INTRODUCTION — This topic will review various devices that are available to continuously deliver oxygen to spontaneously breathing infants, children, and adults. The amount of oxygen that each continuous system can deliver and the advantages and disadvantages of each method are discussed.
Oxygen-conserving devices (eg, Oxymizer, Helios, or Invacare Venture), oxygen therapy for newborns, indications for long-term oxygen supplementation, the use of oxygen in hypercapnic patients, issues regarding oxygen therapy during air travel, and basic airway management are discussed separately:
SELECTION OF OXYGEN DELIVERY SYSTEM — Rapid and effective oxygen delivery is an essential component of the care of critically ill or injured patients. A variety of systems are available to deliver oxygen to spontaneously breathing patients. Factors that influence the appropriate choice for any given situation include the dose of oxygen required and how well the patient tolerates the device. For patients who require assisted ventilation, oxygen can be initially delivered with either a self-inflating or flow-inflating ventilation bag.
General principles regarding oxygen delivery include:
●The choice of system will depend upon the clinical status of the patient and the desired dose of oxygen, which is a function of the fraction of inspired oxygen (FiO2 or concentration) and rate of oxygen gas flow (table 1). For example, a low-flow blow-by system may be suitable for an alert infant or child in moderate respiratory distress who requires a low dose of oxygen. By contrast, an obtunded patient with irregular respirations needs bag-mask ventilation with a high concentration and a high flow of oxygen (eg, 100% FiO2 at a flow of 10 L/minute or greater).
●When oxygen delivery is anticipated to be prolonged, it should be humidified, whenever possible, to prevent dried secretions from obstructing smaller airways.
●The effectiveness of oxygen delivery should be monitored with pulse oximetry. (See "Respiratory support, oxygen delivery, and oxygen monitoring in the newborn", section on 'Pulse oximetry' and "Pulse oximetry".)
Key patient considerations include:
●Young children in respiratory distress may become frightened or agitated when oxygen is administered, causing their clinical conditions to deteriorate. Therefore, they should remain in a position of comfort whenever possible. A parent or caregiver can often hold the oxygen source in proximity to or over the child's face.
●As long as oxygenation is adequately maintained, a nasal cannula may be preferable to a face mask for delivering oxygen to confused or delirious adults.
●Uncontrolled oxygen delivery may promote hypercapnia in adults with chronic obstructive pulmonary disease. (See "The evaluation, diagnosis, and treatment of the adult patient with acute hypercapnic respiratory failure".)
Important safety issues include:
●Although oxygen itself is not flammable, it causes other material, such as hair, skin oils, clothing, and furniture to catch fire at lower temperatures and to burn hotter . Patients receiving oxygen therapy and stored oxygen cylinders should be kept at least five feet away from open flames, a heat source, or electrical devices.
●If oxygen cylinders are used, they should be secured so that they cannot fall over, develop a rapid leak (eg, if the regulator is dislodged from the cylinder), and become propelled like a missile . Regular monitoring of exchanged oxygen cylinders is necessary to ensure that all valves are working properly and that overpressurization with potential bursting of the cylinder cannot occur.
●In health care settings where oxygen supply may be limited (eg, prehospital environment or small free-standing facilities), duration of oxygen administration should also be considered when selecting the mode of oxygen delivery. Using high oxygen flow rates for extended periods of time may rapidly deplete available tanks. Therefore, if prolonged administration is anticipated, use of oxygen-conserving devices (if available) or titrating oxygen delivery to match the minimal clinical requirement in non-critically ill patients may be prudent.
BLOW-BY OXYGEN — Blowing (or wafting) oxygen past a patient's face is not a reliable means of oxygen delivery and is not used in adults. However, this method may temporarily provide oxygen to infants and toddlers who become agitated and more distressed with other methods of oxygen delivery, particularly during the initial evaluation and treatment of a reversible cause of respiratory distress such as croup or bronchospasm. Limited evidence suggests that only low concentrations of oxygen (<30 percent fraction of inspired oxygen [FiO2]) can typically be provided using these systems [3-6].
The following points should be considered when providing blow-by oxygen to children:
●Oxygen can be best delivered at a flow rate of at least 10 L/minute through a reservoir (ie, a simple mask or large cup) .
●The reservoir must remain in proximity to the child's face.
●Oxygen saturation should be monitored.
●Alternative oxygen delivery systems are warranted for children who require >30 percent oxygen concentration or prolonged oxygen therapy.
