ABRs: Time to standardize to a propofol technique?

Myron Yaster MD and Lynne G. Maxwell MD

During this holiday week, we will repost some of the most viewed and discussed PAADs of the last year. Today’s PAAD was first posted on April 18, 2022

There’s this great scene in the 1983 movie classic “Risky Business” that I tried unsuccessfully to find and download that perfectly described my feelings about auditory brainstem responses and today’s PAAD.  Because I couldn’t find it, I’ll have to describe the scene for you as best as I can. In this scene, Tom Cruise in his first movie, is sitting in class and needs to get out, I mean he really needs to get out of class to take care of business…as the clock hands tick away and near 3:30 and the end of school, they start to go backwards!  Cruise’s character goes out of his mind. To be honest that’s how I always felt when I was assigned to ABR cases in Colorado…they took forever, usually more than an hour and a half and more than once I was convinced that the clock hands were going backwards! Indeed, I often thought that anesthesia for ABRs was like watching paint dry and any anesthetic technique that produced immobility would work. So, when I initially saw this article about the best way to provide anesthesia for ABRs, I thought, “really”?  Well, today’s PAAD presents convincing evidence that there really is a better way to do it, namely, spoiler alert, using propofol rather than sevoflurane.  Myron Yaster MD

Original article

Ali I Kandil, Michale S Ok, Kelly A Baroch, Rajeev Subramanyam, Mohamed A Mahmoud, John J McAuliffe 3rd.  Why a Propofol Infusion Should Be the Anesthetic of Choice for Auditory Brainstem Response Testing in Children.  Anesth Analg. 2022 Apr 1;134(4):802-809. PMID: 35113042

“Early, accurate diagnosis of hearing impairment is crucial to a child’s psychological, social, emotional, educational, and intellectual development. Misdiagnosis can have serious, life-long implications. Auditory brainstem response (ABR) testing detects hearing impairment in infants and children” and frequently requires general anesthesia to provide the ideal conditions necessary for accurate testing.  The authors asked this question: “Does the anesthetic agent used during auditory brainstem response (ABR) testing for hearing impairment in children influence interpretability of results?” in response to observations by audiologists at their institution questioning the reliability of ABR results under different anesthetic regimens.  Although volatile anesthetics have long been known to impair other neurometric responses, such as sensory evoked potentials, it has long been thought that auditory evoked responses were more resistant to such impairment. And the findings? “Sevoflurane produced more false positives for hearing loss and suggested more severe hearing loss than propofol.”

Key to this paper: “A false-negative ABR, is an incorrect diagnosis of normal hearing in the presence of hearing loss.  This can lead children to believe they are “crazy” or “stupid” rather than hearing-impaired and can cause delay or omission of potentially life-changing treatment. Conversely, a false-positive ABR, incorrect diagnosis of hearing loss in the presence of normal hearing, and could prompt unnecessary treatment”.

In this single-center (Cincinnati Children’s Hospital Medical Center), prospective, double-blind crossover study, the authors compared the effects of sevoflurane and propofol on interpretation of ABR testing in children.  Each child’s responses were recorded under sevoflurane followed by propofol, allowing adequate time for sevoflurane washout, confirmed by end-tidal sevoflurane measurement. This study design ensured that each child served as his/her own control. The anesthetic technique made a big difference. “Children who received sevoflurane for ABR testing were 75% more likely to have a false-positive hearing test in 1 of their ears (38 vs 19) than those who received propofol”, and the ABR results “suggested more severe hearing loss than those anesthetized with propofol”. Finally, “sevoflurane had poorer responses and is more difficult to interpret responses than propofol.”

The authors conclude: “anesthetic agent choice can significantly alter ABR interpretability. For ABR testing, propofol seems to be a preferable anesthetic choice compared to sevoflurane. Moreover, our results challenge the previously accepted notion that ABRs are very resistant to inhaled anesthetic agents such as sevoflurane”.

Some final thoughts.  In this study, anesthesia was induced with sevoflurane and an IV was then placed.  In a previous PAAD on the anesthetic technique for MRIs, I (MY) wondered why at the Boston Children’s Hospital IVs were placed without sevoflurane.  John Fiadjoe and Amy Vinson in their response to the PAAD pointed out that at Boston, IVs were routinely placed preop without general anesthesia and based on today’s PAAD that may be the better way to go for ABRs.  How do you do this basic technique, IV placement, at your institution?  Let us know and we’ll post in reader responses.  Finally, in this study, ABRs took only 25 minutes to perform…perhaps unlike Colorado and CHOP were they take forever, OK, an hour and half plus, the hands of the clock don’t go backwards.

Myron Yaster MD and Lynne G. Maxwell MD