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Pediatric Pulmonology

Night-to-Night Consistency of At-Home NocturnalPulse Oximetry Testing for Obstructive Sleep

Apnea in Children

Martino Pavone, MD,1* Renato Cutrera, MD, PhD,1 Elisabetta Verrillo, MD,1 Teresa Salerno, MD,1

Serena Soldini,1 and Robert T. Brouillette, MD2

Summary. Rationale: At-home nocturnal pulse oximetry has a high positive predictive value

(PPV) for polysomnographically-diagnosed obstructive sleep apnea (OSA) but no studies have

been published testing the night-to-night consistency of at-home nocturnal pulse oximetry for

the evaluation of suspected OSA in children. We therefore determined the night-to-night con-

sistency of nocturnal pulse oximetry as a diagnostic test for OSA in children. Methods:

We prospectively studied 148 children (96 male) aged 4.9 � 2.4 (1.2–11.8) years, referred for

suspected OSA. To evaluate night-to-night consistency, we compared an oximetry analysis

method, the McGill Oximetry Score (MOS), from two consecutive at-home nocturnal pulse

oximetry recordings. Results: Pulse oximetry metrics were similar on the two nights. The MOS

on the two nights showed excellent night-to-night consistency when analyzed as positive for

OSA versus inconclusive, 143/148 (Spearman’s correlation coefficient ¼ 0.90). A more detailed

analysis using four categories (MOS 1, 2, 3, and 4) of OSA severity showed very good night-

to-night agreement, 133/148 (Spearman’s correlation coefficient ¼ 0.91). Variability was in-

creased in children younger than 4 years of age compared to older children. Conclusions:

Night-to-night consistency of nocturnal pulse oximetry as a diagnostic test for OSA showed

excellent agreement. Night-to-night consistency of pulse oximetry, as analyzed by the MOS, for

diagnosis and severity evaluation further validates this abbreviated testing method for pediatric

OSA. Polysomnography (PSG) is required to rule in or rule out OSA in children if a single night

oximetry testing is inconclusive. Pediatr Pulmonol. � 2012 Wiley Periodicals, Inc.

Key words: night-to-night variability; pulse oximetry; obstructive sleep apnea.

Funding source: none reported.

INTRODUCTION

Obstructive Sleep Apnea (OSA) in children is a dis-order of breathing characterized by partial and/or inter-mittent complete upper airway obstruction that disruptsnormal ventilation during sleep and normal sleep pat-terns.1 OSA affects about 1–4% of children.2,3 Themain risk factors are adenotonsillar hypertrophy, obesi-ty, craniofacial anomalies, and neuromuscular dis-ease.3,4 Commonly reported symptoms include snoring,labored breathing, witnessed apneas, disturbed sleep,and daytime neurobehavioral problems. Complicationsinclude neurocognitive impairment, behavioral, cardio-vascular, and metabolic problems.5,6 Nocturnal poly-somnography (PSG) in a sleep laboratory represents thegold standard for the diagnosing of OSA but is costlyand time-consuming.1,7

Due to these difficulties, some pediatric centers begintesting for OSA with an abbreviated modality such aspulse oximetry or home PSG.8 Pulse oximetry is anincreasingly used abbreviated testing modality for theevaluation of children with suspected OSA.9–11

Normative data12 and technical comparison betweendifferent devices have been published.13 Brouilletteet al.9 demonstrated that an abnormal nocturnal pulseoximetry had a 97% positive predictive value (PPV) fordetecting moderate to severe OSA when compared with

1Respiratory Unit, Department of Pediatrics, Bambino Gesu Children’s

Hospital, Piazza S. Onofrio, Rome, Italy.

2Department of Pediatrics, McGill University and the McGill University

Health Center Research Institute at the Montreal Children’s Hospital

Montreal, Canada.

*Correspondence to: Martino Pavone, MD, Respiratory Unit, Department

of Pediatrics, Bambino Gesu Research Institute, Piazza S. Onofrio 4,

00165 Rome, Italy. E-mail: [email protected]

Received 5 June 2012; Revised 28 August 2012; Accepted 29 August

2012.

DOI 10.1002/ppul.22685

Published online in Wiley Online Library

(wileyonlinelibrary.com).

