Circulation 75,648 • Volume 20, No. 2 • Summer 2005   Issue PDF

Stand Near By in the MRI

Paul M Kempen, MD, PhD

To the Editor

I am writing to suggest it may be appropriate for the ASA/ASPF to specifically address monitoring standards for the provision of sedation, anesthesia, and ventilation of patients in the magnetic resonance imaging (MRI) suite. When I heard Irene P. Osborn, MD, Director (Division of Neuroanesthesia, Mount Sinai Medical Center, NY, NY), speak at the California Society Refresher Course in San Diego earlier this year, I specifically asked if it was appropriate to monitor the patient, not from the scanner room itself (where the patient is in the scanner tube), but from the scanner control room (SCR-the room next door with all controls separated by a wall with a large dark glass window). This question was answered informally by those in attendance, with more than 50% of the attendees (including Dr. Osborn) indicating this was their practice for adult and pediatric patients. I believe this indicated that, typically, NO provider remained in the scanner room itself with the patient—MD or CRNA. I believe this is in contradiction to ASA basic standards for monitoring, which make no provision for such exception. The Standard reads:

Qualified anesthesia personnel shall be present in the room throughout the conduct of all general anesthetics, regional anesthetics and monitored anesthesia care.

Having had opportunity to practice in multiple private and university settings since my graduation from medical school in 1981, I have seen many developments in providing anesthesia for MRI over the years. Historically, many standard items were not “MRI compatible,” yet were made available in the scanner room with exceptional precautions. Until I came to this university center, I had always remained in the scanner room with my patients under anesthesia and had never seen anesthesia provided from the scanner control room, although this methodology was “standard” at Presbyterian University Hospital in Pittsburgh when I arrived. Here infusion and ventilator tubings were run through wall portholes at distances of 40 feet, and of course, direct monitoring of the patient was not done, but rather the anesthesia machines and telemetric monitor screens in the SCR room were observed. I was for a time, however, able to practice MRI anesthesia from within the scanner room using “non MRI approved” pumps and anesthesia machines maintained at a safe distance from the magnet. In this way, all aspects of anesthetic care could be directly observed and actively managed, as in the operating room and per ASA guidelines.

MRI Death Reinforces Precautions

This all changed drastically in 2001, when a child died in the Westchester Medical Center in New York State, after being hit in the head in the MRI scanner by a ferromagnetic oxygen cylinder. I was suddenly personally confronted with absolute restrictions prohibiting anything “non-FDA approved MRI compatible” from entering the scanner room. I was suddenly forced out into the SCR with my “magnetic” equipment, monitoring at 40 feet from the SCR, which created great anxiety to apparently only myself. In the past decade, I am aware of 2 deaths having occurred in this city using these “40 foot/next door” techniques: 1) the expiratory limb of a circle system occluded and the patient succumbed to tension pneumothorax, and 2) a mini-drip infusion of propofol (no volumetric pump) ran uncontrolled with a fatal outcome. Astonishingly, a picture of a mini-drip propofol infusion (without volumetric pump) of this kind is pictured, as well as “monitoring from the scanner control room” in a recent MRI-anesthesia review article.1

Incident Illustrates Need for Monitoring

More astonishing is that modern MRI suites continue to function with antiquated equipment, although modern and MRI-compatible operating room suites have been introduced in the US and Europe!2,3 Here all anesthetic and surgical needs are met in the scanner room itself. MRI-compatible equipment has now been procured here at my institution, including infusion pumps and MRI ventilators. Anesthesia personnel should now remain in the room, as no biological hazard exists to normal human beings in the scanner room, especially at 10 feet from the magnet coil.4 However, individuals continue, by choice, to monitor from the SCR. This recently led to the following incident:

A patient was brought to the MRI from the radiology suite after coils were inserted in an aneurysm of the carotid artery. This 70-year-old female came intubated, paralyzed, with a radial arterial catheter, and on a propofol infusion. The infusion was switched to the MRI compatible, battery operated pump, and she was ventilated with the ventilator without ETCO2 analysis. Neither piece of equipment is electrically connected to alarms visible or audible in the SCR. The arterial pressure trace could not be displayed, because no MRI compatible transducers were available in the institution. The ETCO2 was not monitored, as this was not routine for this ventilator type; however, an airway pressure gauge was connected and viewable in the SCR via 40-foot tubing. The MRI department’s monitor is capable of both arterial tracing and ETCO2, as well as non-invasive blood pressure (NIBP), ECG, and pulse oximetry, and all monitored parameters are viewable both in the SCR and scanner room.

