The Ether Way

I Use The BIS Monitor For A Lot More Than Just Preventing Awareness!

I like knowing how deeply anesthetized my patients are,  not just that they are unaware. How much a patient is unaware as a continuum is a lot more important that the binary notion of awake vs asleep.  I do this with a BIS monitor (and could do the same with Hospira’s PSA monitor) and make lots of decisions based on it and I think provide better care for the effort. My reasons for saying this follow.

 

Hemodynamic and analgesia decisions. The BIS monitor is a hypnosis monitor. There are three other important elements of an anesthetic: analgesia, neuromuscular blockade, and sympathetic reflex control. Let’s say the patient is hypertensive. There are three possible causes for it: insufficient hypnosis, insufficient analgesia, and sympathetic reflexes. Given a BIS value less than 60 then I can give an analgesic trial and if that does not work treat the blood pressure primarily. I might choose to use the anesthetic as my antihypertensive or I might choose to use a specific antihypertensive drug. Whatever I choose, I am doing it rationally. My non BIS-using colleagues just dump in the anesthetic for everything, BP, analgesia, and sympathetic control; thus  explaining the observation that BIS values, blinded to the anesthesiologist, tend to be much lower than when they are not blinded. To avoid the dreaded awareness we all overdose. As an aside Bennett etal presented some interesting data at this year’s ASA on a possible analgesia monitor, so one day we will be able to quantitatively monitor all four elements of an anesthetic.

 

Overdosing with anesthesia. While we are talking about overdosing maybe it is useful to recall that Terri Monk and colleagues report a higher death rate at one year in association with such an overdose method….it seems that these anesthetics leave a biological lesion long after the case is done. Now I agree that this is just an association study but then there is the annoyingly supportive material published by Eckenhoff, Wei, and by Xie in separate publications indicating  dose and time related effects of volatile anesthetics (especially isoflurane) exposure to produce amyloid depositioin (Alzheimers protein) and apoptotic programmed cell death in brain tissue. One wonders if similar bad things happen in nonneural tissue to account for Monk’s observations. In addition, Bohnen etal have their underpowered study that almost showed an effect of cumulative anesthetic exposure to predispose to the genesis of Alzheimers disease.  I am quite sure that more data will be forthcoming that systematic anesthetic overdosing is not a good thing and that the most valuable use of BIS monitoring won’t be to avoid too light anesthesia but quite  the opposite….to prevent too heavy anesthesia.

 

Burst suppression. The device has a handy modality on it called the suppression index. It tells you what percent of the EEG is flat. Very handy for when the brain is swelling out of the head and you have to run maximal doses of thiopental or propofol. Once the eeg is fully suppressed there is no advantage and lots of disadvantages to increasing the dose further. An abstract at a neurosurgery meeting a couple years ago compared this processed EEG calculation of burst suppression with raw eeg with bedside evaluation of the waveform. They were reported to be comparable methods with non comparable cost (raw EEG + neurologist = $$$))

 

Ischemia detection. Occasionally for severe ischemic events this unit will give a faithful reading of something bad happening. I would not rely on it to say all is well but it sure has detected and confirmed bad things at times.

 

Another reason is MONEY!... I did a retrospective review of the financial impact of introducing BIS to our ambulatory care center when I was at WVU using CompuRecord software to track anesthetic usage. Similar to what I stated earlier about too-deep anesthesia when not using BIS, we found significant financial savings accrued from BIS use just in terms of less anesthetic drug use.  In addition we found shorter times to leave the OR after the end of the case, better Aldrete scores in the PACU and shorter times to being discharge ready from PACU. It was difficult to translate these latter advantages into dollars because we could not indentify an FTE to eliminate. Interestingly, however, in this context of high volume high turnover anesthetics, the money saved in anesthetic usage per case did not exceed the cost of the many BIS patches that were needed. However, the financial advantages for long cases is undisputed. I never published this work but someone else did later report the same thing basically.

