British otolaryngologists Pringle and Croft first introduced drug-induced sleep endoscopy (DISE) in 1991 as a technique to identify the anatomic location of obstruction in the airway of patients with snoring and obstructive sleep apnea.1 Since then, DISE, or sleep nasendoscopy, has been widely adopted as a diagnostic tool for dynamic airway evaluation.2 This technique is complementary to polysomnographic data, as it is used to differentiate the site of obstruction. DISE is commonly utilized to direct subsequent management, including selection of specific surgical interventions; however, there remains a general lack of agreement regarding standardization of the technique.3 Areas requiring more investigation include an optimal and standard scoring system as well as a standardized sedation protocol.
In this issue of JCSM, the article by Lo et al. proposes a standardized sedation model for DISE using a propofol infusion guided by a bispectral index (BIS) monitor.4 The authors suggest that sedation maintained at a BIS level of 65–75 provides an objective target to create the ideal conditions for DISE. The BIS level is not a physiologic measurement, but rather a dimensionless number derived from a proprietary algorithm that integrates multiple electroencephalogram tracings. Although prior investigations have examined the relationship of BIS during sedation and natural sleep, as well as the effects of sedation on airway obstruction, the results have not been consistent.5–8 While BIS levels decrease during natural sleep in much the same way as during sedation, the technology does not allow for discrimination of different stages of sleep.9 Furthermore, BIS scores associated with depth of anesthesia are dependent upon the anesthetic agent being used, are relatively ineffective during sedation with ketamine, nitrous oxide, or dexmedetomidine, and can be unpredictable in the presence of opioids.10 And finally, in the B-Unaware trial, BIS was found to be ineffective in guiding the administration of volatile anesthetics.11 Moreover, BIS was not sensitive enough to detect clinically significant changes in minimum alveolar concentration and suffered from interpatient variability.
The Lo study4 investigated the effect of sedation on DISE findings and found that deep sedation levels (BIS levels of 50 to 60) resulted in greater airway collapsibility and more complete collapse at multiple sites than did evaluation at light sedations levels (BIS levels of 65 to 75). They also found that DISE findings were consistent over 2 separate periods at each sedation level (deep and light). Real-time and video evaluation of DISE findings were also shown to have a high level of inter-rater reliability. However, there is no comment on the therapy recommended by this evaluation or correlation with outcomes after these therapies were carried out. In addition, there was no comment on the correlation between BIS levels and clinical symptoms. This makes it difficult to generalize these findings to situations when DISE is performed without BIS or when BIS is not able to be utilized because the anesthetic agents to be used make BIS unreliable.
When considering the limitations of BIS technology combined with the cost of the device and disposables, it is relevant to question the advantage conferred by its use during DISE over clinical assessment. In addition, it would be ideal for any recommendations regarding DISE standardization to be correlated with clinical symptoms as well as surgical outcomes. The study by Lo exemplifies the need for further investigations that will help define a “gold standard” for DISE and highlights the multidisciplinary nature of sleep medicine. There is a profound need for collaboration between the anesthesia, sleep medicine, and surgical providers for these patients. Future research is warranted to facilitate a more thorough understanding of sedative hypnotics and their impact on airway collapsibility and sleep architecture. This research should build upon the results in the Lo study and incorporate clinical findings during DISE, as well as investigate the impact of DISE on outcomes.
The authors have indicated no financial conflicts of interest.
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