The recognition of neurological complications associated with cardiac surgery has been reported since the dawn of the specialty. Cognitive dysfunction is the impairment of perception, memory, and information processing, allowing the individual to acquire knowledge, solve problems and plan for the future [1,2]. With improvement in surgical and anesthesia techniques, survival after major surgeries-cardiac, as well as non-cardiac, has improved and thus postoperative comorbidities have gained major attention including post-operative cognitive dysfunction (POCD). Incidence of POCD after cardiac surgeries worldwide as indicated by previous studies ranges from 5 to 40 percent within the first postoperative week [1,2]. POCD may range from short-term cognitive changes affecting memory and visuospatial functions to post-operative delirium and dementia. But the most common complaint in the first few weeks following coronary artery bypass graft (CABG) relates to memory [3]. Pre-operative co-morbidities like diabetes, hypertension and a history of stroke are associated with an increased risk of POCD as documented by previous studies [4]. The present study is an attempt to assess the cognitive function of patients undergoing CABG using cardiopulmonary bypass (CPB) before and after the surgery. The Addenbrooke’s Cognitive Examination Revised (ACE-R) score has been used for the assessment of POCD in the study. It is a rapid screening battery, including five sub-scales to explore different cognitive domains: attention/orientation, memory, fluency, language, and visuospatial. ACE-R is considered useful in discriminating cognitively normal patients from study patients with mild dementia [5,6].

AIMS AND OBJECTIVES

To test the prevalence of early postoperative cognitive dysfunction after CABG using a bypass machine in study patients having normal cognitive function pre-operatively.

Design: It is a prospective cross-sectional study, conducted in the Cardiovascular and thoracic surgery (CVTS) ward and recovery room in a tertiary care hospital over a period of one year. After institutional ethical committee approval and appropriate consent, patients in the age group of 25 to 65 years of age were included who underwent CABG using a CPB machine and fulfilled the criteria for participation in the study. Patients undergoing CABG using CPB with an on-pump time of fewer than two hours, in whom anesthesia was reversed and trachea extubated at or before 72 hours of surgery, and, a number of education years of more than 5 years were included in the study. Patients having significant neurological deficits pre-operatively, those with known psychological illnesses, and, with pre-operative ACE-R score less than 85 were excluded. Technique of cognitive function assessment: Each patient was visited one day before surgery in the CVTS ward. The procedure to be done was explained to the patient in the language understood by them and written informed consent was obtained for participation in the study. A structured questionnaire that is ACE-R was used to know the pre-operative cognitive function of the patient. ACE-R is free to use in the public domain for research and educational purpose and needs no permission. The same questionnaire was used on the seventh postoperative day and the results were compared to assess the cognitive dysfunction of patients during the postoperative period. A single trainee resident doctor collected the data after training from a Neuropsychologist (assisted Neuropsychologist in interpreting 20 patients’ ACE-R scores). Statistical analysis: The sample size was estimated using the formula, n = Z2*P*(1-P) / d. Under the following assumptions: assuming a level of confidence of 95%, Z score is 1.96, the prevalence of POCD (P) = 40% (1,2), precision corresponding to effect size (d) = 10%, the calculated sample size (n) is 92. Assuming 10% dropouts, the adequate sample size is 101 [7]. Appropriate statistical measures and tests are used for analysis. A p-value <0.05 was considered statistically significant. A statistical package for social science version 23 (SPSS-23 IBM, USA®) was used.

Out of 110 patients, 35(31.81%) were female. The prevalence of POCD was 1.81% in our study. Out of 75(68.18%) male patients, only 1(1.34%) patient developed POCD while 74(98.66%) had normal cognitive function post-operatively. One female patient (2.86%) out of 35 developed POCD while the rest 34(97.14%) had normal cognitive function post-operatively. Odd’s ratio (OR) for males was lower; 0.46(0.03-7.57). OR for age, less than 45 years was higher; 6.71(0.4-113.56). OR for comorbidities, less than 5 years was higher;

Table 1: Gender and POCD

Table 2: Age and POCD

Table 3: Duration of co- morbidities and POCD

Newmann et al reported approximately 50% patients undergoing CABG developed POCD while our study had negligible prevalence. The reason for such higher prevalence might be the age group which was around 60±10 years in their study while in our study population median age was 54±9 years. Ge Y et al reported incidence of POCD 38% on seventh day which was higher compared to our study, possible reason might be inclusion of both on pump and off pump CABG while in our study only on pump CABG patients were included. Odds ratio for gender (male and female) in our study was 0.45(0.03-7.57) which was not statistically significant, similar to Newman et al. Odds ratio for age group less than 45 and more than 45 years is 6.71(0.4-113.5) which showed significant risk in age group less than 45, but this might be due to less sample size in below 45 years age group (n= 15) compared to more than 45 age group (n=95). None of the studies has compared <45 and >45 age group. Odds ratio for co morbidities <5 and > 5 years is 1.63(0.1-26.84), showing significant risk of developing POCD in <5 years age group but again authors feel that this is due to less sample size in < 5years age(n=42) compared to that in comorbidities >5 years group(n=68) none of the previous studies included duration of comorbidities. LIMITATIONS Our study is a cross-sectional one, limitation of a cross-sectional study is that outcome (POCD) and exposure are collected simultaneously and there is no long-term follow-up as with longitudinal studies. The study was conducted in a tertiary care hospital over a period of one year only limiting the sample size, also the sample is not representative of the population and hence results of the study cannot be applied directly. Study patients with a number of years of education more than 5 years were only included in the study, the effect of CABG using bypass on the cognition of illiterate patients was not studied which form a major proportion of the patient’s undergoing CABG in India.

POCD is one of the important morbidity in study patients undergoing CABG; it can limit the neurological function of the subject significantly affecting memory, reasoning, thought process, and mathematical calculations. Neuropsychological tests to determine preoperative cognitive function should be included in the preoperative examination of the study patients undergoing CABG to screen those with impaired cognition, as they are at an increased risk of developing POCD. As per our study, POCD prevalence is not significant in patients having normal cognitive function preoperatively.