Acute Abdomen & GI Surgery

An acute abdomen is not a diagnosis. It is a decision point: does this patient need an operation, and if so, how soon.

Candidates lose marks here by trying to name the disease first. The examiner is usually testing something earlier in the chain, which is whether you recognised that the peritoneum was involved, or that the pain was out of proportion to the signs, or that the patient was too old to mount a normal response.

The organising tool for this chapter is a sequence: pain first, peritoneum second, imaging third. The character and migration of pain tell you which organ. The state of the peritoneum tells you how fast. Imaging confirms and plans, but it very rarely overturns a decision that was already obvious clinically.

Every section below is an application of that sequence.

1. Reading Abdominal Pain

Abdominal pain arrives through two separate nerve supplies, and the whole of clinical localisation rests on the difference between them.

Visceral pain travels in autonomic afferents from the organ itself. It is dull, poorly localised, felt in the midline, and often accompanied by nausea, sweating and restlessness.

Because the gut is a midline structure embryologically, visceral pain localises by embryological origin rather than by anatomical position.

Parietal pain travels in somatic nerves supplying the parietal peritoneum. It is sharp, precisely localised, and made worse by movement, coughing or a jolt to the bed.

The transition from one to the other is the single most useful observation in the acute abdomen. It means inflammation has spread from the organ to the peritoneum overlying it.

That is exactly what the migration of appendicitis pain describes. Early appendiceal distension produces midgut visceral pain at the umbilicus; when the inflamed serosa reaches the parietal peritoneum of the right iliac fossa, the pain moves there and becomes sharp.

Referred pain is the third pattern. Diaphragmatic irritation refers to the shoulder tip through C3 to C5, which is why splenic rupture, a perforated ulcer or blood under the diaphragm may present with shoulder pain.

Renal and ureteric pain radiates from loin to groin, and pancreatic pain bores through to the back because the organ is retroperitoneal.

2. The Peritoneum Decides the Urgency

Once you know the organ, the next question is whether the peritoneum is inflamed and over what area.

Localised peritonism means guarding and rebound over one region. It suggests a contained inflammatory process such as appendicitis, cholecystitis or diverticulitis, and permits investigation before operating.

Generalised peritonitis means a rigid, board-like abdomen with absent bowel sounds and a patient who lies completely still. It suggests free contamination of the peritoneal cavity and is an indication to resuscitate and operate.

Rigidity is involuntary. Guarding can be voluntary and disappears when the patient is distracted, but true rigidity persists, which is why the distinction is worth making carefully.

Rebound tenderness has largely been replaced in practice by percussion tenderness and the cough test, both of which elicit the same information without deliberately hurting the patient.

Absent bowel sounds indicate paralytic ileus, which accompanies peritonitis. High-pitched tinkling sounds indicate mechanical obstruction with a bowel still trying to overcome it.

The clinical trap is the patient who cannot produce these signs. In the elderly, in diabetics, in patients on corticosteroids and in late pregnancy, an abdomen may be soft in the presence of established perforation.

3. Acute Appendicitis

Appendicitis begins with luminal obstruction, most often by a faecolith or lymphoid hyperplasia. Secretion continues behind the obstruction, pressure rises, venous drainage fails, the wall becomes ischaemic, bacteria invade, and eventually it perforates.

That sequence explains the timing. Perforation is unusual in the first twenty-four hours and becomes progressively more likely after forty-eight.

The classical sequence is anorexia, then periumbilical pain, then vomiting, then migration to the right iliac fossa, then fever. Vomiting that precedes the pain argues against appendicitis and towards gastroenteritis.

Signs are named after the position of the appendix, which is why they are inconsistent. A retrocaecal appendix irritates the psoas and gives a positive psoas sign; a pelvic appendix irritates the obturator internus and the rectum.

The Alvarado score aggregates migration, anorexia, nausea, right iliac fossa tenderness, rebound, fever, leucocytosis and neutrophil shift. It is a triage tool, not a diagnostic one.

Imaging is selective rather than routine. Ultrasound is first line in children, in thin patients and in women of reproductive age, because it avoids radiation and simultaneously assesses the ovaries.

Computed tomography is more accurate overall and is preferred in adults where the diagnosis is uncertain, particularly in the elderly, where an appendiceal or caecal tumour may be the underlying cause.

Laparoscopic appendicectomy is standard. It offers a lower wound infection rate, faster recovery, and the diagnostic advantage of inspecting the pelvis when the appendix turns out to be normal.

Non-operative management with antibiotics has genuine evidence behind it and is now endorsed for selected uncomplicated appendicitis, but the recurrence figures matter: in the CODA trial roughly forty-six per cent of the antibiotic group had undergone appendicectomy by two years.

The presence of an appendicolith predicts failure of antibiotic treatment and favours operating.

An appendicular mass presenting after several days is managed conservatively with antibiotics and observation, because operating into an inflamed phlegmon risks injuring the caecum. An appendicular abscess is drained.

