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(Chest. 2003;124:1615-1619.)
© 2003 American College of Chest Physicians

The Long-term Results of Gastric Bypass on Indexes of Sleep Apnea*

Sherry A. Guardiano, DO; Jeffrey A. Scott, MD, FCCP; J. Catesby Ware, PhD and Stephen A. Schechner, MD

* From the Sleep Disorders Center Sentara Norfolk General Hospital, Eastern Virginia Medical School and Sentara Norfolk General Hospital, Norfolk, VA; and George Washington University, Washington, DC.

Correspondence to: Sherry A. Guardiano, DO, 320 B Cross Green St, Gaithersburg, MD 20878; sstadig{at}pol.net


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: Weight loss improves obstructive sleep apnea (OSA), and clinicians regularly recommend dieting to their patients with OSA; however, many morbidly obese patients may be unable to lose weight without medical or surgical intervention. Gastric bypass surgery (GB) facilitates weight loss for morbidly obese patients. Studies show GB will improve symptoms associated with OSA, but little is known regarding the long-term effects of GB on this population.

Design: Historical, retrospective, cohort study.

Setting: Sleep Disorders Center, Sentara Norfolk General Hospital, Norfolk, VA.

Participants: A list of subjects who underwent vertical Roux-en-Y GB was cross-referenced with the Sleep Disorders Center at Sentara Norfolk General Hospital to identify patients with a diagnosis of OSA during the preoperative evaluation prior to undergoing GB.

Interventions: GB.

Measurements: Our primary end point was the respiratory disturbance index (RDI). Secondary variables were body mass index (BMI), mean oxygen saturation, low oxygen saturation, a standardized depression scale, and the continuous positive airway pressure (CPAP) requirement.

Results: Thirty-four subjects with a diagnosis of OSA prior to GB were identified. Of these, 28 subjects were located and offered follow-up polysomnography after GB. Eight subjects returned for repeat polysomnography. The subjects were re-evaluated an average of 28 months after GB. Seven subjects had a lower BMI after GB. Mean BMI was reduced by 31% (p = 0.001). The mean decrease in RDI was 75% (p = 0.01), and five of the eight subjects no longer required nasal CPAP. Mean nocturnal oxygen saturation improved from 95 to 97% (p = 0.04).

Conclusions: Weight reduction following GB is associated with significant improvements in sleep apnea indexes an average of 28 months after GB. Re-evaluation after GB is necessary to identify and treat those patients who, despite subjective improvement, may continue to require CPAP for residual OSA.

Key Words: bariatric surgery • gastric bypass surgery • morbid obesity • obstructive sleep apnea


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Obesity is an epidemic in the United States. Twenty-four percent of adult men and 27% of adult women have a body mass index (BMI) > 30, and this trend continues.1 2 3 Two percent of middle-aged women and 4% of middle-aged men have obstructive sleep apnea (OSA), a condition linked to obesity since the early 1980s.4 5 Obesity and OSA are associated with cardiovascular problems, and the cardiopulmonary risks of obesity may be amplified by the presence of OSA.6 7 8 9 Depression also has an increased prevalence in subjects with obesity and morbid obesity as well as OSA.10 11 12 13

Weight loss improves symptoms associated with OSA.14 15 16 Although clinicians regularly recommend weight loss to their patients with OSA, many patients are unable to lose the necessary weight to improve their OSA or other illnesses associated with obesity. The cost of the treatment of these comorbid conditions has been estimated to be twice the cost of the same comorbid conditions in patients without OSA.17

Gastric bypass surgery (GB) may benefit these morbidly obese patients. GB has proven to be an effective modality employed to decrease BMI, and has been shown in another study18 to be an effective modality to help treat OSA. Most studies show a 1 to 2% mortality rate with open GB, but with the advent of laparoscopic procedures, the risk should be lowered substantially.19 20

A paucity of data exists concerning long-term results of GB-induced weight reduction on indexes of OSA.21 In 1984, one analysis of subjects after GB showed improvement in respiratory disturbance index (RDI) at the 2- to 4-month mark and the 4- to 8-month mark.22 Another larger study23 examined multiple variables in subjects with sleep apnea syndrome as well as obesity hypoventilation syndrome. At an average follow-up of 4.5 ± 2.3 years, subjects with sleep apnea had improvement in BMI from 56 ± 32 to 38 ± 9 (± SD). Although symptoms resolved in 38 of 57 subjects, the group still had moderate OSA.23 A 1994 study conducted a 7.5-year follow-up of 14 patients, in which 5 patients had increases in RDI despite reduction and maintenance of postoperative BMI.24 A study25 conducted from 1990 to 1998 showed subjects demonstrated improvement in various comorbidities such as hypertension, asthma, and diabetes mellitus after GB; 11 of 12 subjects with a preoperative diagnosis of OSA had subjective improvement of OSA symptoms 2.5 years after GB. Although an important end point, subjective improvement may not correlate with objective measurements of improved OSA. For example, a study26 analyzing the long-term effects of uvulopalatopharyngoplasty in subjects with OSA showed that subjects felt subjectively better, but the degree of apnea did not improve objectively.

