Nausea and Emesis Flashcards
What symptoms occur due to nausea?
- pallor
- sweating
- excessive salivation
- relaxation of stomach and lower oesophagus
- upper intestinal contractions
=> forcing intestinal contents by reverse peristalsis into the stomach
Nausea and vomiting can occur independently of each other. TRUE/FALSE?
TRUE
What is retching?
- forceful, involuntary contractions of abdominal muscles and diaphragm
- the cardiac portion of stomach is pushed into the thorax
- Retching is ‘dry’
How are retching and vomiting different?
- Retching = ‘dry’
- Vomiting = forceful expulsion of gastric / intestinal contents out of the mouth
Describe what happens in the body prior to vomiting
- forceful inspiration
- reflex closure of glottis and elevation of the soft palate
=> close off the airways and nasal passages - stomach and oesophageal sphincters RELAX
What part of the body controls vomiting?
- vomiting centre (VC) in medulla oblongata
- not controlled by stomach (remember sphincters are RELAXED)
- medulla signals to abdominal muscles to contract and compress the stomach
What stimuli can induce vomiting?
Toxic materials in gut lumen
- bacteria, salts of heavy metals, ethanol
Systemic toxins (e.g. cytotoxic drugs)
How do toxins cause vomiting to occur?
- toxins stimulate Enterochromaffin cells in mucosa
- these release sensory afferent signals (via 5HT) to brain
- vagal afferents take the signal to the brainstem where the chemoreceptor trigger zone (CTZ) and nucleus tractus solitarius (NTS) are found
- these coordinate vomiting
How does the vestibular system cause activation of the vomiting centre in the brain?
- Signals to CTZ via vestibular nuclei in the brainstem
What are the potential triggers which can cause vomiting?
- Pain
- repulsive sights/ smells
- emotional factors
- Motion (inner ear)
- Pharyngeal stimulation
- gastric/duodenal distension/ irritation
- Endogenous toxins, drugs, vagal afferents
What motor output nerves are involved in coordinating the action of vomiting?
Vagal efferents
- controls oesophagus, stomach and small bowel
Somatic motor neurones
- contracts abdominal muscles and diaphragm
Autonomic/somatic efferents
- increase HR, saliva production, sweating
What are the potential complications of severe vomiting?
- Dehydration
- Loss of gastric protons/chloride (=> hypochloraemic metabolic alkalosis, raised blood pH)
- Hypokalaemia (proton loss accompanied by K+ excretion)
- Loss of duodenal bicarbonate (HCO3) may cause metabolic acidosis
- Oesophageal damage (Mallory-Weiss tear)
What types of drugs are known to cause nausea and vomiting?
- Chemo + radio (release of 5-HT and substance P from enterochromaffin cells in the gut)
- Operations under GA (post-op. N+V common)
- Levodopa used in Parkinson’s (D2 receptors are prevalent in the CTZ)
- Morphine and other opiate analgesics
- Cardiac glycosides (e.g. digoxin)
- Drugs enhancing 5-HT function (e.g. SSRIs)
What type of N+V are 5HT3 receptor antagonists used to treat? How do they achieve this?
- chemo + radio induced N+V
- Post-op. N+V
- Block peripheral and central 5-HT3 receptors
Give examples of 5HT3 receptor antagonists
‘setrons’
e.g. ondansetron, palonosetron
What are the most common side effects of 5HT3 receptor antagonists?
- constipation
- headaches
How do Muscarinic ACh receptor antagonists work to prevent N+V?
- block muscarinic ACh receptors at multiple sites (vestibular nuclei, NTS, vomiting centre)
- Direct inhibition of G.I. movements
- relaxation of the G.I. tract
- can be used for prophylaxis of motion sickness
Give an example of a Muscarinic ACh receptor antagonist
hyoscine
Give examples of side effects caused by Muscarinic ACh receptor antagonists
block parasympathetic ANS => can cause:
- blurred vision
- urinary retention
- dry mouth
- centrally-mediated sedation
How do H1 receptor antagonists aim to reduce N+V?
Histamine H1 receptor antagonists:
- block H1 receptors in vestibular nuclei and NTS
=> used for motion sickness prophylaxis and acute labyrinthitis - may also potentiate blockade of muscarinic receptors which helps their effectiveness
GIve examples of H1 receptor antagonists
Cyclizine
Cinnarizine
What are the main side effects of H1 receptor antagonists?
- CNS depression and sedation => drowsiness
- may affect performance of skilled tasks
How do dopamine receptor antagonists aim to reduce N+V?
- Centrally block dopamine D2 (and D3) receptors in the CTZ
- Peripherally exert a prokinetic action on the oesophagus, stomach and intestine
When are dopamine receptor antagonsists used for N+V?
- drug-induced vomiting (e.g. chemo, Parkinson’s disease agents)
- Vomiting in GI disorders
