6 Oxygen and Medical Gas Therapy

Note 1: This book is written to cover every item listed as testable on the Entry Level Examination (ELE), Written Registry Examination (WRE), and Clinical Simulation Examination (CSE).

The listed code for each item is taken from the National Board for Respiratory Care (NBRC) Summary Content Outline for CRT (Certified Respiratory Therapist) and Written RRT (Registered Respiratory Therapist) Examinations (http://evolve.elsevier.com/Sills/resptherapist/). For example, if an item is testable on both the ELE and the WRE, it will simply be shown as: (Code: …). If an item is testable only on the ELE, it will be shown as: (ELE code: …). If an item is testable only on the WRE, it will be shown as: (WRE code: …).

Following each item’s code will be the difficulty level of the questions on that item on the ELE and the WRE. (See the Introduction for a full explanation of the three question difficulty levels.) Recall (R) level questions typically expect the exam taker to recall factual information. Application (Ap) level questions are harder because the exam taker may have to apply factual information to a clinical situation. Analysis (An) level questions are the most challenging because the exam taker may have to use critical thinking to evaluate patient data to make a clinical decision.

Note 2: A review of the most recent Entry Level Examinations (ELE) has revealed that an average of 12 questions (out of 140), or 9% of the exam, will cover oxygen and medical gas therapy. A review of the most recent Written Registry Examinations (WRE) has shown that an average of 7 questions (out of 100), or 7% of the exam, will cover oxygen and medical gas therapy. The Clinical Simulation Examination is comprehensive and may include everything that should be known by an advanced level respiratory therapist.

MODULE A

Ensure that the patient is adequately oxygenated

1. Oxygen administration

a. Recommend changes in the patient’s position to minimize hypoxemia (Code: IIIG2a) [Difficulty: ELE: R, Ap; WRE: An]

b. Position the patient to minimize hypoxemia (Code: IIID8) [Difficulty: ELE: R, Ap; WRE: An]

Usually a patient who is short of breath when lying supine should be repositioned to sit more upright in a Fowler’s or semi-Fowler’s position. This seems to work best in patients with bilateral pulmonary problems such as congestive heart failure or pneumonia. If the patient cannot sit up and the lung problem is one-sided, roll the patient so that the more functional lung is down. The good lung should be positioned up in the following exceptions:

• Undrained pulmonary abscess that should not be drained into the good lung

• Neonatal congenital diaphragmatic hernia in which the good lung should not be compressed by the bowel in the chest cavity

• Pulmonary interstitial emphysema in which, by lying on the bad lung, the air leak and functional residual capacity can be reduced

In either case, always ask the patient whether the new position helps to make breathing easier. If not, reposition the patient until breathing is more comfortable with less shortness of breath. In general, Trendelenburg is not well tolerated. A patient with a closed head injury and brain edema should not be put into the Trendelenburg position.

c. Administer oxygen to achieve adequate respiratory support (ELE code: IIID6) [Difficulty: ELE: R, Ap, An]

Oxygen (O₂) must be administered in doses (up to 100%) that are adequate to treat hypoxemia, decrease the patient’s work of breathing, or decrease the work of the heart. Because the U.S. Food and Drug Administration has declared supplemental oxygen to be a drug, a physician’s order is required to give it to a patient or to make a change in the percentage. The only exceptions are when recognized protocols exist in your institution to give oxygen under certain limited conditions. For example, all patients with a diagnosed heart attack are given a nasal cannula at 2 L/min, or all patients undergoing cardiopulmonary resuscitation (CPR) receive 100% oxygen.

See Chapter 3 (Module A) for a listing of indications for drawing blood for an arterial blood gas (ABG) measurement. This list should be fairly complete for conditions that justify the need for supplemental oxygen. In general, the goal of giving supplemental oxygen is to keep the patient’s Pao₂ level between 60 and 100 torr. Exceptions include carbon monoxide poisoning, severe anemia, and CPR, when the hope is to fully saturate the hemoglobin and increase the plasma oxygen content as much as possible. Oxygen should not be given without proof of hypoxemia or another clinical justification. When those conditions have been corrected, the oxygen percentage should be adjusted accordingly.

