anaesthetic concern in neurosurgery

1. ANAESTHETIC CONCERS IN
NEUROSURGERY
(STEREOTACTIC SURGERY,EPILEPSY
SURGERY,AWAKE CRANIOTOMY)
PRESENTER: DR. SNIGDHA
MODERATOR: DR. ASHUTOSH KAUSHAL

2. Concerns
• Pre operative councelling and evaluation
• Intraoperative monitoring and complications
• Postoperative monitoring and care

3. Stereotactic Brain Surgery
• Minimally invasive surgical intervention
• Require multimodality neuro- imaging and calculation of coordinates of lesion/
location
Deep Brain Stimulation
Treatment for parkinson’s disease, dystonia, essential tremor, tourette’s syndrome
and psychiatric disorders(Depression, OCD, anorexia)
Mechanism and targets:
During surgery, leads are advanced deep into eloquent areas of the brain in order to
apply electric current to surrounding brain tissue via implanted pulse generator
Parkinsoni’s disease – subthalamic nuclei (STN); GPi in severe dyskinesia;
Ventral intermedius(Vim) nucleus of thalamus – tremors
Generalised Dystonia/ cervical dystonia – globus pallidus pars interna (GPi)
Depression and OCD- subcallosal cingulate gyrus, anterior limb of internal capsule

5. Surgical techniques
MRI / CT of brain to identify target nuclei -> burr hole for placement of DBS electrode
MER electrode inserted along the trajectory toward the target nuclei while
spont. Neuronal discharge recorded  specific brain structure identified on their
unique pattern of firing.
Macrostimulation - to verify that stimulation of electrode at location will improve
symptoms/cause side effects
Effects of anaesthetic agents on Neuromonitoring for target localization:
Microelectrode Recording-
MER from GPi – not obtained under GA
MER from GPi in parkinson’s disease – minimal effect of anaesthetic agents
MER from STN- minimal effect of dexmedotomidine
Macrostimulation testing-
Require awake cooperative patient
Short acting sedative used;stopped before testing.
GA interferes with evaluation-supress tremors,rigidity

9. Monitoring and positioning
• Standard monitors are used with invasive monitoring when indicated.
Supplemental oxygen with monitoring of end tidal CO2 and RR
• Vigilant monitoring of fluid administration
• BIS – to monitor arousal time, total propofol consumption
• Maximum comfort and cooperativeness for awake patients; head and neck
positioned- flexion on lower cervical spine and extension at atlanto- occipital
junction for airway patency
• OSA patient- CPAP therapy
Scalp block : with bupivacaine, ropivacaine, lidocaine for insertion of pins

10. Conscious sedation
• M/C used
• Allows for patient comfort during opening and closure
• Appropriate in patients dystonia/essential tremor where MER and
macrostimulation are needed to localize GPi/ Vim nuclei
• Use -propofol infusion, opioids, dexmedetomidine infusion(better choice d/t
nonGABA –mediated mechanism of action)
• Delayed awakening in patient with dystonia occur with propofol as Gpi neurons
receive higher GABA input than STN neurons
General anaesthesia:
• For patients who fear being awake,
• chronic pain syndromes,
• severe “off- medication” movements,
• severe dystonia/choreoathetosis
• children

11. Complications
• Surgery related:
1. Intracranial hemorrhage- 0.6%- 3.3% incidence.
2. Seizure -0.8%- 4.5%
3. VAE- 4.5% incidence d/t sitting position, hypovolemia, during burr hole creation.
4. Post-op cognitive problems
• Anasthesia – related complication:
1. Respiratory and airway- respiratory depression d/t oversedation/ intracranial
event
2. Cardiovascular – hypertension during procedure cause ICH

12. Post operative care
• Frequent assessment of neurological status, respiratory status, control BP, prompt
treatment of pain or nausea
• Medications for parkinson’s disease should be resumed as soon as possible
Pediatric procedures:
• DBS is highly effective in children with movement disorders
• Very young child/ having developmental delay/ congenital problems – require GA
• Drugs used – dexmedetomidine, propofol, ketamine, remifentanil

