Approach to the Patient with Obstructive Sleep Apnea

Transient episodes of breathing cessation (apnea) or a marked reduction in airflow (hypopnea) are common during sleep. Among adults, it is estimated that as many as 24% of men and 9% of women have five or more episodes of apnea or hypopnea per hour of sleep, which is the consensus threshold definition for obstructive sleep apnea (OSA). Moderate to severe OSA represents a significant threat to a patient’s well-being, associated not only with poor functioning due to excessive daytime sleepiness, but also with increased cardiovascular morbidity and mortality and serious automobile accidents.

Despite its high prevalence, considerable public awareness, and a growing appreciation for its potentially serious consequences, OSA is often overlooked. Symptoms such as daytime tiredness and snoring may be mistaken for normal phenomena of everyday life. Many patients still go undiagnosed and untreated.

Given the prevalence of OSA, its serious consequences, and the availability of effective treatment, it is essential that the primary care team be on the lookout for the condition and capable of initiating the workup. Advances in diagnosis and treatment are making for a more primary care-centric approach to the problem, which primary care teams should become familiar with, especially in areas where access to specialized sleep evaluation and management are not available.

PATHOPHYSIOLOGY AND CLINICAL PRESENTATION(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 and 21)

Definitions and Community Prevalences

OSA is formally defined as an apnea-hypopnea index (AHI) ≥ five per hour, which is calculated from polysomnography results, where the AHI is the total number of episodes of apnea (cessation of breathing for >10 seconds) or hypopnea (30% reduction in respiratory airflow with a 4% decrease in oxygen saturation) divided by hours of sleep. Mild OSA is defined as an AHI of 5 to 15 per hour, moderate OSA of 15 to 30 per hour, and severe OSA of ≥30 per hour. Using the threshold definition of OSA (an AHI of ≥5) in community settings reveals a prevalence of between 9% and 17%, with rates higher among men. Adding daytime sleepiness to criteria for sleep apnea defines the obstructive sleep apnea syndrome (OSAS); its prevalence is about 6%, the same as it is for moderate or severe OSA. Because of the potentially serious health consequences associated with moderate to severe OSA (especially with AHG <20) and the fact that the index does not correlate well with the severity of symptoms, many argue that the definition of OSA should not require daytime somnolence.

Mechanisms

Sleep apnea may result from central suppression of respiration (as occurs with congestive heart failure and carbon dioxide retention) or from upper airway obstruction. In the former condition (central sleep apnea), air flow ceases because of the loss of central respiratory drive; in the latter (obstructive sleep apnea), air flow ceases because of soft tissue obstruction despite chest and abdominal respiratory efforts. OSA is the most common form of sleep apnea encountered in the office setting. Upper airway resistance syndrome is an intermediate category, in which air flow is maintained by increased respiratory effort despite partial airway obstruction.

OSA occurs when the patency of the nasopharyngeal airway becomes insufficient during sleep. Anatomic risk factors include nuchal obesity (cricothyroid neck circumference >17 inches for men, >16 inches for women), deviated septum, nasal polyps, enlarged uvula and soft palate, small chin with deep overbite, enlarged tonsils, and hypertrophy of the lateral pharyngeal musculature.

Although obesity appears to be a major factor (causing fat deposition in the tongue and pharyngeal tissues), persons who are not obese are also at risk if they manifest other anatomic risk factors. Pharyngeal edema may mediate the increased risk of OSA among patients with congestive heart failure. In addition to being anatomically predisposed, patients with OSA appear to be unable to sustain sufficient oropharyngeal muscle dilator activity during sleep to prevent airway collapse during the negative pressure of inspiration. The suppressive effects of alcohol and sedatives on such neuromuscular function may explain their role in exacerbating OSA. Hypothyroidism may be a risk factor.

