pulse oximetry in pediatric practice sotirios fouzas, kostas n. … · 2014. 10. 20. · review...

DOI: 10.1542/peds.2011-0271; originally published online September 19, 2011; 2011;128;740Pediatrics

Sotirios Fouzas, Kostas N. Priftis and Michael B. AnthracopoulosPulse Oximetry in Pediatric Practice

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of Pediatrics. All rights reserved. Print ISSN: 0031-4005. Online ISSN: 1098-4275.Boulevard, Elk Grove Village, Illinois, 60007. Copyright © 2011 by the American Academy published, and trademarked by the American Academy of Pediatrics, 141 Northwest Pointpublication, it has been published continuously since 1948. PEDIATRICS is owned, PEDIATRICS is the official journal of the American Academy of Pediatrics. A monthly

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Pulse Oximetry in Pediatric Practice

abstractThe introduction of pulse oximetry in clinical practice has allowed forsimple, noninvasive, and reasonably accurate estimation of arterialoxygen saturation. Pulse oximetry is routinely used in the emergencydepartment, the pediatric ward, and in pediatric intensive and periop-erative care. However, clinically relevant principles and inherent limi-tations of the method are not always well understood by health careprofessionals caring for children. The calculation of the percentage ofarterial oxyhemoglobin is based on the distinct characteristics of lightabsorption in the red and infrared spectra by oxygenated versus deox-ygenated hemoglobin and takes advantage of the variation in lightabsorption caused by the pulsatility of arterial blood. Computation ofoxygen saturation is achieved with the use of calibration algorithms.Safe use of pulse oximetry requires knowledge of its limitations , whichinclude motion artifacts, poor perfusion at the site of measurement,irregular rhythms, ambient light or electromagnetic interference, skinpigmentation, nail polish, calibration assumptions, probe positioning,time lag in detecting hypoxic events, venous pulsation, intravenousdyes, and presence of abnormal hemoglobin molecules. In this reviewwe describe the physiologic principles and limitations of pulse oxime-try, discuss normal values, and highlight its importance in commonpediatric diseases, in which the principle mechanism of hypoxemia isventilation/perfusion mismatch (eg, asthma exacerbation, acute bron-chiolitis, pneumonia) versus hypoventilation (eg, laryngotracheitis, vo-cal cord dysfunction, foreign-body aspiration in the larynx or trachea).Additional technologic advancements in pulse oximetry and its incor-poration into evidence-based clinical algorithms will improve the effi-ciency of the method in daily pediatric practice. Pediatrics 2011;128:740–752

AUTHORS: Sotirios Fouzas, MD,a Kostas N. Priftis, MD,b

and Michael B. Anthracopoulos, MDa

aRespiratory Unit, Department of Pediatrics, University Hospitalof Patras, Patras, Greece; and bThird Department of Pediatrics,“Attikon” Hospital, University of Athens School of Medicine,Athens, Greece

KEY WORDSpulse oximetry, children, hemoglobin oxygen saturation

ABBREVIATIONSSaO2—arterial blood oxygen saturationSPO2—arterial hemoglobin oxygen saturation by pulse oximetryODC—oxyhemoglobin dissociation curveCOHb—carboxyhemoglobin

www.pediatrics.org/cgi/doi/10.1542/peds.2011-0271

doi:10.1542/peds.2011-0271

Accepted for publication Jun 1, 2011

Address correspondence to Sotirios Fouzas, MD, RespiratoryUnit, Department of Pediatrics, University Hospital of Patras, Rio,265 04 Patras, Greece. E-mail: [email protected]

PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275).

Copyright © 2011 by the American Academy of Pediatrics

FINANCIAL DISCLOSURE: The authors have indicated they haveno financial relationships relevant to this article to disclose.

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The clinical assessment of hypoxemiais notoriously unreliable because itdepends on many factors, includingambient lighting, skin pigmentation,tissue perfusion, and hemoglobin con-centration.1 Even under optimal condi-tions, arterial blood oxygen saturation(SaO2) of �75% is required beforecentral cyanosis becomes clinicallydetectable.1,2

The introduction of pulse oximetry inclinical practice has led to a revolu-tionary advancement in patient as-sessment and monitoring, because itallows for a simple, noninvasive, andreasonably accurate estimation ofarterial oxygen saturation. Pulse oxi-meters have become available forwidespread application in pediatriccare, and oxygen saturation has evenbeen proposed as the “fifth vitalsign.”3,4 However, clinically relevantprinciples and inherent limitationsof pulse oximetry are not alwayswell understood by health careprofessionals.5,6

In this review we describe the physio-logic principles, limitations, and com-mon applications of pulse oximetry indaily pediatric practice.

