Vomiting & Gut Motility Disorders Flashcards
Describe the physiological control of vomiting
Vomiting is controlled by;
The vomiting (emetic) centre - co-ordinates the action of vomiting.
The vomiting centre is a collection of multiple sensory, motor and control nuclei so its not a discrete section we can cut out. Its found mainly in the medullary and pontine reticular formation and also extends into the spinal cord. It receives impulses from both vagal and sympathetic afferent nerve fibres.
It takes info from higher cortical centres (cerebral cortex, brain - where emotions, pain and strong smells can trigger it), from chemoreceptor trigger zone and GI tract (through vagal afferents) - puts all of this together to start contractions from small intestines all the way up to the mouth
Disturbances of higher cortical centres (cerebral cortex, brain), chemoreceptor trigger zone and GI tract can cause vomiting
The Chemoreceptor Trigger zone (CTZ) - Passes signals onto the vomiting centre by detecting drugs and toxins that cross into the blood brain barrier as it is more permeable to them here and picks up on signals from the labyrinth in the inner ear - so a disturbance of your inner ear e.g when your balance is effected your ear detect a motion issue and causes motion sickness.
How may drugs modify the
physiological control of vomiting and gut
motility ?
Most of the anti-emetics we use are antagonist drugs stopping something else from binding to receptor and activating the vomiting reflex
List the drugs which affect bile flow
Drugs that affect bile flow and cholelithiasis;
• Bile salts
• Bilirubin
• Cholesterol - In particular know cholesterol as we have a high cholesterol diet so things like gallstones and that have been going up
• Lecithin
• Plasma electrolytes
- The hormone cholecystokinin (CCK) stimulates
gallbladder emptying
How do local toxins in the GI tract cause vomiting?
Entrochromaphin cells lining the stomach sense toxins release a neurotransmitter which is picked up by the vagal afferent by the stomach and that is fed up to the vomiting centre
What are the different stages of vomiting?
Stages of vomiting:
• Nausea: - Feeling of wanting to vomit - Associated with autonomic effects: salivation / pallor / sweating (pre-faint symptoms) - Often pro-drome of vomiting
• Retching (can’t control gag reflex):
- Strong involuntary effort to vomit
- Unproductive
• Vomiting:
- Expulsion of gastric contents through the mouth
We don’t need all 3 together to cause vomiting or feelings of vomiting!
What are the different stages of vomiting?
Stages of vomiting:
• Nausea: - Feeling of wanting to vomit - Associated with autonomic effects: salivation / pallor / sweating (pre-faint symptoms) - Often pro-drome of vomiting
• Retching (can’t control gag reflex):
- Strong involuntary effort to vomit
- Unproductive
• Vomiting:
- Expulsion of gastric contents through the mouth
We don’t need all 3 together to cause vomiting or feelings of vomiting!
What are some types of vomiting and what might they be signs of?
• Projectile vomiting
- Suggestive of gastric outlet or upper Gl obstruction (seen babies with pyloric stenosis as pyloric sphincter is overthickened through development and cannot relax and when food hits that it comes straight back out - usually requires surgery. Also seen in older patients if they develop a gastric malignancy and it causes an obstruction and the food to come back up)
• Haematemesis
- Vomiting fresh or altered blood (“coffee- grounds”)
- e.g. oesophageal varices, bleeding gastric ulcer - can have catastrophic bleeds
• Early-morning
- e.g. pregnancy (usually not always morning - usually feel all of the day - 12 - 14 weeks of gestation), alcohol dependence, some metabolic
disorders (uraemia - damaged kidneys)
What are some types of vomiting and what might they be signs of?
• Projectile vomiting
- Suggestive of gastric outlet or upper Gl obstruction (seen babies with pyloric stenosis as pyloric sphincter is overthickened through development and cannot relax and when food hits that it comes straight back out - usually requires surgery. Also seen in older patients if they develop a gastric malignancy and it causes an obstruction and the food to come back up)
• Haematemesis
- Vomiting fresh or altered blood (“coffee- grounds”)
- e.g. oesophageal varices, bleeding gastric ulcer - can have catastrophic bleeds
• Early-morning
- e.g. pregnancy (usually not always morning - usually feel all of the day - 12 - 14 weeks of gestation), alcohol dependence, some metabolic
disorders (uraemia - damaged kidneys)
What do anti-emetic drugs do and how should we prescribe them?
- To stop nausea/vomiting
- Only prescribe when the cause of vomiting is known
- Treat the cause where possible
- If indicated pick drug according to the aetiology of vomiting
Potential indications: • Severe vomiting during pregnancy / hyperemesis gravidarum (they are becoming dehydrated putting focus at risk - don't give for mild morning sickness) • Postoperative nausea and vomiting • Motion sickness • Other vestibular disorders • N/V induced by cytotoxic chemotherapy • Palliative care • N/V associated with migraine
These all have no advantage as its not like they need to get a toxin or something bad out and its about quality of life and trying to not make the patient dehydrated
How do we check if a patient is dehydrated?
To see if a patient is becoming dehydrated we check;
- Sunken eyes
- Skin turgor
- Cap refill
- BP and Pulse
- Urine dip for ketones
What are the different types of anti-emetics that we use and when?
