Acute Abdomen

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Chapter 89 Acute Abdomen

Robert Sawin

Pearls

• Observation of a child’s vital signs, position, and demeanor can be as valuable as palpation in assessing the abdomen.
• Decisions about imaging tests to assess the abdomen must consider the differential diagnosis, risks, and whether the results of the study will change therapy.
• Abdominal compartment syndrome cannot be defined by absolute intra-abdominal pressure alone.

The abdomen is both the primary source of disease conditions that require care in the intensive care unit (ICU), and frequently, is a secondary source of additional pathophysiology for children in the ICU being treated for other conditions. In either case, the early recognition of these conditions and the judicious use of surgical intervention can be key to the successful outcome in the ICU population.

Anatomic and Physiologic Considerations

The Peritoneum

The peritoneum provides a protective environment for the intra-abdominal organs, and, because of its marked sensitivity, a valuable “window” for the examining health care provider. It is composed of a single layer of mesothelial cells lining the abdominal cavity along the abdominal wall (the parietal peritoneum) and the intra-abdominal viscera (the visceral peritoneum). The space between these is the peritoneal cavity. Beneath the mesothelium is a submesothelial layer of extracellular matrix, capillaries, and lymphatics.1 The peritoneum’s sensitivity to inflammation, ischemia, and necrosis is mediated by the fluid in the peritoneum that contains macrophages and other leukocytes.2 Thus, with a focus of inflammation anywhere in the peritoneal cavity, inflammatory mediators are released by these leukocytes, often resulting initially in poorly localized, generalized pain. With irritation of the peritoneum associated with early appendicitis, for example, the patient interprets the inflammation as periumbilical pain. This is related to the embryologic development along dermatomes. As more inflammatory cytokines are secreted throughout the peritoneal cavity, the pain becomes more generalized and will eventually result in spasm of the overlying muscles of the abdominal wall, interpreted by the examiner as guarding.

Pain in the gastrointestinal tract is mainly limited to conditions that result in distention of the organ. Inflammation or irritation of the mucosa is generally not the cause of pain, except in the stomach. Disease states that result in full-thickness inflammation of the bowel wall, however, can stimulate the visceral peritoneum, inciting the release of leukocytic and tissue macrophage derived inflammatory mediators that results in pain. Patients who are receiving drugs such as steroids, which blunt the immune response, have reduced production of these peritoneal inflammatory mediators, and consequently can have deceptively little pain despite a significant intra-abdominal disease. Just as in other parts of the body, ischemia associated with any abdominal condition results in severe pain, often out of proportion to what is detected on physical examination.

Visceral Blood Flow

The regulation of visceral blood flow is a tightly controlled balance of neural, humoral, paracrine, and metabolic factors.3 In the gut, enteral feeding increases the blood flow and the metabolic demands on the intestinal mucosa. Some of these effects are directly related to the nutrients in the intestinal lumen, whereas others are dependent on the enteric nervous system and the associated refexes, on gastrointestinal hormones, and on gastrointestinal vasoactive mediators such as adenosine, endothelin-1, and nitric oxide.4 In pathologic states such as sepsis alone or shock, whether from sepsis, hemorrhage, or cardiac failure, visceral blood flow is reduced, which can lead to ischemia of the intestinal mucosa and submuscosa. Even with restoration of blood pressure and cardiac output after treatment of shock, microvascular perfusion of the intestine may remain impaired resulting in mucosal ischemia and persistent lactate production.

Such ischemia can lead to altered integrity of the mucosal barriers to bacteria and other pathogens, thus increasing the entry of endotoxins into the splanchnic venous and lymphatic systems. These pathogens can fuel the inflammatory response. This finding has fostered the theory of “the gut as a central organ of sepsis or multisystem organ failure.”5 Whether the translocation of bacteria or endotoxin from gut lumen to splanchnic drainage is the chicken or egg can be debated; regardless, this perturbation of intestinal blood flow contributes to the pathophysiology of shock and sepsis.

Other conditions in the ICU can affect splanchnic blood flow, especially mechanical ventilation with high inspiratory pressures, high positive end-expiratory pressure, or high tidal volumes.6,7

Physical Exam of the Abdomen

The examination of the child’s abdomen requires keen observation, patience, and sensitivity to the patient’s fears and their parents’ anxiety. One should first notice the child’s position and demeanor. Children with peritonitis do not move or writhe about the bed because this only worsens their pain, whereas a child with visceral ischemia that has not progressed to peritonitis may be actively seeking a more comfortable position. As mentioned earlier, pain out of proportion to the findings on physical exam in an ICU patient is suggestive of ischemia, independent of the location in the body. Tachycardia is a very sensitive marker for significant intra-abdominal disease and therefore its absence should prompt the examiner to look for other explanations of the reported pain. Observation of the patient’s facial expressions is important throughout the physical exam, especially in nonverbal children.

