So. Plenty of oxygen was consumed discussing/arguing/debating the merits of the secret-recipe Aspect BIS cerebral monitor at this year's ASA. Isn't this getting old? First, my disclosures. I have no financial interest in or support from Aspect medical (in fact, given the state of the economy, I have no financial interest or support from anything, aside from my ever-shrinking clinical income.) Second, I use the BIS every day, on almost every case I do longer than 15 minutes, paralyzed or not. I even use it on most functional (awake) craniotomies. I have been known to shave the occiput in order to place a BIS array for ACOM aneurysm clippings (yup, we still do them here, now and then). I liiike it. I've used it at least a thousand times.
But it does have its limitations. Like last month, when a young lumbar patient on 2% Sevo and fent with a reading of 42 "BIStles" (that's what I call 'em-why not?) in one epoch, did his best unconscious imitation of upward facing dog the next... (yes Ira, I know-the brain is not the spinal cord.) Do a hundred BIS cases without paralysis and you'll understand in your gut what I mean. But I still like it.
As monitors go, in my practice, the BIS is worth about 1 pulse-ox units (pou). By comparison, the gold standard monitor, the pulse-ox is a perfect 10 pou's. The Pulse ox is the most perfect anesthesia monitor that ever was, or could be (anybody besides me old enough to remember that feeling in your gut upon hearing a surgeon say "the blood looks dark"?) Blood pressure, maybe 7 or 8 pou's. Gas monitor, about a 6. The ECG, 2 or 3. This score is obviously my subjective weighting of the sensitivity and specificity of each monitor for keeping my patients (and me) out of trouble, and can certainly vary based upon each individual patient's specific situation (for instance, a person with a history of SVT intuitively derives much more utility from intraop ecg monitoring than a fit 20 something, in whom the ecg almost never tells me anything I don't know from the plethysmograph.)
Don't get me wrong, I use them all; why not? Maybe it was my gadget-deprived anesthesia childhood; manual BP, precordial steth, and a "bullet" ecg monitor (encased in a torpedo-like tube so it wouldn't blow up the room, literally, when we still had flammable anesthetics around... ) As Dr Estafanous, then chief of cardiac anesthesia at Cleveland clinic said when I visited 25 years ago, "We ENJOY a swan ganz catheter on every heart." Well put, I thought. There is no physical morbidity associated with any of these monitors, save that implied by Kruel's law; (Kruel was my wise, then young, Wisconsin professor) who used to say "no data is better than bad data." They are inexpensive in application, and I like gadgets. The same applies to nerve stims (about 1pou) and temp (same).
problem, of course, is Aspect, who are economically motivated
evangelists. They are black-and-white, believe-or-be-damned
proselytizers who want to argue all of us into imagining the BIS R.O.I.
(whoops! I meant ROC) looks like the white cliffs of Dover, rather than
a soapbox derby track. They are aided in their
mysticism by the lack of
a true neuro-correlate of consciousness. Therefore, the BIS clinical
criterion is not unconsciousness; it is depth-of-anesthesia (DOA);
which is a horse, as they say, of another color. What does DOA (perhaps an unfortunate acronym) mean clinically. Hell if I know. The semantic distinctions here are, ahem, shall we say, convenient?
OR, as Alfred E Smith said "No matter how thin you slice it, it's still baloney."
IF you can't get anesthesia, amnesia will do...
The literature is nicely seasoned with memory-during -anesthesia studies, parsing explicit vs. implicit and the like. As anesthesiologists, we are phenomenologists. Along this axis, we are mostly seeking to avoid catastrophic recall. That is, as all anesthesiologists and anesthetists will immediately understand, is about wide-the-heck-awake-during-surgery torture.. We have no way to know for sure the state of consciousness of a paralyzed patient, save as they have explicit, or measurable implicit memory, give-or-take a tourniquet-isolated arm study or two. This is not true, by the way, for non-paralyzed patients, who can obviously provide volitional motor feedback; ie, a sock in the jaw, if they are not deep enough... And this, in turn, because memory deposition seems to be more susceptible to abolition by inhalation agents than consciousness, which in turn is more sensitive than movement. We see it every case. On emergence, first they move, then they reach for the tube, then they open their eyes to command, all some minutes before they remember anything.
Catastrophic recall happens two ways; A) the vaporizer was dry, because we didn't check and fill it, or B) we didn't turn on the vaporizer (or in tiva, the pump). During TIVA, we can also forget to rig it up right, too, I suppose. Not delivering anesthetic is like forgetting to deploy your retractable landing gear prior to touchdown; It happens rarely, but it does happen in the absence of a cockpit alarm/annunciator to remind the pilot. All desflurane vaporizers have level/output alarms; no agent=obnoxious alarm. This eliminates a systematic cause of inadvertent intraop awareness. I intuit that this happens more frequently in loooong, middle of the night cases, where the anesthesiologist slows his/her monitor scan rate and drops the vaporizer out of that scan loop because the level changes soooo sloooowly. So why doesn't every vaporizer have a level alarm? Beats me? I just work here, but if I were the APSF, I'd be lobbying for a mandatory changeover.
Forgetting to turn on the vaporizer is a different problem. It is certainly an AUTOMATIC part of every induction sequence, which makes it a problem. Anything that interrupts the induction sequence flow (yelling surgeon, difficulty with airway) and takes the operator out of their routine threatens that step. I use a three check induction routine, based loosely upon my Wisconsin three-check vial label confirmation. At UW, we were taught to check the vial label when we picked it up, when we drew it up, and when we gave it. I check that the vaporizer is on when I push hypnotic, when I turn on the vent, and when I start the chart..
What about the gas monitor alarms? The are great for cruising on long stable cases, but since they are not adaptive, they have the unfortunate tendency of attracting attention at exactly the wrong times; immediately peri-induction and at emergence, when information flow is high. As a consequence, most monitors default to a zero% low agent parameter (Don't yours colleague?) and require pro-activity post induction to reset the low level alarm, and to set it back down on emergence; otherwise the anesthesiologist must hit alarm disable every two minutes, also disabling all other alarms (ie apnea, saturation) as a consequence. A sorry state of affairs, for which there is little excuse now, given the processing power inherent in even the least sophisticated physiologic gas monitors; It would be a simple matter, for instance, to link a low inhalation agent alarm parameter to the mechanical ventilator. It might take a little tweaking, but I can already envision the algorithm.
Finally, of course, there is the old standby known to every pilot; the checklist. Why have we resisted anesthetic checklists for so long? This is one of those issues like ACLS certification. We feel like our professional boundaries are being threatened on the one hand, then we see a QA report where some anesthesia numb-skull has given four 300mg boluses of amiodarone to a vfib patient over ten minutes the next day (he got confused with lidocaine!!?)
And, why have we been beating around the bush on this issue for so long? Perhaps, if we can just shake loose from the fog of BIS info-mercial marketing for a moment, we can get to addressing their valid concern with intraop awareness and institute some appropriate systematic fixes that don't necessarily involve buying their machines. But I do like them...