MRI: Monitoring hazards
Advanced, Physics, Monitoring, & Devices, Special Problems or Issues in Anesthesiology
Patients cannot be seen because they are generally enveloped by the MRI machine (although remote visualization should be employed, if available). EKG is confounded by artifactual T and ST wave changes (from aortic blood flow) as well as artifacts from the magnetic field . EKG wires must not be coiled. Traditional pulse oximeters cannot be used (due to the “antenna effect,” which can cause burns. MRI compatible oximeters do not physically connect the patient to the monitoring equipment).
MRI Monitoring Hazards
Patient Visibility: difficult / impossible to visualize patients in MRI
EKG: T and ST wave artifacts , among others. Keep wires uncoiled
Pulse oximetry: “antenna effect” mandates use of MRI-safe oximeters
Noise: precludes reliable auscultation
Other Points: loud noises (>90 dB) mandate ear protection. Ferromagnetic devices (pacers, AICDs, vascular clips) may be dislodged or broken
Who does this really concern?
children, ranging from newborn to 15 year old.
Some adults with impaired mental status
Why is this needed? The very nature of MRI examination makes it a unique situation in regard to anesthesia : the whole body must be introduced inside the MRI bore and no medical staff can stay near the patient.
This makes it difficult to assess – from the distant control room – the well being of the anesthetized patient.
What are the risks to the pt in the MRI suite?
- allergic shock
- hemodynamic impairment
So how to monitor the pt in the MRI suite?
- staff can’t stay in the room with the pt
- Distant monitoring is the only mean to make sure of the well being of the patient during anesthesia
- often anesthesia machines are bulky and difficult to move from room to room. There are multiple setups of monitoring devices for the pt from room to room (i.e., induction room, transportation, MRI suite).
Physiologic parameters will have to be measured:
- ECG waveform (ECG) and heart rate (HR)
- Blood pressure (BP) with non invasive automatic cuff
- Plethysmographic waveform and SpO2 measure
- Temperature (T°) in case of a long procedure
- Inspired O2 (mandatory)
- Inspired and expired volatile anesthetic agents (mandatory if used)
- CO2 waveform and Expired tidal CO2 (PetCO2) (mandatory if tracheal intubation)
- Tidal volume (Vt) and respiratory rate (mandatory if tracheal intubation)