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Home , Oxygen saturation, Pulmonary gas pressures

Decoding the oxyhemoglobin dissociation curve Understanding the curve helps you put in context. By Julia Hooley, MSN, RN

a 72-year-old fe - The oxyhemoglobin dissociation ture of the pa - MRS . G LENN , male on a medical-surgical curve (OHDC) indicates the rela - tient’s overall oxy - floor, was hospitalized 3 tionship between the satu - genation status, you need to assess

days ago for pneumonia. ration of (Sa O2) and pulse oximetry values in the con - Since her admission, she the of arterial oxy - text of the OHDC. This article de -

has been on continuous gen (Pa O2). Neither linear nor static, codes the curve to make it more pulse oximetry and is re - the curve can change or shift de - understandable and discusses the ceiving oxygen (2 L /minute pending on various factors. Yet un - benefits and limitations of pulse by nasal cannula) and an - derstanding the curve and its impli - oximetry. tibiotics. A chest X-ray taken earli - cations for patient care can be er today showed little change in challenging. The curve: Just the basics her pneumonia. She has a history Pulse oximetry has become an No doubt you remember learning of chronic disease. essential tool in various settings for about the OHDC as a nursing stu - At the beginning of the shift, the a patient’s oxygenation dent. It’s discussed in nearly every nurse hears the low alarm of Mrs. status. It indirectly indicates arterial nursing textbook. Nonethe less, it Glenn’s pulse oximeter sound, indi - hemoglobin saturation, measured as can be a somewhat puzzling con - cating a reading of 89% to 90%. by pulse oxime - cept to grasp and apply in clinical

On assessment, the nurse finds the try (Sp O2). How ever, this technique practice. To understand it, think patient alert, oriented, and in no is limited because oximetry meas - about the oxygenation process oc - apparent distress. Mrs. Glenn’s ures just one component of oxy - curring in the body. Staying alive heart rate is 96 beats/minute; respi - genation. For a more accurate pic - hinges on adequate oxygen mov - ratory rate, 24 breaths/minute with ing from the to body tissues diminished breath sounds; and cells. For this to occur, the pressure, 124/80 mm Hg; and tem - lungs, blood, and environment perature, 38.1° C (100.6° F). CNE within the body must be function - Because the nurse is unfamiliar 1.42 contact ing properly: hours with Mrs. Glenn, she consults the • The lungs must receive enough respiratory therapist (RT), who’s LEARNING OBJECTIVES oxygen to be perfused and ven - preparing to administer a breath - 1. Recall the physiologic basis for the tilated optimally. ing treatment. The RT assures her oxyhemoglobin dissociation curve • Oxygen must be transported via that Mrs. Glenn’s pulse oximetry (OHDC). the blood to the tissues. values are always low, close to her 2. Describe the shifts that can occur Only 2% to 3% of the oxygen baseline of 92%. in the OHDC. going to the tissues dissolves in The nurse wonders how to inter - 3. Discuss the relationship between plasma; the remainder travels in pret the patient’s pulse oximetry the OHDC and pulse oximetry. the plasma by attaching to hemo - values in this context. She vaguely globin molecules. The most impor - The author and planners of this CNE activity have remembers something about the disclosed no relevant financial relationships with tant factor in the amount of oxygen oxyhemoglobin dissociation curve any commercial companies pertaining to this that binds (attaches) to hemoglobin activity. See the last page of the article to learn and wonders if a better under - how to earn CNE credit. molecules is the partial pressure of standing of the curve would aid arterial oxygen (Pa O ); the higher Expiration: 1/1/18 2 her assessment. the pressure, the more readily oxy -

American Nurse Today Volume 10, Number 1 www.AmericanNurseToday.com 18 The curve: Relating Sa O2 to Pa O2 The oxyhemoglobin dissociation curve graphically represents the affinity between oxy - but with little effect on Sa O . gen and hemoglobin—specifically, how the oxygen saturation of hemoglobin (Sa O ) 2 2 Hemo globin can’t be saturated relates to the partial pressure of arterial oxygen (Pa O2). The curve’s position and overall shape (shown in purple below) depend on various factors, including the partial pres - more than 100%, but Pa O2 can rise sure of carbon dioxide (Pa CO 2), body , and blood pH. significantly above 100 mm Hg if the patient receives high oxygen 100 - concentrations (as occurs with a hyperbaric oxygen chamber). 90 - At the steep lower part of the 80 - curve (under the “knee”), where Pa O measures between 40 and 60 70 - 2 mm Hg, oxygen is released from 60 - hemoglobin to the at the

