Audibility of anaesthesia alarms during magnetic resonance imaging: should we be alarmed?

The effects of MRI acoustic noise on anaesthesia safety concerns have not yet been documented. The objectives of this study were to provide subjective and objective evaluations of anaesthesia alarm audibility during MRI and to review the literature to determine whether or not to worry about our results.

Following Institutional Review Board's approval, we tested the audibility of four anaesthesia equipment alarms and selected one of them. Additionally, we selected the least audible of three MRI sequences (spin echo) for the study. The evaluations were conducted inside and outside the scanning room in a subjective and objective manner. First, 20 normal hearing consenting adult volunteers rated their audibility of the anaesthesia alarm using a 10-point numerical scale (0 = not audible to 10 = maximum audibility). Second, a sound level meter was used to measure the intensity of acoustic noise (A-weighted scale) under the above-mentioned conditions. Data, expressed as median [interquartile range], were analysed using the Wilcoxon test with P less than 0.05 considered as significant.

The subjective audibility scores (inside vs. outside the MRI room) were 9.0 [8.5-10.0] vs. 7 [6.5-8.0]. During MRI scanning, the scores were 6.0 [5.5-7.0] vs. 4.0 [3.5-5.0], respectively (P < 0.001). The sound level measurements were 70 [69-71] vs. 55 [54-57] dB (A). During MRI 91 [91-92] dB (A) vs. 68 [65-69] dB (A) (P < 0.001).

The audibility of the anaesthesia alarm is significantly reduced during MRI, particularly outside the scanning room. Consequently, optical alarms and interactive screens (outside the room) must be available without exception.