Choice of Oximeter Affects Apnea-Hypopnea Index

Subooha Zafar, MD; Indu Ayappa, PhD; Robert G. Norman, PhD; Ana C. Krieger, MD, FCCP; Joyce A. Walsleben, PhD and David M. Rapoport, MD, FCCP

* From the New York University School of Medicine, New York, NY.

Correspondence to: David M. Rapoport, MD, FCCP, Department of Medicine, New York University Medical Center, 550 First Ave, New York, NY 10016; e-mail david.rapoport@med.nyu.edu

Study objectives: Current Medicare guidelines include an apnea-hypopnea index (AHI) ≥ 15 events per hour, in which all hypopneas must be associated with 4% desaturation, to qualify for reimbursement for therapy with continuous positive airway pressure (CPAP). The present data demonstrate the effect of pulse oximeter differences on AHI.

Design: Prospective study, blinded analysis.

Setting: Academic sleep disorder center.

Patients: One hundred thirteen consecutive patients (84 men and 29 women) undergoing diagnostic sleep studies and being evaluated for CPAP based on the Medicare indications for reimbursement.

Interventions: Patients had two of four commonly used oximeters with signal averaging times of 4 to 6 s placed on different digits of the same hand during nocturnal polysomnography.

Measurements and results: Apneas and candidate hypopneas (amplitude reduction, > 30%) were scored from the nasal cannula airflow signal without reference to oximetry. Candidate hypopneas then were reclassified as hypopneas by each oximeter if they were associated with a 4% desaturation. Although the use of three oximeters resulted in a similar AHI (bias, < 1 event per hour), the fourth oximeter showed an overall increase in AHI of 3.7 events per hour. This caused 7 of 113 patients to have an AHI of ≥ 15 events per hour (meeting the Medicare criteria for treatment) by one oximeter but not when a different oximeter was used. More importantly, when our analysis was limited to those patients whose number of candidate hypopneas made them susceptible to the threshold value of 15 events per hour, 7 of 35 patients who did not meet the Medicare AHI standard for treatment by one oximeter were reclassified when a different oximeter was used.

Conclusion: In the present study, oximeter choice affected whether the AHI reached the critical cutoff of 15 events per hour, particularly in those with disease severity that was neither very mild nor very severe. As oximetry is not a technique that produces a generic result, there are significant limitations to basing the definition of hypopnea on a fixed percentage of desaturation in determining the eligibility for CPAP therapy.

Mikesus - that was extremely interesting. Thank you.

Its not suprising that one of the researchers is Dr David Rappoport (the same Dr from the lecture last Wed) Basically how we are measuring OSA is still flawed in his opinion, but at the current time it is the best that we have. On top of that, the devices that we use to measure are not the same either. Very interesting stuff...

Whoa! A light bulb just flickered on. I thought Dr. Rapport's name sounded familiar. He and Dr. Colin Sullivan (inventor of the cpap) presented some differing opinions on the value of "AHI". This is a link I once saw posted by -SWS:

THE APNEA-HYPOPNEA INDEX: USEFUL OR USELESS? - at an Atlanta meeting of the American Thoracic Society in 2003

As a side note, here's a link to an old interview with Dr. Sullivan on the American Sleep Apnea Association's website:

Sleep Pioneer Remembers the Early Days of CPAP