Most common;
• Antihistamines (HI)
- Found on viscera and smooth muscles as well
- Pretty effective against lots of types of vomiting
- Including motion sickness + Vestibular disorders
- Side effect - varies but can be drowsy and cause anti muscarinic effect (dry eyes, dry mouth, constipation)
e. g;
1) . Cinnarizine; motion sickness, vestibular disorders
2. Cyclizine; motion sickness (Most commonly prescribed)
3. Promethazine; severe morning sickness
• Antimuscarinics (Ml)
- Just above vestibular nuclei so helpful in motion sickness related to labyrinth and visceral afferents
- Side effects of anti-muscarinics include; constipation,
transient bradycardia, dry mouth (slows everything down)
e.g - Hyoscine hydrobromide Useful in motion sickness
• Comes as patch as well as tablets (Helpful so people can take when vomiting and not need a healthcare professional to help with injection)
• Dopamine antagonists (D2)
- Helpful in treating chemoreceptor trigger zone related vomiting which is predominantly drugs and toxins due to the BBB. So if someone takes a toxic agent and a side effect of it is vomiting then these drugs can help
E.g;
The phenothiazines and related drugs
These are also classed as neuroleptics/antipsychotics:
Chlorpromazine
Prochlorperazine
Domperidone
Metoclopramide
(Has a lot of side effects as its also used as antipsychotics - don’t want to give long term)
Side effect - movement disorder (torticollis - abnormal spasms of neck muscles and neck turns, tick disorder of mouth)
• 5HT3 antagonists;
- GI tract blocking signals from vagal afferent to vomiting centre
- Particularly useful in managing N/V in patients receiving cytotoxics and in postoperative N/V
E.g - Ondansetron
Used more in palliative care and those undergoing chemo
Not as common;
• Neurokinin 1 receptor antagonists;
- Used as an adjunct to dexamethasone (steroid) and a 5HT3 antagonist in preventing N/V associated with
chemotherapy
- Only used if someone has unsustained vomiting that wont go away by 1st line drugs
E.g - Aprepitant
Synthetic cannabinoids (CBI);
E.g - Nabilone
• CB1 receptors
• Used for N/V caused by chemo unresponsive to
conventional anti-emetics
• Common side-effects of drowsiness/dizziness
Steroids;
• Dexamethasone has antiemetic effects
• Can be used alone, to treat vomiting associated with
cancer chemotherapy, or in conjunction with other
antiemetics
N/V = Nausea and vomiting
What are the different types of anti-emetics that we use and when?
Most common;
• Antihistamines (HI)
- Found on viscera and smooth muscles as well
- Pretty effective against lots of types of vomiting
- Including motion sickness + Vestibular disorders
- Side effect - varies but can be drowsy and cause anti muscarinic effect (dry eyes, dry mouth, constipation)
e. g;
1) . Cinnarizine; motion sickness, vestibular disorders
2. Cyclizine; motion sickness (Most commonly prescribed)
3. Promethazine; severe morning sickness
• Antimuscarinics (Ml)
- Just above vestibular nuclei so helpful in motion sickness related to labyrinth and visceral afferents
- Side effects of anti-muscarinics include; constipation,
transient bradycardia, dry mouth (slows everything down)
e.g - Hyoscine hydrobromide Useful in motion sickness
• Comes as patch as well as tablets (Helpful so people can take when vomiting and not need a healthcare professional to help with injection)
• Dopamine antagonists (D2)
- Helpful in treating chemoreceptor trigger zone related vomiting which is predominantly drugs and toxins due to the BBB. So if someone takes a toxic agent and a side effect of it is vomiting then these drugs can help
E.g;
The phenothiazines and related drugs
These are also classed as neuroleptics/antipsychotics:
Chlorpromazine
Prochlorperazine
Domperidone
Metoclopramide
(Has a lot of side effects as its also used as antipsychotics - don’t want to give long term)
Side effect - movement disorder (torticollis - abnormal spasms of neck muscles and neck turns, tick disorder of mouth)
• 5HT3 antagonists;
- GI tract blocking signals from vagal afferent to vomiting centre
- Particularly useful in managing N/V in patients receiving cytotoxics and in postoperative N/V
E.g - Ondansetron
Used more in palliative care and those undergoing chemo
Not as common;
• Neurokinin 1 receptor antagonists;
- Used as an adjunct to dexamethasone (steroid) and a 5HT3 antagonist in preventing N/V associated with
chemotherapy
- Only used if someone has unsustained vomiting that wont go away by 1st line drugs
E.g - Aprepitant
Synthetic cannabinoids (CBI);
E.g - Nabilone
• CB1 receptors
• Used for N/V caused by chemo unresponsive to
conventional anti-emetics
• Common side-effects of drowsiness/dizziness
Steroids;
• Dexamethasone has antiemetic effects
• Can be used alone, to treat vomiting associated with
cancer chemotherapy, or in conjunction with other
antiemetics
N/V = Nausea and vomiting
What happens in chronic constipation ?
A large stool gets stuck and causes back pressure, almost like a mild obstruction which causes the bowel wall to distend
Can get constipation with overflow and you might think they have diarrhoea as the liquid stool goes down either side of the large impacted stool
Only way you can tell the difference if it isn’t going to cause distress to the patient you can do a PR examination so you can give them the right medication
How can we communicate patients bowel habits between healthcare professionals to stop them from reaching extremes and intervene earlier?
By using the Bristol stool chart
What are the different types of laxatives and how do they work ?
Laxatives;
• Before prescribing ensure the problem is constipation
• Check the patient’s “norm”
• Try to reverse the cause; including diet/lifestyle changes
Types;
- Bulk-forming laxatives (Ispaghula Husk) - Provides and increased volume and promotes peristalsis by distension
- Stimulant laxatives (Senna) - Increases peristalsis
- Faecal softeners (Docusate) - Softens stool by coating and breaking up particles
- Osmotic laxatives (Lactulose) - Liquid mixes with stool to soften it
- Peripheral opioid-receptor antagonists (methylnaltrexone bromide) - Opiates act on central pain receptors but also acts on peripheral GI receptors so if you can block the peripheral GI receptors then the patients isn’t losing the analgesic/pain freeing effect of the opiate but they don’t get the constipated side effects associated with it
