PONV

Question 1

Definitions

Answer 1

Nausea is the subjective sensation of the need to vomit.

• Vomiting is the forced expulsion of gastrointestinal contents through the mouth.

Question 2

Incidence

Answer 2

~30% overall after general anaesthesia (GA). • Up to 80% in high-risk patients.

Question 3

Associated morbidity

Answer 3

• Decreased patient satisfaction, delayed hospital discharge, unexpected hospital admission.
• Wound dehiscence, bleeding, pulmonary aspiration, oesophageal rupture.
• Fluid and electrolyte disturbances

Question 4

Anatomy and physiology

Answer 4

• Activation of 5HT 3 receptors in the gut results in stimulation of vagal afferents. Impulses conducted to the area postrema, in the fl oor of fourth ventricle.
• This area has a poorly developed blood–brain barrier, allowing detection of emetogenic substances in blood and CSF.
• Can be considered a ‘chemoreceptor trigger zone’ (CTZ).
• Afferents from CTZ, vestibular apparatus, vagus nerve, gut, and limbic system project to nucleus tractus solitarius.
• Multiple central structures throughout medulla are involved in vomiting, which is no longer considered a vomiting ‘centre’ but now designated a ‘central pattern generator for vomiting’.
• Efferents—cranial nerves V, VII, IX, X, and XII and spinal nerves to GI tract, diaphragm, and abdominal muscles.
• Receptor systems—dopaminergic (D 2 ), muscarinic, serotoninergic (5-HT 3 ), histaminergic (H 1 ), and neurokinin (NK 1 ).

Question 5

Risk factors contributing to PONV

Answer 5

Females (3 × risk).

• Previous PONV or motion sickness (2–3 × risk).

• Non-smokers (2 × risk).
• Use of perioperative opioids

Surgery • Breast, ophthalmic (strabismus repair), ENT, gynaecological, laparoscopic, laparotomy, craniotomy (posterior fossa), genitourinary, orthopaedic (shoulder procedures), thyroid.

Answer 6

Surgery • Breast, ophthalmic (strabismus repair), ENT, gynaecological, laparoscopic, laparotomy, craniotomy (posterior fossa), genitourinary, orthopaedic (shoulder procedures), thyroid.

Answer 7

Anaesthetic • Premedication—decreased risk after benzodiazepines and clonidine, increased risk after opioids. • Type of anaesthesia—GA 11 × risk of regional technique, propofol TIVA less than volatile. • Intraoperative drugs—opioids, nitrous oxide, inhalational drugs, IV drugs (thiopental, etomidate, and ketamine are emetogenic, propofol is possibly antiemetic), neostigmine (muscarinic effects on GI tract). • Dehydration increases risk. Avoid too early resumption of food/fl uids.

Question 8

Management of PONV

Answer 8

Pharmacologic methods • Prophylaxis vs treatment remains controversial. • Prophylaxis with ondansetron is reported to be cost-effective in highrisk patients where PONV >30–33%. • Combination therapy—two or more drugs with different modes of action is more effective, e.g. ondansetron plus dexamethasone or droperidol. Non-pharmacologic methods • Acupuncture—pericardium (P6) point on palmar aspect of wrist. As effective as standard antiemetics but no side effects (NNT = 5).
• Others include ginger root extract, hypnosis, suggestion, and homeopathy.

Question 9

The vomiting patient

Answer 9

• Reassurance.
• Correct vital signs appropriately.
• Ensure adequate analgesia and hydration.
• Look for surgical cause (e.g. distended abdomen—insert or aspirate NG tube).
• Antiemetics:
• Check if a prophylactic antiemetic was given.
• Combination antiemetic therapy—5-HT 3 antagonist plus dexamethasone and/or droperidol.
• Consider other drugs (see above).