4. Intestinal Obstruction

Obstruction produces four cardinal features, and their order tells you the level.

Proximal small bowel obstruction gives early, copious vomiting with little distension. Distal small bowel obstruction gives moderate distension with later, faeculent vomiting. Large bowel obstruction gives gross distension with absolute constipation and vomiting only very late.

The causes differ by population. Worldwide, adhesions from previous surgery are the commonest cause of small bowel obstruction, followed by hernias and malignancy.

In parts of India, and in any patient who has never had an operation, tuberculosis and obstructed hernia rise sharply up the list. Ileocaecal tuberculosis producing a stricture is a diagnosis that must be actively considered rather than reached by exclusion.

The critical distinction is between simple and strangulated obstruction, because it determines whether there is time.

A colicky pain that becomes continuous is the single most important change to detect, because it marks the point at which the bowel has stopped contracting and started dying.

Initial management is decompression with a nasogastric tube, intravenous fluids, correction of electrolytes and careful monitoring. This is often summarised as drip and suck.

Adhesive obstruction without signs of strangulation resolves without surgery in most patients. A water-soluble contrast study serves two purposes at once: contrast reaching the colon within a defined interval predicts resolution, and the hyperosmolar contrast itself draws fluid into the lumen and may help the obstruction settle.

Absolute indications to operate are strangulation, peritonitis, an obstructed hernia, a virgin abdomen with no plausible adhesive cause, and failure of conservative management.

Sigmoid volvulus is the classic exception in management. It produces massive distension in an elderly or institutionalised patient, a coffee-bean loop on plain film, and is treated in the first instance by endoscopic detorsion rather than by laparotomy.

Detorsion relieves the obstruction but does not prevent recurrence, so elective sigmoid resection is offered afterwards to fit patients. Gangrenous bowel at endoscopy contraindicates detorsion and mandates resection.

5. Perforation and Pneumoperitoneum

A perforated viscus releases gas and gastrointestinal contents into the peritoneal cavity, producing sudden, severe, generalised pain in a patient who can usually name the minute it began.

Peptic ulcer perforation is the commonest cause in India and typically perforates anteriorly, whereas a posterior duodenal ulcer erodes into the gastroduodenal artery and bleeds instead.

An erect chest radiograph detecting free gas under the diaphragm is the classic investigation, and it remains useful because it is fast and available everywhere.

It is not sensitive. A substantial minority of genuine perforations show no free gas, so a normal film does not exclude the diagnosis and computed tomography is far more sensitive.

Free gas on imaging in a patient with peritonitis is an indication to operate, not an indication to investigate further. Resuscitation and operation proceed together rather than in sequence.

The operation for a perforated duodenal ulcer is closure with an omental patch, peritoneal lavage, and eradication of Helicobacter pylori afterwards. Definitive acid-reducing surgery has essentially disappeared because medical acid suppression made it unnecessary.

Typhoid ileal perforation remains an important Indian cause, usually occurring in the third week of illness at the antimesenteric border of the terminal ileum.

6. Acute Mesenteric Ischaemia

This is the diagnosis that is missed, and the reason it is missed is written into its presentation.

Pain out of proportion to physical findings is the defining feature. The patient reports agonising central abdominal pain while the abdomen remains soft and unremarkable, because the visceral peritoneum is ischaemic long before the parietal peritoneum becomes involved.

By the time there is guarding, rigidity, a raised lactate and metabolic acidosis, the bowel is infarcted and mortality is very high.

There are four mechanisms, and they are not interchangeable.

Embolism lodges characteristically a few centimetres beyond the origin of the superior mesenteric artery, sparing the proximal jejunum, because the vessel leaves the aorta at a narrow angle.

Computed tomography angiography is the investigation of choice and must be requested specifically, since a routine portal-venous study may not demonstrate the arterial occlusion.

Chronic mesenteric ischaemia is the same disease at a lower grade, presenting with postprandial pain, deliberate avoidance of food and weight loss, and it is regularly mistaken for malignancy.

7. Colonic Emergencies

Acute diverticulitis occurs in a left-sided sigmoid distribution in Western populations and more often in a right-sided caecal distribution in Asian populations, which changes the differential in India, where it may be indistinguishable from appendicitis.

The Hinchey classification grades it from a phlegmon through a pericolic abscess and pelvic abscess to purulent and then faeculent peritonitis, and it determines management.

Uncomplicated diverticulitis is treated conservatively. Antibiotics are increasingly omitted in immunocompetent patients who are not systemically unwell, on trial evidence showing no difference in outcome, which is a reversal of long-standing practice.

Abscesses above a few centimetres are drained radiologically. Perforation with peritonitis requires operation, and the choice between resection with a stoma and resection with primary anastomosis depends on the degree of contamination and the state of the patient.

Colonoscopy is deliberately delayed until the acute episode settles, because insufflating an acutely inflamed colon risks perforating it. It is then performed to exclude a carcinoma masquerading as diverticulitis.

