Medical Gas Therapy: Key Concepts for Respiratory Care

Medical gas therapy is the clinical use of oxygen and other therapeutic gases to support oxygenation, ventilation, pulmonary circulation, and patient stability. In respiratory care, gases such as oxygen, nitric oxide, helium-oxygen mixtures, and carbon dioxide-oxygen mixtures are not simply applied casually.

They must be selected, delivered, monitored, and adjusted according to the patient’s condition and response.

For this reason, medical gases should be treated with the same seriousness as medications. Each gas has specific indications, benefits, hazards, delivery methods, and safety requirements that respiratory therapists must understand.

What Is Medical Gas Therapy?

Medical gas therapy refers to the administration of therapeutic gases for diagnostic or treatment purposes. The most common example is oxygen therapy, which is used to correct or prevent hypoxemia and improve oxygen delivery to the tissues. However, medical gas therapy also includes the use of other gases, such as inhaled nitric oxide for pulmonary hypertension, heliox for certain types of airway obstruction, hyperbaric oxygen for specific emergencies, and carbogen in limited diagnostic or therapeutic situations.

The key point is that medical gases are clinical interventions. They require a clear reason for use, a method of delivery, a dosage or concentration, monitoring, and a plan for adjustment or discontinuation. A patient should not receive oxygen or another gas simply because it is available or because it has always been part of routine care. The respiratory therapist must evaluate the patient’s condition, determine the need for therapy, select the proper device, and monitor whether the therapy is achieving the desired result.

In respiratory care, medical gas therapy is one of the most common responsibilities of the respiratory therapist. It is used in hospitals, emergency departments, intensive care units, neonatal units, long-term care settings, and home care. Because it is so common, it can sometimes be underestimated. However, inappropriate gas therapy can lead to serious complications, including oxygen toxicity, carbon dioxide retention, absorption atelectasis, retinopathy of prematurity, equipment failure, and fire-related injuries.

Goals of Medical Gas Therapy

The goals of medical gas therapy depend on the gas being used and the patient’s condition. For oxygen therapy, the primary goal is to maintain adequate tissue oxygenation. This means supporting enough oxygen delivery to meet the metabolic needs of the body.

Oxygen therapy is commonly used to correct documented or suspected hypoxemia. Hypoxemia occurs when the oxygen level in the blood is lower than normal. It may be identified through pulse oximetry, arterial blood gas analysis, or clinical signs of inadequate oxygenation. Supplemental oxygen increases the amount of oxygen available in the alveoli, which can improve oxygen diffusion into the blood and increase arterial oxygen content.

Another goal is to reduce symptoms associated with chronic or acute hypoxemia. Patients with chronic low oxygen levels may experience shortness of breath, fatigue, poor exercise tolerance, impaired concentration, restlessness, or decreased activity levels. Supplemental oxygen may improve function and comfort in selected patients by improving oxygen delivery to the tissues.

Oxygen therapy can also reduce cardiopulmonary workload. When a patient is hypoxemic, the body tries to compensate. The respiratory rate may increase, accessory muscles may be used, and cardiac output may rise. These responses place more stress on the lungs and heart. By improving oxygenation, oxygen therapy may reduce excessive ventilatory demand and decrease cardiac workload, especially in patients with conditions such as myocardial infarction, pulmonary hypertension, sepsis, shock, trauma, or right-sided heart strain.

Other gases have different goals. Nitric oxide is used to reduce pulmonary vascular resistance and improve ventilation-perfusion matching in selected patients. Heliox is used to reduce airflow resistance and work of breathing in certain obstructive airway conditions. Hyperbaric oxygen increases the amount of oxygen dissolved in plasma and may be used for specific conditions such as carbon monoxide poisoning or decompression sickness.

Treating Medical Gases Like Drugs

A major principle of medical gas therapy is that gases should be treated as drugs. This means the therapist must consider the indication, dosage, delivery system, duration, monitoring parameters, therapeutic response, and possible complications.

For oxygen, the dose is often described as the fraction of inspired oxygen, or FiO₂. The FiO₂ represents the percentage of oxygen in the gas the patient breathes. Room air contains approximately 21% oxygen. Oxygen therapy increases the FiO₂ above this level. Depending on the device and flow rate, the delivered oxygen concentration may be low, moderate, high, or nearly 100%.

However, the set flow rate does not always equal a precise FiO₂. Some devices deliver variable oxygen concentrations because the patient’s breathing pattern affects the final inspired gas mixture. Other devices can deliver a more controlled FiO₂ by meeting the patient’s full inspiratory flow demand. This is why the therapist must understand the difference between low-flow and high-flow systems.

Treating gases like drugs also means avoiding unnecessary therapy. Oxygen should be used when there is a clinical need, and it should be adjusted as the patient improves or deteriorates. If a patient can maintain adequate oxygenation on room air, supplemental oxygen may no longer be needed. Continuing oxygen without a reason can expose the patient to unnecessary risk and may delay appropriate weaning.

Assessing the Need for Oxygen Therapy

Before oxygen therapy is started, the patient should be assessed carefully unless the situation is an emergency. In emergencies, oxygen may be given immediately while assessment continues. Examples include cardiopulmonary arrest, severe trauma, shock, carbon monoxide poisoning, cyanide poisoning, pulmonary embolism, acute myocardial infarction, and other conditions in which tissue hypoxia is suspected.

Assessment includes both clinical observation and objective data. Clinical signs of hypoxemia may involve the respiratory, cardiovascular, and neurologic systems. Respiratory signs can include increased respiratory rate, dyspnea, cyanosis, accessory muscle use, nasal flaring, abnormal breathing patterns, or signs of respiratory distress. Cardiovascular signs may include tachycardia, dysrhythmias, hypertension, hypotension, or signs of poor perfusion. Neurologic signs may include anxiety, confusion, restlessness, agitation, lethargy, or a decreased level of consciousness.

Objective assessment is also important. Pulse oximetry provides a noninvasive estimate of oxygen saturation. Arterial blood gas analysis provides more detailed information, including PaO₂, PaCO₂, pH, bicarbonate, and acid-base status. The therapist may also review the patient’s diagnosis, chest imaging, hemoglobin level, work of breathing, hemodynamic status, and response to previous therapy.

