Extra Topic 6.3 -- MRI/Pacemaker

Question 1

The patient’s pregnancy test comes back positive.

Will you tell her parents?

(A 14-year-old, 88 kg, female with frequent tonic-clonic seizures is scheduled for magnetic resonance imaging of her head. Her mother states that her daughter is asthmatic, claustrophobic, and extremely anxious about the procedure.)

Answer 1

State law concerning the emancipation of minor pregnant patients varies from state to state.

Therefore, I would first attempt to determine whether my state law would declare her emancipated in regards to medical decisions involving her pregnancy, recognizing that this would confer upon her the right to complete confidentiality.

In the absence of this clear emancipation, I would weigh the benefit of maintaining trust in the physician-patient relationship (i.e. the patient that trusts his or her physician is less likely to withhold information, potentially deferring needed care) against the risk of harm to the patient should I fail to inform the parents.

In this case, I would most likely inform only the minor of her positive pregnancy test, encourage her to make her mother aware of the pregnancy, and attempt to facilitate the appropriate follow up care for the patient (i.e. obstetrician and social worker).

Question 2

What are some of your concerns when providing anesthesia for MRi?

(A 14-year-old, 88 kg, female with frequent tonic-clonic seizures is scheduled for magnetic resonance imaging of her head. Her mother states that her daughter is asthmatic, claustrophobic, and extremely anxious about the procedure.)

Answer 2

I have several concerns, including:

1. the unintentional transfer of a ferromagnetic object (i.e. gas cylinders, keys, scissors, etc.) into the scanner room, leading to projectile-induced injury to the patient or hospital personnel;
2. dislodgement or malfunction of an implantable device with exposure to the scanner’s magnetic field (i.e. pacemaker, AICD, implanted infusion, pump, spinal cord stimulator, and/or mechanical heart valves);
3. magnet-induced equipment malfunction (i.e. monitors and infusion pumps) ;
4. thermal injury, secondary to magnetic field affects on monitoring equipment like ECG pads or the pulse oximeter (monitoring cables should be straight where in contact with the patient… i.e. no coiling);
5. temporary or permanent hearing loss secondary to the loud banging produced by the MRI scanner (ear plugs should be utilized to prevent this type of injury);
6. patient anxiety, due to the length of the procedure and the confining nature of the MRI scanner (especially a concern for this patient with claustrophobia); and, for a patient with moderate to severe kidney disease, I would be concerned about
7. kidney damage (more specifically, nephrogenic systemic fibrosis and nephrogenic fibrosing dermopathy) secondary to gadolinium-containing contrast agents.

Question 3

Would you proceed with the case now that you know that she is pregnant?

(A 14-year-old, 88 kg, female with frequent tonic-clonic seizures is scheduled for magnetic resonance imaging of her head. Her mother states that her daughter is asthmatic, claustrophobic, and extremely anxious about the procedure.)

Answer 3

The evidence does not currently suggest that the magnetic fields generated during MRI are harmful to the baby in utero, despite the evidence that gadolinium-based contrast agents enter the fetal circulation and amniotic fluid.

So, if delaying the MRI until late in pregnancy or until after delivery was associated with significant risk to the mother, I would proceed with the case.

Question 4

The patient is wearing braces.

Is this a problem when undergoing MRI?

(A 14-year-old, 88 kg, female with frequent tonic-clonic seizures is scheduled for magnetic resonance imaging of her head. Her mother states that her daughter is asthmatic, claustrophobic, and extremely anxious about the procedure.)

Answer 4

While the presence of braces is not a contraindication to MRI, they could potentially degrade the quality of the image.

Therefore, I would discuss this with the radiologist to determine if MRI is still the optimum modality for this patient.

If I had any doubt about the safety of an object, I would use a small hand-held magnet to test whether the object was ferromagnetic prior to entering the scanner room.

Question 5

You do not have an MRI-compatible anesthesia machine or monitors.

How will you provide anesthesia for this case?

(A 14-year-old, 88 kg, female with frequent tonic-clonic seizures is scheduled for magnetic resonance imaging of her head. Her mother states that her daughter is asthmatic, claustrophobic, and extremely anxious about the procedure.)

Answer 5

While sedation with spontaneous ventilation is often sufficient for MRI, I do not think it would be appropriate for this obese patient (decreased chest wall compliance, rapid desaturation following the onset of apnea) who is likely to require significant sedation (anxiety and claustrophobia), and whose respiratory drive may be particularly sensitive to the depressant effects of sedative hypnotics due to her obesity.

Therefore, considering her claustrophobia and anxiety, the length of the procedure, and the need to avoid the patient movement, I would provide general anesthesia for the procedure.

However, in the absence of an MRI-compatible anesthesia machine, I would:

1. ensure that an Ambu bag was connected to an oxygen source in the scanner room;
2. apply the appropriate monitors with sufficiently long cables to reach the area just outside the scanner room;
3. administer a B2-agonist;
4. induce the patient with lidocaine, fentanyl, versed, and propofol;
5. secure her airway with an ETT, to provide a definite airway in this obese asthmatic patient (an LMA may be considered to reduce the risk of bronchospasm, but would be inferior in the management of bronchospasm should it occur); and
6. maintain anesthesia with either propofol or a volatile agent delivered through lengthy tubing that allows the anesthesia machine and/or infusion pump to remain outside of the scanner room.