Obstructive Sleep Apnoea (OSA) has long been known to be a common condition worldwide, but data from a recent study suggests that OSA may be even more prevalent in Singapore than previously suspected. A cross-sectional population study of adults from the Singapore Health Study 2012 cohort found that 30.5% of the sample population suffered from moderate to severe sleep disordered breathing, with 91% of these subjects remaining undiagnosed and untreated.

RISK FACTORS

With increasing rates of obesity and the ageing of our population, both major risk factors for OSA ¹, the incidence of OSA is expected to rise in tandem. Thus, while it remains a major under-recognised problem, OSA may potentially become a healthcare problem of epidemic proportions in Singapore.

SYMPTOMS

Patients with OSA suffer from severe snoring, and repetitive collapse and obstruction of their upper airway during sleep. This results in recurrent reduction or termination of airflow to the lungs, 30 times per hour or more in severe cases. This causes recurrent hypoxemia with sympathetic activation and sleep disruption.

As a result, OSA patients typically present with excessive daytime sleepiness as they are unable to obtain good quality sleep no matter how long they sleep, and often wake feeling tired and unrefreshed.

OSA patients usually snore, often very loudly, and may be witnessed to have apnoeic episodes during sleep which are associated with choking or grunting noises. They often wake up with a very dry mouth and headaches.

Nocturia and erectile dysfunction (in males) are common, and some OSA patients (especially females) may paradoxically complain of sleep onset or sleep maintenance insomnia due to recurrent sleep disruption caused by apnoeic events.

THE PATIENT PROFILE

OSA sufferers are more likely to be male, overweight and in the middle to older age group. Certain craniofacial features commonly seen in the local Asian population, such as a small, receding mandible or maxillary hypoplasia may also contribute to the higher incidence of OSA locally.

Data from a large local sample of OSA patients also suggests that ethnicity may be important. After accounting for the effects of body weight, the local Chinese population seems to be at an increased risk of OSA followed by the Malays and Indians respectively, possibly due to the higher prevalence of craniofacial restriction seen in the Chinese population ².

Obtaining good quality sleep of sufficient duration is of paramount importance to our mental and physical well-being, as many of our body’s metabolic and homeostatic functions are most effective and efficient while we are asleep.

Untreated OSA has been shown to be associated with poor mood, memory and concentration. OSA also increases the risk of industrial and driving accidents as well as a host of medical complications including ischaemic heart disease, heart failure, stroke, hypertension, diabetes as well as many cancers.

Indeed, the prevalence of OSA in certain medical conditions such as end-stage renal failure, heart failure, refractory hypertension and stroke exceeds 50% or more.

That is why many society guidelines, such as those for hypertension and stroke, now recommend maintaining a high index of suspicion for OSA and having a low threshold to refer a patient for a sleep study and possible OSA treatment if indicated ³.

WHEN TO REFER

If OSA is suspected, General Practitioners or other specialists may refer patients to a specialist centre such as the Sing- Health Duke-NUS Sleep Centre for an assessment.

Where to refer
The SingHealth Duke-NUS Sleep Centre which sees patients across six clinical sites across SingHealth institutions, is the largest multidisciplinary sleep service in Singapore and is staffed by specialists from ENT Surgery, Respiratory Medicine, Neurology, Psychiatry, Psychology and Dentistry who have all undergone further specialised training in the field of Sleep Medicine locally and abroad.

The Singapore General Hospital and Changi General Hospital sites are also amongst the few sleep centres in Asia outside of Australia to have obtained the prestigious Australasian Sleep Association (ASA)/National Association of Testing Authorities, Australia (NATA) accreditation, which is a testament to its technical competence and commitment to quality care for its patients.

DIAGNOSIS

After an initial clinic assessment at the SingHealth Duke-NUS Sleep Centre, patients usually proceed to have a sleep study, which may be performed as an inpatient polysomnography over 1-2 nights utilising multiple channels of monitoring including video EEG, cardiorespiratory signals, abdominal and thoracic movement and EMG.

