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J Thorac Cardiovasc Surg 2003;126:1061-1064
© 2003 The American Association for Thoracic Surgery

Cardiopulmonary support and physiology

Postoperative hypoxia is a contributory factor to cognitive impairment after cardiac surgery

^a Oxford Heart Centre, John Radcliffe Hospital, Oxford, United Kingdom
^b School of Psychology, Cardiff University, Oxford, United Kingdom
^c Rivermead Rehabilitation Centre, Oxford, United Kingdom

Received for publication May 21, 2002; revisions received August 26, 2002; revisions received October 16, 2002; accepted for publication January 14, 2003.

^* Address for reprints: D. P. Taggart, PhD, FRCS, Consultant Cardiothoracic Surgeon, Oxford Heart Centre, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom
david.taggart{at}orh.anglox.nhs.uk

OBJECTIVE: Cognitive dysfunction and postoperative hypoxia are common sequelae of coronary artery bypass grafting, but there has been no study to determine whether there is any relationship between them.

METHODS: Arterial blood gas measurements were performed before surgical intervention and on the second and fifth postoperative day, and neuropsychological assessments were performed before surgical intervention and 5 days and 3 months postoperatively by using a battery of 10 psychometric tests in 175 patients undergoing coronary artery bypass grafting. An estimate of overall performance on the battery at each assessment point was provided by a simple aggregate cognitive index score calculated from the mean z scores of 4 normally distributed test variables. Multiple regression analysis was performed by using the cognitive index score at day 5 as the dependent variable, with age, sex, duration of the operation, presence or absence of cardiopulmonary bypass, preoperative cognitive index score, and arterial oxygenation and percentage of saturation at day 5 as independent variables.

RESULTS: The mean cognitive index score decreased significantly in 115 (66%) patients who agreed to neuropsychological test battery assessment on the fifth postoperative day but improved significantly beyond baseline at 3 months. Mean arterial oxygen tension and percentage of saturation decreased significantly 2 days after the operation and, although improving over the following 3 days, remained decreased at day 5. Decreased cognitive index scores at day 5 strongly predicted cognitive impairment at 3 months (r = 0.36). The only significant independent predictors of the day 5 cognitive index score in the multiple regression analysis were preoperative cognitive index score and arterial oxygenation tension at day 5 (r = 0.24, P < .03).

CONCLUSIONS: We report a significant correlation between postoperative cognitive dysfunction and hypoxia 5 days after coronary artery bypass grafting. This finding might have therapeutic implications because early postoperative cognitive dysfunction influences long-term impairment.