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Print version ISSN 0034-7094
On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.55 no.5 Campinas Sept./Oct. 2005
Postoperative cognitive dysfunction: prevalence and associated factors*
Disfunción cognoscitiva pos-operatoria: superioridad y factores asociados
Gustavo Luchi Boos, M.D.I; Luiz Fernando Soares, TSA, M.D.II; Getúlio Rodrigues de Oliveira Filho, TSA, M.D.III
IME3, CET/SBA Integrado
de Anestesiologia da SES/SC
IIInstrutor Co-responsável do CET/SBA Integrado de Anestesiologia da SES/SC
IIIResponsável do CET/SBA Integrado de Anestesiologia da SES/SC
BACKGROUND AND OBJECTIVES: Postoperative
cognitive dysfunction (POCD) is related to factors such as physical status,
electrolytic, visual and immune disorders, alcoholism, drugs and advanced age.
This study aimed at determining the prevalence of POCD and its associated factors.
METHODS: Participated in this prospective study 55 patients aged 18 to 89 years, scheduled for elective orthopedic, urologic, general or vascular surgeries, under general or regional anesthesia. The Mini-Mental State Examination (MMSE) was applied the day before surgery (M0), at 24 postoperative hours (M1) and 3 to 7 days after surgery (M2). POCD was defined as MMSE score below 24/30 or as a difference equal to or above 4 as compared to M0. Univariate and multivariate analysis variables included age, gender, type of anesthesia and surgery, intraoperative hypotension, hypoxemia or hypocapnia, use of atropine and surgery length.
RESULTS: POCD was observed in eight patients (14.54%). All POCD patients were above 65 years of age. Among these patients, the prevalence of POCD was 28.57%. Only age and preanesthetic MMSE scores were different between patients with or without POCD. The logistic model included only preanesthetic MMSE scores.
CONCLUSIONS: Among the variables included in this study, only preanesthetic MMSE score is a significant independent predictor of POCD.
Key Words: COMPLICATIONS: postoperative cognitive dysfunction
JUSTIFICATIVA Y OBJETIVOS: La disfunción
cognoscitiva pos-operatoria (DCPO) está relacionada a factores como el
estado físico, disturbios electrolíticos, visuales e inmunológicos,
alcoholismo, fármacos y senilidad. Este estudio tuvo el objetivo de determinar
la superioridad de DCPO y sus factores asociados.
MÉTODO: Se estudiaron 55 pacientes, con edad entre 18 y 89 años, sometidos a cirugías electivas ortopédicas, urológicas, digestivas o vasculares, bajo anestesia general o regional. Fue aplicado el Mini-Examen del Estado Mental (MEEM) en la víspera de la fecha de la cirugía (M0), 24 horas después (M1) y 3 a 7 días después la cirugía (M2). La DCPO fue caracterizada por el resultado del MEEM menor que 24/30 puntos o diferencia mayor o igual a 4 puntos con relación al M0. Las variables utilizadas en los análisis uni y multivariadas fueron la edad, el sexo, el tipo de anestesia, el tipo de cirugía, la ocurrencia de hipotensión arterial, hipoxemia o hipocapnia intra-operatorias, el uso de atropina y la duración de la cirugía.
RESULTADOS: DCPO ocurrieron en ocho pacientes (14,54%). Todos los casos de DCPO ocurrieron en pacientes con edad superior a 65 años. En esta banda etária, la superioridad de DCPO fue del 28,57%. Solamente la edad y los valores pre-anestésicos del MEEM difirieron entre los que presentaron y los que no presentaron DCPO. El modelo logístico incluyó solamente el resultado pre-anestésico del MEEM.
CONCLUSIONES: Entre las variables incluidas en este estudio, solamente el valor pre-anestésico del resultado del MEEM puede ser considerado un factor de previsión independiente de la ocurrencia de DCPO.
Postoperative cognitive dysfunction (POCD) is intellectual function deterioration manifested by loss of memory and concentration. Perception and information processing mechanisms, which allow people to acquire knowledge and solve problems, are compromised. These subjective lapses are in general manifested as failure in performing simple tasks. In more severe cases, cognitive disorders are followed by confusion, hallucination and delirium 1.
