The acute abdomen

Pathophysiology of intra-abdominal inflammation

• Irritation of peritoneal membrane (chemical or bacteria) causes increased blood flow, increased permeability and formation of local fibrinous exudate
• Bowel will develop a localised ileus
• Adherence forms between local structures due to fibrin
• Peritonitis = peritoneal inflammation from any cause

Types of pain:

Visceral pain:

• • Mechanism
    • Travels along C-fibres - in effect, autonomic afferent fibres
  • Colicky pain occurs with distension
    • Small bowel - every 5 minutes
    • Large bowel - every 10 minutes
    • Pain should disappear almost completely between attacks
  • Radiates to midline - vague and poorly localised, but often epigastrium/umbilical/hypogastrium
  • Occurs with stretching/distension of viscus
  • Mediated by splanchnic sympathetic nerves
  • Can occur from liver capsule

Peritoneal/parietal pain

• • Pain fibres which pass to spinal cord along segmental nerves
  • Mediates guarding/peritonism - reflex contraction of abdominal wall muscles in response to noxious stimulus of the pain fibres of the same dermatome
  • Often inflammatory - syndrome depends on the type of fluid
    • Gastric contents highly irritating - severe sudden pain
    • Small bowel contents produces less pain
    • Bile is also extremely irritant
    • Blood is irritant but not to the same degree as bile or gastric juice

Referred pain

• • Right shoulder
    • Liver
    • GB
    • Right hemidiaphragm
  • Left shoulder
    • Heart
    • Tail of pancreas
    • Spleen
    • Left hemidiaphragm
  • Scrotum and testicles
    • Ureter
  • Pancreatitis to the back
  • Renal colic to groin
  • Pneumonia to abdomen
  • Testicles to hypogastrium
  • Spinal pathology causing abdominal pain

Specific syndromes

• • Ischaemic bowel - almost all visceral, until transmural ischaemia is present
  • Splenic infarct - almost all peritoneal
  • Acute salpingitis - all peritoneal
  • Acute appendicitis - visceral then peritoneal
  • Perforation - chemical peritonitis causes severe peritonitis, whereas gas does not cause as much peritonitis
    • Sigmoid diverticulitis - generally not much peritonism
    • Perf gastric ulcer - rapid pain and peritonism
  • Acute pancreatitis - both visceral and peritoneal
  • Capsule stretching - visceral (ovary, liver)
  • Biliary obstruction - epigastric discomfort
  • LBO - hypogastric discomfort
  • Ureteric colic - peristalsis is less prominent, so pain is somewhat constant, with exacerbations. Can radiate to groin or even lower, to the testicle or labia, but does not radiate to the back of the leg.
  • Kidney pain - constant gnawing pain in loin/renal angle.

• Patients experiencing paroxysms colic should be unable to lie still. This pain relates to distension and would be experienced in areas of visceral pain referral. Once the actual somatic nerves in parietal peritoneum are affected, pain localises.
• Beware patients taking steroids, who may have a smaller inflammatory response and therefore less tenderness and systemic infective features.

Evaluating the acute abdomen

History

• Age/demographics
  • Think about which conditions are likely
• Exact time and mode of onset
  • Sudden onset - think perforated ulcer, acute pancreatitis, ruptured AAA/ectopic, ovarian torsion
• Pain
  • Character
  • Radiation
  • Shifting
    • Irritation of somatic nerves
    • Either direct inflammation of an organ, or fluid (e.g. gastric contents moving to RIF in perforated ulcer)
  • Postural
    • Retroperitoneal pain is worse when lying back
  • Worse with eating - SBO, biliary colic, pancreatitis, diverticulitis, bowel perforation
  • Better with eating - non-perforated PUD or gastritis
• Vomiting
  1. Severe irritation of peritoneal/mesenteric nerves
     • Vomiting will be early
  2. Obstruction of an involuntary muscular tube
     • Vomiting can be later
     • Early vomiting in SBO indicates high obstruction
     • Pain almost always prior to vomiting in appendicitis
  • Acute gastritis - non-bilious
  • Obstructions - bilious
    • First gastric contents, then bilious, then yellow-green, then yellow, then orange/brown faeculent
  • In surgical conditions, vomiting will come after pain. The vomiting is secondary to stimulation of medullary afferent fibres triggered by visceral afferent pain fibres. In medical causes of vomiting, the vomiting often precedes abdominal pain.
• Bowels
• Menstruation

