Page 16 - Acute Pancreatitis (Viêm tụy cấp)

CHAPTER 58 Acute Pancreatitis 907

unclear reasons. 193 In this prospective study, it was shown that The decrease in serum calcium often seen in patients with AP
20% of type 2 diabetics had an elevated serum lipase, and 2% had is mainly related to the decreased serum albumin. As will be 58
a serum lipase of more than 3-fold elevation despite the absence discussed later, the decrease in calcium is a marker of severity
of symptoms. However, when evaluating serum amylase, only 5% because it is carried bound to albumin-rich intravascular fluid that
of type 2 diabetics were found to have an elevated level and no extravasates to the peritoneum. Decreased serum calcium is not
patient had more than 3-fold elevation. Although the ramifica- from saponification. The erythrocyte mean corpuscular volume
tions of these findings are unclear, there is a recent study that has been shown to help differentiate alcoholic from nonalcoholic
suggested that these low-level elevations in pancreatic enzymes AP. 204 Alcoholic patients tend to have a higher mean corpuscular
may be associated with ductal changes in the pancreas consistent volume due to the toxic effects of alcohol on erythrocyte forma-
with chronic pancreatitis. 194 Although further study is needed, tion in the bone marrow. Serum TG levels increase in AP but
extensive evaluation of patients with asymptomatic elevations of also with alcohol use, uncontrolled diabetes mellitus, or defective
amylase and lipase in the absence of other clinical findings of AP TG metabolism.
should not be performed.
It is also possible to analyze serum lipase subtypes such as the
pancreatic fraction of the lipase. However, in the small study it DIAGNOSTIC IMAGING
was found that such subtype estimation is not superior to a regu- Abdominal Plain Film
lar lipase assay but can be used as an add-on test if required. 195
A report from Australia and New Zealand showed that elevation Findings on a plain radiograph range from no abnormalities in
of lipase on day 1 in children with AP predicted a severe disease mild disease to localized ileus of a segment of small intestine
with a sensitivity of 82% but a modest specificity of only 53%. 196 (“sentinel loop”) or the colon cutoff sign in more severe disease.
Another study also reported that an early 7-fold elevation of lipase In addition, an abdominal plain film helps exclude other causes
in pediatric AP had a sensitivity, specificity, positive and negative of abdominal pain, such as bowel obstruction and perforation.
predictive values, and positive and negative likelihood ratios for Images of the hollow GI tract on an abdominal plain radiograph
severe disease of 85%, 56%, 46%, 89%, 1.939, and 0.27, respec- depend on the spread and location of pancreatic exudate. Gastric
tively. 197 The overall PPV of hyperlipasemia was 38%. Physicians abnormalities are caused by exudate in the lesser sac producing
should maintain caution when interpreting 3-fold hyperlipasemia anterior displacement of the stomach, with separation of the
in critically ill patients due its relatively low PPV. However, the contour of the stomach from the transverse colon. Small intesti-
greater lipase cutoff improves its diagnostic value in AP and helps nal abnormalities are due to inflammation in proximity to small
to reduce unnecessary imaging in these patients. The most com- bowel mesentery and include ileus of 1 or more loops of jejunum
mon primary diagnoses in non-AP patients with elevated lipase (the sentinel loop), of the distal ileum or cecum, or of the duode-
included shock, cardiac arrest and malignancy. 198 Elevated serum num. Generalized ileus may occur in severe disease. Other abnor-
lipase level can have non-pancreatic origins, with liver and renal malities of the hollow GI tract may be present. The descending
failure being the most frequent. 199 According to a recent study duodenum may be displaced and stretched by an enlarged head
with proven AP, lipase was a more sensitive (91%) than amylase of the pancreas. In addition, spread of exudate to specific areas
(62%), with specificity of >91%. Lipase should replace amylase of the colon may produce spasm of that part of the colon and
as the first-line laboratory investigation for suspected AP. 200 A either no air distal to the spasm (the colon cutoff sign) or dilated
Cochrane systematic review looked at the diagnostic accuracy of colon proximal to the spasm. Head-predominant pancreatitis
serum amylase, serum lipase, urinary trypsinogen-2, and urinary predisposes to spread of exudate to the proximal transverse colon,
amylase, either alone or in combination, in the diagnosis of AP producing colonic spasm and a dilated ascending colon. Uniform
in people with the acute onset of a persistent, severe epigastric pancreatic inflammation predisposes spread of exudate to the
pain or diffuse abdominal pain, and found a false negative rate inferior border of the transverse colon and an irregular haustral
of 25% and a false-positive rate of 10%. 201 Serum lipase levels of pattern. Exudate from the pancreatic tail to the phrenicocolic lig-
more than 2.5 times the upper limit of normal prior to refeeding ament adjacent to the descending colon may cause spasm of the
is a potentially useful threshold to identify patients at high risk of descending colon and a dilated transverse colon. Other findings
developing oral feeding intolerance. 202 on plain radiography of the abdomen may give clues to etiology
or severity, including calcified gallstones (gallstone pancreatitis),
Other Pancreatic Enzyme Levels pancreatic stones or calcification (acute exacerbation of chronic
pancreatitis), and ascites (severe pancreatitis). Gas in the retro-
During acute pancreatic inflammation, pancreatic digestive peritoneum may suggest a pancreatic abscess.
enzymes other than amylase and lipase leak into the systemic cir-
culation and have been used to diagnose AP. They include PLA 2 , Chest Radiography
trypsin/trypsinogen, carboxylester lipase, carboxypeptidase A,
colipase, elastase, TAP, urinary and serum trypsinogen-2, and Abnormalities visible on the chest roentgenogram occur in 30%
ribonuclease. None—alone or in combination—are diagnosti- of patients with AP, including elevation of a hemidiaphragm,
cally superior to serum amylase or lipase, and most are not avail- pleural effusion(s), basal or plate-like atelectasis secondary to
able on a routine basis. limited respiratory excursion, and pulmonary infiltrates. Pleural
effusions may be bilateral or confined to the left side; rarely they
Standard Blood Tests are only on the right side. 205 Patients with AP found to have a
pleural effusion and/or pulmonary infiltrate on admission are
The WBC count frequently is elevated, often markedly so in more likely to have severe disease. 206 During the first 7 to 10 days,
severe pancreatitis, and does not generally indicate infection. The there also may be signs of ARDS or heart failure. Pericardial effu-
blood glucose also may be high and associated with high levels sion is rare.
of serum glucagon. Serum AST, ALT, alkaline phosphatase, and
bilirubin also may increase, particularly in gallstone pancreati- Abdominal US
tis. Presumably, calculi in the bile duct account for these abnor-
malities. However, pancreatic inflammation per se may partially Abdominal US is used during the first 24 hours of hospitaliza-
obstruct the distal bile duct in AP. Serum aminotransferases may tion to search for gallstones, dilation of the bile duct due to cho-
help distinguish biliary from alcoholic pancreatitis (see later). 203 ledocholithiasis, and ascites. Ascites is common in patients with