The assessment of postoperative cognitive function

Abstract

Postoperative cognitive function (POCD) has been subject to extensive research. In the literature, large differences are apparent in methodology such as the test batteries, the interval between sessions, the endpoints to be analysed, statistical methods, and how neuropsychological deficits are defined. Traditionally, intelligence tests or tests developed for clinical neuropsychology have been used. The tests for detecting POCD should be based on well-described sensitivity and suitability in relation to surgical patients. In tests using scores, floor/ceiling effects may compromise the evaluation if the tests are either too easy or to difficult. Uncontrolled testing facilities and change of test personnel may affect the test performance. Practice effects are pronounced in neuropsychological tests but have generally been ignored. The use of a suitable normative population is essential to allow correction for practice effects and variability between sessions. Missing follow-up may severely compromise valid conclusions since subjects unable or unwilling to be examined are particularly prone to suffer from POCD. In the statistical analysis of the test results, the evaluation should be based on differences between pre- and postoperative performance. Parametric statistical tests are not relevant unless the appropriate Gaussian distributions are present, perhaps after transformation of data. The definition of cognitive dysfunction should be restrictive and the criteria should be fulfilled in only a small proportion of volunteers. In the literature, these requirements often have not been fulfilled. This precludes a reasonable estimation of the incidence of POCD and the conclusions of comparative studies should be interpreted with great caution. In this review article, we present a number of recommendations for the design and execution of studies within this area. In addition, the critical reader may use these recommendations in the evaluation of the literature.

Postoperative delirium: risk factors and management: Continuing Professional Development

“…2 An operating definition of POCD has emerged from more than a decade of research by The International Study of Postoperative Cognitive Dysfunction and is characterized by subtle deficits in one or more discrete domains of cognition, e.g., attention, concentration, executive function, verbal memory, visuospatial abstraction, and psychomotor speed. 8 Finally, emergence from anesthesia in children may often be associated with inappropriate motor behaviour, disorientation, and emotional lability. 9 This condition lacks the fluctuating course that is characteristic of delirium and would be considered more appropriately as a drug effect.…”

“…» 2 Une définition opérationnelle des troubles cognitifs dysfonctionnels postopératoires a été obtenue après plus d'une décennie de recherche de l'étude internationale qui y a été consacrée (The International Study of Postoperative Cognitive Dysfunction) et se caractérise par des déficits subtils dans un ou plusieurs domaines discrets de la cognition, par exemple, l'attention, la concentration, les fonctions exécutives, la mémoire verbale, l'abstraction visuospatiale et la vitesse psychomotrice. 8 Enfin, l'émergence de l'anesthésie chez les enfants peut être souvent associée à un comportement moteur inapproprié, une désorientation et une labilité émotionnelle. 9 Cette maladie ne présente pas l'évolution fluctuante qui est caractéristique du delirium et serait considérée, de façon plus logique, comme un effet secondaire des médicaments.…”

Increased incidence of postoperative cognitive dysfunction 24 hr after minor surgery in the elderly

“…4 These observations are consistent with the idea that advancing age is a risk factor for POCD. 12 Severe, early POCD is a problem for 15% of patients 12 and may influence rehabilitation. We did not include subjective (self-assessed) measures of POCD because they have been shown to over-estimate its incidence.…”

“…The definition of cognitive dysfunction was based on agreed protocols from the literature. 12 Changes in neuropsychological tests were compared with a control group, which consisted of a matched group of elderly people, drawn from non-surgical patients within the hospital. Analysis commenced with the control group.…”

Early benefit of preserved cognitive function is not sustained at one-year after cardiac surgery: a longitudinal follow-up of the randomized controlled trial

“…A Z-score was calculated for each main variable in each patient by subtracting the preoperative score from the postoperative score and dividing the difference by the preoperative standard deviation of that variable. 9 Subsequently, a combined Z-score was calculated by the summation of all of the individual test scores. Patients with a negative score of \ 1 were considered to have POCD.…”