Complex sentence: One of the most important treatments for high ICP is to ensure adequate airway, breathing, and oxygenation, since inadequate oxygen levels or excess carbon dioxide cause cerebral blood vessels to dilate and ICP to rise.
Split into simpler sentences: One of the most important treatments for high ICP is to ensure adequate airway, breathing, and oxygenation. Inadequate blood oxygen levels (hypoxia) or excessively high carbon dioxide levels (hypercapnia) cause cerebral blood vessels to dilate, increasing the flow of blood to the brain and causing the ICP to rise.