• Advancement in imaging technology and the growing field of interventional neuroradiology have increased the need for anesthesia services in the "out-of-OR" setting. However, several challenges exist:
  • Radiation exposure hazards: Early effects of ionizing radiation are dose-dependent and risk increases with increased radiation dose (may occur many years after exposure).
  • Special OR setup: Suites are often crowded by large radiology equipments that are difficult to move; the anesthesia space is usually small; large radiation protective shields and heavy aprons can make movement and access to the patient difficult; the airway can be distant from the machine and anaesthetist; the room is dark; and paramedical personnel are not familiar with anesthesia support (experienced help is often remote).
  • MRI hazards: Ferrometallic materials can be projectile and may cause accidents; electric noise can distort monitored waveforms; acoustic noise may present a distraction; electromagnetic waves can cause patient burns in areas of contact with monitor cords or in the presence of metallic implants; and in an emergency situation it takes 90 seconds to retract the magnet tube and have a crash cart in the room (patient may need to be removed from the room).
• Angiographic interventions can be broadly classified as those that:
  • Obliterate the lumen. Embolization of cerebral and dural arteriovenous malformation (AVM), vessel-feeding tumors, cerebral aneurysms, and fistulae.
  • Open the lumen and revascularize. Angioplasty of atherosclerotic lesions and thrombolysis or thrombectomy of acute thromboembolic stroke.
• Intraoperative magnetic resonance imaging system (IMRIS) is used for the:
  • Resection of brain tumors
  • Implantation of deep brain stimulators (DBS) and electroencephalographic (EEG) electrodes
• Anesthesia is usually requested for diagnostic procedures in:
  • Pediatric patients
  • Uncooperative or claustrophobic patients
  • Patients with complex medical problems when strict hemodynamic monitoring is needed

• Diagnostic and interventional angiographic procedures: Supine with arms tucked
• Intraoperative MRI: Supine, prone, lateral, and semi-sitting position have been reported.

• Diagnostic and interventional procedures: Typically via femoral catheterization; however, carotid or brachial arteries may be utilized.
• Intraoperative MRI: Craniotomy incision

• Diagnostic: ~30–60 minutes
• Angiographic interventional procedures: ~4–6 hours
• Intraoperative MRI: ~4–6 hours

• Diagnostic and interventional angiographic procedures: None to minimal
• Intraoperative MRI: ~50–500 mL, depending on the location and size of the lesion, and complexity of the procedure

Diagnostic procedures: Out-patient or in-patient

• Contrast material
• Endovascular catheters to deliver coils, detachable balloons, and embolizing agents
• MRI suite specially equipped to provide surgery with compatible anesthesia machines, monitors, and other equipments

Incidence

• In 2009, an estimated 40,663 cerebral angiograms, 109,000 angioplastic carotid endarterectomies, and 700,000 endovascular aneurysmal repairs were performed.
• In 2010, ~1,047 neuro interventional MRI procedures were performed; this is a 300% increase over 5 years since its start.

See "Complications"

IV contrast: 1 out of 170,000 reactions

History

• NPO status
• Shellfish, iodine, IV contrast, or protamine reactions
• Ability to lie flat, snoring, sleep apnea
• Acquired or implanted metallic devices, extensive tattoos, permanent eye make-up

Signs/Physical Exam

• Depends on diagnosis or indication and can include a baseline-focused neurologic exam, Glasgow Coma Scale, disease-specific scoring system (Hunt Hess for subarachnoid hemorrhage and NIHSS for stroke)
• General medical and airway exam

Labs/Studies

• BUN/Cr is often attained prior to IV contrast.
• Depends on comorbidities

• Anxiolysis as needed; caution or avoidance in elderly or altered patients as well as epileptic patients for EEG electrode implantation
• Stroked patients may present with a full stomach; gastric acid and volume-reducing medications should be considered.
• Parkinsonian patients scheduled for DBS should have their morning dopaminergic and anticholinergic medications held.
• Tumor patients may require re-dosing of steroids or antiepileptics.
• Corticosteroids and possibly an antihistamine may decrease the incidence of contrast reactions in "at-risk" patients.
• Radiation safety: Lead aprons, thyroid shields, and protective eye goggles should be considered, as appropriate, for the patient (as well as the anesthesia provider!)
• Setup should be meticulous due to the difficulties encountered with patient manipulation once the procedure has begun.

• Pediatric patients require parent consent.
• Uncooperative or altered patients require a family member or power of attorney consent.

• Diagnostic and interventional angiographic procedures: Usually considered clean procedures; antibiotics are given only in high-risk procedures.
• Intraoperative MRI: Skin organisms, third-generation cephalosporins are usually given.

• Diagnostic procedures may need minimal or conscious sedation and can be performed by non-anaesthetists certified in administering sedation. Anesthesia care providers are often called upon to provide deep sedation/analgesia or general anesthesia; the choice is based upon the procedure, positioning, comorbidities, access/nearness to the patient, and ease of ventilation or intubation in the event that the patient obstructs or becomes apneic.
• Interventional: Typically general anesthesia; deep sedation/analgesia is used in some revascularization procedures.
• Intraoperative MRI: GA. Awake craniotomy is sometimes needed to resect a tumor under MRI near eloquent area.

• Standard ASA monitors
• Intra-arterial pressure monitoring for interventional procedures and intraoperative MRIs
• Neurophysiologic-evoked potential monitoring in some spinal cord pathology embolization procedures
• Intracranial pressure (ICP) monitoring
• Activated clotting time (ACT)
• Neuromuscular twitch monitor
• Neurologic exam in patients under MAC
• Foley catheter to measure urine output
• Oropharyngeal temperature probes will interfere with the angiography pictures; axillary or skin probes are better options. In IMRIS a fiberoptic probe can be used in the groin.

• Be prepared to induce anesthesia and manage the airway in a less than optimal position.
• Extra-long breathing tubes and infusion lines are needed because anesthetic equipments are often relocated after induction to allow for imaging equipment to move freely or to move to safer magnetic fields in MRI scanners.
• Some iMRI suites have an induction room outside the scanner. This provides free access to all anesthesia equipments at induction; the patient is then transported with assisted/controlled ventilation (Ambu bag, Bain circuit) to the scanner.
• An ETT with muscle relaxation can provide a more secure and controllable airway, along with extreme immobilization compared to an LMA.

• Pressure points are secured meticulously since the patient is going to be covered and arms tucked with limited access.
• Renal protection for contrast: No proven strategy is agreed upon; preoperative hydration for impaired renal function is usually used. Approximately 2/3^rd of the severe and fatal contrast reactions occur within the first several minutes.
• Heparinization is required whenever catheters are introduced into blood vessels. ACT monitoring is utilized to guide therapy. Protamine should be standby whenever heparin is used.
• Antiplatelets are used by the neurointerventionalist after the procedure.

• Avoid patient coughing, bucking, or straining which can cause hypertension and increased ICP.
• Patient should be awake enough to have a neurologic exam.