Introduction

Over the past three decades, the prevalence of obesity in pediatric age groups has tripled, reaching epidemic proportions (1, 2). This trend, together with the concomitant increase in a wide range of obesity-related disorders, has become a source of growing medical concern (3). Bariatric surgery has gradually gained acceptance as a weight loss option for a select group of extremely obese adolescents who are affected by such disorders and who have failed to lose weight with less invasive traditional approaches (4, 5). In adults, bariatric surgery results in significant and sustained weight loss, which, in turn, has reversed or reduced the severity of many obesity-related disorders (6), including obstructive sleep apnea (OSA)¹(7).

OSA is a disorder characterized by narrowing of the pharyngeal airway, resulting in repeated episodes of airflow cessation, oxygen desaturation, and sleep disruption (8). The evidence for an association between obesity and OSA is well documented, with obesity shown to be a risk factor for OSA in both adults and children (9, 10, 11). In obese adults, the reported prevalence of OSA is 40% (10) ; in extremely obese adults (BMI 40 kg/m²), the prevalence increases to 98% (12). Of particular significance, a number of studies in extremely obese adults have shown that significant weight loss after bariatric surgery decreases the severity of OSA (7, 13). Comparatively few OSA studies have been conducted in the obese pediatric population. Marcus et al. (14) reported that 36% of obese children and adolescents had abnormal polysomnograms (PSGs), and they also showed a positive correlation between the degree of obesity and the severity of OSA. Silvestri et al. (15) reported a 59% prevalence of OSAs in obese children and adolescents, similarly showing an increased trend as obesity became more severe. In a pediatric population referred for sleep problems, Mallory et al. (16) found that 37% of children and adolescents suffering from severe obesity had abnormal PSGs, and of those patients, 24% were diagnosed with OSA. While these pediatric studies lay the foundation for an association between severe obesity and OSA that parallels that reported in the adult population, gaps in knowledge still remain. Neither the prevalence of OSA in extremely overweight adolescents nor the degree of weight loss required to reverse OSA has been elucidated. The purpose of our study was to determine the prevalence of OSA in a population of extremely overweight adolescents referred to an adolescent surgical weight management program. In addition, we hypothesized that, with postoperative weight loss, OSA severity would significantly improve in this patient population.

Research Methods and Procedures

Study Design

We conducted a retrospective chart review of all patients who underwent laparoscopic Roux-en-Y gastric bypass surgery at Cincinnati Children's Hospital Medical Center between July 2001 and September 2004. Approval for this project was granted by our Institutional Review Board.

Subjects

All subjects were enrolled in the Comprehensive Weight Management Center, which offers a surgical weight loss option for extremely overweight adolescents meeting the following adolescent bariatric guidelines, as previously described (5):

1. Girls, 13 to 18 years of age; boys, 14 to 18 years of age
2. Failure of at least 6 months of medically supervised weight loss attempts
3. BMI 40 kg/m², with presence of at least one severe obesity-related comorbidity (OSA, type 2 diabetes, pseudotumor cerebri)
4. BMI 50 kg/m², with at least one less severe obesity-related comorbidity (hypertension, dyslipidemia, hyperinsulinemia, gastroesophageal reflux disease, non-alcoholic fatty liver disease)

Anthropometric Measures

Body weights were recorded using a digital scale, and heights were measured using a calibrated wall mounted stadiometer. All weights were obtained in light clothing and without shoes. All measurements were obtained in triplicate, and mean values were used. Weight and height information were used to calculate BMI as weight (kilograms) divided by height (meters squared).

PSG Data

Overnight PSG reports were reviewed for the following variables:

1. Apnea-hypopnea index (AHI): number of OSA and hypopnea episodes per hour of sleep
2. Arousal index: number of arousals from sleep per hour of sleep
3. Mean oxygen saturation during sleep
4. Minimum oxygen saturation during sleep

Comparisons were made between pre- and postoperative PSG variables.

OSA

Patients were considered to have OSA if their PSG revealed AHI 5 per hour of sleep.

Data Analyses

Mean values of anthropometric and PSG variables were calculated. Paired Student's t test was used to compare normally distributed variables. The Wilcoxon signed-rank test was used to compare variables not meeting normality criteria. Spearman's correlation coefficient was calculated to measure the association among variables. Two-tailed p values of <0.05 were considered to indicate statistical significance. SAS version 8.2 was used for statistical analysis.

Results

The study population was comprised of 35 subjects (23 girls and 12 boys), with a mean age of 17.57 1.82 years. Thirty-one of 35 (90%) subjects were non-Hispanic white. All patients had a BMI >95th percentile of BMI for age, with a mean BMI of 57.01 10.05 kg/m² (range, 48 to 87 kg/m²). The mean weight of this cohort was 170 31.38 kg.

Of the 35 patients who underwent gastric bypass surgery, 34 underwent preoperative polysomnography. Twenty-five of these 34 (73.5%) patients had an obstructive AHI >1 (normal 1 event/h). Nineteen (55%) had an AHI 5, indicating the presence of OSA. As shown in Figure 1, the percentage of subjects with OSA significantly increased across BMI strata (p < 0.05), with close to 75% of subjects with a BMI >60 kg/m² having OSA.

Figure 1.