HISTORY OF PULSE OXIMETRY

The theoretical background for nonin-vasive assessment of blood oxygen-ation was set in the early 1900s when itwas observed that spectral changes oflight absorbance in vivo are related totissue perfusion.7 Great advancementsin the development of related instru-ments occurred during World War II inan effort tomonitor oxygenation ofmil-itary pilots.7 In 1940, Squire8 reportedon a “blood-oxygen-meter” for use onthe hand, and in 1942, Millikan9 coinedthe word “oximeter” for a portable eardevice that read energy absorption inthe red and infrared light spectra. Im-portant subsequent work was pre-sented by Wood,10 who managed tomeasure oxygen saturation by sus-

pending tissue perfusion. However, allthese “early” oximeters relied eitheron compression and reperfusion of themeasuring site or on the “arterializa-tion” of capillary blood through heat-ing; consequently, they were inconve-niently large, difficult to use, and, mostimportantly, inaccurate.7,11

A true revolution in the development ofnoninvasive oximetry occurred afterthe work of the Japanese electrical en-gineer Aoyagi.12 In an experimentaimed to develop a dye-dilution tech-nique to measure cardiac output, herealized that the untoward changes intissue light absorption caused by thepulsatile nature of the arterial bloodflow could be used to compute oxygensaturation. Thus, the “noise” in his ex-periment became the “signal” for a dif-ferent application, which led to the de-velopment of the first “pulse” oximeterin late 1974.11,12 In the next 2 decades,after the explosive development oftechnologies in light emission andsignal processing, pulse oximetersunderwent astonishing improve-ments and became available forwidespread application throughoutmedical practice.11,13

PRINCIPLES OF OPERATION

The estimation of arterial hemoglobinoxygen saturation by pulse oximetry(SPO2) is based on the specific charac-teristics of oxygenated and deoxygen-ated hemoglobin (oxyhemoglobin anddeoxyhemoglobin, respectively) withregard to light absorption in the redand infrared spectra. Deoxyhemoglo-bin is characterized by greater red-light absorption (wavelength range:600–750 nm) in comparison to oxyhe-moglobin, whereas oxyhemoglobin ex-hibits higher absorption in the infra-red spectrum (850–1000 nm)14,15 (Fig1). By obtaining the ratio of light ab-sorption in the red and infrared spec-tra and then calculating the ratio ofthese 2 ratios (ratio of absorption ra-tios), the percentage of oxyhemoglobincan be calculated.12,15

Light absorption in vivo depends on thecharacteristics of the tissues acrossthe site of measurement.16,17 Duringshort time periods, the absorptionby skin, subcutaneous fat, muscles,bones, and capillary and venous bloodremains practically constant (constantabsorbers). Therefore, any change inlight absorption should be attributed to

FIGURE 1Reference spectra depicting the absorption coefficients of oxygenated hemoglobin (OxyHb), deoxy-genated hemoglobin (DeoxyHb), methemoglobin (MetHb), and COHb as a function of wavelength. Thevertical lines indicate the wavelengths (red and infrared) commonly used in pulse oximetry.

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the variations of the arterial blood vol-ume related to the cardiac cycle12,17–19

(Fig 2; Supplemental Movie 1).

Currently available pulse oximetersare equipped with 2 light-emitting di-odes (LEDs), 1 emitting at the red spec-trum and the other at the infraredspectrum, most commonly at wave-lengths of 660 and 940 nm, respec-tively. Emission of these 2 wavelengthsalternates at frequencies of 0.6 to 1.0kHz,15,20,21 and the nonabsorbed energyis detected by a semiconductor. A mi-croprocessor subtracts the absorp-tion by constant absorbers, thus ren-dering the final signal, which isdisplayed electronically as a plethys-mographic wave form. The SPO2 is cal-culated from the conversion of the ra-tio of absorption ratios by usingdedicated calibration algorithms storedin the microprocessor of the device.These algorithms are derived throughSaO2 measurements in healthy volun-teers breathing mixtures of decreasedoxygen concentrations and are usuallyunique for each manufacturer.15,17–21

The displayed SPO2 represents themean of the measurements obtainedduring the previous 3 to 6 seconds,whereas the data are updated every0.5 to 1.0 second.15,18–20 The perfor-mance of each device is strictly relatedto the reliability and complexity of thealgorithms used in signal processing

and to the speed and quality of the mi-croprocessor. There are numerousstudies of the accuracy and precisionof pulse oximeters in various adult22–24

and pediatric25–27 populations. Mostmanufacturers claim mean differ-ences (bias) of �2% with SDs (preci-sion) of �4%.15,18–20,28 It should benoted, however, that these resultshave been reported in subjects withSaO2 levels that exceed 80%15,18–20,28; theperformance of pulse oximeters dete-riorates remarkably when SaO2 de-creases to�80%.17,24,29

The probe of the device must be posi-tioned in suchmanner that the emitter

and the detector are exactly oppositeto each other with 5 to 10 mm of tissuebetween them.15,30 Typical measuringsites include the finger, the toe, thepinna, and the lobe of the ear, whereasfor neonates and infants measure-ments are commonly obtained fromthe palm or the sole by using speciallydesigned probes.28,30–32 Less commonlyused sites are the cheek and thetongue.30