Note: A complete assessment helps determine not only whether oxygen is needed, but also how much oxygen is needed and which delivery system is most appropriate.

Oxygen Delivery Systems

Oxygen delivery systems are commonly grouped into low-flow systems, reservoir systems, and high-flow systems. Each category has advantages, limitations, and specific clinical uses.

The best device depends on the patient’s oxygen requirement, breathing pattern, stability, comfort, need for precise FiO₂, and ability to tolerate the interface. The therapist must also consider whether the patient needs humidification, portability, emergency support, or long-term therapy.

Low-Flow Oxygen Systems

Low-flow oxygen systems provide only part of the patient’s inspiratory gas. Because the device does not meet the patient’s full inspiratory flow demand, the patient also inhales room air. As a result, the final FiO₂ depends on the oxygen flow from the device and the patient’s breathing pattern.

Factors that affect the delivered oxygen concentration include tidal volume, respiratory rate, inspiratory flow, and the amount of room air entrained during inspiration. If the patient has a high inspiratory demand, more room air is pulled in, which lowers the final inspired oxygen concentration.

Note: Low-flow systems are commonly used for stable patients who do not require a precise FiO₂. They are simple, comfortable, and commonly available.

Nasal Cannula

The nasal cannula is one of the most frequently used oxygen delivery devices. It consists of two small prongs placed in the nostrils and connected to oxygen tubing. It is commonly used because it is inexpensive, easy to apply, and generally comfortable for the patient.

A nasal cannula allows the patient to talk, eat, drink, cough, and move more freely than many mask systems. It is often appropriate for patients with mild hypoxemia or those who need low to moderate oxygen support.

However, a nasal cannula does not provide a fixed FiO₂. The actual inspired oxygen concentration varies depending on the patient’s breathing pattern and the flow setting. It may not be appropriate for patients who need precise oxygen control or high oxygen concentrations.

Nasal Catheter

A nasal catheter is another low-flow oxygen device, but it is used less commonly than a nasal cannula. It is inserted into the nasal passage and positioned so oxygen can be delivered closer to the nasopharynx.

Although it can deliver oxygen effectively, it is less comfortable and may cause irritation. Because the nasal cannula is easier to use and better tolerated, the nasal catheter is rarely preferred in modern practice.

Transtracheal Oxygen Catheter

A transtracheal oxygen catheter delivers oxygen directly into the trachea through a small catheter. This method may be used in selected patients who require long-term oxygen therapy. Because oxygen is delivered directly into the airway, the patient may need lower oxygen flows compared with standard nasal cannula therapy.

Transtracheal oxygen can improve efficiency, but it requires careful patient selection, education, and maintenance. The catheter must be kept clean and patent. Complications can include mucus plugging, infection, bleeding, or catheter displacement.

Reservoir Oxygen Systems

Reservoir systems store oxygen during exhalation so that a greater amount of oxygen is available during the next inspiration. This allows the patient to receive a higher oxygen concentration than would be possible with a simple low-flow device at the same flow rate.

Note: Reservoir systems include reservoir cannulas, simple masks, partial-rebreathing masks, and nonrebreathing masks.

Simple Oxygen Mask

A simple oxygen mask covers the patient’s nose and mouth. The mask itself acts as a small reservoir for oxygen. Room air can enter through the side ports, and exhaled gas can leave through the same openings.

A simple mask can provide a higher oxygen concentration than a nasal cannula, but it still does not deliver a precise FiO₂. The flow must be high enough to flush carbon dioxide from the mask and prevent rebreathing. In general, flows that are too low should be avoided because carbon dioxide may accumulate inside the mask.

Note: Simple masks are often used when a patient needs more oxygen than a nasal cannula can provide but does not require the highest oxygen concentrations.

Partial-Rebreathing Mask

A partial-rebreathing mask includes a reservoir bag attached to the mask. During exhalation, the first portion of exhaled gas enters the reservoir bag. This gas comes from the anatomic dead space and is relatively rich in oxygen while containing little carbon dioxide. The remaining exhaled gas exits through the mask ports.

During the next inspiration, the patient inhales oxygen from the reservoir bag along with fresh oxygen flowing into the system. This allows a higher inspired oxygen concentration than a simple mask.

The respiratory therapist must ensure that the reservoir bag remains partially inflated during inspiration. If the bag collapses completely, the oxygen flow is not adequate to meet the patient’s needs.

Nonrebreathing Mask

A nonrebreathing mask is used when a high oxygen concentration is needed. It includes a reservoir bag and one-way valves that help prevent exhaled gas from entering the bag and limit room air entrainment through the mask ports.

When functioning properly, a nonrebreathing mask can deliver high oxygen concentrations and is commonly used in emergencies or significant hypoxemia. It may be used for trauma, shock, acute respiratory distress, suspected carbon monoxide poisoning, or other conditions requiring rapid oxygen support.

The respiratory therapist must check the system carefully. The reservoir bag should remain inflated, the flow should be high enough to maintain oxygen availability, the mask should fit securely, and the valves should function properly. A malfunctioning nonrebreathing mask may fail to deliver the expected oxygen concentration.

High-Flow Oxygen Systems

High-flow oxygen systems are designed to meet or exceed the patient’s inspiratory flow demand. Because the device provides the full amount of gas the patient needs during inspiration, the FiO₂ can be more stable and controlled.

High-flow systems are especially useful when precise oxygen delivery is needed, when the patient has a high inspiratory flow demand, or when changes in breathing pattern could cause large changes in FiO₂ with a low-flow system.

Examples include Venturi masks, air-entrainment nebulizers, aerosol masks, tracheostomy collars, T-pieces, high-flow nasal cannula systems, oxygen hoods, and systems that use air/oxygen blenders.

Air-Entrainment Devices

Air-entrainment devices use the Bernoulli principle to pull room air into a stream of oxygen. By controlling the amount of air entrained, the device can deliver a specific oxygen concentration.

The Venturi mask is a common example. It is useful when precise FiO₂ delivery is needed, especially in patients at risk of oxygen-induced hypoventilation or carbon dioxide retention. Because the selected oxygen concentration is more controlled than with a simple mask or nasal cannula, Venturi systems are commonly used in patients with COPD who require careful oxygen titration.

