CO2 volumes higher than previous reports in VC

Jul 5, 2010

Using more CO₂ to insufflate the colon during virtual colonoscopy (also known as CT colonography or CTC) doesn't produce better distention, but patients with ileocecal valve incompetence -- most patients presenting for screening -- require more insufflation, say researchers from Ireland.

"Adequate distention is critical to achieving good sensitivity and specificity in the practice of CT colonography," said Patrick McLaughlin, MD, from Cork University Hospital.

Using the most common method of insufflating the colon, automated insufflation of CO₂ gas, the literature suggests that most patients receive about 2 L of CO₂. However, "there is little scientific information about gas volumes" typically used in CTC, though literature suggests approximately 2 L or 20 puffs [if manually administered] for most patients," McLaughlin said in a presentation at the American Roentgen Ray Society (ARRS) meeting in San Diego in May.

"We found no studies in the literature that correlated colonic distention with gas volume," McLaughlin said. The study sought to verify colonic distention in a screening VC cohort and correlate it with CO₂ use in patients presenting for screening CTC.

These days, semiautomatic insufflation devices are the most common way to perform bowel insufflation prior to acquiring images in CTC. The devices administer CO₂ using a pressure cutoff system.

"The end-volume of CO₂ that is administered varies according to the pressure achieved, but the typical cutoff is 25 mm/Hg," according to McLaughlin. Total gas volume is generally limited to 2.5 L on the insufflators, he said.

The 108 screening subjects (mean age, 62 years; range, 24-89) followed a low-residue diet for two days prior to CTC. One day before CTC, 40 mg of Picolax was administered in four divided doses (10 mg sachets) over a two-day period.

CO₂ was administered using automated insufflation (ProtoCO₂l, Bracco Imaging, Milan). Hyoscine-N-butylbromide (Buscopan, Boehringer Ingelheim, Ingelheim, Germany) was not routinely administered. "It is the exception rather than the rule that we would give patients spasmolytics," McLaughlin said.

The results showed a mean gas volume of 3.357 L with a range of 6.777 L. The volume was slightly higher in men than in women (3.7 L versus 3.2 L), and it was slightly higher in the 76% of subjects (n = 82) with ileocecal valve incompetence.

"Patients with ileocecal valve incompetence tolerated or required higher gas volumes" (3.571 L versus 2.675L); however, "distention scores were not significantly less in patients with ileocecal incompetence," McLaughlin said.

Diverticulosis was found in 28% of the patients, which did not significantly affect distention scores; however, "nondistended segments were frequently found in patients with diverticulosis," McLaughlin said. There were 38 patients (36%) with one or more nondistended segments, most frequently involving the sigmoid colon.

Nondistended segments were also more common in older patients, a group that also had significantly lower gas volumes (2.7 L for nondistended segments; 3.7 L for distended segments).

There was no correlation between gas volumes and colonic distention scores, McLaughlin said. But individuals with ileocecal valve incompetence required significantly more gas. In addition, "there were 38 patients with one or more nondistended segments -- and this was more common than previously reported," he said.

Also important was the high percentage of patients with ileocecal valve incompetence, and the higher CO₂ volumes they required for insufflation, McLaughlin said.

By Eric Barnes
AuntMinnie.com staff writer
July 6, 2010

Study reveals lesions most likely to be dismissed by VC CAD, January 14, 2010

New ACR guidelines overhaul VC practice, training standards, November 27, 2009

VC CAD nabs undetected polyps in jumbo screening study, October 29, 2009

VC excels at diverticulosis staging, September 28, 2009