2 tissue level due to increased oxy - O 50 - a

S gen demand. At this part of the 40 - curve, an increase or decrease in Pa O leads to a large Sa O change. 30 - 2 2 This means giving supplemental 20 - oxygen will significantly increase the patient’s Sa O . 10 - 2

0 |||. || || || ||| || | A shift to the left or right 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Now comes the more complicated

Pa O2 part. The OHDC isn’t static or con - stant, because certain factors can alter hemoglobin’s affinity for oxy - gen combines with hemoglobin in about 97% but may range from gen. Depending on oxygen de - red blood cells. This hemoglobin- 93% to 97%. (See The curve: Relat - mand at the tissue level, oxygen oxygen linkage is called oxyhemo - ing Sa O2 to Pa O2.) will bind to hemoglobin more or globin. The OHDC isn’t a straight line. less readily than normal. Various Hemoglobin is made up of four Instead, it’s S-shaped. The flat up - factors cause the curve to shift to strands of amino acids. If oxygen is per portion where the curve is the left or right of its normal posi - linked fully to all four strands, he - more horizontal depicts oxygen tion. (See Why the curve shifts and moglobin is 100% saturated with loading onto hemoglobin in the How 2,3-DPG affects the curve .) oxygen. Transport of sufficient oxy - lungs. The pressure of oxygen en - gen to the tissues depends on an tering the lungs exceeds the oxy - Connecting the curve with pulse adequate number of hemoglobin gen concentration in blood oximetry readings molecules, as well as sufficient returning to the lungs. Pa O2 and Sa O2 values can blood volume and circulation (car - This enables oxygen be obtained only from diac output and ). to bind more easily an arterial blood gas Once hemoglobin transports oxy - to hemoglobin. (ABG) sample. But al - gen to the tissues, the body’s envi - A significant though ABG studies ronment determines how much (or Pa O2 change in are the gold standard how little) of the oxygen dissoci - this relatively flat for obtaining Pa O2 ates (unloads) from hemoglobin for part of the curve and Sa O2 values, fre - use. Oxygen dissociation from he - produces only a quent ABG sampling moglobin is determined by tissue small change in Sa O2. isn’t always feasible or demand for oxygen. That’s where Thus, a patient’s oxy - cost effective. For ongoing the OHDC comes in. genation status is better monitoring, pulse oximetry protected at this flat portion. For provides a convenient, continuous,

example, if Pa O2 drops from 96 to and noninvasive way to measure Relationship between Pa O2 70 mm Hg, hemoglobin saturation Sa O indirectly and monitor trends and Sa O 2 The OH2DC represents the relation - decreases from 97% to approxi - in the patient’s oxygenation status. ship between Pa O2 and Sa O2. Nor - mately 92%. Clinically, this means Be sure to check for subtle or mal Pa O2 ranges from 80 to 100 that if the patient receives supple - sudden changes in oximetry values. mm Hg. Normal Sa O2 measures mental oxygen, Pa O2 will increase— Changes in oxygenation status can www.AmericanNurseToday.com January 2015 American Nurse Today 19 Why the curve shifts The normal oxyhemoglobin dissociation curve (OHDC), shown here by the solid blue precede clinical signs and symp - line, indicates that when the partial pressure of arterial oxygen (Pa O ) is 40 mm Hg, oxy - toms. By detecting these changes 2 gen saturation of hemoglobin (Sa O2) is 75%. At the tissue or level, a Pa O2 of 40 early, clinicians can make timely mm Hg is normal. At this point, about 25% of the oxygen carried on hemoglobin from modifications to the plan of care. the tissues to the lungs has been unloaded and used at the tissue level. Much of the Generally speaking, a pulse oxygen still remains on the hemoglobin molecule, indicating an oxygen reserve isn’t oximetry value of 95% or higher is normally used at the tissue level. However, this reserve is available when extra oxygen clinically acceptable, whereas a val - is needed, as during strenuous exercise or high metabolic demand. ue of 90% or lower is a red flag. Conditions that alter hemoglobin’s affinity for oxygen can shift the OHDC to the On the OHDC, a Sa O value of right or left. 2 • A shift to the right (dotted purple line) decreases hemoglobin’s affinity for oxygen for 90% correlates to a Pa O level of 60 2 a given Pa O value, and the Sa O value decreases below normal. Hemoglobin releas - mm Hg. Pa O pushes or loads the 2 2 2 es oxygen to the tissues more readily in an effort to keep tissues well-oxygenated oxygen onto hemoglobin. So if this (because oxygen demand is higher than normal). Causes of a shift to the right in - level isn’t adequate, suspect the pa - clude increased body temperature, acidosis, exercise, and elevated 2,3-diphospho - tient’s overall oxygenation is abnor - glycerate (2,3-DPG) or partial pressure of arterial carbon dioxide ( Pa CO 2) levels. mally low. • A shift to the left (dotted green line) increases hemoglobin’s affinity for oxygen. It can result from increased blood pH, decreased body temperature, or reduced 2,3- DPG or Pa CO levels. In a leftward shift, less oxygen is released to the tissues but What pulse oximetry values can’t 2 more oxygen is bound to hemoglobin in the lungs; the Sa O value is higher than tell you 2 Pulse oximetry can’t tell you the normal for a given Pa O2 value. patient’s hemoglobin level or iden - tify nonfunctional hemoglobin. In 100 - an anemic patient, hemoglobin may be fully saturated and Sp O2 90 - may be normal—yet the patient may be hypoxic due to lack of 80 - pH pH available hemoglobin to carry oxy - n 5 6

