Nasal Ventilation: Oxygenation, NO DESAT, and THRIVE

Anil Patel, MD, FRCA

Consultant Anaesthetist
Royal National Throat, Nose and Ear Hospital
University College London Hospitals NHS Foundation Trust
London, United Kingdom

S.A. Reza Nouraei, MBBChir, PhD, FRCS

Ear, Nose, and Throat Surgeon
Honorary Senior Lecturer in Otolaryngology,
University College London
London, United Kingdom

High-flow nasal oxygen optimizes preoxygenation and apnea time compared with low-flow techniques, and improves carbon dioxide (CO₂) clearance.

The delivery of oxygen via nasal cannulas is widely used to provide supplemental oxygen or increase airflow to patients in need of respiratory support as a consequence of hypoxemia, hemodynamic insufficiency, or increased work of breathing. Oxygen can be delivered by a number of devices, including nasal cannulas, simple face masks, Venturi face masks, non-rebreathing face masks with a reservoir, transtracheal catheters, and warmed humidified high-flow nasal oxygen systems.

More recently, the use of supplemental oxygen via nasal cannulas has been described to increase apnea times in anesthetized paralyzed patients in the context of:

NO DESAT (nasal oxygen during efforts securing a tube),^1,2 which uses a simple nasal cannula with standard low-flow cold dry oxygen at a rate of 5 to 15 L per minute. NO DESAT allows apneic oxygenation to continue while attempts at tracheal intubation are performed, and it increases apnea times by 2 to 5 minutes.

THRIVE: High-flow nasal cannula preoxygenation. Flow rate of 30 L per minute.

THRIVE (transnasal humidified rapid-insufflation ventilatory exchange),³ which uses high-flow oxygen at a rate up to 70 L per minute with warmed humidified nasal oxygen (Figure 3). THRIVE combines the benefits of apneic oxygenation with continuous positive airway pressure and gaseous exchange through flow-dependent dead space flushing. THRIVE increases apnea time by enhancingapneic oxygenation and provides apneic ventilation, reducing the rate of rise of CO₂ to approximately one-third of that expected (Figure 4). In patients with difficult airways, THRIVE increased the mean apnea time after induction of anesthesia and muscle paralysis to 14 minutes, with no patients experiencing desaturation.³

THRIVE: Following induction of anesthesia, flow rate increased to 70 L per minute. Nasal high-flow cannula placed on forehead. Confirmation of airway patency by face mask ventilation.

History

During World War I, oxygen was administered to the victims of gas poisoning through small-diameter (8- to 10-Fr) rubber catheters placed directly into the nasopharynx.⁴ By the 1920s, nasal oxygen was being used in pediatric care.⁵These oxygen delivery systems developed further with a Y-tube to split oxygen flow into a double nasal catheter, halving the effect of flow on the nasal mucosa,⁶followed by less invasive oxygen prongs that allowed oxygen to be directed just inside the nares.

By the 1940s, early versions of low-flow nasal cannulas had been introduced. As their use increased, the limitations of oxygen administration via the nasal route began to be recognized. Nasal discomfort, pain, drying, and bleeding of the nasal mucosa resulted from the use of cold dry oxygen. This was a particular problem at high oxygen flow, and prevented the use of high-flow nasal oxygen until systems were developed that allowed warming and humidification of oxygen at higher flows. With low-flow nasal oxygen, considerable variability of the fraction of inspired oxygen (FiO₂) also was seen, depending on the breathing pattern. Despite these problems, nasal oxygen allowed patients to eat, drink, speak, and avoid the claustrophobia associated with face masks.^5,7

High-flow nasal oxygen systems were developed to improve the clearance of secretions in patients with cystic fibrosis. High-flow systems allow warmed humidified oxygen–air mixtures at flow rates up to 70 L per minute. Early systems were developed for and used exclusively in racehorses to treat exercise-induced pulmonary hemorrhage. By the 1980s, early systems (Transpirator MT-1000, The Oxygen Company Inc) could reach flow rates up to 20 L per minute. In 2000, the first commercial adult high-flow nasal cannula systems designed to deliver oxygen flow with accompanying humidifiers appeared, manufactured by Salter Labs and Vapotherm.⁸

Today, Vapotherm’s 2000i High Flow Therapy system allows for the high flow of gases to be delivered via a nasal cannula while warming and saturating the gas stream. The device delivers a flow range up to 40 L per minute, with 95% to 100% relative humidity and a temperature range of 33 to 43°C (~91-109°F).⁹

Teleflex offers high-flow nasal cannula therapy through its Comfort Flo Humidification System. The system is designed to provide a heated humidifier to deliver flow rates up to 40 L per minute through a line of specialty nasal cannulas.¹⁰

The Optiflow Nasal High Flow cannula (Fisher & Paykel) began clinical use in 2006 (Figure 5).¹¹ The Optiflow cannula is designed with a wide bore in order to deliver a complete range of gas flows up to 70 L per minute at optimal temperature (37°C/98.6°F) and humidity (44 mg/L), thereby improving patient tolerance and optimizing mucociliary clearance.¹¹

THRIVE: High-flow nasal cannula placed in position. Apneic oxygenation and apneic ventilation allow apnea times between 10 and 60 minutes.

