Screening Sleep Apnea with Pulse Oximeters
Pulse oximetry, along with a clinical score, is an effective screening tool for sleep apnea. This approach, though not as accurate as polysomnography, is much simpler, low cost and can be done at home by the patient.
Polysomnography is performed in a sleep laboratory and a patient is required to stay overnight. The test monitors various physiological factors during sleep, including brain electrical activity, eye and jaw muscle movement, leg muscle movement, airflow, respiratory effort, EKG, and oxygen saturation. These tests are to determine the frequency of apneas during sleep and the body's reaction to the sleep apnea.
Apnea-hypopnea index, or AHI, is an index used to assess the severity of sleep apnea based on the total number of complete cessations (apnea) and partial obstructions (hypopnea) of breathing occurring per hour of sleep. These pauses in breathing must last for 10 seconds and are associated with a decrease in oxygenation of the blood. In general, the AHI can be used to classify the severity of disease (mild 5-15, moderate 15-30, and severe greater than 30).
According to a sleep apnea screening study performed by Adrian Williams and his colleagues, positive oximeter readings will show the existence of sleep apnea; together with a clinical score, false negatives can be drastically reduced. False-negatives can largely be explained by their less sever disease, as evidenced by fewer and shorter apneas. The study concluded that patients with positive oximeter readings or clinical scores of 3 or higher would indicate the presence of sleep apnea. The researchers also recommended repeating the pulse oximeter measurements over multiple nights to increase the accuracy.
Other criterion for screening sleep apnea using clinical data were studied and published. The studies had shown encouraging results.
The clinical score consists of five components and each component has a score of one. These components are :
- Loud and habitual snoring
- Interrupted breathing
- Excessive daytime sleepiness
- Body mass index greater than 25
- Use of hypotensive medications or blood pressure greater or equal to 140/90
The first two components are as reported by patient's spouse or family members. Examples of excess daytime sleepiness are: napping while driving, and difficulty in staying awake. One can also use the Epworth Sleepiness Scale.
The final clinical score is obtained by adding all the scores with a possible maximum of five.
Pulse oximeter readings can be obtained with a wrist or handheld pulse oximeter which can take measurements continuously over the night. The readings follow three different patterns :
- Positive: Cyclical changes with significant oxygen saturation changes
- Negative: Steady readings with little variations during the entire sleep
- Indeterminate: Frequent fluctuation within 4% range regardless of level of saturation
Significant oxygen saturation change is defined as a drop in oxygen saturation of greater or equal to 4 percent and to a level of 90% or below. Each series of changes represents an apnea episode.
Research has shown that obstructive sleep apnea changes heart rate dynamics. During periods of prolonged obstructive sleep apnea, the heart rate typically shows cyclic fluctuation associated with the apneic phase and the resumption of breathing. By analyzing the heart rate, a study has shown that obstructive sleep apnea could be detected in over 93% of the test cases. For more information on this topic, see Sleep Apnea, Cardiac Arrhythmias, and Sudden Death.
The Epworth Sleepiness Scale is a measure on how tired you are and reflects the amount and quality of sleep you are getting. Enter a score for each situation according to the following criterion :
- 0: no chance of dozing
- 1: slight chance of dozing
- 2: moderate chance of dozing
- 3: high chance of dozing
|Sitting and reading|
|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 traffic|
If your total score is 6 or under, you are doing well and deserve a pat on the back; if your score is 7 or 8, you are average; if your score is 9 and above, you have a problem and should seek help.