Emergency Medicine News:
The Speed of Sound
Dr. Butts is the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans.
A 35-year-old man presents to the ED with a complaint of left flank pain with radiation to the left lower quadrant. He also describes nausea and vomiting, but denies fever or chills. He relates a history of renal stones, and a review of his medical records reveals that he has undergone three CT scans this year. He is given IV fluids and analgesics, and a bedside ultrasound is performed.
Suspected renal colic is a common presenting symptom in the ED. Many of these patients experience recurrent episodes and make frequent presentations. CT scan of the abdomen without contrast has traditionally been relied upon for a rapid and reliable diagnosis. Mounting concerns about the recurrent use of ionizing radiation, however, may cause the practitioner to reconsider CT in these patients.
Bedside ultrasound offers several advantages over CT. It is rapid and portable, but perhaps most importantly confers no ionizing radiation. This makes it an attractive choice in patients with recurrent renal stones. Ultrasound typically lacks the ability to visualize a ureteral stone directly, but it can detect indirect evidence of obstruction. Patients without sonographic evidence of obstruction or other concerning clinical findings (fever, etc.) may be discharged home without CT with close urology follow-up. Findings consistent with obstruction may aid the practitioner when determining which patients require further imaging.
Bedside ultrasound in patients with suspected renal colic has typically focused on the presence or absence of hydronephrosis. Relying on this finding to diagnose obstruction, however, may mislead the examiner. Hydronephrosis may exist for a number of reasons, including bladder distention and chronic obstruction. Alternatively, patients with volume depletion may have decreased urine production, and may not have hydronephrosis even in the presence of an obstructing calculus.
The evaluation of the bladder for the presence of bilateral symmetric urine jets offers important additional information. The finding of a decreased or absent unilateral urine jet strongly suggests obstruction, especially in the correct clinical context.
A low-frequency transducer (such as a curvilinear or phased array) is placed over the suprapubic area in the transverse plane (with the indicator pointing toward the patient's right) to identify urine jets. They will be found at the bilateral posterior aspects of the bladder. These jets are typically not visible without the addition of color flow. Enabling the “color” feature should bring up a cone on the screen. This should be centered and adjusted in size so that the entire posterior aspect of the bladder can be evaluated at the same time. Holding the transducer still over this area, the jets will be visible as streams of high-velocity flow. (See image.) The area should be monitored for several minutes for the presence of symmetric, bilateral jets. The absence of a jet on one side strongly suggests obstruction.
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