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YOU ENTER YOUR PATIENT’S roomat the beginning of the shift and findher in severe respiratory distress. She’spale, diaphoretic, tachypneic, and dys-pneic, and her SpO2 is 86%. You acti-vate the rapid response team. Whilewaiting for help to arrive, you obtainher vital signs and prepare to adminis-ter supplemental oxygen. Which oxy-gen delivery device would be the mostappropriate for this patient?

In this article, we’ll help you makethe best choice by presenting an over -view of oxygen therapy for adults in anacute care facility, looking at varioustypes of supplemental oxygen deliverydevices, and discussing the strengthsand limitations of each.

Oxygen therapy: What and who? As you know, oxygen therapy treats orprevents hypoxia by administeringoxygen at concentrations greater thanthe level found in ambient air. Roomair consists of 21% oxygen, 79% nitro-gen, and trace amounts of carbon diox-ide and other gases. Oxygen therapy isindicated for patients with:• documented hypoxemia, or a sub-normal PaO2, defined as less than 60mm Hg (or an SaO2 of less than 90%)in a patient breathing room air, or aPaO2 or SaO2 below the desirable range

for the patient’s clinical situation.• an acute care situation in whichhypoxemia is likely, such as severetrauma, acute myocardial infarction,or surgery.1

Oxygen therapy has no specific con-traindications, but like most otherdrugs, it can cause adverse reactionsand complications. Administer it cau-tiously to patients with chronicobstructive pulmonary disease whohave a hypoxic respiratory drive, andbe aware of the risk of oxygen toxicity.2

Potential adverse reactions to oxy-gen therapy include:• ventilatory depression in sponta-neously breathing patients with ele-vated PaCO2 and PaO2 greater than60 mm Hg• absorption atelectasis, oxygen toxici-ty, and depression of ciliary and leuko-cyte function at FIO2 values above 0.5.

High oxygen concentrations alsopose a fire hazard, and certain nebu-lization and humidification systemscan become contaminated with bacte-ria, raising infection risks.2

Types of oxygen delivery devicesOxygen delivery devices are used toadminister, regulate, and supplementoxygen to increase the patient’s arter-ial oxygenation. The device entrains

(mixes) oxygen and air, creating afixed concentration of oxygen fordelivery to the patient.

Typically in nonemergency situa-tions, the healthcare provider willspecify which oxygen delivery deviceto use. Devices can be low-flow orhigh-flow.

If you’re choosing an oxygen deliv-ery device in an emergency, ask your-self which oxygen concentration thedevice can deliver when connected toan oxygen supply source, and considerif and how the inspired oxygen con-centration varies with the oxygen flowrate. The inspired oxygen concentra-tion typically is expressed as a percent-age for supplemental oxygen, but canalso be expressed as a decimal (FIO2),with values between 0.21 (room air)and 1.0 (equivalent to 100% oxygen).

A patient who can protect her ownairway and is breathing spontaneouslymay be able to use various commonoxygen delivery devices. Let’s look atthe options.

Low-flow devicesLow-flow devices deliver oxygendirectly into the patient’s airway at flowrates of 8 L/minute or less.3 Becausethis flow rate is below the normal adultinspiratory requirements, and because

Getting inspired about

oxygen delivery devices Learn the ins and outs of supplemental

oxygen therapy, including which deliverydevice is best for your patient.

By Maj. John C. Stich, RN, CCRN, MSA, MSN, andMaj. David M. Cassella, RN, CCNS, CCRN, MSN

low-flow devices aren’t sealed to thepatient’s face or nares, the patient takesin a variable mix of room air and deliv-ered oxygen with each breath. As aresult, the inspired oxygen concentra-tion can vary greatly. For example, if thepatient is tachypneic, the supplementaloxygen will be diluted by room air, pro-ducing a lower inspired oxygen concen-tration. If the patient takes slow, deepbreaths, he’ll inhale more supplementaloxygen and less room air, increasing theinspired oxygen concentration.4

Low-flow reservoir devices generallyprovide a higher inspired oxygen con-centration than nonreservoir low-flowsystems, but the concentration remainsvariable. While the patient exhales, thedelivered oxygen is stored in the reser-voir and is available for the next inspi-ration; as a result, the patient inspiresthe stored oxygen and less room air.

Low-flow devices include the nasalcannula, simple face masks (simpleoxygen masks), and rebreather masks(simple masks with a reservoir bag).Let’s look at each device.

Nasal cannulaNasal cannulas are commonly used forstable patients who can tolerate a low,nonfixed oxygen concentration. Thesedevices deliver 100% oxygen, butbecause the patient also breathes roomair, the oxygen concentration ultimately

delivered to the alveoli ranges from24% to 44%. Other factors affecting theinspired oxygen concentration are theoxygen flow rate through the cannula,mouth breathing, respiratory rate andpattern, minute ventilation, and alti-tude.1 The acceptable oxygen flow ratefor this device ranges from 1 to 6L/minute. For more on flow rates, seeConcentrating on nasal cannulas.

