**2. The pathogenesis and natural history of ABP**

In the setting of ABP, biliary stones or sludge material impacted in ampulla vateri induce transient obstruction in the biliary tree and pancreatic ductus, followed by reflux of bile into the pancreatic channel. Consequently, undraining pancreatic channel develops increased ductal pressure leading to backflow of activated pancreatic enzymes into the parenchyma. This starts a cascade of tissue injury with a spectrum of events starting with mild parencymal inflammation ending with loss of pancreatic parenchyma due to severe necrosis [7]. For sure, cholestasis and or cholangitis due to biliary obstruction in addititon to pancreatic inflammation can add into the clinical scenario. There are several evidences indicating the duration of obstruction correlates with te severity of pathology in the pancreas. These evidences reveal that persisting obstruction after 48 hours leads to different degrees of necrosis and if the ductal decompression is obtained before that time period, disease associated morbidity and mortality decreases significiantly [8–16]. Runzi et al. [8] used an animal model of AP by balloon obstructed biliopancreatic ductal system and they relieved the obstruction at 1th, 3rd and 5th days. The authors documented that the severity of parenchymal inflammation, fat necrosis, hemorrhage, acinar cell vacuolisaiton and necrosis were most prominent in animals with obstructed ductal sysytem at 5 th days of the experiment. On contrary, animals having decompressed ductal sysytem at 1th and 3 rd day of experiment, pancreatic injury was able to be avoided. Another report by Acosta et al. [11] investigating the same subject on a clinical study put forth that severe pancreatitis develops significantly more in patients with the obstruction lasting more than 48 hours compared to those having less than 48 hours of obstruction. These authors suggested to wait for 48 hours to implement an ERCP as the impacted stone may fall down spontaneously and if the signs of obstruction persists after 48 hours, then we should think about ERCP. On the grounds that at least half of the cases, the impacted stone in Ampulla Vateri will fall down spontaneously within 24–48 hours after ampullary and duodenal edema diminishes, we know that the pancreatitis in these patients will limit itself and recover within a few days. Acosta et al. [12] investigated the effects of early ductal decompression in a report and they compared 30 patients who underwent ERCP within first 48 hours with 31 patients who got only conservative treatment. Within the first group, 16 had passed the stone into the duodenum during 48 hours and only 14 patients underwent ERCP in whom 11 were shown to have impacted stones. In the second group of patients, 22 patients had got rid of obstuction spontaneously and 9 patients who had persistent signs of obstruction underwent ERCP and only 3 of them had impacted stone. As a result, %78 of patients passed stones spontaneously into the duodenum and E-ERCP was performed on the others within 48 hours without an uneventful clinical course and mortality. Another report by Cavdar et al. [13] indicated that 74% of patients with ABP passed stones into the duodenum within 72 hours of admission.

Based on all this data and our clinical experience about the natural progression of ABP, we suggest conservative approach during the first 24 to 48 hours to limitate the severity of pancreatitis by agressive fluid recessuation correction hypovolemia and organ hypoperfusion. This approach also allows us to evaluate the patients with regard to the presence of cholestasis and cholangitis and to find out which patients need ductal decompression.

APACHE II, Ranson, Glasgow veya Atlanta criteria are used to evaluate the severity of AP. Cholangitis and or cholestasis are assessed according to the presence or absence of severe pain, mental confusion, hipotansiyon, jaundice, elevated serum bilirubin ve liver enzymes and absence of bile in the aspirated gastric juice. Acosta and et al. [14] clearly demonstrated that absence of bile in the aspirated gastric juice hyperbilirubinemia and severe pain are the parameters most sensitive and spesific for the ongoing obstruction of AV. The authors concluded to apply ERCP to this subgroup of patients. However, these findings may also occur in patients with severe pancreatitis and do not indicate the existence of cholangitis. Thus, ERCP performed based only on these findings may worsen pancreatitis, even end up with death. Therefore, we need better methods to show the stone in the biliary tree. Before the area of MRCP and endoscopic ultrasonography (EUS), we would do diagnostic ERCP and endoscopic sphincterotomy in every patient with a diagnosis of ABP even if we did not detect gall stones in the bile duct. This policy has changed to 'never do diagnostic ERCP in ABP' and do first MRCP or if possible more sensitive EUS to decide if ERCP will be done or not.

### **3. The estimation of cholangitis and cholestasis**

On clinical practice, the presence of cholangitis and or cholestasis in a patient with ABP is estimated by clinical and biochemical parameters together with abdominal ultrasonography (USG) [15–19]. Severe abdominal pain, fever, mental confusion, hypotension and jaundice can be seen in severe acute pancreatitis even in the absence of cholangitis. In 20% of patients, the liver enzymes can be persistently

### *Endoscopic Retrograde Cholangiopancreatography in Acute Biliary Pancreatitis DOI: http://dx.doi.org/10.5772/intechopen.96545*

normal. The sensitivity of abdominal USG is very low around 27–50% in the diagnosis of cholestasis and cholangitis. The bile duct diameter can persist several days after spontaneously passing stones. Thus, we need more sensitive methods to detect cholangitis and or cholestasis. Nearly 20 years ago, ERCP has been widely used for a diagnostic purpose. However, there have been important developments with the administration of MRCP and EUS into the gastroenterology practice [20–29]. EUS is better than MRCP to detect gall stones smaller than 5 mm and after detecting the stone by EUS and as an adavantage of this procedure, ERCP can be used to extract the stone from the bile duct at the same session after EUS procedure [21–27]. Moon and his collagues [28] reported the accuracy rates of USG, computed tomography, MRCP, ERCP and intraductal USG to detect bile duct stones are 20%, 40%, %80%, 90%, 95%, respectively. The authors underlined IDUS and ERCP as the most sensitive methods to detect a CBD stone and suggested to use MRCP to choose the suitable patient for ERCP. They also notified that the rate of agreement between ERCP and MRCP is 90.6% and the large common bile duct has been mentioned as a factor for MRCP to overlook the bile duct stones.

MRCP has a low diagnostic value compared to EUS in a patient with dilated CBD having small sized stones. Scheiman and his colleagues [29] investigated and compared the cost and clinical efficacy of EUS and MRCP done 24 hours before the ERCP procedure. The authors identified EUS as the best cost-effective modality to prevent unnecessary ERCP. Thus, this will protect patients from potential complications of ERCP. Furthermore, 20% of bile duct stones smaller than 8 mm and detected by MRCP were found to pass spontaneously into the duodenum until the time comes for an ERCP procedure. Thus, EUS will reliably help us to give final decision to do ERCP or not. Another advantage of EUS is its applicability on bed side for patients warded in intensive care units. Additionally, in patients with normal gall bladder evaluation on percutaneous USG, EUS can detect sludge in the gall bladder in the setting of ABP. We can also use a quick EUS examination performed within 72 hours of hospitalization to decide if patients can be discharged early from the hospital. This strategy can decrease the health expanses as well. Thus, it seems very rational to increase cost effectivity of caring for ABP patients by provoking the motivation of ERCP physicians to get learn how to do EUS and vice versa [25–27].
