Diagnosis is usually clinical; the predominant symptom is invariably intra-abdominal pain which is often steady, severe, and aggravated by movement. Anorexia and nausea are often accompanying symptoms. Most patients look unwell and in acute distress. Body temperature is usually elevated but, in cases of severe septic shock, hypothermia may be present. Tachycardia is common. Abdominal tenderness, particularly referred rebound tenderness, is the hallmark of intra-abdominal sepsis. The abdomen is distended and bowel sounds are heard occasionally or are even absent.
Leukocytosis with a shift to the left supports the clinical diagnosis of peritonitis; however, leukopenia may occur in overwhelming sepsis. An erect abdominal radiograph is particularly useful for demonstrating free air under the diaphragm, which is an indication of a perforated viscus, particularly a perforated duodenal ulcer. However, this diagnostic tool is of limited value in critically ill patients. Abdominal ultrasound and CT scan are indicated when an intra-abdominal abscess is suspected. These modalities may also be used in treatment. CT- or ultrasound-guided drainage has become the treatment of choice for unilocular abscesses located in subphrenic, paracolic, and presacral regions. However, multilocular abscesses, which are located in difficult areas for CT- or ultrasound-guided drainage, are often present in critically ill patients (Fig 3).
Fig. 3 (a) Multilocular intra-abdominal abscesses following treatment of diffuse peritonitis caused by perforation of the small bowel during laparoscopic hernia repair. (b) After percutaneous drainage: a residual abscess located ventrally from the aorta had to be drained surgically.
When the diagnosis of intra-abdominal sepsis is uncertain, for example with altered consciousness as seen in sedated ventilated patients or with the use of immunosuppressive drugs, diagnostic peritoneal lavage or diagnostic laparoscopy are useful tools. Diagnostic peritoneal lavage appears to be a safe and accurate method of determining the presence of intra-abdominal sepsis necessitating operation. The presence of more than 500 white blood cells/mm 3 after a 1-liter saline lavage correlates best with the presence of intra-abdominal sepsis. With diagnostic laparoscopy the error rate was reduced from 40 to 10 per cent in a group of patients with acute abdominal pain whose requirement for laparotomy was considered uncertain ( EMerson-Biown..,§L§L 1989).
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