This one is about: Anesthesia and Awareness / Waking Up During Surgery
(c) 1996 Wide Smiles
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Thu, 11 Jul 1996
I wanted to be sure and reply to the question about the news item on detection of awareness under anesthesia before we go on vacation (Yeah! Hooray!)
First, let me outline the problem. Anesthesia is not an "all or none" kind of phenomenon. It is more of a gradient, ranging from awake but relaxed and care free through sleepy but talking coherently without any memory of the experience afterwards, sleeping and amnestic but still breathing well without any assistance, to deeply asleep, not moving, requiring breathing support. Some procedures, like nasal surgery, may be performed under local anesthesia (the surgeon numbs up the area of the surgery) with sedation. With that, the patient may sleep through the procedure or be drowsy but able to talk and seem awake.
The patient's experience (memory) may or may not include periods of awareness of the operating room, the conversations, and the sensation of the surgery, even if the patient seemed awake the whole time. When a procedure is done with general anesthesia, the anesthesiologist is aiming for the deeper end of the spectrum -- asleep and unaware of the surgery or any other sensation, both during and after the procedure. As Dr. Liu outlined, this is usually done by watching the heart rate, blood pressure, and respiratory rate. The nerve stimulator he mentioned is used to monitor the effect of a medication given to relax the muscles to make sure the patient doesn't move during the surgery. In some types of surgery (like a hysterectomy) it is important to relax the muscles to allow the surgeons to spread the incision widely to see what they are doing. When the muscle relaxant is not used, the anesthesiologist can use the patient's movement as an indication that the patient needs more anesthesia. Just as you move in your sleep without being aware of it (Honey, stop kicking me! :-) ) the patient is almost always unaware of these movements and it does not mean the patient is awake, but may indicate that s/he is on the way to waking up. In spite of looking at all these factors, there are still patients who have some memory of events during their surgery. Usually this only involves a brief period of time, and usually the patient does not remember any pain. It happens most commonly in certain types of surgery: heart surgery, cesarean section, and surgery after major trauma or other circumstances where the patient has lost a lot of blood or is unstable for other reasons. For many years anesthesiologists have been looking for a way to detect the few patients who have awareness in spite of everything we try to do to prevent it. No one has come up with a method that is accurate enough to really help and cheap and easy enough to use routinely.
A medical equipment company has developed a machine which monitors brain waves from several parts of the brain and does some complex calculations to arrive at a number which is supposed to represent awareness or consciousness. In theory the anesthesiologist could watch this monitor and by keeping the number in the recommended range, be more certain that the patient will not be aware of their surroundings. From the data that I have seen, and my personal experience in using the machine during a study of its effectiveness, it is closer to being the answer to the problem than anything else that's been tried, but I am not convinced it is _the_ answer. There are still patients with awareness who are not detected by this monitor, and patients who do not need as deep an anesthetic as the monitor "tells" you to give. It is also a bit cumbersome to use. Like many things that get trumpeted in the press as being the latest, greatest advance in medical science, it is not really proven yet and it will probably be several years before it is either universally accepted as useful, or thrown out as a complete waste of time and money. The company which manufactures this monitor has made sure that it gets a lot of publicity so that patients will demand it and anesthesiologists will have to buy it. The fact that they are pushing it so hard makes me a bit skeptical.
Amy Beth Hilton, MD
Anesthesia Consultant for Wide Smiles
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