Chapter 78

A full-term, previously healthy 20-month-old girl presents for MRI of the brain with and without intravenous contrast. The patient has been experiencing progressive nausea, vomiting, and headaches over the past 4 months.

• Laboratory: Blood urea nitrogen 22; creatinine 0.9

• Physical examination: Patient appears somewhat lethargic.

### PREPROCEDURE CONSIDERATIONS

Administering anesthesia in a remote location such as an MRI scanner is challenging because of patient inaccessibility, as well as the need for specialized MRI-compatible equipment. The scanner is always on. Absolutely nothing ferromagnetic is permitted inside the MRI scanner—this includes, but is not limited to, keys, pagers, phones, pens, needles, medication vials, stethoscopes, and oxygen tanks (unless specifically made out of MRI-compatible material). Credit cards and watch batteries can be ruined if taken inside the MRI. Many implants, such as pacemakers, aneurysm clips, and cochlear implants, are incompatible with MRI; if in doubt, it is best to check with the manufacturer. Gold and silver are okay, so most jewelry is not a problem. Many MRI centers will have a technician move a special wand over both patients and caregivers to ensure that there is no unknown source of ferromagnetic material. MRI imaging is not painful, but it does require the patient to remain absolutely still to obtain good-quality images. This is best accomplished with general anesthesia, using either general endotracheal anesthesia (GETA), a laryngeal mask airway (LMA), or propofol infusion and nasal cannula.

Because the patient has signs and symptoms of increased intracranial pressure (ICP), a rapid-sequence induction of anesthesia is indicated. Propofol and rocuronium are reasonable choices for induction agents. Oral premedication with midazolam may be helpful to prevent anxiety and facilitate IV placement, and to avoid possible further increases in ICP.

Make sure that there are no contraindications to the patient’s receiving IV contrast, such as an allergy or severe renal failure, and plan to keep the patient well hydrated.

### ANESTHETIC MANAGEMENT

• Use rapid-sequence intubation, and consider premedication with oral midazolam.

• Have a full general anesthesia setup both in the induction area and inside the MRI scanner. Use extra-long circuit tubing inside the scanner.

• Induction of anesthesia should be done in a separate induction area; transport the intubated patient with an Ambu bag to the MRI scanner.

• Opioids are unnecessary (this is not a painful procedure).

• Use MRI-compatible electrocardiogram leads, blood pressure cable, pulse oximeter, and temperature probe.

• Use earplugs for noise reduction.

• Maintain anesthesia with sevoflurane or propofol infusion with an MRI-compatible infusion pump; the usual start dose is 200 μg/kg/min.

• Keep the patient adequately hydrated; avoid increases in ICP.

• Monitor temperature carefully. Cover the patient in blankets and/or plastic as much as possible to prevent hypothermia. Hyperthermia can also arise because of the heat produced by the magnetic fields.

### POSTPROCEDURE CONSIDERATIONS

Patients can be extubated either inside the scanner ...

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