Interventional Neuroradiology

The curriculum asks for knowledge of 'the principles of anaesthesia for neuroradiology'.

Resources

The scope of interventional neuroradiology is increasing; a broad range of indications exist for a variety of complex, lengthy procedures
Evidence for IR techniques is growing and anaesthetic input will be required for increasingly complex patients

Some patients will require straightforward neuroimaging, which does not require anaesthetic input
Equally, some procedures may be possible under LA only
Anaesthesia can:

Improve patient comfort
Improve image acquisition by ensuring patient immobility
Facilitate manipulation of physiology
Manage complications

Diagnostic

Patients may require elective, or emergency, CT or MRI imaging of the brain
The highest quality images are produced using digital subtraction angiography (DSA)

The neurovasculature is delineated using IV contrast
This image is then superimposed onto live, bone-subtracted fluoroscopy
This allows radiologists to review the progress of catheters through the vasculature

Therapeutic

Vascular	Other
Endovascular coiling or embolization of intracerebral aneurysms	Intra-arterial chemotherapy
Endovascular embolization of AVM or fistulae	Mechanical thrombectomy
Pre-operative embolization of cerebral or spinal tumours	Stereotactic surgery
Embolization for epistaxis	Pain procedures e.g. trigeminal ganglion ablation
Investigation of idiopathic intracranial hypertension ± venous angioplasty or stenting
Sclerotherapy for venous angioma
Balloon angioplasty for carotid stenosis or vasospasm

Patients present across the spectrum of acuity:

Elective patients undergoing primary prevention techniques following e.g. incidental finding of an aneurysm, AVM or other intracranial pathology
Patients undergoing urgent neuroradiological procedures e.g. cerebral angiography and endovascular coiling of SAH
Emergency treatment of sudden neurological injury e.g. mechanical thrombectomy for thrombotic ischaemic stroke

Environmental/general considerations

Remote-site anaesthesia
Radiation safety
Poor lighting
Restricted access to patient, in particular the airway where the X-ray arm/scanner needs to move about
Monitoring should be AAGBI standard + temperature monitoring + urinary catheter (large volumes of flush, contrast and risk of DI)
Airway and vascular access should be securely fastened and have long circuits/extension lines
Risk of VTE

Anaesthetic and IR considerations

Neurosurgical-style anaesthetic to provide smooth, rapid wake-up
May require transfer of critically unwell patients to/from IR suites

Anticoagulation

Patients are anticoagulated with IV heparin
They undergo activated clotting time (ACT) monitoring to achieve a time of 270 - 390s i.e. 2 - 3x normal
This aims to reduce the risk of vessel thrombosis

Administration of other anticoagulant drugs may be required:

Aspirin
Abciximab (intra-arterial)
Clopidogrel

There is a risk of spontaneous bleeding and/or major haemorrhage

Perioperative management of the patient undergoing interventional neuroradiological procedures

History and examination

Neurological deficits prior to induction/intervention
Current GCS | pupillary responses
Symptoms of raised ICP
PMHx, DHx and allergies inc. risk factors for SAH e.g. hypertension, smoking
Previous neurosurgical procedures
Risk of contrast-induced nephropathy or contrast-associated reactions (or shellfish reaction)
Negative pregnancy test in female patients

Investigations

FBC | Clotting screen | G&S

Baseline haemoglobin is important in view of potential for peri-operative bleeding
Identify existing coagulopathy
May need to pre-order blood or other blood products

U&E | Glucose

Patients with head injuries or aneurysmal bleeds commonly have electrolyte disturbances
Particular attention to hyponatraemia, which may indicate SIADH or CSW
Hyperglycaemia potentiates the injurious effects of cerebral hypoperfusion

ECG; arrythmias and myocardial ischaemia are associated with SAH and TBI

Review of previous imaging; grade of SAH (Fisher score or WFNS Score) can allow fully informed discussion with patient/relatives

Anaesthetic goals include:

Haemodynamic stability and maintenance of CPP
Patient immobility
Rapid management of complications including haemorrhage
Smooth, rapid emergence to avoid undesirable effects on ICP/CVP
Analgesia

