Obstructive Sleep Apnea: Risk Factors, Pathophysiology, Clinical features, Medical Management

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Obstructive sleep apnea (OSA) is a disorder characterized by recurrent episodes of upper airway obstruction and a reduction in ventilation. It is defined as cessation of breathing (apnea) during sleep usually caused by repetitive upper airway obstruction. OSA interferes with people’s ability to obtain adequate rest, thus affecting memory, learning, and decision making.

Risk factors for OSA include obesity, male gender, post-menopausal status, and advance age. The major risk factor is Obesity; a larger neck circumference, short neck, and increased amounts of peripharyngeal fat narrow and compress the upper airway. OSA affects 4% of males and 2% of females. Women are not often referred for evaluation of OSA, possibly because they are less likely to report classic symptoms.  Other associated factors include alterations in the upper airway, such as structural changes (e.g. Tonsillar hypertrophy, abnormal posterior positioning of one or both jaws and variations in craniofacial structures) that contribute to the collapsibility of the upper airway.

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Pathophysiology

The pharynx is a collapsible tube that can be compressed by the soft tissues and structures surrounding it. The tone of the muscles of the upper airway is reduced during sleep. Mechanical factors such as reduced diameter of the upper airway or dynamic changes in the upper airway during sleep may result in obstruction. These sleep related changes may predispose to upper airway collapse when small amounts of negative pressure are generated during inspiration.

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Repetitive apneic events results in hypoxia (decreased oxygen saturation) and hypercapnia (increased concentration of carbon dioxide), which triggers a sympathetic response. As a consequence, patients with OSA have a high Prevalence of hypertension and an increased risk of myocardial infraction and stroke. In patients with pre-existing Cardiovascular disease, the nocturnal hypoxemia may predispose to dysrhythmias. Patients who have a diagnosis of  heart failure and who have untreated OSA are at increased risk of death (Wang, Parker, Newton, et al., 2007). OSA in the absence of identifiable Cardiovascular disease can increase insulin resistance and other metabolic changes that can increase the risk of vascular disease. OSA is more prevalent in people with coronary artery disease, congestive heart failure, metabolic syndrome, and type 2 diabetes.

Clinical features

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OSA is characterised by frequent and loud snoring with breathing cessation for 10 seconds or longer,  for at least five episodes per hour, followed by awakening abruptly with a loud snort as the blood oxygen level drops, patients with sleep apnea may have anywhere from five apneic episodes per hour to several hundred per night.

Classic signs and symptoms of obstructive sleep apnea include snorting, snoring, gasping, choking and witnessed apneic episodes commonly reported by the bed partner. Symptoms typically progress with increase in weight, aging, and during the transition to menopause. Patients are typically unaware of nocturnal upper airway obstruction during sleep. They frequently complain of insomnia including difficulty in going to sleep, night-time awakenings and early morning awakenings with an inability to go back to sleep, as well as chronic fatigue and hypersomnolence (daytime sleepiness). When obtaining the health history, the nurse asks the patient about sleeping during normal activities such as eating or talking. Patients with this symptoms are considered to have pathologic hypersomnolence.

Be alert for the following signs and symptoms:

  • Excessive daytime sleepiness
  • Frequent nocturnal awakening
  • Insomnia
  • Loud snoring
  • Morning headaches
  • Intellectual deterioration
  • Personality changes, irritability
  • Impotence
  • Systemic hypertension
  • Dysrhythmias
  • Pulmonary hypertension, cor pulmunale
  • Polycythemia
  • Enuresis

Diagnostic assessment

  • The diagnosis of sleep apnea is based on clinical features plus a polysomnographic finding  (sleep study), which is the definitive test for OSA.
  • The test is as overnight study that measures multiple physiologic signals to include those related to sleep (electroencephalogram [EEG], respiration  (airflow, thoracoabdominal effort, and oximetry), and cardiac dysrhythmia (electrocardiogram).

Medical management

Patients usually seek medical treatment because their sleeping patterns express concern or because they experience excessive sleepiness at inappropriate times or settings  (e.g. While driving a car). A variety of treatment are provided and are available. Weight loss and avoidance of alcohol and hypnotic medications are the first steps. In more severe cases involving hypoxemia and hypercapnia, the treatment includes continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) therapy with supplemental oxygen via nasal cannula. CPAP is used to prevent airway collapse, whereas BiPAP makes breathing easier and results in the lower average airway pressure. Although these treatments are effective in management of OSA, compliance with treatment continues to be a major concern.

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Surgical procedures also may be performed to correct OSA. Simple tonsillectomy may be effective for patients with larger tonsils and low body mass index. Uvulopalatopharyngoplasty is the section of pharyngeal soft tissue and removal of approximately 15mm of the free edge of the palate and uvula. Effective in about 50% of patients, it is more effective in eliminating snoring than apnea. Nasal septoplasty may be performed for gross anatomic nasal septal deformities. Tracheostomy relieves upper airway obstruction but has numerous adverse effects, including speech difficulties and increased risk of infections. These procedures, as well as other maxillofacial surgeries, are reserved for patients with life threatening dysrhythmias or severe disability who have not responded to conventional therapy.

Pharmacological management

Although medications are not generally recommended for OSA, modafinil (Provigil) has been shown to reduce daytime sleepiness. Protriptyline (Triptil) given at bedtime may increase the respiratory drive and improve upper airway muscle tone. Medroxyprogesterone acetate  (Provera) and acetazolamide (Diamox) have been used for sleep apnea associated with chronic alveolar hypo ventilation, but their benefits have not been well established. The patient must understand that these medications are not a substitute for CPAP or BiPAP. Administration of low-flow nasal oxygen at night can relieve hypoxemia in some patients but has little effect on the frequency or severity of apnea. Further studies on the effectiveness of pharmacologic therapy are needed.

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