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BJA 2024 > Anaesthesia for Paediatric Neurosurgery > Flashcards

Anaesthesia for Paediatric Neurosurgery Flashcards

1
Q

How might a SOL present in paediatrics?

A

Infants - increasing head circumference
Older children - headaches

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2
Q

When do the anterior and posterior fontanelles close in infants?

A

Posterior fontanelle closes around the 2nd or 3rd month of life

Anterior fontanelle closes between 12-18 months

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3
Q

What is normal ICP in infants and children?

A

In neonates ICP is 2-6mmHg
In children normal ICP is < 15mmHg

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4
Q

What does the Monro-Kellie doctrine state?

A

Monro-Kellie Doctrine:

As the size of the volume of one of the intracranial components (brain, blood, CSF) increases, there will be a compensatory reduction on the other components.

Any further increase in volume will result in a rapid increase in ICP

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5
Q

What is the consequence of increased ICP?

A

As ICP increases, cerebral perfusion pressure (CPP) decreases, leading to ischaemia and cell death if left untreated.

CPP = MAP - ICP (or CVP)

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6
Q

What is Cushing’s Triad?

A

Widened pulse pressure (increasing SBP and decreasing DBP)
Bradycardia
Irregular respirations

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7
Q

What are signs and symptoms of increased ICP in children?

A

Headache
Vomiting
Agitation or drowsiness
Behavioural changes
Seizures
Cranial nerve palsies

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8
Q

Where is CSF produced and drained?

A

CSF is produced by ependymal cells in the choroid plexus within the ventricles of the brain (mainly lateral ventricles)

Resorption is CSF occurs via the arachnoid villi into the venous system

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9
Q

What causes impaired reabsorption?

A

Infections
Haemorrhage
Malformations
Rarely, choroid plexus papilloma can lead to CSF overproduction and hydrocephalus

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10
Q

What is the rate of CSF production in children?

A

0.35ml/min
or
500ml/day

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11
Q

What determines cerebral blood flow in children?

A

Glucose requirements and cerebral metabolic rate for oxygen (CMRO2) are higher in children compared with adults.

The higher CBF and increased glucose utilisation is proportional to this increased CMRO2.

Neonates have a lower CMRO2 and a lower CBF, with a relevant tolerance of hypoxaemia

Metabolic demand can increase in seizures or infections where an increase in blood flow can cause an increase in ICP.

The reverse happens in hypothermia and anaesthesia, where the metabolic rate is reduce and blood flow decreases.

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12
Q

What is cerebral autoregulation?

A

Cerebral autoregulation is the process by which CBF is regulated and maintained across a range of BPs.

Autoregulation ensures maintenance of CBF by decreasing cerebral vascular resistance when MAP or CPP decreases

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13
Q

How is cerebral autoregulation impaired?

A

TBI
Medication
Acidosis
Tumours
Cerebral Oedema

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14
Q

What neuroprotective measures can be employed to maintain CPP?

A

Adequate hydration
Vasopressors to sustain MAP
Avoid hypoglycaemia
Normocapnia

Hyperventilation only when acutely treating raised ICP

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15
Q

How is ICP monitored in infants?

A

Non invasive methods:
1. Palpation of an open fontanelle
2. Serial measurements of head circumference
3. MRI
4. Optic Sheath Nerve diameter
5. Transcranial doppler

Invasive methods:
1. Intraparenchymal catheter
2. External ventricular drain

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16
Q

What are complications of an EVD?

A

Rate of complications in paediatric population is 20-25%

Infection
Misplacement
Haemorrhage
Malfunction

17
Q

What are complications of intracranial pressure monitors?

A

Infection
Haemorrhage
Technical errors (baseline drift)

Lack of consensus if true ICP is measured in healthy or damaged hemisphere

18
Q

What will you focus on in your pre-operative assessment?

A
  1. Complications of prematurity:
    - Chronic lung disease
    - Previous IVH
    - Cardiac defects
  2. Neuro exam
    - Level of consciousness
    - Signs of raised ICP
  3. Respiratory
    - bulbar palsy
    - abnormal swallow
    - increased risk of aspiration
  4. U&E
    - Vomiting due to raised ICP can lead to electrolyte imbalance
    - Fluid status
  5. Liver function
    - AEDs
  6. Consent for possible AAGA due to reduced DoA to facilitate IONM
19
Q

What are considerations and maintenance for induction and maintenance of anaesthesia?