MISCONCEPTIONS

Safe use of pulse oximetry requirescomprehension of the information thatthe method offers.33 SPO2 is, in fact, anestimate of SaO2 as derived by arterialblood gas analysis, which in turn doesnot accurately reflect partial oxygentension of the arterial blood (PaO2). In-deed, although SaO2 and PaO2 are re-lated through the oxyhemoglobin dis-sociation curve (ODC), their relation isnot linear. Moreover, a series of fac-tors can further influence the shape ofthe ODC (Fig 3). Hence, SPO2 (as well asSaO2) does not necessarily provide re-liable information regarding the oxy-genation status of tissues.30,34,35

SPO2 represents an estimate of func-tional arterial hemoglobin saturation,

FIGURE 2Principle of operation of pulse oximetry. Shown is a schematic representation of the layers of humantissues that absorb light energy at the measuring site (left) and the components of light absorption(constant—DC and variable—AC) by distinct tissue characteristics (right). A simplified version of theratio of absorption ratios equation used to calculate SPO2 is shown also.

FIGURE 3ODC (continuous line) and factors that influence its shape. The ODC is shifted to the right (lower dottedline) by increased hydrogen ion (H�) concentration (acidosis), increased 2,3-diphosphoglycerate(DPG), increased temperature (To), increased partial pressure of carbon dioxide (PCO2), and thepresence of hemoglobin S (HbS) (sickle cell disease). Decreased H� (alkalosis), DPG, To, and PCO2 andthe presence of fetal hemoglobin (HbF) shift the curve to the left (upper dotted line).


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which refers only to the arterial hemo-globin that is capable of transportingoxygen (functional hemoglobin � oxy-hemoglobin/[oxyhemoglobin� deoxy-hemoglobin]). Functional saturationdiffers from fractional hemoglobin sat-uration (Fractional hemoglobin � oxy-hemoglobin/total hemoglobin), whichcan be measured by most blood gas an-alyzerswith co-oximetry. The total hemo-globin denominator in the calculation offractional hemoglobin might include ab-normal or variant hemoglobin mole-cules with limited oxygen-carrying prop-erties.30,35,36 Therefore, the terms“functional” and “fractional” hemoglobinsaturation are not interchangeable.36 Insituations suchasdyshemoglobinemias,pulse-oximetry readings do not ade-quately reflect the oxygen-carrying prop-erties of arterial blood.15,28,35,37 It shouldbe noted also that pulse oximetry doesnot provide information regarding venti-lation or acid-base status.30,38–40

LIMITATIONS OF PULSE OXIMETRY

The limitations of pulse oximetry canbe generally classified as safe or po-tentially unsafe (Table 1). Safe limita-tions refer to those circumstances inwhich the inaccuracy in the displayedSPO2 can be suspected, and its cause isrecognizable. In this case the observeris usually warned by the device(alarm) about the pitfall. A potentiallyunsafe limitation is considered to beany situation in which the inaccuracyis difficult to recognize; the displayedSPO2 is erroneous, but the observer isnot warned about the pitfall.

Safe Limitations

Motion Artifacts

Motion artifact represents the mostcommon limitation of pulse oxime-try.13,15,28 Because the normally pulsa-tile (arterial) component of light ab-sorption represents no more than 5%of the total absorbed energy, any mo-tion that alters the remaining fraction

of absorption (especially when due tovenous blood) will affect the signal-to-noise ratio and drive SPO2 to lowerthan true values.41,42 Fortunately, mo-tion artifacts can be recognized bymotion alarms or distorted plethysmo-graphic waveforms. However, rhyth-mic motions or vibrations with a fre-quency similar to heart rate (0.5–3.5Hz) can be particularly troublesome.41

Sophisticated read-through-motionand motion-tolerant technologies con-tinue to evolve and have improved theperformance of the new-generationoximeters.30,43–46

Poor Perfusion

Adequate arterial pulsation at the siteof measurement is essential for distin-guishing true signal from backgroundnoise.41,42 Low-perfusion states, suchas low cardiac output, shock, hypo-thermia, vasoconstriction, arterial oc-clusion, or during blood pressure cuffinflation, might impair the functioningof the device and result in lower SPO2readings or delayed recognition ofacute hypoxemia.13,28,46–50 For infantswith cold extremities, local rubbing orheating before the application of theprobe might temporarily improve perfu-sion; however, for hypothermic patients,monitoring by a forehead probe is analternative option.51 New-generationdevices are equipped with signal-extraction algorithms and can performbetter in low-perfusion states.30,46–49

Skin Pigmentation, Nail Polish, andArtificial Nails

In theory, skin pigmentation presentsa constant level of absorption that issubtracted in the calculation of SPO2and, therefore, should not influencethe performance of the device.12,34

However, dark skin pigmentation hasbeen incriminated for erroneous SPO2readings, especially at SaO2 values of�80%.21,52,53

