What are the dynamics of intracranial (within the skull) blood flow in relation to intracranial hemodynamics?

From the Guidelines

Intracranial hemodynamics management should prioritize maintaining cerebral perfusion pressure above 50-70 mmHg and controlling intracranial pressure below 20-25 mmHg to prevent secondary brain injury. Intracranial hemodynamics refers to the blood flow dynamics within the cranial cavity, which is crucial for maintaining proper brain function. The brain requires constant blood supply to deliver oxygen and nutrients while removing waste products. Cerebral blood flow is regulated through autoregulation, a process that maintains consistent perfusion despite changes in systemic blood pressure within a range of 50-150 mmHg, as noted in guidelines for managing spontaneous intracerebral hemorrhage 1.

Key Considerations

• The Monroe-Kellie doctrine is fundamental to understanding intracranial pressure dynamics, stating that the sum of brain tissue, cerebrospinal fluid, and blood volume must remain constant within the rigid skull.
• Disruptions to normal hemodynamics occur in conditions like traumatic brain injury, stroke, and hydrocephalus, requiring prompt intervention.
• Treatment approaches include ensuring adequate oxygenation and sometimes using medications like mannitol or hypertonic saline to reduce cerebral edema, as discussed in the management of spontaneous intracerebral hemorrhage in adults 1.

Monitoring and Management

• Continuous monitoring of intracranial pressure, cerebral perfusion pressure, and other parameters is essential in neurocritical care to prevent secondary brain injury.
• The use of fiberoptic ICP monitors within the brain parenchyma and ventricular catheters can detect dynamic changes in intracranial pressure, but their insertion carries risks such as infection and intracranial hemorrhage, highlighting the need for careful patient selection and management 1.
• Transcranial Doppler sonography has the potential to assess mass effect and track ICP changes, providing valuable information for clinical decision-making 1.

Clinical Decision-Making

• The decision to monitor and treat elevated intracranial pressure should be based on the individual patient's needs and the potential benefits and risks of intervention, considering factors such as the presence of hydrocephalus, mass effect, and the patient's overall clinical status 1.
• Maintaining a balance between controlling intracranial pressure and ensuring adequate cerebral perfusion is critical, and this balance should be guided by the latest clinical evidence and guidelines for managing intracranial hemodynamics in the context of spontaneous intracerebral hemorrhage.

From the Research

Intracranial Hemodynamics Overview

• Intracranial pressure (ICP) is the pressure exerted by cranial contents on the dural envelope, comprising the partial pressures of brain, blood, and cerebrospinal fluid (CSF) 2.
• Normal ICP is below 10 mmHg, but it may increase due to various pathologies such as traumatic brain injury, stroke, or neoplasm 2.
• Elevated ICP above 20 mmHg can damage neurons and jeopardize cerebral perfusion, requiring treatment 2.

Management of Intracranial Hemodynamics

• Head elevation is a conventional nursing intervention to control raised ICP, but it may put patients at risk for intracranial hypertension and cerebral ischemia due to decreased cerebral perfusion pressure 3.
• Optimal head positioning should be decided on an individual basis using both ICP and cerebral perfusion pressure (CPP) measurements 3.
• ICP monitoring and CPP estimation are used to guide targeted therapy of acute brain injury, but there is currently no class I evidence that ICP/CPP-guided therapy improves outcomes 4.

Monitoring and Treatment Thresholds

• ICP monitoring is integral to the clinical care of life-threatening brain insults, such as severe traumatic brain injury, subarachnoid hemorrhage, and malignant stroke 5.
• The percentage of ICP above 20 mmHg and 25 mmHg thresholds correlates with lower glucose and increased lactate-pyruvate ratio, indicating poor cerebral substrate supply 6.
• Keeping ICP below 20 mmHg and CPP at least above 60 mmHg may improve cerebral energy metabolism and clinical outcome 6.

Cerebral Perfusion Pressure and Autoregulation

• CPP estimation requires correct referencing to avoid over-estimation and adverse patient outcomes 4.
• Autoregulatory CPP optimum (CPPopt) insults do not correlate with worse cerebral energy metabolism, but higher percentage of CPP below fixed thresholds correlates with poor cerebral substrate supply and worse clinical outcome 6.
• CPP insults below 60 mmHg are independently associated with higher lactate-pyruvate ratio, indicating poor cerebral energy metabolism 6.