Giving supplemental oxygen is not done without risk. Following are oxygen-related problems that may be seen clinically.

d. Measure the patient’s oxygen percentage, oxygen liter flow, or both (ELE code: IIIE10) [Difficulty: ELE: R, Ap, An]

Always measure the patient’s inspired O₂ percentage (Fio₂) if possible. The gas sample should be taken as close as possible to the patient to minimize the chance of dilution from room air. Record the oxygen percentage on the ABG order slip, in the department records, and in the patient’s chart if needed. As discussed in Chapter 3, the oxygen percentage must be known before the patient’s Pao₂ level can be interpreted.

The oxygen liter flow is all that can be recorded with the following devices: nasal cannula, nasal catheter, simple mask, partial-rebreather mask, nonrebreather mask, and transtracheal oxygen catheter. A direct relation is found between the liter flow and the oxygen percentage, but it is not predictably accurate.

e. Prevent the patient from becoming hypoxemic by using proper technique (ELE code: IIID9) [Difficulty: ELE: R, Ap, An]

Use caution and plan ahead to minimize any time that the oxygen supply to the patient is cut off or reduced. When changing equipment of any kind, have the replacement set up and tested for proper function before replacing the current setup.

It is well known that suctioning the airway reduces the patient’s oxygen level. This can result in dangerous dysrhythmias. Remember to increase the patient’s inspired oxygen percentage about 1 minute before, during, and for at least 1 minute after suctioning. It is acceptable and safe to give 100% oxygen to an adult for short periods like this. Remember to reduce the oxygen percentage or liter flow to the previous level once the patient is stable after the procedure. Reanalyze the percentage if possible.

2. Manipulate oxygen and specialty gas analyzers by order or protocol (Code: IIA26) [Difficulty: ELE: R, Ap; WRE: An]

a. Get the necessary equipment for the procedure

b. Put the equipment together and make sure that it works properly

c. Troubleshoot any problems with the equipment

Because so many different models are available, consult an equipment book or the manufacturer’s literature for details of the various analyzers. All portable, hand-held analyzers fall into one of the following categories: electric, physical/paramagnetic, and electrochemical.

1. Electric analyzers

These analyzers basically operate by comparing the cooling effects of an oxygen-enriched gas sample on a heated wire versus the cooling effects of a room air gas sample on a heated wire. The oxygen-enriched gas cools faster than the room air gas. This is known as the principle of thermal conductivity. Each sample must be drawn into the analyzer through a capillary line. These analyzers are designed to work only in oxygen and nitrogen gas mixes. Do not use them around flammable gases such as those found in anesthesia. Failure to calibrate can be caused by a weak battery, a plugged capillary line, or a defect in an electrical component.

2. Physical/paramagnetic analyzers

These analyzers make use of the fact that oxygen is attracted toward a magnetic field (paramagnetic property). The more oxygen is in a sample gas, the more the magnetic field is altered. These units can be used with all types of gases and are safe in the operating room with flammable and explosive anesthetics. A silica gel–filled container is in line with the capillary tube to dry out the sample gas before it gets to the analyzing chamber. Failure to calibrate can be caused by water or by a defect in the analyzing chamber, a weak battery, or a plugged capillary line.

3. Electrochemical analyzers: polarographic and galvanic fuel cell

Both polarographic and galvanic fuel cells make use of the fact that each oxygen molecule accepts up to two electrons and becomes chemically reduced. The more oxygen is in the gas sample, the more electrons are released from an oxidizing electrolyte solution. This is measured as an electrical current that is proportional to the oxygen percentage. These analyzers can monitor continuously and display the oxygen percentage. Both types are safe by themselves in the presence of flammable gases, but the added alarm systems are powered electrically and may make the units unsafe. Polarographic analyzers use a battery to polarize the gas sampling probe. Because of this, they have a faster response time than do the galvanic fuel cell types. Galvanic fuel cell analyzers do not need a battery for power. However, they usually include alarms that are battery powered.

Failure to calibrate either type can be caused by a weak battery, an exhausted supply of chemical reactant in the gas sampling probe, an electronic failure, or a damaged membrane over the probe. A damaged or torn probe will allow water, mucus, or blood onto the probe. The galvanic units must have their probes kept dry to be read accurately. Both types are pressure sensitive. High altitude causes them to display a lower-than-true oxygen percentage, and high pressure as seen in a ventilator circuit with positive end-expiratory pressure (PEEP) causes the units to display a higher-than-true oxygen percentage.

