nausea and vomiting Flashcards
define vomiting
forceful expulsion of gastric contents from the mouth
what causes vomiting?
o powerful sustained contraction of abdominal muscles
o descent of diaphragm
o opening of gastric cardia
o gastric retropulsion
define retching
Laboured, spasmodic, rhythmic contractions of respiratory muscles without expulsion of gastric contents
what respiratory muscles are used in retching?
diaphragm, chest wall, abdominal wall muscles
how does retching lead to vomiting?
creates a pressure gradient leading to vomiting
define nausea
• Unpleasant sensation at the back of the throat. Awareness of urge to vomit
what is nausea often accompanied by?
cold sweat, pallor, salivation, disinterest in surroundings, loss of gastric tone, duodenal contractions and reflux of intestinal contents into stomach
what normally follows vomiting?
tiredness
if vomiting doesnt go away then what can it lead to?
- Dehydration/anorexia
- Ribs broken
- Refusal of medications
what is cyclic vomiting syndrome?
- Rapid-fire projectile vomiting
- Lasts a few hours to several days, followed by asymptomatic periods
- Can incapacitate
what is the most common symptom of cyclic vomiting syndrome?
Nausea not relieved by vomiting is the most disturbing symptom
what are symptoms of gastroparesis?
Early satiety after eating, postprandial fullness, nausea, vomiting, belching, bloating
what are other causes of vomiting?
chemo-radiotherapy, infections, severe pain, metabolic diseases, pregnancy, migraine, therapeutic drugs etc
where is the area postrema?
base of the 4th ventricle
not protected by the BBB
where is the NTS in relation to the AP?
one synapse away
what information does the NTS receive?
o Receives vagal input from the heart etc.
o Also receives input e.g. pain about nausea
o Motion e.g. motion sickness
o Psychogenic e.g. anxiety about vomiting
what is the vomiting centre?
several structures within medullary reticular formation of hindbrain
what muscles are involved in vomiting and what do they do?
- NTS causes contraction of the diaphragm, abdominal muscles, external intercostal muscle; Relaxation of internal intercostal muscles
- Causes pharynx/larynx closure, closure of glottis/pharynx
- LOS relaxation, oesophagus dilation, duodenal retropulsive contraction
what is Hyoscine (scopolamine) used for and how does it work?
used for motion sickness – blocks effect of ACh in brainstem and/or vestibular nuclei
what is Diphenhydramine and how does it work?
Diphenhydramine – H1 receptor antagonist. Crosses BBB
what has NICE approved the use of cyclizine for?
nausea, vomiting, vertigo, motion sickness and labyrinthine disorders
what type of drug is cyclizine?
H1 receptor antagonist
what is serendipity used for?
noted to block vomiting induced by the D2 receptor agonist apomorphine
• Used for many purposes including prevention of mild chemotherapy induced vomiting
what are the side effects of serendipity?
dry mouth, drowsiness, extrapyramidal reactions (if in brain), hyper-prolactinaemia
why is domperidone free of side effects?
Doesn’t cross the BBB – free of extrapyramidal side effects
what type of drug is metoclopramide?
D2 receptor antagonist
what is metoclopramide used for?
- Widespread use as an enti-emetic
- Post-operative care
- Gastritis, migraine, dysmenorrhoea
- Drug- or treatment-induced emesis including anaesthesia, radiation and/ or chemotherapy for cancer
- Also stimulates gastric emptying (5-HT4 receptor agonist)
- Widespread use as a stimulant of upper gut motility – GORD, gastroparesis, functional dyspepsia
- A 5-HT3 receptor antagonist at higher doses
what are cannabinoid receptor antagonists used for?
mild/moderate emesis
poorly effective vs severe emesis (cisplatin)
what are 5-HT3 receptor antagonists used for?
Prevent chemotherapy-induced emesis, acting mostly at GI vagal nerve endings
what is given for moderately severe forms of emesis?
5-HT3 receptor antagonist + dexamethasone given in combination
name NK1 receptor antagonsists
• Aprepitant (Emend), fosaprepritant (IV formulation of aprepitant), rolapitant, netupitant, the primary differences being potency & duration of action
what is given for severe forms of emesis?
5-HT3 receptor antagonist + NK1 receptor antagonist + dexamethasone given in combination
what drugs are used for partial bowel obstruction?
metoclopramide and prucalopride
what drugs are used for total bowel obstruction and why?
o Dexamethasone to reduce inflammation
o To reduce build-up of fluid in the lumen
Octreotide - somatostatin antagonist - may also reduce pain
Nasogastric tube, venting, gastrostomy tube
what is olanzapine?
- Atypical antipsychotic
* May be used in breakthrough vomiting
where does nausea formation come from?
anterior insular cortex in the forebrain
o Interoceptive brain regions that process stress, fear etc
where does vomiting come from?
area postrema and NTS in the hindbrain
what is gastroparesis?
Gastric retention accompanied by nausea, vomiting and/ or bloating, in the absence of obstruction
what are the causes of gastroparesis?
endocrine diseases (e.g. diabetes), post-surgical, medications, virus infections, idiopathic, Parkinson’s