Air-Entrainment Nebulizers

Air-entrainment nebulizers can deliver a controlled oxygen concentration while also providing aerosolized humidity. They are often used with aerosol masks, face tents, tracheostomy collars, or T-pieces.

These systems are useful when the upper airway is bypassed, such as with a tracheostomy, because the patient may need humidification to prevent drying of secretions. They can also be used when a patient requires a stable FiO₂ with humidified gas delivery.

High-Flow Nasal Cannula

High-flow nasal cannula systems deliver heated and humidified gas at high flow rates through nasal prongs. Unlike a standard nasal cannula, high-flow nasal cannula therapy can provide a more stable FiO₂ because the flow may meet or exceed the patient’s inspiratory demand.

High-flow nasal cannula can also reduce entrainment of room air, wash out some anatomic dead space, improve comfort, and provide a small amount of positive airway pressure. It is commonly used in acute care settings for patients with hypoxemic respiratory failure, increased work of breathing, or the need for high-flow humidified oxygen.

Oxygen Blenders and Analyzers

Oxygen blenders mix compressed air and oxygen to deliver a selected FiO₂. They are commonly used in critical care, neonatal care, mechanical ventilation, and high-flow oxygen systems. A blender allows the clinician to set a specific oxygen concentration rather than relying only on oxygen flow.

However, the set value should not be blindly trusted. Oxygen analyzers are used to measure the actual oxygen concentration being delivered. This is especially important in patients who require precise oxygen control, such as neonates, critically ill adults, and patients receiving mechanical ventilation.

The respiratory therapist should verify that the blender is functioning properly, confirm inlet pressures, check alarms, test bypass function when appropriate, and analyze oxygen concentration at different settings. Failure of a blender or analyzer can lead to delivery of the wrong oxygen concentration.

Hazards of Oxygen Therapy

Oxygen therapy can be lifesaving, but it also has potential hazards. Safe use requires awareness of these risks and careful monitoring.

Oxygen Toxicity

Oxygen toxicity, also called hyperoxic acute lung injury, can occur with prolonged exposure to high oxygen concentrations. High oxygen levels may injure the pulmonary capillary endothelium, increase permeability, cause interstitial edema, and thicken the alveolar-capillary membrane. Continued exposure can damage alveolar cells, worsen gas exchange, and contribute to shunting.

Clinically, this can create a cycle in which worsening oxygenation leads to increased oxygen exposure, which may contribute to further lung injury. For this reason, oxygen should be titrated to the lowest concentration needed to meet the patient’s oxygenation goals.

Depression of Ventilation

Some patients with chronic hypercapnia are at risk for oxygen-induced hypoventilation and worsening carbon dioxide retention. This is especially associated with some patients who have COPD or other chronic respiratory disorders.

This does not mean oxygen should be withheld from a hypoxemic patient. Severe hypoxemia is dangerous and must be corrected. However, oxygen should be titrated carefully, and the patient should be monitored for changes in mental status, respiratory rate, oxygen saturation, and arterial blood gas values.

Absorption Atelectasis

Absorption atelectasis can occur when high oxygen concentrations wash nitrogen out of the alveoli. Nitrogen normally helps maintain alveolar volume because it is not rapidly absorbed into the blood. When nitrogen is replaced by oxygen, the oxygen may be absorbed into the bloodstream, allowing alveoli to collapse.

This can worsen ventilation-perfusion mismatch and reduce oxygenation. The risk increases when high FiO₂ levels are used for prolonged periods.

Retinopathy of Prematurity

Premature infants are especially vulnerable to oxygen-related injury. Excessive oxygen exposure can contribute to abnormal retinal blood vessel growth, which may lead to retinopathy of prematurity and possible visual impairment or blindness.

Because of this, neonatal oxygen therapy requires precise oxygen control, frequent monitoring, and careful adjustment of target oxygen saturation ranges.

Fire Hazard

Oxygen supports combustion. It is not flammable by itself, but it makes materials ignite more easily and burn more intensely. This makes oxygen safety essential in hospitals, clinics, and homes.

Patients and families must be taught to avoid smoking, open flames, sparks, and ignition sources around oxygen equipment. Equipment should be stored properly, and oxygen cylinders should be secured to prevent damage or injury.

Home Oxygen Therapy

Home oxygen therapy is used for patients who require long-term oxygen support outside the hospital. Common systems include oxygen concentrators, compressed gas cylinders, liquid oxygen systems, and portable oxygen devices.

Oxygen concentrators are commonly used because they extract oxygen from room air and provide a continuous supply without requiring frequent cylinder replacement. Portable systems allow patients to move more freely and maintain activity outside the home.

Liquid oxygen systems can provide portability and store oxygen in a smaller volume, but they require special safety precautions. Liquid oxygen is extremely cold and can cause frostbite if it contacts the skin. Patients and caregivers must be trained to fill and handle the equipment safely. Protective equipment may be needed during filling, and ignition sources must be avoided.

Home oxygen therapy also requires patient education. Patients should know how to use the equipment, check flow settings, avoid fire hazards, maintain tubing and cannulas, recognize signs of worsening respiratory status, and understand when to seek medical help.

Protocol-Based Oxygen Therapy

Protocol-based oxygen therapy allows respiratory therapists to assess patients and adjust oxygen therapy according to established guidelines. These protocols help ensure that oxygen is started when needed, adjusted based on response, and discontinued when no longer necessary.

A protocol may include criteria for initiating oxygen, selecting a delivery device, targeting oxygen saturation ranges, reassessing the patient, escalating therapy, reducing oxygen support, or stopping therapy.

Note: This approach can reduce unnecessary oxygen use, prevent delays in care, and improve consistency. It also allows the respiratory therapist to apply clinical judgment within an approved framework.

Hyperbaric Oxygen Therapy

Hyperbaric oxygen therapy involves breathing oxygen at pressures greater than normal atmospheric pressure. This increases the amount of oxygen dissolved in plasma, which can improve oxygen delivery in specific conditions.

Hyperbaric oxygen may be used for air or gas embolism, carbon monoxide poisoning, cyanide poisoning, decompression sickness, and selected wound-healing problems. In carbon monoxide poisoning, hyperbaric oxygen can help displace carbon monoxide from hemoglobin and improve oxygen delivery.

However, hyperbaric oxygen therapy has risks. Complications may include oxygen toxicity, barotrauma, pressure-related injuries, fire risk, and anxiety related to confinement. Because of these risks, it must be provided in a controlled environment by trained personnel.