 

Oh yes. Prevention of awareness. I do use the BIS for that but the way I and others use it to run patients less deep I am a bit surprised we don’t see a higher incidence of awareness through its use.

 

So, here is a classic example of how I use it: Patient presents  for extensive back surgery in the prone position. I know that if I let the patient have prolonged surgery, hypotension or anemia that the risk of blindness, although still low, rises. I also know that intraocular pressure tends to rise with increasing time. I don’t ever want to have to deal with that blindness problem in any of my patients and I do quite a few of these cases every year. Without the BIS monitor I would have to overdose then run phenylephrine. However, with the BIS monitor  my instructions to my residents are this: BIS 55, MAP>80, Hb>10. Once the anesthetic dose is just right to produce the desired BIS then we manipulate the blood pressure with fluids, analgesics, and vasoactive drugs….all centered around the BIS monitor.

 

So, it seems that the BIS monitor really has multiple uses: save money, titrate analgesia, sensible use of antihypertensive meds, prevention of anesthetic toxicity, and prevention of awareness. I cannot think of a reason for  a thoughtful anesthesia practitioner to not use it.

the following added on dec 3, 2007:

A colleague advises me that there is a recent cochrane review that also supports use of bis monitoring for things other than preventing awareness:

http://www.cochrane.org/reviews/en/ab003843.html

Awareness in the Persistent Vegetative State

Every now and then you hear talks that astonish and fundamentally change the way you view some issue or disease state. I heard one of these at this year’s Society for Neurosurgical Anesthesia and Critical Care (http://www.snacc.org/) meeting in San Francisco in October 2007. This one was about the persistent vegetative state (PVS)  and how not all may be as it seems.

Dr Adrian M Owen of the University of Cambridge in the United Kingdom presented his studies of functional Magnetic Resonanace Imaging (fMRI) in patients in the persistent vegetative state (PVS) showing clear evidence of awareness and cognitive ability in some of these patients.( fMRI uses the MRI to indicate areas of the brain that are active) His work has been formally published in Science 313:1402, 2006.

 PVS is a syndrome wherein a patient by every bedside test shows no interaction with his/her environment. The patient does not attend to any external stimuli, does not track with his/her eyes and seems totally unconscious. Families (like the Schiavo clan) however may be struck by the patient’s apparent wakefulness, lack of need for a ventilator, and persistence of ordinary vegetative bodily functions. The patient can look seductively awake but is not. Of this I was certain till I heard this talk.

 Dr Owen presented the fMRI method whereby various inputs to a subject in an MRI scanner can create reproducible patterns. For example tell a patient to think about something and you get a stereotypical fMRI pattern. Tell a patient to think about riding a bike or think about a specific place and different reproducible patterns of activation arise in the brain. OK… neat.

 
Well Dr Owen presented a patient with all the stigmata of PVS from traumatic brain injury with diffuse axonal injury. This vegetative patient, however, when asked to think about a place or to think about riding a bike showed fMRI activation absolutely the same as that produced when an ordinary awake patient responded to the same command. In fact this patient was fully able to interact with the investigators in this manner. “If you can hear me think about riding a bike” leading to the bike riding pattern. I took a picture of this slide showing this and reproduce it here:

The fMRI of the PVS patient is at the top and the control volunteers at the bottom. The left images are those of tennis playing imagery and on the right of spatial recollection imagery. I believe this is going to have implications for decisions about extent of life support in such patients. Certainly many(probably most) PVS patients really are in PVS.  Unlike this case, I don’t expect patients with neocortical death will be responsive like this. Nonetheless it does suggest that before we make such PVS declarations that we should make sure on tests like those presented by Dr Owen that the PVS patient really is in PVS.

For starts, in those patients in whom we find that PVS is really “pseudoPVS,” I expect this will be an objective measure to use for rehab. Just keep thinking about that bike riding and after awhile the physiatrists, wonder workers that they are, may be able to have the patient really bike riding or doing other cognitive things. It will tell them to not give up.

