Coma / Neurology

Bedside Evaluation

• Pupils
  • neuromuscular blockade does not affect pupil size/reactivity
  • Systemic atropine causes pupil dilation (but remain reactive)
  • High-Dose dopamine causes fixed dilated pupils
  • If pupils remain non-reactive for > 6-8hrs after resuscitation from an arrest, cahnces of satisfactory neurologic recovery are very poor.
• Ocular Reflex
  • Brainstem Evaluation
  • Oculocephalic Reflex
    • Rotate head from side-to-side 
    • If lower brainstem is intact --> eyes deviate away from direction of rotation.
    • If lower brainstem impaired --> eyes follow direction of motion
  • Oculovestibular Reflex
    • 50mL of cold saline into external auditory canal
    • If brainstem intact --> both eyes deviate towards cold injection
    • If brainstem impaired --> conjugate movement lost.
• Sensorimotor Exam
  • Clonic Movements?
    • Elicit by flextion of hands or feet (asterixis)
    • Sign of metabolic encephalopathy
  • Focal motor or sensory defect?
  • Pain Response
    • Injury to thalamus --> painful stimuli provoke flexion of upper extremity
      • This is called Decorticate Posturing --> POOR prognosis
    • Injury to midbrain and pons --> arms+legs extend and pronate in response to pain.
      • This is called Decerebrate Posturing --> VERY POOR prognosis

• 

• (Source: "The Little ICU Book" by Paul Marino 2008)

Glasgow Coma Scale

• Eye Opening    4 - Spontaneous    3 - To Speech    2 - To Pain    1 - None	Verbal Communication    5 - Oriented    4 - Confused    3 - Inappropriate but recognized words    2 - Incomprehensible sounds    1 - None	Motor Response    6 - Obey Commands    5 - Localizes to pain    4 - Withdraws to pain    3 - Abnormal flexion (decorticate response)    2 - Abnormal extension (decerebrate response)    1 - No movement

• Clinical Applications:

  • 1.  To define coma	GCS ≤ 8
    2.  To stratify severity of head injury	13-15 = MILD 9 - 12 = MODERATE     ≤ 8 = SEVERE
    3.  To identify candidates for intubation	GCS ≤ 8
    4.  To predict likelihood of recovery from coma	if GCS < 6 @ 72hrs = No chance of satisfactory    neurologic recovery    (Edgren et al (1994))

Brain Death

• Irreversible cessation of function in all areas of the brain, with permanent loss of automatic breathing.
• Most often as a result of traumatic head injury, intracranial hemorrhage and cardiac arrest.

• Clinical Diagnosis of Breath Death   1.  Irreversible Coma 2.  Absence of brainstem reflexes 3.  Absence of spontaneous breathing efforts   Two confirmatory evaluations 6-8hrs apart are required

• Apnea Test
  • Observe patient for spontaneous breathing in presence of hypercapnia (powerful breathing simulus)
  • 100% O2 breathing --> separate from ventilator --> O2 insufflated into ET tube (prevent hypoxemia)
    • Patient observed for spontaneous breathing efforts for 8-10min.  At that point ABG is obtained + ventilator resumed. 
    • Arterial pCO2 rises by 2-3mmHg/min of apnea
    • If arterial pCO2 increases by > 20 mmHg without breathing efforts --> confirms dx of brain death.
  • Note: Apnea test brings hypotension, cardiac arrhythmias (abort if develop this, and test is never repeated once confirmed brain death)
  • Note: spontaneous movement bursts head/torso/upperExtremities are "Lazarus' sign", neuronal bursts from C-spine, not manifestations of brain activity.
• May not be possible to diagnose brain death in following:
  • Severe facial trauma or C-spine cord injury
  • Pre-existing pupillary abnormalities
  • End-stage pulmonary disease with high CO2
  • Drugs that interfere with evaluation (i.e. paralytics)
• In above cases, may need confirmatory test such as EEG, brain scan with Tc-99m, transcranial doppler, or somatosensory evoked potentials.

Organ Donor

• Measures to maintain organ viability:
  • Hemodynamics
    • Urine output < 1mL/kg/hr --> give volume to a CVP of 10-15mmHg
    • Dopamine 5-15 mcg/kg/min (avoid alpha-adenergic vasoconstriction --> can cause anoxic organ injury)
  • Pituitary Failure (50% of brain dead pts)
    • Diabetes Insipidus
    • Adrenal Insufficiency
      • ACTH stim test is not useful
      • If suspected due to hypotension --> give IV hydrocortisone 50mg q6h