Obstructive Sleep Apnoea (OSA) is a part of a spectrum of sleep-disordered breathing ranging from simple snoring to profound hypoventilation and respiratory failure at night.
It is characterized by repetitive episodes of partial or complete upper airway obstruction during sleep, commonly associated with hypoxia (can be profound) and usually terminated by arousal from sleep, resulting in sleep fragmentation and deleterious effects on daytime functioning. OSA in association with daytime symptoms such as sleepiness is termed as ‘OSA syndrome’
Pathogenesis and predisposing factors
Narrowing or collapse of the upper airway during sleep is the primary abnormality is OSA.
Obesity is the strongest risk factor for OSA. Fat deposition around the upper airway can cause airway narrowing and increased airway resistance, predisposing to upper airway closure. Abdominal obesity can reduce lung volume further reducing upper airway size.
Craniofacial/genetic features – a number of craniofacial anatomical variations are associated with narrowing of the upper airway and predisposition to OSA; these include micrognathia and retrognathia class II malocclusion, high-archpalate, adenotonsillar hypertrophy and macroglossia (as in hypo-thyrodism, acromegaly and amyloidosis). Down’s Syndrome and pierre-Robin sequence are strongly associated with OSA. There is a high incidence of OSA in Marfan’s Syndrome, probably related to increased compliance of the upper airway. The familial clustering seen in OSA may be partly related to the inheritance of facial features associated with narrow upper airways.
Gender – The higher incidence of OSA syndrome in men may be related to effects of androgens on upper airway neuro-muscular properties or central fat deposition. Alternatively progesterone may protect against OSA (OSA Syndrome is more prevalent in women following menopause). In premenopausal women, frequent arousals from sleep caused by airway flattening only may occur without frank apnoea; arousals can be so dominant that insomnia may be the presenting complaint.
Reduced muscle tone – Alcohol reduces upper airway muscle tone, increasing the number of obstructive events at night and reducing arousal responses, leading to longer episodes of apnoea with greater oxygen desaturation. Similar effects occur with sedatives and in some neurological conditions. In surgical patients with untreated OSA, the postoperative period can be dangerous.
Nasal obstruction – Any increase in nasal resistance can lead to increased negative upper airway pressure during inspiration, predisposing to OSA. Nasal obstruction related to rhinitis, a deviated septum and nasal packing results in increased numbers of apnoeic and hypopnoeic episodes and sleep arousals in healthy individuals and in patients with OSA syndrome.
The classic symptoms of OSA are heavy snoring, excessive daytime sleepiness and witnessed apnoea; when all three are present, OSA syndrome is more than 90% likely.
Other symptoms associated with OSA include
- nocturnal choking and gasping
- nocturnal reflex
- nocturia, enuresis
- morning headaches
- dry throat / Mouth
- unrefreshing sleep
- restless sleep, frequent awakening
- impaired cognitive functioning (Poor short term memory, reduced concentration)
- mood changes (irritability and depression)
- reduced libido, impotence
An overnight sleep study (polysomnography) is the ‘gold standard’ investigation in the diagnosis of OSA and other sleep disorders.
Alternatives to polysomnography have been sought because of expense and inconvenience. Overnight oximetry can detect the repetitive desaturations seen in severe OSA and may give a diagnosis in some patients
Consequences of OSA
Daytime functioning – OSA is associated with impaired cognition (Particularly memory, sustained attention and vigilance), information processing speed and visual and psychomotor performance.
Hypertension, cardiovascular disease and mortality – OSA may be a small independent risk factor for systemic hypertension after allowing for the confounding effects of obesity, age and alcohol.
Overlap Syndrome – A combination of lung disease (e.g. Chronic Obstructive Pulmonary Disease, COPD) and OSA can lead to earlier development of hypercapnia, pulmonary hypertension and cor pulmonale.
Obesity – Hypoventilation syndrome – Some Obese patients with OSA suffer daytime respiratory failure with hypercapnia and hypoxia in the absence of significant lung disease.
TREATMENT OF OSA
Weight Loss of 10-30% has been shown to significantly reduce the severity of OSA syndrome and should be encouraged, but improvements may not be long term, even with no subsequent gain. Complete cure of all sleep-disordered breathing by weight loss alone is rare – other treatment is often necessary.
Life-Style alcohol use and sedatives worsen OSA and should be avoided. Sleep deprivation can reduce upper airway muscle tone, potentially worsening OSA syndrome. In some patients, OSA occurs prominently when supine, and attempts to avoid this may control mild disease. Control of nasal obstruction with medical therapy may also have a role. Although these measures may have a role in mild OSA, their long term efficacy is unknown and because OSA syndrome can worsen with age, Patients treated conservatively should be followed up closely.
Nasal CPAP therapy is the most effective treatment in OSA syndrome and is usually the treatment of choice. Positive pressure is applied to the upper airway via a nasal mask, providing a ‘pneumatic’ splint to maintain upper airway patency.
Efficacy -CPAP improves daytime sleepiness, daytime cognitive function, mood and quality of life.
Problems – Compliance is probably the main limitation of CPAP. Despite recent advances, machine and mask are cumbersome and inconvenient.
Side effects are common; though usually minor, they may reduce compliance. Poorly fitting masks can cause skin irritation and even ulceration, and the hissing noise and air jet produced by leaks cause eye irritation and may distress the patient’s partner. Rhinorrhoea, stuffiness, congestion and occasionally epistaxis may occur.
Mandibular advancement devices are intra-oral devices that displace the jaw anteriorly, increasing the antero-posterior diameter of the upper airway and reducing collapse when worn at night. They can significantly reduce snoring, but have variable effects in OSA Syndrome. Side effects include temporomandibular joint discomfort, excess salivation and possible jaw occlusion.
Adenotonsillectomy can be curative in children and adolescents with OSA Syndrome and adenotonsilar hypertrophy. Adults may derive some benefit, but cure is rare.
Uvulopalatopharyngoplasty involves removal of the tonsils, uvula and parts of the soft palate and pharyngeal folds. It is the most commonly performed surgical procedure in OSA. It has significant morbidity, and even when success is defined as a decrease in AHI of only 50%, a successful result is seen in less that 50% of patients. Attempts to select patients who may benefit are not reliable. Subsequent use of CPAP may be more difficult following this procedure.
Complex maxillofacial surgery, when performed by experienced groups, can be effective in treating OSA syndrome; success rates of more than 90% have been reported. Surgery is performed in two stages:
- genioglossal advancement via mandibular osteotomy, with uvulopalatopharyngoplasty and nasal surgery
- maxillomandibular osteotomy and advancement if required. These procedures are not widely available.
Tracheostomy is usually only a last resort in patients with severe or complicated OSA who cannot tolerate CPAP. It is effective but has significant morbidity, particularly in the obese.