o DPG DPG i 70 - gen to the tissues. t 6 5 a Temp Temp Likewise, hemoglobin may be r u 6 5 t

a 60 -

fully saturated but with dysfunction - s

al strands, such as carboxyhemo - % (

n 50 - globin or methemoglobin strands. i b o

Hemoglobin binds much more l

g 40 - readily to carbon monoxide than to o m oxygen. Hemoglobin may be fully e

h 30 - saturated and the pulse oximetry y x value may be 98%, yet hemoglobin O 20 - may be saturated with carbon monoxide instead of oxygen. Car - 10 - boxyhemoglobin levels are elevated in heavy smokers. Methemoglo - 0 |||||||. |||| binemia may occur in patients re - 0 10 20 30 40 50 60 70 80 90 100 ceiving nitrate or lidocaine therapy. PO2 (mmHg) Pulse oximetry also reveals nothing about the patient’s partial pressure of arterial carbon dioxide

(Pa CO 2) or ventilation status. Say, line ABG values and recheck them ish, improperly placed sensors, for example, a patient’s receiving a periodically. and patient movement can cause high percentage of supplemental inaccurate readings. Clinicians oxygen by face mask for several should try to control these vari - Factors that can reduce pulse hours after surgery. If the patient is ables to the extent possible. oximetry accuracy too sedated to breathe effectively, Certain technical and patient vari - • Patient variables: Pulse oximetry

Pa CO 2 may rise to a dangerous lev - ables can reduce the accuracy of is less accurate when Sp O2 val - el even though Sa O2 may be near pulse oximetry. ues are below 70%, limiting its normal from the supplemental • Technical variables: Motion arti - effectiveness in severely hypoxic oxygen. So be sure to obtain base - fact, ambient light, dark nail pol - patients. Values also may vary in

American Nurse Today Volume 10, Number 1 www.AmericanNurseToday.com 20 patients with poor (as piratory status, from arrhythmias, hypotension, especially if the or heart failure) or vasoconstric - patient’s receiv - tive conditions (such as sickle ing supplemental cell anemia, hypothermia, smok - oxygen. Is the pa - ing, or certain medications). To tient ade - determine if low perfusion is in - quately? Because of compensa -