Monitoring and access

AAGBI
Wide-bore IV access is required in case of major haemorrhage
Arterial line
Urinary catheter due to long procedures, risk of DI and large volumes of contrast and flush used
Temperature monitoring and management as long procedures and negative sequelae of hypothermia

Induction

Haemodynamic stability is key:

Avoiding surges in blood pressure which will increase transmural pressure and risk rupture of unsecured aneurysms
Avoiding hypotension which will compromise CPP and risk cerebral hypoperfusion

Choices to obtund pressor response include:

Fentanyl (2 - 3μg/kg) or alfentanil
TCI remifentanil
Β-blockers e.g. labetalol 20 - 50mg IV, esmolol IV
IV lidocaine 1.5mg/kg

Otherwise induction agent and NMBA of choice may be used

Patients should be intubated e.g. reinforced ETT or S-F RAE

SAD are typically unsuitable for neuroradiology
Tube should be secured fastidiously, as there will be limited intra-procedural access

Maintenance

Both TIVA and volatile techniques are appropriate

Propofol/remifentanil TCI provides haemodynamic stability, leaves CBF and CMRO₂ coupled and may preclude need for further paralysis
Sevoflurane will leave CBF and CMRO₂ coupled below a MAC of 1.5

Analgesia

Angiography alone is only minimally stimulating
Dural interference and tumour embolization may be stimulating

Managed with opioids, either infused (remifentanil) or as boluses (fentanyl, alfentanil)
Avoid long-acting opioids which may cloud post-operative neurological assessment

Emergence

Aim for a smooth, rapid wake-up to:

Avoid rises in ICP associated with coughing or straining
Allow early neurological assessment

Patients may require HDU care for ongoing haemodynamic monitoring, neurological monitoring and/or BP management

CNS complications	Non-CNS complications
Coil displacement / coil fracture	Contrast anaphylaxis
Vasospasm	Contrast nephropathy
CNS haemorrhage - Perforated aneurysm (2 - 19%) - Intracranial vessel injury or dissection	Non-CNS haemorrhage - Puncture site - Groin haematoma - Retroperitoneal haematoma
	Displacement of lines/tubes by moving XR arm

Haemorrhage

May be spontaneous, iatrogenic or related to surges in BP from inadequate anaesthesia
Management

Alert the radiologist
Depending on the stage of procedure and degree of bleeding, coiling may continue or transfer to theatre may be required for ventriculostomy or rescue craniotomy and clipping
Rapid BP reduction e.g. deepen anaesthesia, IV labetalol
Reversal of anticoagulation e.g. protamine 1mg per 100 units of initial heparin dose
Control of raised ICP if CNS haemorrhage; may require emergency craniotomy and clipping

Vessel occlusion

Thromboembolic events or misplacement/fracture of coils can occur
In thrombotic occlusion, management involves:

Direct lysis e.g. abciximab
Antiplatelet agents e.g. IV aspirin
BP manipulation to increase blood flow to ischaemic areas e.g. raise BP 30 - 40% above baseline

Vasospasm

Comprises of arterial constriction, seen angiographically, which causes clinical signs i.e. neurological deterioration
Thought to be mediated by the presence of extravasated blood in the subarachnoid space
Management involves:

Adequate systolic blood pressure (140 - 160mmHg in unsecured aneurysm, 160-180mmHg in secured aneurysms)
Euvolaemia
Prophylactic nimodipine for patients with a diagnosis of SAH for 21 days

60mg enterally every 4hrs
200 - 2,000μg/hr IV infusion (1 - 10ml/hr of a 200μg/ml solution)

Delayed cerebral ischaemia

A clinical syndrome occurring 4 - 12 days post-aneurysmal SAH
May take form of:

Symptomatic vasospasm
Delayed neurological deficit; typically focal neurological or cognitive deficits
Asymptomatic, delayed cerebral infarction

The only proven therapeutic intervention is nimodipine

Intra-operative MRI (iMRI) techniques are improving

Repeated scanning during surgery helps improve lesion resection or device manipulation
May improve clinical outcomes and provide economic benefit by avoiding repeated interventions

In stereotactic neurosurgery, various 'rings' are applied to the patient's skull and CT or MRI used to map the area of interest, which further restrict airway access