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Nocturnal Oximetry: Aha Moment for the AHI? :

August 7, 2018

Adenotonsillectomy (AT) is a common pediatric procedure and can be beneficial for children with obstructive sleep disordered breathing (SDB). The difficulty, however, lies in identifying which children would benefit from a procedure that is not without risk, albeit a small one.  Doing so has historically involved continuously monitoring a child with polysomnography (PSG) in a specialized sleep laboratory.

Adenotonsillectomy (AT) is a common pediatric procedure and can be beneficial for children with obstructive sleep disordered breathing (SDB). The difficulty, however, lies in identifying which children would benefit from a procedure that is not without risk, albeit a small one.  Doing so has historically involved continuously monitoring a child with polysomnography (PSG) in a specialized sleep laboratory.  The result from this study is the apnea-hypopnea index (AHI) or the frequency at which a child’s airway is obstructed while asleep—the higher the AHI, the more severe the SDB.  For many children, access to a sleep laboratory may be limited, preventing surgeons from obtaining the information necessary to counsel caregivers on whether or not the AT procedure would be beneficial for a child. 

Two nocturnal oximetry measures requiring only the monitoring of pulse oximetry data while a child sleeps may be viable alternatives to the more intensive PSG.  The McGill oximetry score (MOS) utilizes graphical interpretation of pulse oximetry data to detect clusters of desaturation events, where a MOS score of 1 is considered normal/inconclusive and a score of greater than 1 has a greater than 90% positive predictive value of significant AHI >5.  The second, the oxygen desaturation index (ODI3), measures the frequency of drops in oxygen saturation ≥3% per hour.  Children with an ODI3 ≥3.5 have been shown to show clinical improvement in their ODI3 to <2 after the AT procedure.  So why don’t we just rely on these metrics and forgo the PSG?  Neither of these have been prospectively studied as predictors for improvement post-AT.  In this month’s Pediatrics, Papadakis et. al. (10.1542/peds.2017-3382) study whether changes in the MOS or the ODI3 can be detected in children before and after AT.

In this prospective, single blinded randomized study, 140 children aged 4-10 years with at least 6 months of snoring >3 nights per week, a tonsil size of >2+, and who were considered candidates for AT by ENT physicians were included in the final analysis.  Participants were randomized to have nocturnal oximetry testing at baseline and at three months either 1) immediately prior to AT (n = 72) or 2) after AT (n = 68).   One of the primary outcomes of the study was the change in proportion of children with abnormal MOS/ODI3 scores between the baseline and three month testing.  A decrease in the group of children receiving AT and those who did not would suggest we could use the MOS and/or ODI3 to predict which children would benefit from surgery.  So can we get away from the PSG?

As it turns out, there was no difference in the proportion of children with abnormal MOS between those that received AT and those that did not, despite the high PPV of the score for an abnormal AHI value.  On the other hand, children with an ODI3 score ≥3.5 at baseline were more likely like to have a reduction of their scores to <2 post-AT (OR 14.0 [95% CI 2.9-68.4]).  While the confidence interval is wide, authors share that the number needed to treat with AT based solely on ODI3 scores were similar to that of the Childhood Adenotonsillectomy Trial (CHAT), which utilized the gold standard PSG to measure AHI pre- and post-AT.  Accordingly, authors concluded that nocturnal oximetry and the ODI3 score may be helpful in identifying children with SDB that will benefit from AT when PSG is not available or economical.  Check out this article and see for yourself whether nocturnal oximetry could be a viable pre-operative evaluation for SDB in the future.   

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