Identifying Patients at High Risk of Having Pulmonary Dysfunction Before Laparoscopic Bariatric Surgery and Its Impact on Postoperative Pulmonary Complications

Abstract

Background:

Morbid obesity is associated with variable degrees of pulmonary dysfunction that may predispose to postoperative complications. This study aimed to identify high risk patients to have pulmonary dysfunction before bariatric surgery in terms of age, sex, and body mass index (BMI) and the impact of pulmonary dysfunction on postoperative pulmonary complications.

Methods:

Prospective database of patients with morbid obesity who underwent bariatric surgery was reviewed. Data on patients' demographics, parameters of pulmonary function tests, and postoperative pulmonary complications were collected. The correlation between patients' age, sex and BMI, and pulmonary function was investigated using Pearson's correlation coefficient test.

Results:

Ninety-seven patients (82 female) with morbid obesity were included in the study. Twenty-eight (28.9%) patients had pulmonary dysfunction. Patients >40 years had higher odds of pulmonary dysfunction than patients ≤40 years (odds ratio [OR]: 2.54, P = .05). Male patients had significantly higher odds of pulmonary dysfunction than female patients (OR: 2.5, P = .03). Patients with BMI >50 had significantly higher odds of pulmonary dysfunction than patients with BMI <50 (OR: 4.9, P = .002). Patients with pulmonary dysfunction had significantly higher odds of developing pulmonary complications than patients with normal spirometry (OR: 9.13, P = .009).

Conclusion:

Around 30% of patients undergoing bariatric surgery had pulmonary dysfunction. Pulmonary dysfunction in preoperative spirometry was able to predict postoperative pulmonary complications. Men, patients older than 40 years, and superobese individuals had higher odds of having pulmonary dysfunction and are at higher risk to develop pulmonary complications after bariatric surgery.

Introduction

Morbid obesity has been recognized as one of the important public health problems in the last few decades.¹ Although treatment of obesity comprises different lines of management including dietary and life style modification and pharmacologic therapy in addition to surgical treatment, bariatric surgery is considered the most effective method of treatment of morbid obesity and its associated comorbidities.²

Surgical treatment of morbid obesity entails different strategies that can be broadly divided into three main groups: restriction of ingested food, malabsorption of its caloric potential, or a combination of these mechanisms. Different surgical techniques can considerably vary in their level of difficulty and accordingly can have variable outcomes.³ The optimal procedure for the treatment of morbid obesity remains controversial.⁴

It is known that morbid obesity is usually associated with various medical comorbidities including diabetes mellitus, hypertension, dyslipidemia, join pain, and pulmonary dysfunction. Excess weight may induce changes in respiratory functions and may cause restrictive or less frequently obstructive alteration in respiration. It has been noted that obesity is associated with a compromise of respiratory mechanisms causing changes in pulmonary functions.

Several mechanisms have been suggested as possible effects of obesity on lung function including increased respiratory rate, decreased tidal volume, reduced total respiratory system compliance, and lung volumes especially expiratory reserve volume.⁵ Although the impact of obesity on respiratory function has been repeatedly studied, there has been no consensus on the physiologic mechanisms that result in respiratory dysfunction.⁶ Sugerman et al.⁷ reported that the biggest respiratory insufficiency associated with morbid obesity, namely a decrease in expiratory reserve lung volume, is due to compression of the lungs by the chest wall and diaphragm and that the obesity-related pulmonary dysfunction contributed to a higher operative mortality.

Evaluation of pulmonary function before bariatric surgery is imperative to detect any functional respiratory changes that can have a significant impact on anesthesia and require special care. Guimarães et al.⁸ assessed pulmonary function in 36 patients with morbid obesity who were submitted to bariatric surgery. The authors found ∼94% of patients having a decreased functional residual capacity (FRC). Body mass index (BMI) significantly decreased postoperatively and this was associated with a significant improvement in almost all functional parameters with resolution of restrictive disorders. The study proposed a relationship between obesity and pulmonary restriction with a tangible positive impact of bariatric surgery on pulmonary function.

