• For intraoperative functional cortical mapping forlesions close to eloquent areas.• For localisation of epileptic foci, during intraoperativeelectrocorticogram (ECoG).
Indications• Epilepsy Surgery• Excision of lesions adjacent to eloquent areas of the cortex inthe dominant hemisphere• Stereotactic surgery
• Deep brain stimulation (DBS) surgery for Parkinsonsdisease• Pallidotomy, Thalamotomy• Ventriculostomy, Endoscopy, Excision of small lesions
Contraindication• Inability to cooperate or communicate– Small children– Decreased level of consciousness– Profound confusion– Mental Retardation– Severe Language Barrier• Highly vascular lesion with significant duralinvolvement.• Obstructive Sleep Apnoea• Morbid Obesity
Anaesthetic aims1. Maintaining patient cooperation:Optimal analgesic care.Adequate sedation and anxiolysis during the differentstages.Comfortable position.Nausea, vomiting and seizure prevention.
2. Homeostasis:Safe Airway and adequate ventilation.Hemodynamic stability.Normal intracranial pressure.3. Most important for epilepsy surgery: Limited interference with electrophysiological recordings.
TechniqueNumerous techniques have evolved along with surgicalindications:– MAC (Monitored Anaesthesia Care)– AAA (Asleep-Awake-Asleep)
MAC (Monitored Anaesthesia Care)• According to the ASA, MAC is a specific anaesthetic protocolthat includes careful monitoring and support of vital functions.• The anaesthetist administers sedatives, analgesics, andhypnotics, addresses any clinical problems, and provides thepatient with psychological support during diagnostic andtherapeutic procedures.• The ASA recommends that the provider of MAC must beprepared and qualified to convert to general anaesthesia, ifnecessary.
AAA (Asleep-Awake-Asleep)• AAA anaesthetic approach consists of general anaesthesiabefore and after brain mapping.• In the 1950’s, Penfield described blind nasotracheal intubationafter cortical mapping.• In same year, Hall & Ingvar, used nasotracheal intubation tomaintain the tracheal tube during craniotomy for intractableepilepsy.
• In 1993, Weiss placed a tracheal tube in one nostril at 22 cm inorder to support ventilation during propofol administrationwith N2O general anaesthesia.• In 1998,. Huncke et al gave great force to the AAA techniquefor epilepsy surgery by reporting 10 cases, who were intubatedawake using a fibreoptic laryngoscope before & after brainmapping.
Brain mapping• Originally used for epileptic surgery, is now utilized for tumorresection.• More widely used within the last 2 decades.• Identifies:– Regions of language representation (dominant cerebralhemisphere)– Motor cortex (either hemisphere)
Cont..• Intra-op mapping helps distinguish between eloquent cortexand tumor tissue, which facilitates:– Accessing the tumor from safest transcortical route.– Aggressive tumor resection while preserving functionaltissue.
Brain Mapping: Language• Indicated if the surgical site is near language associatedcortical sites or “speech areas”– Broca’s(expression): posterior/inferior/frontal lobe of dominanthemisphere.– Wernicke’s(comprehension): posterior/temporal lobe ofdominant hemisphere.• Direct electrical stimulation of the cortex during languagetasks while observing for speech hesitation, arrest ordysnomia.
Brain Mapping: Motor• Grid of electrodes placed on brain surface to identify a phasereversal of SSEPs recorded over the posterior sensory cortexand precentral motor gyrus.• Direct electrical stimulation of the cortex to elicit motormovement.• MEPs, more recently, used to map and monitor subcorticalmotor pathways.
Depth of Anaesthesia• Bispectral Index: Measures anaesthetic depth (correlates withhypnotic component of anaesthesia)– 40-60 (asleep phase)– >85 (awake phase)• Entropy: Another method of assessing anaesthetic depthcommercially developed by Datex-Ohmeda.– RE (Response Entropy)– SE (State Entropy)
Preoperative Evaluation• Patient’s Preparations:– Obtaining the patient’s confidence & agreement tocooperate during surgery is key.– Developing good rapport with pt & their family is crucial.– Inform pt. of our expectations of them during the awakephase… and what they can expect from us....“Commitment, safety, comfort.”