Inhaled Nitric Oxide

Inhaled nitric oxide is a selective pulmonary vasodilator. When inhaled, it reaches ventilated areas of the lung and relaxes pulmonary vascular smooth muscle. This can reduce pulmonary artery pressure and improve ventilation-perfusion matching.

Nitric oxide is used in selected patients with pulmonary hypertension and severe oxygenation problems. It is especially important in neonatal care for conditions such as persistent pulmonary hypertension of the newborn.

Because nitric oxide is a potent therapy, it requires careful monitoring. Nitrogen dioxide can form when nitric oxide reacts with oxygen, and nitrogen dioxide can be toxic to the lungs. Methemoglobinemia is another concern because it reduces the blood’s ability to carry oxygen. The oxygen concentration should also be monitored downstream from the nitric oxide titration site because nitric oxide delivery can affect the delivered FiO₂.

Nitric oxide should not be stopped abruptly. Sudden discontinuation can cause rebound pulmonary hypertension and worsening hypoxemia. The dose should be reduced gradually to the lowest effective level before discontinuation. The patient should be stable, oxygenating adequately, and closely monitored during withdrawal.

Heliox Therapy

Heliox is a mixture of helium and oxygen. The therapeutic benefit comes from helium’s low density. Because helium is less dense than nitrogen, a helium-oxygen mixture can reduce resistance to airflow when flow is turbulent, especially in the large airways.

Heliox may reduce the pressure required to move gas through narrowed airways and may decrease the patient’s work of breathing. It does not directly treat the underlying disease, but it can provide temporary support while other treatments take effect.

Heliox has been used as an adjunct therapy for upper-airway obstruction, acute severe asthma, croup, postextubation stridor, tracheal tumors, and other reversible obstructive problems. It may help improve gas flow through narrowed airways, especially when obstruction causes turbulent airflow.

Common mixtures include 80% helium and 20% oxygen or 70% helium and 30% oxygen. However, the patient must always receive enough oxygen to support adequate oxygenation. As the oxygen concentration increases, the helium concentration decreases. This reduces the low-density benefit of the mixture. For this reason, heliox is most useful in patients who need relatively low to moderate oxygen concentrations but have significant airflow obstruction.

Heliox also requires special equipment considerations. Flowmeters calibrated for oxygen may not display accurate flow when used with heliox. Specific correction factors or heliox-compatible equipment may be needed. Cylinders, regulators, and delivery systems should be appropriate for the gas mixture being used.

Carbon Dioxide-Oxygen Therapy

Carbon dioxide-oxygen therapy, also known as carbogen therapy, is used much less commonly than oxygen, nitric oxide, or heliox. It involves a mixture of carbon dioxide and oxygen and may be used in limited diagnostic or therapeutic situations.

Carbogen is not routine therapy for most respiratory care patients. Its role is more specialized, and it requires careful attention because carbon dioxide affects ventilation, acid-base balance, and respiratory drive.

Note: Although it is less commonly used, carbogen demonstrates that medical gas therapy includes more than oxygen. Each gas has unique physiologic effects, indications, and safety concerns.

Choosing the Right Medical Gas Delivery System

Selecting the correct medical gas therapy requires attention to three major factors: purpose, patient, and performance.

Purpose refers to the clinical goal. Is the goal to correct acute hypoxemia, maintain chronic oxygenation, reduce pulmonary vascular resistance, decrease airway resistance, or treat a specific emergency? The answer helps determine the gas, concentration, and device.

Patient factors include the patient’s diagnosis, respiratory pattern, oxygen requirement, mental status, ability to protect the airway, comfort, and stability. A stable patient with mild hypoxemia may do well with a nasal cannula. A critically ill patient with severe hypoxemia may need a nonrebreathing mask, high-flow nasal cannula, ventilator support, or another advanced system.

Performance refers to whether the device can reliably deliver the required gas concentration and flow. A low-flow system may be simple and comfortable, but it may not provide a precise FiO₂. A high-flow system may offer better control but require more setup, monitoring, and equipment.

Note: The respiratory therapist should also consider safety, humidification, mobility, cost, and whether the patient can tolerate the interface.

Monitoring Response to Therapy

Monitoring is essential after medical gas therapy is started. The therapist should evaluate whether the therapy is working and whether complications are developing.

For oxygen therapy, monitoring may include pulse oximetry, arterial blood gas analysis, respiratory rate, work of breathing, heart rate, blood pressure, mental status, skin color, and patient comfort. The therapist should also assess the delivery device, oxygen flow, FiO₂ setting, tubing connections, humidification, reservoir bag function, and equipment alarms.

For nitric oxide, monitoring may include oxygenation response, pulmonary pressures when available, methemoglobin levels, nitrogen dioxide levels, FiO₂, hemodynamic status, and signs of rebound pulmonary hypertension during weaning.

For heliox, monitoring includes work of breathing, breath sounds, oxygenation, respiratory rate, patient comfort, and correct flow delivery. The therapist must make sure the mixture provides adequate oxygen and that the device is appropriate for heliox administration.

Note: Monitoring allows the therapist to determine whether therapy should be increased, decreased, changed to another device, or discontinued.

Discontinuing Medical Gas Therapy

Medical gas therapy should be discontinued when the indication for therapy has resolved and the patient can maintain adequate status without it. For oxygen therapy, this usually means the patient can maintain acceptable oxygen saturation and clinical stability on room air.

Weaning oxygen should be done carefully, especially in patients who have been critically ill or who have chronic lung disease. The therapist may gradually reduce the flow or FiO₂ while monitoring oxygen saturation, respiratory rate, work of breathing, and patient symptoms.

Specialty gases also require thoughtful discontinuation. Nitric oxide should be reduced gradually because abrupt withdrawal may cause rebound pulmonary hypertension and hypoxemia. Heliox can be discontinued when airway obstruction improves, work of breathing decreases, or the patient requires oxygen concentrations high enough that heliox is no longer useful.

Note: Discontinuation is not simply removing a device. It is a clinical decision based on assessment and patient response.

Role of the Respiratory Therapist

The respiratory therapist plays a major role in medical gas therapy. This includes assessing patients, recommending therapy, selecting devices, setting up equipment, verifying gas delivery, monitoring response, troubleshooting problems, educating patients, and adjusting therapy according to the care plan.

