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OBSTRUCTIVE SLEEP APNOEA HYPOPNEA SYNDROME – AN OVERVIEW

How do you classify severity of OSAHS?

The severity of OSAHS is determined by the apnoea/hypopnoea index (AHI), which is the number of apnoea and hypopnea per hour of sleep. It can be classified as mild, moderate and severe based on the AHI (Table 4). The minimum criteria for diagnosing OSAHS are excessive daytime sleepiness with AHI of more than 5. The use of an event frequency of more than 5 per hour as a threshold is based on epidemiologic data suggesting that significant adverse health events such as accidents, sleepiness and hypertension occur at or above this threshold.16,17 The minimal threshold value for diagnostic purpose probably varies with the age of the patient. The AHI of 1 in a child may be sufficient to diagnose OSAHS. Therefore, diagnosis and treatment should be tailored to individual patients, especially in presence of adverse physiologic and neurocognitive events.

Table 4: Classification of severity based on AHI

Apnoea hypopnoea index (AHI)

Severity of OSAHS

5-15

Mild

16-30

Moderate

>30

Severe

What are the treatment options available?

Treatment options for OSAHS are conservative, surgical and positive airway pressure. The choice of treatment should be tailored to individual patients, depending on the severity, patient’s preference and presence of comorbidities. Drugs have little role unless a known causative factor such as hypothyroidism is present.

Conservative treatment is usually directed to those with mild OSAHS without significant daytime symptoms or comorbidities. Lifestyle changes such as weight reduction, eliminating precipitating factors such as ethanol and drugs, can improve outcome. Patients with positional OSAHS are advised to adopt a lateral decubitus position or head elevation using pillows when sleeping. In some patients, the use of oral appliances such as mandibular advancement devices is effective.

Driving is a potential hazard is OSAHS, as patients may not be able to make an emergency stop due to sleepiness and reduced concentration. In some countries, regulations are in place to ensure such patients are advised to refrain from driving and to subsequently inform the relevant driving authorities, until further assessment and treatment are given. Unfortunately, such regulations are not available in Malaysia. Nevertheless, appropriate advice on driving should be given when the condition is suspected.

Continuous positive airway pressure (CPAP) is the treatment of choice for patients with moderate to severe OSAHS, and symptomatic mild OSAHS. It has been shown to improve daytime sleepiness, cognitive function, mood and quality of life.18-20 Recent studies have shown that CPAP therapy in moderate to severe disease, also improves BP control and reduces cardiovascular risk factors.21 A flow of pressurized air is delivered via a nasal or face mask to reduce the pressure difference between the upper airway and mask. This prevents closure of the upper airway. The pressure required to act as an effective ‘pneumatic splint’ varies between patients. The effective pressure can be determined by performing a repeat PSG whilst the patient is on CPAP and observe its effects. Alternatively, an auto-CPAP machine, which adjusts pressure depending on needs, can be used. In most centres, a positive clinical outcome is adequate to measure the effectiveness of treatment, without the need to repeat PSG whilst on CPAP.

CPAP therapy is widely available in Malaysia. As mentioned previously, the initiation of such therapy requires a firm diagnosis of OSAHS, based on clinical and physiological evaluation. Upon diagnosis, patients are commonly referred for an overnight trial of CPAP therapy to determine the appropriate pressures and tolerability. In some centres with good support, patients may be able to ‘borrow’ the machine for a short period, for a test drive in an acquainted home environment. This would allow the patient to familiarize usage of the machine and may improve future compliance. Purchasing a CPAP machine can be costly and ranges between RM3000 to RM8000, depending on the available functions. In some cases, with support from the attending physician, reimbursement from certain government or private agencies, use of personal long term savings, such as Employees Provident Funding (EPF) or application from social service, may assist funding.

Surgery can be considered in certain cases, when CPAP has failed or is not tolerated. Presence of bilateral tonsillar hypertrophy in symptomatic patients should prompt a referral for tonsillectomy. Other surgical approach involves resection of various parts of the upper airway, thus increasing its diameter and airflow. This includes uvulopalatopharyngoplasty (UPPP), laser-assisted uvulopalatoplasty (LAUP) and anterior mandibular osteotomy with genioglossus advancement. The success rate of surgical approach varies from 27-67%, with less well documented long-term outcome.22,23 In one study, 63% of patients with moderate OSAHS had worsening AHI post-operatively.24 The gold standard treatment is tracheostomy, whereby air entry bypasses the problematic upper airway. However, it is not without significant physical and psychological implications.

What are the complications of the condition?

Apart from the adverse events related to chronic fragmented sleep, mentioned above, various cardiovascular complications of OSAHS are documented. Studies have shown that presence of OSAHS is an independent predictor for raised BP when all confounding variables have been allowed for.17,19 In normal adults, systemic BP falls during sleep and rises on awakening.  Subjects with variability in BP associated with a normal sleep wake cycle are called ‘dippers’. In OSAHS, repeated and frequent interruption of sleep due to arousal from apnoea and hypopneoa results in a rise in BP. A significant proportion of OSAHS patients may fail to have a mean fall in BP at night and are called ‘non-dippers’.25 ‘Non-dippers’ are at increased risk of developing end-target organ damage such as left ventricular hypertrophy.26 Left ventricular hypertrophy appears to be more common in OSAHS patients and the frequency increases with severity of OSAHS.27,28 Despite evidence that treatment of OSAHS with CPAP results in a drop of 10 mmHg in both night and day time BP, it does not eliminate the need for pharmacological therapy if the need arise.29

Corpulmonale has been reported as a consequence of untreated OSAHS.30 The exact mechanism is difficult to ascertain due to many confounding factors. However, it is thought to be similar to the pathogenesis of other chronic lung disease. Other cardiovascular complications which have been reported include bradycardia-tachycardia pattern, other dysrhythmias and increased risk of coronary artery disease.

CONCLUSION

OSAHS is a condition which tends to go unrecognized and underdiagnosed. With the rising of obesity prevalence worldwide, the condition is thought to become more common in the future. It has serious effects on overall health and is potentially treatable. Careful consideration of the condition, based on complaints or risk factors, is vital to ensure referrals to the appropriate specialty to confirm the diagnosis. Evidence suggests that the mainstay of treatment for moderate to severe disease is CPAP therapy. Surgical intervention may play a role but the outcome is unpredictable and not well documented.

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