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It is usually phrased like a horror story: a patient feels like being trapped in a corpse, unable to move or scream and feeling intense pain, but surgeons continue to operate not noticing that patient is conscious.

It is reasonable to accept occasional failures of anaesthesia, but it is difficult to believe that there are no ways in modern medicine to monitor a patient’s consciousness during a surgery.

How often does anaesthesia awareness happen and are there means to avoid it?

Bonus points: are there studies concerning how many cases are actually noticed in the OR versus the cases reported afterward by the patient?

  • I'm assuming you mean to ask how to avoid not noticing, not how to avoid waking up as a patient? – Nanne Mar 9 '11 at 13:07
  • @Nanne Yes I mean not noticing – Egle Mar 9 '11 at 13:35
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    As worded, this is a medicine question, not a skepticism question. I fail to see what you're being skeptical about. – Borror0 Mar 9 '11 at 13:54
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    I think this question would be much more appropriate if it would just ask more like "Does it really happen and how often?", the question "How to avoid it" is rather off-topic. – Mad Scientist Mar 10 '11 at 7:11
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    @Suma Anesthesia awareness is not myth, it happens. My scepticism is towards rate of it and doubt that doctors can't monitor that. – Egle Mar 10 '11 at 17:37
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Various sources indicate the overall incidence of intraoperative awareness with recall is about 0.2 – 3%.

Modern anaesthesia consists of three agents - a light dose of painkiller, a paralyzing drug, and an amnesic agent that blocks memory of the experience - most patients do not remember awakening and so do not report it to their doctors. The paralyzing drug prevents any struggle or gesture as sign of distress so the surgeon, the anaesthesiologists, and nurse cannot see that the patient is awake. Some experimental studies estimate the rate of awareness may be as high as 44%.*

That means that overall rate would be higher if all cases are added, but it is impossible as patients with amnesia don’t report.

I wanted to know what the rate of UNNOTICED cases is during operation but I failed to get answer. Now I see why – even recorded data is quite loose and doesn’t include all cases.

To put it simple – there is big grey area where data collection is impossible:

  • Awareness with recall / noticed by clinical assessment (pulse, blood pressure, sweating, lacrimation, skin conductance, lower oesophageal contractility, isolated forearm technique, EGG, BIS* ) – possible to collect data

  • Awareness with no recall / noticed by clinical assessment - possible to collect data

  • Awareness with recall / unnoticed by clinical assessment – possible to collect data IF patient is willing to report.

  • Awareness with no recall / unnoticed by clinical assessment - impossible to collect data


Is it possible to monitor depth of the anaesthesia, so awareness is always noticed?

This overview on the currently (2008) available monitoring systems gives the list of methods :

A. Subjective methods

  1. Autonomic response
  2. Patient Response to Surgical Stimulus (PSRT) scoring system
  3. Isolated forearm technique

B. Objective methods

  1. Spontaneous surface electromyogram (SEMG)
  2. Lower oesophageal contractility (LOC)
  3. Heart rate variability (HRV)
  4. Electroencephalogram and derived indices
  5. Evoked potentials

Reliability of all those methods depends on chosen anaesthetic agent, hypnotic drug, type of surgery. Bispectral Index (BIS) seams to be the best method, but it also have some shortcomings.

In conclusion it says:

At present, no monitoring system has been found to measure the depth of anaesthesia reliably for all patients and all anaesthetic agents. All available monitors are no predictors, whether depth of anaesthesia is sufficient for the next painful surgical stimulus. They can only monitor the anaesthetic state at the time of measurement. There is no "golden number" predicting absolutely safely that the patient is in adequate anaesthesia.

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    On the flip side how do we know the anaesthetic usually does work in making us unaware? Given "Awareness with no recall / unnoticed by clinical assessment - impossible to collect data" couldn't most people be aware of the surgery but unable to recall it afterwards? I guess the expectation is the methods used by the doctors to determine if a patient is conscious, work. – Celeritas Nov 22 '15 at 23:09
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This is a complex issue

There is now way to know if anesthesia is causing unconsciousness, or just paralysis, amnesia, and muscle relaxation.

During operation, only paralysis, and muscle relaxation can be directly monitored So in cases where a patient regains consciousness, but remains paralyzed there is no way to know it.

There are other methods to measure anesthetic depth, based mostly on analyzing EEG measurements, but as much as I know if they don't perform better in that respect.

  • EEG/brain activity can help, not sure how much or how often. Did help them though when my father woke up on the operating table 1 hour into a 4 hour procedure, paralysed but fully aware of everything going on around him. – jwenting Jul 5 '11 at 6:48
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About how frequently Anesthesia awareness happens, Wikipedia tells us:

Awareness occurs in 20,000–40,000 patients out of the 20 million US surgeries performed each year (between 0.1% and 0.2%)1 when patients have anesthesia that is inadequate to keep them unconscious during an operation. Large trials have demonstrated that around 1 to 2 per 1000 patients experience some form of awareness.2 3

If anesthesia awareness does occur, about 42% feel the pain of the operation, 94% experience panic/anxiety (sometimes because they cannot breathe), and 70% experience lasting psychological symptoms.4

References:
1: Sebel PS: The incidence of awareness during anesthesia: A multicenter United States study. Anesth Analg 2004; 99:833-9

2: Sandin RH, Enlund G, Samuelsson P. Awareness during anaesthesia: a prospective case study. Lancet 2000;355:707–711

3: Sebels PS, Bowdie TA, Ghoneim MM. The incidence of awareness during anaesthesia: a multi- centre United States study. Anesthesia and Analgesia 2004;99:833–839

4: N. Moerman et al.,Anesthesiology;79:454–464, 1993

  • 0.1% - 0.2% is a total rate of Anesthesia awareness cases. My question was how often it is unnoticed during operation and reported just afterwards? – Egle Mar 10 '11 at 18:02

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