Respiratory therapists must understand the physiology behind gas therapy. They need to know how oxygen improves arterial oxygenation, how high oxygen levels can cause harm, why certain patients require precise FiO₂ control, how heliox reduces turbulent airflow, and why nitric oxide affects pulmonary vascular resistance.

They must also understand equipment. This includes oxygen cylinders, concentrators, liquid oxygen systems, blenders, analyzers, masks, cannulas, humidifiers, nebulizers, high-flow systems, and specialty gas delivery devices.

Note: The respiratory therapist’s role is both technical and clinical. Proper medical gas therapy requires more than connecting tubing to a flowmeter. It requires assessment, decision-making, patient education, and ongoing evaluation.

Medical Gas Therapy Practice Questions

1. What is medical gas therapy?
Medical gas therapy is the clinical use of therapeutic gases, such as oxygen, air, helium-oxygen mixtures, nitric oxide, and hyperbaric oxygen, to support oxygenation, ventilation, and cardiopulmonary function.

2. Why should most medical gases be treated like drugs?
Most medical gases should be treated like drugs because they require a specific dose, delivery device, monitoring plan, and adjustment based on the patient’s response.

3. What is the most commonly used form of medical gas therapy?
Oxygen therapy is the most commonly used form of medical gas therapy.

4. What are the primary goals of oxygen therapy?
The primary goals are to correct hypoxemia, relieve symptoms caused by low oxygen levels, and reduce cardiopulmonary workload.

5. How does oxygen therapy help correct hypoxemia?
Oxygen therapy increases the amount of oxygen in the alveoli, which helps increase arterial oxygen tension and improve tissue oxygen delivery.

6. What is documented hypoxemia?
Documented hypoxemia is commonly defined as a PaO2 less than 60 mmHg or an SaO2 less than 90% while breathing room air.

7. What are common signs and symptoms of hypoxemia?
Common signs include tachypnea, tachycardia, cyanosis, accessory muscle use, confusion, restlessness, and respiratory distress.

8. What are common causes of hypoxemia?
Common causes of hypoxemia include ventilation-perfusion mismatch, shunting, hypoventilation, diffusion impairment, and reduced inspired oxygen.

9. What are common clinical indications for oxygen therapy?
Common indications include documented hypoxemia, suspected hypoxemia, severe trauma, acute myocardial infarction, shock, respiratory distress, perioperative care, and post-anesthesia recovery.

10. What are the AARC indications for oxygen therapy?
AARC indications include documented hypoxemia, suspected hypoxemia in an acute care setting, severe trauma, acute myocardial infarction, and perioperative management.

11. What are the major hazards of supplemental oxygen therapy?
Major hazards include oxygen toxicity, ventilatory depression in susceptible patients, absorption atelectasis, retinopathy of prematurity, and fire risk.

12. What two factors are most important in oxygen toxicity?
The most important factors are the oxygen concentration or partial pressure and the duration of exposure.

13. Which body systems are most affected by oxygen toxicity?
The lungs and central nervous system are most affected by oxygen toxicity.

14. How can a respiratory therapist help reduce the risk of oxygen toxicity?
A respiratory therapist can reduce the risk by using the lowest FiO2 that maintains adequate oxygenation and reducing high oxygen concentrations as soon as clinically possible.

15. What is absorption atelectasis?
Absorption atelectasis occurs when high oxygen concentrations wash nitrogen out of the alveoli, allowing alveoli to collapse as oxygen is absorbed into the blood.

16. Who is at risk for absorption atelectasis?
Patients receiving high FiO2, especially those with low tidal volumes, airway obstruction, or mechanical ventilation, are at risk for absorption atelectasis.

17. Why can supplemental oxygen cause ventilatory depression in some COPD patients?
In some patients with chronic CO2 retention, excessive oxygen can worsen hypercapnia by altering ventilatory drive, worsening V/Q matching, and affecting hemoglobin’s ability to carry carbon dioxide.

18. What is retinopathy of prematurity?
Retinopathy of prematurity is abnormal retinal blood vessel development in premature infants that can be associated with excessive oxygen exposure and may lead to vision loss.

19. Why is oxygen a fire hazard?
Oxygen supports combustion, meaning materials can ignite more easily and burn more intensely in oxygen-enriched environments.

20. Where are oxygen-related fire hazards especially important?
Oxygen-related fire hazards are especially important in operating rooms, intensive care units, neonatal care areas, home oxygen settings, and hyperbaric chambers.

21. What are the main categories of oxygen delivery systems?
The main categories are low-flow systems, reservoir systems, high-flow systems, and enclosure systems.

22. What is a low-flow oxygen system?
A low-flow oxygen system provides oxygen at a flow that does not meet the patient’s total inspiratory demand, so the delivered FiO2 varies with the patient’s breathing pattern.

23. What are examples of low-flow oxygen systems?
Examples include nasal cannula, nasal catheter, simple face mask, reservoir cannula, partial rebreather mask, and nonrebreather mask.

24. What is a high-flow oxygen system?
A high-flow oxygen system provides enough total flow to meet or exceed the patient’s inspiratory demand while delivering a fixed FiO2.

25. What are examples of high-flow oxygen systems?
Examples include Venturi masks, air-entrainment nebulizers, high-flow nasal cannula, and blender-driven heated humidified systems.

26. What is a reservoir oxygen system?
A reservoir oxygen system stores oxygen during part of the breathing cycle so the patient can draw from the reservoir during inspiration.

27. What are examples of reservoir oxygen systems?
Examples include reservoir cannulas, simple masks, partial rebreather masks, and nonrebreather masks.

28. What is an oxygen enclosure system?
An oxygen enclosure system surrounds the patient or part of the patient with an oxygen-enriched environment.

29. What are examples of oxygen enclosure systems?
Examples include oxygen hoods, oxygen tents, and incubators.

30. How is FiO2 estimated with a nasal cannula?
A common estimate is 24% at 1 L/min, with an increase of about 4% for each additional liter per minute.

31. What FiO2 range is typically delivered by a nasal cannula?
A nasal cannula typically delivers an approximate FiO2 range of 0.24 to 0.44, depending on flow and the patient’s breathing pattern.