Alternatively, outpatient sleep studies can also be done in the patients’ own homes albeit with a more limited range of monitoring (e.g. cardiorespiratory and oximetry only in the case of Apnealink device or oximetry with pulse waveform analysis with the WatchPAT device). However, these devices should only be used for selected patients.

Once the sleep study is analysed and reported, a personalised management plan for each OSA patient will then be made by the attending sleep specialist, who needs to take into consideration the type and severity of the sleep disordered breathing, patient’s age, BMI, craniofacial morphology, comorbidities and symptom severity before deciding on the best modality of treatment, which may include CPAP, oral appliances, positional therapy or various surgical modalities.

Hence, having access to a multidisciplinary sleep clinic is crucial for obtaining the best personalised care for any patient with OSA.

TREATMENT

The CPAP Therapy
Generally, Continuous Positive Airway Pressure (CPAP) therapy remains the most effective treatment for OSA and should be offered to all symptomatic OSA patients. CPAP has been shown in multiple studies to reduce AHI (Apnoea Hypopnoea Index, a marker of OSA severity), improve cognitive function, sleepiness and blood pressure.

Although observational studies have suggested a decreased risk of cardiovascular events in patients with severe OSA who are adherent to treatment, recent RCTs (Sleep Apnoea Cardiovascular Endpoints [SAVE] ⁴ and Randomised Intervention with CPAP in Coronary Artery Disease and Sleep Apnoea [RICCADSA] ⁵) did not show any cardiovascular benefit of CPAP treatment in patients with OSA who had preexisting cardiovascular disease and minimal sleepiness.

An important limitation of both studies was that adherence to the use of continuous positive airway pressure was below accepted guidelines for adequate use (mean adherence of less than 4 hours per night) and patients with significant sleepiness or severe nocturnal hypoxemia were excluded from the studies.

Hence, CPAP should not be offered purely for secondary prevention of cardiovascular events in OSA patients who are asymptomatic.

Also, despite significant advances in CPAP machines and interfaces in the last few years, adherence to CPAP treatment remains problematic; a recent study of OSA patients from Singapore General Hospital showed a 1 year CPAP adherence rate of only 52.6% ⁶. For patients who cannot tolerate CPAP therapy, it is very important that alternative treatment options be considered.

The Use of Oral Appliances
Oral appliances such as Mandibular Advancement Splints (MAS) are important alternatives for patients with mild to moderate OSA who are unable to tolerate CPAP therapy. MAS have been shown to improve symptoms and reduce AHI, albeit with less efficacy compared to CPAP.

However, adherence to this form of treatment is higher compared with CPAP (80%–90% v. 50%–70%); thus, in mild to moderate disease, overall treatment effectiveness may be similar to CPAP ⁷.

Not all oral appliances are equal. For e.g. ‘boil and bite’ devices available through retail pharmacies are generally poor fitting and ineffective for the treatment of OSA.

The 2015 update of the American Academy of Sleep Medicine and American Academy of Dental Sleep Medicine clinical practice guideline recommended that, for best effect, these oral appliances should be custom fitted by a dentist with extensive experience or additional training in dental sleep medicine ⁷, such as those from the National Dental Centre Singapore who are part of the SingHealth Duke-NUS Sleep Centre.

After the oral appliance has been custom fitted and jaw protrusion has been optimised, a repeat sleep test may be ordered to evaluate treatment efficacy.

Surgical Treatment Surgical treatment may be effective for a selected minority of OSA patients.

Tonsillectomy and adenoidectomy may help when tonsillar enlargement encroaches on the upper airway, particularly in paediatric patients. Adult OSA patients with severe tonsillar hypertrophy and minimal palatal or tongue base obstruction may also benefit from adenotonsillectomy ⁸.

For OSA patients who have failed treatment with CPAP or MAS, Maxillomandibular Advancement surgery (MMA), with or without genial tubercle advancement, may be an option. MMA is an invasive surgical procedure that has shown good efficacy but carries a significant risk of morbidity ⁹.

Multi-level or stepwise surgery (MLS) to target narrowing of multiple sites in the upper airway has been associated with improved outcomes in the treatment of OSA, but this benefit is largely supported by Level 4 evidence.

