Peritonitis: Shining tender abdomen with rebound tenderness is characteristic of peritonitis. However, these are late signs and their presence usually mean significant peritoneal contamination leading to increased morbidity and mortality. All attempts should be made to diagnose peritonitis early. Being vigilant about the possibility of peritonitis in vulnerable population can lead to early diagnosis. For example, children with suspected appendicitis, intestinal perforation (obstruction, trauma), ascitis, on chronic peritoneal dialysis, ventriculo-peritoneal shunt, asplenia or splenectomy, immunodeficiency etc. should be watched carefully for early signs of peritonitis.

The diagnosis of peritonitis in primary care facilities is mostly clinical with investigations for intestinal perforation (free gas in the peritoneum) and features of generalized infection such as raised white blood cell count with a left shift. CT scan and peritoneal tap can confirm the diagnosis in a specialized center.

Abdominal distension with or without visible peristalsis and altered bowel sound: This is the textbook picture of intestinal obstruction and needs surgical care. However, in less obvious cases, acute gastroenteritis can mimic intestinal obstruction with mild abdominal distension, vomiting, increased bowel sound (cf. early phase of mechanical obstruction), ileus due to dyselectrolytemia and air fluid levels (usually less numerous than in obstruction) on X-ray abdomen. Careful observation over time helps to differentiate between these two. The child with acute gastroenteritis with the above-mentioned signs requires inpatient care including intravenous fluid and electrolytes.

History of intra-abdominal surgery: Any child with history of abdominal surgery and abdominal pain with or without vomiting should be presumed to be having complications from surgery till proven otherwise. In the first 6 weeks post surgery, common complications include local site infection, intra abdominal abscess due to leakage from the anastomosis, intra-abdominal hematomas, peritonitis and intestinal obstruction. After 6 weeks, partial, intermittent or complete intestinal obstruction may occur due to fibrous band formation.

Plain X-Ray abdomen is an excellent screening investigation. Ultrasound and or CT scan may be required for defining intra abdominal lesions.

Blood in stool with abdominal distention and tenderness: Though any dysentery can present with these features, one should be aware of the possibility of a developing megacolon. Both infectious and idiopathic inflammatory bowel disease can cause megacolon. Usually these children show systemic signs such as vasomotor instability, fever, lethargy etc. Serial abdominal girth measurement and abdominal X-rays are useful in diagnosing this condition.

Immediate decompression with a rectal tube is warranted followed by referral for specialized care.

Hematemesis and abdominal pain: This is characteristic of erosive gastritis or acid peptic disease. History of non-steroidal anti-inflammatory drugs (NSAID) intake is an important pointer towards this condition. Any NSAID, even COX-2 inhibitors, can cause gastric mucosal injury. Past history of heartburn, epigastric pain and family history are important pointers towards acid peptic disease with bleeding. However, if blood appears in later episodes of vomiting, secondary causes of bleeding such as Mallory-Weiss tear(s) and traumatic gastropathy should be considered. Bleeding from esophageal varices may be associated with a less severe abdominal pain.

Hemodynamic stabilization with crystalloid, colloid and packed RBC infusion is of paramount importance at the primary care setting. Empirical intravenous acid suppression therapy, preferably with a proton pump inhibitor, should also be initiated.

Appendicitis: This condition should be considered in any right lower quadrant abdominal pain. However, definitive diagnosis depends on evolution of the disease process under close clinical monitoring, white blood cell count, ultrasound and CT examination of the abdomen. Appendicitis, though rare in non-verbal young infants, can be dangerous. Its initial presentation may be peritonitis due to perforation. In older children, sudden relief of pain may indicate perforation and impending peritonitis.

Constipation: Constipation with stool impaction can present with severe abdominal pain, abdominal distention and even vomiting at all ages. It is a relatively common cause of abdominal pain in children of all ages. A simple per rectal examination can be diagnostic. History of constipation, soiling and palpable sigmoid colon also help in the diagnosis. Signs of constipation should be looked for in all abdominal X-rays taken for acute abdominal pain.
Trauma: < Abdominal trauma due to child abuse or accident can present with acute onset abdominal pain and/or irritability. The pain may be due to rupture or hematoma of a hollow viscus, most commonly the second and third parts of the duodenum. These areas are vulnerable as they are fixed retroperitoneal structures overlying the vertebral column. Duodenal hematomas present with features of upper intestinal obstruction, bilious vomiting without abdominal distension usually 2-3 weeks after injury. Intestinal perforation may manifest as peritonitis. Rupture or laceration of solid viscus such as spleen and liver can cause significant bleeding leading to shock. Blunt trauma of the abdomen is the commonest known cause of pancreatitis in children. Carefully taken history should be correlated with the external marks and nature of injury. Free air by plain X-ray abdomen may indicate hollow viscus perforation or rupture. Referral for CT scan abdomen should be considered to detect solid organ laceration, hematomas and intraperitoneal bleeding.