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Obstructive sleep apnoea: what you need to know

 - Obstructive sleep apnoea (OSA) is common, but is only recognised if healthcare workers know what to look out for
 - Obstructive sleep apnoea presents with sleepiness, snoring, and witnessed pauses in the breathing when asleep and tends to occur in overweight individuals
 - Obstructive sleep apnoea is easily treated with continuous positive airway pressure (CPAP), which is highly effective, well tolerated and abolishes symptoms within a few days
 

Quarter of a century ago very few people had heard of obstructive sleep apnoea (OSA), and those who had certainly did not appreciate how widespread and significant the problem would turn out to be. People now know that OSA is the more severe end of the spectrum of snoring, where instead of the upper airway (pharynx) merely vibrating due to it narrowing, it partially or completely blocks breathing during sleep. These blocked breathing episodes, or apnoeas, can only be ended by the sufferer awakening from sleep, nearly always far too briefly for the patient to be aware they have been woken. As the condition worsens, these apnoeas and attendant awakenings become more and more frequent and, at their worst, the patient wakes at least every minute throughout the night, such that they cannot sleep and breathe at the same time.

As can be imagined, one of the main symptoms is excessive daytime sleepiness, for which the patient cannot usually provide an explanation. Therefore, because the sufferer is usually quite unaware that they are being partially woken repeatedly throughout the night, it may take years for the condition to be diagnosed.


Once a sufferer has significant symptoms, obstructive sleep apnoea (OSA) becomes known as obstructive sleep apnoea syndrome (OSAS). It is often the patient's partner who recognises what is going on and encourages presentation to their GP. The combination of heavy snoring, stopping breathing episodes while asleep, and excessive daytime sleepiness is the hallmark triad of obstructive sleep apnoea syndrome.

Other symptoms may include poor memory (probably due to insufficient attention when receiving information), waking with occasional choking episodes, nocturia, nocturnal acid reflux, nocturnal sweating, and restless sleep.1

Most people develop a minor degree of airway narrowing behind the tongue as they fall asleep because the muscles holding open the pharynx partially relax. The reasons the airway becomes threatened, and can finally completely close, are complex. However, we know that the most common risk factor is excess body weight,2 particularly upper body obesity, making the neck circumference (or collar size) the most predictive obesity measure for sleep apnoea. A collar size of 17 inches or more greatly increases the probability of sleep apnoea.

Since not all obese individuals have sleep apnoea, there are of course other factors. Probably the second most important risk factor is subtle differences in the shape of the lower face, usually under-development, or backwards displacement, of the lower jaw. This is sometimes evidenced by overcrowded lower teeth, with extractions as a youngster to improve dental appearance; other factors include enlarged tonsils, particularly in young children.3 However there are some hormonal abnormalities, such as hypothyroidism and acromegaly (increased secretion of growth hormone) that can precipitate obstructive sleep apnoea. It has been estimated that significant obstructive sleep apnoea syndrome probably affects 1-2% of middle-aged men (prevalence is about a third of this in women) and that only about one fifth of sufferers have yet been recognised and treated. Exact estimates will vary depending on the prevalence of obesity and thresholds used for the definition.


 
 

Identifying these patients

Patients with obstructive sleep apnoea usually complain of excessive daytime sleepiness, but will often initially refer to this as 'tiredness'. In reality, tiredness is a sense of exhaustion without necessarily wanting to go to sleep, whereas sleepiness indicates that whenever the individual's attention wanes, they will tend to nod off. Therefore when taking a patient's history, it is important to clearly differentiate sleepiness from tiredness. This is in contrast to fatigue syndromes (often referred to as 'tired all the time', or TATT), where the patient will usually complain of tiredness and not sleepiness at all. Only occasionally do some individuals, particularly middle-aged women, describe their primary symptom of OSA as tiredness rather than sleepiness.

Heavy snoring and witnessed pauses in breathing are commonly reported with OSA, with snoring being present in virtually 100% of patients. However, if the patient sleeps alone, this may not be known. Unless obstructive sleep apnoea is thought of when a patient presents with sleepiness, snoring, or both, it will of course remain unrecognised, and an opportunity to greatly improve somebody's quality of life and overall health will be missed.

There are various tools that have been designed to help recognise these patients and assess the severity of any sleep apnoea. The Epworth sleepiness scale (ESS), or score (see Box 1), is a way of assessing daytime sleepiness.4 It consists of eight questions set in variously stimulating circumstances about the likelihood of nodding off. Each question is scored zero to three, giving a total score varying between zero and 24. It is well validated, but open to individual interpretation and is therefore only a tool, and not an absolute measure of a patient's sleepiness. The average score for a normal population is about six; up to nine is regarded as within normal limits, and over nine is regarded as excessive daytime sleepiness. These thresholds are very arbitrary; interestingly many people with fatigue syndromes score very low on the ESS, as they often get more than enough sleep.

In addition to measures of sleepiness, there are various scores to asses the likelihood of there being any OSA. The OSA50 (see Box 2) is the simplest and has been shown to be reasonably successful at identifying patients with sleep apnoea,5 although once again it is only a tool and should not be regarded as absolute. A more comprehensive score, the STOPBANG (snoring, tiredness during daytime, observed apnea, high blood pressure, body mass index, age, neck circumference, gender) questionnaire (see Box 3) is also fairly well validated,6 but probably has quite a high false positive rate in a relatively unselected population. Ultimately the recognition of patients with obstructive sleep apnoea syndrome requires awareness and good history taking.


