Chapter 6 Validity of sleep nasendoscopy in the investigation of sleep-related breathing disorder
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.
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.
The procedure is carried out in the operating room. A size 14 G cannula is inserted into the patient’s vein. The Diprifusor TCI system (Zeneca Pharma, Wilmslow, Cheshire, UK), incorporating an electronically tagged prefilled syringe of 1% propofol, is placed into a Graseby 3500 (Graseby Medical Ltd, Watford, Herts, UK) dedicated infusion pump. The sex and weight of the patient are entered on the pump and the pump connected to the cannula. Pulse oximetry, heart rate and blood pressure are closely monitored throughout the procedure. No local anesthesia is used in the nasal cavity to avoid any anesthesia in the pharynx.
A starting concentration of 2 μg/ml of propofol is chosen and the dual microprocessor component within the pump then determines the infusion rate required to attain the desired concentration by calculating the absorption, distribution and excretion of propofol. Immediately the pump will administer a bolus dose to fill the pharmacological central compartment followed initially by a high infusion rate to compensate for drug distribution and thereafter the infusion rate decreases with time.
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:
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