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In patients who have high ICP it is particularly important 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 IICP.

Inadequate oxygenation also forces brain cells to produce energy using anaerobic metabolism, which produces lactic acid and lowers pH, also dilating blood vessels and exacerbating the problem.

Conversely, blood vessels constrict when carbon dioxide levels are below normal, so hyperventilating a patient with a ventilator or bag valve mask can temporarily reduce ICP. Hyperventilation used to be part of standard management of traumatic brain injuries but the constriction of blood vessels limits blood flow to the brain in a time when the brain may already be ischemic, and so is no longer widely used.

Furthermore, the brain adjusts to the new level of carbon dioxide after 48 to 72 hours of hyperventilation, which could cause the vessels to rapidly dilate if carbon dioxide levels were returned to normal too quickly. Hyperventilation is still used if ICP is resistant to other methods of control, or there are signs of brain herniation because the damage herniation can cause is so severe that it may be worthwhile to constrict blood vessels even if doing so reduces blood flow.

ICP can also be lowered by raising the head of the bed, improving venous drainage. A side effect of this is that it could lower pressure of blood to the head, resulting in a reduced and possibly inadequate blood supply to the brain. Venous drainage may also be impeded by external factors such as hard collars to immobilise the neck in trauma patients, and this may also increase the ICP. Sandbags may be used to further limit neck movement.