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Malignant bowel obstruction in palliative care |
The incidence of malignant bowel obstruction in the general population is not known. The commonest causes are cancer of the ovary (30-40% become obstructed) and colo-rectal cancers (10-20% become obstructed).
The pathophysiology of malignant bowel obstruction is often multifactorial and a single mechanical block is not the norm. It may include:
- Mechanical block from intraluminal or extrinsic compression;
- Motility/functional block from malignant involvement of autonomic nerves or intestinal muscle;
- Obstruction at multiple sites;
- Other factors such as oedema, faecal impaction, fibrosis, fatigues muscle and constipating drugs may contribute to intestinal obstruction.
Strangulation or bowel ischaemia is rare in malignant bowel obstruction, which makes non-surgical management far less hazardous than in other forms of bowel obstruction.
Clinical features are variable and depend on whether the obstruction is partial or complete, high or low, acute or subacute, etc. Generally vomiting, colic and pain related to abdominal tumour occurs in most patients. Distention is greater in lower bowel obstruction and bowel sounds vary from absent (adynamic obstruction) to hyperactive. Bowel habit varies from absolute constipation to diarrhoea.
Radiological investigations are only useful to:
- Differentiate between severe constipation and malignant obstruction.
- To confirm obstruction and determine its site and nature for a possible surgical patient.
Management must be appropriate to the stage of the patient’s disease and prognosis and follows a 3-step approach.
1. Is surgery appropriate?
2. Is this medically reversible?
3. What’s the best palliation?
1. Is surgery appropriate?
Surgical intervention is appropriate for 10-30% of patients and should be considered if:
- A likely reversible cause, eg. adhesions or single discrete obstruction.
- The patient’s general condition and nutritional status is good.
- Absence of ascites.
- No previous failed chemotherapy/abdominal radiotherapy.
2. Is this medically reversible?
Given that obstructions can resolve spontaneously, with good palliative approach, reversal can be facilitated with:
a) Trial of dexamethasone 8-16mg subcutaneously every 24 hours for up to one week. May be beneficial for low bowel obstruction and reduction of perineural oedema in functional obstruction.
b) Use of prokinetic, eg. metoclopramide (SC) 60mg per day, may overcome functional obstruction. It will exacerbate colic and vomiting in absolute mechanical obstruction and therefore must be discontinued.
c) Stool softeners, eg. plain coloxyl or Movicol, can soften stool to pass through an obstruction.
d) High enemas, eg. olive oil retention enema followed by a high coloxyl enema, can overcome severe constipation, which may have precipitated an obstruction.
3. What’s the best palliation?
If the above measures are not indicated, the final step is good symptomatic management which is best achieved with a syringe driver. A continuous subcutaneous infusion of medications via a portable syringe driver is the preferred route of administration and is ideal for home or hospital use. The commonest symptoms requiring palliation are:
a) Nausea
Can usually be abolished with Haloperidol 5mg SC / day and/or cyclizine 100-150mg SC / day 3rd line ondansetron
b) Vomiting
It may not be possible to eliminate vomiting completely, but the aim is to reduce to 1-2 episodes a day. The patient will need much reassurance that this is okay. Most patients will tolerate occasional vomiting as long as the nausea is under control.
c) Pain
Most patients will have pre-existing abdominal pain and will require their usual analgesia in subcutaneous form. Increased doses may be required. Intestinal obstruction is not a contraindication for opioids.
d) Colic
Can be overcome by:
- Ceasing stimulant aperients (senna, bisacodyl) and prokinetics (metoclopramide and domperidone).
- Peppermint water 10mls qid.
- Buscopan 60-120mg SC/day.
Special drugs
Buscopan – can be useful to reduce gastric secretions and therefore reduce the frequency and volume of vomits. It also reduces peristalsis and therefore colic. However, by paralysing the bowel, it compounds rather than facilitates reversible obstruction.
Octreotide – a synthetic somatostatin analogue – reduces GI secretions and decreases gut peristalsis and is useful in reducing frequency and volume of vomits. Dose 0.3-0.6mg / day in SC infusion. 2nd line agent after buscopan. Very expensive.
Ondansetron – can be given by SC infusion 8-16mg / day. It is expensive and used as a 3rd line agent after haloperidol and cyclizine.
Footnotes
- NG tubes or venting gastrostomies are rarely needed if there is adequate medical management.
- IV/SC hydration is a contentious issue and case dependent. It should be considered if a patient is thirsty. However patients should be allowed to eat and drink as they wish. They will still absorb oral fluids above the level of the block and usually remain hydrated.
- In one study of malignant bowel obstruction at St Christopher’s Hospice, the mean survival time was 3.7 months from onset of symptoms to death in medically managed patients.
Ref. Oxford Text Book of Palliative Medicine
Joanne Doran is the area medical director of palliative care, based in St Vincent’s Hospital, Lismore, NSW, Australia.
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