Low-Flow Nasal Oxygen

Low-flow oxygen delivery systems include the standard nasal cannula, which protrudes into a patient’s nares and delivers an FiO₂ of 24% to 44% at oxygen flow rates ranging from 1 to 8 L per minute. Low-flow systems allow dilution with ambient air as minute ventilation exceeds oxygen flow, resulting in a lower FiO₂than expected.

With quiet breathing, the inspiratory flow rate at the nares of an adult usually exceeds 12 L per minute, and with mild respiratory distress can exceed 30 L per minute. Both breathing rate and tidal volume affect the FiO₂, with lower inspiratory flows generating a higher FiO₂. Conversely, the faster inspiratory flows associated with respiratory distress generate a lower FiO₂.

Low-flow nasal cannulas provide limited FiO₂ to spontaneously breathing patients.¹ After induction of anesthesia and the administration of muscle relaxants, the nasal cannula can be left on while flow rates can be increased to 15 L per minute, allowing the pharynx to fill with oxygen (pharyngeal oxygen reservoir) and increase the FiO₂.² Low-flow apneic oxygenation provides no ventilation or CO₂ clearance.

Apneic Oxygenation

Apneic oxygenation is a physiologic phenomenon in which alveoli will continue to take up oxygen without any diaphragmatic movements or lung movement, provided that a patent air passageway exists between the lungs and the pharynx. The difference between the alveolar rates of oxygen removal (~200-250 mL/min) and CO₂ excretion into the alveoli (~20 mL/min) generates negative pressure up to 20 cm H₂O.² This generates a mass flow of gas from the pharynx to the alveoli, which drives oxygen into the lungs.

Apneic oxygenation has been used both experimentally and clinically as a strategy to extend the apneic window by providing a pharyngeal oxygen reservoir. The application of low-flow oxygen (15 L/min) through a nasal cannula increases pharyngeal FiO₂, which acts as a pharyngeal oxygen reservoir that leads to a greater amount of oxygen delivery during the mass flow of gas from the pharynx to the alveoli. This maintains oxygenation for longer and increases apnea time. Taha et al showed no desaturation during the course of 6 minutes in patients receiving 5 L per minute of oxygen through a nasal catheter, while the control group desaturated in an average of 3.65 minutes to the study cutoff of 95%.¹²

A randomized controlled trial of obese patients receiving 5 L per minute of oxygen through nasal cannulas during their apneic period showed the apneic oxygenation group had significant prolongation of the time spent with peripheral capillary oxygen saturation (SpO₂) of at least 95% (5.29 vs 3.49 minutes), a significant increase in patients with SpO₂ of at least 95% at 6 minutes (8 vs 1 patient), and significantly higher minimum SpO₂ (94.3% vs 87.7%).^7,13

Apneic oxygenation will allow continued oxygenation and increase the apnea time, but will have little effect on CO₂ clearance, resulting in hypercapnia and acidosis.

NO DESAT

Simple nasal cannula for preoxygenation.

Small nasal cannulas can be left on during preoxygenation (Figure 6), mask ventilation (provided a good seal is generated; Figure 7), and tracheal intubation attempts. After the administration of anesthetic agents and muscle relaxants, NO DESAT improves the efficacy of apneic oxygenation during attempts at tracheal intubation and increases apnea time by 2 to 5 minutes.^12,13

NO DESAT: Mask ventilation after induction of anesthesia.

High-Flow Nasal Oxygen

High-flow nasal cannulas deliver nasal oxygen flow rates up to 70 L per minute with warmed humidified oxygen. Heating and humidification are critical for tolerance of these higher oxygen flow rates. Without heating and humidification, pain, drying, and bleeding of the nasal mucosa will occur.

1. Heating and Humidity

Without achieving adequate humidity and temperature, high nasal oxygen flow rates quickly result in drying of the airway mucosa, impairment of ciliary function, and decreased mobilization of secretions. Administering an inspired gas with a relative humidity of 100% at 37°C effectively prevents these complications and minimizes respiratory heat and water loss. Modern high-flow nasal oxygen devices achieve close to 100% relative humidity at a temperature of 37°C at clinically relevant flow rates.^2,11

2. Continuous Positive Airway Pressure

Low-level positive airway pressure is delivered with high-flow nasal oxygen that increases with flow rate during breathing and is greater with a closed mouth compared with open.

The positive airway pressure that is generated reduces atelectasis, improves lung ventilation/perfusion, decreases the work of breathing, improves decreased compliance in adults, and treats atelectasis in surfactant-deficient newborns.