Examination

General inspection

• Observe facial expression
• Check for shock
• Anaemia - conjunctivae, hands
• Posture
  • Colic - restlessness. This is seen in diseases that cause pain without peritoneal irritation, as patients try to get comfortable.
  • Peritonitic - still
  • Hip flexion on one side - psoas irritation
  • Both hips flexed - peritonitis
  • Pancreatic/retroperitoneal - sitting up

Vitals

• Pulse
• RR
  • Tachypnoea is a late sign in abdo disease - metabolic acidosis
• Temperature
  • Fluctuates during day. >37.2 at 0600 and >37.7 at 1600 signify fever
  • Oral temperature is generally 0.6 deg lower than rectal would be
  • TM temp is close to central
  • However, for best real temperature, get bladder/rectal/oesophageal/pulmonary artery catheter
  • We lose the ability to develop a fever with old age, so temperature increases may be modest even with severe sepsis
  • Temperature is known to rise by about 0.6 deg with ovulation and remain at that level until menstruation
  • Hyperpyrexia > 41.5 - probably CNS haemorrhage

Abdomen

• Watch movement with respiration - should move freely
  • Contrast with chest - thorax will move less in pneumonia but abdomen will move more
• Gentle palpation
  • Remember to palpate for bladder
• Percussion/rebound
  • Check for tympanism - if heard all over, suspect free gas. If all but RUQ, could be distended bowel. If any focal dullness other than RUQ, suspect a mass.
• Rigidity
  • If you suspect the patient to be avoiding abdominal breathing by choice rather than because of severe pain, try resting left hand on the sternum with a fair amount of pressure while you examine with the right. This prevents costal breathing
• Hyperaesthesia - can give clues as to which nerve is affected by inflammation - probably more useful in chronic cases
  • Suggests nerve root compression if present
• Psoas sign
• Obturator sign (obturator internus)
• Liver dullness
  • Normal: midclavicular line fifth rib to costal margin; midaxillary line ribs 7-11
  • Resonant note over liver in midaxillary line - consider atrophic liver, abdominal distension, free air. Not a useful test when the abdomen is very distended.
• Shifting dullness - so non-specific as to be not that useful

Specific locations

• Central
  • Acute apendicitis, SBO, pancreatitis, MI
• Central + shock
  • Pancreatitis
  • Mesenteric thrombosis
  • Internal haemorrhage
  • Ruptured AAA
  • Dissecting aneurysm
  • Ectopic
• Pain + vomiting and distension, without rigidity
  • SBO
  • Consider gastritis
• Pain + distension + constipation, but minimal vomiting
  • Likely LBO
• Severe abdo pain with collapse and general rigidity
  • Perforation

Non-surgical causes of acute abdomen

• Endocrine/metabolic
  • Uraemia
  • Diabetic crisis
  • Addisonian crisis
  • Acute intermittent porphyria
  • Hereditary mediterranean fever
• Haematologic
  • Sickle cell crisis
  • Acute leukaemia
  • Other blood dyscrasias
• Toxins and drugs
  • Lead poisoning
  • Other heavy metal poisoning
  • Narcotic withdrawal
  • Black widow spider poisoning

Imaging

• AXR
  • Will detect as little as 1ml of air in peritoneal cavity
• Lateral decubitus xray
  • Useful in detecting pneumoperitoneum in those that cannot stand but needs 5-10ml of air