: The percentage of patients with OSA (AHI 5) across BMI strata. The p value for the trend is <0.05.

Full figure and legend (80K)

Of the 19 subjects with OSA, 10 (53%) underwent postoperative polysomnography after clinically significant weight loss (mean, 58 kg), with a mean interval of 5.1 1.2 months between baseline and repeat PSGs. The failure of the remaining nine to undergo this testing was because of their lack of availability; there were no significant differences in baseline BMI or AHI between these two OSA subject groups (Table 1). Among the 10 OSA subjects who had follow-up testing, there was a mean decrease in BMI of 19 units over a duration of 6 months (p < 0.01). As measured by AHI, all 10 subjects showed a significant reduction in the severity of their OSA (p < 0.01), with only 1 subject having residual OSA severe enough to meet the clinical criterion for treatment (Table 2). AHI values did not, however, show a significant relationship between the reduction in BMI and the resolution of OSA (R = 0.47, p = 0.2). The average O₂ saturation during sleep was 95% at baseline and 96% after weight loss. In contrast, there was a significant improvement in minimum O₂ saturation (p < 0.05). This increased from <90% at baseline to close to 92% after weight loss.

Table 1. - Patients diagnosed with OSA.

Full table

Table 2. - Comparison of obesity and OSA indices before and after bariatric surgery.

Full table

Discussion

In our cohort of extremely overweight adolescents meeting eligibility criteria for bariatric surgery, we found a 55% prevalence of OSA. Furthermore, as BMI increased, there was a trend toward an even higher OSA prevalence. This finding is similar to that reported in other adult and pediatric studies and further supports reported findings of an association between obesity (adiposity) and OSA (9, 10, 11). To avoid possible bias from OSA being used as an inclusion criterion for bariatric surgery in patients with a BMI between 40 and 50 kg/m², we calculated the prevalence of OSA in patients meeting bariatric surgery eligibility criteria because of weight alone (i.e., those with BMI > 50 kg/m²); a similarly high OSA prevalence of 58% (N = 15) was found among the 26 adolescents in this group. The potential impact of this finding on overall health merits major concern in that OSA is associated with cognitive deficits (17), as well as metabolic (18) and cardiovascular (19, 20, 21) morbidity, Moreover, its severity correlates with the degree of metabolic (22) and cardiovascular impairment (19).

Consistent with prior reports in adults, we also found that after weight loss, there was a significant reduction in the severity of OSA (23). As measured by minimum O₂ saturation, a significant improvement in hypoxemia during sleep was also observed after weight loss. Because overnight hypoxemia is considered to be one of the pathways for cardiovascular sequelae of OSA because of increased morning catecholamine levels (24) and prothrombosis (25), the improvement in AHI is particularly significant in obese adolescents, a group that is already at high risk for cardiovascular morbidity. These combined results highlight the benefit of bariatric surgical intervention in the resolution of obesity-related OSA and underscore why it has gradually gained recognition as a useful weight loss tool for a select group of extremely obese adolescents. This is especially important in light of the high attrition rates among obese adolescents participating in traditional medical weight lossprograms (26). Continuous positive airway pressure is typically the first line of therapy for moderate to severe OSA (27). However, because of its inconvenience and discomfort, it is accepted by only 50% of adult patients initially, with only 68% of those patients remaining compliant after 1 year (28), and by an even lower proportion of adolescents (in our experience).

Contrary to our expectations, we did not find a significant correlation between absolute change in OSA indices (AHI, arousal index, and minimum O₂ saturation) and a decrease in obesity (BMI) after bariatric surgery. We conjecture that this finding could be partially attributed to the fact that BMI, although widely used for expressing body fat, is an indirect measure of adiposity. Thus, we are currently exploring whether magnetic resonance imaging provides more precise measurements of adipose tissue. Magnetic resonance imaging is increasingly gaining recognition as a method for assessing visceral adiposity (29) and parapharyngeal fat (30). The importance of body fat distribution in the etiology of OSA is highlighted by recent reports of a higher correlation between OSA and central obesity than between OSA and parapharyngeal fat (31). It may, thus, be prudent for future studies to examine the relationship between changes in visceral adiposity after weight loss and degree of improvement in OSA.

A limitation of this study is that not all PSGs were performed at the same sleep laboratory. Nevertheless, given the striking difference in OSA severity before and after weight loss, we do not feel that variability in personnel and equipment calibration had any significant impact on our PSG results.

In summary, our study indicated that OSA was highly prevalent in extremely overweight adolescents meeting eligibility criteria for bariatric surgery. The significant weight loss after bariatric surgery was associated with either the resolution of OSA in a majority or a significant reduction in OSA severity. This finding should be considered in assessing potential candidates for surgical weight loss. Because OSA is associated with cognitive deficits as well as metabolic and cardiovascular morbidity, the potential positive impact of significant and sustained weight loss on the overall health of extremely overweight adolescents cannot be overemphasized.

Notes

¹ Nonstandard abbreviations: OSA, obstructive sleep apnea; PSG, polysomnogram; AHI, apnea-hypopnea index.

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Acknowledgments

This study was supported by Cincinnati Children's Hospital Research Foundation and U.S.P.H.S. Grant MO1 RR 08084, General Clinical Research Centers Program, National Center for Research Resources, NIH.