT or mechanical ventilation. Contraindications for HFOT may also include epistaxis, nasal masses or facial trauma, increased intracranial pressures and traumatic brain injury, esophageal foreign bodies or obstructions, or patients with increased sensitivity to facial manipulation.
Due to the potential for esophageal or gastric distention from aerophagia, patients with gastrointestinal bleeding may not be candidates for HFOT. Hemodynamically unstable patients or those unable to maintain a functional airway are also not always eligible.
Patients with chronic airway or pulmonary disease may have adapted to higher carbon dioxide levels; therefore, lowering carbon dioxide levels with the use of supplemental oxygen may result in severe hypoventilation. Lowering carbon dioxide levels even a small amount will decrease the respiratory drive and ultimately lead to respiratory failure.11
Nasal prongs are not currently available for use with cats, neonates, micropets, or exotic pets. In these patients, the size of the prongs would completely occlude the nares and prevent proper gas exchange, resulting in hypercapnia or barotrauma. Cats cannot tolerate HFOT due to their inability to pant for prolonged periods of time. They are also obligate nasal breathers. Additionally, the increased pressures associated with HFOT may not be safe for patients with smaller tidal volumes (patients <4 kg).
The High-Flow Oxygen Unit
Most HFOT units consist of the high-flow unit itself, a roll stand for easy transport, the air compressor, detachable/disposable patient circuits, disposable nasal prongs, gas inlet filters, medical air/oxygen hoses, and a power cord. Most units have a backup battery system that allows for up to 15 minutes of power during an emergency outage. Systems are relatively quiet while in use, which is ideal in a critical care setting. See Using the DRE Volumax for an overview of unit setup in the authors’ institution as an example; however, details of setup and use vary by model, and the user manual should always be consulted for each specific unit.
- 1 patient circuit cartridge, chosen based on patient size
- 1 nasal prong oxygen cannula
- 1-L bags of sterile water
- Access to oxygen and medical air
Note: Each circuit cartridge can be used for multiple patients for up to 30 days after the initial setup. It is important to use the date sticker on the side of the cartridge to prevent the circuit from being overused (FIGURE A).
- After proper handwashing, open the new cartridge bag while wearing examination gloves and aseptically attach the new circuit to a 1-L bag of sterile water. Be certain a secondary liter bag of sterile water is available; do not let the bag attached to the unit run dry.
- Hang the sterile water bag from the pole and allow the cartridge to fill with approximately 200 mL of sterile water (FIGURE B).
- Insert the cartridge.
- Attach the oxygen lines and the medical air lines to the outlets.
Note: Medical air is only necessary when providing an Fıo2 (fraction of inspired oxygen) less than 100% to the patient.
- Plug in and turn on the unit. If the air compressor will be used, it must be turned on before the Volumax machine. Medical air must flow through the unit before humidifying so that moisture does not build up inside the machine.
- Set parameters (gas, flow rate, Fıo2, temperature) (FIGURE C). Flow rates are chosen based on the severity of disease and size of the animal (TABLE 1).
- Activate the machine.
Attach the circuit to the nasal cannula. Make sure you do not connect the unit to the patient until the system has had a chance to warm up and purge the excess moisture. Connection immediately after setup can cause the patient discomfort due to improperly heated air or excess moisture in the line. Proper warmup takes about 5 minutes.
Parameters that can be set and adjusted include temperature, Fıo2, and flow rate. Air delivered to the patient may be heated and humidified.
The purpose of the compressor is to blend medical air with 100% oxygen to reach Fıo2 levels lower than full concentration.
Oxygen toxicity (hyperoxia) can occur in patients maintained at 100% Fıo2 in as little as 24 hours.12 Oxygen toxicity is an iatrogenic condition in which supplemental oxygen becomes toxic to the lungs over a prolonged period. Signs range from coughing, nausea, and muscle twitching to disorientation, seizures, and even death.10,12
Choosing and Using Nasal Prongs
Once the HFOT machine is set up, the nasal prongs should be chosen and fitted to the patient. A new set of nasal prongs should be used with every patient.