So it seems that what we thought we knew for sure we’re not so sure of anymore. Déjà vu.

 

Good Anesthesia Matters!

The anesthesia world is spinning up to a tizzy over the upcoming theatrical release of the movie "Awake." For those of you living "off the grid", Awake is a story about a poor victim who has the extraordinary misfortune to be subjected to cardiac surgery awake/paralyzed. None of us have seen this movie, but advanced word is the anesthesia folks aren't favorably depicted.

I am really, really looking forward to its release. For a lifetime, I have wholly devoted myself to my craft; medicine and anesthesiology. While I have not minded being in the background behind my surgeons, I have, over thirty years, grown tired of the surgical attitude that what I do is trivial; of course it is, because if it weren't, well, they'd be doing it themselves, wouldn't they?  And if I and my colleagues had been made of better stuff, we would have gone into surgery.  What a load of nonsense.

One slip of the surgeon's knife, and a patient's meaningful life is over. Just so, one mistake with a syringe of vecuronium, and a patient is dead, or perhaps, worse than dead... The truth is, if I don't practice smartly and on form, patients will suffer and perhaps die in ways both obvious (aka "Awake") and subtle (ie high blood glucose leading to higher post-op infection rates) It's about time everybody understood it. It doesn't help when colleagues (especially CRNA's, I note over the years) minimize what they and we do; "oh you're going to take a little nap while your (big strong) surgeon operates on you." I even avoid the use of the word sleep to describe what I do. I usually say "sleep is what you do at night. It is free and natural, but if your surgeon were to attempt to operate while you are asleep, you would wake up in great pain. What I provide is drug induced unconsciousness, not unlike a temporary coma. You will not wake up until I reverse the process. It is a safe procedure in my hands, and I will stay with you the entire time to maintain this state and see you safely through." I have no tolerance for anybody who suggests that I am scaring patients like this; it is simple truth, which is the stuff of informed consent.

For every patient that  says "oh, doctor, anesthesia is soooo important," I have ten patients who believe that I belly up to the table with a syringe of clear stuff, inject it, and walk on to the next room, or out for a cup of coffee... ("who was that masked man? I don't know, but he left this bill pinned to my dickie...")

A little patient apprehension about their upcoming anesthetic is a good thing-it's appropriate.  And if the patients get the idea that who is giving their anesthetic; their education, dedication, compassion and diligence,  matter to their outcome, well, then, so much the better. Because it's true.

Where I come from, there' was a saying; "a good surgeon deserves good anesthesia. A bad surgeon needs it." I can't remember all the times I've had to hold a patient together physiologically while the surgeon tried to work his way out of a nasty situation. I have auscultated the hearts of 20000 patients to avoid missing that once-in-a-lifetime patient with critical aortic stenosis who would otherwise die on anesthesia induction (I've found 2). I've sniffed around thousands of diabetics for a whiff of the coronary artery disease that might progress to a fatal perioperative MI. I've sat on the floor of the holding area hundreds of times looking up at anxious three year olds and their parents, quickly forging a rapport that I could leverage into a less scary induction.

I can deal with healthy patient fear; it just takes a little time, some patience and explanation. I hope that every patient for the rest of my career has the good sense to ask me what I'm going to do to keep them alive, and how I'm going to prevent the excruciating agony of their being awake "under the knife", and then I hope they look me in the eye as I explain it all, to be sure they see a soul they can trust.

And if anesthesia leadership on both sides of the aisle (AANA and ASA) settle for some bland reassurances about anesthesia diligence and try to undermine the message of "AWAKE"  by pointing out the inevitable inaccuracies they will find in the movie, than they (and we) ought rightly to be banished to the back benches of the medical pecking order.

And if Aspect medical makes a few more bucks on their BIS monitors along the way, so be it; their box isn't perfect, but it isn't bad, either...

I say, "bring it!" I'll be there on opening night with a big bag of popcorn to assuage my vicarious anxiety...