Carotid endarterectomy:

 

Surgery:

Indications

·      TIA and >70% stenosis (NNT 6)

·      TIA and >50% stenosis (NNT 22)

·      Asymptomatic: unclear

·      Urgent procedure

Procedure

·      Expose vessels

·      Isolate bifurcation with clamps

·      ±Shunt

o  High risk anatomy

o  Sign of intra-op ischaemia

·      Endarterectomy

·      Closure

 

Anaesthesia:

Main goals

·      No stroke

·      No AMI

·      No airway disaster

·      No haemorrhage

Pre-assessment

·      Severity of CVD? (TIA, % stenosis, contralateral disease)

·      Presence of CAD? (angina, 12 lead ECG, consult cardiology if severe or unstable)

Preparation

·      Big long IV (in case of bleeding)

·      Arterial line with transducer at brainstem level (BP watch)

·      +/- NIRS

Induction

Drugs:

·      Metaraminol infusion

·      Remifentanil TCI (↓pressor response to laryngoscopy)

·      Propofol 2.5mg/kg

·      Rocuronium 0.6mg/kg

·      IV fluid bolus 10mL/kg

Airway:

·      Remote + shared

·      Must intubate

·      Secure with sleek + tegaderm

Maintenance

Drugs:

·      Sevoflurane 1.4-2%

·      Remifentanil TCI (↓propofol accumulation hence ↓time to neuro assessment)

·      Muscle relaxant (maintain immobility)

·      Heparin upon request

Targets:

·      Keep mAP 20% above baseline during clamping

·      Keep CO2 normal

·      Keep O2 normal

Communication:

·      Clamping and unclamping

·      Carotid manipulation

·      Anticoagulation (ACT 250-300)

Emergence

·      Awake extubation with remi TCI 1-2ng/mL

·      Avoid coughing

Post-op

·      Recommend HDU care

·      Airway complications

·      Cardiac complications

·      Neuro complications

·      Monitoring includes: ABP, ECG, neuro-obs

 

Problems and solutions: GA

Airway

 

   Remote during operation

·      ETT tube

·      Check depth by auscultation

·      Check for leak

·      Secure well with tape or trachie tie

·      Beware migration during head extension – secure deeper rather than shallower

   Risk of swelling/haematoma

·      Rx: relieve obstruction, beware difficult re-intubation

   Risk of RLN injury

·      Dx: stridor

·      Rx: IPPV, ICU care

Cardiovascular

 

   Induction

·      Drugs -> ↓BP (Rx metaraminol infusion)

·      SNS -> ↑BP (Rx remi TCI)

   Intubation

·      SNS -> ↑HR, ↑BP

   Extubation

·      Awake extubation with remi TCI

   Cross-clamp

·      Effect: SNS -> ↑HR, ↑BP, ↑MVO2

·      Aim: SBP ↑20%

   Carotid sinus manipulation

·      PSNS -> ↓HR, ↓BP

·      Rx: surgeons stop, local infiltration, +/- atropine

   Risk of AMI

·      Coronary artery disease very common

·      Monitoring: 5-lead ECG + arterial line

·      Prevention:

o   Metaraminol to ↑coronary perfusion pressure

o   Remi to ↓MVO2 and ↑coronary perfusion time

   Hyperperfusion syndrome

·      Rare but 40% mortality

·      Due to impaired cerebral autoregulation on the operative side

·      Hypertension -> headache, bleeding, swelling, seizure

·      Onset in first few days

·      Rx: anti-hypertensive, stop antiplatelet, send to ICU

Neurological

 

   Ischaemic stroke

·      MCA territory

·      Arterial line

·      Transducer at level of external acoustic meatus = brainstem

·      Metaraminol infusion

·      Aim mAP within 20% of pre-induction BP

·      Therapeutic hypertension during clamping

·      Neuro-monitoring

·      Especially important if contralateral disease or incomplete circle of Willis

   Haemorrhagic stroke

·      Arterial line

·      Remifentanil

·      Antihypertensives

   Embolic stroke

·      MCA territory

·      Mainly the surgeon’s business

·      Major cause of peri-op stroke in CEA patients

·      Ensure aspirin started pre-op

Miscellaneous

 

   Pre-op meds

·      Start aspirin

·      Start statin

·      Start antihypertensive (but withhold ACEi on day of)

·      Continue beta blocker (but don’t start anew)

 

Regional techniques:

Sedation

·      Midazolam 0.025mg/kg prior to block

·      Dexmedetomidine 1mcg/kg load then 0.3mcg/kg/h infusion

Superficial plexus block

·      Enter skin behind SCM

·      Pierce prevertebral fascia

·      5-15mL

Deep plexus block

·      50mm, 25g needle

·      Enter skin behind SCM

·      Hit transverse process of C3

·      Inject

Complications

·      Vertebral artery injection -> seizure

·      Subarachnoid injection -> LOC

·      Horner syndrome

·      Blockade of phrenic, (vagus) recurrent laryngeal

·      Need for conversion to GA

 

Neuromonitoring:

Upshot

·      No method is proven to produce better outcomes

Clinical

·      Awake neurological exam

Electrical activity

·      Unprocessed EEG

·      Processed EEG (e.g. BIS)

·      SSEP

Perfusion

·      Carotid stump pressure

·      Transcranial doppler

Oximetry

·      Jugular venous bulb sats

·      Cerebral oximetry (NIRS)

o   A sticker on either side of the forehead

o   Normal 60-80%

 

GA vs LA:

LA > GA

Logistics:

Neuro exam possible

Medical:

EEG unaffected

Preserved CNS autoregulation

↓AMI, CHF in-hospital

GA > LA

Logistics:

Motionless

Comfortable

Avoid risk of conversion

Medical:

Decreased CMRO2

GA = LA

At 30 days:

Stroke

AMI

Death

 

Note:

Selection bias: LA patients older, comorbid

BP manipulation bias: more in GA group

Impression is that LA is neurologically safer in high risk patients