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.

Sleep nasendoscopy is employed as a diagnostic tool for patients with snoring problems as well as those with obstructive sleep apnea (OSA) as selected by the sleep multidisciplinary team.

3 TECHNIQUE OF SLEEP NASENDOSCOPY

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:

A video and sound recording of the sleep nasendoscopy is carried out during the procedure.

The degree of obstruction is categorized as follows.

4 SPECIFICITY AND SENSITIVITY OF SLEEP NASENDOSCOPY

Previous studies have questioned the value of sleep nasendoscopy because asymptomatic subjects could be induced to snore and obstruct. Marais³ stated that although sleep nasendoscopy is a widely used investigation in patients with sleep-disordered breathing despite its non-physiological basis, there still remains a doubt of its validity as an investigative tool. Marais compared the presence or absence of snoring and its site of generation between a group of 205 snorers and another of 126 non-snorers. Snoring was produced at nasendoscopy in 45.3% of non-snorers but could not be produced in 18.1% of snorers. There was no significant difference in the site of sound production between the two groups and although the noise produced by the non-snoring group was quieter, this difference was not significant. Abdullah et al.⁷ suggested that a clear establishment of the site of obstruction is crucial for subsequent treatment planning. Video sleep nasendoscopy (VSE) is probably the most accurate assessment of the situation and also helps in identifying the situation that needs correction.

Berry et al.⁸ conducted a prospective cohort study involving 107 patients divided into two groups. The two groups of patients were matched for their Body Mass Index (BMI). The first group consisted of 53 patients with a history suggestive of obstructive sleep apnea. The second group consisted of 54 patients with a partner-confirmed history of no snoring. These patients were undergoing anesthesia for other reasons. Both groups of patients were free of associated otorhinolaryngological symptoms. The main outcome measure was assessment of production of snoring or obstruction in patients with no documented history of snoring when sedation was administered as part of general anesthesia using TCI with propofol.

The symptomatic group comprised 53 patients whereas 54 patients made up the non-symptomatic group. The various relevant characteristics are summarized in Table 6.1. Categorical variables (gender) were assessed using the chi-squared test whereas continuous variables (BMI and Epworth score) were analyzed using tests for normality; differences were compared by the paired t-test. Taking gender into account, both the groups are reasonably matched.

Both groups contained similar numbers of males and females but there was a predominance of males in the snoring group whereas females were predominant in the non- snoring group (Table 6.1). The mean age of the patients in the second group was 47.4 years whereas in the first group, it was 51.7 years.

There was a difference (P=0.046) between the means of the Epworth score in the two groups: non-snorers 5.32 (with SD of 3.473) against snorers 7.36 (SD of 3.346). However, gender difference, whether considered alone or as a second factor, was not significantly different (Table 6.1).

Body Mass Index was effectively matched between the two groups overall, and between males and females within these groups. A difference (P=0.038) between the means of the BMI values was observed in the two groups: non-snorers 27.11 (with SD 3.984) against snorers 28.83 (SD 4.462) and also, there was a difference (P=0.027) between the means of the BMI values for men (mean 28.75, SD 3.902) and women (mean 26.91, SD 4.604) (Table 6.1).

All patients in the symptomatic (snoring) group snored or obstructed at different concentrations of propofol (Table 6.2). There was no statistically significant difference (P=0.401) in the distributions of concentrations of propofol at which snoring started between men and women.

In comparison, all patients in the asymptomatic (non-snoring) group could not be induced to snore or obstruct at incremental levels of propofol and this was clearly significant statistically (P<0.001).

Earlier authors who have noted false-positive results with sleep endoscopy did not use this technique. Different individuals may have administered the sedating agent or agents used in these studies. The sedating agents indeed differed between operators in such studies, and no measure of sedation effect was used.3–5 This difference in technique is perhaps an explanation for the encouraging and obvious differentiation of symptomatic from asymptomatic patients demonstrated in this study.

5 CONCLUSION

Sleep nasendoscopy allows for a targeted management of snoring or obstructive sleep apnea in suitable individuals by clarifying the underlying contributing anatomical sites. The procedure has previously been questioned for not beinga true reflection of normal sleep in view of the sedation process required and for the possibility of inducing false- positive results.

This study does, however, confirm the authors’ clinical impression that sleep nasendoscopy performed by a target controlled technique is a useful, specific and sensitive means of assessing patients with sleep-related breathing disorders. It should therefore perhaps be considered for a more prominent role in the investigation of such cases particularly when selection for surgical intervention may be assisted by the anatomical targeting information that may be provided. It may also prove helpful in individuals with OSA who have proved intolerant of nasal CPAP. Such cases may be further assisted by further judicial intervention dependent upon the anatomical information provided by sleep endoscopy.

The authors commend this technique to others involved in the management of such cases where there is appropriate anesthetic interest and availability.