Although data regarding the impact ofnail polish are conflicting,54–58 polish of

black, blue, or green color and syn-thetic nails might interfere with pulseoximetry and result in an underestima-tion of SaO2.54,55,59 This effect can beavoided by mounting the probe on thefinger sideways.34 New-technologypulse oximeters are less susceptibleto these limitations.21,34,56–58

Bilirubin has no effect on pulse oxime-try, because it presents a differentspectrum of light absorption (at�450nm). Therefore, the method can be usedreliably for monitoring jaundiced pa-tients, including neonates.13,15,20,21,28,30,34

However, patients with severe hemo-lytic jaundice might also have in-creased carboxyhemoglobin (COHb) lev-els, which could potentially lead toerroneous pulse-oximetry readings.15 Inaddition, falsely low SPO2 values havebeen reported in bronze babysyndrome.60

Irregular Rhythms

Inaccurate oximetry readings can be ob-served with irregular heart rhythms, es-pecially during tachyarrhythmias.21

These artifacts can usually be recog-nized by observing the plethysmo-graphic wave form. Currently availabledevices possess signal-extraction tech-nologies that are capable of recognizingsuch events.20,21,34

Electromagnetic Interference

Electromagnetic energy from electro-surgical cauterization units and cellu-lar phones might interfere with pulseoximeters and lead to erroneous SPO2readings.61 Special devices with fiber-optic technology should be used dur-ing MRI to avoid both interference withimage quality and potentially danger-ous heating of the sensor with conse-quent thermal injury.61,62

Potentially Unsafe Limitations

Calibration Assumptions

As stated already, the displayed SPO2 isthe result of the conversion of the ratio

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TABLE1LimitationsofPulseOximetry

Limitations

Mechanism

Bias

ProposedAction

Safelimitationsa

Motion

Sensormovement

LowerSPO 2readings

Evaluateplethysmographicwaveform

Increasednoisecausedbychangesinnonpulsatile

componentoflightabsorption

Falsealarms

Stabilizesensor

Changesensorposition

Usenew-generationpulseoximeters

Poorperfusion

Decreasedsignalcausedbydecreasedpulsatile(arterial)

componentoflightabsorption

LowerSPO 2readings


Checkandcorrectskintemperatureandperipheralperfusion

Placesensormorecentrally

Usenew-generationpulseoximetersb

Skinpigmentation

Probablycausedbycalibrationassumptionsfordarkskin

pigmentation

LowerorlessreliableSPO 2readingsatlowerSaO 2

values


NailpolishandartificialnailsDecreasedsignalbecauseofdecreasedlightabsorptionwith

artificialnailsornailpolishofblack,blue,orgreencolorLowerSPO 2readings

Changesensorposition

Irregularrhythms

Increasednoisecausedbytachyarrhythmias

LowerorlessreliableSPO 2readings



ElectromagneticinterferenceExternalelectromagneticenergyinterferencecausedby

electrosurgicalcauterizationunits,cellularphones,orMRI

devices

LowerSPO 2readings


Falsealarms

Avoidexternalelectromagneticenergysources

Heatingofthesensorandthermalinjury(MRI)

Usepulseoximeterswithfiber-optictechnology(MRI)

Potentiallyunsafelimitationsa

Calibration

Device-specificcalibrationalgorithmsderivedbycorrelating

lightabsorptionratiosoveraSaO 2spectrumof80%–100%

inhealthyyoungadults

SPO 2readingsof

�80%–85%arelessaccurate

especiallyattheextremesoftheagespectrum


LowerSPO 2valuescalculatedbymathematicalequations

Timelag

Software-relateddelaybetweensuddenchangesinblood

oxygenationandSPO 2readings

Delayindetectingclinicallyimportantdesaturation,

whichmayexceed15–20s


Donotusepulseoximetryasasubstitutefor

cardiorespiratorymonitoringincriticallyillpatients

Probepositioning

Theemittedlightenergyisprojectedtangentiallytothe

detectorbecauseofinappropriatesensorplacement

(“penumbra”or“opticalshunting”effect)

LowerSPO 2readings

Placesensorwiththeemitterandthedetectorexactly

oppositetoeachother

Useprobesofappropriatesizeinneonatesandinfants

Ambientlightinterference

Intenseexternallightenergy(asinphototherapy)may

interferewiththephotodetector(“flooding”effect)

LowerSPO 2readings


Coverthesensor

Abnormalhemoglobin

molecules

COHbpresentsred-lightabsorptionsimilartooxyhemoglobinIncarboxyhemoglobinemiapulseoximetry

overestimatesbloodoxygenation

CheckarterialSaO 2ifabnormalhemoglobinmoleculesare

suspected(ie,carbonmonoxideintoxication)