terfering with oximetry readings, tory mechanisms, good Sp O2 compare the pulse rate dis - How 2,3-DPG affects values may give false reassur - played on the oximeter to a ance despite deterioration in the good electrocardiographic wave - the curve patient’ respiratory status. For form that correlates to a palpat - A phosphate found in the blood, 2,3- example, patients in near respi - ed pulse. diphosphoglycerate (2,3-DPG) forms ratory failure may be hyperventi - when red blood cells break down lating, resulting in respiratory al - glucose to make adenosine triphos - kalosis. This causes the OHDC Pulse oximetry values in the context phate. It decreases hemoglobin’s to shift to the left, with more he - of the curve Understanding how to use pulse affinity for oxygen, promoting oxy - moglobin hanging on to oxygen oximetry in the context of your pa - gen release in the tissues. instead of releasing it at the tis - tient’s OHDC can improve out - Some hormones, such as thyrox - sue level where it’s needed. ine, human growth hormone, epi - comes. Used correctly, pulse ox- • Patients with similar Sp O values nephrine, and testosterone, increase 2 imetry gives an overall indication 2,3-DPG production and cause the don’t necessarily have the same of a patient’s oxygenation status oxyhemoglobin dissociation curve total oxygen content in their and promotes early intervention for (OHDC) to shift to the right. Also, 2,3- blood. Suppose, for instance, Mr. high-risk patients. It also allows DPG levels are higher in people liv - M and Mr. R both have Sp O2 val - early recognition of conditions that ing in high altitudes. As blood cells ues of 97%, but Mr. M’s hemo - increase tissue demand for oxygen, age, 2,3-DPG levels decrease, causing globin value is 15 g/dL, whereas helping to ensure that the patient’s oxygen to bind tightly to hemoglo - Mr. R’s hemoglobin value is 8 oxygen supply (hemoglobin satura - bin and the OHDC to shift to the left. g/dL. In this case, oxygen-carry - tion) meets demands. ing capacity is greater in Mr M Keep the following key princi - than in Mr. R, who may be ples in mind when caring for pa - Pa O2 value. Is this spot at the showing signs of . tients like Mrs. Glenn—those with flat part or the steep part of the • Interpret values in light of the underlying lung disease who’ve curve? patient’s overall condition. Pa - suffered an acute respiratory insult • When the pulse oximeter’s low tients with chronic disease, such that puts them at risk for impaired alarm goes off, don’t assume as chronic obstructive pulmo - . you need to start giving oxygen nary disease (COPD), may func - • After assessing the patient’s res - or increase the oxygen flow. As - tion adequately despite lower

piratory status and determining sess the patient, not the ma - Sp O2 values. Be sure to check that the pulse oximeter is func - chine: Is the patient in respirato - the patient’s baseline ABG and tioning properly, visualize the ry distress? Check the oxygen pulse oximetry values, watching spot on the OHDC where the supply: Is the oxygen tubing for trends. Also remember that

Sp O2 value kinked? Is the oximeter applied Pa O2 values normally decrease would line properly? Does the patient have with age. Elderly patients typi - up with a disease or condition that in - cally try to compensate for a

the creases oxygen demand, such as low Pa O2 value with a right - fever, acidosis, or infection? If ward shift of the curve. But

so, decreasing Sp O2 values may this shift doesn’t completely indicate the need to contact the compensate for the hypoxic physician for further orders, in changes and hypercapnia that addition to increasing the oxy - come with aging. As a result, gen flow. many older adults have de - • If the pulse oximetry value is creased activity tolerance. within a normal range, don’t as - • Collaborate with other profes - sume the patient is adequately sionals involved in the patient’s oxygenated. Instead, assess res - care. Review the physician’s or -

www.AmericanNurseToday.com January 2015 American Nurse Today 21 The OHDC isn’t static or ders to determine the type of tion. Correlat -