Although previous studies reported the effect of morbid obesity on pulmonary function, determining which patients are more likely to have significant pulmonary dysfunction that may lead to postoperative pulmonary complications is still unclear. This study aimed to investigate the correlation between age, sex, and BMI of patients undergoing bariatrtic surgery and preoperative pulmonary function to identify patients who are more likely to have significant pulmonary dysfunction before bariatric surgery and its impact on postoperative outcome.

Patients and Methods

Study design and setting

This is a retrospective analysis of prospectively collected data of consecutive patients with morbid obesity who underwent bariatric surgery at the General Surgery Department of Mansoura University Hospitals in the period of January 2012–December 2018. Bariatric procedures included laparoscopic sleeve gastrectomy (LSG), Roux-en-Y gastric bypass (RYGB), greater curvature gastric plication (GCP), mini-gastric bypass (MGB), and single-anastomosis sleeve ileal bypass (SASI). Ethical approval for the study was obtained from the Institutional Review Board of Mansoura Faculty of Medicine. This study was conducted in accordance with the declaration of Helsinki. This study is reported in compliance with the STROBE guidelines (See Supplementary Data, STROBE Checklist).

Eligibility criteria

Adult patients of both genders who were investigated with pulmonary function tests before bariatric surgery for morbid obesity were included. Morbid obesity was defined as BMI >40 kg/m² or BMI >35 kg/m² with at least one associated major comorbidity. Patients with incomplete records were excluded.

Preoperative assessment

Patients were thoroughly assessed preoperatively by taking a detailed history of the current condition, previous investigations and treatments, associated medical comorbidities including pulmonary problems, and previous surgery. The STOP-BANG questionnaire was used to screen for obstructive sleep apnea, this questionnaire entails questions on snoring, tiredness, observed apnea, high blood pressure, BMI, age, neck circumference and gender. A score of three to four indicated mild sleep apnea, and a score of five to eight indicated moderate to severe sleep apnea.⁹ The diagnosis of sleep apnea was further confirmed by sleep study (polysomnography).

Patients were then clinically examined to exclude associated ventral hernias, endocrinopathy, or other associated conditions. The weight and height were recorded and then BMI was calculated. Preoperative workup included routine laboratory investigations, electrocardiography, echocardiography in select patients, abdominal ultrasound, and pulmonary function tests.

Pulmonary function tests

Pulmonary function tests were conducted within 1 week before bariatric surgery using a dry rolling spirometer (PFT 2450 system; Sensor Medics, Yorba Linda, CA) in all patients in the sitting position.

Parameters measured included

Forced vital capacity (FVC), which is the amount of air that can be forcibly exhaled from the lungs after taking the deepest breath possible.

Forced expiratory volume (FEV1), which is the volume that has been exhaled at the end of the first second of forced expiration.

FEV1/FVC ratio, which is the ratio between the FEV1 and the FVC.

Peak expiratory flow (PEF), which is the maximal flow achieved during the maximally forced expiration initiated at full inspiration.¹⁰

Classification of pulmonary dysfunction

Pulmonary dysfunction in patients with morbid obesity was classified into restrictive and obstructive patterns based on FEV1/FVC ratio. Restrictive disorders due to pulmonary fibrosis or weak respiratory muscles had decreased lung volumes and normal FEV1/FVC ratio, whereas obstructive disorders as asthma and chronic obstructive pulmonary disease (COPD) had normal lung volumes, impeded flow rates, and low FEV1/FVC ratio (<80%).¹⁰

Data collected

The records were screened by 2 authors to retrieve the following data: patients' demographics including age and sex, body weight and height, BMI, associated comorbidities, findings of pulmonary function tests, type of bariatric surgery, intra- and postoperative complications, particularly pulmonary complications as diagnosed by contrast enhanced CT scanning. Pulmonary complications included pulmonary embolism, atelectasis, pulmonary edema, and respiratory tract infection including pneumonia.

Statistical analysis

Data were analyzed using SPSS^® version 23 (IBM Corp. Released 2015. IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY: IBM Corp.). Normally distributed data were presented as mean and standard deviation; non-normally distributed data as medians quartiles (interquartile range). Continuous data were processed using Student's t-test and categorical data were processed using chi-square analysis or Fisher's exact test where applicable.

