Brain Anatomy and Vital Centers

• The brainstem is divided into:
  • Midbrain: helps coordinate movement and reflexes.
  • Pons (belly of seahorse-shaped): relays signals, respiratory rhythmicity center and cranial nerves control facial movements.
  • Medulla oblongata: houses critical vital centers (heart rate, force of heart contraction, respiration) and reticular activating system (RAS), which regulates consciousness.

RAS and Consciousness

• Reticular Activating System (RAS): a network of neurons in brainstem that regulate wakefulness.
• Damage to RAS causes decreased consciousness, coma, or even death.
• Brain swelling or lesions can compress RAS, impairing consciousness.

Causes of Altered Consciousness

• Direct damage:
  • Stroke, trauma, tumors, bleeding.
• Indirect causes:
  • Ischemia (lack of oxygen, e.g., myocardial infarction).
  • Toxins (alcohol, drugs, uremia).
  • Metabolic disturbances:
    • Hypoxia, acidosis, hypoglycemia.
• Infection or inflammation.

Progression to Coma

• Early signs:
  • Confusion, disorientation, lethargy.
• Progression:
  • Reduced responsiveness, stupor.
• Deep coma:
  • Cannot respond to stimuli.
  • Life-threatening, requires urgent care.

Monitoring and Assessment

• Vital signs:
  • Heart rate, respiration, blood pressure, temperature.
• Reflex testing:
  • Pupillary reflex.
  • Cranial nerve reflexes.

Glasgow Coma Scale (GCS)

• Purpose: assesses level of consciousness.
• Scores:
  • 13-15: mild/no coma.
  • 9-12: moderate impairment.
  • 4-8: coma.
  • 3: deep coma (poor prognosis).
• Lower scores indicate worse prognosis.
• The longer a person remains in a coma, the worse the prognosis.

Brainstem Reflexes:  

1.  Pupillary Light Reflex

• Shine light into eyes.
• Pupils should constrict.
• Dilatation (“blown pupils”) indicates brainstem damage.

2.  Oculocephalic Reflex (Doll’s eyes)

• Turn patient’s head to the side.
• Normal:
  • Eyes move opposite to the the direction of head turn.
• Abnormal:
  • Eyes stay fixed (no movement), indicating brainstem impairment.

3.  Oculovestibular Reflex (Caloric Test)

• Use warm or cold water (or air) to irrigate ear.
• Normal:
  • Eyes gaze toward the cold water or away from the warm water.
• Abnormal:
  • No eye movement, indicating brainstem damage.

4.  Corneal Reflex

• Touch cornea with gauze.
• Normally, eyeblink occurs.
• Absence suggests brainstem or cranial nerve damage.

5.  Gag Reflex

• Touch the back of the throat.
• Normally, the person gags.
• Absence indicates neural impairment.

Summary

• Reflex tests evaluate brainstem and cranial nerve function.
• Good prognosis correlates with higher GCS scores and intact reflexes.
• Deep coma and absence of reflexes suggest brain death or severe brainstem injury.