Shu Hua Li*, Chan Meng, Chunhai Shi and Renyi Hei
Department of Otolaryngology-Head and Neck Surgery, General Hospital of Shenyang Military Area Command, Shenyang, China
Received: 09 March, 2016; Accepted: 28 March, 2016; Published: 30 March, 2016
Shu Hua Li, MD, Department of Otolaryngology-head and neck surgery, General Hospital of Shenyang Military Area Command, No.83, Wenhua Road, Shenhe District, Shenyang, 110840, China, Tel: +86-24-28856253; E-mail:
Li SH, Meng C, Shi C, Hei R (2016) Correlation between Bispectral Index and Sleep Stage of Patients with Obstructive Sleep Apnea-Hypopnea Syndrome. Arch Otolaryngol Rhinol 2(1): 016-019. DOI: 10.17352/2455-1759.000015
© 2015 Li SH, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Obstructive sleep apnea-hypopnea syndrome (OSAHS); Bispectral index (BIS); Polysomnography (PSG); Sleep stage
Objective: The aim of this study was to evaluate the correlation between bispectral indexes (BIS) and sleep staging in patients with moderate to severe obstructive sleep apnea-hypopnea syndrome (OSAHS) under natural sleep conditions.
Materials and Methods: Twelve patients who had been clinically diagnosed with OSAHS were monitored by polysomnography (PSG) and bispectral index (BIS) that were simultaneously recorded to determine the BIS at different sleep stages and analyze the patterns.
Results: One patient did not meet the diagnostic criteria of OSAHS, and another patient lacked non-rapid eye movement stage 3 (N3) during sleep. Both patients were excluded from this study. Ten patients who met the diagnostic criteria of moderate to severe OSAHS were included in the final statistical analysis. The BIS during the following sleep stages, i.e., awake, stages N1, N2, N3, and rapid eye movement (REM) ranged from 75-91, 65-91, 60-86, 47-82, and 66-91, respectively (mean ± standard deviation: 86.3 ± 4.62, 78.4 ± 9.72, 73.8 ± 8.59, 61.8 ± 11.90, and 83.3 ± 7.32, respectively).
Conclusion: BIS gradually decreased in the deeper stages of sleep. However, there was a considerable overlap in BIS values between different sleep stages, making it difficult to use BIS as a marker for sleep staging. To ensure an accurate examination of airways in the patient during sleep induction, these should be executed when the BIS is reduced to 77 or below.
Obstructive sleep apnea-hypopnea syndrome (OSAHS) refers to apnea and inadequate ventilation caused by collapsing upper airways and is associated with snoring, sleep disorders, frequent oxygen desaturation during sleep, and excessive daytime sleepiness [1,2]. Stenosis or occlusion of the upper respiratory tract during sleep is the main reason for the occurrence of OSAHS . Surgery is one of the effective treatment options for OSAHS by preventing the stenosis or occlusion of the upper respiratory tract. Accurate diagnosis of the stenosis or occlusion of the upper respiratory tract is the key for selection of a surgical treatment approach and its efficacy .
In addition to a series of examinations when the patient is awake [5,6], a number of examinations during natural sleep conditions and after sleep-induction have been widely used in recent years to locate the stenosis and occlusion of upper respiratory tract accurately [7-10]. Specifically, drug-induced sleep endoscopy (DISE) is a commonly used technique to examine the upper respiratory tract during sleep. DISE directly identifies the morphological changes in the various parts of the upper respiratory tract during apnea, thereby confirming the site of obstruction in the airway [11-14]. DISE is an important and significant diagnostic tool guiding the surgical treatment and helping select an appropriate operative plan . DISE has been widely used as a routine clinical screening tool.
Even with the advancement of examination equipment and skills, patients should reach a certain depth of sleep during the examination to ensure accurate and reliable examination results. Variations in the depth of sleep can result in different examination results . Although electroencephalography or polysomnography can accurately determine the depth of sleep in the patients, the machines cannot be conveniently placed and used in operating rooms, where most sleep-inducing examinations are performed. Most physicians use BIS to monitor the depth of sedation during DISE [13-15]. However, to date, only one study has reported on the correlation between BIS and sleep stage in mild OSAHS patients . Patients with moderate to severe OSAHS often have sleep structure disorders. However, regarding the correlation between BIS and sleep stage, we do not know if there are any differences among healthy adults, and patients with mild, moderate or severe OSAHS. This study was conducted in a group of patients with moderate to severe OSAHS using PSG with simultaneous recording of BIS of each patient to evaluate the relationship between BIS and sleep stages.
