Question 16

College Answer

General risks of MRI

Magnetic field induced movement of ferromagnetic objects

* Ferrous Projectiles accelerating into scanner causing trauma

* Movement of ferrous implants and prostheses

* Movement of metallic foreign bodies, such as foreign bodies in the eye

Others 
* Malfunction/failure of pacemaker/ IAD

Specific risks with the critically ill patient
* Cold environment and prolonged exposure time away from ICU due to length of time it takes to do an MRI

* Patient inaccessibility

* Monitoring and ventilation equipment is limited and needs to be MRI compatible, often sub-optimal

* Unable to take resuscitation equipment into “magnet zone”

* Infusions may be difficult to run – MRI compatible pumps that can be used in “magnet zone” are not widely available. Long tubing can be used.

* Gadolinium exacerbation of nephrogenic systemic fibrosis

Potential risk of hyperthermia in patients with disordered thermal regulation (ie all critically ill patients)

Potential for burns (ECG dots)

Discussion

Even though the college exclude transportation considerations from their question, they are important because according to one risk/cost/benefit analysis, "transportation of patients from the ICU resulted in a large number of physiologic changes, each requiring changes in support". Of these physiologic changes, 68% were described as "serious" (eg. requiring more vasopressors or a higher FiO₂).

Now, to MRI issues. This article contains a chapter ("MRI Transport") which covers this topic in brief. A substantial detailed exploration can be found in David Olive's article for Australasian Anaesthesia(2005)

Risks from the magnet

• Ferromagnetic material movement
• Malfunction of pacemakers
• Projectile trauma from nearby objects
• Cardiac damage from PA catheters
• Pulse oximeters and ECG dots can overheat and cause burns. ECG cables are made of coiled copper, and will also heat up.

Risks from contrast

• Gadolinium is usually quite safe, but it may cause exacerbation of nephrogenic systemic fibrosis. Anaphylactic reactions are possible.

Risks from the isolated room

• Airway disconnection alarms might go unheard
• Long ventilator tubing creates excessive amounts of dead space
• Extra dead space makes is difficult to trigger.
• MRI-compatible anaesthetic machines are available, but they are expensive (~ $80,000) and frequently the ventilators on them are somewhat unsophisticated.
• Long infusion tubing results in a delay of medication administration
• Some drugs may require pumps, and cannot be given; pumps may require ridiculously long tubing and additional batteries to function
• The MRI chamber is usually cold, and hypothermia can develop
• Monitoring equipment is of poor quality

Risks from being critically ill

• Thermoregulation is impaired, and hypothermia is more likely to develop
• Judgement is impaired, and patient movement delays the process
• Resuscitation equipment cannot be taken into the room. Certainly, plastic disposable laryngoscopes do exist, but the batteries inside them are still affected.
• If cardiac arrest occurs, it can take some time to dismount the MRI couch

INDECK, MATTHEW, et al. "Risk, cost, and benefit of transporting ICU patients for special studies." Journal of Trauma-Injury, Infection, and Critical Care 28.7 (1988): 1020-1025.

Tobin, J. R., E. A. Spurrier, and R. C. Wetzel. "Anaesthesia for critically ill children during magnetic resonance imaging." British journal of anaesthesia69.5 (1992): 482-486.

Blakeman, Thomas C., and Richard D. Branson. "Inter-and Intra-hospital Transport of the Critically Ill." Respiratory care 58.6 (2013): 1008-1023.

ANZCA have an excellent college publication on this exact topic:

D.Olive, "Don't Get Sucked in: Anaesthesia for Magnetic Resonance Imaging" - Australasian Anaesthesia 2005, pp.85