� 2012 Wiley Periodicals, Inc.

PSG. However, children with inconclusive oximetrystudies required PSG for definitive testing to rule in andrule out OSA. Nixon et al.14 subsequently developedthe McGill Oximetry Score (MOS) to classify the sever-ity of OSA and plan appropriate perioperativemanagement.

Night-to-night variability in sleep quality and respira-tory parameters has been previously studied both inchildren15–18 and in adults19 undergoing PSG. Thisnight-to-night variability has also been defined as ‘‘firstnight effect’’.15,19 Pediatric guidelines suggested that asingle night PSG is sufficient to rule out OSA in chil-dren, but there is need for more studies to confirm thisrecommendation.7 Urschitz et al.20 reported excellenttest-retest correlation for oximetry parameters in 34third grade children drawn from a community sample.However, no previous data have been published aboutthe night-to-night variability of at-home nocturnal pulseoximetry in children evaluated for suspected OSA. Theprimary aims of this study were therefore (1) to exam-ine the night-to-night consistency of pulse oximetry asa diagnostic test for pediatric OSA and (2) to comparethe night-to-night variability of the MOS for OSA se-verity evaluation. A secondary aim was to evaluatenight-to-night variability in individual oximetry metrics.

METHODS

We performed a prospective test-retest study compar-ing data from two consecutive nights of at-home noc-turnal pulse oximetry recordings in children beingevaluated for suspected OSA. The study was approvedby the Bambino Gesu Children’s Hospital ScientificBoard (Rome, Italy) and parents signed an informedconsent. We compared night-to-night consistency for in-dividual oximetry metrics and compared night-to-nightagreement of an analysis system used for diagnosisand severity scoring of OSA—the MOS. Consecutivechildren aged 1–18 years old referred to our pediatricsleep laboratory in Rome for suspected OSA betweenMarch 2010 and June 2011 were included. We

excluded children with congenital or genetic abnormali-ties, significant cardiorespiratory disease, neurologicalor neuromuscular conditions, and/or global develop-mental delay. Children whose oximetry recordingswere less than 6 hr duration on each night were alsoexcluded.

Pulse Oximetry

Pulse oximetry was performed as described byBrouillette et al.9 and Nixon et al.14 Parents and chil-dren came to our sleep laboratory. Parents were brieflyinstructed on how to perform oximetry testing and com-pleted a questionnaire that included demographic andclinical data including questions regarding their child’susual sleep and breathing pattern. We performed a com-plete physical examination on each child. Weight wasassessed by a digital scale; height by a stadiometer.BMI was calculated from the ratio of weight/height2

(kg/m2). BMI percentiles were calculated from theWHO standards.21,22

The parents took the oximeter home, performed thestudy on two consecutive nights, and then returned theoximeter to our sleep laboratory. A motion-resistantpulse oximeter set for a 2-sec averaging time for hemo-globin saturation (SpO2) (RAD 5, Masimo, Irvine, CA)was used. The pulse oximeter used a fixed 7-sec averag-ing time for pulse rate (PR) and stored in memory newSpO2 and PR values every 2 sec.

Pulse Oximetry Variables

Saturation and PR data were extracted and analyzedusing Profox Oximetry Software, Version Masimo0706.05D. The program provided the following metrics:Mean oxygen saturation (mean SpO2), lowest SpO2,number of SpO2 dips �4%/hr of study (DI4), mean,minimum, maximum PR and standard deviation of PR,and total effective recording time (TERT). The standarddeviation of the PR was used to estimate PR variability(PRV) over the entire recording.23 Periods of oximetryrecording were excluded from analysis if the oximeterquality signal indicated low signal IQTM (Masimo), lowperfusion, unrecognized, defective or no sensor, inter-ference, or ambient light.

