Background

An abdominal ultrasound is a test that utilizes pulsed high-frequency sound waves (2–5 MHz) to create images of the abdominal organs without ionizing radiation. It creates real-time two-dimensional images of the various abdominal organs that can be displayed in either the longitudinal or transverse planes. There are a few different versions of the abdominal ultrasound. The right upper quadrant ultrasound, a foreshortened test, only includes the organs in the right upper quadrant of the abdomen (e.g., liver, gallbladder, right kidney). An abdominal Doppler is another version that adds Doppler imaging to evaluate the major abdominal arteries for stenosis (e.g., celiac axis, renal arteries, main mesenteric arteries).

How to Use it

Abdominal ultrasound is an inexpensive and readily portable tool that is useful in interrogating the abdominal organs including the liver, gallbladder, pancreas, spleen, and kidneys. In some institutions, it is used to evaluate the appendix as well. It is extremely useful in differentiating between solid and cystic lesions and gathering information regarding the global structural anatomy of the organ being visualized. It is used to find masses, thrombosis, stenosis, cholecystitis, cholelithiasis, cirrhosis, and nephrolithiasis, and as a guide for biopsies. Fluid-filled structures appear black/dark on imaging, with a posterior enhancement, that means that the structures are brighter. solid masses may be many shades of gray. Calcified lesions or gallstones will appear echogenic or bright with a posterior shadowing. The test is typically ordered as a complete abdominal ultrasound, and if a limited right upper quadrant is warranted, it can be specified in the order.

How It Is Done

The patient is positioned in both a supine and left-lateral decubitus position for this test. It is typically performed by a sonographer but may be performed by physician, nurse practitioner, or physician assistant. It is utilized in the emergency department, radiology department, or intensive care unit and can be used in the inpatient and outpatient settings. The operator uses ultrasound gel and a high-frequency ultrasound probe to obtain images of the abdominal organs. The images are obtained in the sagittal/long axis and in the transverse/short axis. Pulsed high-frequency sound waves are emitted from an ultrasound probe, and the echoes from those pulsed sound waves are sent back to the probe. The echoes are displayed as pictures based on the speed of the waves when they hit the probe and the time it takes for the echoes to return to the probe. See Chapter 50: Renal Ultrasound , Fig. 50.1 , for an example of an ultrasound image. Ideally, patients fast for 8 hours before the exam to optimize image acquisition and minimize bowel gas, which obstructs the clarity of the images by casting a shadow over the target organs. In an emergent situation, an abdominal ultrasound can be performed on a patient who has not fasted, but the image quality will likely be compromised due to increased bowel gas, and the gallbladder may be contracted and difficult to fully assess. The organs are interrogated with color Doppler and pulsed-wave Doppler to evaluate blood flow velocity. The test takes approximately 30 minutes to complete. A normal test result is typically a homogeneous liver texture without masses or cysts; a gallbladder without cholelithiasis, polyps, or masses; a common bile duct (CBD) <6 mm; normal renal parenchyma without hydronephrosis; and homogeneous splenic parenchyma without masses.

Medication Implications

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  Routine medications do not need to be held prior to the exam.

  
  
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  The abdominal ultrasound is noninvasive, and no medications are administered prior to the test, including sedation or pain control medications.

  
  
  
  
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    Ultrasound contrast administered intravenously (e.g., brand names Lumason, Definity, Optison, or Sonazoid) may be utilized to enhance visualization of masses with vascular components. This contrast is composed of encapsulated microbubbles in suspension. A thin shell of albumin or lipids contain the gas core, which is made up of perflutrens or sulfur hexafluoride. The bubbles persist in circulation for several minutes. It does not contain any iodine and therefore can be utilized in patients with renal and liver impairment or failure.

    
    
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    Ultrasound contrast products share some common warnings and precautions. All products include a boxed warning in the prescribing information for serious cardiopulmonary reactions including fatalities. These reactions tend to occur within 30 minutes of administration, so resuscitation equipment and trained personnel should be available when using these agents. Patients with unstable cardiac conditions are at higher risk of cardiopulmonary events. These events include cardiac and pulmonary arrest, shock, syncope, arrhythmias, and others.

    
    
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    Patients with cardiac shunts are at risk of arterial embolization by the contrast microbubbles as they may not be filtered by the lungs. Known or suspected cardiac shunts are contraindications to some of these agents, and all patients should be assessed for embolic phenomena after administration. For this same reason, contrast agents should never be given by intra-articular injection.

    
    
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    Some contrast agents include albumin, a human blood product that carries its own risks of administration and may be refused by certain populations (e.g., Jehovah’s Witnesses).

  
  
  
  
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  Biopsies of solid organs, such as liver or renal biopsies, are commonly performed under ultrasound guidance.

  
  
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    There are no medications that need to be given prior to the biopsy, but it is common practice that lidocaine 1% is injected locally along the path that the biopsy needle will take.

    
    
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    Bleeding is one of the more common and serious complications of a renal biopsy, and at times, desmopressin is used prior to biopsy in patients who are at high risk of bleeding. It can decrease the risk of bleeding and the size of the hematoma in the instance that postbiopsy bleeding occurs. See Chapter 34: Hemodialysis Access for more details.

    
    
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    Bleeding after a liver biopsy may be secondary to an intraperitoneal hemorrhage, hematoma, or hemobilia. Intraperitoneal hemorrhage can be diagnosed by visualizing free fluid in the peritoneal cavity. The fluid is visible with ultrasound and is seen as hypoechoic (dark) fluid surrounding the abdominal organs in the most dependent portion of the abdominal cavity.

    
    
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    Warfarin is held prior to a renal or liver biopsy. Typically, the international normalized ratio (INR) is allowed to drift below 1.5 to minimize the risk of bleeding; however, this is a general recommendation and may differ based on individual patient bleeding risk and procedurist preference. If a patient is taking warfarin and requires an urgent biopsy, then warfarin’s effect can be reversed. See Chapter 4: Anticoagulation Management in the Periprocedural Period for details about bleeding risks and reversal strategies.

    
    
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    Heparin should be held 6 hours prior to biopsy, and the activated partial thromboplastin time (aPTT) should be allowed to normalize prior to the procedure. Heparin should be held for at least 12–24 hours postprocedure. In some instances, it is preferred to hold heparin for up to 1 week postbiopsy as bleeding can occur up to 1 week after the procedure.

    
    
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    Direct oral anticoagulants (e.g., dabigatran, rivaroxaban, apixaban, edoxaban) should be held 2–4 days prior to the biopsy depending on renal function and other patient-specific factors. See Chapter 4: Anticoagulation Management in the Periprocedural Period for details about holding and resuming these medications. ^,