Nausea, Vomiting, Constipation and Malignant Bowel Obstruction

Question 1

What are the main receptors at the vomiting centre?

Answer 1

• ACh, H1, 5-HT2, NK1

Question 2

What are the main receptors at the GI tract involved in nausea and vomiting? How do they reach the vomiting centre? What drugs act here?

Answer 2

• GI tract (5HT4, NK1, D2, H1, ACh, stretch)
• Stimulates CTZ and vomiting centre by vagal afferents
• Metoclopramide, domperidone, erythromycin

Question 3

What are the main receptor types at the chemoreceptor trigger zone? Which drugs act here?

Answer 3

• Chemoreceptor trigger zone (5HT, D2, NK1)
• Haloperidol, metoclopramide, “trons”, aprepitant

Question 4

What are the main receptors at the vestibular system involved in nausea and vomiting? Which drugs act well here?

Answer 4

• Vestibular system (ACh, H1)
• Promethazine, prochlorperazine, cyclazine

Question 5

Which receptors involved in nausea and vomiting are located in the cerebral cortex? Which drugs act well here?

Answer 5

• Cerebral cortex (5HT, GABA, NK1, stretch)
• Dexamethasone (ICP), lorazepam (anxiety etc.)

Question 6

Outline the general management principles of bowel care related to constipation

Answer 6

• Non-pharmacological - fiber, fluids, gastrocolic reflex (highest chance of action 30mins post-meal)
• Pharmacological
  
  • Softening laxatives - coloxyl
  • Stimulating laxatives - senna
  • Osmtoic laxatives - movicol, lactulose
  • Opioid antagonist - methylnaltrexone
  • Enemas
• Monitoring - Bristol stool chart

Question 7

Which first-line anti-emetic also has pro-kinetic effects?

Answer 7

Metoclopramide

Question 8

Describe the management principles of a patient with malignant bowel obstruction

Answer 8

• Non-surgical
  
  • NGT decompression, bowel rest, fluids
  • Ranitidine/PPI (reduce secretions)
  • Steroids (swelling), radiochemotherapy (shrink tumour)
• Surgical
  
  • Stenting, stoma, bypass, resection
• Partial
  
  • Bowel rest, prokinetics, laxatives, dexamethasone