MOS Classification

For each night, oximetry recordings were evaluatedfor patterns suggestive of pediatric OSA and for OSAseverity grading. Oximetry recordings that had at leastthree clusters of desaturation events and at least threedips in saturation to less than 90% were regarded asdiagnostic of OSA.9 Recordings that did not meet thesediagnostic criteria were regarded as inconclusive forOSA. This method has been previously shown to have a97% PPV against PSG as the reference standard.9 The

ABBREVIATIONS:

OSA obstructive sleep apnea

PSG polysomnography

PPV positive predictive value

MOS McGill oximetry score

NPV negative predictive value

BMI body mass index

SpO2 oxygen saturation

DI4 number of SpO2 falls �4%/hr of study

PR pulse rate

PRV pulse rate variability

TERT total effective recording time

T&A adenotonsillectomy

SDB sleep disordered breathing

2 Pavone et al.


MOS was used to assess severity of OSA as previouslydescribed by Nixon et al.14 MOS of 2, 3, and 4were considered diagnostic for increasing severity ofOSA; a MOS of 1 was considered as inconclusive andunable to rule out OSA.9 Briefly, MOS category 2 hadat least three clusters of desaturation events and at leastthree dips in saturation to less than 90%; MOS category3 had at least three clusters of desaturation eventsand at least four dips in saturation to less than 85%;MOS category 4 had at least three clusters of desatura-tion events and at least four dips in saturation to lessthan 80%.14

Data Analysis

Statistical analysis was performed with Statistica 7.0.(StatSoft) and IBM SPSS Statistics 20. Continuous datawere summarized as mean � SD. Correlation for con-tinuous oximetry metrics across the two recordingnights were expressed using Pearson correlation coeffi-cients, r. Spearman’s correlation coefficient, rho, with95 percentile limits was used to analyze the levels ofagreement between inconclusive (MOS 1) versus diag-nostic (MOS 2–4) studies and between the differentMOS categories in the first and second night recordings.During data analysis we noted different levels of agree-ment between younger and older children and thereforereport a post-hoc exploratory subgroup analysis by age.For all analyzed parameters, P < 0.05 was consideredstatistically significant.

RESULTS

For this study, 211 children were recruited. Sixty-three children were excluded because one (36) or both(27) recordings did not reach the required duration of aminimum of 6 hr per night. Amongst 36 children witha single night sufficient duration recording, 33 childrenhad two inconclusive tests (MOS 1) and three childrenhad a single MOS 2 result. Excluded children did notdiffer statistically from included children on age(4.5 � 2.7 years vs. 4.9 � 2.4 years) or gender distribu-tion (59% vs. 65% males). Thus, our study sampleincluded 148 children (96 males) aged 4.9 � 2.4 (1.2–11.8) years. Body mass index percentile averaged56.8 � 34.7. Twenty-six (17.6%) were obese (>95thBMI percentile) and 22 children (14.9%) were at riskfor overweight (85–95th BMI percentile). Average noc-turnal pulse oximetry metrics were similar on nights 1and 2 (Table 1). Individual oximetry metrics variedwidely in the degree of correlation across nights(Table 1 and Fig. 1). The frequency of desaturations�4%, DI4, was most highly correlated across nights,r ¼ 0.95; saturation nadir across nights showed moder-ate correlation, r ¼ 0.80; TERT was not closely corre-lated across nights, r ¼ 0.23. An example of nocturnal

pulse oximetry trend graphs from one subject recordedon two consecutive nights is shown (Fig. 2).

Night-to-Night Agreement of Pulse Oximetry as aDiagnostic Test for OSA

There was excellent night-to-night agreement foroximetry testing as diagnostic versus inconclusive forOSA, (143 of 148 (97%) subjects), Spearman’s correla-tion coefficient ¼ 0.90 (0.81,0.99), (Table 2). Of 34children found to have an abnormal oximetry diagnosticof OSA on either night, 32 were found to have an ab-normal oximetry on night 1 and 31 were found to havean abnormal oximetry on night 2. The 34 childrenfound to have abnormal studies on either night weresignificantly younger than the 114 children with twoinconclusive studies, 3.6 � 1.6 years versus 5.2 � 2.4years, P < 0.001, t-test. Amongst children less than4 years old, night-to-night agreement was 0.93; 17 chil-dren had positive tests on both nights, 46 children hadan inconclusive test on both nights and five childrenhad a positive test on one of the two nights. Amongstchildren 4 years or older, there were no discrepanciesbetween the two nights; 12 children had abnormalresults on both nights and 68 children had inconclusiveresults on both nights.

