"Accidental awareness" is the terrifying phenomenon when patients can actually hear and feel surgeons cutting into them with no way to communicate that they are conscious. Needless to say, the experience can be extremely terrifying and even cause post-traumatic stress disorder.

The largest study to date investigating the prevalence of this phenomenon has found that it is quite rare, and the researchers identified risk factors that can be addressed in an effort to prevent it entirely. The study was the focus of the 5th National Audit Project, which seeks to better understand relatively rare anesthesia-related conditions. The findings were published in the journal Anaesthesia, with Jaideep Pandit of Oxford University Hospitals as lead author.

While previous studies have found that accidental awareness occurred in one out of 1,000 patients, this new study found that the overall odds of waking up during surgery is about one in 19,600, or roughly 0.005% of the time. In the United States alone, there are over 21 million surgeries each year that require general anesthesia, and about 1,050 will experience an episode of consciousness during the procedure.

It is important to note that the majority of the episodes lasted fewer than five minutes, and typically occur when the patient was either being put under or being brought out of anesthesia; not when the surgery was happening. However, whether or not the awareness actually happens when the patient is opened up, they reported feeling pain, hallucinations, and asphyxiation.

Half the patients who wake up under anesthesia will experience psychological trauma from the experience. General anesthesia is designed to cause temporary paralysis and relax the muscles in order to allow surgeons to operate more easily. If the patient wakes up and isn’t able to move, they aren’t able to let the surgeons know that they are awake. This can be an incredibly terrifying and painful experience. Increased heart rate or blood pressure would alert the doctors, but those physiological cues can be muted by medications given as part of the surgical procedure.

Why does this happen? There are some significant risk factors associated with waking up during surgery. These include gender (females are more likely than males to wake up), age (young adults, though not children or teens), obesity, emergency surgeries and C-sections (where less anesthetic is typically used) and anesthesiologists who are early in their training.

It was previously believed that brain monitors would help solve accidental awareness; if surgeons saw spikes in brain activity, they would know the patient was waking up. However, previous studies have had mixed results about whether or not this works.

Another possible approach is the use of nerve stimulators, which would monitor the body’s state of paralysis. This could lessen the amount of medication required, granting the patient the freedom to move if they regain consciousness. This could minimize the number of accidental awareness episodes that occur.

The researchers also stress that if a patient wakes up during surgery, surgeons need to be very supportive of the psychological needs, and be armed with services to provide them before they become a long-time sufferer of depression or PTSD.

[Hat tip CNN]