BIS and My Butt

February 3, 2013 EDT at 7:19 am

The Neurotrac

I had my first colonoscopy a while back and having had very few surgeries in my lifetime I thought this would be an interesting time to experiment with some “depth of anesthesia” technology.  A product that my pals Gary and Matt and I developed back in the 1980’s (the Neurotrac), had a number on it called the spectral edge frequency (SEF). The SEF was computed from the EEG and indicated the highest frequencies active in the EEG.   The product was the first digital system made for recording and processing continuous EEG in the OR and ICU.  The SEF was sensitive to anesthetic drug action as this edge tends to go through a repeatable change from light anesthesia to deep anesthesia. The Neurotrac was quickly used in studies of depth of anesthesia by academic sites around the world.  So I have followed this field from nearly the beginning.

Aspect Medical Systems was the first company to raise venture capital and fund major investigations into developing a single number that reflected depth of anesthesia and that was independent of the type anesthetic agent.  They were a very cool company with a scientist, Nassib Chamoun, at the helm. The number they computed, called the bispectral index (BIS) pretty accurately monitored the depth of anesthesia and sedation.  They manufactured a small box and sensors to allow anesthesiologists to monitor anesthetic drug action directly, rather than indirectly through vital signs.  It was not without its critics as with any new technology, but it has become a mainstay in many institutions to make sure surgical patients do not wake up during surgery nor suffer the side effects of too much anesthetic.

So…back to my experiment.  The day before the colonoscopy I grabbed an Aspect monitor from the company (we were doing several projects for them) and brought it home for the notorious “night before”.  This is where you take some laxatives and drink a week’s worth of water in an hour until you literally explode with the worst case of colon blow you’ve ever had.  It’s a mess but it does improve the view for the GI docs looking for those pesky polyps.

The day of the ordeal, I put the BIS monitor in a canvas bag and headed into the hospital.  I was “processed” the same as every patient but they saw the bag and said I had to leave my clothes in a locker.  I told them this was a brain monitor and that I wanted to hook myself up and monitor my depth of anesthesia.  It was apparent they had never had this conversation before as they didn’t know how to answer.  The attendant said this wasn’t allowed, but I asked him who was going to monitor my brain…if I didn’t.   He never heard this either.  So he excused himself, returned about ten minutes later and said it was OK.  I asked what had changed his mind.  He said he talked to the head anesthesiologist who ran this out-patient clinic.  As luck would have it, she remembered me when I was a medical student at this same hospital, told the resident that I was a bit “different”…and to just let me do what I wanted.

I entered the room, with my paper gown on (opening to the rear), and put on the BIS sensor and plugged in the monitor.  I had a nice conversation with the nurse anesthetist who was very cooperative and as curious as I was as to what this would show.  He put in an IV line and, I got into position on my side, and watched the display.  I was going to see at what number I blanked out.  The highest value of BIS is 98 so that’s where it started drawing the trend line.  He started to push the Propofol, I felt a slight stinging as it entered and I had no sooner looked at the number when…“poof”….I was out.

I woke up at the end of the procedure to see a perfect “bathtub” curve, as they call it, on the display:  a nice induction followed by a relatively stable surgical level and then a mirror of the induction for the recovery (see the picture).

BIS small

BIS during my colonoscopy

Monitoring the brain makes a lot of sense when you are giving “poisons” that target the brain (as one anesthesiologist described his profession)…and it has amazed me that there was such an initial resistance to monitoring the brain (which is a reason I’m not retired by now).  In spite of this, anesthesia has done a remarkable job of promoting safe practice, probably more so than any other specialty in medicine.  Their Closed Claims Project is similar to the investigation of plane crashes that has made flying so safe.  I have followed that project since its early days with the work of Dr. Karen Domino.

Members of the anesthesia community have policed themselves to where they are the model for other specialties.  It keeps their butt out of trouble and my butt safe.  I like that.