When the obstruction is mild and not physiologically disturbing, snoring is the only manifestation, and sleep is not interrupted. With increasing degrees of obstruction, snoring becomes louder and compensatory respiratory efforts are triggered, causing electroencephalographically detectable arousals from sleep. Frequent arousals during the night disrupt normal sleep “architecture” and result in daytime sleepiness. In the upper airway resistance syndrome, near-normal air flow is maintained by compensatory respiratory efforts but at the cost of sleep arousals. More severe degrees of obstruction can lead to hypopnea (30% to 50% reduction in air flow with oxygen desaturation 4% or greater) or apnea (cessation of air flow for at least 10 seconds). The more severe and more prolonged the obstruction, the more likely and more severe are blood oxygen desaturation and hypoxemia, consequences of ventilation-perfusion mismatching as a result of the perfused lung not being adequately ventilated.

The adverse cardiovascular consequences of sleep apnea are related to hypoxemia. The decline in arterial oxygen increases pulmonary vascular resistance; when severe and chronic, it can lead to sustained pulmonary hypertension and ultimately cor pulmonale, particularly in persons with underlying chronic obstructive pulmonary disease or morbid obesity. Airway obstruction, episodes of apnea, and hypoxemia trigger compensatory increases not only in ventilatory effort but also in sympathetic tone, leading to vascular endothelial dysfunction and a rise in inflammatory markers, believed contributing to the independent association between severe degrees of sleep apnea and risks of hypertension, stroke, coronary disease, and cardiac death.

The increase in sympathetic tone resulting from hypoxemia and frequent arousals is also believed linked to the observed independent association of OSA with type 2 diabetes. Purported mechanisms include increased cortisol secretion and other adverse metabolic consequences of hypothalamic-pituitary-adrenal axis stimulation. Risk of diabetes appears proportional to OSA severity.

Severe degrees of OSA can also lead to hypercarbia and central suppression of respiration, as seen in persons with the obesity-hypoventilation (pickwickian) syndrome. Dysmenorrhea and amenorrhea are consequences in women of reproductive age.

The disturbance in sleep caused by OSA may impair cognition and psychomotor performance. In severe sleep apnea, hypersomnolence develops, markedly increasing the risk for injuries during work and driving. The risk ratio for traffic accidents increases to 6.3 and appears to be independent of other risk factors.

Clinical Presentations

Often, the patient presents at the insistence of a bed partner who is bothered or worried by loud and intermittent snoring, disturbed or restless sleep, periods of irregular or halted breathing, and choking or gasping. Patients presenting with OSA typically complain of excessive daytime sleepiness; they may note falling asleep at work or at a meeting. Women are somewhat more likely to report chronic fatigue. Patients find that they awaken not feeling refreshed and may have a morning headache. Work performance may be suffering, and the history of a work-related or automobile accident resulting from sleepiness may be elicited. Driving performance is excessively impaired by alcohol intake and sleep restriction. Family and friends may note a personality change. Obesity is common but is not a necessary part of the clinical presentation; approximately 70% of patients with sleep apnea are obese and have manifestations of the metabolic syndrome. Nearly half of premenopausal women with disordered nocturnal breathing are thin but have another contributing anatomic feature, such as a severe overbite or a high hard palate. A positive family history is noted, usually in persons with a contributing anatomic factor or obesity.

DIFFERENTIAL DIAGNOSIS (6,10)

Because OSA may present as daytime tiredness, it must be differentiated from other causes of chronic fatigue (see Chapter 8 for detailed differential diagnosis). In patients who present with interrupted sleep, other sleep disturbances deserve consideration (see Chapter 232). In those whose presentation is predominantly one of difficulty in breathing at night, heart failure (see Chapter 32), chronic obstructive lung disease (see Chapter 47), and other causes of snoring (see Chapter 223) should be considered. Hypothyroidism (see Chapter 104) and acromegaly have been associated with sleep apnea. Studies find that in the absence of obesity (BMI < 25) and snoring, the posttest probability of clinically significant OSA is very low (<1%).

WORKUP (6,10,22, 23, 24, 25, 26, 27, 28, 29, 30 and 31)

Overall Approach

History and physical examination can serve to risk-stratify patients and identify those who are candidates for additional evaluation and treatment. Previously, all patients deemed at risk for sleep apnea required referral for overnight supervised polysomnography in a sleep laboratory. However, the elaborateness of such testing, limited capacity, and the large number of potential candidates led to marked delays in diagnosis and treatment and high expenditures. Emerging evidence suggests that risk stratification can identify high-probability patients who need only undergo home oximetry testing to confirm the diagnosis, obviating the need in many for overnight sleep laboratory study. In randomized trial, outcomes are similar. Such an outpatient approach has the potential to speed access to confirmatory testing, shorten time to initiation of treatment, and reduce cost of care.

