Intracranial Pressure

Intracranial pressure (from Latin intra — inside and cranium — skull) refers to the physical pressure exerted by brain tissue, circulating blood, and cerebrospinal fluid (CSF) on the solid inner walls of the cranial bones.

Etiology and pathophysiology

The physiology of this process is described by the fundamental Monro-Kellie doctrine. The adult cranial cavity is a hermetically sealed and completely inextensible bony sphere of fixed volume. This volume is always 100% filled with three components: brain tissue (about 80%), blood in the vessels (10%), and cerebrospinal fluid (10%).

According to the laws of fluid physics, an increase in the volume of any of these components (or the appearance of a new, pathological volume, such as a hematoma or tumor) must inevitably be compensated by an equivalent reduction in other components. The body initially attempts to restore equilibrium by reducing the volume of cerebrospinal fluid and venous blood in the cranial cavity. When this mechanism is exhausted, the pressure inside the bony box starts to increase rapidly and uncontrollably.

Clinical significance

In a healthy adult in the supine position, ICP ranges from 5 to 15 mmHg. A condition where it consistently exceeds 20 mmHg is called intracranial hypertension.

High ICP is extremely dangerous for two reasons. Firstly, it prevents arterial blood from entering the cranial cavity, causing total oxygen starvation (ischemia) and brain death. Secondly, it forces brain tissue into anatomical openings at the skull base (herniation process), leading to brainstem compression and cessation of respiration. In severe trauma, ICP control is a primary task for the resuscitator; special electronic sensors are implanted directly into the patient’s brain for this purpose.