Definition
OSA is the most common form of sleep-disordered breathing. History and the severity of the condition has implications for the management for OSA.
During sleep, breathing may be interrupted by partial or complete obstruction of the upper airway which may lead to sleep fragmentation / disturbed sleep, and complaints/symptoms related to (excessive) daytime sleepiness and fatigue (See Assessment - History), as well as affecting cardiovascular and metabolic functions (See Comorbidities & Complications). Partial obstruction (hypopnoea) is defined as reduction of airflow ≥ 10 seconds associated with oxygen desaturation and/or EEG arousal. Complete obstruction (apnoea) is defined as cessation of airflow ≥ 10 seconds.
Apnoeas and hypopnoeas are measured during an overnight sleep study (See Investigations & Referral) via nasal pressure cannula with or without a thermistor that detect changes in airflow. Conventionally the apnoea hypopnoea index (AHI), i.e. the number of apnoea and hypopnoea events per hour of sleep, is used as the primary parameter for severity of OSA.
OSA has been defined as an AHI ≥ 5 per hour. The severity of OSA, which has implications for the management plan is determined by the level of the AHI. The American Academy of Sleep Medicine (AASM) criteria of OSA, published in the International Classification of Sleep Disorders (ICSD), include AHI ≥ 15 and AHI ≥ 5 in combination with drowsiness, non-invigorating sleep, tiredness or insomnia, and waking up gasping for breath or suffocating.1 Recent evidence shows that normal AHI values may vary with age, decreasing slightly in younger adults (Ages 18-34; Absent, mild, moderate, severe OSA; AHI: <2, 3-12, 13-25, >25) and increasing markedly in the elderly (Ages 65-79; Absent, mild, moderate, severe OSA; AHI: <20, 20-30, 31-45, >45).2
Obstructive sleep apnoea syndrome (OSAS) is defined as OSA (AHI ≥ 5) with daytime sleepiness symptoms and/or cardiometabolic comorbidities (e.g. arterial hypertension).
Patients with positional OSA (the majority of apnoeas can be attributed to a supine sleep position) tend to have less severe OSA.3
Table. Apnoea hypopnoea index (AHI, number of events per hour of sleep) and OSA4
Severity of OSA Absent Mild Moderate Severe | AHI values < 5 > 5 - 15 > 15 - 30 > 30 |
*Based on age-dependent normal AHI values (upper limit of 95%CI range) reported in healthy subjects using AASM 2007 “Recommended” PSG scoring criteria.5
A therapeutic trial of treatment can be used to confirm the causal role of OSA on symptoms - daytime sleepiness may also be caused by another sleep disorder, illness, or the use of medication, alcohol or drugs. Therapeutic treatment can be continued in patients experiencing symptomatic improvement.
Of note, in patients with AHI 5-15 the manifestation of symptoms is required for the diagnosis of OSA, while this is not the case for AHI > 15. It has however been reported that there is no linear relationship between AHI and clinical symptoms, including sleepiness, elevated blood pressure or dyslipidemia.6, 7 - suggesting that AHI and clinical symptoms need to be considered independently. Also, it is unclear which patients should be treated. Patients may be treated needlessly when AHI 5-15 (or in the elderly, with AHI values < 30) and reported symptoms are unrelated, or in asymptomatic patients with AHI > 15.8, 9
AHI - Apnoea-Hypopnoea Index
BBTi - Brief Behavioural Therapy for Insomnia
BMI - Body Mass Index (kg/m2)
BQ - Berlin Questionnaire
CBTi - Cognitive Behavioural Therapy for Insomnia
CELL - Coblation Endoscopic Lingual Lightening
COPD - Chronic Obstructive Pulmonary Disease
CVA - Cerebrovascular Accident
CPAP - Continuous Positive Airway Pressure
CSA - Central Sleep Apnoea
DASS - Depression Anxiety Stress Scale
DBAS - Dysfunctional Beliefs and Attitudes about Sleep
DBP - Diastolic Blood Pressure
DIMS - Difficulties Initiating and/or Maintaining Sleep
DISE - Drug-Induced Sleep Endoscopy
DISS - Daytime Insomnia Symptom Scale
ENT - Ear Nose and Throat
ESS - Epworth Sleepiness Scale
FOSQ - Functional Outcomes of Sleep Questionnaire
FSH - Follicle-Stimulating Hormone
FTP - Friedman Tong Position
GP - General Practitioner
HANDI - RACGP Handbook of Non-Drug Interventions
HGNS - Hypoglossal Herve Htimulation
ISI - Insomnia Severity Index
K10 - Kessler Psychological Distress Scale
MAD - Mandibular Advancement Device
MAS - Mandibular Advancement Rplint
MBS - Medicare Benefits Schedule
MMA - Maxillomandibular Advancement Surgery
MRA - Mandibular Repositioning Appliance
ODI - Oxygenation Desaturation Index
OSA - Obstructive Sleep Apnoea
PLMD - Periodic Limb Movement Disorder
PT - Positional Therapy
PTSD - Post-Traumatic Stress Disorder
PSG - Polysomnography
QSQ - Quebec Sleep Questionnaire
REM - Rapid Eye Movement
RFTB - Radiofrequency Thermotherapy of the Tongue Base
SBP - Systolic Blood Pressure
SCI - Sleep Condition Indicator
SE - Sleep Efficiency
SF36 - Short-Form (36) Health Survey
SMILE - Submucosal Minimally Invasive Lingual Excision
SNRIs - Serotonin-Norepinephrine Reuptake Inhibitors
SOL - Sleep Onset Latency
SSRI - Selective Serotonin Reuptake Inhibitors
TFTs - Thyroid Function Tests
TIB - Time In Bed
TORS - Transoral Robotic Surgery
TST - Total Sleep Time
UPPP - Uvulopalatopharyngoplasty
WASO - Wake After Sleep Onset