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 Table of Contents  
Year : 2019  |  Volume : 3  |  Issue : 2  |  Page : 36-39

McGill oximetry score to predict risk of obstructive sleep apnea in pediatric patients

Department of Paediatrics, Kwong Wah Hospital, Hong Kong SAR

Date of Web Publication8-Aug-2019

Correspondence Address:
Wing-Shan Chan
Department of Paediatrics, Kwong Wah Hospital, 25 Waterloo Road
Hong Kong SAR
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/prcm.prcm_7_19

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Objective: The aim of this study is to investigate the use of overnight oximetry to predict high Apnea–Hypopnea Index (AHI) in Hong Kong children with habitual snoring. Methodology: We have retrospectively analyzed the polysomnography (PSG) of 573 patients with habitual snoring with age ranged from 6 months to 18 years old. Patients with syndromal diagnosis or neuromuscular disorders were excluded from the study. The sensitivity, specificity, positive predictive value , and negative predictive value (NPV) of oximetry to predict AHI were calculated. Results: McGill score >1 had high specificity 99.07% and low sensitivity 16.81% to detect AHI >1. SpO2 nadir <95% has high sensitivity 98.56% and NPV 97.56% to predict AHI >5. Conclusion: The use of the McGill score together with nadir SpO2 in overnight oximetry can help in stratifying the severity of obstructive sleep Apnea and thus prioritizing PSG testing.

Keywords: Apnea–Hypopnea Index, McGill score, obstructive sleep Apnea

How to cite this article:
Chan WS, Chan EY, Ng DK, Kwok KL, Yip AY, Leung SY. McGill oximetry score to predict risk of obstructive sleep apnea in pediatric patients. Pediatr Respirol Crit Care Med 2019;3:36-9

How to cite this URL:
Chan WS, Chan EY, Ng DK, Kwok KL, Yip AY, Leung SY. McGill oximetry score to predict risk of obstructive sleep apnea in pediatric patients. Pediatr Respirol Crit Care Med [serial online] 2019 [cited 2023 Jun 6];3:36-9. Available from: https://www.prccm.org/text.asp?2019/3/2/36/264103

  Introduction Top

Obstructive sleep Apnea (OSA) is common in children. OSA syndrome is associated with snoring, excessive daytime sleepiness, morning headache, hyperactivity, and nocturnal enuresis. This might be complicated by learning difficulty, growth failure, and increased risk of cardiovascular events (e.g., dysregulation of blood pressure).[1],[2] Polysomnography (PSG) is the gold standard to diagnose OSA. PSG is a resource-dependent investigation.[3] A screening tool to triage patients with potentially severe OSA for early PSG is, therefore, reasonable and valuable.

OSA is frequently accompanied by nocturnal desaturations.[4],[5],[6] Compared to PSG, oximetry is simple, inexpensive, and readily available in most hospitals. Brouillette et al. stated that in the setting of a child suspected of having OSA, positive nocturnal oximetry has at least 97% positive predictive value (PPV) to OSA, while negative oximetry cannot exclude OSA.[7] By retrospectively analyzing 349 patients, Nixon et al. commented that higher oximetry scores were associated with a higher Apnea–Hypopnea Index (AHI; P<0.001), higher desaturation index (P< 0.001), lower SaO2 nadir (P< 0.001), and higher respiratory arousal index (P< 0.001).[8] Based on these findings, he has devised the McGill oximetry score. The score has 4-level severity (McGill 1–4), based on the numbers and depth of desaturations in an overnight pulse oximetry recording. A score above one was suggested to be indicative of OSA.[8]


In this study, we aim to investigate the use of overnight oximetry to predict high AHI in Hong Kong children with habitual snoring.

  Methodology Top

We retrospectively analyzed the PSG of Chinese patients with habitual snoring, who were being followed up in the Sleep Clinic of the Department of Paediatrics, Kwong Wah Hospital from January 2010 to December 2014. All patients aged 6 months to 18 years old who underwent PSG were included in the study. Patients with syndromal diagnosis (e.g., Down syndrome, Crouzon syndrome) or neuromuscular disorders (e.g., Duchene Muscular Dystrophy) were excluded from the study.

The PSGs were scored by pediatricians according to 2007 and 2012 American Academy of Sleep Medicine (AASM) scoring criteria. AHI is the total number of apneas and hypopneas divided by the total sleep time in h. An apnea is defined as a drop in the peak thermal sensor excursion of ≥90% from baseline for the whole event. An obstructive apnea is scored if it meets apnea criteria for at least the duration of 2 breaths during baseline breathing and is associated with the presence of respiratory effort throughout the entire period of absent airflow. A hypopnea is identified as a drop-in nasal pressure signal by ≥30% of pre-events baseline for at least 2 breaths, in association with either ≥3% oxygen desaturation or an arousal.

