Opinion Creative Commons, CC-BY
Postoperative Cognitive Decline
*Corresponding author: Phillip Gordon, Department of Anesthesiology, California Pacific Medical Center, PO Box 7999, San Francisco, CA 94120, USA
Received: July 23, 2019; Published: August 06, 2019
Post-operative cognitive decline (POCD), described many years ago , remains a challenge for all physicians who care for elderly patients. A lot of work has been done in this area but investigators need to be mindful about incorporating some basic precepts into their research protocols. While central nervous system dysfunction after surgery and anesthesia has been described to occur, especially in older adults, it is important to bear in mind that, as Silverstein and colleagues  point out, any illness requiring hospitalization may be associated with cognitive decline. This introduces the possibility that cognitive decline occurs as a concomitant of generalized illness rather than being causally related to surgery and anaesthesia and speaks to the need for not only age-matched controls but also disease-matched and hospitalization-matched clinical cohorts, as well. Another confounder of the correlation between POCD and mortality reported by Monk and colleagues 3] is the observation made by a number of investigators that cognitive decline itself increases the risk of mortality in older adults [4,5]. As suggested by Newman and colleagues , the very term POCD as a binary definition of what may be, in reality, a continuous process may require modification to reflect the necessity of examining cognitive change as a continuum that marches through discrete events such as surgery and anesthesia. This will necessarily influence the methodology by which changes in test performance are analyzed.
Of major but little-recognized importance is the 15-minute neurological examination developed by Inzitari and colleagues  to elicit subtle but clinically detectable neurological abnormalities (SNAs). These SNAs are defined as abnormalities demonstrated in the absence of patient complaints which are also not associated with any neurological disease. Follow-up examination at four and eight years revealed that patients who had three or more SNAs at initial evaluation had an increased risk of cognitive decline, cerebrovascular events, and death, possibly because the SNAs signaled a concomitant decline in cognitive reserve . The authors did not track whether patients had had surgery and anesthesia during the follow-up period. In light of the progression of the otherwise non-detected neurological deterioration demonstrated by Inzitari and colleagues , it is therefore essential that studies of POCD include a uniform neurological examination of all patients and control subjects. The neurological examination must have good inter-rater agreement and reproducibility. Without prior knowledge of SNAs, it is impossible to assign causation to the cognitive dysfunction that may occur after surgery and anesthesia. Is it the normal progression of a condition, however subtle, present preoperatively or is it the effect of surgery and anesthesia alone or have surgery and anesthesia worked in some way to hasten the progression of the preoperatively present condition? Clearly, whatever else the experimental protocols include to achieve uniformity and facilitate inter-study comparison (age- and disease-matched controls in every study and uniformity of operation, anesthesia, neuropsychological evaluation tools, testing intervals, statistical analysis, control subjects), neurological examination for both gross and subtle neurological abnormalities must be included too.
Even in the absence of POCD study protocols, preoperative information about SNAs would facilitate the discussion of informed consent when older adults are contemplating surgical procedures as neurological abnormalities, even in the absence of overt symptoms, have been correlated with POCD . It may thus be advisable for an SNA “score,” as developed by Inzitari and colleagues  with their brief neurological examination, to be included with the other vital signs measured in older adults before surgery. Clinicians can work to mitigate some of the risk factors associated with POCD. For example, postoperative delirium , a correlate of POCD , is associated with increased intraoperative blood loss and postoperative transfusions, a postoperative hematocrit of less than 30%, and severe postoperative pain. The Hospital Elder Life Program has also developed interventions to decrease the incidence and severity of delirium. These include the frequent presentation of orienting information, physical activity, cognitive stimulation activities, use of visual aids and auditory amplifying devices, sleep inducement through non-pharmacological methods, assistance with alimentation, geriatric-psychiatric consultations, and patient and family education. The risk of delirium has been shown to be reduced using these techniques [11,12] and thus perhaps the incidence of POCD.
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