Blow-by oxygen may be delivered using oxygen tubing, corrugated tubing, or a simple mask. Alternatively, some young children will accept blow-by oxygen more readily if the end of the oxygen tubing is poked through the bottom of a Styrofoam or paper drinking cup. Blow-by oxygen is typically held at a short distance from the child's face by a parent or other caregiver. For children who may require bag-mask ventilation, a flow-inflating (anesthesia) ventilation bag is preferred as a means of providing blow-by oxygen because it does not have a valve to obstruct oxygen flow from the oxygen source and therefore provides a constant delivery of oxygen. (See 'Ventilation bags' below.)
By contrast, self-inflating (Ambu) ventilation bags do not reliably deliver oxygen to spontaneously breathing children [3,7]. This type of system typically has a one-way valve to prevent rebreathing. Oxygen flow through the valve is significantly limited unless the bag is squeezed. With a mask tightly applied to the face, some spontaneously breathing patients may be able to generate sufficient inspiratory pressure to overcome the valve. However, younger children cannot reliably achieve this negative inspiratory force. Therefore, delivery of blow-by oxygen with self-inflating bags requires the bag to be squeezed repeatedly to open the one-way valve. Alternatively, for bags with reservoirs constructed of corrugated tubing, this tubing can be directed toward the face and used to delivery blow-by oxygen, provided the bag is appropriately connected to an oxygen source .
NASAL CANNULA — A simple nasal cannula consists of oxygen supply tubing with two soft prongs that are inserted into the patient's anterior nares. Oxygen flows from the cannula into the patient's nasopharynx, where it mixes with room air. The concentration of oxygen that can be delivered by nasal cannula varies depending upon factors such as the patient's respiratory rate, tidal volume, oxygen flow rate, and extent of mouth breathing (table 1).
Many nasal cannula models used to detect end-tidal carbon dioxide (eTCO2) can also simultaneously deliver supplemental oxygen. Some designs deliver oxygen directly into the nasopharynx though the prongs, while others create an oxygen cloud across the mouth and nose through microperforations in the nasal cannula hub. When using oxygen flow rates greater than 4 L/minute, the latter have been shown to deliver lower concentrations of oxygen than models that deliver the oxygen directly through the nasal prongs . This effect may be further exaggerated in non-spontaneously breathing patients (eg, if these devices are utilized during apneic oxygenation during endotracheal intubation). (See "Preoxygenation and apneic oxygenation for airway management for anesthesia".)
Oxygen can be delivered by simple nasal cannula using either low- or high-flow rates:
●Low flow — One hundred percent oxygen is typically run through a bubbler humidifier at a rate of 1 to 4 L/minute. The oxygen concentration that is delivered varies from 25 to 40 percent, depending upon factors such as the patient's respiratory rate, tidal volume, and extent of mouth breathing [10,11]. Flow rates greater than 2 L/minute are irritating to the nares, unless the oxygen is heated and humidified. The nares may become dry and prone to bleeding after prolonged use. Flow rates greater than 2 L/minute are not recommended for routine use in newborns and infants because inadvertent administration of positive airway pressure may occur at higher flow rates [12,13].
Low-flow nasal cannulae are used to deliver oxygen to an adult with a low oxygen requirement or to an infant or child with patent nares who requires low levels of supplemental oxygen and does not tolerate a simple mask. This system is lightweight, inexpensive, and mobile. In addition, the infant can feed without interruption of oxygen delivery. However, low-flow nasal cannulae are of limited use as the primary system of oxygen delivery during the stabilization of acutely ill patients because they cannot reliably deliver high concentrations of oxygen.
●High flow — High-flow nasal cannula oxygen therapy involves delivery of heated and humidified oxygen via special devices (eg, Vapotherm, Comfort Flo, or Optiflow (figure 1)) initiated at rates up to 8 L/minute in infants and, based on weight, up to 60 L/minute in children and adults (table 2). In patients with respiratory distress or failure, humidified high-flow nasal cannulae may be better tolerated than oxygen by face mask in terms of comfort. In observational studies, high-flow nasal cannula has been associated with decreased respiratory rate, decreased work of breathing, and better oxygenation than oxygen delivery by face mask. High-flow nasal cannula can be used in patients of all ages and with a variety of conditions, including premature infants with respiratory distress syndrome, infants with bronchiolitis, and adults with hypoxemic respiratory failure. (See "High-flow nasal cannula oxygen therapy in children" and "Respiratory support, oxygen delivery, and oxygen monitoring in the newborn", section on 'High-flow nasal cannula' and "Noninvasive ventilation for acute and impending respiratory failure in children" and "Bronchiolitis in infants and children: Treatment, outcome, and prevention", section on 'Noninvasive ventilation'.)
