A study of Ethicon Endo-Surgery Inc's computerized system to help sedate patients undergoing a colonoscopy showed it was effective but other factors may have played a role, the U.S. Food and Drug Administration said in a memo released on Wednesday.

The unit, called Sedasys, monitors patients' vital signs while intravenously delivering the sedative drug propofol - made by a variety of manufacturers as a generic and also by AstraZeneca under the brand name Diprivan.

Ethicon Endo-Surgery, part of Johnson & Johnson, is seeking FDA approval to market the device for use among healthcare providers who have no special training in anesthesia for patients undergoing a colonoscopy.

The FDA document was released ahead of a public meeting on Thursday when the agency will seek recommendations from outside advisers on whether to approve the product.

While a company study showed Sedasys was superior to current sedation methods, FDA staff noted "a marked study site effect" that showed "investigator behavior rather than product performance may have favored the Sedasys System."

Ethicon Endo-Surgery is also seeking approval for use in tests to diagnose upper gastrointestinal tract disorders, or esophagogastroduodenoscopy, but data for that indication did not meet its goals, the FDA said.

Company officials, in a separate document, said Sedasys provides automated sedation with fewer side effects that could help ease patients concerns about colonoscopies and encourage more people to get the procedure.

Studies have shown low compliance among Americans who are supposed to undergo a colonoscopy, which is generally recommended for those age 50 or older to detect colon cancer.

Sedasys does not change the actual colonoscopy procedure itself, but company officials said it helped better control dosing and allowed patients to recover faster.

A company-funded study of 1,000 patients showed patients sedated with Sedasys recover in a mean time of 2.7 minutes compared to 6.3 minutes in patients sedated traditionally.

But the FDA said a top safety concern is the number of cases where patients became unresponsive or lapsed into deep sedation or general anesthesia. It said it would ask its outside experts whether the device was safe and effective for use in clinicians without anesthesia training.

While Sedasys monitors patients to help deliver the most accurate drug dose possible, Ethicon Endo-Surgery's general manager for sedation products Mike Gustafson said it would allow clinicians giving the tests to focus more on patients.

"The device is only going to make conservative drug dosing decisions ... the clinicians are watching the patient using the device as a tool," he told Reuters.

It is unclear how many doctors' offices, clinics or hospitals would invest in such a device. Gustafson said it was too soon to say how much Sedasys would cost but said that there are 16 million gastroenterological procedures in the United States each year, including 12 million colonoscopies.

The American Gastroenterological Association, which represents doctors who give colonoscopies and other similar tests, said it supported computerized sedation and that propofol can be given safely by clincians not specifically trained in anesthesia.

Requiring anesthesia doctors or nurses "add(s) significant costs to endoscopic procedures, despite no evidence for improved patient outcomes for average risk patients." it said.

Representatives for the American Society of Anesthesiologists had no immediate comment.