Nausea and Vomiting Flashcards
What is nausea
Subjective, unpleasant sensation
Normally result of Upper intestinal contractions forcing contents via reverse peristalsis into the stomach.
Usually before vomit but can be in isolation
How does nausea present?
Unpleasant sensation Pallor Sweating XSive salivation Relaxation of the stomach and lower oesophagus
What is retching?
Rhythmic reverse peristalsis of the stomach and oesophagus
- forceful and involuntary contraction of the abdominal muscles and diaphragm which causes cardiac portion of stomach to be pushed into thorax
- upper intestinal contractions which force intestinal contents via reverse peristalsis into the stomach
How does retching present?
Dry vomiting
Pallor
Sweating
Excessive salivation
What is emesis?
Forceful expulsion of gastric/intestinal contents of the mouth
Controlled via the vomiting centre in the medulla oblongata of the brain stem
Process of Emesis?
- Forceful inspiration and reflex closure of glottis and elevation of soft palate to close of airways/nasal passages
- Stomach, oesophagus and associated sphincters are relaxed
- Suspension of intestinal slow wave activity
- Retrograde contractions from ileum to stomach
- Breathing has been suspended
- Lower oesophageal sphincter relaxes and the diaphragm/abdominal muscles contract to compress the stomach
- Gastric contents are ejected through the open upper oesophageal sphincter
Who vomits?
Patients who:
- Ingested toxic materials
- Mechanical stimuli
- Pathology in Gi tract
- Vestibular system (motion s)ickness)
- Stimuli in CNS (pain, smells
How does vomiting present?
Prior to:
- Profuse salivation
- Sweating
- Elevated heart rate
- Nausea
How is emesis managed?
- 5HT3 receptor antagonists (chemo/radiation/post-op)
- Muscarinic acetylcholine receptor antagonists (motion sickness)
- Histamine H1 receptor antagonists (motion sickness/nausea)
- Dopamine receptor antagonists (drug induced vomiting)
- NK1 receptor antagonists (chemo)
- Cannabinoid receptor agonists (chemo)
How 5HT3 receptor antagonists work? +example
Setrons (ondansetron)
- Block peripheral and central 5HT3 receptors stopping stimulation of vagal afferents in GI tract.
- For Chemotherapy, radiation and post-operative emesis
How Muscarinic acety-5-choline receptor antagonists work?
Block muscarinic acetylcholine receptors at the vestibular nuclei, the NTS and the VC, they also cause the GI tract to relax.
Lots of side effects because they block the parasympathetic system
Side effects of Muscarinic acety-5-choline receptor antagonists?
Blurred vision
Sedatory effect
How are muscarinic acety-5-choline receptor antagonists delivered. What type of emesis do they treat?
Transdermal patch
-Used for motion sickness
Example of histamine H1 receptor antagonists?
Cyclizine
Cinnarizine
What type of sickness do H1 receptor antagonists treat?
Motion sickness
Nausea and emesis caused by irritants in stomach
How do histamine H1 receptor antagonists work?
Block the receptors in the vestibular nuclei and the NTS and can generally cause CNS depression and sedation
How dopamine receptor antagonists work?
Block the dopamine receptor in the CTZ and peripherally exert prokinetic action on the oesophagus, intestine and stomach.
What type of emesis are dopamine receptor antagonists for?
Drug induced vomiting
Vomiting in GI disorders
Contraindication for dopamine receptor antagonists?
NOT IN CHILDREN
Doperamidine doesn’t?
Cross the blood brain barrier
Therefore
Doesn’t treat motion sickness
Example of an NK1 receptor antagonist?
Aprepitant
Cannaboid receptor agonist example?
Nabilone
Side effects of emesis?
Dehydration
Loss of gastric protons and chloride
Hypokalaemia
Oesophageal tear
What does loss of gastric protons and chloride cause?
Hypochloraemic metabolic acidosis
Raising of blood pH
What is the vomiting centre?
Group of interconnected neurones within the medulla which are driven by central pattern generator CPG which receives information from the NTS
What coordinates oesophageal shortening, stomach proximal relaxation, giant retrograde contraction of small intestine in vomiting?
Vagal efferents
What do somatic neurones coordinate in vomiting?
Anterior abdominal muscle contraction and diaphragm contraction
What do the autonomic/somatic efferents coordinate in vomiting?
Increased HR & Force Increased saliva secretion Skin to sweat pallor Anal/bladder sphincters to contract
