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ELECTRONIC ARTICLE: Gillian M. Nixon, Andrea S. Kermack, G. Michael Davis, John J. Manoukian, Karen A. Brown, and Robert T. Brouillette Planning Adenotonsillectomy in Children With Obstructive Sleep Apnea: The Role of Overnight Oximetry Pediatrics 2004; 113: e19-e25 [Abstract] [Full text] [PDF]

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Use of McGill Oximetry Score in planning adenotonsillectomy in children

Qun Ui Lee   (24 June 2008)

Use of McGill Oximetry Score in planning adenotonsillectomy in children 24 June 2008
Qun Ui Lee, Paediatrician Department of Paediatric & Adolescent Medicine, Princess Margaret Hospital, Hong Kong SAR Send letter to journal: Re: Use of McGill Oximetry Score in planning adenotonsillectomy in children leequnui{at}gmail.com Qun Ui Lee	I refer to the paper by Nixon et al(1) on the use of McGill Oximetry Score (MOS) in planning adenotonsillectomy (T&A) in children with obstructive sleep apnea. His approach resulted in 22% of positive oximetry (MOS category 2 or above). In other words, 78% eventually required a formal sleep study. I think the proportion of positive oximetry is too low to be helpful in reducing polysomngography (PSG) workload. For patients having MOS 1 requiring subsequent sleep study, the waiting time for T&A was actually prolonged by 2.5 times. Besides, the majority of patients needed two procedures instead of one. This is obviously not desirable. In Phase 2 of the study, patients with MOS 1 (normal + inconclusive oximetry) have an average apnea-hypopnea index (AHI) of 4.1 (95% CI 3.0- 5.1). I think patients with normal oximetry should have much lower AHI. Unfortunately both inconclusive and normal oximetries were grouped under category 1, and we do not know how many within these two subcategories eventually received T&A. In Phase 3, OSAS was later diagnosed in 58 (49%) among 119 with either MOS 1 or failed oximetry. A second oximetry done simultaneously was ¡§inconclusive¡¨ in all 58. That means that patients with normal oximetry are unlikely to have OSAS. Even if they have mild OSAS, most parents will prefer medical treatment rather than T&A. I have actually tried the MOS on 40 snoring children, the average AHI for normal VS inconclusive oximetry was 0.86 VS 2.37 (unpublished data). MOS is a semi-quantitative measure of the ¡§depth¡¨ of desaturation, while desaturation index (DI) is a quantitative measure of the ¡§frequency¡¨ of desaturation. Hence, MOS and DI are looking at different aspects of the same hypoxic process. MOS is unable to detect frequent, mild desaturations >90%, a situation probably classified as MOS 1- inconclusive. In fact, the ability to detect this ¡§fluctuating pattern¡¨ can enhance the sensitivity of oximetry(2). This may be achieved by introducing DI to supplement MOS. The average DI in asymptomatic normal children is below 1(3). MOS 1 with DI >1 may indicate the presence of significant OSAS. On the other hand, MOS 1-normal with a DI <1 can be quite reassuring, especially if the symptoms and signs are mild. These patients can be safely followed up with conservative treatment. PSG can be spared, unless symptoms persist or get worse. A larger scale study that combines MOS and DI in diagnosing OSAS is indicated to test this modified approach. Reference: 1. 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-e25. 2. Epstein LJ, Dorlac GR. Cost-effectiveness analysis of nocturnal oximetry as a method of screening for sleep apnea-hypopnea syndrome. Chest. 1998;113(1):97-103. 3. Urschitz MS, Wolff J et al. Reference values for nocturnal home pulse oximetry during sleep in primary school children. Chest. 2003;123(1):96-101. Conflict of Interest: None declared