Methemoglobinabsorbsequalamountofenergyinthered

andinfraredspectra,whichaffectstheratioofabsorptionInsignificantmethemoglobinemia,SP O2tends

toward85%

SuspectabnormalhemoglobinmoleculesiftheSaO 2–SPO2

differenceexceeds5%

Usepulseco-oximetryc

Pulsatileveins

Increasednoisebecauseofpulsationsofvenousblood(ie,

significanttricuspidregurgitation,hyperdynamic

circulationstates)

LowerorlessreliableSPO 2readings


Intravenousdyes

Intravenousdyessuchasmethyleneblue,indocyaninegreen,

andindigocarmineinterferewithlightabsorption

LowerSPO 2readings

Donotusepulseoximetryorinterpretpulse-oximetry

readingswithcaution

CheckSaO 2

aSafelimitationsarecircumstancesinwhichapossibleinaccuracyinthedisplayedSPO 2canbeeasilysuspected;theobserverisusuallywarnedbythedevice(alarm)aboutthepitfall.Potentiallyunsafelimitationsarethosesituationsinwhichthe

inaccuracyisdifficulttorecognize;thedisplayedSPO 2iserroneousbuttheobserverisnotwarnedaboutthepitfall.

bNew-generationpulseoximetersarelesssusceptibletotheselimitationsbecauseofmoresophisticatedcalibrationandsignal-extractionalgorithms.

cPulseco-oximetersarecapableofdetectingabnormalhemoglobinmoleculesbyusingmultiwavelengthtechnology.



of absorption ratios into percent satu-ration by using specific calibration al-gorithms. These algorithms are de-rived by correlating the ratio of theabsorption ratios with arterial gasSaO2 measurements in healthy youngvolunteers over a range of desatura-tion values. Because it is unethical todesaturate volunteers below SaO2 lev-els of�80%, lower SPO2 values are de-rived by extrapolation and, therefore,are less accurate.15,17,24,29,34 Moreover,because the subjects recruited for cal-ibration purposes are healthy youngadults, the applicability of calibrationdata to patients at the age extremeshas been questioned.13,15,25,30,34

Time Lag in the Detection of HypoxicEvents

Most conventional pulse oximeterspresent a clinically significant delaybetween a sudden change in blood ox-ygenation and the related change inthe displayed SPO2 values. This time lagdepends on the complexity of the algo-rithms used and might exceed 15 to20 seconds.34,63–65 Although new-generation devices have improved re-sponse times, and desaturation eventscan be detected earlier if the probe isplaced more centrally (eg, at the earlobe),13,21,63 pulse oximetry should notbe used as a substitute for cardiore-spiratory monitoring in critically illpatients.30,34

Probe Positioning

Lower SPO2 readingsmight occurwhenthe probe is inappropriately placed,especially on the small fingers of neo-nates and infants.13,28 In this case, theemitted light can be projected tangen-tially to the detector, sometimes with-out crossing an arterial bed, phenom-ena which have been described as the“penumbra” and “optical shunting” ef-fects, respectively.66,67 This pitfall canbe avoided by positioning the emitterand the detector exactly opposite toeach other and by using probes of ap-

propriate size for neonates andinfants.13,28,34

Ambient Light Interference

Intense white or infrared light mightinterfere with pulse oximetry and leadto falsely low SPO2 readings. This phe-nomenon, known as the “flooding” ef-fect, is caused by the excessive in-crease of the light energy that literallyfloods the photodetector and drivesthe ratio of absorption ratios towardthe unit; this corresponds to an SPO2of 85%.16 Although new-generationdevices can detect light interfer-ence,16,21,34,68 health care professionals,particularly those who handle neo-nates exposed to phototherapy, mustbe aware of this potential limitation.Ambient light interference can beavoided by simply covering the sensorwith nontransparent material.

Abnormal Hemoglobin Molecules

Abnormal or variant hemoglobin mole-cules might interfere with pulse oxim-etry and lead to inaccurate resultsthat might influence clinical decision-making.69 Carboxyhemoglobinemiarepresents the most dangerous limita-tion of pulse oximetry, because in thepresence of COHb the method overes-timates arterial oxygenation. Thiseffect is caused by the specific charac-teristics of COHb, which exhibits red-light absorption similar to that of oxy-hemoglobin14 (Fig 1). Therefore,increased COHb levels affect the ratioof absorption ratios and cause thepulse oximeter to overread by�1% forevery 1% increase of circulatingCOHb.70,71 Therefore, SPO2 valuesshould be verified by SaO2 measure-ments using a co-oximetry methodwhen the presence of COHb is sus-pected (eg, carbon monoxideintoxication).21,69,72,73

Methemoglobinemia also representsan important but less dangerous limi-tation of pulse oximetry.69 Methemo-globin (MetHb) absorbs approximately

equal amounts of energy in the red andinfrared spectrums14 (Fig 1). In signifi-cant methemoglobinemia (MetHb �30%), the ratio of absorption ratioswilltend toward the unit (SPO2 � 85%),thus underestimating high saturationvalues and overestimating severe hy-poxemia.71,73,74 If the difference be-tween SaO2 and SPO2 (the “SaO2–SPO2gap”) exceeds 5%, the presence of ab-normal hemoglobin molecules shouldbe investigated by co-oximetry.72,73