A
  1. Avoid acute changes in ICP due to hypoxia, hypercapnia, volatile agents or changes in MAP
  2. Avoid nitrous oxide as it increases CBF and CMRO2
  3. Sevoflurane is the least vasoactive agent
  4. Give high dose opioids such as Alfentanil or Remifentanil to suppress the stress response to larynscoscopy
  5. Propofol has minimal effects on autoregulation. Consider TIVA
20
Q

What are signs and symptoms of raised ICP?

A

Neonates & infants:
1. Tense fontanelle
2. Irritability
3. Separation of cranial sutures
4. Increased head circumference

Children > 1 year:
1. Vomiting
2. Headache
3. Papilloedema
4. Diplopia

Neonates, infants and children:
1. Reduced LOC
2. 3rd and 6th CN palsy
3. Change in pupils, signs of herniation
4. Loss of upward gaze (setting sun sign)

21
Q

What intraoperative monitoring will you use?

A

AoA min standards of monitoring
CVC access to monitor trends in CVP
Urinary catheter to monitor U/O, and for DI, and when mannitol is used
Core temperature monitoring (oesophageal or rectal probe)

22
Q

Name some intraoperative neurophysiological modalities

A
  1. Somatosensory Evoked Potentials
    - monitor the integrity of the ascending tracts, mainly in the dorsal columns
  2. Motor Evoke Potentials
    - give info on the descending tracts in the anterior spinal cord
  3. Brainstem responses
  4. Brainstem Auditory Evoke Potentials (BAEP)
  5. Direct wave monitoring
  6. Electromyography
    - monitors function of motor root axons of specific nerves by measuring activity of muscle each nerve innervates
  7. Cranial Nerve monitoring
23
Q

What options are available to measure Depth of Anaesthesia>

A
  1. Bispectral Index
  2. Spectral Entropy

(analyse raw EEG data)

NAP5 and 2021 AoA guidelines recommend that anaesthetists are able to interpret and understand raw EEG waveforms and where TIVA and NMB is used, DoA monitoring shoud be used.

24
Q

What are considerations in positioning patient for neurosurgery?

A
  1. Prone position with excessive neck flexion can produce macroglossia and pharyngeal or airway swelling as a result of impaired venous or lymphatic drainage.

A moderate head up tilt can augment venous drainage but increases risk of VAE

Eyes should be lubricated and covered with waterproof dressing t protect them from surgical skin prep.

Pressure areas should be padded and protected

Insertion of pins can cause marked HTN - mitigate with bolus dose of opioid.

Access to airway is limited - ETT to be securely taped in place

Abdomen should be free from pressure using rolls nad padding.

25
Q

What factors increases risk of VAE in children?

A
  1. Head constitutes greater body surface area - more susceptible to VAE
  2. Diploic veins, bridging across cranium and dural venous sinuses are relatively non-collapsible, with potential to allow air entrapment.
  3. Sitting position - pressure gradient between head and heart
  4. PFO, ASD or VSD are increased risk from paradoxical VAE
26
Q

What are initial signs of VAE?

A
  1. Acute decrease in EtCo2
  2. Drop in BP
  3. Arrhythmia
27
Q

What is immediate management of VAE?

A
  1. Alert surgeon
  2. Patient head down where possible
  3. Flood surgical field with normal saline to prevent further air entrainment
  4. 100% oxygen
  5. Compress jugular veins to increase venous pressure
  6. Fluids, vasopressors +/- adrenaline
28
Q

How would you manage blood loss and transfusion?

A

Blood loss can be monitored using trends in HR, arterial BP, CVP, ABG measurements and Hb.

Use of TXA with TEG may reduce blood loss.

29
Q

What post operative analgesia would you prescribe?

A
  1. Regular Paracetamol and opioids as required
  2. Nurse or PCA using IV opioids needed after spinal or posterior fossa surgery
  3. NSAIDs if no contraindication, in agreement with surgeons.
  4. Benzodiazepines or Baclofen can be used for muscle spasms
  5. Anti emetics

BJA 2024 (9 decks)

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