Postoperative Cognitive Dysfunction (POCD): Confusion After Surgery
What Is Postoperative Cognitive Dysfunction?
Most people realize that after surgery and anesthesia, they will be confused or "out of it" for a while. It has long been known, however, that some people remain confused or have mental slowing for quite some time after surgery. Some patients say, in fact, that they are never the same. Short-term memory loss, trouble with focus, and generalized slowness are the most common complaints.
Postoperative cognitive dysfunction (POCD) is a state in which a decline in learning, memory, and/or personality changes persist long after the surgery.
Researchers are beginning to study and define this phenomenon. It seems that we are a long way from being able to reliably predict or prevent it, though.
POCD occurs most often in elderly patients, but can be detected to a lesser degree in younger patients, as well, when using specialized mental function tests.
Before continuing, it is important to emphasize once again that POCD is different from the confusion that typically occurs right after surgery. Some confusion and mental slowing are expected. This postop "delirium" (this is the medical term) is not unusual and does not constitute POCD.
Great Video Lecture on POCD from UCSF
Risk Factors and Factors Influencing POCD
- Socioeconomic status
- Pre-existing mental status
- Preoperative state of health
- Type of surgery
Risk Factors for POCD
It used to be assumed that general anesthesia was the main risk factor for POCD. However, this has been shown not to be true.
Despite much speculation regarding the reasons for POCD, there are only two main factors that, so far, have been shown to predispose to this condition. The first—being over 70 years of age—is not really a surprise. Older patients are more likely to have issues with memory after surgery and anesthesia. Elderly patients who have pre-existing mental dysfunction may very well get worse, temporarily or permanently, after surgery and anesthesia.
Low socioeconomic status has also been shown to correlate with cognitive dysfunction after surgery for reasons that are not clear. Further studies may provide clarity on this or help figure out if there are other factors at play.
People who develop POCD have received all types of anesthetics. Some received none at all.
The most surprising findings that arise from studies on the subject show that the type of anesthesia does not necessarily influence the incidence of POCD to a significant degree. Despite the assumption by almost everyone that general anesthesia would be the cause of postop confusion and mental changes, this did not turn out to be true. Epidural, spinal and even local anesthesia have been given to patients in whom post-op cognitive dysfunction then developed. Different types of patients and surgeries DO affect the likelihood of having difficulty with mentation after surgery.
Of course, nothing in medicine is simple and other studies have variable results. For example, after having a surgery called a carotid endarterectomy, POCD occurred more often during the first day after surgery with general anesthesia compared to local anesthesia. By a week after surgery, though, there was no difference in function (the "fog" had lifted). That surgery is specifically to remove clots from the big blood vessels in the neck that supply the brain, so other factors are likely to be involved here as well.
Other factors that may play a role in POCD:
It may be the case that other factors are contributing to the decline. Surgery and anesthesia of any type are physiologic stressors on the body and brain. Other physiologic stressors, such as critical illness in the elderly, also cause the same type of difficulty with mental function. In addition, when the body endures these types of physical insults, chemical changes occur in the body. Stress hormones, inflammatory mediators, and other chemicals are released and influence the body's functioning. Substances, like the amyloid found in Alzheimer's patients, that are deposited in the brain may also be increased after surgical stress. It is likely that one or a combination of these chemical changes affect a person's mental ability after surgery.
Unfortunately, we are just in the stage where we are recognizing and defining POCD. Progress has been made, but we are a long way from understanding—and being able to prevent—this condition. Studies and research are ongoing. Stay tuned.