The acute abdomen
The aim of this chapter is to provide a broad set of guidelines for the management of patients presenting with acute abdominal pain. The detailed clinical, laboratory and radiological features of the numerous causative conditions are provided elsewhere in this text book.
The management of patients with acute abdominal pain comprises two concurrent processes - diagnostic and therapeutic - culminating in the decision to operate or to observe (Management of the acute abdomen).
Regardless of the severity of the presenting illness, management of patients with acute abdominal pain depends heavily upon early and accurate establishment of the clinical diagnosis or, at least, a workable differential diagnosis. This is an important discipline to develop and the label ‘acute abdomen, for surgical review’ should be regarded as unsatisfactory.
History and examination
The process of making a diagnosis on the basis of history and examination is achieved by a combination of pattern recognition (drawn from clinical experience) and probability (based on theoretical knowledge).
The pattern of pain (its site, periodicity, radiation, aggravating and relieving factors, etc.) immediately establishes a ‘shortlist’ of diagnostic possibilities (or differential diagnosis). Each of these options can then be explored in more detail. The age and sex of the patient along with any history of causative, aggravating or precipitating factors make certain diagnostic alternatives more or less probable.
In this manner, clinical assessment can be abbreviated, permitting the focus to fall quickly upon the realistic alternatives. More detailed history and examination can then be used to select the most likely diagnosis (see clinical example, Clinical scenario: a 65-year-old man presents with the sudden onset of generalised abdominal pain and collapse. On examination, he is pale, sweaty and distressed, with pulse rate = 110 beats per minute, blood pressure = 90/50 mm Hg and temperature = 36.0°C).
Some examples of clinical patterns in patients with acute abdominal pain are:
- Pain that commences instantaneously suggests either hollow organ perforation (e.g. perforated peptic ulcer) or a vascular accident (e.g. mesenteric occlusion, ruptured intra-abdominal aneurysm)
- Syncope associated with abdominal pain suggests acute blood loss (e.g. ruptured abdominal aortic aneurysm, ruptured ectopic pregnancy)
- The combination of vomiting and diarrhoea suggests gastroenteritis
- Colicky abdominal pain suggests hollow organ obstruction (e.g. ureteric calculus, small bowel obstruction) or excessive peristalsis (gastroenteritis)
- Pain made worse by movement suggests peritoneal irritation (e.g. appendicitis) or muscular strain.
Some examples of the application of probability in the clinical setting are:
- Recent onset of abdominal pain and anorexia in a previously well young man (acute appendicitis)
- Left iliac fossa pain and tenderness in a 60-year-old (sigmoid diverticulitis)
- Upper abdominal pain and vomiting in a known alcoholic (acute pancreatitis).
It is beyond the scope of this chapter to cover all of the possible clinical scenarios that account for patients who present with acute abdominal pain. At the heart of their management, however, is a determination on the part of the clinician to establish an accurate clinical diagnosis on the basis of history and examination.
It is not possible, at the outset, to anticipate all of the investigations that might ultimately prove helpful in patient diagnosis and management. In the event of a confident clinical diagnosis - e.g. acute appendicitis - in a fit individual, no confirmatory or diagnostic investigations may be deemed necessary. Numerous factors affect the choice of initial diagnostic investigations.
- The severity of the presenting illness
- urea and electrolytes if the patient is clinically dehydrated
- full blood count and cross-match if haemorrhage is suspected
- Specific diagnostic possibilities
- serum beta HCG in suspected ruptured ectopic pregnancy
- serum amylase or lipase in suspected acute pancreatitis
- abdominal ultrasound in cases of suspected biliary disease, obstructive uropathy, ruptured abdominal aortic aneurysm.
- 12-lead ECG in suspected acute myocardial infarction.
- If surgery is anticipated
- prior to undergoing a general anaesthesia, certain investigations may be obtained, particularly in older patients, as a routine. This will vary from centre to centre; these tests include urea and electrolytes, full blood count, ECG, chest X-ray as well as cross-match in appropriate cases.
- General investigations in patients with acute abdominal pain of uncertain origin
- even before a clinical diagnosis is formulated, certain diagnostic investigations may have been instigated in anticipation of subsequent need. Amongst these, the two most frequently of value are:
- full blood count: an elevation of the white cell count is a cardinal sign of sepsis but it may also be raised by the ‘stress’ of pain alone; it is also mildly elevated during normal pregnancy. In general, an elevation of white cell count should never be dismissed and a very high white cell count (>30) in the context of a patient with acute abdominal pain raises the possibility of intestinal ischaemia (mesenteric infarction, closed-loop small-bowel obstruction).