In this study, we define normals as having an AHI ≤1. OSA was diagnosed when AHI >1. The severity of OSA was graded as mild (AHI 1.1–5 per h) and moderate-to-severe (AHI >5 per h). The tracing for the oximetry scoring was extracted from that used for the full PSG (model: Siesta, Compumedics). A trained nurse who was blinded to the diagnoses and PSG results was responsible for grading all of the McGill scores.

All statistical analyses were conducted using IBM SPSS Statistics for Windows, Version 22.0. (IBM Corp., Inc., Armonk, NY, USA). A value of P < 0.05 was taken as statistically significant. Continuous variables were presented as the mean ± standard deviation (SD). Differences in the variables between groups were analyzed using Student's t-test. Categorical variables were analyzed using the Chi-square test. Kruskal–Wallis statistic was used to compare ordinal variables among the four McGill score groups. Post hoc analysis was performed using the Mann–Whitney test with Bonferroni correction. The sensitivity, specificity, PPV, negative predictive value (NPV), and Youden's index (sensitivity + specificity − 1)[9] of oximetry to predict AHI were calculated.

This study was approved by the Research Ethics Committee of the Kowloon West Cluster of the Hospital Authority in Hong Kong (KW/EX-15-073[86-09]).

  Results Top

Polysomnograms of 573 patients (males 419, females 154) with a mean age of 10.86 ± 4.22 years (mean ± SD, range: 0.5–17.9 years old) were analyzed. Three hundred and fifty-seven (63%) patients had AHI more than 1, in which 139 (39% of the OSA group) had AHI >5 [Table 1].
Table 1: Demographic characteristics between those Apnea-Hypopnea Index ≤1 versus Apnea-Hypopnea Index >1

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[Figure 1] shows the AHIs of different McGill scores, with the number of patients in each group. There were significant differences between all groups (P< 0.05) except McGill score 3 and 4. Five hundred and eleven patients were scored McGill Grade 1. Among them, 214 (42%) had AHI <1. The remaining 58% comprised OSA with different degrees of severity (AHI 1.1–5 = 208, AHI >5 = 89). [Figure 2] shows that SpO2 nadir was significantly lower in patients with AHI >1 (P< 0.0001*).
Figure 1: Apnea–Hypopnea Index of McGill scores 1–4. *Denotes significant differences among the groups (P < 0.05). n: Number of patients.

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Figure 2: SpO2 nadir between Apnea-Hypopnea Index ≤1 and Apnea-Hypopnea Index >1 (P < 0.0001).

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[Table 2] shows the specificity, sensitivity, PPV, and NPV of McGill scores and nadir SpO2 to predict AHI >1. McGill score >1 had specificity 99.07%, sensitivity 16.81%, PPV 96.77%, and NPV 41.88% to detect AHI >1. McGill score ≥3 had 100% specificity and PPV to detect OSA. [Table 3] shows the specificity, sensitivity, PPV, and NPV of McGill scores and nadir SpO2 to predict AHI >5. SpO2 nadir <95% has high sensitivity 98.56% and NPV 97.56% to predict moderate OSA.
Table 2: Different cutoffs of McGill scores and nadir SpO2 to predict Apnea-Hypopnea Index >1

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Table 3: Different cutoffs of McGill scores and nadir SpO2 to predict Apnea-Hypopnea Index >5

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  Discussion Top

We are one of the pediatric sleep centers in Hong Kong receiving referrals for suspected sleep-disordered breathing. After clinical evaluation in the sleep clinic, patients who were considered high risk for OSA would proceed to PSG. This preselection accounted for the high prevalence (62%) of OSA in our study.

Our data showed a low sensitivity 16.81% of McGill score ≥2 to predict OSA. This was lower than the sensitivity 43% from the originally validated study by Nixon et al.[8] Unlike us, the Nixon et al. group only evaluated children who were scheduled for adenotonsillectomy instead of all referrals with suspicious OSA, and they might, therefore, at higher risk.

McGill score of 1 did not imply normal PSG study and in fact, missed 58% of patients with OSA. This is not surprising as desaturation is not ubiquitous, especially in mild OSA. In the AASM definition of apnea, desaturation is not a prerequisite. Therefore, patients with McGill score 1 should still be put in the normal queue for formal PSG.

