Increased Intracranial Pressure and Cerebral Blood Flow

Study Notes

Increased Intracranial Pressure (ICP)

The rigid cranial vault contains the brain parenchyma (80%), blood (10%), and cerebrospinal fluid (CSF) (10%).
Normal ICP is 5-15 mmHg.
ICP greater than 20 mmHg is considered increased.

Cerebral Blood Flow

Normal cerebral blood flow is 750 mL/minute, which accounts for 15% of cardiac output.
The brain requires 50-54 mL of blood per 100 gm of brain tissue per minute.
Cerebral blood flow regulation is tightly controlled to meet the brain's metabolic demands.
Cerebral blood flow increases with increased ICP.
Cerebral blood flow decreases with ischemia.
Brain death occurs when cerebral blood flow is less than 8-10 mL/100 gm.
Factors that determine cerebral blood flow: Viscosity of blood, Dilation of blood vessels, Net pressure of blood flow to the brain (CPP)

Cerebral Perfusion Pressure (CPP)

CPP is the pressure required for adequate oxygenation and glucose supply for brain metabolism.
CPP formula: CPP = MAP - ICP
Normal CPP is 50-60 mmHg.
Irreversible neuronal hypoxia occurs when CPP is less than 30 mmHg.
Increased ICP decreases Mean Arterial Pressure (MAP).
MAP formula: (2 x Diastole) + Systole / 3

Autoregulation Process

Cerebral blood vessels constrict in response to increased systemic blood pressure and dilate in response to decreased systemic blood pressure (hypotension).
Arterioles constrict and dilate in response to different chemical concentrations.
Increased CO2 causes vasodilation.

Monro-Kellie Hypothesis

The Monro-Kellie hypothesis states that to maintain a constant intracranial volume, an increase in any of the three components (brain parenchyma, blood, or CSF) must be accompanied by a decrease in one or both of the other components.

Causes of Increased ICP

Cerebral Edema: Swelling of the brain tissue.
Mass Lesions: Tumors, abscesses, hematomas, which compress cerebral vessels.
Increased Intracranial Blood Volume:
- Intracerebral hemorrhage (ICH)
- Venous outflow obstruction
- Increased intra-thoracic pressure
- Increased intra-abdominal pressure
- Give laxative to prevent straining.
Increased Amount of CSF:
- Normal CSF production is 500mL/day.
- Causes of increased CSF include obstruction of CSF flow, decreased reabsorption, and increased production.
- Emotional Distress: Can increase ICP.
- Suctioning: Can increase ICP if done incorrectly.
- Overstimulating Environment: Can increase ICP.

Description

This quiz explores the critical concepts of increased intracranial pressure (ICP), cerebral blood flow, and cerebral perfusion pressure (CPP). Understand the normal values, their physiological significance, and the factors regulating brain metabolism. Test your knowledge on the consequences of abnormal ICP and blood flow to the brain.