Most POCD patients have mild neurocognitive disorders only diagnosed by specific neuropsychological tests, such as the Mini Mental State Examination (MMSE).
The incidence of postoperative delirium varies from 5% to 10% in general population and increases to 9% to 26% in the elderly 2.
Several factors have been related to POCD, among them physical status, electrolytic, visual and immune disorders, alcoholism, drugs and advanced age 2. The magnitude of metabolic and endocrine responses to surgical stress has been directly related to POCD 3-6.
Hospital admission results in sensory overload for elderly patients due to hostile characteristics of the environment (noise, lights, immobilization). Similarly, anxiety generated by sleep deprivation, pain and removal from family environment may contribute to POCD. For these reasons, elderly patients may develop cognitive dysfunction even when submitted to minor procedures 7.
POCD, in its different manifestations, increases morbidity and mortality, delays postoperative movements and prevents early rehabilitation 8, contributing to significant increase in hospital costs 6. This study aimed at determining the incidence of postoperative cognitive dysfunction and identifying potential predicting factors.
This study was approved by the Medical Ethics Committee, Hospital Governador Celso Ramos. All patients gave their informed and written consent.
In the period September 24 to December 7, 2001, 100 patients aged above 18 years and admitted for elective orthopedic, urologic, general or vascular surgeries were randomly selected as from the surgical procedures schedule. To assure equal number of patients aged below or above 65 years, patients above 65 years of age were initially selected from each schedule. A second patient scheduled for the same procedure and aged below 65 years was then randomly selected.
Clinical history and previous diseases were recorded the day before surgery and medical records were reviewed. Patients were submitted to physical evaluation and lab tests included blood count, glycemia, creatinine, electrolytes and ECG. Other tests were requested if suggested by history or physical evaluation. Mini Mental State Examination (MMSE) was applied at the same time (M0) 9.
As from this evaluation, patients with depression, dementia (MMSE scores below 20/30) 9, anxiety, illiteracy, hypacusis, severe vision decrease, limitation of upper limbs movements, hyper or hypothyroidism, hyponatremia, hypoglycemia, uremia, cerebral-vascular diseases, brain trauma, neoplasias or central nervous system infections, drug intoxication, liver disease, lung diseases followed by hypoxemia or hypercarbia or degenerative central nervous system diseases were excluded.
Patients under benzodiazepines, anti-psychotic, methyldopa, reserpine, thiazides, beta-adrenergic blockers, aspirin, opioids, cimetidine, insulin or other drugs known to impair cognitive function were also excluded (Chart I) 2.
Patients were not premedicated and the procedure was performed under general or regional anesthesia, decided by the anesthesiologist in charge. An investigator, blind to the anesthetic technique and to peri-anesthetic events, applied new cognition evaluations by MMSE 24 hours after surgery (M1) and between 3 and 7 postoperative days (M2). Patients discharged with less than 3 postoperative days were excluded.
For statistical analysis, POCD was defined as MMSE scores below 24/30 10 or by decrease of 4 or more points during M1 or M2 evaluations, as compared to initial score. Patients were classified as having or not POCD according to this definition and were compared in terms of age, gender, preanesthetic MMSE scores, type of anesthesia and surgery, incidence of intraoperative hypotension (systolic blood pressure decrease above 30% as compared to baseline values, lasting more than 5 minutes or needing vasopressants or inotropics), hypoxemia (peripheral hemoglobin saturation below 90%) or hypocapnia (partial CO2 pressure in expired gas below 25 mmHg), use of atropine and surgery length by Fisher Exact test (categorical variables) Student's t test (continuous variables) or Mann-Whitney test (ordinal variables).
Statistically significant variables were submitted as independent variables to logistic regression, the dichotomous variable of which was the presence or absence of POCD. MMSE of patients with or without POCD were compared among studied moments by two-factor analysis of variance for repeated measures. Significance level was 5% for all statistical tests.