Night-to-Night Agreement of Pulse Oximetry forAssessing Severity of OSA

There was very good night-to-night agreement (133/148) for oximetry as a method to assess severity ofOSA, Spearman’s correlation coefficient ¼ 0.91 (0.84,0.98), (Table 2). Amongst 80 children older than4 years, the MOSs were concordant in 78; the MOS

TABLE 1— Night-to-Night Consistency of Pulse OximetryMetrics

Oximetry metrics (148 pts)

First night Second night r

TERT (hr) 8.3 � 1.3 8.1 � 1.1 0.23

Mean SpO2 (%) 97.7 � 1.1 97.8 � 1.0 0.74

Lowest SpO2 (%) 87.7 � 11.4 88.3 � 10.2 0.80

SpO2 <90% (% TERT) 0.5 � 2.0 0.5 � 1.7 0.91

DI4 (falls in saturation

by �4%/hr)

3.5 � 6.4 3.8 � 7.3 0.95

Mean PR (BPM) 87.3 � 11.6 88.2 � 12.5 0.89

Minimum PR (BPM) 59.6 � 10.1 61.3 � 10.2 0.63

Maximum PR (BPM) 132.0 � 15.1 134.6 � 16.1 0.81

PRV (SD of PR in BPM) 8.4 � 2.2 8.6 � 2.4 0.76

TERT, total effective recording time; SpO2, oxygen saturation; DI4,

oxygen desaturation �4% index; PR, pulse rate; PRV, pulse rate

variability (data expressed as mean � SD); r values are Pearson cor-

relation coefficients; the significance of correlation across nights

exceeded 0.01 for all metrics.

Night-to-Night Consistency of Pulse Oximetry in Children 3


increased from level 3 to level 4 in two children fromnight 1 to night 2. Amongst 68 children 4 years old orless, the MOSs were concordant in 55; nine subjectshad a difference in MOSs of one severity category andfour subjects had a difference of two severity catego-ries. An example of oximetry recordings concordant forresults suggestive of OSA but discordant for OSA se-verity scoring is provided in Figure 2.

DISCUSSION

In this study we investigated the night-to-night agree-ment of at-home nocturnal pulse oximetry in childrenwith suspected OSA. When evaluated as a diagnostictest for OSA, the MOS showed excellent night-to-nightconsistency. When evaluated as a severity assessment

tool, the MOS showed very good night-to-night consis-tency. Individual oximetry metrics showed variable cor-relations but the DI4 was highly correlated acrossnights, r ¼ 0.95.

When evaluated as a diagnostic test for OSA, theMOS showed excellent night-to-night consistency. Asthe two recordings were made on separate nights, somedegree of night-to-night variability would be expected.In our study the first night pulse oximetry identified 32of 148 (21.6%) patients as having OSA. In earlier seriesfrom Montreal the prevalence of oximetry studies diag-nostic for OSA was much the same, 22 and 27%.9,14 Ittherefore seems likely that other pediatric sleep labora-tories would have similar proportions of diagnosticstudies and thereby could avoid the need for PSG inmany of their referrals. Our results suggest that there

Fig. 1. Oximetry metrics: Degree of correlation across two nights. These graphs demonstrate

the variable correlation between individual oximetry metrics from night 1, shown on the x

axes, and night two, shown on the y axes. Filled circles show the 34 children with an oximetry

diagnostic of OSA; ‘‘X’’ shows those with inconclusive results. Pearson correlation coeffi-

cients, r, are shown. The frequency of desaturations �4 %, DI4, was most highly correlated

across nights, r ¼ 0.95, upper left, and more easily appreciated in the log–log plot, upper

right. The saturation nadir across nights showed moderate correlation, r ¼ 0.80, lower left.

Total effective recording time (TERT) was not closely correlated across nights, r ¼ 0.23,

lower right.

