GPAtlas🧭 When to suspect
Nausea (the sensation) and vomiting (the act) are distinct symptoms that are common and often deeply distressing in advanced disease, and in any one patient the cause is frequently multifactorial. The governing principle in palliative care is to identify the most likely underlying mechanism, match a targeted antiemetic to it, and give it by a route that will actually be absorbed.
Each mechanism maps to a site and a set of receptors: chemical/toxic stimulation of the chemoreceptor trigger zone (CTZ); gastric stasis or outflow delay in the gut; visceral/mechanical causes (bowel obstruction, constipation, serosal stretch); raised intracranial pressure (ICP) and vestibular input acting on the vomiting centre; and cortical/anxiety causes. Persistent nausea can itself generate fear of eating and ‘anticipatory’ or ‘total’ nausea, so anxiety often needs treating alongside the antiemetic.
The key primary-care skills are to identify the likely mechanism, treat reversible factors (constipation, offending drugs, hypercalcaemia, infection, gastritis, oral thrush), choose the drug by mechanism, and switch to the subcutaneous route when vomiting prevents oral absorption.
| Mechanism (site) | Common causes | First-line antiemetic |
|---|---|---|
| Chemical / metabolic (CTZ) | Opioids, digoxin, antibiotics, chemotherapy; hypercalcaemia, uraemia, hepatic/renal failure | Haloperidol |
| Gastric stasis / outflow delay (gut) | Opioids, anticholinergics, ascites, hepatomegaly, gastritis, autonomic failure | Metoclopramide (a prokinetic) |
| Visceral / mechanical (gut & serosa) | Bowel obstruction, severe constipation, serosal/capsular stretch | Cyclizine (± antisecretory) |
| Raised ICP / vestibular (vomiting centre) | Cerebral metastases, cerebral oedema, meningeal disease, motion, base-of-skull tumour | Cyclizine (± dexamethasone for ICP) |
| Cortical / anxiety | Anxiety, fear, anticipatory nausea, uncontrolled pain | Address cause; benzodiazepine if anxiety-driven |
| Multifactorial / unclear | Often more than one mechanism coexisting in advanced disease | Levomepromazine (broad-spectrum) |
Source: Scottish Palliative Care Guidelines
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