Nausea and Vomiting Flashcards
What are the risk factors for post-op nausea and vomiting?
Patient factors: Female Age - declines through adult life Previous PONV or motion sickness Use of opioid analgesics Non-smoker
Surgical factors: Intra-abdominal laparoscopic surgery Intracranial or middle ear surgery Squint surgery Gynaecological surgery esp. ovarian Prolonged operative times Poor post op pain control
Anaesthetic factors: opiate analgesia or spinal analgesia Inhalation agents - NO Prolonged anaesthetic time Intraoperative dehydration or bleeding Overuse of bag and mask ventilation (gastric dilation)
What are the patient risk factors for post-op nausea and vomiting?
Patient factors: Female Age - declines through adult life Previous PONV or motion sickness Use of opioid analgesics Non-smoker
What are the surgical risk factors for post-op nausea and vomiting?
Surgical factors: Intra-abdominal laparoscopic surgery Intracranial or middle ear surgery Squint surgery Gynaecological surgery esp. ovarian Prolonged operative times Poor post op pain control
What are the anaesthetic risk factors for post-op nausea and vomiting?
Anaesthetic factors: opiate analgesia or spinal analgesia Inhalation agents - NO Prolonged anaesthetic time Intraoperative dehydration or bleeding Overuse of bag and mask ventilation (gastric dilation)
What are the areas of the brain involved in vomiting and nausea?
Brainstem:
Vomiting centre - located within the lateral reticular formation of medulla oblongata controls and coordinates movements in vomiting
Chemoreceptor trigger zone - located in the area postrema, located outside the BBB and therefore can respond to stimuli in the circulation
How does womiting happen?
Vomiting centre receives input from chemoreceptor trigger zone, GI tract, vestibular system and higher cortical structures - sight, smell, pain
If the stimuli are sufficient it acts of the diaphragm, stomach and abdominal musculature to initiate vomiting,
What neurotransmitters are involved in vomiting?
Chemoreceptor trigger zone: dopamine, 5HT3 receptors Vestibular apparatus: ACh and Histamine GI tract: dopamine Vomiting centre Histamine and 5HTs
What is important in assessing a patient with PONV
A-E approach
Airway - aspiration of vomit risk
Protection - use of NG tube
What are alternative causes of post-op NV
Anaesthetic/post op drugs
Infection
GI causes (post-opileus, bowel obstruction)
Metabolic causes (hypercalcaemia, uraemia, DKA)
Medication
CNS causes (raised ICP_
Psychiatric (Anxiety)
How is post op NV managed?
Prophylactic
Conservative
Pharmaceutical
What are prophylactic measures for post op NV?
Anaesthetic mesures - reduce opiates, reduce volatile gases, a void spinal anaesthetics
Prophylactic anti-emetics
Dexamethasone at induction of anaesthesia
What are conservative measures for NV?
Adequate fluid hydration
Adequate analgesia
Ensure no obstructive cause
What are pharmaceutical measures
Antiemetics
Multimodal therapy is more effective
Patients with impaired gastric emptying or gastric stasis should be trialed on pro kinetic agent such as metoclopramide (dopamine antagonist), unless bowel obstruction is suspected.
Hyoscine (anti-muscarinic) can help reduce secretions and subsequent NV in its with bowel obstruction
Suspected metabolic or biochemical imbalance such as uraemia, electrolyte imbalance, cytotoxic agents should be trialed on metoclopramide (dopamine antagonist)
Opioid induced NV typically responds well to cyclizine (H1Histamine receptor antagonist) or odansetron (5HT3 antagonist)
What type of drug is metoclopramide? Where does it act? What are indications? What are ADRs?
Dopamine receptor antagonist (D2)
Acts ont he postera on the floor of the fourth ventricle (vomiting centre) Increases rate of gastric emptying. Anticholinergic effects and blocks vagal afferent serotonin receptors.
GI causes of nausea/vomiting, migraine and post-operatively (oral,IM, IV)
Extrapyramidal side-effects (avoid in PD), galactorrhea due to prolactin release
What type of drug is odansetron? What is the mechanism of action? Indications? ADRs?
5HT receptor antagonist
Antagonises vagal afferent nerves in GI tract and antagonises receptors on the vomiting centre
High doses in radiation sickness, chemo and post-op enhanced by single dose of corticosteroids.
Headaches, constipation, flushing
