Neuroanaesthesia Flashcards
Incidence of neurological damage during scoliosis correction
0.5%
SSEP stimulation electrodes placement
Pair of stimulating electrodes placed bilaterally:
1. Posterior tibial nerves (lumbar surgery)
2. Median nerves (cervical surgery)
Frequency of SSEP stimulation
30mA at 5Hz
SSEP recording electrode placement
Proximal to site of surgery:
1. 2 or more scalp electrodes (frontal and cervical)
2, Reference electrode
3. Ground electrode
Band filter width for SSEP
20-1000 Hz
Shape of characteristic response in SSEP
W
Changes seen in SSEP with spinal cord compromise
Increased latency
Decreased amplitude
Critical change in SSEP
50% increase in latency
What is an MEP?
Motor Evoked Potential
What is a SSEP?
Somatosensory Evoked Potential
What does MEP monitor?
Territory of the anterior spinal cord artery (corticospinal tracts)
What does SSEP monitor?
Ascending sensory pathways (dorsal columns)
Source of stimulation for MEP
Transcranial electrical stimulation Transcranial magnetic stimulation Direct rostral spine stimulation
Risk of transcranial electrical stimulation
Injury secondary to mandibular contraction
How are MEPs recorded?
SC / IM needle electrodes in arm and leg muscles
Time taken for MEP response
Less than 1 minute ???
Latency of SSEP
20 ms upper limb
37 ms lower limb
Define Serious Traumatic Brain Injury
GCS < 9 post resuscitation → mortality 40%
List some primary prevention strategies for serious traumatic brain injury
Helmets
Airbags
Reducing alcohol consumption
Speed limits
Define secondary brain injury
A hypoxic insult to the brain from oedema, haematoma or low systemic pressure following a primary insult
Indications for CT head within 1 hour of TBI
GCS <13 at any time
GCS 13-14 2 hours post-injury
Open fracture
Skull base fracture
More than 1 episode of vomiting Seizure
Coagulopathy
Event amnesia
Focal deficit
Oxygen targets in TBI
PaO₂ >13
CO₂ targets in TBI
ETCO₂ 4.5-5
MAP target in TBI
> 80
Glucose targets in TBI
6-10 mmol/L
Describe the features of diabetes insipidus
Raised sodium
Polyuria
Low urine osmolality
(Caused by lack of ADH / lack of response to ADH → polyuria + dehydration)
CPP target in neuroprotection
> 60
ICP target in neuroprotection
<20
Rescue therapies in TBI
ABC
Ensure good venous drainage
Increase sedation
Hyperventillate to ETCO₂ 4-4.5
Hypertonic saline (1-3ml/kg 5%, 3-5ml/kg 3%) or mannitol (0.25-2g/kg)
Barbiturate coma (burst suppression)
What causes the blown pupil in a decompensating head injury?
Falsely localising nerve injury (CN III) - due to uncal herniation → mechanical compression of CN III → subsequent brain stem compromise
How should you treat seizures in TBI?
Thiopental or benzodiazepine immediately
Phenytoin or levetiracetam loading immediately afterwards
The role of steroids in TBI
Generally none
Why early fixation in unstable spinal injury?
Allows for proper nursing care, PT, cough etc.
Classical timing for early complications of SAH
Day 1: hydrocephalus
Day 1-7: rebleed
Day 7+: ischaemia
SAH risk factors (7)
Smoking
HTN
Alcohol
Polycystic kidney
Family history
Female gender
Age 40-50
SAH incidence
6/100,000 patient years
SAH outcomes
10% die before hospital
40% die within 1 month
Modified Fisher Scoring System
Grade 0:
- No SAH
- No IVH
Grade 1:
- Focal or diffuse, thin SAH
- No IVH
- Incidence of symptomatic vasospasm: 24%
Grade 2:
- Focal or diffuse, thin SAH
- IVH present
- Incidence of symptomatic vasospasm: 33%
Grade 3:
- Thick SAH
- No IVH
- Incidence of symptomatic vasospasm: 33%
Grade 4:
- Thick SAH
- IVH present
- Incidence of symptomatic vasospasm: 40%
Hunt and Hess Scoring System
Clinical grading system
Grade 1: asymptomatic/mild headache
Grade 2: moderate-severe headache or nuchal rigidity, or cranial nerve palsy
Grade 3: lethargy, confusion, or mild focal deficit
Grade 4: stupor and/or hemiparesis
Grade 5: deep coma, decerebrate posturing, or moribund appearance
Modified WFNS Scoring System
Grade I: GCS 15
Grade II: GCS 14
Grade III: GCS 13
Grade IV: GCS 7-12
Grade V: GCS 3-6
What are the hallmarks of a cholinergic crisis?
SLUDGE + other
Salivation
Lacrimation
Urination
Defecation
GI upset
Emesis
Miosis
Muscle weakness
Flaccid paralysis (initially spasm)
Respiratory failure
What are the indications for urgent (within 1 hour) CT head?
GCS < 13 when first assessed in emergency department
GCS < 15 when assessed in emergency department 2 hours after the injury
Suspected open or depressed skull fracture
Sign of fracture at skull base haemotympanum, ‘panda’ eyes, cerebrospinal fluid leakage from ears or nose,
Battle’s sign (bruise behind ear)
Post-traumatic seizure
Focal neurological deficit
> 1 episode of vomiting
Cerebral ischaemia monitoring in CEA
Awake
Transcranial doppler
Stump pressure
EEG
SSEP
NIRS
What are the diagnostic criteria for SIADH?
Hypotonic hyponatraemia
- Serum sodium <135 mmol/l
- Serum osmolality <280 mOsm/kg
Urine osmolality > serum osmolality
Urine sodium concentration >18 mmol/l
Normal thyroid, adrenal, and renal function
Clinical euvolaemia - absence of peripheral oedema or dehydration
How do you treat SIADH?
Conservatively
Fluid restrict (1000mL/day)
Hypertonic saline (1.8%) if Na <120 mmol/L
Consider diuretics (furosemide)
Consider demeclocycline (inhibits ADH)
Cerebral Salt Wasting Syndrome biochemical diagnostic criteria
Low/normal serum sodium;
High/normal serum osmolality;
High/normal urine osmolality
High urine sodium
Increased haematocrit/urea/bicarbonate/albumin as a consequence of hypovolaemia
