At least three of the following signs and laboratory findings:
Heart rate > 120/min
Temperature > 38.6 °C
White cell count > 10.5 × 103/mm3
Anemia
AND, at least one of the following:
Dehydration
Altered mental status
Electrolyte disturbances
Hypotension
Toxic megacolon is a medical emergency, potentially fatal if not appropriately managed, and if the patient presents with features suggestive of toxic megacolon, it is mandatory for the patient to be admitted and managed jointly by the gastroenterology and surgical team. It is preferable for a colorectal surgeon experienced in management of inflammatory bowel disease to be directly involved. A patient with acute severe colitis may also develop toxic megacolon while an in-patient undergoing treatment, and immediate joint management by the surgical and gastroenterology team is necessary. The patient should be closely monitored in a high dependency unit. There is high risk of colonic perforation and peritonitis with associated mortality. The mortality of acute severe colitis is 1 %, and the mortality when toxic megacolon develops is much higher though population-based data is scant in this condition.
Different Scenarios of Toxic Megacolon
Approximately 5 % of patients with acute severe colitis admitted to hospital will have toxic dilatation [3]. Toxic megacolon may present de novo in the emergency in a patient known to suffer from ulcerative colitis or rarely as the first presentation of ulcerative colitis. Toxic megacolon is unusual in patients with longstanding colitis with shortened, chronically inflamed colon. Careful assessment of the patient is necessary jointly by medical and surgical teams and options discussed. Significant abdominal pain is an indicator of impending perforation and such patients should undergo emergency colectomy. Otherwise the patients may be managed medically and the therapeutic options are delineated below. The therapeutic options depend on the presentation and previous treatment as well as the time course of the development of toxic megacolon and presence of reversible risk factors. A patient suffering from severe ulcerative colitis and already an in-patient on intravenous steroids may also deteriorate and develop toxic megacolon. The majority of such patients will undergo emergency colectomy, and only a few selected patients may be offered second-line salvage therapy with infliximab or ciclosporin if in the opinion of the colorectal surgeon such an option is safe and signs of impending perforation are absent. Careful monitoring is mandatory. In a patient already on salvage therapy such as infliximab or ciclosporin, development of toxic megacolon mandates emergency colectomy.
Risk Factors for Toxic Megacolon
Risk factors predisposing to toxic megacolon include hypokalemia, hypomagnesemia, bowel preparation, and the use of antidiarrheal therapy as well as coinfections such as Clostridium difficile (Table 33.2). Small bowel distension may predict the onset of toxic megacolon. Early diagnosis of acute severe colitis using the Truelove and Witts or the American College of Gastroenterology criteria and in pediatric patients using the Pediatric UC Activity Index (PUCAI) may help the introduction of timely intensive medical management and if necessary timely colectomy before toxic megacolon may set in. Recognizing and dealing with the risk factors associated with toxic megacolon, advising the patients appropriately and prevention by early intensive management of acute severe ulcerative colitis are the best strategies to reduce incidence of toxic megacolon [4].
Hypokalemia |
Hypomagnesemia |
Narcotic analgesics |
Antidiarrheals, including narcotic antidiarrheals |
Infections, especially Clostridium difficile |
Bowel preparation especially barium enema |
Monitoring of a Patient with Toxic Megacolon
The patients need to have their vital signs monitored at least every 4 h and a CT scan of the abdomen and pelvis or an abdominal X-ray with the lower chest taken to exclude perforation and determine the severity of megacolon every day. In some instances of severe toxic megacolon, abdominal X-ray may be done twice daily [1]. Infections need to be excluded by stool culture, Clostridium difficile toxin assay or real-time PCR, CMV quantitative PCR in blood (as obtaining colonic histology in toxic megacolon may be difficult), and blood culture as patients are usually febrile. A complete blood count, C-reactive protein (or erythrocyte sedimentation rate), electrolytes and creatinine, and urea concentrations should be monitored every day, and plasma albumin concentrations and liver function tests should be monitored every 3–4 days. The patients need to be reviewed by the gastroenterologist and colorectal surgeon every day. In a patient with known ulcerative colitis, procedures such as flexible sigmoidoscopy or colonoscopy should be avoided, but a cautious diagnostic flexible sigmoidoscopy with minimal insufflation may be performed without bowel preparation or enema if the diagnosis is not known.
General Management
It is important to optimize general supportive management of these very ill patients as this may make a significant difference to overall outcome.
