Neurology and TBI

Major Divisions of the Nervous System

• Central Nervous System (CNS):

  • Brain

  • Spinal Cord

• Peripheral Nervous System (PNS)

• Autonomic Nervous System (ANS):

  • Sympathetic nervous system: fight or flight

  • Parasympathetic nervous system: rest

Neurons

• Basic unit of the nervous system, transmitting impulses (messages).

  • Motor Neurons (Efferent): Carry impulses from CNS to PNS.

  • Sensory Neurons (Afferent): Carry impulses from PNS towards CNS.

• Axons may be covered by a myelin sheath:

  • White matter: Myelinated axons.

  • Gray matter: Non-myelinated axons.

The Brain

• Regulates and functions of the nervous system and all body systems consist of:

  • Forebrain: Diencephalon, Cerebrum, Cerebral cortex.

  • Cerebellum: Responsible for voluntary and involuntary movements.

  • Brainstem: Midbrain, Pons, Medulla.

Meninges

• Protective covering of brain and spinal cord:

  • Dura Mater: Tough outer layer.

  • Arachnoid Membrane: Middle layer with subarachnoid space containing CSF.

  • Pia Mater: Thin, tough inner layer covering the brain.

Cerebral Spinal Fluid (CSF)

• Produced by the choroid plexus in the brain ventricles:

  • Volume: 125-150 ml at any given time, 650 ml produced daily.

  • Circulates in subarachnoid space and through the spinal cord.

  • Contains water, protein, glucose, and ions (Na, Cl, K).

Blood-Brain Barrier

• A selective permeability barrier that protects the brain:

  • Controls exchange of O2, CO2, metabolites between blood and brain.

  • Prevents large molecules (like albumin) from entering…

  • Allows passage of O2, glucose, CO2, ETOH, anesthetics, water.

Intracranial Pressure (ICP)

• ICP is the pressure exerted by CSF within the brain's ventricles:

  • Normal ICP: $0-15$ mmHg. Treatment threshold: sustained ICP of $22$ mmHg.

  • Causes of increased ICP:

  • Cerebral edema

  • Hemorrhage/hematoma/mass

  • Excess CSF (hydrocephalus)

  • Increased cerebral blood flow

Signs of Increased ICP

• Symptoms indicating raised ICP:

  • Headaches, nausea & vomiting

  • Behavioral changes: irritability, confusion, impaired judgement

  • Altered level of consciousness, aphasia, cranial nerve dysfunction

  • Cushing's triad:

  • Widening pulse pressure

  • Bradycardia

  • Irregular respirations

The Glasgow Coma Scale (GCS)

• Measures consciousness and severity of head injury:

  • Scores range from $3$ (deep coma) to $15$ (fully awake).

  • Assessed by:

  1. Eye opening

  2. Verbal response

  3. Motor response.

Traumatic Brain Injury (TBI)

• TBI is damage to the brain from external mechanical forces:

  • Causes: Falls, MVCs, sports.

• Injuries can be classified as:

  • Primary injury: Immediate physical damage from trauma.

  • Secondary injury: Processes after the initial injury worsening outcomes (e.g., hypotension, hypoxemia).

Types of TBIs

• Mild TBI (GCS 13-15): Symptoms resolve within 72 hrs.

• Moderate TBI (GCS 9-12): Could have brain injury visible on scans.

• Severe TBI (GCS < 8): Significant risk of secondary injury, often needing ICU care.

Complications of TBI

• Diabetes Insipidus: Loss of ADH secretion, polyuria & polydipsia.

• SIADH: Excess ADH secretion, leading to hyponatremia.

• Seizures: Increased ICP, hypoxia, secondary injury.

• Brain Herniation: Increased ICP causing brain tissue shift, pressing on medulla.

• Brain Death: Irreversible loss of consciousness and brainstem function.

Organ Donation

• Determined post brain death (loss of blood flow to the brain).

• Organ viability requires maintained mechanical ventilation post-death determination.

• Key criteria: absence of brain function, no severe electrolyte disturbances, and confirmed test results for brain death assessment.

Important Priorities and Interventions in TBI Care

• Maintain adequate perfusion to the brain.

• Prevent secondary injuries.

• Early intubation and mechanical ventilation if required.

• Keep patient’s head elevated to reduce ICP.