Pearson's correlation coefficient test was used to assess the correlation between different parameters of pulmonary function and patients' age and BMI. Correlation coefficients were classified as strong (−1.0 to −0.5 or 0.5 to 1.0), moderate (−0.5 to −0.3 or 0.3 to 0.5), and weak (−0.3 to −0.1 or 0.1 to 0.3). P < .05 was considered statistically significant. P values <.05 were considered significant.

Results

Patients' characteristics

Ninety-seven patients with morbid obesity were included to the study. Patients were 82 (96.8%) women and 15 (3.2%) men. The mean age of patients was 34.6 ± 9.3 (range, 17–61) years. The mean weight of patients was 141.5 ± 24.4 (range, 85–210) kg and the mean height was 163.3 ± 7.7 (range, 145–180) cm.

The mean BMI of patients was 52.3 ± 8.1 (range, 35.8–77) kg/m². Two male patients were ex-smokers and one of the patients was an active smoker at the time of surgery. Fourteen (14.4%) patients had associated comorbidities. None of the patients were under medical treatment for bronchial asthma, COPD, or pulmonary hypertension at the time of surgery. Twelve patients had obstructive sleep apnea (mild = 2, moderate to severe = 10). Sixty-nine (71.1%) patients underwent LSG, 16 (16.5%) underwent SASI, 7 (7.2%) underwent GCP, 4 (4.1%) underwent MGB, 1 (1%) underwent RYGB.

Pulmonary function tests

The mean FEV1 was 2.7 ± 0.6 (range, 1.3–4.4) L and the mean FVC was 3.1 ± 0.7 (range, 1.8–5.5) L. The mean FEV1/FVC ratio was 85.9 ± 7.6 (range, 67–100) and the mean PEF was 4.8 ± 1.3 (range, 2.3–9.8) L/minutes.

Sixty-nine (71.1%) patients had normal pulmonary function tests, 17 (17.5%) had mild restrictive pattern, 9 (9.3%) had moderate to severe restrictive pattern, and 2 (2.1%) had an obstructive respiratory pattern.

Correlation between age and pulmonary function tests

Patients' age had a moderate negative correlation with FEV1 (r = −0.514, P < .00001), FVC (r = −0.448, P < .00001), and a weak negative correlation with FEV1/FVC (r = −0.11, P = .28), and PEF (r = −0.17, P = .09).

Patients aging ≤40 years had significantly higher FEV1 (2.8 ± 0.54 versus 2.2 ± 0.5, P < .0001), FVC (3.3 ± 0.7 versus 2.6 ± 0.6, P < .0001), and PEF (5 ± 1.2 versus 4.3 ± 1.25, P = .01) than patients aging more than 40 years (Table 1). Patients >40 years had higher odds for having pulmonary dysfunction than patients ≤40 years (odds ratio [OR]: 2.54, 95% confidence interval [CI]: 0.97–6.63, P = .05).

Table 1.

Differences in Parameters of Pulmonary Function Tests According to Patients' Age

Variable	Age ≤40	Age >40	P
Number	72	25	—
Mean age (years)	30.3 ± 5.7	47.4 ± 1.4	<.0001
Mean FEV1	2.8 ± 0.54	2.2 ± 0.5	<.0001
Mean FVC	3.3 ± 0.7	2.6 ± 0.6	<.0001
Mean FEV1/FVC	86.3 ± 7.9	85.1 ± 6.5	.49
Mean PEF	5 ± 1.2	4.3 ± 1.25	.01
Pattern
Normal (%)	55 (76.3)	14 (56)	.17
Mild restrictive (%)	11 (15.2)	6 (24)
Moderate to severe restrictive (%)	5 (6.9)	4 (16)
Obstructive (%)	1 (1.4)	1 (4)

Values shown in bold indicate significant p values < 0.05.

FEV1, forced expiratory volume in one second; FVC, forced vital capacity; PEF, peak expiratory flow.

Correlation between sex and pulmonary function tests

Patients' sex had a moderate negative correlation with FEV1 (r = −0.332, P = .0009), FVC (r = −0.322, P = .001), and PEF (r = −0.312, P = .002) and had a weak negative correlation with FEV1/FVC (r = −0.0533, P = .6).

Male patients had significantly higher FEV1, FVC, and PEF and significantly higher odds of pulmonary dysfunction compared to female patients (OR: 2.5, 95% CI: 1.14–11, P = .03) (Table 2).