Oxygen supplied via nasal cannula atflow rates of 4 L/minute or less doesn’tneed to be humidified.2 However, oxy-gen flow rates above 4 L/minute shouldbe humidified to prevent discomfortand prevent nasal mucosa from drying.

Reservoir nasal cannulaThe reservoir nasal cannula, originallydesigned for outpatient use, is relative-

ly new for hospitalized patients. Thesedevices store oxygen in a reservoirwhile the patient is exhaling and deliv-er a bolus of 100% oxygen on the nextinhalation. Because these devices areoxygen-conserving, they can deliverhigher oxygen concentrations than asimple nasal cannula despite deliveringoxygen at lower flow rates. For exam-ple, a flow rate of 2 L/minute with areservoir cannula produces an FIO2equivalent to that delivered by a tradi-tional nasal cannula set to deliver4 L/minute.1 Sizes vary by manufac -turer, but a 20-mL reservoir is typical.

Reservoir nasal cannulas come intwo styles: mustache and pendant. Themustache style, which positions thereservoir under the nose, may be morecomfortable for some patients. Themore discreet pendant style is lessnoticeable but weighs down the earloops. Because reservoir nasal cannulascapture water vapor when patientsexhale and return the vapor duringinhalation, humidification isn’trequired.1

The reservoir nasal cannula can pro-vide FIO2 rates of 0.5 or greater whileletting the patient eat, talk, ambulate,and use incentive spirometry. Becausethe device is more comfortable and lessanxiety-provoking than other devices,the patient may also be more willing toadhere to therapy.1

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Concentrating on nasalcannulas5

Starting at 1 L/min, increasing theoxygen flow by 1 L/min willincrease the inspired oxygen con-centration about four percentagepoints:• 1 L/min = 24%• 2 L/min = 28%• 3 L/min = 32%• 4 L/min = 36%• 5 L/min = 40%• 6 L/min = 44%

Nasal cannula

Mustache-stylereservoir nasal cannula

Pendant-stylereservoir nasalcannula

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Simple face maskLike the nasal cannula, the simple facemask (also known as the simple oxy-gen mask) mixes oxygen with roomair. But because the mask itself acts as

a reservoir, it can deliver an FIO2 of0.35 to 0.50, using oxygen flow ratesfrom 5 to 10 L/minute.2 A minimumflow rate of 5 L/minute is needed toflush the expired carbon dioxide outof the mask so that the patient doesn’trebreathe it.

Patients who are mouth breathersmay also benefit from a face mask overa simple nasal cannula, but to flush outcarbon dioxide, the flow rate mustremain above 5 L/minute even if thepatient doesn’t require a flow rate thathigh to maintain his SpO2.

Some patients may find any type offace mask, including the simple facemask, uncomfortable and claustropho-bic. Also, the higher flow rates neededfor a simple face mask may dry oraland nasal mucous membranes, makingthe patient uncomfortable and discour-aging him from continuing therapy. Inaddition, prolonged use of a face maskcan irritate the skin, potentially leadingto skin breakdown and even pressureulcers.

Partial rebreather maskA partial rebreather mask, another typeof reservoir device, consists of a simpleface mask with a reservoir bag. It’s astep up from a simple face mask and astep down from a non-rebreathermask. A low-flow device, the partialrebreather mask can deliver 40% to70% oxygen at flow rates of 6 to 10L/minute. The oxygen flow shouldkeep the reservoir bag at least one-third to one-half full on inspiration.2

Because this mask’s range of oxygendelivery can be accommodated byeither the simple face mask or non-rebreather mask, many hospitals nolonger use them.

Non-rebreather maskSimilar to the partial rebreather mask,the non-rebreather mask also has aseries of one-way valves. The valvebetween the reservoir bag and themask prevents exhaled air from return-ing to the bag.2

The non-rebreather mask is idealfor emergency situations when thepatient needs a high inspired-oxygenconcentration (60% to 80%) for ashort time. The mask can be placedquickly and provide a flow rate of upto 10 L/minute in an emergency.2,5

Theoretically, an inspired oxygenconcentration of close to 100% couldbe achieved if the patient breathed inonly the stored oxygen from the reser-voir and inspired no room air. But in

practice, a concentration over 75% israre because the mask doesn’t createa perfect seal on the patient’s faceand inspiration of some room airis inevitable. (For more, see Non-rebreather masks: Pumping up the volume).

To maximize function of a non-rebreather mask, make sure that themask fits snugly with no visible gapsbetween it and the patient’s face. Theoxygen flow rate should always main-tain the reservoir bag at least one-thirdto one-half full on inspiration, just likethe partial rebreathing mask.

