In a study presented at the 2008 annual conference of the American Society of Anesthesiologists, investigators applied “hemispheric-synchronised” sounds (Hemi-Sync) to 60 patients undergoing outpatient surgery. Sounds are played through headphones and, according to the product website, ensure the “left and right hemispheres are working together in a state of coherence”. Patients used the Hemi-Sync before and during surgery, while control patients listened to music or a blank cassette.
A similar study (76 patients) was done in 1999, but in the current investigation the level of anesthesia was controlled using a brainwave monitor called the Bispectral Index.
Hemi-Sync is one of several gizmos marketed to harness human brain waves. Purported benefits include financial success, improved sleep, weight loss, spiritual growth and more.
Do they help with anesthesia and recovery from surgery?
Results
Hemi-Sync patients required less fentanyl (a strong analgesic) during the surgical procedure. The other outcomes, overall, were pretty similar in all the study groups, including analgesic needs after surgery, recovery time, nausea, awareness, etc.
Results from the 1999 study were rather similar.
Does it Matter?
This result suggests that Hemi-Sync is doing something useful in the brain. The study findings imply that hearing pathways in the brain are preserved to some extent during general anesthesia, and that given certain stimuli these pathways can somehow modulate pain signals coming to or processed in the brain.
The earlier study did not exactly revolutionise the practice of anesthesia. Small reductions in the need for certain inexpensive drugs are not going to change the way we do things.
A reduction in the amount of morphine or fentanyl needed during anesthesia can lead to lower rates of postoperative nausea, which would be a benefit, as nausea continues to be one of the most troublesome problems during recovery from anesthesia, especially for outpatient surgery. However this study did not find such a benefit. It probably did not have sufficient numbers to detect a statistically significant difference in the study groups.
On the other hand, there don’t seem to be drawbacks to the use of this sort of technology, other than their purchase expense. So it’s unlikly that your anesthesiologist will object if you bring your Hemi-Sync tape or MP3 to the outpatient surgery center, or anything else you choose to soothe your brain and calm its waves.
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