4. Specialty gas analyzers

Specialty gas analyzers (helium, nitrogen, and carbon monoxide) are used mainly with pulmonary function testing procedures and are discussed in Chapter 4. It may be necessary to use a helium analyzer if a helium and oxygen mix is given to a patient.

Nitric oxide (NO) is delivered through the INOvent delivery system (Datex-Ohmeda, Inc., Madison, WI). It is able to deliver set amounts of therapeutic NO and to continuously monitor the amount of NO given to the patient along with nitrogen dioxide (NO₂) and oxygen.

3. Perform quality control procedures for oxygen analyzers (Code: IIC2) [Difficulty: ELE: R, Ap; WRE: An]

A two-point calibration procedure is done on all oxygen analyzers by sampling room air, adjusting a calibration control if necessary to have the unit show 21% oxygen (first point or low oxygen check), sampling 100% oxygen, and adjusting a calibration control if necessary to have the unit show 100% oxygen (second point or high oxygen check). When room air is sampled again, the analyzer should read 21% oxygen. In general, always follow the manufacturer’s guidelines for setup and calibration. If an analyzer does not pass the two-point calibration check, it should not be used.

MODULE B

Storage, hardware, and distribution of medical gases

1. Manipulate oxygen and other gas cylinders, bulk storage systems, and manifolds, by order or protocol (ELE code: IIA9a) [Difficulty: ELE: R, Ap, An]

a. Get the necessary equipment for the procedure

b. Put the equipment together and make sure that it works properly

c. Troubleshoot any problems with the equipment

1. Oxygen and other gas cylinders

The different types of gases in cylinders are identified by the color code of the cylinder and the cylinder label. Note that only E cylinders have mandatory color coding. Color codings on the other cylinders are voluntary but usually are followed by the manufacturers. However, always read the label to be sure of the contents of the cylinder. The most important cylinder colors to remember are those of oxygen and air, but all are included in Table 6-1 for the sake of completeness.

TABLE 6-1 Color Codes for Gas Cylinders

Gas	Color
Oxygen	Green (white for international)
Air	Yellow
Helium	Brown
Helium and oxygen	Brown and green (check the label for the percentage of each gas)
Carbon dioxide	Gray
Carbon dioxide	Gray and green (check the label for oxygen and the percentage of each gas)
Nitrous oxide	Light blue
Cyclopropane	Orange
Ethylene	Red

Exam Hint 6-2 (ELE)

The NBRC is known to ask the examinee to calculate how long a certain cylinder lasts at a given gas flow. To date, only the durations of E-, H-, and K-sized oxygen cylinders have had to be calculated.

To review how to calculate the duration of flow for a particular type of cylinder, see Table 6-2 for the cylinder duration factors, the following equation, and the following examples.

TABLE 6-2 Oxygen Cylinder Duration of Flow Factors

Cylinder Size	Factor, L/psig
E	0.28
H	3.14
K	3.14
D	0.16
M	1.36
G	2.41

psig, Pounds per square inch gauge.

1. Calculate the duration of flow of an E cylinder with 1500 pounds per square inch gauge (psig) that is running at 6 L/min.

Minutes of flow = 70 (1.16 hr, or 1 hr and 10 min)

2. Calculate the duration of flow of an H cylinder with 1950 psig that is running at 9 L/min.

Minutes of flow = 680.33 (11.34 hr, or 11 hr and 20 min)

2. Bulk storage systems

The bulk liquid oxygen (LOX) storage system is the main source of a hospital’s oxygen. A reducing valve is used to decrease the gas pressure to 50 pounds per square inch gauge (psig) before it is piped throughout the hospital for easy access. Alarms will sound if the pressure is low or too high. Pressure relief valves will open if the pressure is greater than 75 psig. Zone valves are located throughout the hospital so the gas can be turned off if a leak develops or if a fire occurs.

3. Manifolds

A manifold is a piping system that connects the bulk storage system and the hospital gas piping system with a bank of H- or K-sized cylinders. These free-standing cylinders are a backup source of oxygen in case the bulk system fails. A 24-hour supply of gas must be available.

The manifold system includes a reducing valve to decrease the gas pressure to 50 psig. Check valves are built into the manifold so that a leak in one cylinder connection cannot result in all of the gas cylinders leaking out.