Prophylaxis of Thromboembolic Complications
Patients with toxic megacolon are very ill, often confined to bed, and dehydrated and have a hypercoagulable state. Active inflammation may play a direct role in producing a thrombophilic state [5] and all patients should receive prophylactic heparin. Administration of heparin is safe and does not increase the incidence of colonic bleeding [6]. Either unfractionated or low molecular weight heparin may be used for prevention of venous thrombosis, at least as long as the patient is on intravenous steroids or is confined to bed [7].
Management of Nutritional Status
Oral feeding should be avoided when toxic megacolon is diagnosed [8]. Bowel rest via total parenteral nutrition has no therapeutic benefit in reducing the inflammation in toxic megacolon. However, a number of patients are admitted with very poor nutritional status and are too ill to have adequate oral nutritional intake. A dietician should always be involved in managing such patients, and parenteral nutrition should be considered on nutritional grounds if oral intake has been persistently inadequate, so that emergency surgery in a nutritionally debilitated patient can be avoided. As these patients are at high risk of colectomy and are kept nil by mouth, supported nutrition by parenteral route is even more important.
Management of Fluid and Electrolyte Disturbances
Many of these patients are dehydrated and hypokalemic especially after high doses of steroids, and careful monitoring and replacement are necessary. In the presence of toxic megacolon, intravenous fluids will be required and tailored to vital signs and renal and electrolyte monitoring. In some cases hypokalemia may be a precipitating cause of megacolon and early restoration of electrolyte balance may help reversal of megacolon. In elderly patients, consideration has to be given to possible drug related electrolyte imbalance.
Blood Transfusion
Anemia may be due to inflammation, blood loss, and inadequate nutrition [9]. Blood transfusion with packed red cells and parenteral iron replacement should be considered in patients in order to maintain a hemoglobin concentration above 10 g/dL. This is important in terms of keeping a patient in a fit state for surgery if medical management fails.
Antibiotics
In the absence of infections, there is no evidence for empiric use of antibiotics. In hospitalized patients with developing toxic megacolon, oral vancomycin may be considered till the stools are negative for Clostridium difficile. Real-time PCR on feces might permit a rapid diagnosis of Clostridium difficile and early treatment with vancomycin. Broad-spectrum antibiotics are occasionally used in patients with significant abdominal tenderness [1]; however, there is no definite evidence for efficacy and there is the risk of Clostridium difficile infection. There is scant evidence for fecal microbial transplant in toxic megacolon associated with Clostridium difficile in the setting of severe ulcerative colitis.
Abdominal Decompression
Naso-enteral decompression tubes do not help in reducing colonic dilatation but may be considered if there is accompanying significant small bowel ileus. Changing position to evacuate gas may only be considered after flexible sigmoidoscopy but is generally unnecessary. Patients are generally too ill to roll around in bed or lie in knee-elbow position every 30 min though it is recommended in some guidelines [8].
Management of Abdominal Pain
Narcotic analgesics should be avoided as it may worsen colonic dilatation. Severe pain in the setting of toxic megacolon generally represents transmural inflammation and impending perforation, and hence, surgical review and emergency colectomy may be required rather than pain management. It is important that adequate vigilance is maintained to trigger surgical intervention as a matter of urgency in the event of severe abdominal pain.
Principles of Specific Management
The initial medical management of toxic megacolon is similar to management of acute severe ulcerative colitis, and these patients require hospitalization and close monitoring, as the colectomy rates even if the patient initially responds to initial treatment is high. Therefore, it is important to monitor the patient in a gastroenterology (not a general) ward with an accurate record of stool frequency, blood in stool, temperature, pulse rate, and abdominal tenderness. Infection must be eliminated by stool culture and Clostridium difficile toxin assay, but commencement of treatment should not wait until the stool culture reports become available. The management of severe ulcerative colitis patients is a team effort between gastroenterologists, surgeons, inflammatory bowel disease nurses, dieticians, and clinical psychologists. In a patient admitted with acute severe ulcerative colitis and dilatation of the colon, joint assessment by a gastroenterologist and a colorectal surgeon is required urgently. In all other patients admitted with acute severe colitis, a colorectal surgical assessment will be required within 24 h, but vital signs should be monitored to trigger alarm at signs of impending toxic megacolon. The different scenarios in which toxic megacolon may develop will necessitate different strategies of management as illustrated in Fig. 33.1.
