A study published by the journal PLoS One suggests that 2 relatively simple measures can help to reduce the incidence of post-operative cognitive dysfunction (POCD) in older patients: administering a small dose of the anti-inflammatory drug dexamethasone immediately before an operation and avoiding profound anaesthesia during the operation.
Opinions on the adequate depth of anaesthesia and the risks of very profound anaesthesia currently diverge. Excessively superficial anaesthesia is known to incur a risk of patient recall of the procedure, which is undesirable.
“Our findings confirm recent evidence that the deeper the anaesthesia-induced hypnosis, the higher the incidence of POCD. The literature points to a link with the systemic inflammatory response induced by surgical trauma, damaging the central nervous system. If so, the use of an anti-inflammatory drug may have a protective effect,” said principal investigator Maria José Carvalho Carmona, University of São Paulo’s Medical School (FM-USP), São Paulo, Brazil.
The researchers evaluated 140 patients aged between 60 and 87 who underwent surgery under propofol-induced general anaesthesia at the Central Institute of Hospital das Clínicas, FM-USP’s teaching hospital, in most cases for removal of gallstones.
Pre-operative assessment included a battery of tests to measure mental and cognitive status. Patients who failed to achieve a cutoff score were excluded. The remaining subjects were divided randomly into 4 groups. In the operating room, deep anaesthesia typical of major surgical procedures was induced in the first and third groups, and more superficial anaesthesia in the second and fourth. Only the third and fourth groups received dexamethasone.
The depth of anaesthesia was monitored using bispectral index (BIS) technology, which processes electroencephalogram signals to measure drug-induced unconsciousness. The researchers classified a BIS of 35-45 as deep anaesthesia and a BIS of 46-55 as superficial anaesthesia.
In the fourth group (superficial anaesthesia with dexamethasone), the incidence of POCD was 15.3% immediately after surgery, but after 6 months the pre-operative cognitive status was restored in all patients.
“The results reinforce recent evidence of the importance of avoiding deep anaesthesia,” Dr. Carmona said. “With regard to the use of dexamethasone, more research is needed to confirm our finding, preferably in multicentre trials, but there are strong indications that it can be beneficial in many cases.”
“The causes of and risk factors for POCD are still being discussed,” she said. “Little is said about rehabilitation or ways of helping patients recover pre-operative cognitive function.”
One of the obstacles to reliable diagnosis and rehabilitation is a lack of practical and secure instruments for pre- and post-operative cognitive assessment. “The tests available today are either too time consuming or quick but unreliable,” Dr. Carmona said. “This makes it hard to follow up on patients.”