Once there is a clinical suspicion of obstructive sleep apnoea syndrome, then some form of sleep study is appropriate to prove the diagnosis and measure its severity. Sleep studies range from simple overnight measures of oxygen saturation and pulse rate using a pulse oximeter (see Figure 1), to full scale polysomnography requiring extensive physiological measurements (which in the vast majority of cases is not required). A good compromise is the measurement of a limited number of relatively simple signals, in addition to oximetry, such as snoring, airflow at the nose/mouth, body position, and respiratory movements (from the chest and/or abdomen). Such studies are now well established and increasingly being carried out in the patient's home.

The prevalence of OSA means that a large number of patients need sleep studies with the result that secondary care services are being overwhelmed. Primary care has a major role to play in conditions with a high prevalence of OSA, for example the management of hypertension and diabetes. There are now general practices that have their own sleep apnoea monitors (or utilise external partners), and are organising their own sleep studies. This is often on behalf of several practices as part of the preliminary triage before onward referral to a sleep unit; this practice must increase if patients who will benefit from having their OSAS treated are to be identified.

What are the treatment options?

Obesity is the commonest risk factor, so losing weight is an important treatment option that has been proven to work well. However, as with any other illnesses associated with obesity, patients find it extremely difficult to lose weight and particularly to maintain any weight lost. If the patient is significantly symptomatic, it is not enough to simply tell them to go away and lose weight.



One of the main consequences of concern resulting from the excessive daytime sleepiness is of course road traffic accidents, with increased risks variously estimated to be three to six times above average.7 Treatment options should be rapidly effective in order to reduce this risk, and allow potentially unsafe drivers safely back on the road as soon as possible, with no delay introduced by awaiting the results of a weight loss program, which should only aim for slow weight loss anyway. Sleep units should be providing fast-track services to commercial drivers to ensure they are confident to come forward without fear of losing their livelihood.

The most successful treatment is continuous positive airway pressure (CPAP) applied to the upper airway. The concept behind this treatment is that by applying gentle air pressure to the upper airway while asleep, the pharynx is held open; this abolishes the snoring, the obstructed breathing, and prevents the recurrent awakenings. The positive pressure is applied via either a nasal or face mask, and, although rather unattractive, is extraordinarily effective and totally non-invasive. It has been estimated that over 200,000 patients in the UK with obstructive sleep apnoea use CPAP regularly to good effect. Compliance rates are extraordinarily high, with anywhere between 70-90% of patients still using CPAP at 10 years.8

The National Institute for Health and Care Excellence (NICE) fully supported the use of CPAP in patients with significant symptoms, and all healthcare purchasers have to commission services to look after patients with obstructive sleep apnoea syndrome; after a few years the reduced health costs more than pay for the CPAP treatment.9 Establishing a patient on CPAP requires significant skills to achieve good compliance and thus full relief of symptoms. NICE recommended that most of the care of these patients, particularly the provision and monitoring of CPAP, should be provided by a specialist unit.

Less effective, but sometimes more acceptable, treatments include the use of intra-oral appliances that hold the lower jaw forward during sleep. These devices work similarly to holding the lower jaw forward in an unconscious patient whose airway is compromised. There are many different types that have in general been poorly researched, but a comfortable device (that advances the lower jaw by 5-10mm) clearly has a role in mild to moderate disease, when CPAP is truly unacceptable or poorly tolerated. Surgical treatments have failed to deliver their early promise and are now rarely used. The only truly successful surgical solution for many cases of obstructive sleep apnoea is one of the bariatric operations now being provided for some patients with morbid obesity (BMI>40) who have failed to lose weight despite pro-active weight reduction programmes.

What are the associated risks of sleep apnoea?

There is no doubt that hypertension, cardiovascular disease, type 2 diabetes, and other components of the metabolic syndrome are much more common in patients with obstructive sleep apnoea. However, because patients with obstructive sleep apnoea and patients with the metabolic syndrome share upper body obesity as the major risk factor, it has been extremely difficult to prove that obstructive sleep apnoea on its own is a significant risk factor for vascular complications, although evidence from uncontrolled trials is compelling.10 There is now good evidence, though, that obstructive sleep apnoea is an independent risk factor for hypertension11 and therefore presumably for the consequences of hypertension. Perhaps what is more important when considering the association between obstructive sleep apnoea and these co-morbidities, is to appreciate that the prevalence of sleep apnoea is going to be very much higher among such patients. Indeed in some studies the prevalence of sleep apnoea has been as high as 50% in patients with type 2 diabetes and secondary complications, such as retinopathy.12 Therefore a higher level of suspicion for sleep apnoea is required when dealing with these patients. The routine use of simple questions about sleepiness and snoring, coupled with a neck circumference measure, would be a simple way of identifying many of these patients.

Case history

Ralph had previously presented to his GP many times in the past, complaining of being tired all the time. He had a recent history of depression and, after a series of normal blood tests (including thyroid function), his symptoms were thought to be mainly due to a recurrence of the depression. The tiredness had led to considerable problems at work, as he had been found asleep over his desk on a number of occasions, consequently his job was at risk with threats of an early retirement at only 55. Over a year or so he put on more weight and his symptoms had worsened. Things came to a head when he strayed onto the hard shoulder on the motorway and was only prevented from having an accident due to his wife's timely intervention. Following seeing his GP again, further blood tests were organised. The practice nurse taking his blood knew about sleep apnoea, and asked the right questions about snoring and apnoeic episodes (his OSA50 was the maximum of 10, and his ESS was 14); it transpired that his wife has long since stopped sleeping in the same room for this very reason. He was referred for a sleep study which showed severe OSA, with over 40 apnoeic episodes per hour of sleep. He was established on CPAP with rapid resolution of all the 'tiredness' which had really been sleepiness all along, his depression disappeared, as the threat to his employment was removed.

References
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