Medical Grand Rounds

Sleep apnea ABCs: Airway, breathing, circulation

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Modifiable risk factors

Obesity (body mass index ≥ 30 kg/m2) is a firmly established risk factor, but not all obese patients develop obstructive sleep apnea, and not all people with sleep apnea are obese.

Obesity increases risk by altering the geometry and function of the upper airway, increasing collapsibility. The changes are particularly pronounced in the lateral aspects of the pharynx.35

Obesity also affects respiratory drive, likely in part from leptin resistance. Load compensation is another contributing factor: the increased mass in the thorax and abdomen increases the work of breathing and reduces functional residual capacity, increasing oxygen demands and leading to atelectasis and ventilation-perfusion mismatch.

Although obesity is an important risk factor, it is important to recognize that obesity is not the only one to consider: most people with an apnea-hypopnea index of 5 or greater are not obese. The relationship between body mass index and sleep apnea is weaker in children and in the elderly, probably because other risk factors are more pronounced.36

Craniofacial structural abnormalities such as retrognathia (abnormal posterior position of the mandible) and micrognathia (undersized mandible) can increase the risk of OSA because of a resulting posteriorly displaced genioglossus muscle. Other conditions can alter chemosensitivity, affecting the pH and carbon dioxide level of the blood and therefore affecting ventilatory control mechanisms, making the person more prone to developing sleep apnea. Children and young adults may have tonsillar tissue that obstructs the airway.

The site of obstruction can be behind the palate (retropalatal), behind the tongue (retroglossal), or below the pharynx (hypopharyngeal). This helps explain why positive air way pressure—unlike surgery, which addresses a specific area—is often successful, as it serves to splint or treat all aspects of the airway.

FATIGUE, SLEEPINESS, SNORING, RESTLESS SLEEP

Sleep apnea can result in presentation of multiple signs and symptoms (Table 1).

Daytime sleepiness and fatigue are the most common symptoms. Although nonspecific, they are often quite pronounced. Two short questionnaires—the Epworth Sleepiness Scale37 and the Fatigue Severity Scale—can help distinguish between these two symptoms and assess their impact on a patient’s daily life. In the Epworth Sleepiness Scale, the patient rates his or her chance of dozing on a 4-point scale (0 = would never doze, to 3 = high chance of dozing) in eight situations:

  • Sitting and reading
  • Watching television
  • Sitting inactive in a public place
  • As a passenger in a car for an hour without a break
  • Lying down to rest in the afternoon
  • Sitting and talking to someone
  • Sitting quietly after a lunch without alcohol
  • In a car while stopped for a few minutes in traffic.

A score of 10 or more is consistent with significant subjective sleepiness.

The Fatigue Severity Scale assesses the impact of fatigue on daily living.

Snoring is a common and specific symptom of sleep apnea; however, not all patients who snore have OSA.

Restlessness during sleep is very common—patients may disturb their bed partner by moving around a lot during sleep or report that the sheets are “all over the place” by morning.

Nocturia can also be a sign of sleep apnea and can contribute to sleep fragmentation. A proposed mechanism of this symptom includes alterations of intrathoracic pressure resulting in atrial stretch, which release atrial natriuretic peptide, leading to nocturia. Treating with CPAP has been found to reduce levels of atrial natriuretic peptide, contributing to better sleep.38

Morning headache may occur and is likely related to increased CO2 levels, which appear to culminate in the morning hours. End-tidal or transcutaneous CO2 monitoring during polysomnography can help elucidate the presence of sleep-related hypoventilation.

Libido is often diminished and can actually be improved with CPAP. This is therefore an important point to discuss with patients, as improved libido can often serve as an incentive for adherence to OSA treatment.

Insomnia exists in about 15% of patients, primarily as a result of sleep apnea-related with treatment.

Sweating, particularly forehead sweating associated with sleep apnea, more commonly occurs in children.

The STOP-BANG questionnaire (Table 2)39 was primarily validated in preoperative anesthesia testing. However, because of its ease of use and favorable performance characteristics, it is increasingly used to predict the likelihood of finding OSA before polysomnography. A score of 3 or more has a sensitivity of 93%.

PHYSICAL EXAMINATION PROVIDES CLUES

Although the physical examination may be normal, certain findings indicate risk (Table 3). Obesity alone is not an accepted indication for polysomnography unless there are concomitant worrisome signs or symptoms. Of note, those who are morbidly obese (BMI > 40 kg/m2) have a prevalence of sleep apnea greater than 70%.

The classification by Friedman et al40 provides an indicator of risk. The patient is examined with the mouth opened wide and the tongue in a neutral natural position. Grades:

  • I—Entire uvula and tonsils are visible
  • II—Entire uvula is visible, but tonsils are not
  • III—Soft palate is visible, but uvula is not
  • IV—Only the hard palate is visible.

Especially in children and young adults, enlarged tonsils (or “kissing tonsils”) and a boggy edematous uvula set the stage for obstructive sleep apnea.

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