Pulse co-oximeters, by taking advan-tage of novel multiwavelength technol-ogies, have been shown to accuratelymeasure both COHb and MetHb.71,75–78

Fetal hemoglobin and hemoglobin Spresent light-absorption characteris-tics similar to those of adult hemoglo-bin and do not interfere with pulseoximetry.14,79–81 However, physiciansshould remember that abnormal he-moglobin molecules affect ODC (Fig 3);thus, the displayed SPO2 value mightnot reliably reflect tissue oxygenation,particularly for children with sicklecell disease.30,82

Anemia does not seem to affect the ac-curacy of pulse oximetry, at least forhemoglobin levels of �5 g/dL andif cardiovascular function is pre-served.34,80,83,84 Similarly, polycythemiadoes not seem to interfere with pulseoximetry.80

Venous Pulsation

In case of significant tricuspid regurgi-tation and in hyperdynamic circulationstates, the pulsatile variation of ve-nous bloodmight affect signal-to-noiseratio and result in erroneous SPO2readings.85,86

Intravenous Dyes

Intravenous dyes such as methyleneblue (actually used as a first-line treat-ment for severe methemoglobinemia),indocyanine green, and indigo carminemight cause lower SPO2 readings.15,34,87,88

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APPLICATIONS OF PULSE OXIMETRYIN PEDIATRIC PRACTICE

Pulse oximetry has become widelyavailable in various aspects of pediat-ric care. It is routinely found in theemergency department and the pedi-atric ward, and it is regarded as anessential element of patient monitor-ing in pediatric intensive and perioper-ative care. Its use in the assessment ofrespiratory and hemodynamic param-eters in advanced pediatric care set-tings is beyond the intentions of thisreview.

Normal Values

Normal pediatric SPO2 values have notyet been established. Pulse-oximetryreadings vary with age and altitude.89,90

The substantial variation of normalSPO2 values among studies can be at-tributed to differences in sample size,instruments used, health of partici-pants, probe positioning, and mea-surement protocols. Thus, in healthyinfants and children, mean SPO2 valuesat sea level have been reported to be97% to 99% (�2 SDs, 95%–96%),91–93

and they might be lower in neonatesand young infants (range: 93%–100%).93 At moderate altitudes SPO2values are somewhat lower (mean:97%–98%; �2 SDs, 93%–96%)94,95 anddecrease further at high altitudes(�3000 m; mean: 86%–91%; �2 SDs,74%–82%).89,90,96–98 Authors of a recentsystematic review concluded that sup-plemental oxygen should be adminis-tered to children who reside at alti-tudes of �3000 m if the SPO2 is�85%.99

Most children also exhibit a progres-sive fluctuation in SPO2 during a 24-hour cycle. Maximal values occur inthe late afternoon, whereas minimalvalues appear in the first morninghours. This pattern is evident regard-less of whether children are asleep orawake.100 Basal SPO2 values reportedby polysomnography or homemonitor-

ing range from 95% to 100%, but nor-mal saturation nadirs can be as low as84% to 86%.101–103 However, althoughSPO2 values in the range of 90% to 93%are not uncommon during sleep, theymight be associated with poorer aca-demic performance.104

Disease-Specific Applications

Respiratory Applications

In pediatric practice, pulse oximetrymust be readily available in any situa-tion associated with hypoxemia. Oxy-gen saturation is a particularly sensi-tive indicator of disease severity inconditions associated with ventilation/perfusion (V/Q) mismatch, such as ex-acerbations of asthma or chronic lungdisease of prematurity, acute bronchi-olitis, and pneumonia.3,4,21,26,105–108 Con-versely, SPO2 is not a reliable indicatorof disease severity in proximal (laryn-geal or tracheal) airway obstructionsuch as acute laryngotracheitis,foreign-body aspiration, and vocalchord dysfunction.34 The principlemechanism of hypoxemia in suchcases is hypoventilation, which pri-marily leads to an increase in PaCO2.These patients might not present withparticularly low SPO2 readings,38–40 be-cause, per the alveolar gas equation,109

an SPO2 of �90% requires a PaCO2 of�80 mm Hg. It should be noted thatcoexistent diffuse peripheral airwayobstruction (eg, laryngotracheobron-chitis)might cause V/Qmismatch lead-ing to a lower SPO2 level. In the laterscenario, however, hemoglobin de-saturation reflects a secondary patho-physiological process rather than theprimary mechanism of the disorder.

