Nausea & Vomiting

Question 1

What kind of response is vomiting?

Answer 1

A defensive mechanism against the external environment

Question 2

What is vomiting?

Answer 2

A forceful expulsion of gastric contents from the mouth

Question 3

What causes vomiting?

Answer 3

• powerful/sustained contraction of abdominal muscles = increased abdominal pressure
• diaphragm descent and contraction
• gastric cardia opens
• vomiting centre relaxes LOS
• tachycardia
• peristalsis
• epiglottis closes so food doesn’t travel down the lungs

VC LOS to relax, diaphragm contracts, abdominal muscles contact, food pushed back up, increased abdominal pressure when contract muscles, tachycardia, salivation, peristalsis, epiglottis closes at top so food doesn’t travel down into lungs

Question 4

What is retching?

Answer 4

Laboured, spasmodic, rhythmic contractions of respiratory muscles (diaphragm, chest wall, abdominal wall muscles)

• no expulsion of gastric contents
• generates pressure gradient which can lead to vomiting

Question 5

What is nausea?

Answer 5

unpleasant sensation at the back of throat

urge to vomit

Question 6

What is nausea accompanied by?

Answer 6

cold sweats
pallor
salivation
loss of gastric tone
duodenal contractions
reflex of intestinal contents into stomach

Question 7

What happens if nausea does not stop?

Answer 7

• life prolonged refusal of medications
• ribs broken
  -dehydration/anorexia
  seen in cancer patient undergoing chemotherapy
  nausea can be relieved b vomiting

Question 8

What are the 3 main types of vomiting syndrome?

Answer 8

Life prolonged nausea and vomiting (chemotherapy cancer patients)
Cyclic vomiting syndrome
Gastroparesis

Question 9

What is cyclic vomiting syndrome?

Answer 9

nausea not relieved by vomiting
can incapacitate
rapid fire, projectile vomiting

Question 10

What is gastroparesis?

Answer 10

delayed gastric emptying
higher with diabetes
less intense but more widespread
belching and bloating
early satiety after eating

Question 11

What is the NTS?

Answer 11

nucleus of solitary tract

dorsal motor nucleus of vagus + reticular formation + ventrolateral medulla

Question 12

What are some sensory inputs to the vomiting center?

Answer 12

ischaemia of heart
liver blood circulation
visual/vestibular motion sickness compression/psychogenic
pain

Question 13

What is another word for vomiting?

Answer 13

Emesis

Question 14

What are the 3 main anti-emetics?

Answer 14

• muscarinic receptor antagonists
• histamine receptor antagonists
• dopamine D2 receptor antagonists

Question 15

What are some examples of dopamine D2 receptor antagonists?

Answer 15

• phenothiazines
• metoclopramide
• domperidone

Question 16

What is hyoscine?

Answer 16

Muscarinic receptor antagonist
Blocks effects of acetylcholine in the brainstem/vestibular motor nuclei
For motion sickness
Cannot get through BBB to work directly on M3 in vomiting center

Question 17

What are the main histamine receptor antagonists?

Answer 17

• diphenhydramine (crosses BBB so can act directly on muscarinic in vomiting centre, M2 receptor antagonist and H1 receptor antagonist in vestibular nuclei for motion sickness), given with Dramamine (counteracts drowsiness, motion sickness)
• cyclizine (inhibits pre-ganglionic cholinergic activity again for motion sickness)

Question 18

What is the action of dopamine D2 receptor antagonists?

Answer 18

inhibit blood circulation from the liver to the area prostrema so it doesn’t act on nuclei

Question 19

What is metoclopramide?

Answer 19

• dopamine D2 receptor antagonist
• has 2 actions: anti-emetic by antagonising the dopamine receptors in the area of prostema so that cytotoxins from the blood from the liver cannot stimulate them -> not signalling to vomiting centre
• 2nd action is that it stimulates gut motility

Question 20

When might metoclopramide be used?

Answer 20

anti-emetic: post operative care, gastritis/migraine

upper gut motility: gastro-oesophageal reflux, gastroparesis

Question 21

Where is the vomiting centre and area of prostema?

Answer 21

In the medulla oblangata

However area of prostrema is outside the BBB so more permeable to cytoxic agents (released by chemotherapy)

Question 22

What pathways feed into the vomiting centre?

Answer 22

• CTZ (area of prostema) from chemicals in the gut travel in blood acting on dopamine receptor there(cytotoxins, poisons, damage)
• motion sickness stimulates vestibular cochlear nerve which stimulates vestibular nuclei histamine-1 and muscarinic receptors -> CTZ -> vomiting centre
• emotional response/smell bad/see bad detected by higher brain centre -> vomiting centre
• enterochromaffin cells release serotonin in response to cytotoxic agents which stimulates 5HT3 receptors on bagal afferent endings -> vagus nerve brings this to the NTS -> vomiting centre

Question 23

What receptors are in the vomiting centre and the area of prostema?

Answer 23

VC - Muscarinic receptors

AOP - dopamine and serotonin

Question 24

Where are the vestibular nuclei?

Answer 24

In the pons of the brainstem

Question 25

What is a cannabinoid?

Answer 25

Can stop vomiting but not in severe cases
Work directly on CB1 receptors in brain
Treat mild
side effect limited

Question 26

What is the role of corticosteroids?

Answer 26

Dexamethasone

• anti-inflammatory
• increase effectiveness of other anti-emetics but also can give alone for some effect
• can increase appetite
• anti-nausea effects

Question 27

What should you give in severe emesis?

Answer 27

5-HT3 receptor antagonist
NK1 receptor antagonist
dexamethasone (corticosteroid)
all together

Question 28

What is the difference between partial and total bowel obstruction?

Answer 28

Partial - GI propulsion stimulated

Total - emesis, pain and retropropulsion

Question 29

How would you treat bowel obstruction?

Answer 29

Partial -> cytotoxins to the area of prostrema due to obstruction, so give metoclopramide (DT antagonist)
Total -> reduce inflammation (dexamethasone which is a corticosteroid) and reduce fluid build up in the lumen (somatostatin antagonist with NG tube)