Colonoscopy in Obese Patients: Time to Change Position
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Improvements in the diagnostic and therapeutic potential of digestive endoscopy over the past few decades have notably increased the number of procedures performed, to the point that endoscopy is now almost considered to be routine. Changes in the epidemiology of colorectal cancer (CRC), which now represents the second leading cause of cancer-related death in America  and Europe , have also contributed to an increase in colonoscopies, since this procedure is considered the most accurate and effective method for early detection and prevention of CRC and premalignant precursor lesions. Colonoscopic removal of adenomatous polyps was proven to prevent approximately 80 % of CRCs [3, 4], and to lower the overall death rate from the disease . In this context, several studies have reported that CRC screening is clinically useful  and cost-effective  in the average-risk population, significantly reducing mortality .
Obesity is a well-accepted risk factor for CRC [9, 10]; excessive body mass index (BMI) and physical inactivity are interrelated risk factors reported to account for between a fourth and a third of CRCs . BMI is associated with an increased risk of incident CRC in men of all ages and in women between the ages 50–66 . Indeed, excessive BMI is a modifiable risk factor associated with increased risk of adenoma and advanced adenoma recurrence ; unfortunately, weight loss has no effect on this risk of recurrence.
In this context, and taking into account that obesity has reached epidemic proportions in America  and Europe , colonoscopy in obese patients represents a challenging issue for endoscopists, with much research focusing on the special features of colonoscopy in this population. For example, while a higher waist circumference has not been associated with a difficult cecal intubation [16, 17, 18], obesity constitutes an independent predictor of inadequate bowel preparation for colonoscopy , although these results were not reproduced when using a sodium picosulphate-based bowel preparation . Furthermore, some endoscopic techniques and maneuvers normally required during the examination, including patient repositioning and the application of abdominal pressure, are more difficult to perform on obese patients. Extra difficulty is added when changing the position of a sedated obese patient. A recent study in which abdominal compression obtained with a fitted corset facilitates colonoscopy reported that extra abdominal compression and a change of position was used less frequently in the study subjects accompanied by less procedural pain . In contrast, no definite data are available on the effect of a change from standard left lateral decubitus to prone position in facilitating colonoscopy in obese patients.
This number of Digestive Diseases and Sciences includes a prospective randomized trial by Uddin and colleagues  which reports for the first time that starting sedated colonoscopy in prone position for male obese subjects (BMI > 30 kg/m2) significantly shortens cecal intubation times with less need for patient repositioning. Additionally, the authors reported no differences in subjects’ perception of pain or their willingness to repeat the procedure when compared with obese subjects in whom the exploration was started using the standard left decubitus position. The subjects were sedated with benzodiazepines and narcotics under the endoscopist’s supervision due to safety concerns; patients scheduled for deep sedation with propofol or general anesthesia were excluded. Although 18 % of recruited patients had antecedents of sleep apnea, half of them were explored in the prone position with no complications. Despite the fact that obesity is associated with an increased frequency of sedation-related complications, non-anesthesiologist-administered propofol sedation is safe and efficient [23, 24], with exceptionally rare complications with respect to airway management. In this context, propofol sedation has also been used safely by trained professionals in obese patients undergoing advanced endoscopic procedures , even when explored in the prone position, as frequently occurs in endoscopic retrograde cholangiopancreatography. The prone position may actually be associated with a lower risk of obstructive apnea during sedation since the tongue is less likely to fall back. In this sense, performing the procedure with the patient in the prone position may be a non-invasive way to increase oxygenation in patients with acute respiratory distress . While patients with morbid obesity have been excluded from most studies evaluating carbon dioxide (CO2) insufflation in colonoscopy, those obese patients with a BMI < 40 kg/m2 have not; thus, a recent study did not report higher levels of end-tidal CO2 or adverse respiratory events in morbidly obese subjects .
Even if some safety aspects regarding deep sedation administered by non-anesthesiologists in prone subjects remain unresolved, the original article included in this issue of Digestive Diseases and Sciences  constitutes a clear confirmation of how a simple, inexpensive, and easily reproducible measure can improve colonoscopy performance in obese patients. From these results, we should reconsider whether it is time to change patients’ position towards easier, but efficient procedures.
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