Table 2.

Differences in Parameters of Pulmonary Function Tests According to Patients' Sex

Variable	Male	Female	P
Number	15	82	—
Mean FEV1	3.2 ± 0.7	2.6 ± 0.5	<.0001
Mean FVC	3.8 ± 0.9	3 ± 0.6	<.0001
Mean FEV1/FVC	85.2 ± 7.6	86.1 ± 7.6	.67
Mean PEF	6 ± 1.8	4.6 ± 1	<.0001
Pattern
Normal (%)	7 (46.6)	62 (75.6)	.009
Mild restrictive (%)	4 (26.6)	13 (15.8)
Moderate to severe restrictive (%)	2 (13.3)	7 (8.5)
Obstructive (%)	2 (13.3)	0

FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; PEF, peak expiratory flow.

Correlation between BMI and pulmonary function tests

The preoperative BMI had a weak negative correlation with FEV1 (r = −0.236, P = .02), FVC (r = −0.248, P = .01), FEV1/FVC (r = −0.007, P = .59), and PEF (r = −0.137, P = .18).

Patients with BMI >50 kg/m² had significantly lower FVC than patients with BMI <50 (2.9 ± 0.6 versus 3.3 ± 0.8, P = .006) whereas both groups had comparable FEV1, FEV1/FVC, and PEF (Table 3). Patients with BMI >50 had significantly higher odds of pulmonary dysfunction than patients with BMI <50 (OR: 4.9, 95% CI: 1.74–13.9, P = .002).

Table 3.

Differences in Parameters of Pulmonary Function Tests According to Preoperative Body Mass Index

Variable	BMI ≤50	BMI >50	P
Number	48	49	—
Mean BMI	40.1 ± 3.6	58.6 ± 6.2	<.0001
Mean FEV1	2.8 ± 0.66	2.6 ± 0.5	.09
Mean FVC	3.3 ± 0.8	2.9 ± 0.6	.006
Mean FEV1/FVC	85.5 ± 7.1	86.1 ± 7.7	.69
Mean PEF	5 ± 1.3	4.6 ± 1.3	.13
Pattern
Normal (%)	42 (87.5)	27 (55.1)	.0004
Mild restrictive (%)	2 (12.5)	15 (30.6)
Moderate to severe restrictive (%)	4 (8.3)	5 (10.2)
Obstructive (%)	0	2 (4.1)

BMI, body mass index; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; PEF, peak expiratory flow.

Postoperative complications

The mean operation time was 75.4 ± 21.1 minutes. A total of 15 patients experienced early postoperative complications within the first 30 days after surgery. Eight (8.2%) patients experienced pulmonary complications and 7 had other complications. Pulmonary complications included pneumonia (n = 3), atelectasis (n = 4), and pulmonary embolism (n = 1). Other complications included surgical site infection (n = 1), urine retention (n = 1), and severe vomiting (n = 5). There were no recorded cases of staple line bleeding or leak.

Of 69 patients with normal spirometry, 2 (2.9%) experienced pulmonary complications, when compared to 6 (21.4%) of 28 patients with pulmonary dysfunction (P = .006). Patients with preoperative pulmonary dysfunction had significantly higher odds of developing pulmonary complications than patients with normal spirometry (OR: 9.13, 95% CI: 1.71–48.6, P = .009).

Patients who developed pulmonary complications were 4 male and 4 female of a mean age of 34.6 ± 9.5 years and mean BMI of 58.5 ± 5.9 kg/m². As shown in Table 4, patients with pulmonary complications were significantly older, had significantly higher BMI, and significantly lower FEV1, FVC, and PEF than patients who did not experience pulmonary complications.

Table 4.

Differences in Demographics and Parameters of Pulmonary Function Tests Between Patients Who Developed or Did Not Develop Pulmonary Complications

Variable	Complication	No complications	P
Number	8	89	—
Mean age (years)	34.6 ± 9.5	40.8 ± 1.8	<.0001
Male/female	4/4	11/78	.018
Mean BMI (kg/m²)	58.5 ± 5.9	51.7 ± 8.1	.02
Mean FEV1	2.2 ± 0.5	2.8 ± 0.6	.007
Mean FVC	2.6 ± 0.8	3.2 ± 0.75	.03
Mean FEV1/FVC	82.7 ± 6.9	86.3 ± 7.6	.19
Mean PEF	4.05 ± 1.4	4.9 ± 1.1	.04
Mean operation time (minutes)	71.2 ± 3.5	75.7 ± 21.2	.55

BMI, body mass index; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; PEF, peak expiratory flow.

