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How Conscious Am I in Twilight State?



I am scheduled for an ACL reconstruction surgery. I have been given the choice of a general anesthesia or a regional anesthesia (conscious sedation, twilight state). I am not clear about the state of awareness which is involved with the twilight state. Would I be aware of my surroundings, sounds, smells etc. in a conscious sedation or would I be asleep. This is a 2-3 hour procedure and I do not want to be awake, however I am apprehensive about the side effects which can incur with a general, with intubation, nausea, etc. Also, if I have a regional and have a panic attack, is the option open to have a general half way through the procedure, or would I be given additional meds to sedate me? I appreciate your input and expertise.


Thanks for your question. As you indicated, ACL reconstruction can be done under general anesthesia, or with what is known as “regional anesthesia”. Regional anesthesia, in the case of a knee operation, is usually either an epidural or spinal anesthetic. In our center femoral nerve blocks are also used to provide an extended period of pain relief after the surgery. Most of our patients receiving regional anesthesia are given intravenous sedative medications to produce what some people call a “twilight state”. This is a state somewhere between wakefulness and complete unconsciousness. Official definitions and terminology are given below. This state is somewhat similar to normal sleep, although individuals rarely dream. Because levels of wakefulness vary, you may not be in a sleep state throughout, and may be aware of certain activities going on at some times. Your anesthesiologist can attempt to minimize these periods of wakefulness, especially if you discuss your concerns with him or her before the surgery.

A small minority of patients ask us to be allowed to stay fully awake during ACL reconstruction. Some people even want to watch the procedure, and in fact it is possible for the patient to see some of what the surgeon does on television-type monitors. By contrast the vast majority of patients in our practice who elect regional anesthesia are not this adventurous, and request to be asleep enough to be unaware of their surroundings. This is fairly easily accomplished with modern anesthetic agents such propofol, which allow for rapid adjustment of sedation level, and rapid awakening after the agent is discontinued.

As you note, a twilight state in combination with regional anesthesia means that intubation (breathing tube insertion) is not necessary, and there is not much risk of nausea during recovery from the operation. If you are someone who is susceptible to panic attacks you should definitely mention this to your anesthesiologist. If you become uncomfortable or anxious during the surgical procedure, you can certainly be given more sedative medication. There is a continuous process of adjusting the dose and monitoring the response anyway. If general anesthesia really becomes necessary (this is unlikely), additional anesthetic agents will again be given, and the anesthesiologist may decide to insert a breathing tube. I hope you have a pleasant experience with your anesthetic and a good outcome from surgery!

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.


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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