SEATTLE – Oral contrast is almost always unnecessary when performing a CT scan to work up adults with acute abdomens. Further, intravenous contrast is needed only when vascular causes of pain are suspected, according to Dr. Phillips Perera, a clinical associate professor of emergency medicine at Stanford (Calif.) University Medical Center.
As with everything in medicine, there are rare exceptions to this advice, he said. Oral contrast can be helpful to confirm the presence of a fistula in a postcolectomy patient, for example.
With the growth of endovascular repair of abdominal aortic aneurysms, patients with procedural complications including leaks and postop pain are increasingly presenting in emergency departments. Intravenous contrast is needed in those cases, and "more and more of these patients will be coming into the emergency department in the next few years," he said.
Dr. Phillips Perera
Forgoing oral contrast "allows us to get our patients through the emergency department much faster, and we don’t lose [diagnostic] accuracy." It also reduces radiation exposure, because noncontrast CT studies take less time, he said. The sensitivity of noncontrast CT is 93% for detecting acute appendicitis, with a specificity of 96% (Ann. Emerg. Med. 2010;55:51-59).
Recent studies indicate noncontrast CTs work well to diagnose most causes of acute abdominal pain in adults, including appendicitis, diverticulitis, kidney stones, and large ovarian cysts at risk for ovarian torsion (J. Endourol. 2008;22:2441-5).
"You only [lose] about two percentage points" on diagnostic accuracy by forgoing contrast, and the difference in one large study (World J. Surg. 2010;34:699-703) "was not statistically significant, which I think is the most important thing," Dr. Perera said in a literature review discussion at the annual meeting of the American College of Emergency Physicians.
Radiologists still require emergency physicians in some places "to make patients drink those big bottles" of contrast. "It takes about 6 hours to drink that contrast and let it pass through; that bed is pretty much done for your shift," he observed.
"We would like not to have to do IV contrast [too], but we need to move with radiologists" on that decision, and the literature has not reached that conclusion, he said. Meanwhile, "if you’re thinking about mesenteric ischemia, thrombosis, abdominal aortic aneurysm" or some other vascular cause of abdominal pain, "you want to consider giving IV contrast."
Pancreatic and intestinal fluid alone adequately opacifies the lumen of the bowel, enabling visualization of bowel loops and abrupt, diagnostic changes in lumen caliber, he said.
Alternatively, IV contrast is needed to detect bowel ischemia. The wall of ischemic intestines will not take up contrast, and the twisting of mesenteric vessels will often be apparent.
Dr. Perera reported having no relevant conflicts of interest.