Materials and Methods
This study was approved by the Ethics Committee of our hospital. Twelve consecutive patients were suspected of OSASH and scheduled to be examined by PSG in our hospital during March 2015. All patients signed the written informed consents prior to the participation of PSG and BIS monitoring. PSG confirmed moderate to severe OSAHS in patients and all components of the sleep stages were included in this study.
PSG for sleep apnea and sleep staging
In this study, PSG using Respironics ALICE®5 Diagnostic Sleep System (Philips Healthcare, Andover, MA) was performed for sleep monitoring in all patients via the 10-20 neural input layout connecting to the heads of patients. Electroencephalogram (EEG), electrooculogram (EOG), and electromyogram (EMG) activities of frontal, parietal, and occipital regions in each patient were monitored. The obtained sleep electroencephalograms were used to interpret the sleep stages according to the American Academy of Sleep Medicine (AASM) Manual for the Scoring of Sleep and Associated Events published in 2007 . This manual divides sleeping into several stages, including wakefulness (W), non-rapid eye movement 1 (N1), non-rapid eye movement 2 (N2), non-rapid eye movement 3 (N3), and rapid eye movement (REM). Nasal air pressure and flow, thermal airflow, snoring, chest and abdominal movements, posture, electrocardiogram (ECG), activity of lower extremity EMG, and blood oxygen saturation were measured simultaneously. In addition, interpretation of respiratory events was based on the same rule to determine the apnea hypopnea index (AHI) and the lowest oxygen saturation during sleep as the primary diagnostic indicators of OSAHS. Diagnostic criteria of OSAHS were confirmed when AHI reached or exceeded 5 times per hour (mild OSAHS: AHI < 15 times/h; moderate OSAHS: 15-29.99 times/h; severe OSAHS: 30 times/h).
All patients underwent PSG and BIS (BIS-Vista, Aspect Medical System, Newton, MA) monitoring simultaneously according to the methods described previously in the literature . The methods are summarized as follows: BIS system clock and PSG system was synchronized before the examination. After the patient’s skin had been cleaned, the supporting BIS electrode strips were installed according to the manufacturer’s instructions. Electrodes were located on the forehead, on the right orbit, between the right preauricular region and the right lateral cheekbone. The high-pass and low-pass filters of EEG were set to 0.5 Hz and 30 Hz, respectively. The signal quality index (SQI) was >95%, and the electrode impedance was <5 kΩ. After the machine had passed the self-examination, BIS system continuously recorded EEG activities and automatically converted the data into BIS. The BIS values were stored automatically in the system every minute.
Data processing and statistical analysis
After overnight monitoring, the sleep stages were determined according to PSG data recorded in 30-second intervals throughout the night and the corresponding BIS values were recorded. The BIS values during sleep stages (e.g., W, N1, N2, N3, and REM) were recorded throughout the night from the same patient and the mean BIS was calculated for each sleep stage. The mean BIS of individual patients at different sleep stages were included in the final statistical analysis. SPSS 17.0 statistical software was used for data processing. BIS at different sleep stages of all patients were used for descriptive statistics. ANOVA analysis was used to explore the differences between the sleep stages. Rank correlation analysis was performed between BIS and different sleep stages.
Twelve patients who consecutively visited our hospital participated in this study. Their PSG and BIS were monitored simultaneously. One of the PSG results did not meet the diagnostic criteria of OSAHS, and the patient was excluded. Another patient without N3 sleeping component throughout the night was also excluded from the study. Ten patients with moderate to severe OSAHS were included in the statistical analysis (8 males and 2 females; age ranged 19–48 years; mean age 33.1 ± 10.72 years), with 3 cases of moderate OSAHS and 7 cases of severe OSAHS; AHI ranged 17.8–98.0 times/h (average: 49.1 ± 31.92 times/h); LSaO2 0.58–0.90 (average: 0.75 ± 0.12); BMI ranged from 21.0–44.1 kg/m2 (average: 29.5 ± 5.93 kg/m2; and Epworth Sleepiness Scale ranged 2–21 scores (average: 12.4 ± 4.37 scores). All patients were snoring throughout the night. The severity of excessive daytime sleepiness and fatigue varied from case to case.
Ten OSAHS patients successfully completed PSG and BIS monitoring. All patients had basal stages of W, N1, N2, N3, and REM throughout the night. Table 1 shows the time distributions of different sleep stages.
BIS analysis in different sleep stages
Table 2 and Figure 1 shows the BIS distribution of 10 patients in different sleep stages. Mean BIS values gradually decreased from W to N3 stages. ANOVA showed significant differences of BIS among all sleep stages (F value: 11.789, P < 0.001). Rank correlation analysis between BIS and sleep stages of W, N1, N2, and N3 demonstrated a significant correlation (correlation coefficient: 0.699, P < 0.001).
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