In comparison, McGill score ≥2 had a high PPV of 96.77% to rule in patients with OSA. Hence, these patients are recommended to have an earlier referral for PSG. In a Cohort by Horwood et al.,[10] children with clinical adenotonsillar hypertrophy and preoperative McGill score ≥2 had expedited surgery without the need for further testing, and the major complication rate was found to be low. While this could be considered in resource-limited countries, we still advocate PSG in a relative resourceful place like Hong Kong before definitive surgery. It is more affirmative to perform surgery, in parents' and patient's perspective, when OSA is diagnosed based on PSG, which is the current gold-standard.

Independent of McGill score, we found that a SpO2 nadir ≥95% excluded nearly all moderate OSA (AHI >5) with sensitivity of 98.56% and NPV 97.56%. This is one additional factor to consider when prioritizing patients in PSG queue who have the same McGill score of 1.

With PPV of 96.15%, we are confident that most of the patients with a McGill score of 3 or 4 have moderate-to-severe OSA. They should be arranged with urgent PSG to facilitate management. While awaiting PSG, immediate intervention, including positive airway pressure, should be administered.

Compared to PSG, oximetry is readily accessible in the hospital. The McGill score, together with the lowest SpO2 is a simple way to provide a more reliable and objective triage method. In addition, reading an oximetry examination takes much shorter duration then scoring a full PSG.

There are two major limitations of this study. First, owing to a high pretest probability, our results and recommendations are only applicable to specialized centers with high-risk OSA cases. Second, this study is not applicable to patients with syndromes and neuromuscular disorders because their nocturnal desaturations might be secondary to central instead of obstructive apnea, which is indistinguishable in oximetry. [Figure 3] shows the proposition of the use of oximetry in prioritizing a long PSG queue.
Figure 3: Flow chart for the proposition of oximetry in prioritizing polysomnography.

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  Conclusion Top

In a referral population of children suspected to have OSA, the use of the McGill score together with nadir SpO2 in overnight oximetry can help in stratifying the severity of OSA and thus prioritizing PSG testing.

Financial support and sponsorship

This study was funded by the Tung Wah Group of Hospitals' Research Fund 2015/2016. The funder had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Conflicts for interest

There are no conflicts for interest.

  References Top

Li AM, Chan DF, Fok TF, Wing YK. Childhood obstructive sleep apnoea: An update. Hong Kong Med J 2004;10:406-13.  Back to cited text no. 1
Kwok KL, Ng DK, Chan CH. Cardiovascular changes in children with snoring and obstructive sleep apnoea. Ann Acad Med Singapore 2008;37:715-21.  Back to cited text no. 2
Pang KP, Terris DJ. Screening for obstructive sleep apnea: An evidence-based analysis. Am J Otolaryngol 2006;27:112-8.  Back to cited text no. 3
Chiner E, Signes-Costa J, Arriero JM, Marco J, Fuentes I, Sergado A, et al. Nocturnal oximetry for the diagnosis of the sleep apnoea hypopnoea syndrome: A method to reduce the number of polysomnographies? Thorax 1999;54:968-71.  Back to cited text no. 4
Urschitz MS, Wolff J, Von Einem V, Urschitz-Duprat PM, Schlaud M, Poets CF. Reference values for nocturnal home pulse oximetry during sleep in primary school children. Chest 2003;123:96-101.  Back to cited text no. 5
Zamarrón C, Gude F, Barcala J, Rodriguez JR, Romero PV. Utility of oxygen saturation and heart rate spectral analysis obtained from pulse oximetric recordings in the diagnosis of sleep apnea syndrome. Chest 2003;123:1567-76.  Back to cited text no. 6
Brouillette RT, Morielli A, Leimanis A, Waters KA, Luciano R, Ducharme FM. Nocturnal pulse oximetry as an abbreviated testing modality for pediatric obstructive sleep apnea. Pediatrics 2000;105:405-12.  Back to cited text no. 7
Nixon GM, Kermack AS, Davis GM, Manoukian JJ, Brown KA, Brouillette RT. Planning adenotonsillectomy in children with obstructive sleep apnea: The role of overnight oximetry. Pediatrics 2004;113:e19-25.  Back to cited text no. 8
Youden WJ. Index for rating diagnostic tests. Cancer 1950;3:32-5.  Back to cited text no. 9
Horwood L, Brouillette RT, McGregor CD, Manoukian JJ, Constantin E. Testing for pediatric obstructive sleep apnea when health care resources are rationed. JAMA Otolaryngol Head Neck Surg 2014;140:616-23.  Back to cited text no. 10


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3]

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