Measuring the Prong Diameter
The cannula diameter should be carefully measured to be sure it does not exceed approximately 50% of the diameter of the nares (FIGURE 2). Too large a diameter can obstruct the patient’s ability to ventilate, while too small a diameter will provide inadequate flow and offer poor respiratory support. Prong size can be assessed by placing a hand or cotton ball in front of the animal’s nose. If air flow can be felt, or if the cotton ball moves, the prongs are likely not occluding more than 50% of the nares. Additionally, if the prongs are the right size, there should be an audible “break” in the flow each time the patient exhales. The HFOT unit manufacturer may also provide recommendations for cannula diameter related to patient size and compatible flow rate.
Securing the Cannula
The nasal prong cannula should be secured to the patient in a way to prevent inadvertent disconnection. A variety of techniques can be used; however, the authors have found suturing the nasal prongs to each side of the patient’s muzzle using a finger-trap method to be the most successful (FIGURE 3).
Some nasal prongs may be better secured by creating a small tape “bridge” over the muzzle to help the prong tubing hold the proper shape as well as decrease suture tension on the patient’s face (FIGURES 4 AND 5).
The prongs can also be secured using a tape butterfly method. When using the taped butterfly method or when using a tape bridge, waterproof surgical tape is usually more effective than porous tape. The tubing should be completely dried with a piece of gauze prior to applying the tape to the prongs, as waterproof tape may slip if the tube is wet.
Placing the Nasal Prongs
The direction of the prongs is very important. The curvature of the nasal prongs should always point downward to prevent trauma to the mucous membranes and properly direct the flow without obstruction (FIGURE 6).
When placing nasal prongs, nasoesophageal and nasogastric tubes may be left in place; however, it is recommended to remove all red rubber nasal cannulas prior to initiating HFOT. Red rubber nasal cannulas often become occluded with nasal secretions and are ideally replaced every 2 days. A new red rubber cannula may be placed after HFOT is discontinued.
HFOT is a fairly new treatment in veterinary medicine. Hospital staff should be properly educated on the use and equipment management prior to launching the use of HFOT in any hospital.
At the authors’ institution, an Fıo2 of 100% is chosen initially unless the clinician requests otherwise (compressor use is required to reduce Fıo2). The temperature can be set between 34 °C and 38 °C; however, the authors suggest starting at 37 °C for nearly all patients.
The flow rate may be calculated at 0.5 to 2 L/kg.2 The initial flow rate should be set lower and titrated up as needed based on patient response. The authors suggest taping a printout of flow rate settings to the HFOT machine for quick reference (FIGURE 7).
TABLE 1 lists suggested initial HFOT flow rates; however, it is important to remember that each patient’s need and response are individual, and flow rates and Fıo2 should be titrated based on need, comfort, and tolerance.
Patient Monitoring and Nursing Care Requirements
Once HFOT is initiated, patients must be carefully monitored for response to therapy or worsening of clinical signs. A patient on HFOT will generally exhibit a positive response within 30 to 60 minutes after initiation of therapy.
Serial venous blood gas or arterial blood gas measurements should be assessed frequently to gauge response to HFOT. Blood gas results, in conjunction with continuous pulse oximetry (i.e., Spo2) evaluation, will help determine if HFOT is effective for the patient. Nasal prongs should be checked frequently for proper fit/location and connection to the unit, as patients may inadvertently become disconnected.
Most patients seem to tolerate HFOT and the nasal prongs fairly well. Elizabethan collars are occasionally used to deter a patient from pawing or rubbing at the nasal cannula and accidentally becoming disconnected (FIGURE 8). Once the nasal prongs are secured, if the patient seems irritated or uncomfortable, unit settings should be adjusted and inspected to ensure that the irritation is not a sign of continued hypoxia.
