Rest Easy? Anesthesia and Cognitive Health

If you've ever gotten a shot of Novocain before a tooth filling or an epidural to ease your labor pains, you can appreciate the benefits of anesthesia. Anesthetic drugs, usually administered before major or minor surgery, are useful for both the patient and the surgeon—keeping the pain at bay and the patient still. There are three main types of anesthesia:

Local anesthesia numbs small, very specific parts of the body through an injection.

Regional anesthesia numbs a specific but large portion of the body through an injection near a cluster of nerves. The patient may remain awake or be sedated.

General anesthesia numbs the entire body and causes a full loss of consciousness. It is typically inhaled as a gas or vapor or injected into the veins.

WHAT THE EVIDENCE SAYS
There is a common perception that anesthesia may compromise cognitive health. While post-surgical cognitive impairment is common, scientists are still evaluating whether it is caused by anesthesia or other aspects of surgery. Postoperative delirium (POD) involves rapidly fluctuating mental status with inattention and altered consciousness, while postoperative cognitive dysfunction (POCD) is a more subtle impairment of memory, understanding, and attention. Neither of these conditions constitutes dementia and both are usually temporary, typically resolving within days or weeks.

A small percentage of surgery patients do experience persistent cognitive decline after surgery, but researchers are still examining whether a similar decline would have occurred without surgery [1-3] and, if surgery did cause the decline, was it due to anesthesia or other aspects of surgery. Surgery itself is inherently serious, regardless of the anesthesia used. It can trigger neuroinflammation, activate stress hormones, disrupt blood flow and oxygen delivery to the brain, damage the blood-brain barrier, and alter chemical signaling in the brain [2][4]. Surgery may also disrupt sleep and the 24-hour circadian rhythm, which impacts brain health [4].

Patients with preexisting cognitive impairment have a higher risk of POD and patients who experience POD have a higher risk of future cognitive decline [2][5][6]. Neither condition has yet been linked to the type of anesthesia used but the depth of anesthesia may be important [7][8]. Special brain electrical activity monitors (i.e., bispectral index) used during surgery have been reported in small clinical trials to reduce the risk of postoperative delirium [9]. The results of a more conclusive clinical trial will be available in 2020 [10].

WHAT YOU CAN DO
There are major gaps in our knowledge about who is at risk for long-term cognitive decline after surgery and how that risk can be reduced [11]. In the meantime, older adults can reduce their risk of POD by consulting with a geriatrician (i.e., a physician who specializes in the unique needs of older patients). In three randomized controlled trials, involving a geriatrician during the surgical process reduced the risk of delirium by more than 40 percent [9], most likely because the geriatrician influenced clinical care to avoid known risk factors [12].

Resources for more information include:
• A review of the evidence that, although very limited as of 2015, suggests that anesthesia is not a primary factor in the long-term risk of dementia.
• A 2016 Research News editorial highlighting the need for research to protect patients from postoperative cognitive decline, authored by Alzheimer’s Drug Discovery Foundation staff and collaborators

 

1. Avidan, M.S. and A.S. Evers, The Fallacy of Persistent Postoperative Cognitive Decline. Anesthesiology, 2016. 124(2): p. 255-8.
2. Fong, T.G., et al., The interface between delirium and dementia in elderly adults. Lancet Neurol, 2015. 14(8): p. 823-32.
3. Inouye, S.K., et al., The short-term and long-term relationship between delirium and cognitive trajectory in older surgical patients. Alzheimers Dement, 2016.
4. Maldonado, J.R., Neuropathogenesis of delirium: review of current etiologic theories and common pathways. Am J Geriatr Psychiatry, 2013. 21(12): p. 1190-222.
5. Ags/Nia Delirium Conference Writing Group, P.C. and Faculty, The American Geriatrics Society/National Institute on Aging Bedside-to-Bench Conference: Research Agenda on Delirium in Older Adults. J Am Geriatr Soc, 2015. 63(5): p. 843-52.
6. Dyer, C.B., C.M. Ashton, and T.A. Teasdale, Postoperative delirium. A review of 80 primary data-collection studies. Arch Intern Med, 1995. 155(5): p. 461-5.
7. Whitlock, E.L., et al., Postoperative delirium in a substudy of cardiothoracic surgical patients in the BAG-RECALL clinical trial. Anesth Analg, 2014. 118(4): p. 809-17.
8. Radtke, F.M., et al., Monitoring depth of anaesthesia in a randomized trial decreases the rate of postoperative delirium but not postoperative cognitive dysfunction. Br J Anaesth, 2013. 110 Suppl 1: p. i98-105.
9. Moyce, Z., R.N. Rodseth, and B.M. Biccard, The efficacy of peri-operative interventions to decrease postoperative delirium in non-cardiac surgery: a systematic review and meta-analysis. Anaesthesia, 2014. 69(3): p. 259-69.
10. Wildes, T.S., et al., Protocol for the Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) study: a pragmatic, randomised clinical trial. BMJ Open, 2016. 6(6): p. e011505.
11. Dacks, P.A., et al., Prevention of cognitive dysfunction following surgery: An unmet clinical opportunity. Alzheimer's & Dementia, 2016.
12. American Geriatrics Society Expert Panel on Postoperative Delirium in Older, A., Postoperative delirium in older adults: best practice statement from the American Geriatrics Society. J Am Coll Surg, 2015. 220(2): p. 136-48 e1.

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