February 22, 2018

expert reaction to study looking at surgery, anaesthesia and memory

Scientists publishing in Anaesthesia investigate whether surgery and anaesthesia can affect memory.

Dr Robert Stephens, Consultant in Anaesthesia, UCLH, and Honorary Senior Lecturer in Anaesthesia and Perioperative Medicine, UCL, said:

“The study links having a surgical condition and an operation for that condition with a worsening of memory in this group of people, but the memory worsening appears on average to be subtle and probably noticed only by tests.

“It’s not possible to pick apart whether it’s the surgical condition, the operation for that condition, the anaesthetic (which was a general anaesthesia or ‘awake’ regional anaesthesia) or anything else that can happen around that time (such as a problem after surgery) that is linked to memory worsening.

“The study does show that more surgery and/or more anaesthesia is associated with more significant memory worsening, although even then the effect is still small.

“There is one unusual thing about the study: 1 in 20 to 30 people in the study had had ECT (electroconvulsive therapy, used mainly for very severe depression) which we know is associated with memory changes.  This seems a high number in a general population, and it may have affected the results.  For example only 2,200 people had ECT in the whole of the UK in 2015-16, by comparison.”

Dr Peter Odor, Research Fellow, St George’s, University of London, said:

“This is the first study to demonstrate an association between surgery and/or anaesthesia and slightly lower scores on short term memory tests in otherwise apparently healthy middle-aged people (albeit with a family history of AD).

“The effect observed is very small (but dose-dependent) and very unlikely to be one that would be detectable without specialised testing.  There is no evidence that the public should be dissuaded from undergoing surgery if indicated.

“The question remains whether it is the process of surgery or effects of anaesthetic drugs that are attributable as the cause of this effect.  We are now beginning to appreciate that the stress surgery exerts on the body has effects that last far longer than the initial recovery period.  This is particularly true when patients suffer a complication, such as an infection after an operation.  Whilst this often extends the hospital stay, it also has measurable effects on physical fitness lasting years after surgery.  The cognitive effects detected in this study may be a manifestation of the effects of post-operative complications, but the data does not explicitly describe rates of complications on the included patients.

“I think this is subtle evidence that adds to a growing understanding of the trauma that surgery can represent.  Whilst this study shows only a small effect, it remains true that healthcare professionals need to be careful and sensitive in detecting problems and managing changes in patients after operations.”

Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“I think there is an important difficulty in interpreting the results of this study, and it’s as follows.  People have surgery for a reason.  Therefore there must be some health differences, on average, between the people who had surgery and the people who didn’t.  Maybe the observed differences in performance on memory tests were due to these health differences, and not directly to the surgery or anaesthesia.  It’s also possible that the memory differences are due to some other underlying differences between those who had surgery and those who didn’t, something in their previous lives or their genetics for example, that led to health differences and in turn led to the need for surgery.

“This study does provide evidence of an association between surgery and performance on some memory tests, though the association is not very strong.  But the nature of the study means that it can’t tell us anything direct about what causes the association.  The top line of the press release asks, “Can Surgery and Anaesthesia Affect Memory?”  For me, the answer is, “Well, it might, but we just can’t tell from this research”.”

Prof Thom Baguley, Associate Dean for Research and Professor of Experimental Psychology, Nottingham Trent University, said:

“The authors have observed an association between having surgery and memory, but the differences are small.  This is a potentially important finding, however, they are very clear about the limitations their work in terms of the small sample size, and it is premature to conclude that the effect is causal.  In particular the number and length of surgeries is not randomly allocated and so there are a number of confounding factors that could explain the findings including biases in the sample and other unaccounted for risk factors.  The work could be valuable in motivating larger studies able to tease apart some of the confounding factors, or in confirming that any long-term risks in terms of memory are low relative to the benefits of surgery.”

* ‘Cognitive decline in the middle-aged after surgery and anaesthesia: results from the Wisconsin Registry for Alzheimer’s Prevention cohort’ by L. C. Bratzke et al. published in Anaesthesia on Thursday 22 February 2018.

Declared interests

Prof Kevin McConway: “I am a member of the SMC Advisory Committee.”

None others received.