The exam of a child with abdominal pain should begin by avoiding palpation of the abdomen. Testing for rebound tenderness is only valuable in older children and should be avoided in children younger than adolescence as it is too startling, and thus has a high false-positive rate. Shaking the bed, asking the child to cough, or gently grabbing the hips and moving them from side to side will cause a painful response in conditions with peritonitis and is much less threatening to younger children. Once the manual examination is to begin, the examiners should make certain that their hands and stethoscopes are warm. For the verbal child who has localized the pain to a specific portion of the abdomen, the examiners should start the palpation in the opposite quadrant. In generalized peritonitis, spasm of the rectus abdominis can be detected regardless of where the source of the inflammation is located. When rectus spasm is detected on one side of the abdomen, a comparison to the rectus on the other side is helpful; when both are in spasm, it could be a manifestation of guarding by an anxious child, and therefore distraction should be employed. Distraction can often be created by engaging in conversation with the verbal child, or by using the warmed stethoscope to listen with light pressure over the area of the abdomen in question, followed by gradually increasing the pressure to elicit a response. Asking the child to take a deep breath and “blow it all the way out” while feeling the rectus can overcome the spasm if it is due to voluntary guarding, whereas a child with peritonitis will fail to relax the rectus spasm. Bowel sounds are highly variable and their assessment is not usually useful in the ICU patient.

If palpation in one area causes referred pain in a different location (Rosvig sign), that is suggestive of localized peritonitis in the area of pain, classically seen in appendicitis, but also can be seen in other localized abdominal conditions.

In addition to steroids, other medications can interfere with the reliability of the physical exam of the abdomen. Although patients receiving opiates may have a blunted response to painful stimuli, significant intraperitoneal pathology can still be ascertained by careful observation. Those patients who are receiving paralytic drugs are particularly challenging because the rectus abdominis spasm that is associated with peritonitis may be substantially blunted. Observation of the face, heart rate, or blood pressure can still be valuable, especially by comparing these findings during examination to other areas of the body. Just as in the nonsedated, non-ICU patient, beginning the exam on another portion of the body gives the examiner a baseline for comparison.

Laboratory Tests

Assessment of possible intra-abdominal conditions should include blood and serum tests that measure inflammation, acid-base abnormalities, possible coagulopathy, and those focused on suspected involved organs. The leukocyte count and differential, hematocrit, and platelet count should always be checked for patients with suspected abdominal disease. Leukocytosis, especially with an increased percentage of neutrophils or immature forms should raise one’s concern about an infectious process. Neutropenia suggests a more severe infection or a suppression of the patient’s bone marrow from medications or from the infection; such a situation might make clearance of a bacterial infection more difficult. Similarly, both an increased and decreased platelet count can indicate an intra-abdominal infection. Serial declines in the platelet count are particularly suggestive of a continuing inflammatory consumption seen in conditions such a necrotizing enterocolitis. Hematocrit levels must be followed in any child in the ICU because they can demonstrate intra-abdominal bleeding or hemolysis related to disseminated intravascular coagulopathy. Other coagulation tests should be considered, especially in children with severe infections or those with liver dysfunction. In such situations the prothrombin time, partial thromboplastin time, d-dimers, and fibrin split products are helpful to characterize and monitor the coagulopathy.

Abnormalities of acid-base balance should be monitored regularly in a child hospitalized in the ICU with an abdominal disease process. The source of increased acid can either be an overproduction, such as ongoing lactate generation by ischemic bowel, or decreased acid clearance by the liver or kidneys in conditions associated with shock and decreased visceral blood flow. Lactate is a very sensitive measure of intestinal ischemia, especially when monitored serially for trends. Arterial blood samples are more reliable than venous samples in that measurement. Hyperlactemia is not specific to intestinal ischemia and can be associated with any tissue necrosis or underperfusion of organs.

Liver function test, more accurately termed liver injury tests, include transaminases (ALT and AST), bilirubin, and gamma glutamine transferase. These can be elevated with trauma to the liver, active hepatic inflammation, hepatic ischemia, or obstruction of the hepatic venous outflow, known as Budd Chiari syndrome. The latter can result in extremely elevated transaminase levels. Elevation of the gamma glutamine transferase without a significant rise in the transaminase suggests a biliary condition such as common bile duct obstruction or cholecystitis.

Amylase is a valuable diagnostic test for children with abdominal pain or unexplained intra-abdominal sepsis as hyperamylasemia can indicate pancreatitis. Elevated amylase is not specific to pancreatic insults and can be elevated with head trauma, decreased renal clearance, and intestinal obstruction. Serum lipase can be an additive test to the assessment of the pancreas. It tends to be more specific to the pancreas, but can be mildly elevated in intestinal obstruction as well. When both amylase and lipase are markedly elevated, pancreatitis is most likely. Children with a history of severe or chronic pancreatitis might not have marked elevations, so the level of the enzyme does not always correlate with the severity of the disease.

Imaging Options

The reliability of abdominal exam is subjective and highly variable, and may be dependent on the experience of the observer, the fluctuating status of the patient and his or her medications, the patient’s level of anxiety, and many other factors. Consequently, most ICU providers have developed a dependency on imaging studies to ascertain whether intra-abdominal pathology warrants intervention. For reasons of resource efficiency as well as considerations about the potential risks of ionizing radiation, prudence needs to be exercised before ordering expensive, potentially obfuscating data from imaging studies. The following factors should always be evaluated before performing each study:

1. Specifically, what is one looking for (i.e. what is the differential diagnosis)?
2. How reliably will this study rule-in or rule-out those diagnoses (i.e. what is the specificity and sensitivity of the study)?
3. Will the results of this study change the management (i.e. will a negative result prompt the termination of a drug regimen or life-supporting technology, and will a positive study necessitate surgical intervention or initiation of a new therapy)?
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