Contd..• Aspects to be considered in Preoperative evaluation:– Upper airways:• Prediction of difficult tracheal intubation (physicalconfirmation and past intubation)• Obstructive apnea risk (obesity, sleep apnea,retrognathia)– Epilepsy:• Pharmacotherapy• Antiepileptic drug serum concentration• Type & frequency of seizures
Contd..– Nausea & Vomiting:• Past anaesthesia• Kinetosis (Motion Sickness)– Intracranial pressure estimation:• Type of lesion• Radiological & clinical signs– Hemorrhagic risk:• Type & localization of lesion• Therapy (Antiplatelet drugs)• Medical history
Contd..– Patient cooperation:• Anxiety• Pain tolerance• Neurological deficits“A visit to the operating room before surgery is a good idea inorder to familiarize the patient with the sounds & equipment inthe operating rooms”.
Premedication• There is no general consensus regarding premedication, anddecisions should be made based on the patient’s clinicalcondition, the anaesthetists opinion, and hospital standards.• Some anaesthetist do not administer any premedication.
Contd..• NSAID’s (e.g diclofenac or acetaminophen)• α- 2 adrenoceptor agonists (e.g. Clonidine, demetomidine)• Antiepileptics as per the treatment protocol of the patient.• Any other medications patient is taking for any other systemicmanifestation.“Most important of all is the thorough explanation of thePROCEDURE”
Local Anaesthesia• Anaesthetic care always includes scalp block.• A 40 to 60 mL of local anaesthetic volume is used forinfiltration.• High local anaesthetic volume and well-vascularized areasmay predispose to anaesthetic toxicity.• The use of adrenaline (5 μg/mL, 1:2,00,000 dilution) bothminimizes acute rises in plasma anaesthetic concentration andmaximizes the duration of the block.
Contd..• Clinical vigilance is particularly indicated within 15 minutesafter scalp block.• With regards to toxicity, ropivacaine and levobupivacaineappear to be safer than bupivacaine.• Despite this difference, bupivacaine is the most commonlyused local anesthetic in the literature.
Nerves Block1. Auriculotemporal nerve (mandibular branch of trigeminalnerve): infiltration over zygomatic process and distaltemporal artery.2. Zygomaticotemporal nerve (zygomatic nerve’s terminal rootthat originates from maxillary branch of trigeminal nerve).3. Supraorbital nerve (root of frontal nerve which originatesfrom ophthalmic branch of trigeminal nerve): infiltration fromthe nasal root to the midpoint of the eye.
Contd..4. Supratrochlear nerve (root of frontal nerve which originatesfrom ophthalmic branch of trigeminal nerve): infiltrationtogether with supraorbital nerve.5. Greater occipital nerve (posterior ramus of C2): infiltrationabout 2.5 cm lateral to the nuchal’s median line, directlymedial to occipital artery.6. Lesser occipital nerve (anterior branches of C2 and C3):infiltration 2.5 cm lateral to greater occipital nerve one.
Maintanence of Anaesthesia• Propofol: Widely employed for neurosurgical anesthesia (andawake craniotomy) due to:– Easily titratable sedative effect– Rapid recovery with clear-headedness– Decreased CMRO2– Reduced ICP– Potent anti-convulsant properties– Antiemetic properties
Contd..• Remifentanil: Ultra short-acting opioid, is becoming more popular:– Rapid onset of action– Remifentanil has an ester linkage which undergoes rapidhydrolysis by non-specific tissue and plasma esterases. Thismeans that accumulation does not occur with remifentanil andits context-sensitive half life remains at 4 minutes after a 4 hourinfusion– Rapid awakening for neurologic testing– Smoother hemodynamic profile
• Dexmedetomidine: Alpha-2 adrenoceptor agent.– Sedative, anxiolytic & analgesic properties.– Imidazole derivative, greater specificity for the α-2adrenoceptor.– Distribution half life of 6minutes, with completebiotransformation by the liver & very little unchangedexcreted in urine & faeces.
Airway DevicesMonitored Anesthesia Care Asleep-Awake-Asleep
Surgical Related• Focal seizures• Generalized seizures• Aphasia• Bleeding• Brain swelling• Venous air embolism• Conversion to general anaesthesia
ConclusionAwake craniotomy for tumor resection involvingfunctional areas is a surgical approach that offers greatadvantages with respect to patient outcomes. This is a complextechnique that requires great patient and equipment engagement.Personal experience, careful planning, and attention arethe basis for obtaining good results.