The purpose of this study was to analyze specifically the RDI >= 1 year after GB. We hypothesized that GB would reduce BMI and, subsequently, improve objective indexes of OSA over a period of several years.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Subjects
A list of subjects who underwent vertical Roux-en-Y GB was cross-referenced with the Sleep Disorders Center at Sentara Norfolk General Hospital to identify patients who received a diagnosis of OSA during a preoperative assessment. We identified 34 subjects who met our criteria, and 8 subjects returned for follow-up evaluation. Inclusion criteria included diagnosis of OSA prior to GB with a split-night polysomnography and prescription of nasal continuous positive airway pressure (CPAP). Split-night polysomnography is defined as a combined diagnostic and CPAP titration study during the same night. Patients were not excluded if they were noncompliant with nasal CPAP use. Subjects were at least 18 years of age and not enrolled in another research project. Table 1 details the subject characteristics. These subjects were in stable medical condition prior to and following GB.


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  		Table 1.. Subject Characteristics and Results

 
Protocol
We contacted each subject by telephone and encouraged him/her to return to the Sleep Disorders Center at Sentara Norfolk General Hospital for follow-up polysomnography. Over a 6-month period, eight subjects returned for follow-up testing, seven women and one man. Potential subjects were contacted every 2 weeks for 2 months to encourage follow-up.

Our primary end point was the RDI, an objective measure of severity of OSA. Secondary variables were BMI, mean oxygen saturation, low oxygen saturation, a standardized depression scale, the Beck depression inventory, and nasal CPAP.27 28

Subjects underwent a split-night polysomnography during 1 night at the Sleep Disorders Center at Sentara Norfolk General Hospital. Subjects reported to the sleep disorders center 2 h before their usual bedtime. Technicians attached transducers to measure EEG (central and occipital leads), electrooculographic (left and right eyes), ECG (V2), and electromyographic (geniohyoid, intercostal and anterior tibialis) activities. We measured nasal-oral airflow using a thermistor and oxygen saturation using a pulse oximeter. Relative tidal volume was recorded by inductance plethysmography with bands around the chest and abdomen. Calibration was with an isovolume maneuver.

In general, those subjects with an RDI >= 20 were titrated to CPAP during split-night polysomnography. In addition to the apnea criteria, subjects needed a minimum of 180 min of recording time and a period of rapid eye movement sleep. If no rapid eye movement sleep occurred, titration could begin after 180 min and an oxygen desaturation of <= 85%.

The CPAP pressure started at 5 cm H2O and increased by 2.5 cm H2O increments every 15 min in order to eliminate apnea events. The pressure was then titrated to eliminate snoring and any remaining upper airway resistance syndrome (UARS) activity. At the time of this review, polysomnographic records were screened for UARS. In the absence of apnea and hypopnea events, UARS was suspected if there were increased arousals from sleep, snoring, increased intercostal activity, and out-of-phase thoracic and abdominal respiratory efforts. These findings then had to match with the clinical picture for a diagnosis of UARS.

At the completion of each study, a technician visually scored the test for sleep stages, arousals, and apnea/hypopnea episodes. They also evaluated for other events, including leg movements, bruxism, heart rhythm disturbances, and snoring.29 30 Respiratory events lasted a minimum of 10 s, as measured from the end of exhalation to the beginning of inhalation. This was determined from the tidal volume (sum) and airflow channels. Hypopnea events occurred when tidal volume dropped by 50%, oxygen saturation fell by two percentage points, and an EEG arousal or movement artifact lasted at least 2 s. An apnea occurred when airflow ceased for at least 10 s. The RDI is the sum of all apneas and hypopneas per hour of sleep. Because central apnea events were a minority of the events, they were included in the RDI for this report. A diplomate of the American Board of Sleep Medicine then reviewed and validated all polysomnographic information before statistical analysis.

The Beck depression inventory was administered at the presleep evaluation, and was scored as follows: 0 to 9 = within normal limits, 10 to 14 = mild depression, 15 to 22 = moderate-to-severe depression, and >= 23 = profound depression. Table 1 details the scores before and after GB.

