Many patients who experienced immediate cognitive decline after surgery involving anesthesia also showed signs of impairment two years later, according to the results of a study presented Tuesday at the American Society of Anesthesiologists annual meeting in Las Vegas.

Immediately after surgery, 59% of the elderly patients displayed cognitive decline. The number went down to 34% when tested after three months, but jumped again to 42% two years later, the study found.

More elderly now than ever are undergoing elective major surgery as surgical techniques, such as anesthesiology, have advanced. This study is one of the first to examine the effects on non-cardiac surgery; in the past, researchers have said that patients experienced cognitive decline after cardiac surgery.

All 354 participants in the study underwent major, non-cardiac, elective surgery involving general anesthesia. Most surgeries were either intra-abdominal or orthopedic, such as knee and joint replacements. The average age of the patients was 69.5 years.

The researchers now aim to examine the factors of anesthesia that cause cognitive decline in so many, such as potential neurotoxic responses to the procedure. The researchers will also determine if there is a subset of participants more susceptible to cognitive failure after surgery.