Discussion

The negative impact of morbid obesity on health extends to involve several associated comorbidities that substantially affect patients' quality of life. One of the well-known adverse effects of morbid obesity is its effect on the respiratory system. Pulmonary dysfunction associating morbid obesity is attributed to the mechanical effect of obesity on the lung physiology and the influence of the systemic inflammatory mediators produced by the excess adipose tissues on the central respiratory control. Therefore, it is understandable to know that asthma and COPD are more common among patients with morbid obesity than the general population.¹¹

Since bariatric surgery is on the rise, being the most effective treatment for morbid obesity, the effect of preoperative pulmonary dysfunction on the complication rate of the procedure has been investigated. Similarly, the improvement in pulmonary dysfunction after bariatric procedures also gained equal attention. Accordingly, pulmonary function screening has been recommended for patients with morbid obesity before bariatric surgery.¹²

Data on the utility of preoperative pulmonary function screening in predicting postoperative pulmonary complications are spare and yet conflicting. While some investigators¹³ found preoperative abnormal spirometry not predictive of postoperative complications after gastric bypass, other researchers¹⁴ reported that pulmonary function tests help predict complications after open bariatric surgery and that the reduction in vital capacity may reflect increased intra-abdominal pressure and decreased chest wall compliance.

This study aimed to identify the criteria of patients with morbid obesity who are more likely to have pulmonary dysfunction before bariatric surgery and the impact of this dysfunction on postoperative pulmonary complications. Knowing which patients are at higher risk to develop respiratory complications after surgery may alter the decision of the surgeon and may warrant further measures to avoid postoperative morbidities.¹⁵

The study included 97 patients and the majority of which were female in concordance with previous literature that highlighted the female predominance in bariatric surgery. More than two-third of patients underwent LSG, in agreement with the increasing popularity of the procedure that became the most frequently performed bariatric procedure across the world.¹⁵

Approximately 10% of patients in our study had restrictive pattern of pulmonary dysfunction before surgery and <20% had mild restriction of pulmonary function. This finding was close to the incidence of restrictive pulmonary dysfunction among morbidly obese patients reported by Guimarães et al.,⁸ which was around 17%. Only in 2 patients an obstructive pulmonary dysfunction pattern was observed that emphasizes the fact that the restrictive pattern of pulmonary dysfunction is more common than the obstructive one in patients with morbid obesity.¹⁶

We studied the correlation between patients' demographics including age, sex, and BMI and the likelihood of pulmonary dysfunction before surgery. We found male patients, patients older than 40 years, and superobese patients with BMI >50 are more likely to have pulmonary dysfunction on testing with spirometry, despite having no symptoms of respiratory problems preoperatively.

Men tend to have higher lung volumes than women owing to several anatomic and physiologic differences involving the airways, lungs, chest wall, and diaphragm.¹⁷ However, with morbid obesity the incidence of pulmonary dysfunction in men can be quite higher than women. This study highlighted this phenomenon as more than 50% of male patients had abnormal pattern of respiratory function compared to 25% of female. This may be explained by the different pattern of obesity among men and women. Male patients have an android pattern of fat deposition in the abdominal region, which generates a greater resistance to diaphragmatic contraction, hindering the ventilatory mechanics and resulting in a higher incidence of pulmonary dysfunction when compared to female patients where the gynoid pattern of obesity does not encumber the respiratory muscles.¹⁸

We found patients aging more than 40 have higher odds of having pulmonary dysfunction than younger patients. This observation is explained by the normal aging-related anatomical and physiologic changes in the respiratory system. These changes include decrease in the total respiratory system compliance, loss of supporting structures of the lung parenchyma causing dilation of air spaces, decrease in respiratory muscle strength, increase in the alveolar dead space, and functional changes in the airway, all lead to a progressive decline in lung function.¹⁹ Perhaps this is why this study found patients older than 40 years had significantly lower FEV1, FVC, and PEF than younger patients.

