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Preparing for a colonoscopy

If you shudder at the thought of having a colon cancer–screening colonoscopy, chances are it’s the “prep” that’s stoking your apprehension. It’s certainly a major inconvenience: getting ready for the procedure takes much longer — according to one study, 16.5 hours, on average — than the time you’ll spend at a medical center the day of your colonoscopy (usually no more than three hours). But what’s most off-putting is the purgative part — taking a powerful bowel-clearing substance and coping with the resulting diarrhea.

A Guide to Women's Health
Midlife can be a woman’s halftime celebration. Not only can it be an opportunity to reflect on and rejoice in the life you’ve lived, but it is also a good time to plan your strategy for the future. This report will help you determine the conditions for which you are at greatest risk and do your best to avoid them. It will also help you to better manage chronic conditions that may erode your quality of life, and to deal with physical changes that are more bothersome than serious. It is designed to give you the information to make the choices today that will ensure you the best health possible tomorrow.

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What’s involved?

Emptying the contents of the colon is the first requirement for a successful colonoscopy. If the bowel prep isn’t up to par, polyps and lesions can be missed; the colonoscopy may take longer (increasing the risk of complications); or the whole process may need to be repeated or rescheduled.

You’ll need to stop eating solid foods the day before the colonoscopy, and starting the evening before the procedure, you must take a substance that triggers bowel-clearing diarrhea. Exact instructions will depend on the bowel prep prescribed, the time of your colonoscopy, and any prior experience you’ve had with colon preps (if one didn’t work before, you’ll likely be prescribed a different one).

Here are some common bowel preparations. Please contact your clinician to discuss the one that is best for you.

Common bowel preparations

Name/type What’s involved Comments
Diet On the day preceding and up to a few hours before the procedure, consume clear liquids only: broths, soft drinks, tea and coffee (with no milk or creamer), clear juices, Jell-O; but no red, blue, or purple coloring. You may also be asked to avoid nuts, seeds, hulls, skins, or other insoluble fiber for a day or more before beginning clear liquids. Used in conjunction with colon-cleansing preparations, never as the sole bowel preparation. Recommendations vary and may depend on individual situation, clinician preference, or both.
Polyethylene glycol (PEG)
Brand names: Golytely, Colyte, Nulytely, Trilyte, Halflytely
This is an electrolyte-balanced solution consumed in large amounts (4 liters, or about 1 gallon) the evening before a colonoscopy. Patients drink 8 ounces every 10 minutes until the bowel’s output runs clear or the solution is completely consumed. In another approach, the dose is divided into 3 liters the night before and 1 liter the morning of the colonoscopy. A newer preparation (for example, Halflytely) uses 2 liters (about 2 quarts) of PEG solution taken in conjunction with a laxative (bisacodyl or magnesium citrate). PEG solutions work by pushing a large volume of fluid through the bowel to force out waste. They cause no significant electrolyte shifts, so they are considered safer than OSP solutions (see below). The salty taste may be unpalatable, and the large fluid volume can cause nausea, vomiting, bloating, and cramping. An antinausea drug may be prescribed.
Oral sodium phosphate (OSP) solution
Brand names: Fleet Phospho-soda EZ-Prep, Fleet Accu-prep
Two small doses of OSP solution diluted in at least 8 ounces of fluid are taken 10 to 12 hours apart. Each dose must be followed by 16 ounces or more of liquid. Adequate fluid intake is needed throughout the preparation and after the colonoscopy. OSP draws water into the gut to promote cleansing. It’s as effective as PEG and easier to tolerate, but it can cause dehydration and electrolyte imbalances.
Oral sodium phosphate (OSP) tablets
Brand names: Visicol, OsmoPrep
Twenty tablets are taken the evening before the colonoscopy, 4 at a time with 8 ounces of clear liquid every 15 minutes. Depending on the preparation, 12 to 20 more are taken the same way a few hours before the procedure. Bisacodyl may be added. OSP tablets are as effective as liquid OSP or PEG and may be more tolerable. They may cause dehydration and electrolyte imbalances in some people.
Magnesium citrate
Either laxative may be used with lower-volume (2 liters) PEG. Both laxatives may be used in combination with a restricted diet. Magnesium citrate may be used alone. There are rare reports of ischemic colitis (loss of blood supply to the colon) associated with bisacodyl use.

Tips for a successful colonoscopy prep

Preparing for a colonoscopy may be uncomfortable and time-consuming, but it needn’t be an ordeal. Here are some things you can do to help it go as smoothly and comfortably as possible:

  • Make sure you receive your colonoscopy prep instructions well before your procedure date, and read them completely as soon as you get them. You’ll need to stop certain medications and foods up to a week ahead of time. This is also the time to call your clinician with any questions and to buy the bowel prep she or he has prescribed. Pick up some medicated wipes (for example, Tucks or adult wet wipes with aloe and vitamin E) and a skin-soothing product such as Vaseline or Desitin — you’re going to be experiencing high-volume, high-velocity diarrhea.
  • Arrange for the time and privacy you need to complete the prep with as little stress as possible. Clear your schedule, and be at home on time to start your prep. If you have children or aging parents who need attention, have someone else be available to them while you’re indisposed.
  • Water can get boring, so keep a variety of clear liquids on hand. On the day before your colonoscopy — when you’re restricted to clear liquids — you can have popsicles, Jell-O, clear broth, coffee or tea (without milk or creamer), soft drinks, Italian ice, or Gatorade. But take nothing with red, blue, or purple dye. Drink extra liquids before, during, and after your bowel prep (usually until a few hours before your procedure), as well as after your colonoscopy.
  • To make a bad-tasting liquid prep like PEG easier to swallow, try one or more of the following: if the PEG doesn’t come flavored, add some Crystal Light or Kool-Aid powder (again, not red, blue, or purple); add some ginger or lime; drink it chilled; drink it through a straw placed far back on your tongue; hold your nose and drink it as quickly as possible; quickly suck on a lemon slice after you finish each glass; hold a lemon or lime under your nose while you drink; suck on a hard candy after each glass.
  • Wear loose clothing, and stay near the bathroom. Better yet, once the preparation starts to work, stay in the bathroom — because when the urge hits, it’s hard to hold back. Consider setting up shop near the toilet with music, your laptop, magazines, or books.

A Guide to Men's Health
This Special Health Report offers steps and strategies to lessen — or prevent — threats to a man's well-being and longevity. It provides a wide-ranging, clear-eyed look at the leading causes of death for men at midlife and beyond. It examines those factors that put them at risk for a variety of health problems and explains the important measures than can be taken to reduce risk and live a longer, healthier life.

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December 2008 update

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