13. Pre- existing DBS for other Surgery
• Pre operative:
Information of patient’s symptoms when DBS system is turned off  if severe
symptoms, oral medication started before turning off .
• Intra operative:
DBS system interfere with recording of ECG ; use of cautery can burn neural tissue
around stimulator/ reprogram device  turning off decreases damage or use
of bipolar cautery
Diathermy should’nt be used  produce radiofrequency current and heating of
electrodes
In case of Cardio version – paddle position as far as possible from generator and
lowest clinically appropriate energy output used  function of generator
checked following that
• ECT, radiofrequency neuroablation, peripheral nerve stimulation safe if
stimulator turned off

14. Advances
• Stereotactic Biopsy of Intracranial Lesions:
Deep intracranial lesion biopsed for diagnosis
Done with MAC, conscious sedation or GA.
• Therapeutic stereotactic Radiosurgery:
Deliver high dose radiation beams to lesions
GA needed in children, uncooperative patient
Prolonged procedure- TIVA and inhalation

15. EPILEPSY SURGERY
• Candidates:
Drug resistant, uncontrolled, disabling focal epilepsy originating from a region
that can be removed with minimal risk of neurologic or cognitive dysfunction,
eg.
1. Treatment of choice for medically intractable temporal lobe epilepsy
2. Epilepsy due to discrete lesions like mesial temporal sclerosis, low grade
neoplasms (meningiomas, gangliogliomas, dysplastic neuroepithelial
tumors, astrocytomas, oligodendrogliomas), vascular malformations,
encephalomalcia from stroke or trauma, focal cortical dysplasias.

18. Types of epilepsy surgery
1. Standardized Resections-
• Anterior temporal resections
• Amygdalohippocampectomy
• Anatomical hemispherectomy
2. Tailored Resection –
• Localized cortical resections
• Lesionectomies
• Multilobar resections
3. Disconnections –
• Corpus callosotomy
• Multiple subpial transections
• Functional hemispherectomy

19. 4. Neurostimulation –
• Stimulation of cranial nerves
• Vagus nerve stimulation
• Trigeminal nerve stimulation
• Deep brain stimulation (cerebellum, thalamus, basal ganglia)
• Stimulation of seizure focus – repetitive transcranial mabnetic
stimulation, Invasive cortical stimulation
• Responsive stimulation
5. Gamma knife radiosurgery

20. Anaesthetic management of pre –operative
procedures
• Ensure sedative agents donot interfere with testing or influence results
sevoflurane and propofol based regimes suitable for hypometabolic cerebral
lesion detection
dexmedetomidine- ideal for MEG recording
etomidate – pharmacological activation of epileptic foci using PET, SPECT , MEG

21. Anaesthesia for intracranial electrode
insertion
Subdural electrodes are placed stereotactically in depth of suci/ deep cortical
structure, in form of grids/ strips for chronic extraoperative ECoG monitoring for
days to weeks to record typical seizure activity.
Method –
• AEDs withdrawn to detect and characterize seizure
• Anaesthesia given ( similar to craniotomy procedure in epilepsy patient) should
have minimum effects on ECoG
• Placed via burr hole
• Blood loss/VAE necessitates placement of arterial catheter, large bore IV catheter
• Brief hyperventilation as it precipitates seizure activities
• Electrodes removed by gentle traction under conscious sedation/ GA

22. Effect of Anaesthetic agents in patients with
epilepsy
Anaesthetic drugs have both pro- and anticonvulsant properties
Seizure a/w anaesthesia – 0.8% of adult / 3% of pediatric procedure
Patient with seizure disorder – 2% chance of seizure under GA( intubation or
extubation, when drug conc. Is low)- increased GABAergic inhibition can
sensitize cortex so any small amount of excitation causes seizure
Nitrous oxide:
70% N2O + O2produce – fast oscillatory EEG activity, but no evidence of seizure
activity ( no anticonvulsant Activity either)
N2O + Hyperberic O2 therapy – myoclonus
N2O + Isoflurane – convulsion with spike and wave activity in EEG