32. When should humidification be considered with a nasal cannula?
Humidification is commonly considered when nasal cannula flow exceeds 4 L/min or when the patient reports nasal dryness or irritation.

33. How does mouth breathing affect FiO2 during low-flow oxygen therapy?
Mouth breathing can reduce the amount of oxygen entering through the nose and may lower the effective FiO2 delivered by nasal devices.

34. What should be considered if a patient is mouth-breathing while using a nasal cannula?
A simple face mask, Venturi mask, or another appropriate device may be considered if oxygen delivery is inadequate with a nasal cannula.

35. What is a simple face mask?
A simple face mask covers the nose and mouth and provides moderate oxygen concentrations for short-term oxygen therapy.

36. What is the minimum flow for a simple face mask?
A simple face mask should generally be run at a minimum of 5 L/min to help prevent carbon dioxide rebreathing.

37. What FiO2 range can a simple face mask deliver?
A simple face mask can typically deliver an FiO2 of about 0.35 to 0.50, depending on flow and patient breathing pattern.

38. What is a partial rebreather mask?
A partial rebreather mask is a reservoir mask that allows the patient to rebreathe some oxygen-rich gas from the anatomic dead space while also receiving fresh oxygen.

39. What is a nonrebreather mask?
A nonrebreather mask is a reservoir mask with one-way valves designed to deliver high oxygen concentrations while limiting room air entrainment and exhaled gas rebreathing.

40. What should be done if the reservoir bag collapses during inhalation?
The oxygen flow should be increased because the patient’s inspiratory demand is exceeding the flow into the reservoir.

41. What may be wrong if the reservoir bag stays fully inflated during inspiration?
A mask leak, poor mask fit, or malfunctioning valve may be preventing the patient from drawing properly from the reservoir.

42. Why should reservoir masks not be run at very low flows?
Low flow can allow carbon dioxide to accumulate in the mask and increase the risk of CO2 rebreathing.

43. What is an air entrainment system?
An air entrainment system uses a high-velocity oxygen jet to pull in room air and mix it with oxygen to deliver a fixed FiO2.

44. What are common air entrainment oxygen devices?
Common devices include Venturi masks and air-entrainment nebulizers.

45. What is a Venturi mask?
A Venturi mask is a high-flow oxygen device that uses air entrainment to deliver a precise FiO2.

46. What is another name for a Venturi mask?
A Venturi mask is sometimes called a Venti mask.

47. Why are Venturi masks useful for patients who need precise oxygen control?
They provide a fixed FiO2 that is less affected by the patient’s breathing pattern when total flow meets or exceeds inspiratory demand.

48. What two factors affect air entrainment in a Venturi system?
The jet orifice size and the air entrainment port size affect the amount of room air mixed with oxygen.

49. How does a smaller jet orifice affect air entrainment?
A smaller jet orifice increases jet velocity, entrains more room air, produces a lower FiO2, and increases total flow.

50. How do larger air entrainment ports affect FiO2?
Larger ports allow more room air to enter, which lowers the delivered FiO2 and increases total flow.

51. What effect does downstream resistance have on an air entrainment system?
Downstream resistance reduces air entrainment, which may increase FiO2 but decrease total flow.

52. What is the air-to-oxygen ratio for 40% oxygen?
The air-to-oxygen ratio for 40% oxygen is approximately 3:1.

53. What is the air-to-oxygen ratio for 60% oxygen?
The air-to-oxygen ratio for 60% oxygen is approximately 1:1.

54. What is the “Magic Box” used for in oxygen therapy?
The “Magic Box” is a shortcut used to estimate the air-to-oxygen ratio needed to deliver a specific FiO2.

55. What is a high-flow nasal cannula?
High-flow nasal cannula is a system that delivers heated, humidified gas at high flows with an adjustable FiO2.

56. What are key benefits of high-flow nasal cannula?
Benefits include stable oxygen delivery, heated humidification, improved comfort, washout of nasopharyngeal dead space, and a small amount of positive airway pressure.

57. What flow range is commonly associated with adult high-flow nasal cannula?
Adult high-flow nasal cannula systems can often deliver flows up to approximately 60 L/min.

58. What is an oxygen blender?
An oxygen blender mixes medical air and oxygen to deliver a precise FiO2.

59. Where are oxygen blenders commonly used?
Oxygen blenders are commonly used in neonatal care, mechanical ventilation, high-flow systems, and other settings where precise FiO2 control is needed.

60. What is an oxygen hood?
An oxygen hood is an enclosure placed over an infant’s head to deliver a controlled oxygen concentration.

61. Why are oxygen hoods useful for infants?
Oxygen hoods allow controlled oxygen delivery while providing access to the infant for care and monitoring.

62. What is an oxygen tent?
An oxygen tent is an enclosure used mainly for pediatric patients to provide oxygen-enriched gas and sometimes aerosol therapy.

63. What is a disadvantage of oxygen tents?
Oxygen tents can be difficult to regulate because FiO2 and temperature may change when the tent is opened.

64. What is a reservoir cannula?
A reservoir cannula stores oxygen during exhalation so a bolus of oxygen is available during the next inhalation.

65. What are the two common types of reservoir cannulas?
The two common types are the nasal reservoir cannula and the pendant reservoir cannula.

66. What do demand and pulse-dose oxygen systems do?
Demand and pulse-dose systems conserve oxygen by delivering oxygen primarily during inhalation.

67. What is a transtracheal oxygen catheter?
A transtracheal oxygen catheter is a small catheter placed directly into the trachea through the neck to deliver oxygen.

68. What is a benefit of transtracheal oxygen delivery?
Transtracheal oxygen can reduce oxygen requirements compared with a nasal cannula because oxygen is delivered directly into the trachea.

69. What is a potential disadvantage of transtracheal oxygen therapy?
Potential disadvantages include the need for surgical placement, infection risk, mucus plugging, and the need for careful cleaning and maintenance.

70. What should a respiratory therapist do if a humidifier pop-off valve activates?
The therapist should check for an obstruction distal to the humidifier, excessive flow, blocked tubing, or a blocked delivery device and correct the problem.

71. What is a bag-mask device?
A bag-mask device is a manual resuscitation device used to provide positive-pressure ventilation and oxygen during emergency care.

