How should patients with acute cholecystitis be prepared

How should patients with acute cholecystitis be prepared? What manipulations are used to shorten the study or increase its reliability? 

Traditionally, acute cholecystitis is diagnosed on functional cholescintigraphy by noting a lack of filling of the gallbladder on both the initial 60-minute study and subsequent 4-hour delayed images. Patient preparation is vital in ensuring that lack of gallbladder visualization is a true-positive finding. Instead of 4-hour delayed images, morphine can be used to shorten the time needed to complete this study. 

Because food is a potent and long-lasting stimulus for endogenous cholecystokinin (CCK) release, the patient should not eat for 4 hours prior to the study because endogenous CCK will prevent normal gallbladder relaxation and consequently impair normal filling, leading to a false-positive study. These patients should wait 4 hours to ensure an optimal study. On the other hand, patients who have had a prolonged fast (longer than 24 hours), are receiving intravenous hyperalimentation, or are severely ill can develop viscous bile formation, which may not be adequately emptied out of a normal gallbladder. This can impair radiopharmaceutical filling of the gallbladder, which in turn can also cause a false-positive study. In these patients at risk for viscous bile formation, the short-acting CCK analog sincalide can be administered (0.02 mcg/kg intravenously in 20-30 minutes), prior to cholescintigraphy. This ensures proper emptying of the gallbladder before the radiopharmaceutical is administered and will prevent a false-positive event from occurring. 

Despite these manipulations, the gallbladder may not be visualized during the initial 60 minutes of the study. Rather than reimage at 4 hours, the study can be expedited using morphine (0.04 mg/kg intravenously), provided small bowel activity is seen within the initial 60 minutes. After morphine administration, imaging is continued for another 30 minutes. Because morphine causes sphincter of Oddi contraction, the resultant increased biliary tree pressure will overcome a functional obstruction of the cystic duct. If the gallbladder is still not seen, delayed imaging is not necessary and acute cholecystitis is diagnosed. Overall, the sensitivity for acute calculous cholecystitis is 97% with a specificity of 85%. The sensitivity and specificity are slightly lower in acute acalculous cholecystitis with a sensitivity and specificity of 79% and 87%, respectively. If there is pericholecysitic hepatic activity with a subsequent rim sign, the potential for a complicated cholecystitis (i.e., gangrenous or perforated gallbladder) is significantly higher. In adults, absence of activity in the intrahepatic ducts or small bowel can represent a high grade obstruction. In the early stages, conventional imaging will be normal. Fortunately, scintigraphy will demonstrate abnormal excretion before anatomic abnormalities are detectable.

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