In healthy volunteers, the expiratory pharyngeal pressure varied from 0.8 to 7.4 cm H₂O, with flow rates ranging from 0 to 60 L per minute during mouth-closed breathing and from 0.3 to 2.7 cm H₂O during mouth-open breathing at the same flow rates.¹⁴

At 35 L per minute, spontaneously breathing intensive care patients generated a mean nasopharyngeal pressure of 2.7 cm H₂O (mouth-closed) and 1.2 cm H₂O (mouth-open), respectively,¹⁵ compared with pressures generated by humidified Hudson mask oxygen therapy (at 35 L/min) of 0.2 (mouth-closed) and 0.1 cm H₂O (mouth-open) breathing, respectively. At flow rates of 50 L per minute, the average nasopharyngeal airway pressure was 3.1 cm H₂O, and an average expiratory pressure of 3.8 cm H₂O was seen with mouth-closed breathing.¹⁶ A clear positive linear relationship between flow and mean airway pressure exists.¹⁷

3. Increased FiO₂

High-flow nasal oxygen prevents secondary entrainment of room air by delivering a higher FiO₂ than face mask oxygen.¹⁸ High-flow nasal oxygen also provides optimal nasopharyngeal and oropharyngeal oxygen reservoirs as well as improved washout of anatomic dead space, reducing dead space breathing and improving ventilatory efficiency.¹⁹ The higher the nasal flow rate, the faster the clearance of gas from the upper airway and the lower the minute ventilation required to maintain the same effective alveolar ventilation, which can lead to reduced arterial CO₂ concentration.

The reduction in anatomic dead space can decrease a patient’s minute ventilation requirement and respiratory rate.^20,21

4. Patient Comfort

Warmed humidified nasal oxygen is better tolerated than conventional oxygen therapy.²²

THRIVE

THRIVE describes a technique that maintains oxygen saturation for significant periods of time after commencement of apnea in surgical patients and reduces the rise of CO₂ over time.³ This suggests that utilizing high-flow nasal oxygen at 70 L per minute during the apneic period allows apneic oxygenation (maintaining oxygen saturations) and apneic ventilation (reducing the rise of CO₂; Figure 8). This is in contrast to low-flow nasal cannula techniques in which classic apneic oxygenation improves oxygenation without affecting ventilation.

THRIVE: Flow rate of 70 L per minute after induction of anesthesia and administration of muscle relaxants.

THRIVE combines the benefits of “classic” apneic oxygenation with continuous positive airway pressure and flow-dependent dead space flushing. A major advantage of THRIVE is that it can be continued during laryngoscopy and airway instrumentation. Any reduction in oropharyngeal FiO₂ as a consequence of oral suctioning of secretions (~45 L/min of air are suctioned from a Yankauer suction tip) is immediately replenished with high nasal flow rates. THRIVE describes a technique that could transform the practice of anesthesia by changing the nature of securing a definitive airway in emergency and difficult intubation settings from a highly pressured stop–start process to a smooth and unhurried undertaking (Figure 9).

THRIVE: Laryngoscopy and tracheal intubation transformed from a pressured stop–start process to a smooth and unhurried undertaking.

Preoxygenation

High-flow nasal oxygen also is used to optimize preoxygenation (Figure 10). High-flow nasal cannulas significantly improved oxygenation in patients undergoing intubation in the intensive care unit when compared with standard oxygen therapy with a non-rebreathing mask.²³ High-flow nasal oxygen also improved preoxygenation in morbidly obese patients undergoing bariatric surgery.²⁴

THRIVE: Flow rate of 30 L per minute during preoxygenation.

Unlike face mask preoxygenation, in which an “active” decision is taken to hold a face mask and ensure a good seal, using high-flow nasal oxygen is a “passive” process in which the nasal cannula can be placed as soon as the patient enters the operating room while other preparations are made for induction of anesthesia. No additional time is required compared with “active” face mask preoxygenation.

Awake Fiber-Optic Intubation

High-flow nasal oxygen has been used to optimize oxygenation and intubating conditions during awake fiber-optic intubation (AFOI).²⁵ High-flow nasal oxygen was well tolerated in spontaneously breathing patients undergoing AF OI with improved oxygenation during the procedure and prevention of apnea- and hypoventilation-associated desaturations. High-flow nasal oxygen therapy is currently the only option to provide continuous delivery of 100% FiO₂ in high-risk patients undergoing AFOI.

Conclusion

Nasal oxygen is a well-established treatment for patients breathing spontaneously in need of respiratory support. More recently, it has been used to improve oxygenation in patients breathing spontaneously during preoxygenation, fiber-optic bronchoscopy,²⁶ and AFOI. After induction of anesthesia and muscle relaxants, low-flow nasal oxygen (NO DESAT) improves apneic oxygenation and increases apnea time by a few minutes. High-flow nasal oxygen (THRIVE) optimizes preoxygenation and significantly improves apnea time compared with low-flow techniques while enhancing CO2 clearance.

References

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