Thursday, June 18, 2015

Oral contrast for abdominal CT?


PO, IV contrast for abdominal CT
This material is educational, and is not intended to serve as hospital protocol.
 
Mostly, it's here to serve a quick reference for myself, and for impromptu discussions with PAs and residents.

SUMMARY

Suspected SBO
Oral contrast is contraindicated in suspected SBO.
IV contrast is preferred, but not required.

Suspected appendicitis
Oral contrast is not required, but may be beneficial in extremely thin individuals (e.g. BMI < 18), or non-obese children.

Suspected diverticulitis
Oral contrast is not required

Unclear etiology
PO contrast is suggested by some experts in undifferentiated abd pain if the patient
1)   Is very thin (e.g. < 120 pounds, BMI < 18);
2)   Has had a Roux-en-Y gastric bypass; or
3)   Has and inflammatory bowel disease that could produce a fistula

Discussion and References

SBO
Per the American College of Radiology guidelines, in a patient with suspected SBO, PO contrast is contraindicated. They explain that: “Oral contrast will not reach the site of obstruction, wastes time, adds expense, can induce further patient discomfort, will not add to diagnostic accuracy, and can lead to complications, particularly vomiting and aspiration.”    

Appendicitis
Multiple studies have shown that the use of PO contrast does not increase the accuracy of the diagnosis of appendicitis (references below). An editorial in a recent radiology journal concluded that “routine administration of oral contrast medium may not be necessary in the setting of suspected acute appendicitis.” American College of Radiology guidelines state that PO contrast “may not be needed,” leave the decision to use PO contrast to “institutional preference.”
Some have suggested that PO contrast might be needed in extremely thin individuals (e.g. BMI < 18). See the discussion below in "Unclear etiology."

A 2005 systematic review from the American Journal of Surgery concluded that: “Noncontrast CT techniques to diagnose appendicitis showed equivalent or better diagnostic performance compared with CT scanning with oral contrast.”

A 2009 randomized study in the American Journal of Radiology found that “nontraumatic abdominal pain imaged using 64-MDCT with isotropic reformations had similar characteristics for the diagnosis of appendicitis when IV contrast material alone was used and when oral and IV contrast media were used.”

A 2011 retrospective study in the Journal of Surgical Research found that oral contrast did not reach the cecum in 1/3 of patients. Furthermore, “there appears to be no diagnostic compromise in those without contrast in the terminal ileum.
A 2014 prospective study in the Annals of Surgery concluded that: “Enteral contrast should be eliminated in IV-enhanced CT scans performed for suspected appendicitis.”

Diverticulitis
The American College of Radiology guidelines state that PO contrast “may be helpful for bowel luminal visualization.” Despite this, they conclude that “regardless of the [the use or lack of IV or PO contrast], the accuracy is high for depicting findings of acute diverticulitis.”

A 2006 prospective study in Emergency Radiology looked at patients with undifferentiated abdominal pain in the ED; 1/5 of them had LLQ tenderness, and diverticulitis was the second-most common suspected diagnosis. All patients had CT scans with and without PO contrast; no IV contrast was used. Although there were discordant interpretations between the (+) PO and (-) PO CT scans, the authors found that a “significant portion of the discordance was attributable to interobserver variability.” Thus, it would appear that a CT scan without either PO or IV contrast could be accurate in the diagnosis of diverticulitis.

Unclear etiology
Oral contrast may not be needed for undifferentiated abdominal pain, as per the discussion of the study in Emergency Radiology noted above.

However, in a 2012 study in Emergency Radiology that examined the use of PO contrast in undifferentiated non-traumatic abd pain, the authors excluded 2 groups of patients.  They excluded all “subjectively thin” patients, but did not provide cut-offs. They noted the research that suggests this exclusion is unnecessary, and may be dropped in the future.  They also excluded patients at high risk for having an intra-abdominal fistula. Primarily, they targeted patients who had had a Roux-en-Y gastric bypass, or who had IBD, disposing them to fistula formation.

Thursday, June 4, 2015

Is the shoulder in? Use ultrasound!



It was a classic “good news/bad news” sign out.

The  attending who was signing out to me admitted that this wasn't the cleanest sign-out, but they had a plan.


The bad news: the patient likely had a shoulder dislocation, but the read on the X-ray was equivocal.
  
"Can I order a clinical correlation?"
Given this unclear picture, the plan was to try sedation, and pop it back in place. 

The good news: the attending had already tasked a senior resident and the orthopedics PA-C to perform the sedation and (attempted) reduction, and they were champing at the bit to do the procedure. 

My evaluation

I looked at the X-ray, and re-examined the patient. As he was young chubby guy, it was difficult to be sure of the exam. Since both my exam and the X-ray were so unhelpful, I stalled the resident and PA-C while I grabbed the ultrasound.

Now, ultrasound is not usually thought of as a great test for shoulder dislocation. The usual approach to definitively excluding a glenphumeral dislocation (especially posterior dislocation!) is to obtain an axillary view, shooting up through the armpit. And of course we can always get a CT of the joint.

But you can get much the same image with the ultrasound. So, placing the probe on the posterior shoulder, I aimed anteriorly, with the left side of the screen oriented to the lateral aspect, like this:


This produced a clear image of the glenohumeral joint:

 
As usual, US is best appreciated dynamically, with this clip showing the patient rotating his arm:

video

I hope you can see how the head of the humerus is well-seated in the glenoid. But despite this dazzling proof, x-rays and a CT were needed to convince ortho that the shoulder was not dislocated, and that no sedation and tugging were needed.

The (ionizing radiation) proof

The axillary view of the shoulder X-ray (needs to be specifically ordered), oriented similarly to the US:


 The CT of the shoulder, with the slices and orientation similar to the US:


If you want to check out some other US examples of dislocated shoulders, you can also check out this great video from ALiEM:



Ultrasound for the ... Wait, what?!

I would have liked to say this was an ultrasound win, but I'm not so sure. The downsides of this approach, in retrospect, were:
  • The patient didn't get to enjoy some of our high-grade ketamine;
  • We didn't get to high-five each other after our "subtle reduction;" and
  • The resident was cheated out of a procedure!
So, know the downsides ahead of time.