"When it works, it works great," he said. "But this is a therapy, not a cure. It's not like getting your appendix out and you're fine. ... The goal is to get them off intravenous feeding and get them a normal life. They still may be nauseated a few times a week or throw up a couple of times, but we always see improvement in symptoms."
Ordinarily, strong muscular contractions propel food through the body's digestive tract, but in gastroparesis, the wall muscles work poorly or not at all. Some doctors suspect that the vagus nerve, which helps manage the digestive tract, has been damaged, causing food to remain in the stomach longer.
Early symptoms include stomach distention, nausea and vomiting, a feeling of fullness and unintentional weight loss.
The nerves in the stomach are like a "second brain," according to Dr. Lee M. Kaplan,, a gastroenterologist and director of the Weight Center at Massachusetts General Hospital in Boston.
"The nervous system in the gut is larger than any other part of the body except the brain itself.
"If you think about the gut, it has to propel food along in an organized way," he said. "Imagine you have a tube of toothpaste and have to start at the bottom and push to the top."
The disorder, which is rarer than leukemia in children younger than 18, interferes with digestion, causing nausea and vomiting and wreaking havoc with blood sugar levels and nutrition.
About 35 million Americans have gastrointestinal motility disorders, including gastropaesis, irritable bowel syndrome and gastroesophageal reflux disease. As many as 8 million people of all ages are hospitalized each year, according to the Centers for Disease Control and Prevention.
Complications can include weight loss and malnutrition, overgrowth of bacteria in the stomach and blood sugar fluctuations. Undigested food can also harden into a solid mass called a bezoar, which causes nausea and vomiting and can be life-threatening.
In adults, gastroparesis is most commonly associated with diabetes or a disease such as Parkinson's, but in children, the cause is usually a virus, according to Dr. Carlo Di Lorenzo, Gentrie's pediatric gastroenterologist at Nationwide.
"Like getting a virus and the stomach doesn't work for a few days, in some cases the infection lasts much longer," he said. "Something affects the nerves of the stomach that provide the message how to contract.
"If things don't move well, the stomach doesn't break down well and it takes forever for the food to leave the stomach. The longer food is in the stomach, it eventually comes out the wrong end."
Sometimes, the condition gets better over time. When it doesn't doctors turn to dietary changes; small feedings with less fat and fiber, medication and even botox injections.
"Most definitely a pacemaker is a last resort," Di Lorenzo said.
So far, Gentrie has been receiving nutrients through a peripherally inserted central catheter in the veins. She still throws up several times a day and has to drain the bile-like substances from her stomach.
The danger of prolonged use of the catheter is infection, which can sometimes be fatal.
It took five months to diagnose Gentrie's condition because her doctors at first suspected anorexia or bulimia, and even her insurance company initially gave her parents the run-around.