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The patient’s bedside ultrasound reveals a large kidney stone with some surrounding hydronephrosis. The stone that you visualize is almost 10 mm in width and will likely need lithotripsy or interventional retrieval to help alleviate the patient’s pain (Image 2). As you wheel out the ultrasound machine, you overhear your intern telling the patient that a nurse will be in shortly to start an IV and provide the patient with intravenous analgesics. He finishes explaining the diagnosis and plan to the patient, and meets you at the computer station to finish his charting. You take a moment to finish your own note on the patient and look over to find a message taped to the chair next to you:
Cost of performing a quick bedside ultrasound:
- 5 minutes
- Cost of a bounce-back ED visit for a missed kidney stone: $3000
- Cost of a valuable lesson learned: priceless
Pearls & Pitfalls for PERFORMING Renal Ultra-sonography
01 Getting Started: Use the low frequency (5 to 1 MHz) phased array or curvilinear transducer. Remember that lower frequency transducers enable better visualization of deeper structures. Start with the right kidney, which is easier to find, by placing your probe in the coronal plane at the right flank. Use the liver as a window and obtain a view of the kidney in the long axis. You may need to tilt your probe in an oblique angle to get in between the ribs.
02 Be Thorough: Image the entire organ using a fanning motion. If you have a difficult time viewing either kidney, have the patient take a deep breath and then halt their inspiration. This brings both kidneys inferiorly. Obtain both long-axis and short-axis views of both kidneys.
03 Look for the Hydro: Hydronephrosis is seen as a black or anechoic area in the center of the kidney and usually represents downstream obstruction. Every so often, you may be able to visualize the culprit causing the obstruction. Large stones in the proximal ureter can be easily seen on ultrasound.
04 Compare Sides: Because most people have two kidneys, any questionable findings on one side may benefit from a comparison view of the other kidney. If your patient has bilateral hydronephrosis, always consider other causes besides kidney stones: bladder outlet obstruction, bladder cancer or intravesicular clots, valvular disease and reflux, or compression of the bilateral ureters by pregnancy, a mass, or intraperitoneal abnormalities.
05 Remember the Big Picture: During an emergency bedside ultrasound you don’t need to visualize the actual kidney stone or determine if there are ureteral jets into the bladder. The main focus of a bedside renal ultrasound is to determine if hydronephrosis is present. However, if there is a major abnormal finding, like it this case, take your time and get a good look at the sonographic abnormalities so that you are more likely to recognize abnormal scans when you see them.
06 Avoid Pitfalls: The best way to minimize errors is through experience, so scan lots of normal kidneys. With bedside ultrasound, there is no substitute for experience. The more scans you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is. An image library of normal and abnormal ultrasounds helps immensely, and we can help. Just visit the Ultrasound section on EPMonthly.com.
07 Stay Current: Stay up to date on how you can use bedside ultrasound to enhance your clinical practice. Check out the ultrasound app “SonoSupport”. Available now for smartphones and tablets.
Brady Pregerson (@TheSafetyDoc) manages a free online EM Ultrasound Image Library and is the editor of the Emergency Medicine Pocketbook series. For more info visit EMresource.ORG.
Teresa S. Wu (@TeresaWuMD)is the Associate Residency Director, and Director of Ultrasound and Simulation Programs and Fellowships, for the Maricopa EM Program in Phoenix, Arizona. She is an Associate Professor in EM at the University of Arizona, School of Medicine.