23. Inhaled anaesthetics:
• Sevoflurane - enhances non specific spike activities / provoke seizure like activities
in children even in normal brain in high concentration.
But with balanced anaesthesis technique it suppress ECoG acivities
• Isoflurane , desflurane - low epileptogenic potential, even at MAC 1 suppress
spont. interictal spike
• Enflurane- max. epileptogenecity , active both interictal spikes and ECoG 
pharmacoactivation of silent epileptogenic foci intraop. to delineate site of seizure
activity
Intravenous Anaesthesics:
1. Barbiturates – have anti convulsant property, effective in treatment of RSE
Methohexital- cause spike activation in TLE used for intraop. ECoG to activate
epilectic foci during temporal lobectomy

24. 2. Etomidate – at induction dose- subcortical seizure activity – used in ECT
At higher dose- produce burst suppression pattern analogus to barbiturates
3 . Ketamine- dose dependent threshold for seizure (>4mg/kg clinical seizure
activity)
4. Propofol-depress ECoG recoding, decrease frequency of spike activity
5. Dexmedetomidine- most prefered : sedation,analgesia, anxiolysis,absense of
motor stimulatory effect and respiratory depression, donot alter ECoG
6. Opioids- doesnot increase risk of Seizure / ECoG changes in standard dose
• Fentanyl, remifentanil: increase spike wave activity
• Alfentanil : short elimination half- life, facilites neurologic function testing
immediate postop.
• Morphine, hydromorphone: no pro convulsant activity

25. 7. Local anaesthetics- both pro- and anti convulsant property d/t membrane-
stabilizing activities.
• Sub toxic dose- anticonvulsant,sedative
• Higher dose – GTCS
8.Neuromuscular blocking agents: NDMR no effects. Succinyl choline- EEG activation
d/t increase CBF,ICP

26. Anaesthetic management of resection of
seizure focus
Pre – anaesthetic evaluation and preparation:
Detailed H/O neurologic , medical comorbidities, associated syndromes (eg. Tuberous
sclerosis, neurofibromatosis type 1)
Nature, frequency, type of seizure
Medical history- Timing of AEDs, other drug therapy
Pharmacokinetic and dynamic interactions between AEDs and anaesthetic medications
Optimize other medical problems

27. Preoperative lab test –
• Elevations in hepatic enzymes with anticonvulsant therapy
• Coagulation/ platelet function abnormality with AEDs (valproic acid, gabapentin).
• Establish rapport, psychological preparation, reassurance, reinforce indication for
awake surgery
• Continue antiepileptic medications on day of surgery for tumor surgery.
• H/O PONV , motion sickness; Antiemetics to decrease risk of aspiration
• Continue steroid coverage for tumor surgery
• Avoid benzodiazepines for preoperative sedation in epilepsy surgery
• Assessment of airways- might need instrumentation on emergency basis
• Ketogenic diet – adjuvant therapy for intractable epilepsy Intraop. NS prefered

28. Pre medication:
Anxiolytic
Antiemetics
1. Awake craniotomy:
It is a procedure where patient is awake to allow neurological testing
• INDICATION:
Seizure focus located within or in close proximity to eloquent regions of brain,
intraop ECoG and functional testing will facilitate maximal resection of seizure
focus without damage to eloquent areas.
For Surgery two criteria must be fulfilled-
Presence of surgically treatable epileptic syndrome
Presence of disabling seizures resistant to medical therapy, benefits of
surgery outweigh the risk

29. RATIONALE
• For tumors within proximity of eloquent areas of brain function, it allows
neurological assessment and cortical mapping facilating greater extent of
resection and minimal damage.
• Decreased risk of permanent neurological worsening
• Detailed language mapping
• Use of less invasive monitoring and anaesthesia drugs, avoidance of GA,
shorter hospital stay.