- abdominal X-rays: a supine abdominal X-ray reveals distension of intra-abdominal gas (intestinal obstruction), thickness of intestinal wall (mesenteric ischaemia), abnormal calcification (ureteric colic, chronic pancreatitis) and outlines the psoas shadows (possibly obscured in ruptured abdominal aortic aneurysm). The erect abdominal X-ray reveals fluid levels (confirmation of intestinal obstruction). Decubitus films are used to detect free intraperitoneal gas (perforated hollow viscus) although this may be better demonstrated by an erect chest X-ray.
At the same time as these diagnostic steps are being taken, it is often appropriate - and not infrequently essential - to initiate treatment.
Unwell patients may require preliminary resuscitation before any practical diagnostic steps can be taken. Tachycardia, hypotension, pallor, sweating and cool extremities all suggest a more severe clinical presentation and the possibility of sepsis or hypovolemia. Immediate intravenous access should be established and fluid replacement appropriate to the clinical setting commenced. An oxygen mask to maximise vital organ oxygenation is usually appropriate. A MAST suit is occasionally required in cases of profound haemorrhagic shock (e.g. ruptured abdominal aortic aneurysm).
In cases of haemorrhagic shock, a blood transfusion should commence as soon as practicable. Transfusion should not, however, be allowed to delay the commencement of urgently needed surgery (e.g. ruptured abdominal aortic aneurysm) where the need to control the bleeding point outweighs the desire to restore intravascular volume by transfusion.
In the acute setting it is easy to overlook the need to provide basic symptom control. Analgesia should not be withheld pending ‘surgical review’. Anti-emetic therapy usually accompanies opiate analgesics; for repeated vomiting (e.g. intestinal obstruction, acute pancreatitis) and a nasogastric tube should be passed. This will relieve the symptoms, permit more accurate measurement of fluid loss and protect the patient from the risks of aspiration of gastric content.
Monitoring the patient
In the unwell patient, it is important to monitor the outcome of resuscitation and fluid replacement. Apart from the standard vital signs (pulse rate, blood pressure, temperature), additional information can be obtained by measuring urine output (indwelling urinary catheter) or central venous pressure (central venous catheter). These tools are more sensitive to changes in intravascular fluid status than are the pulse rate and blood pressure.
Broad-spectrum antibiotics should be administered according to the likely clinical diagnosis. This may precede the formulation of an accurate clinical diagnosis especially in unwell patients. Agents active against Gram-negative bacilli (aminoglycosides, thirdgeneration cephalosporins) and anaerobic organisms (metronidazole) are generally preferred in patients presenting with acute abdominal pain.
In cases of acute pancreatitis, subcutaneous octreotide (a somatostatin analogue) may be instituted in an attempt to moderate the course of the pancreatitis.
Surgery vs. observation
Ultimately, an assessment needs to be made about the need for surgery. This may be clear-cut where a confident diagnosis has been made (e.g. appendicitis appendicectomy, ureteric colic analgesia and initial observation).
In some cases, advanced age or infirmity might caution against surgery even where a confident diagnosis points to a surgical remedy (e.g. ruptured abdominal aortic aneurysm in a frail 90-year-old).
Often, however, the precise diagnosis is uncertain and the need for urgent surgery is made obvious by virtue either of the clinical features of generalised peritonitis (e.g. perforated hollow viscus, mesenteric infarction, closed-loop small bowel-obstruction) or the severity of the presenting illness (e.g. associated shock). In this situation, clinical experience (pattern recognition) enables early identification of the need for prompt surgical intervention.
Where the need for surgery is unclear - e.g. some cases of right iliac fossa pain or small intestinal obstruction - observation rather than exploratory surgery is appropriate. This involves regular clinical review conducted at a frequency appropriate to the severity of the illness (e.g. review in 12 hours for a 20-year-old woman with mild right iliac fossa pain and tenderness or 1–2-hourly review in a 75-year-old with small bowel obstruction and associated abdominal tenderness). At times, such review may be augmented by further laboratory or radiological investigations. Of these, the white cell count is most often of practical value; a rising white cell count generally indicates progression of the underlying pathological process.