The new AASM criteria for scoring hypopneas: Impact on the apnea hypopnea index

Abstract

Study Objectives: To compare apnea-hypopnea indices (AHIs) derived using 3 standard hypopnea definitions published by the American Academy of Sleep Medicine (AASM); and to examine the impact of hypopnea definition differences on the measured prevalence of obstructive sleep apnea (OSA). Design: Retrospective review of previously scored in-laboratory polysomnography (PSG). Setting: Two tertiary-hospital clinical sleep laboratories. Patients or Participants: 328 consecutive patients investigated for OSA during a 3-month period. Interventions: N/A Measurements and Results: AHIs were originally calculated using previous AASM hypopnea scoring criteria (AHIChicago), requiring either > 50% airflow reduction or a lesser airflow reduction with associated > 3% oxygen desaturation or arousal. AHIs using the "recommended" (AHIRec) and the "alternative" (AHIAlt) hypopnea definitions of the AASM Manual for Scoring of Sleep and Associated Events were then derived in separate passes of the previously scored data. In this process, hypopneas that did not satisfy the stricter hypopnea definition criteria were removed. For AHIRec, hypopneas were required to have ≥ 30% airflow reduction and ≥ 4% desaturation; and for AHIAlt;, hypopneas were required to have ≥ 50% airflow reduction and ≥ 3% desaturation or arousal. The median AHIRec was approximately 30% of the median AHI Chicago, whereas the median AHIAlt was approximately 60% of the AHIChicago, with large, AHI-dependent, patient-specific differences observed. Equivalent cut-points for AHIRec and AHI Alt compared to AHlChicago cut-points of 5, 15, and 30/h were established with receiver operator curves (ROC). These cut-points were also approximately 30% of AHlChicago using AHIRec and 60% of AHIChicago using AHIAlt. Failure to adjust cut-points for the new criteria would result in approximately 40% of patients previously classified as positive for OSA using AHIChicago being negative using AHIRec and 25% being negative using AHIAlt. Conclusions: This study demonstrates that using different published standard hypopnea definitions leads to marked differences in AHI. These results provide insight to clinicians and researchers in interpreting results obtained using different published standard hypopnea definitions, and they suggest that consideration should be given to revising the current scoring recommendations to include a single standardized hypopnea definition.