Raised Intracranial Pressure and Cerebral Blood Flow Control

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Questions and Answers

In the skull, an increase in the volume of one component must be accompanied by an equal reduction in the volume of which other components?

Brain and blood

Brain and cerebrospinal fluid (CSF)

Blood, brain, and cerebrospinal fluid (CSF) (correct)

Blood and cerebrospinal fluid (CSF)

What is the ultimate consequence of unchecked raised intracranial pressure (ICP)?

Increased cerebral blood flow (CBF)

Hypertension and bradycardia

Hypoperfusion and cerebral oedema (correct)

Cerebral atrophy and neuronal death

What is a cause of raised intracranial pressure (ICP)?

Asthma

Hypothyroidism

Chronic obstructive pulmonary disease (COPD)

Traumatic brain injury (correct)

What is the initial compensatory mechanism for an increase in the volume of brain matter or blood?

Extrusion of cerebrospinal fluid (CSF) into the spinal sac Signup and view all the answers

What is a common clinical sign of raised intracranial pressure (ICP)?

Headache, worse after waking, which is exacerbated by lying down Signup and view all the answers

What aggravates raised intracranial pressure (ICP)?

All of the above Signup and view all the answers

What increases intracranial pressure (ICP) significantly but transiently?

Fiber-optic bronchoscopy Signup and view all the answers

What is the optimal head-up tilt angle for maximal venous drainage and minimal reduction in cerebral arterial pressure?

30° Signup and view all the answers

What is a consequence of brain swelling?

Brainstem torsion with reduced cerebral blood flow (CBF) and sudden obstruction of CSF flow Signup and view all the answers

What is the normal range of cerebral perfusion pressure (CPP) in healthy individuals?

70-85 mmHg Signup and view all the answers

What is the range of mean arterial pressure (MAP) within which autoregulation of cerebral blood flow is maintained?

50-150 mmHg Signup and view all the answers

What is the normal cerebral blood flow (CBF) per 100 g of brain tissue?

50 mL min-1 Signup and view all the answers

What is the effect of pyrexia on cerebral metabolic rate for oxygen (CMRO2)?

Increases CMRO2 Signup and view all the answers

What is the effect of hyperventilation on cerebral blood flow?

Reduces CBF only temporarily Signup and view all the answers

What is the indirect effect of isoflurane on cerebral blood flow?

Reduction in CMRO2 Signup and view all the answers

At what MAC of isoflurane does the vasodilating effect predominate?

1.5 MAC Signup and view all the answers

Study Notes

Raised Intracranial Pressure (ICP)

The skull contains three components: brain, blood, and cerebrospinal fluid (CSF), which must maintain a balance in volume to maintain a stable ICP.
An increase in the volume of one component must be accompanied by an equal reduction in the volume of the others.
Initial compensation for increased brain or blood volume is the extrusion of CSF into the spinal sac.
When this mechanism is exhausted, further volume increases result in a sudden large increase in ICP.

Consequences of Raised ICP

Impedes cerebral perfusion, leading to a 'vicious cycle' of hypoperfusion, ischemia, and cerebral oedema.
Brain swelling causes herniation of the temporal lobe and cerebellar tonsils, brainstem torsion, reduced cerebral blood flow, and acute hydrocephalus.

Clinical Signs and Symptoms of Raised ICP

Headache, worse after waking and exacerbated by lying down
Nausea and vomiting
Papilledema
Decreased conscious level
Hypertension and bradycardia
Abnormal respiratory pattern (irregular, bradypnea, apnea)

Causes of Raised ICP

Traumatic brain injury
Space-occupying lesions (e.g., tumor, abscess)
Hemorrhage
Venous thrombosis
Infection (e.g., meningitis, encephalitis, abscess)
Hydrocephalus
Metabolic encephalopathy (e.g., hypoxia, hypercapnia, hypoglycemia, hepatic)
Status epilepticus

Aggravating Factors

Venous obstruction (e.g., from poor neck positioning, tube ties, etc.)
Raised intrathoracic pressure
Fiber-optic bronchoscopy (transiently increases ICP)

Ameliorating Factors

Head-up tilt of 30° (maximizes venous drainage and minimizes reduction in cerebral arterial pressure)

Cerebral Perfusion Pressure (CPP)

Defined as the difference between systemic MAP and ICP
Typically 70-85 mmHg in health
Guidelines for traumatic brain injury recommend maintaining a CPP of 50-70 mmHg

Cerebral Blood Flow (CBF)

Normal CBF is approximately 50 mL min−1 per 100 g of brain tissue
CBF is the only intracranial component that can be manipulated nonsurgically
Autoregulation of CBF is maintained between a mean arterial pressure (MAP) of 50 and 150 mmHg

Regulating Factors

Cerebral metabolic rate for oxygen (CMRO2): CBF increases proportionally with increasing CMRO2
PaO2: little change in CBF above 6.7 kPa; below this, CBF increases
PaCO2: near-linear relationship between CBF and PaCO2 between 2.7 kPa (maximal vasoconstriction) and 10.6 kPa (maximal vasodilation)
Hyperventilation: reduces CBF only temporarily, with a return to normal values after approximately 5 hours

Pharmacological Agents that Affect CBF

Inhalational agents:
- Isoflurane: indirect vasoconstricting effect secondary to a reduction in CMRO2 and a direct vasodilating effect
- Isoflurane: provides cerebral protection; ischemic changes do not develop until CBF is reduced to 8-10 mL min−1 100g−1
- Sevoflurane: similar effects to isoflurane
- Desflurane: produces...

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Description

This quiz covers the concept of raised intracranial pressure, cerebral blood flow control, and the compensatory mechanisms that occur when there is an increase in brain matter or blood volume.