Sleep nasendoscopy

Sleep nasendoscopy (SNE) which is also known as drug induced sedation endoscopy (DISE) was pioneered at our institute.13 The beauty of this technique lies in the fact that it allows a three dimensional visualisation of the upper airway during sleep albeit drug induced. This assessment is carried out in an operating theatre setting with the help of an anaesthetist who provides sedation to the patient and closely monitors the patients cardiovascular and respiratory parameters. The sedative agents commonly used are midazolam or propofol, however in some units both the drugs are used.

Drug induced sleep is different from natural physiological sleep but one could argue that the drug used for sedation has the same effect on the different segments of the pharynx thus it would allow us to compare the proportionate obstruction caused at each anatomical level in a similar manner that may exist in natural sleep.

An audit of 2,485 procedures performed over a period of 10 years at our institute has demonstrated that SNE correlates well with apnoea-hypopnoea index and mean oxygen desaturation.14 We have also demonstrated the usefulness of SNE in predicting treatment success in snorers using MAS.15,16 Similarly, SNE has allowed site specific target selection in surgical patients and improved surgical outcomes in our group of patients undergoing laser assisted palatoplasty with or without tonsillectomy has been reported.17-19 Sleep nasendoscopy assessment of snoring is useful as it provides evaluation of the upper airway in the dynamic mode during sleep. However, numerous controversies and debates have arisen and attempts have been made to address some of these by various authors. For instance, criticisms made by Marais20, whilst comparing snorers and non-snorers, it was claimed that snoring was produced during SNE in a large number of the non-snorers and was not produced in many of the snorers. This was challenged by Berry et al21, demonstrating in their study using target controlled infusion of propofol during SNE that all their snorers and non-snorers responded as expected.

Similarly, questions and concerns that arose about test-retest reliability and of inter-rater reliability of SNE have been elegantly addressed by studies conducted by Rodriguez-Bruno et al22 and Kezirian et al23 respectively.

Bispectral index monitoring (BIS) has provided an adjunct to the assessment of sleep nasendoscopy in determining the level of sedation required for snoring assessment.24 BIS (figs. 7 & 8) monitor is a neurophysiological monitoring device which continually analyses a patient's electroencephalogram during sedation and general anaesthesia to assess the level of consciousness and depth of anaesthesia.

Fig. 7. Four sensor BIS electrode attached on patient's forehead
Fig. 8. BIS Monitor reading during Sleep Nasendoscopy

The issue of assessing the patient at the correct moment has not previously been addressed and this indeed is an important point as one has to bear in mind the pharmacology and the pharmacokinetics of the different drugs used during sedation. If the patient is assessed too early, the muscle relaxation effect of the drug may be over emphasised and if the patient is assessed too late then important anatomical aspect of the obstructive episodes may be missed. Thus the depth of sedation during which the assessment is conducted should be as close to the levels of depth of natural sleep. Evaluation only occurs as a snap shot of a patients whole sleep cycle. However, combining it with BIS values of patients undergoing natural sleep allows a more accurate assessment of sleep disordered breathing. Finally, a couple of studies have compared awake assessment with SNE in the same group of patients and advocate that SNE is superior; further highlighting the point that there is muscle tone variation in control of upper airway during wakefulness and that during obstructive episodes in sleep. It appeared that hypopharyngeal or laryngeal obstruction could be missed in up to a third of the patients if the assessment was carried out in the awake state only.25, 26

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