In the latest research concerning general anesthesia during surgery, researchers in Sweden say patients who wake up during the procedure and have a clear memory of the event may develop acute distress and emotional reactions, and in some cases long-term psychological symptoms.
According to Dr. Peter Samuelsson at the County Hospital in Kalmar, of 2,681 patients who underwent general anesthesia between 2001 and 2002, ninety-eight patients (3.7 percent) believed they woke up during general anesthesia.
However following more detailed questioning only 46 patients met the criteria for evaluation.
This involved a 45-minute interview where the patient's detailed description of the awareness event, as well as sensory perception, emotions, and cognition during the episode were recorded and the subjects were also asked about delayed psychological symptoms.
The researchers found that awareness episodes occurred between the ages of 6 and 62 years old even though some events had occurred many years earlier, and the memories remained quite clear.
All the patients had some kind of sensory perception, 20 had experienced pain, which was severe for 14 of them and 17 had felt paralyzed.
Thirty reported an acute emotional reaction, characterized as helplessness, fear, and panic; fifteen patients reported late psychological symptoms, including nightmares, anxiety and flashbacks, and for six the symptoms persisted for years afterwards.
During subsequent surgeries, 19 patients reported a lack of trust in medical staff.
Although some patients never reported their awareness experience to anyone, of the 39 who did, 13 were greeted with skepticism.
Australian researchers too have been examining the effects of anaesthesia and they say dreaming under anaesthesia does not necessarily mean that the anaesthesia is wearing off.
Lead author Dr Kate Leslie, from Royal Melbourne Hospital, and colleagues were interested in the phenomenon as patients who have remembered dreams can be distressed, with some thinking their experience was actual awareness resulting from inadequate anaesthesia.
In their study, the researchers assessed 300 consecutive healthy patients, aged 18-50, who were undergoing elective surgery that required general anaesthesia.
The researchers used the Bispectral Index, a measure of the anaesthetic effect on the brain, to gauge the depth of anaesthesia during surgery.
After the surgery was over, the researchers interviewed the patients about their experience and found that more than one-in-five (22%) of patients reported dreaming.
But they found no significant difference in the average depth of anaesthesia as measured by the Bispectral Index between the dreamers and non-dreamers.
It appears that younger patients, men and those who frequently remembered dreams at home were among characteristics that were associated with dreaming during anaesthesia.
The dreamers where also more likely to be treated with the anaesthetic propofol or receive regional anaesthesia, and were more likely to open their eyes sooner after surgery.
The authors say the dreams experienced under anaesthesia were similar to those during sleep, were usually pleasant and unrelated to the surgery.
The researchers suggest that the similarities between the patients' dreams while under anaesthesia and during natural sleep indicate that the dreams during anaesthesia occur during the early recovery period when patients are still lightly sedated, but are in a definite sleep state.
The researchers say the findings should reassure patients who may think dreaming during surgery is a sign of inadequate anaesthesia.
Both studies are published in Anesthesiology, January 2007.