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What Are Conscious Sedation, MAC Sedation, and Twilight Sleep?

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Even procedures done under sedation require careful monitoring of vital signs. Only professionals qualified to ensure oxygen delivery and skilled in airway management should administer sedation.

Even procedures done under sedation require careful monitoring of vital signs. Only professionals qualified to ensure oxygen delivery and skilled in airway management should administer sedation.

Different Types of Anesthia

Not all surgeries have to be done with general anesthesia; i.e., the type that renders the patient unconscious. Sometimes, sedation (usually used to supplement local numbing injections) is enough to keep the patient comfortable. Possible options for sedation are light, moderate, or deep—depending on the situation.

You may hear various terms used to describe sedation protocols. Perhaps, you've been told you will be in "twilight sleep" or have "conscious sedation." Sometimes, you will hear surgeons, nurses, and anesthesiologists talk about "moderate sedation" or "MAC anesthesia."

Some of these terms mean the same thing or have overlapping connotations. Sometimes, the phrases are used interchangeably but are technically a little different. And some of these descriptors for sedation techniques are actually quite specific. Confused yet? Don't be. All of these things mean you will have a level of sedation that will keep you comfortable and relaxed throughout your procedure.

The continuum of consciousness, as relates to anesthesia, proceeds as follows:

  • awake (no sedation)
  • lightly sedated
  • moderately sedated
  • deeply sedated
  • unconscious (under general anesthesia)

It is not always possible to predict the level of sedation that will be needed by a specific patient for a specific procedure. The sedation can be adjusted to make sure you are comfortable, but not so sleepy that it isn't safe. So sedation can be made deeper or lighter, depending on needs at the time.

Sedation of any level should only be administered by qualified health practitioners. It definitely should not be administered in the bedroom of someone's home—even if that person is famous and rich—and even if the medication is administered by a licensed physician.

So, what exactly do each of these terms mean?

Twilight Sleep

The phrase, "twilight sleep," is often used when speaking to patients because it seems to describe a state of semi-consciousness. It is less frequently used now and has been replaced by the more descriptive "conscious sedation." While this terminology does seem to indicate that you will be both conscious and sedated (true), it again does not indicate whether light, moderate, or deep sedation will be needed or used.

To confuse the issue more, most practitioners actually mean moderate sedation (see below) when they say "conscious sedation." The phrase "twilight sleep" is a more general term that does not indicate the level of sedation to be used.

So, to recap: both of the above phrases can mean any level of sedation. The term "conscious sedation" can, therefore, mean any level of sedation, but often refers to moderate sedation.

Light Sedation or Minimal Sedation

Minor surgeries and procedures may be done with light sedation. Light sedation implies that you will have your anxiety suppressed and will be a bit relaxed with medication. However, you will remain fully interactive with your surroundings.

  • You can hold a conversation and are able to answer questions.
  • You will not require the support of cardiac or respiratory function.
  • Minimal or no supplemental oxygen will be used.
  • It is normal to remember most of your experience.
  • You will need minimal recovery time.
  • Side effects and complications are very, very rare.

Moderate Sedation

Moderate sedation is used when some discomfort (that's doctor-speak for pain) is expected. Emergency room doctors often use moderate sedation to help them with procedures such as fracture reduction or correction of a dislocated joint.

To make the whole subject more confusing, most practitioners understand the phrase "conscious sedation" to mean moderate sedation.

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  • You will respond to speech prompts or light touch.
  • You are able to support your own airway and ventilation without support.
  • Blood pressure and heart rate remain within normal limits.

Deep Sedation

Deep sedation can be thought of as being on "just this side of consciousness." Most people will sleep through a procedure with deep sedation and require quite a bit of stimulation to respond.

  • Breathing is usually adequate, although respiratory rate and depth of breathing may be decreased.
  • Oxygen will be given with a cannula in the nose or mask over the nose and mouth.
  • Deeper or more noxious stimulation is needed to get you to awaken or respond.
  • Heart rate and blood pressure may minimally decrease.

Medications Used in Sedation Analgesia

These are commonly used medication examples. The actual medications used for specific cases done under sedation will vary and are at the discretion of the anesthesia provider.

MedicationDrug ClassFunction



Anxiety reduction (anxiolysis), relaxation, amnesia

Fentanyl or Morphine

Narcotic Opioid Pain Medicine

Minimize pain


Sedative Hypnotic

Anxiolysis, depress consciousness


NMDA antagonist

Depress consciousness, pain suppression, amnesia

Insider's Note: If we refer to a "Big MAC," this implies that we think heavy sedation will be needed.

