Update on Paediatric Neuroanaesthesia

Andrew DavidsonAnaesthetist, Royal Children’s

Hospital

No more anaesthetists!

• Common conditions• Anaesthesia issues • Future issues

Paediatric neurosurgery

• Hydrocephalus – shunts• “Tumours”• Trauma • Vascular malformations• Epilepsy• Encephalocoeles, myelodysplasia• Chiari malformations• Craniosynostosis

Tumours

• Brain tumours are the most common solid tumours in children

• Majority are infratentorial (60%)– Medulloblastomas, cerebellar astrocytomas,

brainstem gliomas, 4th ventricle ependymomas

• Midbrain (15%)– Craniopharyngiomas, optic gliomas, pituitary

adenomas, hypothalamic tumours

• Hemispheric tumours (25%)– Astrocytomas, oligodendrogliomas, ependymomas,

glioblastomas

Ganglioglioma

Posterior fossa craniotomy

• Narrow window from symptoms to death – early surgery

• Often curative, so aim for total resection rather than just debulking

• Prone position– Airway!

• Surgery close to the brainstem

Epilepsy surgery

• Increasing frequency with better localisation

• Temporal lobectomy• Hemispherotomy • Lesionectomy

Electrocorticography

before

Electrocorticography

• “Normal” conditions– Temperature

– CO2

– Anaesthetic agent: remifentanil and low dose isoflurane

• Be consistent!

Hemispherotomy

Hemispherotomy

• Long • Lots of blood loss• Slow to wake up

• Not as bloody as hemispherectomy

Vagal nerve stimulator

• Indication– not candidates for resection

• Outcome– 50% >50% seizure reduction– <10% seizure freedom– replace battery 5yrs

• Anaesthesia – bradycardia

Anaesthesia for craniotomy in children

Access

• Once draped almost impossible to reach most of the child

• Lines must be perfect • At least 2 IV access points• Tend to “over monitor” • Separate TIVA line• Meticulous airway positioning

• Don’t start till your happy

Blood loss

• Blood loss can be substantial – avoid the “cycle of death”

Blood loss

Rapid transfusion

Hyperkalaemia

Death

Acidosis & hypothermia

Coagulopathy

Blood loss

Rapid transfusion

Hyperkalaemia

Death

Acidosis & hypothermia

Coagulopathy

“Permissive anaemia”

Hypovolaemia

Transfusion • Avoiding blood is “good”, but • Anaemia is bad for injured brain

• Theoretical risk versus the big issues– Biggest risk of transfusing is incompatibility

error– Biggest risk from avoiding blood is “getting

behind”

• Ideal transfusion trigger is unknown for paediatric neurosurgery/ neurotrauma

• Transfuse early

Temperature

• Cold is good in theory • Cold worsens coagulopathy • Cold children are hypotensive

• Children get cold quickly, and get hot quickly

• Hypothermia and trauma – possible benefit if cool early enough and long enough

Blood pressure

• Hypotension– Reduced CPP– Reduced perfusion – Ischaemia

• Hypertension– Increased flow – Oedema– Increased interstitial fluid – increased gradient

from capillary to neuron

0 50 100 150 200

Perf

usi

on

Mean blood pressure

Adult

0 50 100 150 200

Perf

usi

on

Mean blood pressure

Child

Blood pressure

• Ideal perfusion pressure unknown for children

• Low threshold for blood pressure support

• Noradrenaline or Metaraminol • Avoid excessive propofol or volatile anaesthesia • Beware remifentanil • Beware hypothermia • Optimal filling

Central lines

• Poor IV access– Intra operative and post operative

• If need frequent post operative bloods (DI risk)• Vasopressors for blood pressure support• Central pressure estimate • ? VAE diagnosis and treatment

• Jugular or femoral

Which anaesthetic?

• Stable blood pressure• Preserve autoregulation (coupling between flow

and oxygen need) • Wake up quickly and smoothly

• Reduce CMRO2

• Neuroprotection

• Allow electrocorticography

• The evidence is patchy and contradictory in adults• The evidence is very sparse in children

• Do children really need to wake up quickly? • Avoid emergence delirium

• None are perfect

• Focus on the important and practical, rather than the theoretical fine print

• Sevoflurane: – good for autoregulation and possibly neuroprotection – but slow awakening after long procedures and bad for

electrocorticography

• Desflurane: – good for awakening – but perhaps not so good for autoregulation

• Isoflurane: – neither good nor bad

• Avoid volatile > MAC

• Nitrous oxide: – mixed evidence but generally bad for autoregulation

• Propofol: – Good for autoregulation and neuroprotection – But, TIVA algorithms are less accurate in

children, so easier to overdose – hypotension, disrupted autoregulation and slow awakening

• Ketamine: – Traditionally thought to be bad for every reason – But new evidence is contradictory – Good choice for the quick CT scan???

• Remifentanil – Stable & Rapid smooth awakening– Hypotension and rebound pain and hypertension

on awakening

Fluids

• Renal function has less capacity to adjust• Children are more susceptible to cerebral

oedema with hyponatraemia • 0.9% saline

– Good for tonicity – But rapidly leads to hyperchloraemic acidosis

• Post operative– Beware Diabetes Insipidus– Beware increased antidiuretic hormone secretion

– never use hyptonic fluids, check the electrolytes daily

Pain• Neurosurgery is painful – but do children need opioids and

are they “safe”

• Audit at RCH • 50 children post craniotomy

• 71% of children received parenteral morphine, • No episodes of significant respiratory depression were noted

• Over the 72 hours the median pain score was 1.3• For most of the time children had little or no pain • However, 42% of children had at least one episode of a pain

score >3

Post craniotomy pain

• Highly variable • Perhaps worse with posterior fossa craniotomies

• Most children have PCA or continuous morphine initially

• Wide variety of adjunct analgesics

• “Low” incidence of sedation or respiratory depression

Awake craniotomy

midline

sylvian

fron

tal

parietal

hipflexion(1.75)

R trunk flexion& shoulderdepression

(2.5)

thumb ext & wrist

flexion(2.0)

wrist ulnar dev. &

pronation(1.75)

elbow & wristflexion

(2.0)

finger (MCP)flexion(1.75)

finger (MCP)flexion & wrist

ulnar dev.(1.5)

finger (MCP)flexion &

thumb opp.(2.0)

wrist sup.& finger (IP)

flexion(1.25)

wrist extension &

ulnar dev.(1.5)

finger extension &supination

(2.5)

lip & face(2.0)

finger(F2)

sensory

finger(F2,3)

sensory

fingersensory

finger(F4,5)

sensory

sensorimotor mapping midline

sylvian

fron

tal

parietal

MF1 = ankle dorsiflexion + hip/trunk/head movement (2.5)MF2 = hip, trunk & head movement to R (2.5)

elbowflexion &

shoulder abd. (3.0)

elbowsensory

armsensory

shoulder depression

& head turn R(3.0)

elbow flexion & shoulderposterior

(3.5)

R trunk flexion

(3.0)

undercut

Awake craniotomy in children

• Mature & motivated children

• Familiarization with environment and the team• Favourite music• Use the parents

• Asleep for lines, urinary catheter, scalp blocks and pins• Wide awake to get comfortable on table then fix mayfield• Remifentanil & very low dose propofol sedation

Intraoperative MRI

Summary – key messages

• Secure everything before they drape• Low threshold for central lines• Ideal anaesthetic unknown • Ideal blood pressure unknown, but avoid

hypotension • Ideal transfusion trigger unknown, but

transfuse early