An impedance study is a test done to find out if contents from the stomach are coming up into the esophagus (food tube), by evaluating acid and non-acid gastroesophageal reflux.
In this test, a thin, flexible tube is passed through the nose, down the back of the throat and into the esophagus. The tube is carefully taped into place on your child's cheek. The end of the tube is attached to a computer that will remain at your child's bedside throughout the study.
Because of the computer, your child will need to stay overnight in at Boston Children's Hospital. Your child will need to stay in the room close to his or her bed. He or she will also need to use a bedside toilet instead of walking to the bathroom.
An impedance study takes 18 to 24 hours. The tube is left in place for this time. You will be asked to keep a diary of your child's activity during the study. The doctor will use the diary to compare the computer reading with your child's activity.
What happens before an impedance study?
- Your child must have an empty stomach for an impedance study.
- If your child is younger than 6 months, he or she must have NOTHING to eat or drink for two hours before the impedance study takes place.
- If your child is older than 6 months, he or she must have NOTHING to eat or drink for four hours before the impedance study takes place.
- If your child takes any medication to reduce the amount of acid in the stomach, please speak with your doctor a week before the test about altering your usual medication schedule—some medications interfere with the impedance study.
What happens during an impedance study?
- The nurse will check your child's height to determine where to place the tube.
- To help calibrate the computer, your child will dip his or her finger into liquids in two test tubes.
- The nurse will pass a tube through your child's nose into the stomach. You may stay with your child while the tube is passed.
- Infants and young children will be snuggled in a blanket to help them to feel secure and stay still while the tube is being passed.
- Older children, who are more likely to cooperate, may prefer to sit in a chair while the nurse passes the tube.
- Passing the tube may cause your child to cough, sneeze or gag. This feeling will pass after the tube is taped in place. Once in place, the tube should not bother your child.
- Once the tube is taped in place, your child will have an x-ray to check the exact position of the tube. Depending on the x-ray results, the tube may have to be repositioned and re-taped.
- Special sleeves may be put on infants and small children to prevent them from bending their elbows and pulling out the tube.
- You will be asked to write down what your child is doing while the tube is in place, such as eating, sleeping and coughing. Your child's nurse will explain exactly what needs to be written down to help with the study.
- The tube will be removed the next day by a member of the gastroenterology staff. Removing the tube takes less than a minute and does not hurt.
How will we be informed of the results?
When the tube is removed the information recorded in the computer will be interpreted by a Boston Children's gastroenterology doctor. Call your child's primary doctor one week after the study for the results.