72. How can a bag-mask device deliver a high oxygen concentration?
It can deliver a high oxygen concentration when connected to oxygen with adequate flow and an oxygen reservoir.

73. What is the role of oxygen therapy in chronic hypoxemia?
In chronic hypoxemia, oxygen therapy can improve oxygen delivery, reduce cardiopulmonary strain, improve exercise tolerance, and support quality of life.

74. How can chronic hypoxemia affect the heart?
Chronic hypoxemia can contribute to pulmonary hypertension and right ventricular strain, which may lead to cor pulmonale.

75. What is cor pulmonale?
Cor pulmonale is right-sided heart enlargement or failure caused by pulmonary hypertension related to lung disease or chronic hypoxemia.

76. What is hyperbaric oxygen therapy?
Hyperbaric oxygen therapy is the administration of 100% oxygen at pressures greater than atmospheric pressure inside a pressurized chamber.

77. How is hyperbaric oxygen therapy administered?
Hyperbaric oxygen therapy is administered in a monoplace or multiplace hyperbaric chamber.

78. What are common indications for hyperbaric oxygen therapy?
Common indications include carbon monoxide poisoning, air embolism, decompression sickness, selected non-healing wounds, gas gangrene, and some radiation injuries.

79. Why is hyperbaric oxygen useful for carbon monoxide poisoning?
Hyperbaric oxygen increases dissolved oxygen in plasma and helps remove carbon monoxide from hemoglobin more quickly.

80. What are potential complications of hyperbaric oxygen therapy?
Potential complications include ear or sinus barotrauma, oxygen toxicity, claustrophobia, worsening of an untreated pneumothorax, and fire risk.

81. What is heliox therapy?
Heliox therapy is the administration of a helium-oxygen mixture to reduce airway resistance and work of breathing in selected patients with airflow obstruction.

82. What property of helium makes it useful as a therapeutic gas?
Helium has a low density, which promotes more laminar airflow and reduces resistance in narrowed airways.

83. What conditions may benefit from heliox therapy?
Heliox may benefit selected patients with upper airway obstruction, post-extubation stridor, croup, severe asthma, or other conditions with increased airway resistance.

84. What is the most common heliox mixture used clinically?
Common heliox mixtures include 80% helium and 20% oxygen or 70% helium and 30% oxygen.

85. Why does heliox become less effective when the oxygen concentration is increased?
Heliox becomes less effective as oxygen concentration increases because the mixture becomes denser and loses some of helium’s low-density benefit.

86. How should heliox be administered to maximize its effect?
Heliox should be administered with a tight-fitting delivery system, such as a nonrebreather mask or ventilator setup calibrated for heliox, to limit room air dilution.

87. What is inhaled nitric oxide?
Inhaled nitric oxide is a selective pulmonary vasodilator used to reduce pulmonary vascular resistance and improve oxygenation in selected patients.

88. What is the main clinical benefit of inhaled nitric oxide?
Its main benefit is improving ventilation-perfusion matching by dilating blood vessels in ventilated areas of the lung.

89. In which neonatal condition is inhaled nitric oxide commonly used?
Inhaled nitric oxide is commonly used in term or near-term infants with hypoxemic respiratory failure associated with persistent pulmonary hypertension of the newborn.

90. What are potential complications of inhaled nitric oxide therapy?
Potential complications include methemoglobinemia, nitrogen dioxide formation, rebound pulmonary hypertension, rebound hypoxemia, and poor or paradoxical response.

91. Why should inhaled nitric oxide not be stopped abruptly?
Abrupt discontinuation can cause rebound pulmonary hypertension and sudden worsening hypoxemia.

92. What is nitrogen dioxide?
Nitrogen dioxide is a toxic gas that can form when nitric oxide reacts with oxygen.

93. What is methemoglobinemia?
Methemoglobinemia is a condition in which hemoglobin is altered so it cannot effectively carry oxygen.

94. What is carbon dioxide-oxygen therapy?
Carbon dioxide-oxygen therapy is the administration of a controlled carbon dioxide and oxygen mixture, but it is rarely used in modern respiratory care.

95. What are possible historical uses of carbon dioxide-oxygen therapy?
Historical uses include stimulating ventilation in selected cases, treating persistent hiccups, and limited use in certain neurologic or carbon monoxide poisoning scenarios.

96. How is medical-grade oxygen commonly produced for hospital use?
Medical-grade oxygen is commonly produced by fractional distillation of air.

97. What is fractional distillation?
Fractional distillation is a process that separates gases based on their boiling points, allowing oxygen to be collected from air.

98. How is oxygen commonly produced in home oxygen concentrators?
Home oxygen concentrators commonly use molecular sieves to separate nitrogen from room air and concentrate oxygen.

99. What is medical air?
Medical air is compressed, filtered atmospheric air that is used for respiratory care equipment and gas blending.

100. What is the typical oxygen concentration of medical air?
Medical air contains approximately 21% oxygen.

101. How are medical gases stored?
Medical gases may be stored in high-pressure cylinders, liquid oxygen reservoirs, bulk storage systems, or central hospital piping systems.

102. What is the most reliable way to identify the contents of a medical gas cylinder?
The most reliable way is to read the cylinder label.

103. Why should color-coding not be the only method used to identify a gas cylinder?
Color-coding may vary by country or facility and should never replace checking the cylinder label.

104. What is the color code for oxygen cylinders in the United States?
Oxygen cylinders are commonly color-coded green in the United States.

105. What is the color code for helium cylinders?
Helium cylinders are commonly color-coded brown.

106. What is the color code for nitrous oxide cylinders?
Nitrous oxide cylinders are commonly color-coded blue.

107. What is the color code for heliox cylinders?
Heliox cylinders are commonly color-coded brown and green.

108. What is a gas cylinder service pressure?
Service pressure is the pressure to which a gas cylinder is normally filled at a specified temperature.

109. What does a plus sign near the hydrostatic test date on a cylinder indicate?
A plus sign means the cylinder may be filled up to 10% above its marked service pressure when allowed by regulation.

110. What is the purpose of hydrostatic testing?
Hydrostatic testing checks the strength and safety of compressed gas cylinders at required intervals.

111. What is the purpose of a pressure-relief device on a gas cylinder?
A pressure-relief device helps prevent cylinder rupture by releasing gas if pressure rises dangerously high.