monitoring needed and specific constant, because certain ing Sp O2 with protocols to follow. Consult with Pa O2 values the respiratory therapist about provides valu - proper pulse oximetry alarm set - factors can alter able clues tings and correct use of the de - about the bal - vice. Make sure you’re familiar hemoglobin’s affinity ance between with evidence-based practice oxygen supply guidelines for using pulse and demand. When oximetry, such as those from the for oxygen. combined with astute assessment, American Association of Critical- understanding this relationship Care Nurses and the American Depending on oxygen can lead to earlier detection of Association for Respiratory Care. oxygenation problems and allow at the tissue prompt intervention. Ignoring or Clinical scenario revisited demand misinterpreting the relationship Mrs. Glenn’s pulse oximetry values between Sp O2 and Pa O2 can lead continue to remain low, in the up - level, oxygen will bind to to disastrous consequences for per 80% range. Her vital signs are vulnerable patients, such as Mrs. unchanged. The physician calls Glenn . O with orders to obtain a urine cul - hemoglobin ture and start another I.V. antibi - Selected references otic. The nurse clamps the catheter more or less readily Casey G. Pulse oximetry—what are we real - to obtain the culture, but when she ly measuring? Nurs N Z . 2011;17(3):24-9. returns to collect the culture, she Elliott M, Coventry A. Critical care: the eight sees that only scant urine has been than normal. vital signs of patient monitoring. Br J Nurs . 2012;21(10):621-5. collected. Mrs. Glenn remains alert but Korkushko OV, Ivanov LA, Pisaruk AV, Chebotarev ND. The respiratory function of seems a bit restless. The nurse helps of quickly developing hypoxia. Al - blood in elderly and old age and the factors her to the chair to eat dinner. though Mrs. Glenn was a COPD that determine it. (Translated.) Human Phys - Twenty minutes later, she walks by patient and thus her pulse oxime - iol . 2009;35(2):40-6. and sees Mrs. Glenn slumped over try values were lower than normal, McCance KL, Huether SE. : in her chair and unresponsive. She the nurse didn’t carefully review The Biologic Basis for Disease in Adults and calls for help to get her back to bed. her ABG values and previous pulse Children . 7th ed. St. Louis: Mosby; 2014. Although the nurse oximetry values. If she had re - Morton PG, Fontaine DK. Critical Care attempts oral viewed these in light of the OHDC, Nursing: A Holistic Approach . 10th ed. Philadelphia: Lippincott Williams & Wilkins; suctioning, the she might have realized the Sp O 2 2012. patient re - decrease from 91% to 88% placed Pruitt B. Interpreting ABGs: an inside look mains unre - Mrs. Glenn at the steep part of the at your patient’s status. Nursing . sponsive. curve. Her estimated Pa O2 would 2010;40(7):31-36. Because have been lower than 60 mm Hg. Tortora GJ, Derrickson, BH. Principles of Mrs. Glenn As her Pa O2 continued to drop, her Anatomy and Physiology . 12th ed. Danvers, has “do not re - Sp O2 value would have fallen rap - MA: Wiley; 2012. suscitate” orders, idly. Getting her up to eat in - Valdez-Lowe C, Ghareeb SA, Artinian NT. no further interven - creased her oxygen demands and Pulse oximetry in adults. Am J Nurs . 2009;109(6):52-60. tions are taken. The nurse contributed to further Sp O2 lower - calls the patient’s husband. When ing. Her increased pulse and res - Wagner KD, Hardin-Pierce MG. High-Acuity he arrives 30 minutes later, he tells piratory rates and decreased blood Nursing . 6th ed. Boston: Prentice-Hall; 2013. the nurse, “I know you gave her pressure and urinary output also World Health Organization. Pulse Oximetry good care and probably didn’t indicated worsening hypoxia. Training Manual . 2011. www.who.int/pa - know she was going to die, but I tientsafety/safesurgery/pulse_oximetry/who_ ps_pulse_oxymetry_training_manual_en.pdf. would have liked to have been here Pulse oximetry is used in a wide Accessed October 30, 2014. when it happened.” range of care settings to assess Later, the nurse reflects on her oxygenation status. But it must be Julia Hooley is the director of the Center for Study experience with Mrs. Glenn. She re - correlated with the OHDC to get a and Testing at Malone University School of Nursing alizes she missed or ignored clues full picture of the patient’s condi - and Health Sciences in Canton, Ohio.

American Nurse Today Volume 10, Number 1 www.AmericanNurseToday.com 22 CNE Decoding the oxyhemoglobin dissociation curve POST-TEST • CNE: 1.42 contact hours Earn contact hour credit online at www.AmericanNurseToday.com/ContinuingEducation.aspx

Instructions accredited provider status refers only to CNE activities and does not im - To take the post-test for this article and earn contact hour credit, please ply that there is real or implied endorsement of any product, service, or go to the blue link above. Simply use your Visa or MasterCard to pay company referred to in this activity nor of any company subsidizing the processing fee. (ANA members $15; nonmembers $20.) Once costs related to the activity. The planners and author of this CNE activity you’ve successfully passed the post-test and completed the evalua - have disclosed no relevant financial relationships with any commercial tion form, you’ll be able to print out your certificate immediately . companies pertaining to this CNE. Provider accreditation The American Nurses Association’s Center for Continuing Education PURPOSE /GOAL and Professional Development is accredited as a provider of continuing To provide nurses with information on how to use the nursing education by the American Nurses Credentialing Center’s oxyhemoglobin dissociation curve to better assess a patient’s Commission on Accreditation. ANCC Provider Number 0023. oxygenation status. Contact hours: 1.42 LEARNING OBJECTIVES ANA’s Center for Continuing Education and Professional Development 1. Recall the physiologic basis for the oxyhemoglobin dissociation is approved by the California Board of Registered Nursing, Provider curve (OHDC). Number CEP6178 for 1.69 contact hours. 2. Describe the shifts that can occur in the OHDC. 3. Discuss the relationship between the OHDC and pulse Post-test passing score is 75%. Expiration: 1/1/18 oximetry. ANA Center for Continuing Education and Professional Development’s

