Gastrointestinal system

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CHAPTER 6 GASTROINTESTINAL SYSTEM

Gastrointestinal tract in critical illness 168
Reduced gastrointestinal motility 170
Diarrhoea 170
Stress ulceration 172
Gastrointestinal ischaemia 172
Gastrointestinal bleeding 172
Intra-abdominal sepsis 174
Abdominal compartment syndrome 174
Hepatic dysfunction during critical illness 176
Hepatic failure 176
Acute pancreatitis 181

GASTROINTESTINAL TRACT IN CRITICAL ILLNESS

The gastrointestinal tract plays a major role in the pathophysiology of critical illness. In addition, to being a common site for surgical intervention and a common source of intra-abdominal sepsis, the gut is pivotal during critical illness in a number of ways:

image As a large ‘third space’ for fluid loss within the lumen of the gut.
image As a bed for altered blood flow (AV shunting) during shock states.
image As a reservoir for bacteria and endotoxins, which may translocate into the portal, lymphatic and systemic circulations, producing systemic inflammatory response syndrome, sepsis and multiorgan failure, particularly during periods of altered blood flow. (See Sepsis, p. 326).
image As a reservoir for bacteria which may colonize/infect the respiratory tract. (See Ventilator associated pneumonia, p. 143)
image As a site of secondary nosocomial infections e.g. Clostridium difficile.
image The maintenance of gastrointestinal integrity and function is therefore of major importance during critical illness.

Maintenance of gastrointestinal tract integrity

The pathophysiology of gastrointestinal integrity is complex. Maintenance of adequate splanchnic blood flow is thought to play a key part. In this respect, early aggressive resuscitation in shock states is crucial. Several studies have shown that both volume resuscitation and the maintenance of adequate perfusion pressure using vasopressor agents are independently important. In the ‘Rivers study’, early effective resuscitation, as guided by optimization of mixed venous oxygen saturation (a good surrogate for adequacy of tissue oxygen supply), was shown to reduce the patient’s stay in the intensive care unit, reduce the number of organ failures and reduce eventual mortality in patients undergoing early resuscitation in sepsis. Importantly, resuscitation goals had to be achieved early (i.e. within the first 6 h). In those patients who are adequately resuscitated, early enteral nutrition may also be of value in helping to preserve mucosal integrity and gastrointestinal function.

Manifestations of gastrointestinal tract failure

Failure of the gastrointestinal tract during critical illness may present in a number of ways. These are listed in Box 6.1.

Box 6.1 Clinical features of gastrointestinal tract failure

Delayed gastric emptying

Failure to absorb feed

Ileus, pseudo-obstruction

Diarrhoea

Stress ulceration

Gastrointestinal tract haemorrhage

Gastrointestinal ischaemia

Acalculous cholecystitis

Liver dysfunction

Systemic infl ammatory response syndrome

The principle aim of investigation of gastrointestinal dysfunction in the critically ill patients is to exclude serious, remediable, intra-abdominal pathology. In some cases, the combination of history, clinical examination and blood results in the context of the overall clinical picture will suffice. In many cases however, intra-abdominal imaging will be required. Occasionally laparotomy or laparoscopy may be necessary to exclude serious pathology.

Plain abdominal X-rays

This is a first-line investigation in most cases. Check the position of the nasogastric tube and any other intra-abdominal drains. Look for gastric air and normally distributed gas pattern throughout the large bowel. Check for distended loops of thickened bowel walls and for any air bubbles visible in the gut walls (implies ischaemic gut). Check outline of major viscera and psoas shadow. Look for free air, suggesting perforation of a viscus, and air in the biliary tree, suggestive of biliary tract sepsis.

Ultrasound

This is a valuable imaging technique, which can be performed at the bedside. It is particularly useful for imaging around the liver, biliary tract, kidneys, spleen and pelvic organs and can be used to identify intra-abdominal collections of fluid for drainage. It may be difficult to obtain good images because of obesity or the presence of excessive gas in the bowel.

CT scan

This is the definitive investigation for most acute intra-abdominal problems. CT generally requires oral and intravenous contrast. Its value may be limited in the very unstable patient by the need to transport the patient to the CT scanner. Images require expert interpretation.