Patients with super obesity (BMI >50) had higher odds of having pulmonary dysfunction than patients with BMI <50. The impact of obesity on the pulmonary function has been studied in cross-sectional and longitudinal studies that have shown that the increase in BMI is associated with an exponential decrease in FEV1, FVC, and FRC.^10,20 However, we found that BMI had a weak negative correlation with FEV1, it was previously implied that the relation between FEV1 and BMI is not straightforward and that the correlation between increased BMI and decrease in FVC is stronger than with FEV1 because obesity is more often associated with a restrictive pulmonary defect than an obstructive one.^11,21

Approximately 8% of patients in this study experienced postoperative pulmonary complications, within the range (5%–10%) expected after nonthoracic operations. However, patients with preoperative pulmonary dysfunction had much higher rate of pulmonary complications (21%), close to that reported after nonthoracic operations in high risk patients.²²

Patients who experienced pulmonary complications had significantly lower lung volumes than those who did not develop complications. This underscores the value of pulmonary function testing before bariatric surgery in predicting the risk of postoperative complications. van Huisstede et al.²³ concluded that “subjects with abnormal spirometry test results have a threefold risk of complications after laparoscopic bariatric surgery.” Other investigators^12,14,23,24 also documented that abnormal pulmonary function tests can predict postoperative complications after bariatric surgery, these investigators included all types of complications, even nonpulmonary morbidities, in their analysis whereas our analysis was restricted to the pulmonary complications only, and thus could be more specific and precise.

The ability to identify patients at high risk for development of postoperative pulmonary complications before bariatric surgery can help improve their postoperative outcome by employing risk-reduction strategies in these patients.

Preoperative risk-reduction strategies include cessation of smoking, lung rehabilitation, and continuous positive airway pressure (CPAP), whereas intraoperative measures include lung-protective ventilation, CPAP during preoxygenation, restriction of fluid therapy, avoidance of long-acting neuromuscular blockers, minimization of opioids, and extubating patients in the reverse Trendelenburg position with gentle recruitment maneuver taking care to avoid hyperoxygenation by 100% O². Finally, postoperative strategies comprise early ambulation, adequate postoperative analgesia, avoidance of nasogastric tubes, incentive spirometry, and the use of CPAP.^25–27

CPAP and bi-level positive air pressure (BiPAP) help prevent airway collapse, improve pulmonary function, and are recommended by the American Society of Metabolic and Bariatric Surgery (ASMBS) guidelines²⁶ to be used before bariatric surgery in patients with moderate to severe sleep apnea. It has been also recommended to use CPAP after bariatric surgery at the discretion of the surgeon until clinical evaluation demonstrates resolution of sleep apnea.

Although not investigated in this study, an improvement in pulmonary functions after bariatric surgery has been documented in former studies,^8,28 which emphasizes the efficacy of bariatric surgery in improving medical comorbidities associated with morbid obesity.

Limitations of this study include its retrospective nature that may be associated with the risk of selection bias. The impact of bariatric surgery on pulmonary function and the extent of improvement in restrictive and obstructive pulmonary dysfunction were not explored because the main purpose of the study was to identify which patients are at higher risk to have pulmonary dysfunction before bariatric surgery and, subsequently have higher risk of postoperative pulmonary complications.

Conclusion

Around 30% of patients undergoing bariatric surgery had pulmonary dysfunction. Pulmonary dysfunction in preoperative spirometry was able to predict postoperative pulmonary complications.

Males, patients older than 40 years, and superobese individuals had higher odds of having pulmonary dysfunction and are at higher risk to develop pulmonary complications after bariatric surgery. Therefore, this high risk group needs adequate optimization of the pulmonary function preoperatively and careful postoperative monitoring and prophylaxis against respiratory complications by using the appropriate risk reduction strategies.

Informed Consent

Informed consent was waived because the study is a retrospective analysis of data.

Footnotes

Authors' Contributions

S.H.E. designed the study. S.H.E., and M.A.A.-R. contributed to data collection and analysis, writing, and revising the article. M.E., A.E., and M.S. contributed to data interpretation, writing, and critical revision of the article. H.G.E., A.A., and A.F. contributed to data analysis and revision of the article.

Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Supplementary Material

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