RANSON’S CRITERIA

Although the overall mortality rate for acute pancreatitis is approximately 10%, the vast majority of deaths occur in those with the severe form of the disease. Since 1974 the standard means of documenting the severity of disease and risk of mortality has been by Ranson’s criteria (Table 37.2).⁴ These factors were determined following the analysis of 100 patients with predominantly alcohol-induced pancreatitis using clinical and laboratory data obtained on admission and after 48 hours, and the number of positive criteria should predict outcome. A decade later these criteria were re-evaluated and the first eight were found to be most predictive – this is now known as the Glasgow criteria, or Imrie score.⁵

Table 37.2 Adverse prognostic factors in acute pancreatitis: Ranson’s score⁴

Blamey et al.⁵ found only eight variables (not lactate dehydrogenase, base deficit and fluid deficit) were predictive and are often referred to as the Glasgow criteria or Imrie score.

SCORING

The Acute Physiology and Chronic Health Evaluation (APACHE) II scoring system has also been used in predicting the severity of pancreatitis, and can be used daily throughout the patient’s hospital admission rather than solely within the first 48 hours, thus potentially documenting progress or deterioration. However, such scoring systems are complex to perform and have only been evaluated prospectively 24–48 hours after the onset of pancreatitis, which means that the criteria may not be valid for patients subsequently admitted to the intensive care unit (ICU). Those factors with most predictive value for mortality include advanced age, presence of renal or respiratory insufficiency and presence of shock.

The scoring of patients with acute pancreatitis is important for a number of reasons. Firstly, the clinician can be alerted to the presence of potentially severe disease. Secondly, comparisons of severity can be made both within and between patient series; and thirdly, rational selection of patients can be made for inclusion in trials of potential new treatments or interventions. Unfortunately the scoring systems used at present are often inadequate in patients with severe ANP, which is characterised by rapidly progressive multiple-system organ dysfunction. In this setting the Ranson criteria and APACHE score do not take account of the effects of treatment upon measured parameters. The way forward may be to use a combination of the Ranson score, the radiological scoring systems (see below) and a descriptive organ failure score such as the Sepsis-related Organ Failure Assessment.⁶

IMAGING

Dynamic contrast-enhanced computed tomography (CT) provides the best means of accurately visualising the pancreas and diagnosing pancreatitis and its local complications. It may also be used for guiding percutaneous catheter drainage. Guidelines have been suggested for the efficacious use of CT scanning and these are shown in Table 37.3.⁷

Table 37.3 Guidelines for efficacious use of computed tomography scanning in suspected acute pancreatitis⁶

APACHE, Acute Physiology, Age and Chronic Health Evaluation.

In severe acute pancreatitis, there is lack of normal enhancement to contrast of the gland or a portion thereof. This is consistent with pancreatic necrosis, defined as diffuse or focal areas of non-viable parenchyma. Microscopically, there is evidence of damage to the parenchymal network, acinar cells and pancreatic ductal system and necrosis of perilobular fat. Areas of necrosis are often multifocal and rarely involve the whole gland, and may be confined to the periphery with preservation of the core. Necrosis develops early in the course of the disease and is usually established 96 hours after the onset of symptoms.⁸ The extent of pancreatic necrosis and the degree of peripancreatic inflammation have been used to determine outcome. A grading system combining the two CT prognostic indicators (the extent of necrosis and the grade of peripancreatic inflammation) has been developed to give the ‘CT severity index’. Most complications of acute pancreatitis occur in patients in whom the initial diagnosis is based upon peripancreatic fluid collections, and a strong correlation has been established between the CT depiction of necrosis and the development of complications and death.⁹ For patients with necrosis in the pancreatic head, the outcome is as severe as when the entire pancreas is affected. By contrast, for patients with necrosis in only the distal portion of the gland, the outcome is favourable, with few complications.¹⁰ The mechanism may be that necrosis in the pancreatic head causes obstruction of the pancreatic duct, and produces a rise in pressure in the acinar cells leading to damage and leakage of activated destructive proteases.

Following the initial CT scan, additional scanning is only indicated if the patient’s clinical condition deteriorates, usually through the development of pancreatic necrosis, abscess or pancreatic pseudocyst, haemorrhage, or colonic ischaemia or perforation.

Ultrasonography in acute pancreatitis is less useful since visualisation of the gland may be obscured by ‘gas-filled’ bowel. Moreover, the degree of necrosis, which determines prognosis, cannot be assessed. However, there may be a role for this mode of imaging indemonstrating gallstones, or in the subsequent management when ultrasound-guided fine-needle aspiration (FNA) of the pancreas or surrounding tissue may help to establish the presence of infection.

SURGERY IN SEVERE PANCREATITIS

The role of surgery remains a controversial area in the management of severe ANP.¹¹ During the 1980s, most patients with acute pancreatitis of even moderate severity underwent operative intervention. The results were poor, with mortality rates in excess of 50%, although this was without ICU facilities. In 1991, Bradley and Allen introduced the concept of a conservative, non-surgical approach to severe ANP.¹² During the past decade, targeting surgical intervention according to infection status, based on Gram stain and culture of CT-guided FNA, has refined this conservative approach with beneficial results.¹³

A laparotomy for an acute abdomen is essential when the diagnosis of pancreatitis is in doubt. Surgery may increase the incidence of subsequent infection, but this risk is outweighed by the dangers of delaying the diagnosis and treatment of other serious intra-abdominal conditions. Accepted and controversial indications for surgery in severe ANP are summarised in Table 37.4. If severe acute pancreatitis is an unsuspected ‘chance’ finding at laparotomy, a T-tube should be inserted into the common bile duct, particularly if it has been explored and the opportunity taken for placement of a feeding jejunostomy tube. Some surgeons oppose this approach, as opening a hollow viscus risks peritonitis.

Table 37.4 Indications for surgery in severe acute pancreatitis