23.5 PONV + Antiemetics Flashcards
a) List the patient-related (7 marks) risk factors for postoperative nausea and vomiting (PONV) in adult patients.
Patient factors:
» Female gender.
> > History of postoperative nausea and vomiting.
> > History of motion sickness.
> > Non-smoker.
> > Other possible risk factors include anxiety,
ASA 1 or 2 status, history of
migraine, and age
(children less affected under three years of age,
then risk declines through adulthood).
anaesthetic-related (3 marks) risk factors for postoperative nausea and vomiting (PONV) in adult patients.
Anaesthetic factors:
» Volatile use.
> > Nitrous oxide use.
> > Intra- and postoperative opioid use.
> > Increased duration of anaesthesia.
b) What are the unwanted effects of PONV in adults? (6 marks)
> > Reduced patient satisfaction.**
> > Delayed discharge from PACU.
> > Delayed discharge from hospital/
unexpected hospital stay in day case
patients
(with the implications of cost,
inconvenience, poor bed usage)
> > Delayed return to oral intake**
(especially important in diabetic patients).
> > Suture dehiscence.
> > Aspiration of gastric contents.*
> > Dehydration,
electrolyte imbalance, metabolic alkalosis.
> > Oesophageal rupture.*
c) Which non-pharmacological interventions have been shown to be effective in reducing PONV in
adults? (2 marks)
> > Avoidance of general anaesthesia (no anaesthesia/regional anaesthesia).
> > Acupressure, acupuncture.
> > Aromatherapy.
> > Avoidance of dehydration (avoid excessive starvation period).
d) Briefly explain the proposed mechanisms of action of 5HT3 antagonists such as ondansetron when
used as anti-emetics. (2 marks)
> > Enterochromaffin cells in the
small intestine release 5-hydroxytryptamine
(5HT) in response to stimulation by drugs.
5HT stimulates the vagus,
fibres of which terminate in
the chemoreceptor trigger zone (CRTZ) +
the vomiting centre.
> > There are also 5HT3 receptors in the CRTZ.
> > Ondansetron blocks 5HT3 receptors.
