Warranted if,
(1) Pt looks toxic but the abdomen is soft and non-tender
(2) Chronic vomiting of insidious onset and progressive severity
(3) Neurological features e.g. headache, seizures, focal deficits, giddiness, history of head injury, focal weakness, unequal pupils, or very high fever.
Meningitis: febrile, toxic pt, altered mental state, neck stiffness, meningococcal purpuric rash.
↑ Intracranial pressure: multiple causes e.g. intracranial haemorrhage, infarction, abscess, tumor, hydrocephalus, or post-traumatic, etc. There may also be headache, false localizing VI nerve lesion, papilloedema.
Vestibular causes: vertigo is prominent (but beware central vertigo) – e.g. BPPV, labyrinthitis, motion sickness, etc.
Migraine: can present as cyclical vomiting.