Why do people with raised intracranial pressure (ICP) vomit more in the mornings?

ICP is dependant primarily on cerebro-spinal fluid(CSF). CSF reabsorption is lowest overnight and the recumbent postition both combine together meaning that ICP is generally highest in the morning. Hence, people vomit in the morning.


The combination of headache, papilloedema, and vomiting is generally considered indicative of raised ICP, although there is no consistent relation between the severity of symptoms and the degree of hypertension. Pressure headaches are often described as throbbing or bursting and are exacerbated by any factors that further increase ICP such as coughing, sneezing, recumbency or exertion. Classically the headache of raised ICP is worse in the morning. This has been attributed to a rise in ICP during the night as a consequence of recumbency, a rise in PCO₂ during sleep caused by respiratory depression, and probably a decrease in CSF absorption. Papilloedema is a reliable sign of raised ICP but can require several days of raised pressure to develop. Fundal haemorrhages develop in response to acute and severe rises in ICP (as in subarachnoid haemorrhage and some cases of head injury). Longstanding raised ICP may fail to cause papilloedema if the subarachnoid sleeve around the optic nerve does not communicate with the subarachnoid space. Vomiting tends to be a late feature, usually occurs after waking, and frequently accompanies morning headache.

Normal ICP in an adult is usually around 15 mm Hg