From 100 selected patients, 45 were considered ineligible for the following reasons: 12 patients with brain trauma, 1 patient with temporary repetition ischemic stroke, 2 patients with history of stroke, 1 patient with hypothyroidism, 1 patient with hypothyroidism and chronic renal failure, 1 patient with depression, 9 patients under drugs affecting cognitive function, 14 illiterate patients, 3 patients with Mini Mental State Examination score equal to or below 20 and 1 patient who refused to participate in the study.
Statistical analysis was performed with remaining 55 patients.
POCD was detected in 8 patients (14.54%) in M1. Three patients (5.45%) have maintained MMSE scores below 24/30 in M2. All POCD patients were above 65 years of age with a prevalence of 28.57%. There has been no statistically significant difference between patients with and without POCD in gender, anesthetic technique, surgical specialty, intraoperative hypoxemia, hypocapnia or hypotension and surgery length, as shown in table I. There were significant differences in age. No intravenous anesthetic drug has influenced the incidence of POCD as shown in table II.
Table III shows mean values and standard deviations of sub-scales values (orientation, data retention, attention, memory and speech) and of total MMSE scores in each studied moment. Among POCD patients, there has been significant decrease in orientation scores in M1 (24 hours after surgery), with significant difference between groups in this moment (F (2,106) = 3.32; p = 0.04). Data retention scores were only significantly decreased in the POCD group in M1 and M2, as compared to M0, without significant differences between groups (F (2.106) = 4.18; p = 0.02). There were no intra or inter-group differences in attention (F (2.106) = 2.61; p = 0.08) and memory (F (2.106) = 0.76; p = 0.47) scores. Speech (F (2.106) = 8.75; p = 0) and total MMSE (F (2.106) =19.15; p = 0) scores were significantly lower for the POCD group as compared to those without cognitive disorders during this study.
Logistic regression has detected preanesthetic MMSE score as the single significant independent predicting factor for POCD (odds ratio and 95% confidence interval equal to 0.41 (0.22 - 0.76) for each MMSE score point (p = 0.0038). The logistic model, the parameters of which were a = 21.77 and b = 0.87, has correctly classified 50% of patients with POCD at the 0.5 logit cutoff point when reapplied to the original sample.
All POCD cases in this study were observed in patients above 65 years of age. The prevalence of 29% of patients in this age bracket is in line with the findings of other studies in which prevalence has varied from 9% to 26% 2,3,5,11-13. However, only preanesthetic Mini Mental Status Examination scores were identified as independent predicting factors. Although the age of patients developing POCD was significantly higher as compared to those not developing it, the logistic model rejected age because there were no POCD cases among patients below 65 years of age.
The cutoff point used in this study (23/24 case/no case) was based on a sample of Brazilian literate patients. Sensitivity and specificity of this cutoff point were 78% and 75%, respectively. For illiterate patients, the cutoff point recommended by the same authors is 19/20, with sensitivity and specificity of 80% and 71%, respectively 10. However, illiterate patients were excluded from our study.
As in other studies, gender, type of surgery and anesthesia or their respective length were not considered POCD predicting factors 2,13,14.
Among drugs used in this study, benzodiazepines, etomidate and anti-cholinergic have been involved in postoperative cognitive dysfunction 15,16. In our study, probably due to limitations imposed by the small sample size, no drug used in the peri-anesthetic period was identified as predicting factor for POCD.
The conclusion is that preanesthetic Mini Mental Status Examination may identify patients at risk of developing postoperative cognitive dysfunction.
The authors acknowledge Dr. Glauco da Luz, for applying Mini Mental State Examinations.
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Dr. Getúlio Rodrigues de Oliveira Filho
Address: Rua Luiz Delfino 111/902
ZIP: 88015-360 City: Florianópolis, Brazil
Submitted for publication January 26, 2005
Aceito for publication April 28, 2005
* Received from Hospital Governador Celso Ramos, CET/SBA Integrado de Anestesiologia da Secretaria de Estado da Saúde de Santa Catarina (SES/SC), Florianópolis, SC