Data Analysis
SYSTAT Version 9 (Focus Corporation; Seoul, Korea) was used for data analysis. Paired t testing was used comparing the pre-GB data to the post-GB data for the primary and secondary variables. Because of the small number of participants and the large variation between subject results, nonparametric testing, the Wilcoxon signed-rank test, was also performed to ensure statistical significance (p < 0.05) for both parametric and nonparametric testing analysis.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Subjects were re-evaluated with split-night polysomnography 28 ± 20 months after GB. Eight subjects were studied. Seven of the eight subjects were women (88%). UARS was not diagnosed in any of our subjects. The mean age, BMI, and RDI prior to GB were 44 ± 7 years of age, 49 ± 12, and 55 ± 31 events per hour, respectively. At the Sentara Norfolk General Hospital Sleep Disorders Center, the mean age, BMI, and RDI are 46 years, 32, and 23 events per hour, respectively, and 73% are male.31

Using the parametric paired t test, statistically significant improvements were obtained following GB for RDI, BMI, nasal CPAP requirements, mean oxygen saturation, and low oxygen saturation (p < 0.05). Analysis of the eight subjects yielded a mean reduction in RDI by 75%, decreasing the RDI by 41 ± 33 events per hour. Central apnea events were included in the RDI but were not the predominant or significant apneic events for any of the subjects. The mean BMI was reduced by 15 ± 7, yielding a 31% reduction in BMI. Mean nasal CPAP requirements were reduced in 100% of the subjects, and five of the eight subjects no longer required nasal CPAP. The mean oxygen saturation improved by 2 ± 2%. The mean low oxygen saturation also improved 15%, from 74 to 87%.

Nonparametric testing with the Wilcoxon signed-rank test confirmed the statistical significance yielding p <= 0.05 for changes in RDI, BMI, nasal CPAP requirements, and mean oxygen saturation. The change in mean low oxygen saturation was not significant by nonparametric testing.

The mean Beck inventory score did trend toward an overall reduction in the mean value, signifying an improvement in depression score, but was not found to be statistically significant by either parametric or nonparametric testing. Table 1 details all statistical data for each subject.

Twenty-six people were identified as potential subjects but did not undergo repeat polysomnography. Eight subjects could not be located due to outdated contact information. One subject refused testing. Seventeen other potential subjects initially agreed to return. Five of the 17 subjects made appointments and had authorization for polysomnography by their insurer, but then cancelled or did not present to the Sleep Disorders Center for their appointments. Two potential subjects agreed to return, but their primary care physicians would not refer them back to the Sleep Disorders Center as required by their insurance companies. Without clear reason, the remaining 10 subjects did not schedule for follow-up testing.


   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
This study confirms our hypothesis that GB leads to objective long-term improvement in RDI and other indexes of OSA. Although GB did not normalize the BMI of all of the study subjects, GB did improve the overall BMI of all subjects and, subsequently, RDI was improved significantly in all subjects except subject 3 (Table 1) . Subject 3 had the highest initial BMI and did have a 14% BMI reduction, although her RDI only decreased by one event. Compliance with CPAP can be problematic; thus, the reduction or resolution of the need for CPAP has positive personal implications for patients requiring CPAP for OSA.16 32 Although improvement in the Beck depression inventory, an index of depression, was not statistically significant, the trend was favorable and with further study may show a significant improvement.

Roux-en-Y GB improves BMI.33 34 The mean BMI changes in previous studies were similar to our patients. Complications were also similar. A previous study25 looked at subjective improvement of OSA, but we wanted to focus on objective improvement. Many studies18 22 24 35 used weight in kilograms for analysis, making comparison between studies more difficult; in these studies, weight was reduced by 26 to 72%, and RDI was reduced by 72 to 91%. Our mean BMI was reduced by 31% and mean RDI was reduced by 75%.

We note the percentage of women in our study (88%). The percentage of women at the Sleep Disorders Center is only 27%.31 This may also add a potential bias. A larger study would be needed to ensure this is not a confounding factor.

Despite our best efforts, many potential participants did not return for repeat polysomnography. Of these potential subjects, 18 subjects reported subjective improvement in daytime wakefulness after GB; however, no information is available regarding the changes in objective indexes of OSA in these individuals. We recognize this as a significant source of potential bias in this study.

We considered possible reasons for subjects’ unwillingness to participate in this study. Many were concerned about the time requirement involved and did not want to miss work. Others expressed concern regarding the adequacy of insurance coverage, although none of our appointed patients were denied by their insurance carriers. Some patients and their providers did not believe re-evaluation was necessary. Perhaps a common sentiment may have been they simply felt better and did not wish to invest the time because they subjectively were symptomatically improved. Future evaluation of this issue is pending.

Our study confirms weight loss associated with GB improves indexes of OSA significantly 28 months after GB. Future studies should focus on the relationship between continued long-term weight reduction and RDI in a larger study population. Education describing the need for follow-up testing should begin prior to GB for patients and their primary care physicians. This will ensure patients continue to receive appropriate treatment for their OSA, especially when subjective improvement is not reinforced by objective parameters. Untreated OSA may cause continued morbidity.25 Through continued medical evaluation and ongoing education, we hope to ensure patients receive appropriate medical care.


   Footnotes
 
Abbreviations: BMI = body mass index; CPAP = continuous positive airway pressure; GB = gastric bypass surgery; OSA = obstructive sleep apnea; RDI = respiratory disturbance index; UARS = upper airway resistance syndrome

Received for publication January 22, 2002. Accepted for publication April 14, 2003.


   References
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 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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