Depth of Anaesthesia and Postoperative Cognitive Decline in Patients Undergoing Heart Surgery

Effect of Depth of Anaesthesia on Postoperative Cognitive Decline in Patients Undergoing Coronary Artery Bypass Graft Surgery - a Prospectively Randomized Controlled Study

Post-Operative Cognitive Decline (POCD) is common after cardiac surgery and associated with increased morbidity and mortality. The pathophysiology of POCD is only poorly understood. Causes include hypoperfusion, microemboli and the systemic inflammatory response, which result in a reduction of cerebral oxygen delivery. Cerebral oxygenation can be monitored non-invasively by measuring frontal lobe oxygen saturation (rSO2). The bispectral index (BIS) of the electroencephalogram is widely known to measure depth of anaesthesia, and there is a high correlation between BIS, a dimensionless calculated number between 0 and 100, and clinical criteria of sedation. With BIS below 60 recall is extremely low. The investigators demonstrated recently that inappropriately high levels of anaesthesia may be associated with poorer long-term outcomes in cognition after non-cardiac surgery (Ballard et al. 2012). Whether optimisation of the depth of anaesthesia and cerebral oxygenation has an effect on postoperative cognitive function in patients undergoing cardiac surgery is unknown. The investigators hypothesize that the incidence of POCD in elderly patients (> 65 years old) at 6 weeks is less with mildly deep anaesthesia (BIS 50 +- 10) and optimised rSO2 (interventions when rSO2 drops below 15% of baseline reading) when compared with current practice (BIS blinded anaesthesia, reflecting moderately to highly deep anaesthesia and blinded rSO2 measurements).

Cardiac Bypass Surgery in Adult Patients 65 Years and Older, Postoperative Cognitive Dysfunction, Postoperative Delirium

Postoperative cognitive dysfunction, Coronary artery bypass graft surgery, Postoperative cognitive improvement, Postoperative delirium

The intervention group receives isoflurane at a concentration that results in a BIS value between 40-60 intra-operatively.

Difference in degree of postoperative cognitive decline at 5 days, 6 weeks or 1 year after bypass surgery

Inclusion Criteria: patients undergoing elective coronary artery bypass graft surgery patients at 65 years of age and older Exclusion Criteria: diseases of the central nervous system including dementia inadequate knowledge of English a current or past psychiatric illness current use of tranquilizers or antidepressants severe visual, auditory, or motor handicap

Ballard C, Jones E, Gauge N, Aarsland D, Nilsen OB, Saxby BK, Lowery D, Corbett A, Wesnes K, Katsaiti E, Arden J, Amoako D, Prophet N, Purushothaman B, Green D. Optimised anaesthesia to reduce post operative cognitive decline (POCD) in older patients undergoing elective surgery, a randomised controlled trial. PLoS One. 2012;7(6):e37410. doi: 10.1371/journal.pone.0037410. Epub 2012 Jun 15. Erratum In: PLoS One. 2012;7(9). doi:10.1371/annotation/1cc38e55-23e8-44a5-ac2b-43c7b2a880f9. Amaoko, Derek [corrected to Amoako, Derek]. PLoS One. 2013;8(9). doi:10.1371/annotation/c0569644-bea1-4c38-af9a-75d1168e3142.