Respiratory rate and effort, temperature, and heart rate monitoring are invaluable. Setting the temperature on the HFOT unit too high may result in iatrogenic hyperthermia. Temperature probes are available to limit patient handling and stress. Electrocardiography (ECG) monitors allow continuous evaluation of heart rate and rhythm and provide early indications of distress and hypoxemia. Eye lubrication is important to prevent corneal ulceration and irritation of ocular mucosa.
Patients on HFOT are occasionally sick enough to be recumbent. Turn orders to prevent atelectasis and aid in potential alveolar recruitment are necessary for these patients. Additionally, passive range of motion exercises may assist in venous return and increased circulation of oxygenated blood.
Patients should also be monitored for stomach distention, prong-related side effects such as nose sores or skin lesions over the bridge of the nose, and difficulty synchronizing breathing. If the patient is not responding adequately to HFOT, mechanical ventilation should be considered.
Anxiolytics such as gabapentin and trazodone can be given as needed to keep the patient calm. On rare occasions a patient may require sedation to tolerate either the high-flow nasal prongs or their current respiratory distress. Boluses of butorphanol at 0.2 mg/kg IV are preferred for these circumstances. Butorphanol boluses can be escalated to a continuous rate infusion or dexmedetomidine can be added (when not contraindicated due to comorbidities) only when absolutely necessary.
If continued anxiety and activity centered on removing the nasal prongs persist, this may be an indication the patient is feeling well enough to discontinue HFOT.
De-escalation of HFOT
Much like weaning a patient from conventional oxygen therapies, discontinuing the use of HFOT is initiated by the gradual decrease of oxygen concentration and flow rate. Continued patient monitoring is crucial, and other sources of oxygen should be available should a need arise. If the patient is not responding well to weaning, therapy should be reinstituted and maintained for an additional 12 to 24 hours. In the authors’ experience, patients routinely require conventional oxygen therapy for some time following the use of HFOT. Similar de-escalation techniques are used to transition the patient to room air oxygen concentrations.
Once the patient no longer requires high-flow support, the unit should be properly shut down and cleaned to prevent delays in treating the next patient.
For patients that do not respond adequately to conventional oxygen therapy, HFOT is an effective alternative method of delivering high volumes and pressures of oxygen without the use of mechanical ventilation. Cost-effective equipment, easily obtained supplies, and patient tolerance are advantages of HFOT in any practice. If the patient is not responding to traditional therapy or HFOT, referral to a specialty practice for mechanical ventilation is indicated.
Atelectasis Collapse of the lung
Barotrauma Trauma caused by rapid changes in air pressure
Fıo2 (fraction of inspired oxygen) Concentration of oxygen in a gas mixture
Flow rate Volume of oxygen per unit of time (L/min)
Hypoxemia Low blood oxygen level
Mesocephalic Having a head of medium proportions, not brachycephalic or dolichocephalic
Orthopneic Body position indicating respiratory distress and dyspnea in which the patient elevates its head and stretches its neck out to maximize its ability to breathe
PEEP (positive end-expiratory pressure) Alveolar pressure that exists at the end of expiration
Tidal volume Amount of air that moves in and out of the lungs during each breath
Editor’s Note: A previous version of this article incorrectly stated that a patient is considered hypoxemic when the the oxygen saturation (Spo2) is greater than 95%. This has been corrected in the text.
