Five Z’s – Journal Review – Case Report – AHI variability

Article:  Long-term variability of the apnea-hypopnea index in a patient with mild to moderate obstructive sleep apnea.

Date of Publication: February 15, 2020

Reference:  Fietze I, Glos M, Zimmermann S, Perzel T.  Long-term variability of the apnea-hypopnea index in a patient with mild to moderate obstructive sleep apnea.  Journal of Clinical Sleep Medicine Vol 16 (2);2020.

Reason/Problem/Purpose:Demonstrate the variability of night-to-night apnea measurements results in a single patient over 28 days.

Type of work:  Case Report

Study Performed:  A single patient (age unclear but >18 years) underwent testing at home for 28 days. A 6-channel unit was applied in the center each evening and removed each morning for the 28 days. 

Observed Results:  Long-term variability of the apnea-hypopnea index in a patient with mild to moderate obstructive sleep apnea is significant.  

This patient had changes in overall AHI that appear to be only partially related to positional changes.

There were several important and somewhat surprising (to me) facts in this paper.

            In this single individual over the 28 nights of recording:

                        Full night AHIs varied:  15.1 +7.5  (That’s 22.6 to 7.6)

                        Supine AHIs varied:  44.6+– 16.9   (That’s 61.5 to 27.7)

                        Non Supine AHIs varied:  4.8+4.7  (That’s 8.9 to 0.7)

Authors’ Thoughts:  In appropriate clinical situation, repeat testing is indicated with normal values. They could find no reason for observed variability in supine or non-supine position night to night.  The classification of the apnea severity based on AHI can vary night to night.

RGH Comments:  A major component of this patient’s variability is related to the well recognized effect of position on AHI.  The amount of the variation in the patient’s same position AHI is very concerning .  While recognized as an issue, I have assumed much of the variations seen in practice to be only positional. In this single case, that does not appear to be the situation.

 It causes one to be more skeptical of our widely accepted mild, moderate and severe classification of a patient’s apnea based on a one night or a 2-hour split night sleep test.  

It should cause concern about the science of our field and the study of apnea.  Population studies, large clinical series and even shorter reports regarding patients with OSA are based on one or sometimes two nights of study and will undoubtedly include patients like this one.  How many patients have significant same position variability night to night?  It does mean we should view the studies in our field with some skepticism?  

From a clinical standpoint, the question we must ask ourselves is how many nights should be studied for the clinician to feel confident that apnea is not an issue for the patient?   When is a negative study really negative?

RGH Mar 2020