Anesthesia for MRI

Pediatric anesthesiologists debate the best way to anesthetize children for diagnostic radiology, particularly MRI. Although some anesthesiologists believe that there is less of a chance of postanesthetic nausea and vomiting with propofol anesthesia and less likelihood of airway complications in a spontaneously breathing patient, others feel that patients wake up faster after anesthetic gas maintenance and prefer to place a laryngeal mask airway (LMA) or endotracheal tube to secure the airway. To date no studies have directly compared intravenous and inhaled anesthesia in children undergoing MRI studies.

In this month’s issue of Anesthesia & Analgesia, Dr. Christopher Heard, Department of Anesthesiology, Division of Pediatric Critical Care and Department of Community and Pediatric Dentistry, Women and Children’s Hospital of Buffalo, State University of New York at Buffalo and University of Rochester, Rochester, New York, and colleagues from Women and Children’s Hospital of Buffalo, State University of New York at Buffalo and University of Rochester, Rochester, New York, and Children’s Hospital and Medical Center, Omaha, Nebraska, set out to answer this question in the article titled “Propofol Anesthesia for Children Undergoing Magnetic Resonance Imaging: A Comparison with Isoflurane, Nitrous Oxide, and a Laryngeal Mask Airway.” They prospectively collected data from 150 healthy children between the ages of 1 and 10 randomized to receive either propofol infusions starting at a rate of 300 µg.kg^-1.min^-1 with oxygen via nasal cannula or isoflurane with 70% nitrous oxide in oxygen delivered via laryngeal mask airway, both after a sevoflurane/N₂O/oxygen induction. The primary outcome variable was the frequency of perianesthetic airway events in the two groups.

The authors found that adverse airway events such as airway obstruction and mild desaturation during emergence and recovery were more likely to occur in the isoflurane group (49%) than in the propofol group (12%). The events easily resolved. They also found that early recovery (the time from PACU admission until patients opened their eyes and were wakeful) was more rapid after isoflurane (an average of 14 minutes) than after propofol (an average of 20 minutes). Overall recovery and discharge times were similar, however. The frequency of nausea and vomiting after propofol administration, 3%, was significantly less compared with isoflurane/N₂O, 17%. In contrast to other published studies in which children who were sedated with propofol required repeat scans due to movement, all of the scans in this study were completed without requiring repeat sequences.

The same practitioner administered anesthesia for all scans. Having only one practitioner and the same observer in every case may limit the replicability of the results. Also, the fairly high doses of propofol were used. This may explain why movement was not a problem with propofol, and may also account for the longer awakening time with propofol. Also, not all institutions have isoflurane available in the MRI suite, and the results with isoflurane may not predict the results with sevoflurane.

This is an important study showing the safety and efficacy of two different anesthetic techniques in MRI. An interesting question is how adjuncts to anesthesia can be used to help perform MRI in children while decreasing anesthetic exposure. As possible toxic effects of anesthesia on the developing brain are under investigation, many parents ask about potential alternatives to general anesthesia. Some MRI scanners come equipped with video goggles for older patients, or have pediatric-friendly themes such as pirate ships or spacecrafts that can help with periprocedural anxiety for older children. For younger children, there may be no alternative to general anesthesia to successfully complete the scan.