30. Patient selection
1. Cooperative,motivated, and have understanding of procedure
2. Must not have dysphasia,impaired motor function, confusion, language barrier,
cognitive impairement, delirium,somnolence, claustrophobia
3. Morbid obesity, OSA, psychiatric disorders, poorly controlled seizure, raised ICP,
uncontrolled coughing, anticipated difficult airways- relative containdications,
4. patient refusal -absolute contraindication

31. 2. Asleep – Awake- Asleep technique-
• For initial phase, GA induced with propofol and maintained with infusion
dexmedetomidine, propofol and volatile anaesthetics
• Analgesia with fentanyl / remifentanil, alfentanil
• Airway include spontaneous ventilation or controlled ventilation
• After opening dura, patient is awakened and airway removed for cortical
mapping (propofol infusion terminated 15- 20 min prior)
• After mapping, GA induced again with/ without controlled ventilation

32. Anaesthetic drug dosing for monitored anaesthesia
care and asleep – awake – asleep technique

33. Scalp block
1. Bilateral selective sensory nerve block:
• blocks auriculotemporal, zygomaticotemporal, supraorbital, supratrochlear, lesser
occipital and greater occipital nerve ,infiltration in pin insertion site and along
incision
• More effective in minimizing hemodynamic and stress responses to head pinning
2. Ring block:
Infiltration of local anaesthetic (in circular fashion) around surgical incision and pin
insertion sites; faster to perform but higher risk of LA toxicity
Local Anaesthetics used:
Lidocaine (7mg/kg max.)at pin sites
Bupivacaine (2.5 mg/kg max.), levobupivacaine (2.5mg/kg max.), ropivacaine (4mg/kg
max) –scalp block

34. Intraoperative management:
1. Surgical position may be supine, lateral, or semisitting- ensure comfortable
positioning with adequate padding and pillow, ensure cooperation for cortical
brain mapping
2. Standard monitors are used with invasive monitoring when indicated.
Supplemental oxygen with monitoring of end tidal CO2 and RR; Maintain patent
airway
3. BIS in monitoring hypnosis and guide drug dosing
Maintainance of CBF, cerebral perfusion, control blood loss
4. Foley’s catheterization to prevent discomfort
5. Precordial doppler for VAE
6. Ensure adequate LA for pin sites, scalp, and insicion

35. 7. Continuous vigilance and rapid treatment of complications like seizure,
respiratory adverse events and lack of patient cooperation
8. Discontinue propofol infusion 20 min before cortical mapping or
electrocorticography monitoring

36. • Complication
SEIZURES:
• Short localized
• Reccurent generalised
• After dural opening
• Loss of patient
cooperation,severe
aggitation,somnolence, delirium
RESPIRATORY:
Desaturation, decrease RR,
hypercarbia, apnea, airway
obstruction
• Management strategies
• No treatment
• Propofol/midazolam; protect
from injury, airway control
(convert to GA), hemodynamic
stability, add phenytoin
• Ice saline (4 C) on cortex
• Identify cause, increase sedation,
wake patient up / convert to GA
Identify cause, stop/ decrease
sedation,airway adjustment,
convert to GA

37. Hemodynamic Disturbances:
• Hypertension, tachycardia
• Hypotension, bradycardia
• Nausea, vomitting
• Tight brain
• Anxiety, inadequate analgesia.
Ensure adequate sedation,
antihypertensives if required
• Hypovolemia, excessive sedation,
drug effect, trigeminocardiac
reflex. Treat with fluids,
vasoactive agent, appropriate
sedation
• Treat cause, give antiemetics/
propofol/ minimize opioids,
adequate hydration
• d/t Airway obstruction,
hypercarbia. Encourage
hyperventilation, head elevation,
mannitol

38. • Neurologic deficits
• Pain
• Anxiety/ fear
• Venous air embolism
• May be temporary. Exclude ICH,
stroke
• During pin fixation, dissection of
temporalis, traction of dura,
manipulation of intracerebral
vessels.
Give LA, analgesia
• reassurance, sedation, analgesia
• d/t open venous sinuses or veins
from burr hole or craniotomy. c/f
cough, chest pain . Warn
surgeons, irrigate surgical area
with saline, head down if
possible,administer 100% FiO2,
supportive care

