By Will Boggs MD
About one in 20 patients might be aware of sensory stimuli during anesthesia, a rate lower than previously reported, according to an international, multicenter study.
“We were pleased that the incidence of connected consciousness after intubation was lower than we feared, but we must be cautious, given the low event rate, with any recommendations based on our secondary analyses,” Dr. Robert D. Sanders from the University of Wisconsin-Madison told Reuters Health by email.
Although explicit recall of intraoperative events is rare, such recall is likely to be impaired by the amnesic effects of anesthetics. The isolated forearm technique (IFT), however, provides clinically relevant real-time information about the presence of consciousness of sensory stimuli (so-called connected consciousness) under anesthesia.
Previous studies based on IFT suggest a connected consciousness rate of about 37% of patients under general anesthesia, but many of the studies were small and had variable dosing of anesthetics.
Dr. Sanders and colleagues collected data on the incidence of IFT responsiveness before and after intubation and on variables that may be associated with the likelihood of responsiveness, including patient and anesthetic factors.
Of the 260 patients studied, 4.6% were IFT responsive after intubation, and five of these (42% of IFT responders; 1.9% of the total cohort) reported pain through a second hand squeeze, the researchers report in Anesthesiology, online December 15.
When queried within 24 hours of the operation, however, none of the patients reported explicit awareness of intraoperative events.
IFT responders were younger than nonresponders, on average, but otherwise did not differ in terms of baseline characteristics.
Depth of anesthesia was higher for responders than for nonresponders before and after intubation, and responders had a higher incidence of observer-rated signs of sympathetic activation (lacrimation, tachycardia, or hypertension) after intubation.
“Having established the incidence of connected consciousness, future studies must focus on reducing this incidence and improving the care of our patients,” Dr. Sanders concluded.
Dr. Michael Wang from the University of Leicester in the U.K., who has studied the psychological aspects of anesthesia and surgery, told Reuters Health by email, “It is heartening that at last the anesthesiology establishment is beginning to take note of the IFT and its relevance to the detection of consciousness which Dr. Ian Russell and I have been advocating for the last 25 years. For much of that period most anesthesiologists have dismissed the IFT as ‘invalid’ or ‘impractical’ mainly due to the absence of correlation with post-operative recall, content to rely on post-operative patient complaint.”
“Many may feel reassured that the rate of positive IFT response was only 4.6%, but it needs to be emphasized that a further 7% had spontaneous movement in the isolated hand making verification of a positive response unavailable,” he noted. “So the figure could be as high as 11.5%, i.e., more than one in 10. Moreover, the period of intubation, whilst highly stimulating, represents a very short period in the context of the total duration of a general anesthesia (GA), and in our experience, positive IFT responses are possible at any point during surgery. So again, this is an underestimate of the total incidence of positive IFT responding during GA.”
“The IFT is not only a valid measure of anesthetic effectiveness,” Dr. Wang concluded. “It is the gold standard for intraoperative monitoring of consciousness when a muscle relaxant is being used.”
Dr. Wang has co-produced a training video on the application of IFT, available at http://bit.ly/2htAepG.
Dr. Thomas Hamp from Medical University of Vienna, Austria, has also used IFT. He told Reuters Health by email, “The main message should be: yes, connected consciousness actually occurs at a relevant frequency. We do not yet know how to reduce this frequency or if this is a real problem in terms of psychological problems/outcomes, etc., but we should think about it. And the IFT seems to be the only method to pick this up.”
He added, “I think none of our patients would accept such a high rate of connected consciousness. ‘Dr. are you sure I will not recognize anything?’ ‘Well, we are not sure; about 4% of our patients seem to be connected to the environment during anesthesia and about 2% report pain during anesthesia, but don’t worry, you will not know afterwards.'”
Dr. Jaideep J. Pandit, a consultant anesthetist at Oxford University Hospitals in the U.K., said, “The finding of a positive patient response to command remains fascinating and intriguing. The main debate revolves around how to interpret this.”
“The authors use the complex term ‘connected consciousness’ which is not easily understood or explained,” he told Reuters Health by email. “An alternative interpretation is that these responsive patients are in a unique state of mind called ‘dysesthesia’, in which they move only to command, but not spontaneously. In this state, patients are aware of their surroundings, but disinterested in them. It is unfortunate the authors did not discuss this alternative interpretation.”
“The authors make no mention of recent reports that this finding cannot be reproduced in patients who remain unparalysed by neuromuscular blocking drugs during surgery: it is only seen in patients in whom these paralyzing agents are used,” he said. “This raises much more interesting questions about the role of these neuromuscular blocking drugs in this response.”
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