2. Manipulate adjunct hardware, such as reducing valves, flowmeters, regulators, and high-pressure hose connectors, by order or protocol (ELE code: IIA9a) [Difficulty: R, Ap, An]

a. Get the necessary equipment for the procedure

b. Put the equipment together and make sure that it works properly

c. Troubleshoot any problems with the equipment

1. Reducing valves

Reducing valves are used to reduce the high pressure seen in a bulk oxygen storage system, manifold, or gas cylinder. One or more stages (pressure-reducing steps) can be used to reach the working pressure of 50 psig. Single-stage reducing valves reach the pressure in a single step. Multiple-stage reducing valves give finer control over pressure and flow by decreasing pressure in the first stage to about 200 psig and to 50 psig in the second stage. Occasionally, three stages are seen. All reducing valves (and regulators [combined reducing valve and flowmeter]) have the following built-in safety features:

• A frangible disk that breaks to release gas pressure in the event of mechanical failure or breakage

• A fusible plug that melts to release gas pressure in the event of a fire

• American Standard Compressed Gas Cylinder Valve Outlet and Index Connections (usually called the American Standard Safety System [ASSS]), which prevent the accidental connection of the wrong reducing valve (or regulator) to a large gas cylinder

• The Pin Index Safety System (PISS) is a special section of the American Standard System that applies to gas cylinders that are E-sized and smaller. It is designed to prevent an accidental connection of the wrong gas to a reducing valve or regulator. These reducing valves and regulators are designed with a specifically pinned yoke to wrap around the valve stem of a gas cylinder. A soft plastic O-ring washer is included to help ensure a tight seal. Figure 6-1 shows the location of the pinholes in the cylinder valve face. Table 6-3 shows the gases and pinhole positions. It is important to know the positions for oxygen and air; the others are included for the sake of completeness.

Figure 6-1 Locations of the Pin Index Safety System holes in the cylinder valve face.

(Modified from Branson RD, Hess DR, Chatburn RL: Respiratory care equipment, ed 2, Philadelphia, 1999, Lippincott Williams & Wilkins.)

TABLE 6-3 Pin Index Safety System Gases and Pinhole Locations

Gas	Pinhole Locations
Oxygen	2-5
Air	1-5
Oxygen/carbon dioxide (≤7%)	2-6
Oxygen/carbon dioxide (>7%)	1-6
Oxygen/helium (not >80% helium)	2-4
Oxygen/helium (helium >80%)	4-6
Nitrous oxide	3-5
Ethylene	1-3
Cyclopropane	3-6

It is necessary to “crack” or blow some gas out of a cylinder before putting any reducing valve or regulator onto the cylinder. Do this by attaching the tank wrench to the valve stem and slowly turning the valve stem in a counterclockwise (so-called “lefty-loosy”) direction to release some gas. This cracking is done to prevent any dust or debris from being forced into the reducing valve or regulator, which might cause a fire. See Figure 6-2 for a schematic drawing of an “E” tank of oxygen and how its yoke is connected. If the O-ring is missing or the yoke is misaligned on the post, a high-pressure gas leak will occur when the tank is opened with the tank wrench. Close off the tank to stop the leak by turning the tank wrench on the valve stem in a clockwise direction (so-called “righty-tighty”). Investigate the yoke-to-post connection to identify causes of the leak.

Figure 6-2 Details of an “E” size tank of oxygen and its yoke connector. A, A cross section through the stem (also called the control valve) of the tank shows its key features. B, A three-dimensional view shows how the yoke with its two pins aligns with the corresponding pin holes (locations 2 and 5) on the yoke. The plastic washer ensures a seal between the gas outlet on the stem and the yoke. (Not shown is the regulator that attaches to the yoke. See Figure 6-9.) C, A tank wrench that is attached to the valve stem (also called a control valve). Turn the wrench in a counterclockwise direction to open the tank and allow gas flow; close the tank to stop gas flow by turning the wrench in a clockwise direction.

(Redrawn from Sills JR: Respiratory care for the health care provider, Albany, 1998, Delmar Publishers.)

2. Flowmeters

Flowmeters are designed to regulate and indicate flow. They come with the following safety features so that they cannot be attached to the wrong reducing valve, regulator, high-pressure hose, or appliance:

• Diameter Index Safety System (DISS) inlets and outlets that are specific to the various gases, so a mixup with the wrong appliance or connector cannot occur. The DISS system applies to flowmeters that attach to all American Standard and DISS reduction valves.