In adults with acute hypoxemic respiratory failure without hypercapnia, high-flow oxygen therapy by nasal cannula is a reasonable alternative to standard oxygen therapy or noninvasive positive pressure ventilation. Such patients should be managed in settings with appropriate monitoring (eg, emergency departments or intensive care units). (See "Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications", section on 'Hypoxemic nonhypercapnic respiratory failure not due to ACPE'.)
The safe use of oxygen in patients with hypercapnia is discussed separately. Noninvasive positive pressure ventilation may avoid the need for endotracheal intubation and is preferred to high-flow oxygen therapy in these patients. (See "Noninvasive ventilation for acute and impending respiratory failure in children" and "The evaluation, diagnosis, and treatment of the adult patient with acute hypercapnic respiratory failure".)
Although used for acute respiratory insufficiency in infants, especially those with bronchiolitis, further study of high-flow nasal cannula therapy is needed to better define pediatric indications and effectiveness. (See "High-flow nasal cannula oxygen therapy in children", section on 'Indications' and "Bronchiolitis in infants and children: Treatment, outcome, and prevention", section on 'Noninvasive ventilation'.)
The use of high-flow nasal cannula for the treatment of respiratory distress syndrome in premature infants is discussed in greater detail separately. (See "Respiratory support, oxygen delivery, and oxygen monitoring in the newborn", section on 'High-flow nasal cannula'.)
FACE MASKS — Masks are the most frequently used oxygen delivery system for acute care and hospitalized patients who are breathing spontaneously. General considerations when using an oxygen mask include the following:
●The mask should fit over the patient's nose and mouth. It is secured around the head with an elastic strap.
●A variety of sizes must be available from which to choose the proper size for any given patient.
●Transparent masks should be used whenever possible.
●Masks may be difficult to use for some patients who become more anxious and uncooperative when a mask is applied.
●Oxygen masks may pose a risk for aspiration in the vomiting patient.
Characteristics of the mask, mask fit, and the addition of a reservoir determine the amount of oxygen that can be delivered (table 1). The types of masks that are typically used include simple (Venturi), small diffuser (OxyMask), partial rebreathing, and nonrebreathing systems.
Specialized face masks are also used for noninvasive positive pressure ventilation in patients with acute respiratory failure. (See "Noninvasive ventilation for acute and impending respiratory failure in children", section on 'Interface' and "Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications".)
Simple masks — Simple masks (eg, Venturi) fit loosely over the nose and mouth. With oxygen flow rates between 6 and 10 L/minute, simple masks can provide concentrations of oxygen between 35 and 50 percent, depending on the patient's respiratory rate and the mask fit [10,13,14].
The plastic mask itself serves as a reservoir for oxygen that is delivered through a small-bore tube connected at the base of the mask. Exhaled gas escapes through holes (exhalation ports) on each side of the mask. Room air enters through these ports as well as between the face and mask and mixes with oxygen, thereby decreasing the percentage of oxygen delivered to the patient. An oxygen flow rate greater than 5 L/minute is recommended to prevent rebreathing of carbon dioxide (CO2) [13,15].
A simple mask is useful for patients who need moderate amounts of oxygen to maintain acceptable oxygen saturation. It can provide higher concentrations of oxygen than a nasal cannula. However, precise concentrations of oxygen cannot be reliably delivered.
Mask with small diffuser — In contrast to the common simple mask, the OxyMask directs oxygen towards the mouth and nose using a patented "diffuser system." The ability to provide a wide range of oxygen concentrations by one device, using lower oxygen flow rates, and avoidance of CO2 rebreathing are possible benefits for this mask, although evidence is limited .
Clinical trials in healthy adults have shown that OxyMask has the ability to provide a range of oxygen concentrations (25 to 80+ percent) by adjusting the oxygen flow rate (1.5 to 15 L/minute). Flow rates beyond 15 L/minute did not achieve significantly higher oxygen concentrations . Data from adult patients with chronic, stable respiratory disease confirmed the ability to adjust oxygen concentrations with the OxyMask by controlling the flow rate. In this study, a modification of the OxyMask to the open design demonstrated reduced rebreathing of CO2 and the ability to maintain predetermined oxygen saturation levels at lower oxygen flow rates than with simple masks . A single randomized controlled trial in pediatric patients compared OxyMask with high-flow nasal cannula in children younger than two years of age with moderate to severe bronchiolitis. Patients treated with the OxyMask tolerated the device well; however, they were more likely to require escalation of care and took longer to wean from oxygen therapy than those randomized to high-flow nasal cannula .