Current guidelines state that oxygensaturation should be monitored bypulse oximetry during asthma exacer-bations to assess severity of the dis-ease and response to treatment.110,111

Mild asthma exacerbations are associ-ated with SPO2 values of�95%, moder-ate exacerbations with values of 90%

to 95%, and severe exacerbations withvalues of �90%.110,111 Although SPO2values of �92% at presentation havebeen suggested to predict hospitaliza-tion or return to the hospital,112 morerecent studies have not confirmed thisfinding.113–116 Instead, a 1-hour post-treatment SPO2 of �92% to 94% hasbeen shown to be a better predictor ofthe need for hospitalization.113–115

To date, there is no consensus on theSPO2 thresholds that should be used toadmit, treat, and discharge infantswith acute bronchiolitis.117–120 TheAmerican Academy of Pediatricsguideline recommends administrationof supplemental oxygen if SPO2 valuesfall to�90%.117 The Scottish Intercolle-giate Guidelines Network (SIGN) rec-ommends admission for all symptom-atic infants with SPO2 values of�92%,whereas the decision to admit and/ortreat patients with an SPO2 value of93% to 94% should be made on an in-dividual basis.118 Intermittent is pre-ferred over continuous SPO2 monitor-ing in hospitalized infants, andpatients should be considered for dis-chargewhen the SPO2 is�94% in roomair after an observation period of 8 to12 hours.118 SPO2 values of�94% havebeen shown to increase the likelihoodof admission and to predict longerhospital stay121–123; however, small dif-ferences in SPO2 (92% vs 94%) mightsignificantly influence the decision toadmit or discharge.124 Therefore, it isevident that, on the basis of SPO2 val-ues alone, many infants with bronchi-olitis will be hospitalized and treatedfor prolonged periods of time while allother problems have resolved.125,126

Pulse oximetry is essential for promptdetection and management of pediat-ric pneumonia, because infants andchildren might not appear cyanotic de-spite significant hypoxemia.127 The Brit-ish Thoracic Society guideline for themanagement of community-acquiredpneumonia recommends that symp-



tomatic infants and children with anSPO2 of �92% should be treated withoxygen and admitted to the hospital.128

However, despite its very good positivepredictive value, themethod cannot re-liably exclude the disease in emer-gency settings.127,129 Pulse oximetry ismandatory formonitoring hospitalizedpatients with pneumonia to guideman-agement and to assess response totreatment. It is recommended that theSPO2 be maintained at �92% with afraction of inspired oxygen of �0.6;otherwise, transfer to intensive careshould be considered.128

Cardiovascular Applications

Pulse oximetry can be used for heartrate monitoring or might serve morespecialized applications, such as theassessment of peripheral perfusionand hemodynamic status.130,131 The ple-thysmographic waveform has beenshown to be useful in the estimation ofblood pressure when manometryfails.131 It can also offer a semi-quantitative evaluation of “pulsusparadoxus” by identifying an exagger-ated decrease of pulse-wave ampli-tude during inspiration.132

Neonatal Resuscitation

Assessment of skin color is not a reli-able indicator of oxygenation statusduring the immediate postnatal pe-riod.133 Moreover, the optimal manage-ment of oxygenation during neonatalresuscitation is critical, because thereis strong evidence that both hypoxiaand hyperoxia can be harmful.134 Thefeasibility and reliability of pulse oxim-etry during neonatal resuscitationhave been proven in several stud-ies.135–138 Thus, SPO2 monitoring in thedelivery room is currently recom-mended for neonates with persistentcyanosis, when assisted ventilationand supplementary oxygen adminis-tration are required, or when neonatalresuscitation is anticipated (high-riskdeliveries).133 Under acceptable condi-

tions of peripheral perfusion, SPO2 val-ues can be reliably measured�2 min-utes after birth.137,139,140 Use of new-generation devices and sensors ofappropriate size, as well as probe at-tachment to a preductal location (ie,right upper extremity), preferably be-fore connecting the probe to the de-vice, might result in more accurateand timely readings.133,134 However,health care professionals should beaware that, even in uncompromisedneonates, an increase in SPO2 at levelsof �90% might take �10 minutes toachieve.135–140 Therefore, pulse oxime-try should be used in conjunction with,but not as a substitute for, clinical as-sessment during the transitional pe-riod after birth.133,134

Neonatal Screening for CongenitalHeart Disease

Pulse oximetry has been proposed as areasonable screening tool for the earlydetection of asymptomatic newbornswith critical congenital heart disease(CCHD).141,142 Single lower-extremitySPO2 values obtained after 24 postnatalhours seem to be convenient for large-scale screening.142 An SPO2 thresholdof �95% at low altitudes seems to beappropriate.142 Although the methodhas been shown to have excellent spec-ificity and negative predictive value,its sensitivity and false-positive ratemight vary substantially.142–144 Thecost/benefit balance of routine univer-sal screening has not been well quan-tified; however, important cost savingscould emerge because of early diagno-sis and treatment of infants withCCHD.141 Future studies, designed toassess the impact of routine neonatalscreening by pulse oximetry on mor-bidity, mortality, and hospital costs re-lated to CCHD, are expected to clarifythis issue.144

