Chapter 6 Validity of sleep nasendoscopy in the investigation of sleep-related breathing disorder
1 INTRODUCTION
Croft and Pringle introduced the technique of sleep nasendoscopy for use in the assessment of snoring to aid proper case selection for surgical intervention.1
The attraction of sleep nasendoscopy lies with its ability to provide a dynamic visualization of the anatomical areas responsible for the generation of noise (snoring) or obstruction, under conditions which mimic sleep. Prior to the introduction of sleep nasendoscopy various methods including lateral cephalometry, computerized tomography and the Mueller maneuver had been used in an attempt to achieve the above objective.2
Sleep nasendoscopy has been criticized for not being a true reflection of normal physiological sleep in view of the sedation process involved. Various techniques of sedation have been used.3–5 Bolus injections of sedatives are commonly used and may lead to fluctuating blood, plasma and tissue levels leading in turn to fluctuating drug effects. The correct level of sedation is crucial to produce sufficient muscle relaxation to recreate snoring but not cause respiratory depression.3 Roblin et al. adopted a computer-controlled infusion system that employs the concept of target controlled infusion (TCI)2 using propofol as the sedating agent. Propofol has the attraction of possessing a rapid onset of action and recovery period, with minimal side effects.6 In addition it allows for standardization and reproducibility between different operators.
2 PATIENT SELECTION
Sleep nasendoscopy has the potential to be a valuable investigation for making an accurate dynamic anatomical assessment in patients with snoring and obstructive features. Determination of the anatomical site of the obstruction in this way allows an appropriate or targeted choice of treatment options to be made.1 Although commonly used, questions have been raised regarding the potential for false-positive results; that is, the production of symptoms (snoring/obstruction) in individuals with no history of sleep-disordered breathing.
During sleep endoscopy the correct level of sedation is vital to induce symptoms of snoring with or without obstruction but not cause respiratory depression.3 This window of sedation can be narrow, may differ from patient to patient and be difficult to maintain for any length of time.
3 TECHNIQUE OF SLEEP NASENDOSCOPY
The blood concentration level is increased in 2 μg/ml incremental doses and the system automatically adjusts the rate of propofol infusion to achieve the required blood concentration level. The flexible nasendoscope (Olympus P4) is introduced when the patient begins to snore; if the patient obstructs the target concentration level is reduced. In the location of obstructive sites, attention is paid to the following levels:
