Chapter 21: The Acute Abdomen

An “acute abdomen” denotes any sudden, spontaneous, nontraumatic, severe abdominal pain, typically of less than 24 hours duration. The acute abdomen requires rapid and specific diagnosis as several etiologies demand urgent operative intervention. Because there is frequently a progressive underlying intra-abdominal disorder, undue delay in diagnosis and treatment may adversely affect outcome.

The approach to a patient with an acute abdomen must be orderly and thorough. An acute abdomen should be suspected even in a patient with only mild or atypical presentations. Increasingly, certain patient populations present with atypical complaints, including the immunocompromised, elderly and gastric bypass patients. The history and physical examination often suggest the probable cause, allow formation of a differential diagnosis, and guide the choice of initial diagnostic studies. The clinician must then decide if in-hospital observation is warranted, if additional tests are needed, if early operation is indicated, or if nonoperative treatment would be more suitable.

All clinicians should be familiar with the presenting pattern of the most common causes of an acute abdomen (Table 21–1) and their atypical presentations in certain patient populations. Moreover, they should be familiar with regional specific disease patterns. While the most common cause of abdominal pain in patients presenting to the emergency department is nonspecific discomfort, missing treatable causes of abdominal pain can be disastrous for the patient.

Abdominal Pain

History taking by an experienced physician is key to focusing the evaluation of a patient with an acute abdomen. Taking a patient history is an active process whereby a large number of diagnostic possibilities are considered in order to systematically eliminate less likely conditions.

Pain is the most common and predominant presenting feature of an acute abdomen. Careful consideration of the location, severity, mode of onset and progression, and the character of the pain will suggest a preliminary list of diagnoses.

A. Location of Pain

The location of pain serves only as a rough guide to the diagnosis; “typical” descriptions are reported in only two-thirds of cases. This variability is due to atypical pain patterns, a shift of maximum intensity away from the primary site, or advanced or severe disease. In patients presenting with diffuse peritonitis, generalized pain may completely obscure the precipitating event. Fortunately, some general patterns do emerge that provide clues to diagnosis and narrow the differential of the acute abdomen. Pain confined to either upper quadrant may be evaluated by anatomic consideration of acute conditions affecting underlying organs.

Because of the complex dual visceral and parietal sensory networks innervating the abdominal area, pain is not as precisely localized in the abdomen as in the extremities. Visceral sensation is mediated primarily by afferent C fibers located in the walls of hollow viscera and in the capsules of solid organs. Unlike cutaneous pain, visceral pain is elicited by distention, inflammation or ischemia stimulating the receptor neurons, or by direct involvement (eg, malignant infiltration) of sensory nerves. Visceral pain is a centrally perceived sensation, generally slow in onset, dull, poorly localized and protracted. The pain may be due to increased wall tension or luminal distention or forceful smooth muscle contraction (colic) producing diffuse, deep-seated pain. Visceral pain is most often felt in the midline because of the bilateral sensory supply to the spinal cord. Because different visceral structures are associated with different sensory levels in the spine (Table 21–2), visceral pain may be felt in the midepigastrium, periumbilical area, lower abdomen, or flank areas (Figure 21–1) depending on the organ involved.

In contrast, parietal pain is mediated by both C and A delta nerve fibers, the latter being responsible for the transmission of more acute, sharper, better localized pain sensation. Direct irritation of the somatically innervated parietal peritoneum by pus, bile, urine, or gastrointestinal secretions leads to a more precisely localized pain. Parietal pain is more easily localized than visceral pain because the somatic afferent fibers are directed to only one side of the nervous system. The cutaneous distribution of parietal pain corresponds to the T6-L1 areas. Abdominal parietal pain is conventionally described as occurring in one of the four abdominal quadrants or in the epigastric or central abdominal area.

Abdominal pain may be referred or may shift to sites removed from the primarily affected organs (Figure 21–2). Referred pain denotes noxious (usually cutaneous) sensations perceived at a site distant from that of a strong primary stimulus. Distorted central perception of the site of pain is due to the confluence of afferent nerve fibers from disparate areas within the posterior horn of the spinal cord. For example, pain due to subdiaphragmatic irritation by air, peritoneal fluid, blood, or a mass lesion is referred to the shoulder via the C4-mediated (phrenic) nerve. Pain may also be referred to the shoulder from supradiaphragmatic lesions such as pleurisy or lower lobe pneumonia. Although more often perceived in the right scapular region, referred biliary pain may mimic angina pectoris if it is perceived in the anterior chest or left shoulder areas.

Spreading or shifting pain parallels the course of the underlying condition. The site of pain at onset should be distinguished from the site at presentation. The chronology of a patient’s pain may be as important as the location itself. Beginning classically in the epigastric or periumbilical region, the initial visceral pain of acute appendicitis shifts to become sharper parietal pain localized in the right lower quadrant when the overlying peritoneum becomes directly inflamed (Figure 21–2). With a perforated peptic ulcer, pain almost always begins in the epigastrium, but as leaked gastric contents track down the right paracolic gutter, pain may descend to the right lower quadrant.

B. Mode of Onset and Progression of Pain

The mode of onset of pain reflects the nature and severity of the underlying process. Onset may be explosive (within seconds), rapidly progressive (within 1-2 hours), or gradual (over several hours). Unheralded, excruciating generalized pain suggests an intra-abdominal catastrophe such as a perforated viscus or rupture of an aneurysm, ectopic pregnancy, or abscess. Accompanying systemic signs (tachycardia, sweating, tachypnea, shock) soon supersede the abdominal disturbances and underscore the need for rapid resuscitation and laparotomy.

A less dramatic clinical picture is steady, mild pain becoming intensely centered in a well-defined area within 1-2 hours. Any of the above conditions may present in this manner, but this is more typical of acute cholecystitis, acute pancreatitis, strangulated bowel, mesenteric infarction, renal or ureteral colic and proximal small bowel obstruction.

Finally, some patients initially have slight—at times only vague—abdominal discomfort that is fleetingly present diffusely throughout the abdomen. It may be unclear whether these patients even have an acute abdomen or whether the illness is likely to be a matter for medical rather than surgical attention. Associated gastrointestinal symptoms are infrequent at first, and systemic symptoms are absent. Eventually, the pain and abdominal findings become more pronounced, steady and are localized to a smaller area. This gradual onset pattern leading to a more localized pain may reflect a slowly developing condition or the body’s defensive efforts to cordon off an acute process. This broad category includes acute appendicitis (especially with the appendix in a retrocecal position), incarcerated hernias, distal small bowel and large bowel obstructions, uncomplicated peptic ulcer disease, walled-off (often malignant) visceral perforations, some genitourinary and gynecologic conditions, and milder forms of the rapid-onset group mentioned in the first paragraph.

C. Character of Pain

The nature, severity and periodicity of pain provide useful clues to the underlying pathology (Figure 21–3). Pain may be continual or intermittent. Steady pain is more common and often indicates a process that will lead to peritoneal inflammation. It may be constant in severity or fluctuate, but it is always present. Sharp superficial constant pain due to peritoneal irritation is typical of perforated ulcer or a ruptured appendix, ovarian cyst, or ectopic pregnancy. Intermittent, crampy pain (colic) may occur for short or long periods but is punctuated by pain free intervals and is most characteristic of obstruction of a hollow viscus. The gripping, mounting pain of small bowel obstruction (and occasionally early pancreatitis) is usually intermittent, vague, deep-seated and crescendo at first but becomes sharper, unremitting and better localized. Unlike the disquieting but bearable pain associated with bowel obstruction, pain caused by lesions occluding smaller conduits (bile ducts, uterine tubes, ureters) rapidly becomes unbearably intense. The pain-free intervals reflect intermittent smooth muscle contractions. In the strict sense, the term “biliary colic” is a misnomer because biliary pain does not remit as bile ducts do not have peristaltic movements.

The quality of a patient’s pain leads to the use of certain descriptors to describe different types of pain and may be typical of certain pathologies. The “aching discomfort” of ulcer pain, the “stabbing, breathtaking” pain of acute pancreatitis and mesenteric infarction, the “gripping” pain of a bowel obstruction and the “tearing” pain of ruptured aortic aneurysm remain apt descriptions. Despite the use of such descriptive terms, the quality of visceral pain is not a reliable clue to its cause.

The intensity of a patient’s pain may relate to the severity of the insult. Agonizing pain denotes serious or advanced disease. Colicky pain is usually promptly alleviated by analgesics. Ischemic pain due to strangulated bowel or mesenteric thrombosis is only slightly assuaged even by narcotics. Nonspecific abdominal pain is usually mild, but mild pain may also be found with perforated ulcers that have become localized and in mild acute pancreatitis. An occasional patient will deny pain but complain of a vague feeling of abdominal fullness that feels as though it might be relieved by a bowel movement. This visceral sensation (gas stoppage sign) is due to reflex ileus induced by an inflammatory lesion walled off from the free peritoneal cavity, as in retrocecal appendicitis.

Past episodes of pain and factors that aggravate or relieve pain should be noted. Pain caused by localized peritonitis, especially when it affects upper abdominal organs, tends to be exacerbated by movement or deep breathing.

The location, character and severity of the pain in relation to its duration of onset and presence of systemic symptoms help to differentiate rapidly progressive surgical conditions (eg, intestinal ischemia) from more indolent or medical causes (eg, ruptured ovarian cyst) and allows formation of a differential diagnosis.

Other Symptoms Associated with Abdominal Pain

Anorexia, fever, nausea and vomiting, constipation/obstipation, or diarrhea, often accompany abdominal pain, but are nonspecific symptoms and have limited diagnostic value.

A. Vomiting

When sufficiently stimulated by secondary visceral afferent fibers, the medullary vomiting centers activate efferent fibers to induce reflex vomiting. Hence, pain in the acute surgical abdomen usually precedes vomiting, whereas the reverse holds true in medical conditions. Vomiting is a prominent symptom in upper gastrointestinal diseases such as Boerhaave syndrome, Mallory–Weiss syndrome, acute gastritis and acute pancreatitis. Severe, uncontrollable retching provides temporary pain relief in moderate attacks of pancreatitis. The absence of bile in the vomitus is a feature of pyloric stenosis or gastric outlet obstruction. Where associated findings suggest bowel obstruction, the onset and character of vomiting may indicate the level of the lesion. Recurrent vomiting of bile-stained fluid is typical of proximal small bowel obstruction. In distal small or large bowel obstruction, prolonged nausea precedes vomiting, which may become feculent in late cases. Although vomiting may present in either acute appendicitis or nonspecific abdominal pain, coexisting nausea and anorexia are more suggestive of the former condition.

B. Constipation

Reflex ileus is often induced by visceral afferent fibers stimulating efferent fibers of the sympathetic autonomic nervous system (splanchnic nerves) to reduce intestinal peristalsis. Hence, paralytic ileus undermines the value of constipation in the differential diagnosis of an acute abdomen. Constipation itself is hardly an absolute indicator of intestinal obstruction. However, obstipation (the absence of passage of both stool and flatus) strongly suggests mechanical bowel obstruction if there is progressive painful abdominal distention or repeated vomiting.

C. Diarrhea

Copious watery diarrhea is characteristic of gastroenteritis and other medical causes of an acute abdomen. Blood-stained diarrhea suggests ulcerative colitis, Crohn disease, or bacillary or amebic dysentery. It is also found with ischemic colitis but often absent in intestinal infarction due to superior mesenteric artery occlusion.

D. Fever

Fever is a marker of inflammation and may be present in a variety of surgical conditions in the abdomen if they are allowed to progress. The sensitivity of this finding is low as the ability of many patient populations to mount a fever is compromised and for most diseases leading to acute abdomen fever is low grade or absent.

E. Other Specific Symptoms

These are extremely helpful if present. Significant weight loss may suggest cancer or more chronic mesenteric ischemia. Jaundice suggests hepatobiliary disorders. Hematochezia or hematemesis may suggest a gastroduodenal lesion or Mallory–Weiss syndrome; melena a lower GI bleed or colonic ischemia and hematuria, ureteral colic, or cystitis. The passage of blood clots or necrotic mucosal debris may be the sole evidence of advanced intestinal ischemia.

Other Relevant Aspects of the History

A. Past Medical History

A complete past medical history is crucial to identify both medical conditions related to the presentation of the acute abdomen as well as conditions of associated pulmonary, renal and cardiac systems that may mimic the acute abdomen in their presentation. Many chronic medical conditions complicate the patient’s presentation and increase their surgical risk. An assessment of the patient’s cardiovascular and pulmonary status should always be done before proceeding to the operating room. Liver disease should be noted as it increases risk for gastrointestinal bleeding, and in severe disease may be complicated by ascites and spontaneous bacterial peritonitis. In patients with vascular disease or atrial fibrillation mesenteric ischemia should be included in the differential. Inflammatory bowel disease can cause severe abdominal pain often treated medically but may be complicated by processes requiring more emergent intervention including intra-abdominal abscess, stricture, obstruction, or perforation.

A patient should also be asked about any history of recent trauma. Delayed splenic bleeding is one of the more common examples of traumatic injuries presenting in delayed fashion.

B. Operation History

Any history of a previous abdominal, groin, vascular, or thoracic operation may be relevant to the current illness. Particular attention to the mode of operation (laparoscopic, open, endovascular) and any anatomic reconstructions may clarify aspects of the current complaint. If possible within the time constraints imposed by the urgency of the current problem, operative notes and pathology reports should be obtained and reviewed.

C. Gynecologic History

The menstrual history is crucial to the diagnosis of ectopic pregnancy, mittelschmerz (due to a ruptured ovarian follicle) and endometriosis. A history of vaginal discharge or dysmenorrhea may denote pelvic inflammatory disease. A complete sexual history should be performed if indicated, and all women of childbearing age should be evaluated for possibility of pregnancy.

D. Medication History

The average patient is taking an increasing number of medications, which may have direct impact on their management. NSAIDs or aspirin may be a cause of a gastric or duodenal ulcer. Anticoagulants have been implicated in retroperitoneal and intramural duodenal and jejunal hematomas. Additionally, patients who are anticoagulated, or are on antiplatelet therapy may require correction or further consideration prior to operative management. Oral contraceptives have been implicated in the formation of benign hepatic adenomas and in mesenteric venous infarction. Corticosteroids or other chemotherapeutics and immunosuppressive medications, may mask the clinical signs of even advanced peritonitis.

Alcohol use should be interrogated as it can be associated with liver disease, ulcers, gastritis and pancreatitis.

E. Family History

Family history often provides the best information about medical or hereditary causes of an acute abdomen.

F. Travel History

Travel history may raise the possibility of amebic liver abscess or hydatid cyst, malarial spleen, tuberculosis, Salmonella typhi infection of the ileocecal area, or dysentery.

Following a thorough history, the examiner should formulate an early differential diagnosis list using the subsequent physical examination findings to test the various diagnostic possibilities. The age and gender of the patient should assist in guiding the development of the differential diagnosis. Mesenteric adenitis mimics acute appendicitis in the young, gynecologic disorders complicate the evaluation of abdominal pain in women of childbearing age, and malignant and vascular diseases are more common in the elderly. Knowledge of the common causes of abdominal pain and their incidence in various populations is also helpful. Acute cholecystitis, appendicitis, bowel obstruction, cancer and vascular conditions are the common causes of a surgical acute abdomen in older patients. In children, appendicitis accounts for one-third of all abdominal pain and nonspecific abdominal pain for much of the remainder. Causes of an acute abdomen reflect disease patterns of the indigenous population, and awareness of common causes within the physician’s locale improves diagnostic accuracy.

PHYSICAL EXAMINATION

The tendency to concentrate on the abdomen should be resisted in favor of a methodical and complete physical examination. Examination should begin with an initial assessment of the patient’s vital signs. A patient with systemic signs of shock should be aggressively resuscitated concurrently with any ongoing evaluation. Auscultation of the heart and lungs should also be performed both to rule out sources of abdominal pain due to disorders within the chest (esophageal, cardiac, pulmonary) as well as being part of the preoperative evaluation.

The abdominal examination should be done with the patient in the supine position. A systematic approach to the abdominal examination (Table 21–3) is key to success. The physical examination allows the clinician to search for specific signs that confirm or rule out differential diagnostic possibilities (Table 21–4).

1. General observation General observation affords a fairly reliable indication of the severity of the clinical situation. Most patients, although uncomfortable, remain calm. The writhing of patients with visceral pain (eg, intestinal or ureteral colic) contrasts with the rigidly motionless bearing of those with parietal pain (eg, acute appendicitis, generalized peritonitis). Diminished responsiveness or an altered sensorium is suggestive of more advance or significant disease and may herald imminent cardiopulmonary collapse.

2. Systemic signs Systemic signs usually accompany rapidly progressive or advanced disorders of the acute abdomen. Extreme pallor, hypotension, hypothermia, tachycardia, tachypnea and diaphoresis suggest major intra-abdominal hemorrhage (eg, ruptured aortic aneurysm or tubal pregnancy). Given such findings, one must proceed rapidly with the examination and any tests to exclude extra-abdominal causes and institute treatment. If extra-abdominal pathology is excluded, these are markers of severe or rapidly progressive intra-abdominal pathology and are indication for emergent laparotomy.

3. Fever Constant low-grade fever is common in inflammatory conditions such as diverticulitis, acute cholecystitis and appendicitis. High fever with lower abdominal tenderness in a young woman without signs of systemic illness suggests acute salpingitis. Disorientation or extreme lethargy combined with a very high fever (> 39°C) or fever with chills and rigors signifies impending septic shock. This is most often due to advanced peritonitis, acute cholangitis, or pyelonephritis. However, fever is often mild or absent in elderly, chronically ill, or immunosuppressed patients despite a serious acute abdomen.

4. Examination of the Acute Abdomen

   • (a) Inspection The abdomen should be thoughtfully inspected before palpation. One should look for old surgical scars, hernias, evidence of trauma, stigmata of liver disease, obvious masses, distension and signs of peritonitis. A tensely distended abdomen with an old surgical scar suggests both the presence and the cause (adhesions) of small bowel obstruction. A scaphoid contracted abdomen is seen with perforated ulcer; visible peristalsis occurs in thin patients with advanced bowel obstruction; and soft doughy fullness is seen in early paralytic ileus or mesenteric thrombosis.

   • (b) Auscultation Auscultation of the abdomen should also precede palpation. Peristaltic rushes synchronous with colic are heard in mid-small bowel obstruction and in early acute pancreatitis. They differ from the high-pitched hyperperistaltic sounds unrelated to the crampy pain of gastroenteritis, dysentery and fulminant ulcerative colitis. An abdomen that is silent except for infrequent tinkly or squeaky sounds characterizes late bowel obstruction or diffuse peritonitis. Except for these more extreme patterns, the many auscultatory variants heard in abdominal conditions render them largely useless for specific diagnosis.

   • (c) Coughing to elicit pain The patient should be asked to cough and point to the area of maximal pain. Peritoneal irritation so demonstrated may be confirmed afterward without causing unnecessary pain by rigorous testing for rebound tenderness. This same localization may also be achieved with a foot tap or bed bump. Unlike the parietal pain of peritonitis, colic is visceral pain and is seldom aggravated by deep inspiration or coughing.

   • (d) Percussion Percussion serves several purposes. Tenderness on percussion is akin to eliciting rebound tenderness; both reflect peritoneal irritation and parietal pain. With a perforated viscus, free air accumulating under the diaphragm may efface normal liver dullness. Tympany near the midline in a distended abdomen denotes air trapped within distended bowel loops. Free peritoneal fluid may be detected by demonstrating shifting dullness.

   • (e) Palpation Palpation is performed with the patient resting in a comfortable supine position. Incisional and periumbilical hernias are noted. Tenderness that connotes localized peritoneal inflammation is the most important finding in patients with an acute abdomen. Its extent and severity are determined first by one- or two-finger palpation, beginning away from the area of cough tenderness and gradually advancing toward it. Tenderness is usually well demarcated in acute cholecystitis, appendicitis, diverticulitis and acute salpingitis. If there is poorly localized tenderness unaccompanied by guarding, one should suspect gastroenteritis or some other inflammatory intestinal process without peritonitis. Compared with the degree of pain, unexpectedly little or vaguely localized tenderness is elicited in uncomplicated hollow viscus obstruction, walled-off or deep-seated perforations (eg, retrocecal appendicitis or diverticular phlegmon) and in very obese patients. Severe pain out of proportion to examination is a hallmark for mesenteric ischemia.

Rebound tenderness is elicited by applying deep gentle pressure to the area of concern and then releasing the pressure rapidly. It is a marker of peritoneal inflammation but its usefulness may be confounded if the patient is startled by the abrupt release and interprets that as pain.

Guarding is assessed by placing both hands over the abdominal muscles and depressing the fingers gently. Properly performed, this maneuver is comforting to the patient. If there is voluntary spasm, the muscle will be felt to relax when the patient inhales deeply through the mouth. With true involuntary spasm, however, the muscle will remain taut and rigid (board like) throughout respiration. Except for rare neurologic disorders—and, for unknown reasons, renal colic—only peritoneal inflammation produces rectus muscle rigidity. Unlike peritonitis, renal colic induces spasm confined to the ipsilateral rectus muscle.

When the patient raises his or her head from the bed, the abdominal muscles will be tensed. Tenderness persists in abdominal wall conditions (eg, rectus hematoma), whereas deeper peritoneal pain due to intraperitoneal disease is lessened (Carnett test). Hyperesthesia may be demonstrable in abdominal wall disorders or localized peritonitis, but it is more prominent in herpes zoster, spinal root compression and other neuromuscular problems. Trigger point sensitivity, lateral costal rib tip tenderness and pain exacerbated by spinal motion reflect parietal abdominal wall conditions that subside dramatically after infiltration with local anesthetic agents.

Abdominal masses are usually detected by deep palpation. Superficial lesions such as a distended gallbladder or appendiceal abscess are often tender and have discrete borders. Deeper masses may be adherent to the posterior or lateral abdominal wall and are often partially walled off by overlying omentum and small bowel. As a result, their borders are ill-defined and only dull pain may be elicited by palpation. Examples include pancreatic phlegmon and ruptured aortic aneurysm.

• (f) Maneuvers Even if a mass cannot be directly felt, its presence may be inferred by other maneuvers. A large psoas abscess may cause pain when the hip is passively extended or actively flexed against resistance (iliopsoas sign). Internal and external rotation of the flexed thigh may exert painful pressure (obturator sign) on a loop of the small bowel entrapped within the obturator canal (obturator hernia). Bump tenderness over the lower costal ribs indicates an inflammatory condition affecting the diaphragm, liver, spleen, or its adjacent structures. Referred pain to McBurney’s point from the left lower quadrant (Rovsing’s sign), is associated with acute appendicitis. If one suspects abdominal guarding is masking an acutely inflamed gallbladder, the right subcostal area should be palpated while the patient inhales deeply. Inspiration will be arrested abruptly by pain (Murphy’s sign), or the gallbladder fundus may be felt as it strikes the examining fingers during descent of the diaphragm. Pain in the shoulder indicates irritation of the diaphragm by fluid such as blood, pus, gastric contents, or stool. Kehr sign is left shoulder pain associated with hemoperitoneum. Costovertebral angle tenderness is common in acute pyelonephritis.

Since they are not invariably present, these special signs are helpful in conjunction with a compatible history and related physical findings.

• (g) Inguinal and femoral rings; male genitalia The inguinal and femoral rings in both sexes and the genitalia in male patients should be examined.

• (h) Rectal examination A rectal examination should be performed in most patients with an acute abdomen. Diffuse tenderness is nonspecific, but right-sided rectal tenderness accompanied by lower abdominal rebound tenderness is indicative of peritoneal irritation due to pelvic appendicitis or abscess. Other useful findings include a rectal tumor, blood-stained stool, or occult blood (detected by guaiac testing).

• (i) Pelvic examination An acute abdomen is incorrectly diagnosed more often in women than in men, particularly in younger age groups. A pelvic examination is vital in women with vaginal discharge, dysmenorrhea, menorrhagia, or left lower quadrant pain. A properly performed pelvic examination is invaluable in differentiating among acute pelvic inflammatory diseases that do not require operation and acute appendicitis, twisted ovarian cyst, or tubo-ovarian abscess.

INVESTIGATIVE STUDIES

The history and physical examination by themselves provide the diagnosis in two-thirds of cases of an acute abdomen. Supplementary laboratory and radiologic examinations are indispensable for diagnosis of many surgical conditions, for exclusion of medical causes not treated by operation and for assistance in preoperative preparation. Even in the absence of a specific diagnosis, there may be enough information on which to base a rational decision about management. Additional studies are worthwhile if they are likely to significantly alter or improve therapeutic decisions. A more liberal use of diagnostic studies is justified in elderly or seriously ill patients, in whom the history and physical findings may be less reliable.

The availability and reliability of certain studies vary in different hospitals. When selecting a study the invasiveness, risk and cost-effectiveness should be considered. Test results must be interpreted within the clinical context of each case. Basic studies should be obtained in all but the most desperately ill patients, while other less vital tests may be requested later as indicated.

Laboratory Investigations

A. Blood Studies

Hemoglobin, hematocrit, white blood cell and differential counts taken on admission are highly informative. Both a rising or marked leukocytosis (> 13,000/μL) as well as a leucopenia (< 5000/μL) are indicative of serious infection. The differential counts should be reviewed as the presence of increased neutrophils (left shift) may suggest the presence of infection, even when the white blood cell count is normal. Additionally, the presence of bands may indicate severe infection.

Serum electrolytes, urea nitrogen and creatinine are important, especially if hypovolemia is expected (ie, due to shock, copious vomiting or diarrhea, or delay in presentation). Creatinine is considered imperative prior to obtaining radiographic imaging with iodized contrast agents due to potential renal injury. Arterial blood gas with lactate should be obtained in patients with hypotension, generalized peritonitis, pancreatitis, possible ischemic bowel and septicemia. Elevated serum lactate may indicate bowel ischemia due to the correlation with anaerobic metabolism. However, this is nonspecific and may be elevated in other clinical scenarios, such as dehydration, cocaine use, or liver failure. Unsuspected metabolic acidosis may be the first clue to serious disease.

A raised serum amylase or more specifically lipase level corroborates a clinical diagnosis of acute pancreatitis. Moderately elevated amylase values must be interpreted with caution, since abnormal levels frequently accompany strangulated or ischemic bowel, twisted ovarian cyst, or perforated ulcer. Lipase is more specific to pancreatitis.

In patients with suspected hepatobiliary disease, liver function tests (serum bilirubin, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, albumin and globulin) are useful to differentiate medical from surgical hepatic disorders and to gauge the severity of underlying parenchymal disease.

Clotting studies (platelet counts, prothrombin time and partial thromboplastin time) may be obtained in certain patients in anticipation of surgical intervention. They should be evaluated in patients on anticoagulants such as Coumadin, to ensure therapeutic levels or alert the clinician that correction is needed prior to surgical intervention. Prothrombin time is also a marker of the synthetic function of the liver in those with advanced liver disease. A peripheral blood smear should be considered if the history hints at a hematologic abnormality (cirrhosis, petechiae, etc). The erythrocyte sedimentation rate, often nonspecifically raised in the acute abdomen, is of dubious diagnostic value; a normal value does not exclude serious surgical illness.

A specimen of clotted blood for cross matching should be sent whenever urgent surgery is anticipated or there is suspicion of hemorrhage. Beta HCG serum testing is routinely performed at many institutions in lieu of urine testing. This should be performed on all women of childbearing age.

B. Urine Tests

Urinalysis is easily performed and may reveal useful information. Dark urine or a raised specific gravity reflects mild dehydration in patients with normal renal function. Hyperbilirubinemia may give rise to tea-colored urine that froths when shaken. Microscopic hematuria or pyuria can confirm ureteral colic or urinary tract infection and obviate a needless operation. Dipstick testing (for albumin, bilirubin, glucose and ketones) may reveal a medical cause of an acute abdomen. Pregnancy tests should be ordered on all women of childbearing age if serum testing was not performed.

C. Stool Tests

Gastrointestinal bleeding is not a common feature of the acute abdomen. Nonetheless, testing for occult fecal blood should be routinely performed. A positive test points to a mucosal lesion that may be responsible for large bowel obstruction or chronic anemia, or it may reflect an unsuspected carcinoma.

Stool samples for culture should be taken in patients with suspected gastroenteritis, dysentery, or cholera. Clostridium difficile should be on the differential of anyone with a recent course of antibiotic therapy.

Imaging Studies

Radiographic imaging has become an invaluable aid in the evaluation, diagnosis and even treatment of the acute abdomen. It is of utmost importance that the surgeon, who is familiar with the clinical scenario of the patient, reviews all images. It should be remembered that patients in distress with concern for abdominal catastrophe may be moved to the operating room without any confirmatory imaging.

A. Plain Chest X-Ray Studies

An upright chest x-ray is essential in all cases of an acute abdomen. Not only is it vital for preoperative assessment, but it may also demonstrate supradiaphragmatic conditions that simulate an acute abdomen (eg, lower lobe pneumonia or ruptured esophagus). An elevated hemidiaphragm or pleural effusion may direct attention to subphrenic inflammatory lesions. Subdiaphragmatic air, if present, suggests perforated viscous and may forego the need for additional imaging. An upright chest radiograph is more sensitive than abdominal plain films for free intraperitoneal air.

B. Plain Abdominal X-Ray Studies

Plain supine films of the abdomen should be obtained only selectively. In general, erect (or lateral decubitus) views contribute little additional information except in suspected intestinal obstruction and rarely eliminate the need for further imaging. Plain films are indicated in patients with signs and symptoms of intestinal obstruction, or in patients with suspected foreign body ingestion. They are inappropriate in pregnant patients, unstable individuals in whom clear physical signs mandating laparotomy already exist, or patients with only mild, resolving nonspecific pain. When looking at plain radiographs one should observe the gas pattern of the hollow viscera; an abnormal bowel gas pattern suggests paralytic ileus, mechanical bowel obstruction, or pseudo-obstruction. Bowel obstructions are usually accompanied with findings of gaseous distention, air-fluid levels, distended cecum and a paucity of air in the rectum. Colonic dilatation is seen in toxic megacolon or volvulus (Figure 30–15). “Thumbprint” impressions on the colonic wall are noted in about half of patients with ischemic colitis. Radiopaque densities may be seen with biliary, renal, or ureteral calculi; as well as in the case of foreign bodies. Although gallstones and renal calculi can be seen on plain films further imaging is almost always obtained obviating the need for a plain radiograph.

Free air under the hemidiaphragm suggests a perforated viscous, although it does not identify the source. Its presence in approximately 80% of perforated ulcers corroborates the clinical diagnosis. Massive pneumoperitoneum is observed in free colonic perforations. Biliary tree air designates a biliary-enteric communication, such as a gallstone ileus. Air delineating the portal venous system characterizes pylephlebitis.

C. Ultrasonography

Ultrasonography is becoming more common in the early evaluation of abdominal pain and may be used at the bedside by a trained physician. It is one of the first examinations for right upper quadrant pain that is biliary in nature. Ultrasonography has a diagnostic sensitivity of about 80% for acute appendicitis and is most useful in pregnant patients due to its safe modality and lower cost. It becomes technically difficult in the third trimester due to the large gravid uterus. Ultrasound also plays a role in evaluating a variety of gynecologic causes of abdominal pain. Color Doppler studies can distinguish avascular cysts and twisted masses from inflammatory and infectious processes. Ultrasound with Doppler may also be useful in evaluating for flow through the mesenteric vessels.

D. Computed Tomography Scan

Computed tomography (CT) scan of the abdomen is now generally routinely and rapidly available. This has proved extremely useful in the evaluation of abdominal complaints for patients who do not already have clear indications for laparotomy or laparoscopy. CT provides excellent diagnostic accuracy. Whether contrast is used should be carefully weighed on an individual basis. IV contrast administration may be limited by creatinine impairment. Oral contrast is useful to distinguish bowel from remaining abdominal contents. It can be administered orally or rectally; oral administration adds significant time to obtaining imaging and may not be appropriate in severely ill patients. With newer scanners the use of oral contrast is often unnecessary unless looking for bowel perforation or anastomotic leak. Newer low-dose CT scans are becoming available which reduce radiation exposure and provide advantages for pediatric imaging. CT scans should be used sparingly in pregnancy because of the risk radiation poses to the fetus, especially in the first trimester. Ultrasound or MRI are preferred imaging techniques in pregnancy.

CT can identify small amounts of free intraperitoneal gas and sites of inflammatory diseases that may prompt (appendicitis, tubo-ovarian abscess) or postpone (noncomplicated diverticulitis, pancreatitis, hepatic abscess) operation. It should not replace or delay operation in a patient for whom the findings will not change the decision to operate. CT has proven helpful in the diagnosis of appendicitis, especially where examination and laboratory data may not be clear, and is recommended in women, where other pelvic pathology may explain the presence of right lower quadrant pain.

E. Angiography

CT angiography (CTA), percutaneous invasive angiographic studies, or magnetic resonance angiography (MRA), are indicated if intestinal ischemia or ongoing hemorrhage are suspected. They should precede any gastrointestinal contrast study that might obscure film interpretation. Selective visceral angiography is a reliable method of diagnosing mesenteric infarction. Emergency angiography may confirm a ruptured liver adenoma or carcinoma or an aneurysm of the splenic artery or other visceral artery. Additionally it can be therapeutic for coiling or embolizing aneurysmal disease. In patients with massive lower gastrointestinal bleeding, angiography may identify the bleeding site, suggest the likely diagnosis (eg, vascular ectasia, polyarteritis nodosa), and be therapeutic if embolization can be performed. Angiography is of little value in ruptured aortic aneurysm or if frank peritoneal findings (peritonitis) are present. It is contraindicated in unstable patients with severe shock or sepsis and seldom warranted if other findings or tests already dictate the need for laparotomy or laparoscopy. A patient’s renal function should be considered before contrast is administered. MRA is useful when a patient is unable to undergo IV contrast administration (due to either renal impairment or contrast dye allergy). It is additionally used as an alternative imaging modality in pregnancy.

F. Gastrointestinal Contrast X-Ray Studies

Gastrointestinal contrast studies should not be requested routinely or be regarded as screening studies. They are helpful only if a specific condition being considered can be verified or treated by a contrast x-ray examination. For suspected perforations of the esophagus or gastroduodenal area without pneumoperitoneum, a water-soluble contrast medium (eg, meglumine diatrizoate [Gastrografin]) is preferred. If there is no clinical evidence of bowel perforation, a barium enema may identify the level of a large bowel obstruction or even reduce a sigmoid volvulus or intussusception. Upper GI contrast studies can also be helpful in the bariatric patient population to evaluate for leak or gastric pouch emptying.

G. Radionuclide Scans

The utility of radionuclide scans has been greatly decreased by the routine availability of urgent CT scans. Liver-spleen scans, HIDA scans and gallium scans may be useful for localizing intra-abdominal abscesses in rare cases. Radionuclide blood pool or Tc-sulfur colloid scans may identify sources of slow or intermittent intestinal bleeding. Technetium pertechnetate scans may reveal ectopic gastric mucosa in Meckel diverticulum.

Endoscopy

Proctosigmoidoscopy is indicated in any patient with suspected large bowel obstruction, grossly bloody stools, or a rectal mass. Minimal air should be used for bowel insufflation to minimize iatrogenic bowel perforation. Besides reducing a sigmoid volvulus, colonoscopy may also locate the source of bleeding in cases of lower gastrointestinal hemorrhage that has subsided. Gastroduodenoscopy and endoscopic retrograde cholangiopancreatography (ERCP) are usually done electively to evaluate less urgent inflammatory conditions (eg, gastritis, peptic disease) in patients without alarming abdominal signs. However, urgent ERCP may be indicated in cases of suspected cholangitis.

Paracentesis

Although performing paracentesis is becoming increasingly rare, it is important to understand that in patients with free peritoneal fluid, aspiration of blood, bile, or bowel contents is a strong indication for laparotomy. On the other hand, infected ascitic fluid may establish a diagnosis in spontaneous bacterial peritonitis, tuberculous peritonitis, or chylous ascites, which rarely require surgery.

Laparoscopy

Laparoscopy is a therapeutic as well as diagnostic modality. The role of laparoscopy has broadened to be a useful modality in the treatment of abdominal emergencies. In certain cases it has been associated with decreased pain and faster recovery times. Its use is dependent on surgeon experience and hospital and OR equipment and staffing.

In cases of unclear diagnosis, laparoscopy helps guide surgical planning and avoid unneeded laparotomies. In young women, it may distinguish a nonsurgical problem (ruptured graafian follicle, pelvic inflammatory disease, tubo-ovarian disease) from appendicitis. In obese patients, it may allow for a smaller, less morbid incision. In obtunded, elderly, or critically ill patients, who often have deceptive manifestations of an acute abdomen, it may facilitate earlier treatment in those with positive findings while eliminating the added morbidity of a laparotomy in negative cases. Any patient undergoing laparoscopy must be suited to tolerate conversion to an open procedure when necessary.

Laparoscopy has become the standard of care for operative treatment of appendicitis and cholecystitis. For acute cholecystitis, laparoscopy performed within 48 hours of symptom onset significantly reduces the risk of conversion to an open procedure, reinforcing the importance of early diagnosis. Laparoscopy may also be used in treating small bowel obstructions, and can result in lower morbidity and a faster return to normal diet.

DIAGNOSTIC UNCERTAINTY

As the surgeon gathers data, the differential diagnosis is narrowed and associated with a clear direction of plan. The plan of action should focus on whether the patient will need to:

• go directly to the operating room,

• be admitted for surgical observation and expected operative intervention,

• be admitted for surgical observation or further diagnostics, or

• be admitted to medical service for nonoperative abdominal pain.

Several patient populations may fall out of the expected presentation of the patient with an acute abdomen. The clinical picture in early cases is often unclear. The following observations should be borne in mind:

1. Acute abdominal pain persisting for over 6 hours should be regarded as having a surgical problem requiring in-hospital evaluation. Well-localized pain and tenderness usually indicate a surgical condition. Systemic hypoperfusion with generalized abdominal pain is seldom nonsurgical.

2. Acute appendicitis and intestinal obstruction are the most frequent final diagnoses in cases erroneously believed at first to be nonsurgical. Appendicitis should remain a foremost concern if sepsis or an inflammatory lesion is suspected. It is the commonest cause of bizarre peritoneal findings producing ileus or intestinal obstruction. Pelvic appendicitis, with mild abdominal pain, vomiting and frequent loose stools, simulates gastroenteritis. Atypical presentations of appendicitis are encountered during pregnancy.

3. Salpingitis, dysmenorrhea, ovarian lesions and urinary tract infections complicate the evaluation of the acute abdomen in young women. Diagnostic errors can be avoided by taking a careful gynecologic history and performing a pelvic examination and urinalysis. Always consider a pregnancy test.

4. Unusual types or atypical manifestations of intestinal obstruction are easily missed. Emesis, abdominal distention and air-fluid levels on x-ray may be negligible in Richter hernia, proximal or closed-loop small bowel obstructions and early cecal volvulus. Intestinal obstruction in an elderly woman who has not had a previous operation suggests an incarcerated femoral hernia or, rarely, an obturator hernia or gallstone ileus.

5. Elderly or cardiac patients with severe unrelenting diffuse abdominal pain but no peritoneal signs may have intestinal ischemia. Arterial blood pH and lactate should be measured and visceral angiography or CTA performed expediently.

6. Medical causes of the acute abdomen should be considered and excluded if possible before exploratory laparotomy is planned (Table 21–5). Upper abdominal pain may be encountered in myocardial infarction, acute pulmonary conditions, pancreatitis and acute hepatitis. Generalized or migratory abdominal discomfort may be felt in acute rheumatic fever, polyarteritis nodosa and other vasculitides. Acute bursitis and hip joint disorders can produce pain radiating into the lower quadrants.

7. Beware of acute cholecystitis, acute appendicitis and perforated peptic ulcer in patients already hospitalized for an illness affecting another organ system.

SPECIAL POPULATIONS

Elderly

Due to the rising elderly population, physicians should expect to encounter more patients in this age group. Elderly patients presenting with an acute abdomen are more likely to require surgical intervention. These patients often have one or more medical comorbidities complicating their presentation. For example, patients with cardiovascular disease, whether known or unknown, will be more likely to present with acute mesenteric ischemia as a cause of abdominal pain. One of the most frequent causes of acute abdominal pain in the elderly is bowel obstruction. The etiology of these bowel obstructions will differ from younger populations with malignancy and hernias higher on the differential. Elderly patients tend to present later in their course of illness. Many will have past surgical history, which can make operative intervention technically challenging. Although surgical intervention for the acute abdomen in the elderly is safe and necessary, the perioperative morbidity and mortality rates are higher, largely due to medical comorbidities and more limited reserve.

Bariatrics

Obesity is increasingly prevalent in the United States and weight loss surgery has become relatively commonplace. This patient population presents both its own differential for the acute abdomen and its own anatomic challenge to the surgeon. Physical examination findings may be vague due to the patient’s body habitus. Tachycardia is an ominous sign that should not be dismissed. Common causes of acute abdomen in the bariatric population include marginal ulcers, obstruction due to internal hernias or adhesions and gastric band complications. Due to the common formation of gallstones following rapid weight loss, cholecystitis is another frequent cause of the acute abdomen in post bypass patients.

Pregnancy

Pregnant women can present with confounding symptoms. Normal pregnancy may be associated with nausea and vomiting, or mild leukocytosis. Physical examination may also be misleading due to the shift in organs secondary to their enlarged uterus. The most common cause of the acute abdomen in pregnancy is appendicitis. Appendicitis in pregnancy may present with pain in atypical locations due to displacement by the uterus. Pain may be present in the right upper quadrant or if the appendix is pushed posteriorly, patients may not demonstrate peritoneal pain. Once diagnosed, early operative intervention is indicated as ruptured appendicitis leads to increased risk of fetal loss.

Immunocompromised

Immunosuppressed patients present a unique challenge, as their immune response will not mount the same presentation as an otherwise healthy patient. This population includes patients with HIV/AIDS, diabetics, patients on chemotherapy, transplant patients and patients on steroid therapy. Immunosuppressed patients have a wider differential including many obscure medical etiologies, such as various opportunistic infections. Due to the lack of inflammatory response, physical examination may present as not concerning. The examiner should be wary of a “benign examination” in light of an otherwise concerning clinical picture. These patients often do not mount an expected leukocytosis. Delayed diagnosis may be devastating as patients often present with advanced disease, shock, or peritonitis, with limited reserve.

INDICATIONS FOR SURGICAL EXPLORATION

The need for operation is apparent when the diagnosis is certain, but surgery sometimes must be undertaken before a precise diagnosis is reached. Table 21–6 lists some indications for urgent laparotomy or laparoscopy. Among patients with acute abdominal pain, those over age 65 years more often require operation (33%) than do younger patients (15%).

A liberal policy of exploration is advisable in patients with inconclusive but persistent right lower quadrant tenderness. Pain in the left upper quadrant infrequently requires urgent laparotomy and its cause can usually await elective confirmatory studies.

PREOPERATIVE MANAGEMENT

After initial assessment, parenteral analgesics for pain relief should not be withheld. In moderate doses, analgesics neither obscure useful physical findings nor mask their subsequent development. Indeed, abdominal masses may become obvious once rectus spasm is relieved. Pain that persists in spite of adequate doses of narcotics suggests a serious condition often requiring operative correction.

Resuscitation of acutely ill patients should proceed based on their intravascular fluid deficits and systemic diseases. Medications should be restricted to essential requirements. Particular care should be given to use of cardiac drugs and corticosteroids and to control of diabetes. Antibiotics are indicated for some infectious conditions or as prophylaxis in the perioperative period.

A nasogastric tube should be inserted in patients with hematemesis or copious vomiting, suspected bowel obstruction, or severe paralytic ileus. This precaution may prevent aspiration in patients suffering from drug overdose or alcohol intoxication, patients who are comatose or debilitated, or elderly patients with impaired cough reflexes. A urinary catheter should be placed in patients with systemic hypoperfusion. In some elderly patients, it eliminates the cause of pain (acute bladder distention) or unmasks relevant abdominal signs.

Informed consent for surgery may be difficult to obtain when the diagnosis is uncertain. It is prudent to discuss with the patient and family the possibility of multiple-staged operations, temporary or permanent stomal openings, impotence or sterility and postoperative mechanical ventilation. Whenever the exact diagnosis is uncertain—especially in young or frail or severely ill patients—a frank preoperative discussion of the diagnostic dilemma and reasons for laparotomy or laparoscopy will reduce postoperative anxieties and misunderstanding.

References