Laser-assisted uvuloplasty or uvulopalatopharyngoplasty (UPPP) are unreliable for reducing the AHI or improving patient outcomes, and are not recommended as sole procedures for the treatment of OSA ¹⁰.

Bariatric surgery may also be a good surgical treatment option for severely obese OSA patients as it has been shown to result in dramatic improvements in AHI as well as other metabolic paramaters (e.g. glycaemic and blood pressure control) for those patients who manage to lose weight successfully ¹¹.

For optimal outcomes, patients being considered for any type of upper airway or Bariatric surgery should be carefully assessed and managed at an expert surgical unit with high volumes, such as the ENT/Dental service of the SingHealth Duke-NUS Sleep Centre and the Bariatric Clinic at the LIFE Centre in SGH.

Finally, a prospective multicentre cohort study has proven the safety and efficacy of an implantable hyperglossal nerve stimulator for the treatment of patients with moderate to severe OSA who have failed CPAP therapy. Unlike traditional CPAP which functions as a pneumatic splint for the upper airway, upper airway stimulation maintains upper airway patency by augmenting the neural drive supplying the pharyngeal dilator muscles.

In this study, there was a 68% reduction in the AHI (29 to 9 events/h) at the 12-month follow-up interval. Similar improvements were seen in the Epworth Sleepiness Scale (ESS) and the Functional Outcomes of Sleep Questionnaire (FOSQ).

Adverse events were few and usually minor ¹². This treatment is currently only approved for clinical use in the USA and certain European countries but not in Singapore.

In summary, OSA is surprisingly prevalent in Singapore and incidence rates are expected to rise due to increasing rates of obesity and the ageing population. Most patients with OSA remain undiagnosed and untreated, which contributes significantly to the burden of chronic disease in Singapore, especially due to the association between OSA and many other cardiovascular and metabolic diseases.

Healthcare practitioners need to be vigilant and refer patients with suspected OSA for further assessment and treatment preferably at a specialist multidisciplinary sleep service.

CPAP remains the current treatment of choice for most OSA patients as it has proven efficacy in reducing AHI and improving symptoms. Patients who fail CPAP therapy may benefit from alternative options such as MAS, adenotonsillectomy, multi-level surgery or Bariatric Surgery, but patient selection is key to treatment success.

TAKE HOME MESSAGES

• 1/3 of adult Singaporeans may suffer from moderate to severe OSA with the majority being undiagnosed and untreated.
• Screening for OSA may be indicated in patients with ischaemic stroke or TIA and difficult to control hypertension.
• CPAP remains the treatment of choice for most patients with OSA with proven efficacy, but compliance rates are low.
• For a minority of OSA patients, Oral appliances and various surgical modalities are also effective treatment options but patient selection and a multidisciplinary approach are key to success.

GPs can call for appointments through the GP Appointment Hotline at 6321 4402 for more information.

By: Dr Leow Leong Chai, Consultant, Respiratory and Sleep Physician Department of Respiratory and Critical Care Medicine, Sleep Disorders Unit, Singapore General Hospital; SingHealth Duke-NUS Sleep Centre

Dr. Leow Leong Chai graduated with degree in medicine from the University of Calgary in Canada before completing postgraduate specialist training in Sleep and Respiratory Medicine in New Zealand. He moved to Singapore in September 2013 and started work as a Consultant at the Department of Respiratory and Critical Care Medicine as well as the Sleep Centre here at the Singapore General Hospital.

Apart from his work in Respiratory Medicine, he has a special interest in Sleep Medicine and Chronic Non-Invasive Ventilation(NIV), and runs the Chronic NIV service in SGH, the largest such service in Singapore. He manages patients with a wide range of Respiratory conditions such as chronic cough, asthma, COPD and bronchiectasis, and Sleep Disorders ranging from obstructive sleep apnoea, circadian rhythm disorders to narcolepsy and chronic respiratory failure.

He has published research on Vitamin D and respiratory tract infections as well as cardiac biomarkers in obstructive sleep apnoea. He is currently involved in research on CPAP interfaces and the use of AutoPAP in selected CPAP populations.

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