Prevention of Hyperoxia

Although for ventilator-dependent pa-tients pulse oximetry can assist in the

titration of inspired oxygen concentra-tion, it cannot reliably prevent hyper-oxic events.13,19,30,34 SPO2 values of�92%do not accurately correlate withPaO2, as is clearly depicted by theshape of the ODC (Fig 3). At such highSPO2 values, small variations of SPO2might relate to disproportionallywider variations of PaO2.145 Therefore,caution is required when interpretingpulse-oximetry readings in situationsin which hyperoxia is to be avoided, es-pecially in case of preterm and lowbirth weight neonates for whom exces-sive oxygen administration can be par-ticularly harmful.146–151 Although asingle best range has not been estab-lished yet, there is convincing evidencethat SPO2 values between 85% and 93%are sufficient to maintain normox-emia152 and to decrease the incidenceof retinopathy of prematurity in in-fants receiving supplemental oxy-gen.148–151 In extremely preterm neo-nates, however, lower SPO2 targets (ie,85%–89%) have been associated withan increased risk of mortality com-pared with higher SPO2 levels (ie, 91%–95%).153 Further ongoing trials on thisissue are expected to resolve the un-certainties surrounding optimum SPO2range in premature neonates receiv-ing supplemental oxygen.154

NOVEL TECHNOLOGIES AND FUTUREDIRECTIONS

Pulse oximetry has been proven to bean extremely useful tool in patient as-sessment and monitoring in pediatricpractice. However, its widespread useover the last 3 decades has also re-vealed its inherent limitations.

The theoretical model of conventionalpulse oximetry assumes that the arte-rial blood is the only light-absorbingpulsatile component. However, this as-sumption has been challenged by SPO2readings during motion that fall to�85% (which corresponds to a ratioof absorption ratios equal to 1); this

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should not be the case if these desatu-rations were merely the result of un-characterized noise. New theoreticalmodels assume that nonarterial ab-sorbers also generate a pulsatile signalwhenmotion occurs and that the ratio ofabsorption ratios should be considereda composite of arterial and nonarterialpulsatile components. These novel con-ceptualmodels arealsoapplicable to sit-

uations of low signal-to-noise ratio suchas low-perfusion states. Thus, new-generation devices use improved algo-rithms of signal extraction, which ulti-mately result in more accurate SPO2readings, especially under critical con-ditions.155,156 In addition, new theoriesof multiwavelength pulse oximetry areexpected to further improve the per-formance and applicability of these de-

vices.157 Reflectance pulse oximetersthat are based on absorption analysisof reflectedrather than transmitted lighthave been also introduced into clinicalpractice.158 In light of these ongoing tech-nologic advancements, clinical trials onhow to incorporate pulse oximetry intoevidence-based diagnostic and manage-ment algorithms in daily pediatric prac-tice are urgently required.

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HOW MUCH IS ENOUGH?: Many of my friends exercise all the time, whereasothers hardly ever do. When I ask those not exercising why they don’t, most saythey don’t have enough time, that it is too hard to start, or that exercising just afew minutes a day is unlikely to be beneficial. Exercise physiologists and othershave long wondered just how much aerobic exercise each day or each week isnecessary to produce a health benefit in adults. As reported in USA Today(Fitness & Food: August 2, 2011), it turns out that it doesn’t take much at all.Federal guidelines suggest that adults should engage in 150 minutes ofmoderate-intensity activity each week; this is still a reasonable goal. However,new data suggest that almost any amount of exercise may be beneficial. Adultsengaging in as little as 10 to 15 minutes/day of moderate-intensity exerciseaccrue some benefit in the prevention of heart disease. In studies evaluating therisk of heart disease in sedentary and exercising adults, the most dramatichealth benefits were seen in those who went from not exercising at all toexercising a little bit. The data also show that there is an indirect relationshipbetween the amount of exercise and the risk of heart disease. Compared tosedentary people, those who engaged in 150 minutes of moderate-intensityexercise each week had a 14% reduced risk of heart disease. Those who exer-cised 300 minutes/week had a 20% risk reduction, and a 25% risk reduction ifthey exercised 750 minutes/week. Women, for unknown reasons, derive agreater benefit from exercise than men. Bursts of activity followed by longperiods of inactivity, however, were not beneficial. This suggests that for betterhealth, one needs to keep moving. Although researchers have not been able toquantify the exact health benefit to 75 minutes of weekly moderate-intensityexercise, the American College of Sports Medicine recently revised its guide-lines. Although the guidelines still recommend that adults engage in at least 150minutes of moderate-intensity exercise each week to achieve weight reductionand help maximize the health benefits of exercise, just a little exercise, such as75 minutes/week, is likely to be beneficial. The data are fairly clear. To borrow amarketing phrase from Nike: just do it.

Noted by WVR, MD



DOI: 10.1542/peds.2011-0271; originally published online September 19, 2011; 2011;128;740Pediatrics

Sotirios Fouzas, Kostas N. Priftis and Michael B. AnthracopoulosPulse Oximetry in Pediatric Practice

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