Gastrointestinal obstruction

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Malignant obstruction of the gastrointestinal tract may be due to occlusion of the lumen by tumour or distortion of gut and mesentery by tumour, or may be functional due to a failure of normal peristalsis. Obstruction may be partial or complete and may develop gradually with self resolving episodes of partial obstruction preceding a complete obstruction. The treatment of choice for a single level of occlusion is surgery, but when the patient is unfit for surgery, or when there are multiple levels of obstruction, an alternative treatment regimen is necessary to palliate symptoms of nausea, vomiting, colic, abdominal distension, and peritoneal pain.

The amount of vomiting depends on the level of obstruction, with more proximal upper gastrointestinal obstruction causing larger volume vomiting. If the level of obstruction is beyond the mid-jejunum, the mucosa of the upper gastrointestinal tract can continue to absorb fluids from the lumen. This reduces the volume of intestinal contents and, in turn, reduces the gut distension that triggers nausea and colic. Thus, vomiting is less frequent and of smaller volumes with more distal obstruction.

Nausea is triggered by distension of the bowel lumen, stimulating the vomiting centre via autonomic afferents. The antiemetics of choice are cyclizine or levomepromazine, and a non-oral route is required to ensure its activity. Absorption of bacterial toxins from a stagnant or ischaemic area of obstructed bowel can also trigger nausea via the chemoreceptor trigger zone: this situation would require the use of a CTZ antiemetic in addition to cyclizine, and haloperidol is the drug of choice, again by a non-oral route.

Dehydration can complicate proximal obstruction, as intestinal secretions are vomited along with any ingested fluids. The volume of intestinal secretion can be reduced by using antisecretory agents: hyoscine butylbromide and octreotide have both been used successfully to reduce pancreatic and upper gastrointestinal secretions. Hyoscine butylbromide also reduces colic. The inhibition of gastric secretions is described above. Dehydration can cause neuromuscular irritability and thirst: good mouth care is essential. If parenteral fluids are required, subcutaneous fluids are well tolerated and can be administered

Gastrostomy tube feeding. Reproduced with permission from Dr P Marazzi/ Science Photo Library

Palliation of symptoms of intestinal obstruction

Drug/dose

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Cyclizine 150 mg/24 hours sc infusion may require addition of haloperidol 1.5-3 mg sc once a day

Acts on vomiting centre

Nausea is controllable but vomiting will persist in total obstruction

Haloperidol 1.5-3 mg sc once a day

Acts on CTZ

Hyoscine butylbromide 60-200 mg/24 hours

Reduces motility and secretions

Both drugs reduce distension reducing nausea and colic

Octreotide 300-1200 ^g/24 hours

Reduces secretions

Levomepromazine 6.25-25 mg/24 hours

Acts on VC and CTZ, useful second line antiemetic

Sedating at higher doses

Pictures Nurse Ray Showing Limbs
Coloured x-rays showing a healthy human intestine, and the same intestine which has become obstructed. Reproduced with permission from Bsip Vem/Science Photo Library

at home if necessary.

Nasogastric intubation does not relieve nausea and may exacerbate nausea by irritating the pharynx. Use of a nasogastric tube to empty the stomach before surgery is entirely appropriate, however, and occasionally it may be appropriate to use intermittently. This depends entirely on the individual patient. In patients with high obstruction, a venting PEG may palliate frequent vomiting.

It is important that patients and families understand that intermittent vomiting is likely to continue despite the control of nausea and colic. Patients with intestinal obstruction, however, may still enjoy the pleasure of eating and drinking; those with low obstruction will be able to absorb some nutrition in this way. Eating and drinking as desired should be encouraged.

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