After a short period in the scanner, the NIBP was not obtaining results, and a second stat attempt yielded no result. The airway pressure was now noted to cycle between 20-40 torr and at a rate of 30-40. This was noted from the SCR, and after a short interval to interpret the situation and to enter the scanner room, the patient was withdrawn urgently from the scanner. At this time, no radial pulse was detected, although heart and breath sounds were present. Recycling the BP cuff yielded 44/20, immediately after which she was placed on bag-valve ventilation, while no visible or auscultatory problems were noted with ventilation. Phenylephrine was obtained from the SCR. Before the phenylephrine could be administered, renewed NIBP measurement now yielded 169/110. The propofol infusion pump was noted to display a red light indicating “downward occlusion” of the CVP line — duration unknown. A second MRI ventilator was obtained, propofol reinstituted, and the patient returned to the scanner for scan, with the anesthesia provider instructed to remain at the patient’s side.

The first ventilator was isolated for inspection and found to function within parameters. These ventilators are gas powered, non-electrical/ mechanical ventilators using “Bird-1970s technology.” The problem appeared to be due to changes in patient compliance resulting in “autocycle” of unwanted, yet available, SIMV programming, atypical of anesthesia ventilators. These ventilators are managed by the respiratory therapy department and are unfamiliar to anesthesia personnel. This incident resulted in a period of hypoperfusion from the sustained high airway pressures, a “valsalva maneuver” of sorts, as well as the potential for awareness due to interruption of the propofol infusion. The interruption of the propofol may have been life-saving in this situation (as well as perhaps causative). Had the anesthesia provider been present in the room, the rapid cycling of the mechanical ventilator and audible alarm of the infusion pump would have been noticed. Visual observation from the SCR is significantly impaired by the reduced transparency of the glass windows, which are part of the Faraday cage screen for radiofrequency energy, and audio alarms typically remain unheard in the SCR. Emphasis on the use of audible alarms has been recently noted, and MRI alarms may need to be much louder than in the OR, due to the significant scanner noise.5 Had the arterial trace been available, earlier recognition might have prevailed in this instance, but as the NIBP was cycling at 5-minute intervals, a significant period of compromise of up to 10 minutes may have occurred. The patient was not found to have sustained awareness or other lasting injury upon emergence.

In conclusion, it would seem appropriate to have specific national standards for MRI anesthesia which meet general published OR guidelines. Education of colleagues regarding the complete lack of danger in the MRI for personnel without metal implants appears necessary, while individuals with contraindications to undergo MRI scanning may need to exclude themselves from work in this area. MRI-compatible equipment can seem very expensive, until the cost of the scanner or patient death puts it into perspective. Equipment chosen by MRI departments may be so foreign to anesthesia personnel (as in this instance) as to present an additional danger due to non-familiarity. Oddly enough, even some of these MRI-approved devices are highly magnetic and non-“MRI-FDA approved devices” have been used safely for years. Modern standards should enhance safer, modern anesthesia techniques and may serve to facilitate the acquisition of appropriate equipment in financially trying times. Anesthesia safety should not be compromised by historic patterns, unfounded fears, or a reluctance to remain at the side of the patient without specifically identified dangers. The separation of anesthesia providers and equipment from the patient’s side in the MRI suite should be relegated to the annals of history.

Paul M Kempen, MD, PhD
Pittsburgh, PA

References

  1. Gooden CK, Dilos B. Anesthesia for magnetic resonance imaging. Int Anesthesiol Clin 2003;41:29-37.
  2. Hall WA, Liu H, Martin AJ, et al. Safety, efficacy, and functionality of high-field strength interventional magnetic resonance imaging for neurosurgery. Neurosurgery 2000;46:632-42
  3. Schmitz B, Nimsky C, Wendel G, et al. Anesthesia during high-field intraoperative magnetic resonance imaging experience with 80 consecutive cases. J Neurosurg Anesthesiol 2003;15:255-62.
  4. Menon DK, Peden CJ, Hall AS, Sargentoni J, Whitwam JG. Magnetic resonance for the anaesthetist. Part I: Physical principles, applications, safety aspects. Anaesthesia 1992;47:240-55.
  5. Stoelting RK: APSF stresses use of audible monitor alarms. ASPF Newsletter 2004;19:1, 19