History

A high index of suspicion is appropriate when a patient, whether obese or not, presents with symptoms of excessive daytime sleepiness, tiredness, or fatigue. Patients found to have symptoms suggestive of excessive daytime sleepiness (see Table 46-1) are especially good candidates for further inquiry. Historical features strongly associated with OSA include a history of habitual snoring, disruptive snoring at least three times per week, and spells of nocturnal gasping or choking. The presence of nocturnal choking or gasping has highest predictive value (likelihood ratio of 3.3). Snoring by itself does not have high discriminant value (likelihood ratio of 1.1) and must be interpreted in the
context of other symptoms. For example, minimal snoring in persons who are not overweight (BMI < 26) virtually rules out clinically significant OSA (posttest probability <1%).

TABLE 46-1 The Epworth Sleepiness Scale

How likely are you to doze off or fall asleep in the following situations, in contrast to feeling just tired? This refers to your usual way of life in recent times. Even if you have not done some of these things recently try to work out how they would have affected you.
Use the following scale to choose the most appropriate number for each situation:
0 = Would never doze
1 = Slight chance of dozing
2 = Moderate change of dozing
3 = High chance of dozing
Situation		Score
	Sitting and reading	____
	Watching TV	____
	Sitting, inactive in a public place (e.g., a theater or a meeting)	____
	As a passenger in a car for an hour without a break	____
	Lying down to rest in the afternoon when circumstances permit	____
	Sitting and talking to someone	____
	Sitting quietly after a lunch without alcohol	____
	In a car, while stopped for a few minutes in the traffic	____
Scores are from 0 to 24. Score greater than 16 indicative of a high level of daytime sleepiness and correlates with moderate to severe OSA.
Adapted from Johns MW. A new method for measuring daytime sleepiness: the Epworth Sleepiness Scale. Sleep 1991;14:541, with permission. Copyright © 1991 American Sleep Disorders Association and Sleep Research Society.

Also worth noting are any accidents, job performance difficulties, and personality changes or cognitive difficulties, especially if they occur in the context of daytime sleepiness. Additional historical and epidemiologic risk factors to take note of include marked obesity, hypothyroidism, increasing age, and regular use of sedatives or alcohol.

Physical Examination

The weight and height should be measured and the body mass index calculated; a body mass index greater than 28 kg/m² predicts increased OSA risk. Similarly, the blood pressure should be taken—hypertension is a consequence of OSA, and its presence increases pretest probability. The integument is examined for cyanosis, clubbing, and any signs of hypothyroidism (see Chapter 104). The upper airway is checked for overbite, a high hard palate, other potentially obstructing nasopharyngeal lesions (e.g., nasal polyps, tonsillar hypertrophy, large uvula), and nasopharyngeal narrowing. Nuchal obesity manifested by increased neck circumference significantly increases OSA risk, especially when the neck circumference is in excess of 48 cm (21.8 inches).

In persons with suspected severe or long-standing OSA, one should check for signs of pulmonary hypertension and cor pulmonale (e.g., right ventricular heave, loud pulmonic component of the second heart sound, jugular venous distention, leg edema).

Risk Stratification to Determine Need for Further Workup

By utilizing elements of the history and physical examination that correlate with risk of OSA, investigators have developed and validated risk-stratification instruments that can be used to guide workup. The Epworth Sleepiness Scale (commonly referred to as the ESS—see Table 46-1) helps to identify persons with significant daytime sleepiness indicative of need for further clinical inquiry, while the Sleep Apnea Clinical Score (SACS—see Tables 46-2 and 46-3) gives likelihood ratios for varying degrees of OSA, informing decisions regarding OSA testing. For example, a patient determined to be at high pretest risk for OSA might forego formal overnight sleep laboratory study in favor of home oximetry. The sensitivity of the SACS for recognition of clinically significant OSA approaches 90%, making its determination useful for identifying those who need laboratory testing.

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