Vomiting is initiated in the vomiting centre of the medulla, which itself receives input from higher centres, the chemoreceptor trigger zone (CTZ), afferent somatic and visceral fibres, and the vestibular apparatus of the middle and inner ear. Of these, the CTZ in the area postrema (floor of 4th ventricle) is probably the most important.
Complications:
Dehydration
Electrolyte imbalance
Metabolic imbalance (metabolic alkalosis)
Pulmonary aspiration
Hernia formation
Damage to site of surgery (direct e.g. ENT or indirect e.g. neurosurgery).
Inability to take oral medication.
Delayed discharge.
Risk factors:
- Patient: Female, younger than 16y, Hx, obesity, motion sickness, pre-op anxiety.
- Anaesthetic agents: Opioids, N2O nitrous oxide, etomidate, ketamine.
- Surgery: GI, GU, neurosurgery, middle ear, ophthalmic.
- Post-op: Dehydration, hypotension, hypoxia, early oral intake.
Entiemetics:
- H1: Cyclizine (GI causes), cinnarizine (Vestibular causes).
- D2: Metoclopramide (GI causes, prokinetic), domperidone (prokinetic), prochlorperazine (vestibular/GI causes), haloperidol (chemical causes e.g. opioids).
- 5HT3: Ondansetron - doses can be high e.g. for emetogenic chemotherapy.
- Others:
- Hyoscine hydrobromide (antimuscarinic therefore also antispasmodic and antisecretory - don't prescribe with a prokinetic).
- Dexamethasone (unknown mode of action).
- Midazolam (unknown mode of action; anti-emetic effect outlasts sedative effect).
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