• Flowmeters with quick-connect inlet adapters instead of DISS inlets. These quick-connects are designed specifically for the hospital’s piped-in oxygen and air outlets. They are not interchangeable between gases or between manufacturers. Occasionally a piped oxygen outlet will jam open and will let gas rapidly escape. Insert the proper flowmeter into the outlet, and turn the flowmeter off. This stops the leak until the defective wall outlet can be repaired.

Flowmeters usually are categorized by how they react to backpressure. To complicate matters further, we must remember that the three different manufactured types of flowmeters may or may not be backpressure compensated:

1. Non–backpressure-compensated (pressure-uncompensated) flowmeters will inaccurately indicate the flow through them in the face of backpressure. Figures 6-3 and 6-4 show non–backpressure-compensated kinetic and Thorpe types of flowmeters, respectively. Note that the Thorpe and kinetic flowmeters have the flow-control valve upstream from the meter. They read accurately if they are kept upright and do not have to “push” against any backpressure. If laid on their sides, the plunger and ball bearing do not indicate the set flow. They both read a lower flow than that actually delivered when faced with a backpressure.

2. The Bourdon flowmeter is designed similarly to the Bourdon gauge in the reducing valve (Figure 6-5). The face piece is marked in liters of flow rather than pressure. It is the flowmeter of choice in a transport situation because it may be laid flat with no effect to its flow if no backpressure is present. These flowmeters will display a higher flow than that actually delivered when faced with a backpressure.

3. Backpressure-compensated (pressure-compensated) flowmeters accurately indicate the flow through them in the face of backpressure. For this reason, they should be used whenever possible. Figures 6-6 and 6-7 show backpressure-compensated kinetic and Thorpe types of flowmeters, respectively. Note that both of these flowmeters have the flow-control valve downstream from the meter. Because of this, they read accurately in the face of backpressure as long as they are kept upright. Besides reading the label, this simple test enables the practitioner to tell whether a flowmeter is backpressure compensated:

1. Make sure the flowmeter is turned off.

2. Plug the flowmeter into a gas outlet.

3. If the float or ball bearing bounces, the flowmeter is backpressure compensated.

Figure 6-3 Kinetic-type non–backpressure-compensated (pressure-uncompensated) flowmeter.

(Modified from McPherson SP: Respiratory care equipment, ed 4, St Louis, 1990, Mosby.)

Figure 6-4 Thorpe-type non–backpressure-compensated (pressure-uncompensated) flowmeter.

(Modified from McPherson SP: Respiratory care equipment, ed 4, St Louis, 1990, Mosby.)

Figure 6-5 Bourdon-type non–backpressure-compensated (pressure-uncompensated) flowmeter.

(From McPherson SP: Respiratory care equipment, ed 4, St Louis, 1990, Mosby.)

Figure 6-6 Kinetic-type backpressure-compensated (pressure-compensated) flowmeter.

(Modified from McPherson SP: Respiratory care equipment, ed 4, St Louis, 1990, Mosby.)

Figure 6-7 Thorpe-type backpressure-compensated (pressure-compensated) flowmeter.

(Modified from McPherson SP: Respiratory care equipment, ed 4, St Louis, 1990, Mosby.)

d. Perform quality control procedures for flowmeters (Code: IIC6) [Difficulty: ELE: R, Ap; WRE: An]

When a quality control procedure for a flowmeter is performed, it is critical that a known flow be sent through it so that the flowmeter can be checked for accuracy. This should be done without any backpressure against the flowmeter. Review the previous discussion on troubleshooting flowmeters for the effects of backpressure on non–backpressure-compensated flowmeters and Bourdon flowmeters. Do not use any flowmeter that does not give an accurate reading.

Exam Hint 6-3 (ELE)

Choose a backpressure-compensated flowmeter in all situations except during patient transport, when the oxygen tank and flowmeter might be laid flat. Then a Bourdon flowmeter should be used.

1. Regulators

Regulators combine a reducing valve and a flowmeter (Figure 6-8). Everything that has been discussed so far relates to regulators. Bourdon gauge reducing valves usually are seen and can have a second Bourdon gauge added as a flowmeter (Figure 6-9) or a Thorpe or kinetic flowmeter. As mentioned earlier, use a backpressure-compensated flowmeter in all situations except for patient transport.