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Anesthesia

What is Monitored Anesthesia Care?

06/06/2005

Question:

My mother just had outpatient surgery for a blocked tear duct, and had MAC anesthesia. She was told point-blank before going into the operating room that she would be asleep, yet she states that she was aware and awake during the whole thing. She remembers bones crunching (or a sound like it), pulling, pushing, suturing, etc., and stated that time went very slowly. The promised state seems MUCH different that the reality. What`s going on? I had a colonoscopy under MAC, stated beforehand that I did not want to be aware, and only woke up when it was done. This sure makes me not want to ever have MAC again if it is not dependable for comfort during surgery.

Answer:

This is a really good question because it raises a very common concern - thank you!

MAC anesthesia is a term which stands for Monitored Anesthesia Care. What does that mean? Well, rather than "just putting you out", the use of anesthetic medications results in a range of anesthetic states, or "levels of sedation". Which level you get to depends on a number of things, including the age and general condition of the patient, genetic factors, and the choice and amount of anesthetic drug.

The American Society of Anesthesiologists (ASA) has defined four levels of sedation: (1) minimal sedation, (2) moderate sedation (conscious sedation), (3) deep sedation, and (4) general anesthesia. Official definitions are reproduced below. As sedation is increased, or deepened, the patient becomes progressively more sleepy (less easily roused) and more able to tolerate painful or uncomfortable procedures, (in the definitions this is assessed by the response to stimulation or verbal command), ending in the state of unconsciousness known as general anesthesia.

What is not always realized by the lay public is that as sedation becomes deeper, the patient also gradually loses the ability to breathe normally. This is usually accompanied by a depression of heart function and blood pressure.

You will notice that MAC does not appear in this classification. It is a term which has fallen out of favor somewhat, but probably corresponds most closely with levels 2 and 3 - moderate and deep sedation.

Given that most patients prefer to be unaware during their surgery, one may ask why a lesser or lower level of sedation is desirable. The answer is that recovery is quicker, and, as I have said above, that there is less depression of the heart, blood pressure and breathing from the anesthetic agents at these lower levels of sedation.

Problems arise when patients do not understand the type of anesthesia they are to receive. It is important for the anesthesiologist to clearly communicate the intended level of anesthesia and sedation, and for the patient to anticipate what is likely to happen. It is also important to offer an explanation, as the ASA points out, that "because sedation is a continuum, it is not always possible to predict how an individual patient will respond". Problems occur when patients do not respond in exactly the way intended or expected. That is, they get either too light (less sedation) or too deep (too much). In the case of anesthesia that is too light, the patient may become aware or awake, as you so vividly describe. (What is surprising to many is the fact that recent studies show that even with general anesthesia, there is an incidence of unintended awareness of around 2 per 1000 cases).

If a patient wants to be unconscious during a procedure (general anesthesia) this may be possible but there are trade-offs - more drugs, slower recovery, more risk of nausea afterward, need for a breathing tube, greater risk of depression of the heart.

For a procedure such as a colonoscopy, what is typically offered is minimal or moderate sedation. The drugs used, such as midazolam, have the happy benefit of causing amnesia. In other words, patients forget almost the entire experience, despite having been awake enough during the colonoscopy to respond normally and purposefully to commands or conversation. This perhaps was your experience.

For your mother on the other hand, undergoing a more invasive procedure, the results were less desirable. It sounds as though she experienced no pain during the surgery but was distressingly aware of certain unpleasant aspects of what the surgeon was doing. The outcome could have been different perhaps if your mother had been told that during the anticipated state of moderate sedation she was likely to feel some of what the surgeon was doing, but would experience no pain.

Your mother may then have been more willing to accept what she was experiencing in the knowledge that she would, in return for her tolerance, be able to leave the facility more quickly, recover with fewer side-effects, and have less risk of heart or breathing complications. Finally, if during the procedure she was really uncomfortable she could have expressed this to the anesthesiologist who may have been able to administer more medication to increase her comfort. Perhaps this vital aspect was not explained to her before the procedure took place.

I hope that your mother has no need of further surgery. But in the event that she does undergo another procedure lets hope she has a more satisfactory experience with anesthesia. Be sure to discuss your concerns with your anesthesiologist who will be glad to explain all of this in more detail and to tailor your anesthetic to your needs, always with safety in mind.

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American Society of Anesthesiologists Definitions of Levels of Sedation

1. Minimal Sedation (Anxiolysis) is a drug-induced state during which patients respond normally to verbal commands.

2. Moderate Sedation/Analgesia ("Conscious Sedation") is a drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation.

3. Deep Sedation/Analgesia is a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully following repeated or painful stimulation.

4. General Anesthesia is a drug-induced loss of consciousness during which patients are not arousable even by painful stimulation.

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Response by:

Gareth S Kantor, MD Gareth S Kantor, MD
Assistant Professor of Anesthesiology
School of Medicine
Case Western Reserve University