Malignant large bowel obstruction is the presentation of a substantial share of colorectal cancers in India, where screening is not established.

A competent ileocaecal valve converts the obstruction into a closed loop, and the caecum, having the largest diameter, is the site that perforates first by the law of Laplace. A caecal diameter beyond about twelve centimetres is an urgent warning.

Toxic megacolon complicates severe colitis, whether inflammatory or infective, and is defined by colonic dilatation with systemic toxicity. Antimotility agents and opioids worsen it and are contraindicated.

8. When the Signs Are Absent

Some patients cannot generate the findings the previous sections rely on, and the examination knows it.

The elderly have reduced pain perception, a blunted febrile response and less abdominal wall muscle, so peritonitis may present as confusion, tachycardia or simply as being unwell. Mortality is far higher because presentation is later.

Immunosuppressed patients, including those on corticosteroids or chemotherapy and those with advanced human immunodeficiency virus infection, cannot mount the inflammatory response that produces guarding, fever and leucocytosis.

In pregnancy the appendix is displaced upwards and laterally by the enlarging uterus, so appendicitis presents higher in the abdomen, and the physiological leucocytosis of pregnancy removes the value of the white cell count.

Ultrasound is the first-line imaging study in pregnancy, with magnetic resonance imaging as the second choice, and appendicectomy is performed when indicated because untreated appendicitis is far more dangerous to the fetus than the operation.

Children cannot localise pain reliably, present with vomiting and irritability, and perforate faster because the omentum is short and less able to wall off infection.

9. Worked Examples

Example 1. A 22-year-old man has 18 hours of pain that began around the umbilicus and is now sharp in the right iliac fossa. Temperature 37.8 degrees Celsius, localised guarding, white cell count 14,000.

The migration from a periumbilical visceral pain to a localised parietal pain in the right iliac fossa is the diagnostic sequence of appendicitis, and localised guarding confirms parietal peritoneal involvement.

The presentation is characteristic enough that imaging is not required in a young man. Laparoscopic appendicectomy is appropriate. Ultrasound would be added in a young woman to assess the ovaries and exclude ectopic pregnancy.

Example 2. A 70-year-old woman with atrial fibrillation, not anticoagulated, has two hours of severe central abdominal pain. The abdomen is soft with no guarding. Lactate is 4.2.

Severe pain with a soft abdomen is pain out of proportion to the findings, and in a patient with atrial fibrillation the mechanism is embolic occlusion of the superior mesenteric artery.

The raised lactate indicates that ischaemia is already established. The correct investigation is urgent computed tomography angiography, requested as an arterial study, and the patient should be resuscitated and referred for revascularisation or resection without waiting for signs to develop.

Example 3. A 55-year-old man with a previous laparotomy has colicky central pain, vomiting and distension for a day. There is no guarding, bowel sounds are tinkling, and vital signs are normal.

This is simple adhesive small bowel obstruction. Colicky pain, tinkling sounds and the absence of tenderness or tachycardia argue against strangulation, so a trial of conservative management is correct.

Nasogastric decompression, intravenous fluid and electrolyte correction are started, and a water-soluble contrast study both predicts and may hasten resolution. Should the pain become constant, or tachycardia and localised tenderness appear, the decision changes immediately to operation.

Summary

• An acute abdomen is a decision about operating, not a diagnostic label.
• Visceral pain is midline and localises by embryological gut segment; parietal pain is sharp and precisely localised.
• Migration from visceral to parietal pain means inflammation has reached the peritoneum.
• Foregut pain is epigastric, midgut periumbilical, hindgut suprapubic.
• Diaphragmatic irritation refers to the shoulder tip; pancreatic pain bores to the back.
• Localised peritonism allows investigation; generalised rigidity means operate.
• Appendicitis follows luminal obstruction, so perforation risk rises after 48 hours.
• Vomiting before pain argues against appendicitis.
• Appendiceal signs vary because the appendix position varies.
• Antibiotics alone are an option in uncomplicated appendicitis, but nearly half come to surgery within two years.
• An appendicolith predicts failure of non-operative management.
• Proximal obstruction vomits early with little distension; distal obstruction distends before it vomits.
• Adhesions lead worldwide; tuberculosis and hernia matter more in India.
• Colicky pain becoming constant is the warning sign of strangulation.
• Sigmoid volvulus is treated first by endoscopic detorsion, not laparotomy.
• A normal erect chest film does not exclude perforation.
• Perforated duodenal ulcer is closed with an omental patch, not with acid-reducing surgery.
• Pain out of proportion to findings is mesenteric ischaemia until disproved.
• Computed tomography angiography must be requested as an arterial study.
• Right-sided diverticulitis is commoner in Asian populations and mimics appendicitis.
• Antibiotics may be omitted in uncomplicated diverticulitis in well patients.
• A competent ileocaecal valve makes malignant obstruction a closed loop, and the caecum perforates first.
• The elderly, the immunosuppressed and the pregnant may have peritonitis without the signs of it.