High-flow devicesHigh-flow devices deliver a prescribedlow or high oxygen concentration atrates that exceed patient demand,thereby providing more than enoughoxygen for each inspiration. Thesedevices include Venturi masks (alsoknown as Venti masks) and aerosolmasks. Unlike low-flow and reservoirdevices, these devices control the mix-ture of room air so the inspired oxygenconcentration is consistent.

Venturi maskVenturi masks typically come in a kit thatincludes five to seven interchangeable air

Non-rebreather masks: Pumping up the volume5

Starting at 6 L/min, each increase of1L/min in flow with a non-rebreathermask will increase the inspired oxy-gen concentration by 10 percentagepoints:• 6 L/min = 60%• 7 L/min = 70%• 8 L/min = 80%• 9 L/min = 90%• 10 L/min = almost 100%

entrainment devices used to achievean inspired oxygen concentrationbetween 24% and 50%, depending onthe manufacturer. The concentration iscontrolled using interchangeable color-coded valves, not the oxygen flow rate,so increasing the flow rate withoutusing the appropriate valve won’tincrease the concentration.

Because they deliver a consistentinspired oxygen concentration, Venturimasks are good for patients withchronic hypercarbia and moderate-to-severe hypoxemia, such as patientswith chronic obstructive pulmonarydisease. Humidification usually isn’tneeded—because the mask entrains amuch greater flow of room air, themixture of gas delivered to the patientapproaches room air humidity. If thepatient experiences upper airwaymucosal dryness, he may be morecomfortable using an aerosol devicewith the appropriate mask.

Aerosol masksAerosol face masks, tracheostomycollars, T-tube adapters, and facetents work in the same fashion butattach to the patient differently. Theaerosol mask uses a mixture of oxy-gen, entrained room air, and water to

achieve the desired humidified oxy-gen concentration. A jet flow nozzleproduces aerosol water particles;the aerosol mask provides a specificoxygen concentration (ranging upto 100%).

Assessing oxygenationWhen your patient is receiving supple-mental oxygen, monitor her responseto therapy using pulse oximetry, arterialblood gas analysis, and physical assess-ment findings, such as respiratory rateand pattern and breath sounds. Oxygenis a drug, and as with all drugs, you’llwant to administer the smallest amountnecessary to achieve the desired effect.If the patient’s SpO2 is 90% to 94%, shehas mild to moderate hypoxia andshould receive supplemental oxygenvia nasal cannula or simple face maskas needed to achieve the desired SpO2.(A reading of 95% to 100% is consid-ered normal, although your facility mayset a lower threshold.) An SpO2 of 85%to 89% indicates moderate to severehypoxia; provide supplemental oxygenvia a face mask with a reservoir. AnSpO2 below 85% indicates severe to life-threatening hypoxemia requiring endo-tracheal intubation and mechanicalventilation.5

Helping your patientNow let’s return to the patient we metat the beginning of this article. She’s insevere respiratory distress, on the vergeof respiratory arrest, and her deterio-rating SpO2 indicates moderate tosevere hypoxia. In this emergency situ-ation, administer 100% oxygen vianon-rebreather mask and continue toreassess the patient until help arrives.

The rapid response team arrives andintubates the patient to control the air-way and correct the hypoxia. She’staken to the ICU for ventilatory sup-port and further treatment.

By understanding oxygen deliv-ery devices and how to assess yourpatient’s response to supplemental oxygen therapy, you can help herbreathe easy. ✧

REFERENCES

1. Dumont CP, Tiep BL. Using a reservoir nasalcannula in acute care. Crit Care Nurse. 2002;22:41-46.

2. Kallstrom TJ, American Association for Res-piratory Care (AARC). AARC clinical practiceguideline: oxygen therapy for adults in theacute care facility—2002 revision & update.Resp Care. 2002;47(6):717-720.

3. Urden LD, Stacy KM, Lough ME. Thelan’sCritical Care Nursing: Diagnosis and Manage-ment. 5th ed. Mosby Elsevier; 2006.

4. Pruitt WC, Jacobs M. Basics of oxygen ther-apy. Nursing. 2003;33(10):43-45.

5. American Heart Association. ACLS: Principlesand Practice. Dallas, TX: American Heart Asso-ciation; 2003.

RESOURCES

Berry BE, Pinard AE. Assessing tissue oxygena-tion. Crit Care Nurse. 2002;22:22-40.

Giuliano KK, Higgins TL, Connell WF. New-generation pulse oximetry in the care of criti-cally ill patients. Am J Crit Care. 2005;14(1):26-37.

Mathews PJ. Ask the expert. Nursing. 2005;33(5):34.

Rogers P. Respiratory distress with arterial hypoxemia. In: Fink MP, Abraham E, VincentJ, Kochanek PM, eds. Textbook of Critical Care.5th ed. Philadelphia, PA: Elsevier Saunders;2005.

At Walter Reed Army Medical Center in Washington,D.C., John C. Stich is director of the critical care nursecourse and David M. Cassella is head nurse of ortho-pedics.

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Venturi mask Tracheostomy collar