39. 2. Resection of epileptogenic focus under GA:
Anaesthetia for resection under GA with / without brain mapping, ECoG is similar.
Pre- operative and intra- operative managements are almost similar.
Inhalational or propofol- based TIVA
For intraop. ECoG/ Cortical mapping –
• Anaesthetic agent given should not provoke seizure
• BZD premedication avoided, small dose narotics prefered as anxiolytics
• Inhalational agent / TIVA stopped before ECoG; during thid low dose
dexmedetomidine/ remifentanil infusion given
• Seizurogenic effects of enflurane (0.78 MAC) , etomidate (0.2 mg/kg), methohexitol
(25- 100mg) used to identify epileptic foci
For Motor and sensory function mapping- EMG, DES – triggered muscle motor- evoked
potential, SSEPs; during this TIVA with propofol commonly used

40. • No C/I to emergence and extubation immediately after resection
• Most AEDs have sedation, somnolence- side effect, slow emergence common
• Complex surgeries likely to delay emergence and require icu care
Post operative management:
• Rapid emergence helpful for post- op neurological assessment (long AED therapy
cause lethergy, slow emergence)
• Phenytoin d/t intra- op seizure – delay emergence
• Coughing, bucking, hypertension – increase intracranial bleeding risk , CSF leak -->
avoided
• Prophylactic antiemetic given to avoid nausea, vomiting
• If AED tapered/ discontinued prior surgery – BZD ,propofol ,phenytoin administered
to control seizure

41. Neurostimulation for Drug – resistant Epilepsy
• Alternative to failed AED
Reduce seizure occurance by manipulating vagus/ trigeminal/ deep brain stimulation
or by interfering with repetitive transcranial magnetic stimulation/ direct cortical
stimulation
Vagus nerve stimulation:
Cause activation of NTS ,brain stem centre  activate limbic system, noradrenergic
neurotranamitter/ generalized brainstem arousal system modulate cerebral
neuronal excitability
Peri operative Concers:
AED continued till morning
Done under GA ; Hyperventilation avoided
Vocal cord palsy ; Cardiac complications during vagus (right>left) manipulation –
bradycardia , ventricular asystole
Seizure; Change in post op mental status
Post op respiratory distress – peritracheal hematoma(emergency)

42. AWAKE CRANIOTOMY
• It is a procedure where patient is awake to allow neurological testing
Indications
• epilepsy surgery
• resection of supratentorial intra – axial tumors located near or within
eloquent areas of brain, controlling somatosensory, motor, language and
executive functions,
• vascular malformations
• infratentorial tumors
• tumors with extensive dural involvement

43. Anaesthetic techniques
1. Conscious sedation:
Aim- achieve sedation score of around 3 on Modified Observer’s Assessment of
Alertness/sedation
Patient respond only after their name is called loudly or repeatedly
Drugs used – propofol infusion (50 – 150 mcg/kg/min), boluses of fentanyl (0.5 -
1mcg/kg) or remifentanil infusion (0.01 – 0.05 mcg/kg/min), dexmedetomidine
infusion (0.2- 0.7 mcg/kg/hr) after a bolus dose of 0.5 – 1mcg/kg over 10 min
Procedure:
• Sedation administered during initial stimulating parts of procedure, then stopped
or reduced during cortical mapping and resumed for resection and closure
• Spontaneous ventilation is maintained with oxygen supplement via face mask, if
needed nasopharyngeal airways used

44. 2. Asleep – awake – asleep technique:
• GA induced with propofol and maintained with infusion dexmedetomidine,
propofol/volatile anaesthetics
• Analgesia with fentanyl / remifentanil
• Airway include spontaneous ventilation or controlled ventilation
• After opening dura, patient is awakened and airway removed for cortical mapping
(propofol infusion terminated 15- 20 min prior)
• After mapping, GA induced again with/ without controlled ventilation
• Advantage:
Comfortable and stress free environment for patient during painful part of
procedure, Facilitates patient cooperation during cortical mapping
• Risk:Laryngospasm , uncontrolled cough – increase ICP,bleeding

45. Thank you