1. Spicuzza L, Schisano M. High-flow nasal cannula oxygen therapy as an emerging option for respiratory failure: the present and the future. Ther Adv Chronic Dis. 2020;11:2040622320920106. doi: 10.1177/2040622320920106
2. Jagodich TA, Bersenas AME, Bateman SW, Kerr CL. Comparison of high flow nasal cannula oxygen administration to traditional nasal cannula oxygen therapy in healthy dogs. J Vet Emerg Crit Care (San Antonio). 2019;29(3):246-255. doi: 10.1111/vec.12817
3. Benavides K, Rozanski E, Anastasio JD, Bedenice D. The effect of inhaled heliox on peak flow rates in normal and brachycephalic dogs. J Vet Intern Med. 2019;33(1):208-211. doi: 10.1111/jvim.15385
4. Keir I, Daly J, Haggerty J, Guenther C. Retrospective evaluation of the effect of high flow oxygen therapy delivered by nasal cannula on Pao2 in dogs with moderate-to-severe hypoxemia. J Vet Emerg Crit Care (San Antonio). 2016;26(4):598-602. doi: 10.1111/vec.12495
5. Jagodich TA, Bersenas AME, Bateman SW, Kerr CL. High-flow nasal cannula oxygen therapy in acute hypoxemic respiratory failure in 22 dogs requiring oxygen support escalation. J Vet Emerg Crit Care (San Antonio). 2020;30(4):364-375. doi: 10.1111/vec.12970
6. Haskins SC. Hypoxemia. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 2nd ed. WB Saunders; 2015:81-86.
7. Ramesh M, Thomovsky E, Johnson P. Conventional versus high-flow oxygen therapy in dogs with lower airway injury. Can J Vet Res. 2021;85(4):241-250.
8. Vapotherm Inc. Precision flow instructions for use. 3101458-01-EN REV.B. Vapotherm; 2022.
9. Jagodich TA, Bersenas AME, Bateman SW, Kerr CL. Preliminary evaluation of the use of high-flow nasal cannula oxygen therapy during recovery from general anesthesia in dogs with obstructive upper airway breathing. J Vet Emerg Crit Care (San Antonio). 2020;30(4):487-492. doi: 10.1111/vec.12971
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This article discusses what high-flow oxygen therapy (HFOT) is and how it differs from current traditional oxygen therapies, as well as its benefits, contraindications, and complications. Instances in which HFOT would be used are presented, and sedation protocols, nasal prong application techniques, and nursing care concerns are provided.
Upon completion of this article, readers should be able to identify appropriate candidates for HFOT, as well as understand how to prepare and care for patients receiving this therapy.
1. Which of the following oxygen delivery methods is not appropriate for a patient needing support for 24 hours or more?
a. High-flow oxygen
b. Oxygen cage
c. Flow-by oxygen
d. Nasal cannula
2. Nasoesophageal and nasogastric tubes must be removed before placing nasal prongs for HFOT.
3. Nasal prongs should always be positioned upward during placement.
4. Which patient is not a candidate for HFOT?
a. 7-kg domestic shorthaired cat with hypertrophic cardiomyopathy
b. 1.2-kg puppy with aspiration pneumonia
c. Chronically hypercapnic Doberman
d. All of the above
5. Which of the following statements regarding HFOT is false?
a. HFOT may be attached to the patient immediately following the setup of the unit.
b. HFOT can provide 1 to 40 L/min of humidified oxygen.
c. HFOT is not appropriate for patients <4 kg.
d. The air compressor is only necessary when using an Fıo2 <100%.
6. Patients on HFOT should be monitored for which of the following?
a. ECG, Spo2, temperature probe
b. ECG, Spo2, end-tidal carbon dioxide
c. Spo2, blood pressure, ECG
d. None of the above
7. Which treatments may be useful in patients less tolerant of nasal prongs?
c. Gabapentin, trazodone
d. Elizabethan collar, butorphanol bolus
e. C and D
8. A corgi has fallen from a 20-foot balcony. He presents with anisocoria, ataxia, and respiratory distress. Which of the following initial interventions is most appropriate?
b. Mechanical ventilation
c. Flow-by oxygen with mask
d. Red rubber nasal cannula
e. Oxygen cage
9. Approximately how long after the initiation of HFOT should a patient show improvement?
a. 24 hours
b. 3 days
c. 30 to 60 minutes
d. 6 hours
10. Nasal prongs should be _____ of the diameter of the nares.