Diagnosis of the Obstructive Sleep Apnoea Syndrome
Diagnosis of the Obstructive Sleep Apnoea Syndrome
Published: October 2008
In the last two decades, the awareness of obstructive sleep apnoea (OSA) and its deleterious consequences on patients’ health, quality of life and cognitive performance (such as driving capacity and attention capacity) have been steadily increasing. Repeated episodes of upper-airway obstruction – associated with increased respiratory effort – cause repetitive complete or incomplete cessation of air flow, so-called apnoeas and hypopnoeas, and may trigger cortical arousals in order to restore normal breathing.
Apnoeas and hypopnoeas per hour of sleep are calculated as apnoea/hypopnoea index (AHI) or respiratory-disturbance index (RDI). Daytime fatigue and sleepiness from respiratory-related sleep disruption (AHI >5 episodes per hour (>5/h)) are commonly referred to as the OSA syndrome (OSAS). According to an updated International Classification of Sleep Disorders, the diagnosis is also made with an RDI ≥15, irrespective of symptoms.1 OSAS is now the best-recognised and most prevalent breathing disturbance in sleep,2 affecting between 2 and 26% of the general population, depending on sex, age and criteria for syndrome definition.3,4
The syndrome has attracted even more interest recently, as it was recognised as an independent cardiovascular risk factor and studies on the treatment of OSAS have postulated a risk reduction of fatal and non-fatal cardiovascular events.5,6 Nonetheless, it is estimated that 90% of people with the condition remain undiagnosed.7 Therefore, the primary objective of clinical pre-test evaluation and overnight testing should focus on a timely, cost-effective and targeted diagnostic approach to identify those who will benefit from treatment. Ideally, diagnosis would lead physicians to identify those patients with potential benefit from treatment and avoid trying it on those who will not.8 Focusing on symptoms rather than respiratory parameters may better address outcome parameters that are relevant for patients, which should be adopted as the gold standard of OSAS diagnosis instead of number counts of respiratory disturbance parameters, oxygen dip rates or arousals.
Pre-test Evaluation for Suspected OSAS
Patient History
The diagnosis of OSAS is first suspected on clinical grounds based on a typical history. Patients complain of non-restoring sleep, daytime fatigue and sleepiness, sometimes even sleep attacks. Sleepiness is frequently reported in situations of reduced attention, such as driving on motorways, and at times of rest or inactivity. Some patients also complain of morning symptoms such as headaches and fatigue; others suffer from mood disturbance. Loud snoring, apnoeas and gasping or choking are witnessed by bed partners. Notably, partners often ask patients to seek medical help because they better recognise the loss of attention, concentration and interest, as the disease evolves gradually and patients become accustomed to their sleepiness, unaware of their evolving symptoms. Some patients even report previous workplace or driving accidents, or near misses. Quality of life and social contacts are often seriously impaired. Subjective rating tests of sleepiness include the Epworth Sleepiness Scale, Profile of Mood States and the Stanford Sleepiness Scale.9-11 Of these, the Epworth Sleepiness Scale is most commonly used as, in different studies, a more significant effect on the extent of impairment with OSAS was shown, compared with normal subjects.12,13 Impaired-health-related quality of life may be assessed by the SF-36 questionnaire.14
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