Monitored Anesthesia Care (MAC)

The acronym "MAC" stands for monitored anesthesia care. MAC means that an anesthesiologist (or nurse anesthetist, anesthesia resident, anesthesiology assistant) is present and responsible for the sedation, care, and monitoring of the patient during the procedure.

Any level of sedation can be a MAC anesthetic, but it usually implies a deeper level of sedation. Alternatively, anesthesiologists may be requested to administer sedation to very sick or high-risk patients.

For a MAC anesthetic, the anesthesiologist will assess the patient pre-op, monitor and medicate intra-op, and direct the recovery post-operatively.

According to the American Society of Anesthesiologists (ASA), MAC may progress to general anesthesia and back again. Their statement includes the following:

"Due to the strong likelihood that 'deep' sedation may, with or without intention, transition to general anesthesia, the skills of an anesthesia provider are necessary to manage the effects of general anesthesia on the patient as well as to return the patient quickly to a state of 'deep' or lesser sedation." (Source: Paper entitled "Distinguishing Monitored Anesthesia Care ("MAC") From Moderate Sedation/Analgesia (Conscious Sedation)." Approved 2004, amended 2009, by ASA.)

Now You Know!

The decision of whether or not to do a procedure under sedation vs. other types of analgesia/anesthesia is complex. Your surgeon and anesthesiologist will be able to let you know of your choices or options for your particular situation and may have a recommendation based on their experience.

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.


Sumer on September 06, 2012:

You made me laugh! But I actually do understand so thank you. I believe you are absolutely correct in that I know propofol and versed among many others were on board for the cocktail, at least initially. I think I've just been fortunate in the past to maintain more of a constant state (thanks to the team) and haven't ever dealt with the wearing off of the drugs so to speak, at least not that I remember. This was certainly not intended to be general and I do understand it was not intraoperative awareness, my curiosity was more around why I knew I was in that OR to start with ;-). You are also correct in that I had no pain just intense pressure and the movement wasn't purposeful. I knew I was doing it, but I couldn't do anything about it either. Thankfully surgeon and rest of OR team were fab and all was well and thank you again for going above and beyond with your clarification. It really does help, prob more than you know!

TahoeDoc (author) from Lake Tahoe, California on September 05, 2012:

Hi Sumer,

The levels of anesthesia really exist on a continuum. During any given procedure, the level of anesthesia may change expectedly or unexpectedly, based on surgical, surgeon, anesthesiologist and patient factors.

Sounds like you were under deep sedation with agents that MOSTLY caused amnesia along with the sedation. When those agents were less prominent or wore off to some degree, you were able to be 'more conscious' if that makes sense and form and retain memories.

It doesn't sound like you were under general anesthesia since you remember, and were making sounds and moving. It gets a little more confusing since general anesthesia can occur from time to time when deep sedation is being used. But a patient can go into and out of general to vacillate between different levels of sedation. In any case, your overall anesthetic would seem to qualify as a sedation.

In this case, having some memories is not really considered 'coming to' or of having intraoperative awareness as it would be if you were intended to be unconscious with general anesthesia. I hope that makes a tiny bit of sense.

So, the short(er) answer is that yes, it is within normal limits to have some memories of being in the operating room. The local anesthetic used by the surgeon should prevent you from feeling pain, but not pressure. When your level of sedation lightens, it is common to be confused and 'pull away' from a stimulus, even if its just pressure until you are able to understand what is going on OR be sedated deeper again to prevent the movement or memories.

Good lord, I hope that makes sense….

Sumer on September 05, 2012:

Hi Dr. I have a question regarding MAC anesthesia. I recently had a procedure requiring several biopsies under my arm and it was agreed upon to use MAC anesthesia. During pre-op, the anesthesiologist prepared me that we may transition more into general vs just MAC (which was fine obviously) however when the nurse anesthetist came and took me, she informed me we would only be doing a lighter MAC and that would be sufficient. I was fine with that as long as I would be out of it and she said I would be. Problem was, I came to during the middle of the procedure. Could hear everything, began moving, couldn't talk but could make noise. Couldn't feel pain, but def pressure. My surgeon is the one who noticed I was pulling away and requested more meds be administered. I'm just curious if this is common or expected with MAC for future reference. I'm not upset about what happened I would just like to be prepared for the next time. I was a little confused as during pre-op I was prepared for general and it ended up being (You were the first place I thought to come to and sure enough you had a hub posting :) Thank you!!

Marcy Goodfleisch from Planet Earth on May 20, 2012:

I would love to have had this information when I had surgery a few years ago - I had questions and of course was anxious. Everything went well, but I would have benefitted from understanding it a bit more! I will refer back to this hub if I ever need a procedure again!

Voted up and up!

Lisa McKnight from London on May 15, 2012:

Great explanations about sedation. I love the way you write, it makes medical procedures and effects much easier to understand.

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