112. How are the contents of a compressed gas cylinder estimated?
The contents are estimated by reading the pressure gauge because pressure is proportional to the amount of gas remaining.

113. How are the contents of a liquid oxygen cylinder estimated?
The contents are estimated by weighing the cylinder, because pressure mainly reflects vapor pressure rather than the amount of liquid remaining.

114. What is an E cylinder commonly used for?
An E cylinder is commonly used for patient transport and short-term portable oxygen delivery.

115. What is an H cylinder commonly used for?
An H cylinder is a large compressed gas cylinder often used as a stationary gas source or backup supply.

116. What is a cylinder factor?
A cylinder factor is a number used to estimate how long a cylinder will last based on pressure and flow rate.

117. What is the formula for calculating cylinder duration?
Cylinder duration is calculated as available pressure multiplied by the cylinder factor, then divided by the flow rate.

118. What is the E cylinder factor for oxygen?
The commonly used E cylinder factor for oxygen is 0.28.

119. What is the H cylinder factor for oxygen?
The commonly used H cylinder factor for oxygen is 3.14.

120. How long will an E cylinder last if it has 1,000 psig and is running at 4 L/min?
Using the E cylinder factor of 0.28, it will last about 70 minutes before allowing for a safe residual pressure.

121. How long will an H cylinder last if it has 2,000 psig and is running at 5 L/min?
Using the H cylinder factor of 3.14, it will last about 1,256 minutes, or approximately 21 hours, before allowing for a safe residual pressure.

122. What is the Pin Index Safety System?
The Pin Index Safety System is a safety system used with small cylinders to prevent the wrong gas from being connected to a yoke.

123. What is the Diameter Index Safety System?
The Diameter Index Safety System is a safety system that uses gas-specific threaded connections to prevent misconnections in medical gas systems.

124. What safety system is commonly used for E-size cylinders?
The Pin Index Safety System is commonly used for E-size cylinders.

125. What safety system helps prevent attaching the wrong flowmeter to a wall outlet?
The Diameter Index Safety System helps prevent incorrect gas connections at station outlets and equipment connections.

126. What is a central piping system?
A central piping system delivers medical gases from a central source to outlets throughout a healthcare facility.

127. What is the typical working pressure in a hospital medical gas piping system?
A typical working pressure for many hospital medical gas systems is about 50 psig.

128. What is a zone valve?
A zone valve is a shutoff valve that allows medical gas flow to a specific hospital area to be stopped during maintenance or an emergency.

129. Why are zone valves important?
Zone valves allow staff to isolate a section of the medical gas system without shutting down gas flow to the entire facility.

130. What is a reducing valve?
A reducing valve lowers high cylinder pressure to a safe, usable working pressure.

131. What is a regulator?
A regulator reduces cylinder pressure and may include or connect to a flow-control device for patient gas delivery.

132. What is a flowmeter?
A flowmeter regulates and displays the flow rate of gas being delivered to the patient.

133. What is a Thorpe tube flowmeter?
A Thorpe tube flowmeter is a variable-orifice flowmeter with a float that rises in a tapered tube to indicate gas flow.

134. How should a ball float be read in a Thorpe tube flowmeter?
A ball float should be read at the center of the ball.

135. How should a non-ball float be read in a Thorpe tube flowmeter?
A non-ball float should usually be read at the top of the float.

136. What is a pressure-compensated Thorpe tube?
A pressure-compensated Thorpe tube is designed to maintain accurate flow readings despite downstream resistance.

137. What happens if downstream resistance occurs in an uncompensated Thorpe tube?
The flowmeter may display a falsely high reading while actual flow delivered to the patient is reduced.

138. What is a Bourdon gauge?
A Bourdon gauge is a flowmeter that uses pressure against a fixed orifice to estimate gas flow.

139. When is a Bourdon gauge especially useful?
A Bourdon gauge is useful during transport because it can function in positions where a Thorpe tube would not read accurately.

140. What is the limitation of a Bourdon gauge?
A Bourdon gauge may display a falsely high flow if there is an obstruction distal to the gauge.

141. What are safe storage practices for compressed gas cylinders?
Cylinders should be stored upright, secured with chains or racks, protected from heat, separated by gas type and status when required, and handled with valve caps in place when not in use.

142. Why should oil or grease never be used on oxygen equipment?
Oil or grease can ignite in an oxygen-enriched environment and create a serious fire hazard.

143. What precautions should be used around oxygen delivery systems?
Precautions include avoiding open flames, posting no-smoking signs, keeping equipment away from sparks or heat, and ensuring electrical devices are safe for use near oxygen.

144. What is nitrous oxide?
Nitrous oxide is a medical gas used mainly for analgesia and anesthesia, often in combination with oxygen.

145. What are key physical properties of nitrous oxide?
Nitrous oxide is colorless, has a slightly sweet odor, supports combustion, and is stored as a liquid-vapor mixture under pressure.

146. What are key physical properties of nitric oxide?
Nitric oxide is colorless, nonflammable, toxic at high concentrations, and can react with oxygen to form nitrogen dioxide.

147. What is the main safety concern with liquid oxygen systems?
Liquid oxygen is extremely cold and can cause frostbite, while oxygen-enriched environments increase fire risk.

148. What is the purpose of medical gas alarms?
Medical gas alarms warn staff about abnormal gas pressure, supply failure, or system malfunction.

149. What should be checked before transporting a patient with oxygen?
The therapist should check cylinder pressure, estimated duration, flow setting, delivery device, backup supply, and patient oxygen requirements.

150. What is the key concept to remember about medical gas therapy?
Medical gas therapy requires the correct gas, correct dose, correct delivery device, careful monitoring, and attention to safety hazards such as toxicity, hypoventilation, misconnections, and fire risk.

Final Thoughts

Medical gas therapy is one of the most common and important areas of respiratory care. Oxygen remains the most frequently used gas, but therapy may also include nitric oxide, heliox, hyperbaric oxygen, and less common gas mixtures such as carbogen.

Each gas has specific indications, delivery methods, hazards, and monitoring requirements. The respiratory therapist must treat medical gases as medications by selecting the correct dose, device, and plan of care.

Safe and effective gas therapy depends on careful assessment, proper equipment use, patient monitoring, and timely adjustment as the patient’s condition changes.