Perioperative Cognitive Protection

There is ample evidence that surgical patients undergoing anesthesia are at risk of cognitive decline, either in the form of dementia post-operatively or ongoing cognitive dysfunction. Cognitive issues after surgery are a major public health issue, with up to 60% of cardiac surgery patients and 10% of general surgery patients experiencing some level of cognitive dysfunction several months after surgery. Furthermore, still an active area of research is the correlation between delirium and longer term cognitive dysfunction, but it’s becoming more clear that helping to prevent delirium and immediate postoperative cognitive issues is an important step in preventing longer term cognitive decline in surgical patients. Currently, there is little agreement on the actual mechanism of post-operative cognitive dysfunction, however numerous research groups have been examining perioperative strategies for cognitive protection. These strategies can be split into pre-operative, intra-operative, and post-operative approaches to patients undergoing surgery requiring an anesthetic.

Pre-operatively risk stratifying patients is an important first step in preventing delirium and cognitive decline. The risk factors for delirium in patients undergoing anesthesia have been fairly well studied and include advanced age, a decreased cognitive baseline, and a low education level. One study by Rudolph et al. looking at cardiac surgery patients found four major risk factors for postoperative delirium – history of stroke, low albumin, depression, and a low mini-mental state exam. Another study with non-cardiac patients by Marcantonio et al. found risk factors for delirium to include alcohol abuse, cognitive or physical impairment, age > 70, and abnormal electrolytes. There are fewer studies that have looked at risk factors for longer term cognitive decline, but it’s clear from work that’s been done that advanced age is an independent risk factor. Further research is focusing on risk from the molecular level, with evidence that intracerebral amyloid-β (Aβ) deposition and high tau/Aβ ratio in cerebrospinal fluid, as well as specific Aβ genotypes, may indicate cognitive risk. Risk stratifying patients prior to surgery based on these criteria is a crucial step in helping to identify and protect patients with low cognitive reserve.

Intra-operative strategies for cognitive protection have been increasingly studied in recent years, but conclusions have been mixed. For example, some studies have indicated that the use of volatile anesthetics results in less cognitive decline in the days after surgery than propofol, but other studies have indicated the opposite, so it’s unclear if the mechanism of anesthesia maintenance has any effect on cognitive function post-operatively. There is some evidence that limiting depth of anesthesia and avoiding burst suppression is protective against delirium in both cardiac and non-cardiac patients. However, studies have been mixed correlating depth of anesthesia with long-term cognitive function, with studies published that have shown better, worse, and no difference. Furthermore, studies on avoiding the use of general anesthesia in favor of regional or neuraxial anesthesia have not shown less incidence of cognitive decline. However, these studies have not been controlled for level of sedation when regional or neuraxial anesthesia was used.

Another aspect of intraoperative care that’s been explored in relation to cognitive decline is MAP goals, with higher MAP goals (80-90) during cardiopulmonary bypass in one study being associated with better cognitive outcomes; however other studies have not shown longer term cognitive benefits (after six months). An active area of study is the use of near-infrared spectroscopy (NIRS) or middle cerebral artery Doppler to individuate autoregulation goals and maintain proper cerebral perfusion pressure intraoperatively. Finally, specific drugs intraoperatively, most studied being benzodiazepines and anticholinergics, can increase the risk of postoperative delirium. While continuous use of these medications has been studied thoroughly (and shown to be harmful cognitively), it’s still unclear whether a single dose of benzodiazepine increases postoperative delirium.

Postoperatively, there are numerous interventions that have been shown to reduce delirium, including non-pharmacologic interventions (replacing hearing aids, eyewear post-operatively, re-orienting, etc.), pain management, avoiding anticholinergics, and accurate medication reconciliation. Overall, cognitive protection perioperatively is an evolving field, and its goals are an incredibly important aspect of patient care.

References:

C. Brown, S. Deiner, Perioperative cognitive protection, BJA: British Journal of Anaesthesia, Volume 117, Issue suppl_3, December 2016, Pages iii52–iii61,

Monk TGWeldon BCGarvan CW, et al. . Predictors of cognitive dysfunction after major noncardiac surgery. Anesthesiology  2008; 108: 18–30

Brown CHIVLaflam AMax L, et al. . The impact of delirium after cardiac surgical procedures on postoperative resource use. Ann Thorac Surg  2016; 101: 1663–9

Steinmetz JRasmussen LS. Peri-operative cognitive dysfunction and protection. Anaesthesia  2016; 71: 58–63

Inouye SKMarcantonio ERKosar CM, et al. . The short-term and long-term relationship between delirium and cognitive trajectory in older surgical patients. Alzheimers Dement  2016; 12: 766–75

Rudolph JLJones RNLevkoff SE, et al. . Derivation and validation of a preoperative prediction rule for delirium after cardiac surgery. Circulation  2009; 119: 229–36

Marcantonio ERGoldman LMangione CM, et al. . A clinical prediction rule for delirium after elective noncardiac surgery. JAMA  1994; 271: 134–9

Le Freche HBrouillette JFernandez-Gomez FJ, et al. . Tau phosphorylation and sevoflurane anesthesia: an association to postoperative cognitive impairment. Anesthesiology  2012; 116: 779–87

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