Pre-Operative Cognitive Screening for Elderly Patients
Surgery often entails stress, inflammation, pain, medications, and anesthesia, all of which may temporarily compromise a patient’s cognitive function. In addition, risk of perioperative cognitive impairment heightens with aging: depending on the procedure, 30 to 80 percent of elderly patients experience delirium following major surgery1, and older patients are more likely to develop both early and late postoperative cognitive dysfunction.2 Postoperative cognitive functioning has a demonstrated negative correlation with length of hospital stay, cost of care, and risk of early retirement due to health concerns.1 It is therefore of significant clinical interest to perform pre-operative cognitive screening in elderly patients to assess risk of adverse outcomes and identify surgery-related cognitive decline.
One study by Evered et al. revealed both the complexity and importance of pre-operative cognitive screening.3 The authors examined 152 patients aged 60 and older for two different diagnoses of impairment: preexisting cognitive impairment (PreCI), based on neuropsychological measurements, and mild cognitive impairment (MCI), identified using both neuropsychometric assessments and formal memory/cognitive tests. It was found that approximately 20 percent of patients had either a PreCI and MCI, and that frequency of detected cognitive impairments was increased in higher age groups, as expected.
The authors reported that undergoing major orthopedic surgery was frequently associated with development of cognitive deficits in older patients with preexisting mild cognitive impairment. Significantly, it was found that most of these deficits would have otherwise gone undetected in both typical post-operative assessments and daily life, indicating that a large proportion of patients within this demographic may experience undiagnosed surgical complications which ultimately result in cognitive disability and increased need for care. Being able to anticipate this outcome in elderly patients is therefore critical for improving post-operative care management.
Interestingly, Evered et al. also were able to identify which measures most effectively assessed cognitive performance. For example, when patients were given the chance to subjectively report on their own cognitive state, diagnostic rates of cognitive deficits were reduced from 50 percent to 22 percent. This finding would suggest that subjective reporting may be considered a confounding variable in the diagnosis of surgery-induced cognitive deficits. Instead, the authors recommended evaluating for MCI, for a few key reasons: 1) the MCI scale is based on fairly objective cognitive tests, 2) such testing was shown to detect early manifestation of neurological diseases disproportionately prevalent in elderly populations, such as Alzheimer’s disease, and 3) pre-operative MCI can be used to detect mild dementia and predict long-term cognitive outcome.4 Therefore, evaluating for MCI may successfully anticipate increased need for care and long-term cognitive decline, both of which may be exacerbated by the stress of surgery. In fact, following this study, evaluation for MCI has been strongly recommended by both The American College of Surgeons and the American Geriatrics Society.
Taken altogether, the findings of Evered et al. suggest a possible causal relationship between pre-operative cognitive disability and postoperative cognitive morbidity and demonstrate the need for pre-operative cognitive screening, especially for elderly patients. The MCI scale should thus be considered an integral part of pre-operative assessments on patients aged 60 and older.
References
1. Leung JM: Postoperative delirium: Are there modifiable risk factors? Eur J Anaesthesiol 2010; 27:403–5. doi: 10.2147/cia.s2759
2. Monk TG, Weldon BC, Garvan CW, Dede DE, van der Aa MT, Heilman KM, Gravenstein JS: Predictors of cognitive dysfunction after major noncardiac surgery. Anesthesiology 2008; 108:18–30. doi: 10.1097/01.anes.0000296071.19434.1e
3. Evered LA, Silbert BS, Scott DA, Maruff P, Ames D, Choong PF: Preexisting cognitive impairment and mild cognitive impairment in subjects presenting for total hip joint replacement. Anesthesiology 2011; 114:1297–1304. doi: 10.1097/ALN.0b013e31821b1aab
4. Gauthier S, Reisberg B, Zaudig M, Petersen RC, Ritchie K, Broich K, Belleville S, Brodaty H, Bennett D, Chertkow H, Cummings JL, de Leon M, Feldman H, Ganguli M, Hampel H, Scheltens P, Tierney MC, Whitehouse P, Winblad B, International Psychogeriatric Association Expert Conference on mild cognitive impairment: Mild cognitive impairment. Lancet 2006;367:1262–70. doi: 10.1016/S0140-6736(06)68542-5