Partial rebreathing masks — A partial rebreathing mask consists of a simple mask with an attached reservoir. Oxygen concentrations from 50 to 60 percent can be achieved with oxygen flow rates between 10 and 12 L/minute [13,19].
With this system, air is drawn during inspiration predominantly from the fresh oxygen inflow and the reservoir. Entrainment of room air through the exhalation ports and any gap between the face and mask is minimized.
Gas in the reservoir is oxygen rich, despite the fact that it contains some exhaled gas. This is because the early exhaled air that flows into the reservoir (from respiratory dead space in the mouth and upper airways) is oxygen rich and contains little CO2 [19-21]. In order to maintain a high percentage of oxygen in the reservoir and minimize CO2 rebreathing, the oxygen flow rate must be adjusted to keep the reservoir from collapsing.
A partial rebreather mask is used primarily to conserve oxygen supply (for instance, during transport) for patients who require higher oxygen concentrations. Although the concentration of oxygen that is delivered is more reliable than a simple mask, it is diluted by room air that can still be drawn into the system through the exhalation ports and any gap between the face and mask.
Nonrebreathing masks — As a single device, a nonrebreather mask reliably supplies the highest concentration of oxygen that can be provided to a spontaneously breathing patient in the short term (oxygen concentration up to 95 percent). Using high oxygen flow rates can optimize oxygen delivery when using nonrebreathing devices. Alternatively, concomitant use of a nasal cannula at 10 L/minute has been shown to further increase oxygen delivery when using a nonrebreather device at 10 to 15 L/minute .
Patients who are anticipated to require such high concentrations of oxygen for longer periods of time should be transitioned to positive pressure ventilation. Both noninvasive ventilation and endotracheal intubation provide higher concentrations of oxygen secondary to decreased entrainment of room air, as well as through increased mean airway pressures to further improve oxygenation.
A nonrebreathing mask is a mask and reservoir system modified with one-way valves that limit the mixing of the oxygen supply with exhaled gases and room air. A one-way valve is located between the reservoir and the mask. It prevents flow of exhaled gas into the reservoir [19-21]. Exhalation ports of the mask also have one-way valves that permit the egress of expired gas during exhalation and prevent room air from entering the mask during inspiration. When valves are placed over both exhalation ports, oxygen flow rates of 10 to 15 L/minute are delivered, and a tight mask seal is achieved, a nonrebreather mask provides inspired oxygen concentrations (FiO2) of up to 95 percent [19,23]. However, as a safety precaution, nonrebreather masks are manufactured with only one of the two exhalation ports on the mask containing a one-way valve so that the patient can still receive room air through the open port if the flow of oxygen to the mask is inadvertently interrupted . Entrainment of room air through this open exhalation port results in a lower FiO2 . In addition, nonrebreathing masks may not routinely achieve a tight seal against the face. Such a leak with a nonrebreathing mask lowers oxygen delivery . Thus, in clinical practice, nonrebreathing masks typically deliver oxygen concentrations lower than 95 percent.
Oxygen flow into the mask should be adjusted to prevent collapse of the reservoir. When oxygen flow rate does not exceed the patient's ventilation demands, room air is entrained. While equipment will vary across institutions, standard medical oxygen flowmeters can commonly achieve flows significantly higher than 15 L/minute. By turning the adjuster knob on the flowmeter past the highest gradation until it cannot be rotated farther, "flush rate" flows of 50 to 54 L/minute have been demonstrated . These higher rates have been shown to increase the fraction of expired oxygen (FeO2), which serves as a proxy for oxygen concentration delivery, likely by minimizing entrainment of room air though open exhalation ports and gaps in the mask seal .
ENCLOSURE SYSTEMS — Enclosure systems such as oxygen hoods or tents may be used for infants or children who require prolonged administration of oxygen but cannot tolerate a nasal cannula or mask. They are not usually used in adults. Hoods and tents can also supply good humidification and temperature control. Both systems are very noisy for the patient .
Hoods — Oxygen hoods are clear, plastic cylinders that encompass the infant's head. Oxygen concentrations of 80 to 90 percent can be achieved with oxygen flow rates of ≥10 to 15 L/minute .
Oxygen enters the hood through a gas inlet. Exhaled gas exits through the opening at the neck .
The hood is usually well tolerated by newborns. Infants in an oxygen hood are accessible for monitoring and other care. Most hoods are too small to use for infants older than one year of age .
Tents — Oxygen tents are clear, plastic shells that surround the child's head and upper body. Although a tent can provide up to 50 percent oxygen using high oxygen flow rates, mixing with room air occurs whenever the tent is opened. As a result, oxygen tents are generally not a sufficient source of oxygen for children who require concentrations greater than 30 percent .