Please mark the correct answer b. At the very start and very end of the curve, 10. Which statement about pulse oximetry is online. giving supplemental oxygen will significantly correct? increase the patient’s Sa O2. a. An Sa O2 level of 70% signifies a Pa O2 level of 1. What percentage of the oxygen going to c. At the steep lower part of the curve (under 60 mm Hg. the tissues dissolves in plasma? the “knee”), giving supplemental oxygen will b. An acceptable pulse oximetry level is 85%. a. 2% to 3% have little effect on the patient’s Sa O2. c. Pulse oximetry is useful for determining a b. 15% to 18% d. At the steep lower part of the curve (under patient’s ventilation status. c. 20% to 21% the “knee”), giving supplemental oxygen will d. Pulse oximetry reveals nothing about the d. 30% to 32% significantly increase the patient’s Sa O2. patient’s Pa CO 2. 2. Which statement about hemoglobin is 6. Which of the following can cause the OHDC 11. Which statement about hemoglobin correct? to shift to the right? saturation is correct? a. Hemoglobin is made up of four strands of a. Alkalosis a. A pulse oximetry (Sp O2) value of 100% carbohydrates. b. Increased body temperature indicates hemoglobin is fully saturated with b. Hemoglobin is made up of four strands of c. Decreased 2,3-diphosphoglycerate (2,3- oxygen. amino acids. DPG) b. An Sp O2 value of 98% indicates hemoglobin c. If oxygen is linked fully to two strands, d. Decreased partial pressure of arterial carbon is fully saturated with oxygen. hemoglobin is considered to be 100% dioxide (Pa CO 2) c. Hemoglobin may be fully saturated with saturated with oxygen. 7. Which of the following can cause the OHDC dysfunctional strands. d. If oxygen is linked fully to two strands, to shift to the left? d. Hemoglobin binds more readily to oxygen hemoglobin is considered to be 10% a. Increased 2,3-DPG than to carbon monoxide. saturated with oxygen. b. Acidosis 12. Which of the following reduces the accuracy 3. The flat upper portion of the S-shaped c. Hypothermia of pulse oximetry readings? OHDC represents: d. Hypercarbia a. Smoking a. oxygen loading onto hemoglobin in the 8. Which statement about shifts in the OHDC b. Hyperthermia lungs. is correct? c. Hypertension b. oxygen exiting hemoglobin in the lungs. a. With a shift to the right, hemoglobin d. Sp O2 value of 85% c. oxygen released from hemoglobin to releases oxygen to the tissues more readily. 13. What key principle should you keep in mind capillaries at the tissue level. b. With a shift to the right, hemoglobin is less when caring for patients being monitored by d. oxygen loading onto hemoglobin from likely to release oxygen to the tissues. pulse oximetry? capillaries at the tissue level. c. With a shift to the left, hemoglobin’s affinity a. Patients with chronic obstructive pulmonary 4. The steep lower part of the OHDC (under for oxygen is decreased. disease need higher Sp O2 values to function the “knee”) represents: d. With a shift to the left, hemoglobin is more well. a. oxygen loading onto hemoglobin in the likely to release oxygen to the tissues. b. Patients with similar Sp O2 values have the lungs. 9. Which statement about 2,3 DPG is accurate? same amount of total oxygen content in b. oxygen exiting hemoglobin in the lungs. a. It decreases in the presence of epinephrine. their blood. c. oxygen released from hemoglobin to b. It increases as a person ages. c. When the pulse oximeter’s low alarm goes capillaries at the tissue level. c. It forms when red blood cells synthesize off, don’t assume you need to start giving d. oxygen loading onto hemoglobin from glucose to make adenosine triphosphate. oxygen or increase the oxygen flow. capillaries at the tissue level. d. It forms when red blood cells break down d. If the Sp O2 value is within a normal range, 5. Which statement about the OHDC and glucose to make adenosine triphosphate. you know the patient is adequately oxygenation is correct? oxygenated. a. At the flat upper portion where the curve is more horizontal, giving supplemental oxygen will significantly increase the patient’s oxygen saturation of hemoglobin (Sa O2). www.AmericanNurseToday.com January 2015 American Nurse Today 23