Saturday 20 January 2007

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

2 comments:

foret said...

Great information.
I have a question: Is using a paper bag effective if someone is fainting? What is the rationale behind it?

Unknown said...

Hello Forret!

Did you mean when someone is panting? Because in this situation when someone is hyperventilating, a condition called respiratory alkalosis results, whereby your blood pH goes up. And the rationale behind the use of paper bag is that, you will be breathing in the air that you breath out which contains higher concentration of CO2. This is required because increase in CO2 decreases the blood pH thus restoring blood pH back to normal. Hope this answers your question:)