Although not extensively studied, both short-and long-term postoperative cognitive dysfunction are well-recognized problems in elderly patients. To evaluate the frequency of these problems and to identify possible risk factors, Moller and colleagues conducted a multicenter study to determine the occurrence of long-term postoperative cognitive dysfunction in patients 60 years of age and older.
The study included 1,218 elderly patients who underwent major abdominal or orthopedic surgery at 13 hospitals in eight European countries and the United States. The operations were performed between 1994 and 1996. Priority was given to patients undergoing elective abdominal and noncardiac thoracic surgery, and no more than one quarter of the cases from each hospital could be orthopedic. Patients were excluded if they had diseases of the central nervous system or low scores on the Mini-Mental State examination, were taking psychotropic medications or were not expected to be able to participate in follow-up assessments three months following surgery.
Neuropsychologic testing was performed on the day before surgery, one week after surgery or on discharge from the hospital (whichever was earlier) and three months after the surgery. Extensive demographic and physiologic data were collected on each patient, including continuous pulse oximetry data collected the night before and continuing for three days after the surgery. Blood pressure was measured every three minutes during surgery and every 15 to 30 minutes for 24 hours following surgery.
One week after surgery, cognitive dysfunction was documented in 266 of the patients (26 percent). At the second assessment three months after surgery, cognitive dysfunction was present in 94 of the patients (10 percent).
Factors that showed significant relationships to postoperative cognitive dysfunction at one week were increased age, a long duration of anesthesia, a low educational level, postoperative infection, respiratory complications and a second operation. Only increased age was related to dysfunction that persisted at least three months after surgery.
Although episodes of hypoxia and hypotension were frequently documented, no relationship was found between postoperative cognitive function and different degrees or durations of hypotension or hypoxia. Similarly, postoperative cognitive dysfunction was not related to factors such as the patient's physical status, lung disease, heart disease, hypertension, smoking status or sex. Nor was an association found between cognitive dysfunction and procedure-related variables such as type of anesthesia, use of an intensive care unit, amount of blood loss, type of procedure or drugs used.
The authors conclude that major surgical procedures cause cognitive decline in a significant proportion of elderly patients and that the risk increases with age. Even though relatively healthy persons were included in the study, significant cognitive decline was documented in 26 percent of the patients one week after surgery and in 10 percent three months after surgery. None of the variables studied except age appeared to be related to the occurrence of cognitive decline. The authors speculate that anesthetic effects on central neurotransmission, such as cholinergic and glutamatergic function, may be among the causes of cognitive dysfunction after major surgery in elderly patients.
editor's note: This study validates the frequent observation by patients and families that “they aren't quite as sharp as they were before the surgery.” Many elderly patients have little margin of safety in maintaining daily survival in the community, and any cognitive decline can tip the balance into dependency. The finding that 10 percent of the patients had a measurable decline in cognitive function three months after surgery is very worrisome, especially since the study selected relatively healthy patients undergoing elective noncardiac surgery. Most worrisome of all is the lack of correlation with hypoxia and other conditions associated with cerebral circulation. The entire topic of subtle postoperative effects on patients of all ages warrants much further study. This study had a high dropout rate and provides relatively little information about the types or severity of cognitive decline. Ethically, do we now tell elderly patients considering hip replacement, for example, that there might be a 10 percent chance of a decline in cognition, or do we wait for further studies?—a.d.w.