4 Pavone et al.


would be little benefit to routinely performing a secondnight of pulse oximetry if a first night is inconclusive.Of 34 children diagnosed on either night, 32 were diag-nosed on the first night. To detect the additional twopatients with oximetry findings suggestive of OSA, 116tests would have to be performed and PSG would stillbe required to definitively rule in or rule out OSA in114 patients. Test retest studies for pediatric PSG havelikewise indicated that a second PSG night has a lowyield for detecting OSA or other sleep disorderedbreathing.15–18

Adenotonsillectomy is an effective, common treat-ment for pediatric OSA and severity of OSA is a knownrisk factor for perioperative problems.24–26 The MOShas been proposed as a method for detecting and grad-ing severity of pediatric OSA and for planning periop-erative care.14 In the current study we found that theMOS showed very good night-to-night consistencywhen assessing severity of OSA. Our results further val-idate the use of home nocturnal pulse oximetry to esti-mate the severity of OSA, to shorten and simplify thediagnostic process for those with severe OSA, and toprioritize and plan perioperative management.14,27

Using our abbreviated testing protocol, about one quar-ter of children evaluated for OSA do not require in lab-oratory PSG. Those with more severe OSA who are atsignificant risk of perioperative respiratory complica-tions can be prioritized for immediate surgery in a pedi-atric facility where postoperative overnight monitoringis available. Previous studies have also suggested thatchildren with recurrent severe hypoxemia require lowerdoses of perioperative narcotics for adequate pain con-trol.28,29 Although many factors should be consideredwhen implementing perioperative care protocols, thedata in Table 3 suggest that both MOS 3 and MOS 4results should be regarded as indicative of OSA requir-ing prompt treatment.

Individual oximetry metrics showed variable correla-tions but the frequency of desaturations �4%, DI4, washighly correlated across nights, r ¼ 0.95. In a previousstudy of 349 children referred for possible OSA, wereported that the DI4 determined by pulse oximetry was

Fig. 2. Variability of McGill Oximetry Score across two conse-

cutive nights in a 2-year-old boy. These graphs show the he-

moglobin saturation values from the first night, (A) and

second night, (B) pulse oximetry recordings in a 2.7-year-old

boy referred for suspected OSA. The first night recording was

classified as McGill Oximetry Score (MOS) 3, with 10 SpO2

dips below 85% and two SpO2 dips below 80%. The second

night recording was classified as MOS 4, with seven dips be-

low 80%. Both recordings are suggestive of severe OSA

requiring prompt evaluation and treatment including careful

perioperative management.

TABLE 2— Test-Retest Reliability of Pulse Oximetry as aDiagnostic Test for Obstructive Sleep Apnea

Night 2

Inconclusive

Diagnostic

of OSA Totals

Night 1 Inconclusive 114 2 116

Diagnostic of OSA 3 29 32

Totals 117 31 148

TABLE 3— Test-Retest Reliability of Pulse Oximetry forAssessing Severity of Obstructive Sleep Apnea Using theMcGill Oximetry Score (MOS)

Night 2

MOS 1 MOS 2 MOS 3 MOS 4 Totals

Night 1 MOS 1 114 1 1 0 116

MOS 2 2 8 0 0 10

MOS 3 1 2 3 3 9

MOS 4 0 2 3 8 13

Totals 117 13 7 11 148



highly correlated with the obstructive apnea-hypopneaindex determined polysomnographically, r ¼ 0.88.9 Pre-vious studies have suggested that the overnight nadir ofoxygen saturation in children with OSA is predictive ofperioperative complications; however, we found a loweracross-nights correlation for saturation nadir than forDI4, 0.80 versus 0.95, respectively.24,26,27

There are several limitations to our study. Childrenbetween 1 and 12 years of age without complex comor-bidities were included. Thus our findings may not applyto younger infants, to adolescents, or to children withcomplex comorbidities. Our study included childrenwho were referred to a pediatric sleep laboratory spe-cializing in sleep disordered breathing. In other settings,the proportion of children with diagnostic oximetrystudies may vary.

CONCLUSIONS

The MOS on two consecutive nights showed excel-lent night-to-night consistency when analyzed as abnor-mal, suggestive of OSA versus inconclusive for OSA.Analysis using the MOS for assessing OSA severityshowed reduced but still very good night-to-night agree-ment. Night-to-night consistency of the MOS for diag-nosis and severity evaluation further validates thisabbreviated testing method for pediatric OSA. Additionof a second night of oximetry testing is unlikely to ob-viate the need for polysomnography when nocturnal ox-imetry testing is inconclusive and is likely to support adiagnosis of OSA when the first night testing waspositive.

ACKNOWLEDGMENTS

The authors thank Dr. Evelyn Constantin for criticalreview of the manuscript and Xun Zhang PhD for ad-vice on statistical approaches.

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