REDUCED GASTROINTESTINAL MOTILITY

Delayed gastric emptying and persistent ileus

Failure of gut motility is common in the critically ill. It is usually manifest as a simple ileus, with large nasogastric losses and failure to absorb feed. It will usually improve spontaneously as the patient’s condition improves. Ensure that the patient’s electrolyte balance is normal. Disturbances of potassium and magnesium in particular can contribute to gastrointestinal tract dysfunction. Prokinetic agents such as metoclopramide and low dose erythromycin may promote motility

Rarely, cholinergic agents such as neostigmine may be required, either as a low dose bolus (up to 1 mg) or by infusion. Neostigmine has potentially alarming cardiovascular and systemic side-effects, including abdominal pain, salivation and bradycardia. Do not embark upon this treatment lightly, and only if you are certain that there is no mechanical gut obstruction. Seek advice from your consultant.

(See Common problem: Feed not absorbed, p. 59.)

Pseudo-obstruction

Occasionally ileus will progress to marked intra-abdominal distension, with obvious signs of gut obstruction in the absence of any apparent mechanical cause. This is called pseudo-obstruction. The diagnosis is supported by plain abdominal X-ray or CT, which shows widely dilated loops of bowel.

If the colon is distended to greater than 10–12 cm in cross-section, there is a risk of colonic rupture. The use of prokinetic agents in this setting may be hazardous, and mechanical decompression is usually necessary to prevent colonic rupture. This may be achieved by flexible sigmoidoscopy, or may require surgical intervention. Seek surgical opinion.

DIARRHOEA

Diarrhoea is a common manifestation of gastrointestinal tract failure in the intensive care unit and may arise in a number of ways

image As a manifestation of multisystem disorder. For example, generalized tissue hypoxia, tissue oedema and vascular endothelial failure affect the function of all tissues. The gut is no exception to this. These pathological abnormalities are associated with a failure in cellular function and metabolic pathways, which may persist for some time. Consequently, gut failure (either diarrhoea or constipation) is often a characteristic feature of the patient in the intensive care unit.
image As a result of the osmotic load placed on the gut. This may reflect overfeeding, or feeding with a diet whose electrolyte composition is unsuitable for a particular patient.
image As a consequence of more sinister conditions, such as ischaemic colitis.
image As a consequence of infection with a gut pathogen. This is a particular problem in intensive care patients, as the widespread use of broad-spectrum antibiotics suppresses the normal gut flora and allows the emergence and predominance of potentially pathogenic organisms such as Clostridium difficile.

Clostridium difficile

Clostridium difficile is a spore forming organism that produces an enterotoxin. Clostridium difficile infection is a serious problem, as in addition to torrential diarrhoea, it gives rise to an inflammatory condition in the gut which results in pseudomembranous colitis, and potentially toxic megacolon and gut perforation. The diagnosis can be made on clinical grounds, by stool culture or by detection of the Clostridium difficile toxin. Additionally, pseudomembranes may be visible on sigmoidoscopy, or gut dilatation on X-ray (toxic megacolon).

Clostridium difficile is readily transmitted from patient to patient. It is transmitted by contact, for example on the hands of health care workers. Unfortunately, because it is a spore forming organism, it is resistant to decontamination by alcohol hand rub. Rigorous hand washing using soap and water is much more effective. Patients suffering from Clostridium difficile diarrhoea, should be barrier nursed while in the critical care unit.

The specific treatment of Clostridium difficile relies on appropriate antibiotics. You should seek guidance from your unit microbiologist, as local infection control policies are an important element in limiting the spread of this pernicious infection. Antibiotics that are most commonly effective (usually enterally) include metronidazole and vancomycin. Occasional patients may require a colectomy.

Management of diarrhoea

Supportive measures include:

image Fluid resuscitation if evidence of hypovolaemia.
image Replacement of on-going losses with an appropriate electrolyte solution usually 0.9% or 0.45% saline.
image Sending of stool samples for culture and Clostridium difficile toxin.

In mild cases enteral feed can be continued. Seek advice from a dietician as to the most appropriate feed. In severe cases consideration should be given to ‘resting the gut’ by stopping enteral feeds and instituting parenteral nutrition.

STRESS ULCERATION

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