MRI

Key Points:

  1. MRI safety awareness

  2. Evaluate risk vs benefit of anesthesia on add-on patients

  3. In an emergency, call for help early and remove patient from zone IV

General:

  • Unlike CT, MRI uses no ionizing radiation. In presence of external magnetic field a ferromagnetic object (anything with iron content) can develop its own intrinsic magnetic field which can propel the object toward the scanner (O2 tank, stethoscope, pump, laryngoscope handle, stylet).

  • The MRI generates radiofrequency radiation that is absorbed by the child and may offset heat lost to the environment. Warm blankets wrapped around patient, no bair hugger needed. Children may become hyperthermic during longer scans.

  • Contraindications:

    • Hemodynamic instability (including patients with arterial lines)

    • MRI incompatible metal (must look up i.e. metal surgical clips or coils, pacemaker, prosthetic heart valves, fresh surgical clips [ex. recent PDA ligation], cochlear implants)- check with MRI tech

    • Tracheostomy tubes should be checked before the children enter the MRI scanner. It is generally advised to switch a child’s tracheostomy tube to a cuffed tracheal tube for MRI scanning to ensure a secure airway during the scan. Currently small-diameter cuffed tracheostomy tubes (Bivona) are considered MRI-conditional (at www.MRIsafety.com, search for the MRI-compatible object to determine MRI compatibility).

  • If difficult airway or IV access, consider inducing in OR on 3rd floor (video-laryngoscopes and ultrasound are not MRI compatible).

  • Gadolinium is the primary agent in use and have a higher safety margin than iodinated contrast agents. Adverse reactions occur in ~1% of patients and include headache, N/V, dizziness, hemodynamic instability, dysrhythmias, and nephrogenic systemic fibrosis. Gadolinium should only be administered if necessary in children with advanced kidney failure then prompt dialysis considered following scan.

  • MRI zones:

    • I- general public

    • II- unscreened MRI patients; immediately outside area of hazard

    • III- Strictly restricted; MRI scanner’s environment

    • IV- MRI scanner magnet room

  • In case of emergency inside of MRI: Initiate CPR while immediately removing the patient from zone IV to the "designated resuscitation area”, call for help (x728## for anesthesia STAT), transport the patient to the designated safe location outside of the MRI suite, apply 100% O2, and emergency response personnel should be restricted from entering zone IV.


Location:

  • From family waiting room à go to the end of the hallway à straight in front will be a set of stairs to go down with a sign "cytology” à elevators will be on the right à take the stairs on the right, past the elevators to first floor à turn right à straight in front will be a buffalo picture à follow MRI signs


Flow:

  • NO metal in scanner- ALWAYS think before entering.

  • In MRI suite, turn on vital sign monitor (bottom first then monitor).

  • In control room, turn on monitor (on right side) and pump. Ensure capsule on (below monitor).

  • No pipeline N2O, turn on tank in morning and remember to turn off tank at end of day.

    • Be careful changing tanks on anesthesia machine- MUST be MRI compatible.

  • Chart on centricity outside of room, use Peds MRI script.

  • Must add patients manually in morning.

  • Nurse will spike IV fluids and have IV setup ready.

  • May go in and out during MRI scan but quickly shut door.

  • Restock room, break down machine, and turn N2O tank off at end of day.


Set up:

  • 5-10 mL propofol syringe for bolus depending on size

  • 20-50 mL propofol on MRI pump depending on size/length of scan

  • 500 mL LR with microdrip/buretrol

  • Green EtCO2 (longer)

  • Straight connector (attach to EtCO2 and place with elbow, remove elbow after induction)

  • Circuit extension (placed after induction)

  • Emergency drugs: Epi, succinylcholine, and atropine with syringes + IM needles + flush

  • Emergency airway: appropriate sized ETTs, LMA, and oral airway


Preoperative:

  • Tests- as indicated by H&P

  • Premedication- PO versed may be utilized although most patients are induced with parents present

  • Thorough questioning regarding potentially ferromagnetic implants (neurostimulators, cochlear implants, pacemakers, surgical clips, infusion pumps, etc.) is critical.

  • Need separate anesthesia consent.

  • Brain: if signs/symptoms of ­ ICP are present (2o to tumor or hydrocephalus), anesthesia plan should be ETT with controlled ventilation

  • Abdomen: MRI 1; ETT with controlled ventilation (Roc/sugammadex) due to need for breath holds.

  • Rapid Sequence Induction: May be needed if patient has vomiting 2/2 intracranial process and scan is required for surgical planning.


Intraoperative:

  • Anesthetic technique- general with LMA

  • Position- supine, arms at side

    • Ensure patient, IV, and monitors are well padded and not touching patient.

  • Special instrumentation- ear plugs

  • Surgical time- 0.5-3 h (depending on area- brain and spine w and w/o longest 3 h, brain w/o shortest 0.5 hr)

  • 1 PIV

  • Standard monitoring- MRI compatible equipment (InVivo monitor with skin temp probe)

  • Complications- hypothermia, burn injury, IV contrast reaction, hearing loss

  • Induction

    • Parent usually accompanies child to scanner.

    • Click patient in room first before entering MRI.

    • Inhalation induction unless IV present.

    • If ETT used, be careful with blade. Do NOT set it down after DL (must hand it off).

    • Maintain spontaneous ventilation, +/- PSVPRO (usually used if scan length > 1h).

    • Attach circuit extension after induction.

    • Ear plugs placed by MRI tech.

    • Ensure pilot balloon is taped on circuit (spring in pilot balloon can cause imaging artifact)

    • Before leaving scanner after induction, ensure IV fluid running appropriately.

  • Maintenance

    • 0.5 MAC Sevo (1-1.5%) + 100 mcg/kg/min Propofol

    • Check timeout time with nurse.

    • No narcotics needed.

  • Emergence

    • Extubate deep unless contraindicated in scanner- 100% O2, d/c propofol, increase sevo to 4-5%.

    • Keep sevo on until move to stretcher to for patient to remain deep for transport.


Postoperative:

  • Patients will be recovered in MRI PACU until discharge criteria met.


Cottrell, J. E. & Young, W. L. (2010). Cottrell and Young’s Neuroanesthesia (5th ed.). Philadelphia, PA: Esevier/Saunders.

Vargo, M. (2016). Vargo Anesthesia (7.51) [Mobile application software]. Retrieved from http://www.vargoanesthesia.com