I am so sorry to hear about this. The kind of changes your husband suffered after his bypass surgery are most likely caused by mini strokes. A small percentage of patients complain of mental changes that may be the result of new mini-strokes, also called transient ischemic attacks (TIA), because the symptoms are like those of a stroke but do not last long. A TIA happens when blood flow to part of the brain is blocked or reduced, often by a blood clot. After a short time, blood flows again and the symptoms go away. With a stroke, the blood flow stays blocked, and the brain has permanent damage. In your husband’s case it appears permanent damage may have happened.
A study, published in 2001 indicated that half of people undergoing bypass surgery developed memory or thinking problems in the days following it, and that these problems were occasionally still evident five years later. Another study found that short-term confusion, memory loss, and poorer problem solving and information processing may happen in some patients after bypass surgery, but are usually temporary and reversible. Most people return to their pre-bypass level of function between 3 and 12 weeks after surgery. Long-term changes occur, too, but these are usually mild and tend to affect things such as how fast you can solve problems or process information.
It doesn’t help for you to know that this is a rare event, certainly to the extent you mention:
Treatment starts with, first of all, recognizing the problem and is aimed preventing other strokes and help with functional rehabilitation. If indeed his problems were a direct result of the surgery and not associated other medical problems, full recovery should be possible.
Hope this helps,