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OBSTRUCTIVE SLEEP APNOEA: ASSESSMENT, OXYGEN SATURATION AND SLEEP STATES
Assessment
Although a physical examination and detailed medical history can tell a great deal about the likelihood of OSA, confirmation of the syndrome can only be done in properly equipped sleep laboratories which are now established in many large public hospitals and some private institutions. Formal sleep studies (technically referred to as polysomnography) make it possible to observe the patient in a clinical setting under the supervision of trained personnel.
Many of the functional and physiological changes mentioned previously, such as airway obstruction, hypoxaemia and irregularities of heart rate, are monitored during the study, giving investigators enough information to decide on the best course of action for the hapless snorer. Most people are apprehensive about the need for hospital admission and comprehensive testing procedures, and it is important that they be informed and reassured of the non invasive nature of these procedures. A nervous patient is likely to have a poor night\'s sleep from which little useful information can be extracted.
Oxygen saturation
Probably the single most important measure of the severity of OSA is the level to which blood oxygen falls. Blood oxygen concentration, or saturation, can be estimated quite accurately by attaching a probe to either a finger or ear lobe. A special light emitted from the probe is able to detect oxygen saturation in the blood supply of the site to which it is attached, which in turn reflects the circulating oxygen level.
Sleep states
Airway obstruction is more pronounced in deep sleep, particularly during REM, and it is therefore important to document sleep stages to confirm that the patient slept soundly, preferably with several episodes of REM. Sleep states are monitored via several electrodes which are glued to various sites on the head which detect electrical activity of the brain, eye movements and muscle tone, all of which help to define sleep states.
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GENERAL HEALTH
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