MRI anaesthesia




Magnet very strong: e.g 1.5T = 15,000 Gauss (c.f. planet Earth 0.5 Gauss)

Magnet is always on


1.Many hazards to self, staff and patient

2.Many constraints on equipment allowed

3.Remote environment

4.Limited access to patient



Zone 1

Public access (e.g. reception, waiting area)

Zone 2

In between (e.g. store bag and steth here)

Zone 3

Control room (i.e. access restricted, people must be checked)

Zone 4 (5 Gauss)

Magnet room (i.e. consequential magnetic field; only approved people and equipment can enter)

Danger (30 Gauss)

Projectile hazards become significant


Equipment designation:

MRI safe

Non-ferromagnetic, non-electrically conductive

e.g. IV cannula needle (stainless steel)

MRI conditional

Ferromagnetic or electrically conductive

Conditions for safe use must be defined and observed

e.g. pilot tube of ETT/LMA must be taped still

MRI unsafe

Significantly ferromagnetic

e.g. standard laryngoscope, prostheses, surgical clips etc


MRI anaesthesia considerations:


Magnet issues:


·      Physical injury: external projectiles, internal prostheses

·      Monitoring interference: ECG spikes, ST/T abnormalities

·      Pacemaker interference: asynchronous, inactivation, reprgramming


·      Formal check of patient

·      Formal check of self and assistants

·      Labelling of all equipment

·      Barricade the 5 Gauss line

·      MRI safe equipment

·      Basic monitoring only


Other physical threats:


·      No conducting material on patient

·      e.g. no normal ECG dots, no normal sats probe

Hearing loss

·      Very noisy 110-130dB (max safe ~90dB)

·      Putty or earmuffs for the patient


·      Table moves in and out a long way

·      Need secure airway / IV line


Remote environment:

Bring your stuff

·      Helpers if complex patient

·      Airway equipment if anticipating difficulty

·      Emergency drugs present

Case planning

·      Consider GA (sevo) rather than sedation (midazolam, dexmed)

·      Consider IV rather than inhalational induction

·      Consider ETT rather than LMA

·      Consider awake rather than deep extubation

·      Low threshold for transfer patient to main PACU

Disaster planning

·      Get patient out ASAP and shut the door

·      Call for help early (since slow to arrive)

·      Need designated resus area

·      Defibrillator cannot enter MRI scanner room


Remote patient:


·      Closed room

·      Opaque window

·      Patient in tunnel


·      Ensure patient stable, attachments secured before leaving the room

·      Consider ETT rather than LMA (in case of laryngospasm or aspiration)

·      Consider inhaled rather than IV anaesthesia (in case of disconnection)


Scanning requirements:


·      Awake: hard to keep still if young, intellectually disabled, claustrophobic

·      Sedation: difficult - movement if not enough, airway obstruction if too much

·      GA: need adequate hypnotic concentration; not painful, hence opioid and hypnotic usually unnecessary

Contrast anaphylaxis

·      e.g. gadolinium

·      Note again remote environment



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