Dear Dennis, you have a decreased renal function, that may be the expression of the aortic valve replacement (increased the risk of cholesterol embolism) and the splenectomy (risk of AKI). Since you are 80 year old, kidneys have a very limited functional reserve. Thus, any clinical condition, like dehydration, may rise sharply your serum creatinine. Thus, be sure to be followed by a good nephrologist and make sure that your physician do not prescribe you nephrotoxic drugs. Avoid NSAIDS, control your blood pressure, limit the salt intake to less than 2 g/day. Moreover, ask your doctor to perform a urinalysis, since renal inflammation (e.g. glomerulonephritis) are frequently observed in older age.