Oxygen tents limit access to the child by family and clinical staff. In addition, highly humidified air typically results in the formation of mist, which obscures the patient from view, preventing the early recognition of changes in the child's condition such as cyanosis or obtundation. In addition, expert guidelines recommend use of low-flow devices such as nasal cannula or masks over enclosure systems for the consistent delivery of oxygen for pediatric patients .
VENTILATION BAGS — Ventilation bags are typically used to provide oxygen and assisted ventilation, either with a mask or through an artificial airway (ie, an endotracheal tube). (See "Technique of emergency endotracheal intubation in children".) Flow-inflating bags can be used to provide supplemental oxygen to spontaneously breathing children. (See 'Blow-by oxygen' above.)
Self-inflating bags — A self-inflating (Ambu) bag reinflates with a recoil mechanism. It does not require a gas source to re-expand. However, during reinflation, room air is entrained in the system, diluting the concentration of oxygen that is delivered to the patient. Therefore, in order to consistently deliver high concentrations of oxygen, a reservoir must be attached to the bag. The addition of a one-way valve over the exhalation port can also reduce entrainment of room air during reinflation of a self-inflating bag attached to an oxygen source. (See "Basic airway management in children", section on 'Bag-mask ventilation' and "Basic airway management in adults", section on 'Bag-mask ventilation'.)
Flow-inflating bags — Flow-inflating (anesthesia) bags require a gas source to remain inflated. When oxygen is used as the source, 100 percent oxygen can be delivered to the patient. These systems are more complicated to use than a self-inflating bag. The flow of oxygen and an outlet control valve must be adjusted to ensure safe and effective ventilation. Consequently, flow-inflating bags should only be used by clinicians with specific training and experience .
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Supplemental oxygen".)
SUMMARY AND RECOMMENDATIONS
●Critically ill or injured patients frequently require oxygen therapy. The choice of an oxygen delivery system will depend upon the clinical status of the patient, the desired dose of oxygen, and how well they will tolerate the system (table 1). Spontaneously breathing patients should remain in a position of comfort whenever possible. Pulse oximetry should be monitored to ensure that oxygen is being effectively delivered. (See 'Selection of oxygen delivery system' above.)
●Blow-by (wafting) oxygen can be provided with oxygen tubing, corrugated tubing, or a simple mask to infants or children who require less than 30 percent oxygen concentration for short periods of time. For patients who may require bag-mask ventilation, flow-inflating (anesthesia) bags are preferred to self-inflating (Ambu) bags as a source of blow-by oxygen. (See 'Blow-by oxygen' above.)
●A low-flow nasal cannula can deliver 25 to 40 percent oxygen, depending upon the patient's respiratory rate, tidal volume, and extent of mouth breathing. Flow rates 2 L/minute or less are recommended for infants. (See 'Nasal cannula' above.)
●High-flow nasal cannula oxygen therapy involves delivery of heated and humidified oxygen via special devices (eg, Vapotherm, Comfort Flo, or Optiflow) at rates up to 8 L/minute in infants and, based on weight, up to 60 L/minute in children and adults. (See 'Nasal cannula' above and "High-flow nasal cannula oxygen therapy in children".)
●A simple mask with 6 to 10 L/minute of oxygen flow delivers 35 to 50 percent oxygen. Partial nonrebreathing masks with oxygen reservoirs deliver maximum concentrations of 60 percent. Nonrebreathing masks deliver the highest concentration of oxygen, which may approach 95 percent when entrainment of room air is minimized. (See 'Face masks' above.)
●In contrast to the common simple mask, a mask with a diffuser (OxyMask) directs oxygen towards the mouth and nose using a patented "diffuser system." This device has the ability to provide a range of oxygen concentrations (25 to >80 percent) by adjustment of the oxygen flow rate (1.5 to 15 L/minute). (See 'Mask with small diffuser' above.)
●Enclosure systems include hoods and tents and are used only for infants and children. Hoods can deliver up to 90 percent oxygen and may be used for infants less than one year of age. Tents deliver less oxygen and are generally not sufficient for children who require concentrations >30 percent. Mist that accumulates in the tent may also obscure the child from view. For these reasons, low-flow devices such as nasal cannula or masks are preferred over tent enclosure systems. (See 'Enclosure systems' above.)
●Ventilation bags are used to provide oxygen to patients who require assisted ventilation. A reservoir must be attached to self-inflating bags in order to provide high concentrations of oxygen. (See 'Ventilation bags' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Pamela Bailey, MD, who contributed to earlier versions of this topic review.
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