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Gastroscopy and Colonoscopy are very common procedures. They are termed ‘Endoscopy’ which is broadly defined as inserting a scope with a camera into any body cavity. This can range from the Esophagus, Stomach, Colon, Rectum, Nose, Throat, Chest and Abdominal Cavity.

Gastroscopy (OGD, EGD)

A Gastroscopy is performed by inserting a flexible scope through the mouth and examines the Esophagus, Stomach and the first and second part of the Duodenum. It is sometimes called an ‘Esophago-Gastro-Duodenoscopy’ (OGD or EGD). It is commonly referred to as an ‘Endoscopy’ although it is not the correct terminology.

Common abnormalities that can be detected are ulcers, cancers, reflux esophagitis and gastritis. Polyps in the stomach can also be seen and removed, although the common polyps in the stomach are not cancerous. Helicobacter Pylori infection/inflammation in the stomach can also be diagnosed with biopsies.

Gastroscopies are usually performed for patients with symptoms. It is not generally performed in patients for screening without symptoms, except in populations where the Stomach Cancer rates are high.

Gastroscopy is a very low risk procedure and can be performed very comfortably with sedation and usually takes about 5 to 7 minutes.


A Colonoscopy is performed by inserting a flexible scope through the anus and is the best test to inspect the mucosa or inner lining of the colon and rectum. This is where most polyps and cancers are seen. When seen, polyps can be removed by inserting various instruments though the colonoscope.

A Colonoscopy is a low-risk procedure and can usually performed very comfortably under sedation and usually takes about 15 to 20 minutes. However, if there are polyps that need to be removed, it may take a few minutes longer.

A Colonoscopy is the procedure of choice for screening of individuals who are at an increased-risk of developing Colorectal Cancer or Polyps. It has the added advantage of being able to remove polyps if they are seen during the Colonoscopy. A screening colonoscopy is to not only look for early cancers, but also to ‘look-for and remove’ polyps in the colon. It is also usually the procedure of choice to investigate patients with symptoms associated with Colorectal Disease/Disorders.

The Colonoscopy is performed as a Day-Surgery Procedure and the total admission time to the hospital endoscopy centre is usually about 3 to 4 hours from the time of registration to discharge, including the procedure and recovery time from sedation.

Most patients feel that the colonoscopy procedure itself is very comfortable and almost painless! However, some patients do not like the ‘bowel preparation’ prior to the colonoscopy. This entails taking oral medication and fluid to clear the colon so that a good view is obtained during the colonoscopy. Good ‘bowel preparation’ is a very important part of the process as if a good view is not obtained, the colonoscopy becomes very much less useful as polyps and, sometimes even, small cancers may be missed. With the appropriate counselling, this process may not be as unpleasant as it is perceived to be.

Comfort and Safety of Gastroscopy and Colonoscopy

Many patients worry about discomfort or pain during the procedure.

However, the procedures are usually performed under sedation and patients are very comfortable. Most are ‘asleep’ and are not aware of the procedure.

Sedation is different from General Anesthesia (GA).

In GA, patients are injected with medications that induce sleep and most times, they are ‘completely paralysed’ and a ‘breathing tube’ is inserted to the windpipe and lungs and connected to a ‘breathing machine (ventilator)’. In GA, patients do not feel any awareness or pain at all. GA is used for most major surgical procedures.

Sedation is much milder than GA. In sedation for endoscopy (Gastroscopy and Colonoscopy), patients are injected with medication to induce sleep with some mild analgesics. Patients are generally asleep, like a normal sleep, breathing themselves without any mechanical (machine) assistance, only with some oxygen prongs. Usually, there is no pain, and no clear awareness and patients are very comfortable during the procedures. Sedation is also very safe and is conducted under close monitoring and after the procedure, patients wake up with minimal side effects.

Risks of Gastroscopy and Colonoscopy

Gastroscopy and Colonoscopy are very safe procedures. However, as in any procedure, there are some risks involved.

Risk of Sedation

The risk of Sedation is very low. Sedation can be performed safely in most patients. This can be administered by the endoscopist performing the procedure or with an anesthetist. Anesthetists administering the sedation reduces the risk even further and is recommended for ill patients, older patients, patients with many medical problems, obese patients, patients who snore a lot, or patients who want an added margin of safety with a slight added cost.

Risk of perforation

There is a very small risk of causing a perforation of the colon. With caution, this risk is extremely low (< 0.1%) but can still occur with abnormal bowel, adhesions or during the removal of polyps, especially when cautery is applied. If a perforation does occur, it may be very serious and may require surgery to treat it.

Risk of Bleeding

When polyps are seen and removed and, rarely, with biopsies, there is a small risk (<1%) of bleeding. This bleeding is termed ‘secondary hemorrhage’ and usually occurs a few days or up to about 2 weeks after the procedure. This is usually unpreventable. Although it may look dangerous with blood passing out from the anus, it is usually not life-threatening. However, a colonoscopy may be required to stop the bleeding.

Risk of ‘Missed Lesions’

Although the colonoscopy is likely the ‘best test’ for diagnosing colon lesions, there is still a chance of missing lesions. This rate is about 6%, no matter how diligent the endoscopist conducting the procedure is. Many factors can reduce the accuracy of the scope including inadequate cleanliness of the bowel, diverticular disease, lesions in the ascending and sigmoid colon, lesions at the flexures, inadequate sedation, long loopy colons, flat lesions, lesions behind folds and inadequate distension of the colon, among others. Careful withdrawal and hence, careful inspection of the colon and a minimum cecal withdrawal time of at least 6 minutes is recommended.

Patients who continue to have suspicious symptoms even after a recent ‘normal’ colonoscopy are advised to consult their doctors and, sometimes, a repeat scope may be required in persisting, unexplained symptoms.

Insurance Policy

Integrated Shield Plans

Medical expenses are a concern for many patients. It can, sometimes, be overwhelming to deal with the various health insurances, especially if this is your first encounter. Our staff will assist you with the administrative part of your insurance, as far as possible. Dr Teoh is on the panel for the following Integrated Shield Plans : NTUC, AIA, Great Eastern (GE), Singlife (Aviva), AXA. We are also willing to assist with any other insurer, Local or International.

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