Postoperative Cognitive Dysfunction

In the mid 1950s, Dr. Bedford reported on a number of older adults who exhibited cognitive problems (memory or planning or being able to sustain attention) following surgery where anesthesia was used. This effect is now called postoperative cognitive dysfunction (or decline; POCD). POCD typically lasts for a few months to a year with a small minority of patients exhibiting permanent decline. Studies about it were few at first, with most focusing on cognition following cardiac surgery. Over time and especially more recently, there has been an increase in research of POCD following non-cardiac surgeries (e.g., abdominal or orthopedic) as well as continued interest in POCD following cardiac surgery.

There is considerable evidence that age is the single strongest risk factor for the development of POCD – outside of actually having surgery, of course! This means that the older a surgery patient is, the more likely they are to develop POCD. There is also evidence that prior cognitive impairment, lower education, and pre-surgery depression also place adults at risk for POCD following both cardiac and major non-cardiac surgery. Perioperative events (e.g., strokes and other neurological events) and postoperative pain are additional risk factors for POCD.

As mentioned previously, age is the most consistent predictor of POCD. Those who are older are more susceptible to POCD and for longer periods after surgery. For patients undergoing coronary artery bypass graft (CABG) surgery, the best studies show that 33% of patients have POCD at one week post-surgery. This rate falls to 4% at three months. Other studies show rates as high as 50-60% at one week and 13-20% at three months. However, these have been criticized for less-than-ideal methods. For major non-cardiac surgeries, the trend with POCD in older adults is similar, if with somewhat lower rates. For most studies, about 20% of noncardiac older patients exhibit POCD at one week following surgery with virtually no POCD at three months. However, some studies show higher rates (up to 50% at hospital discharge and 30% at three months post-discharge) of POCD in older adults following noncardiac surgery.

Past research showed widely variable rates in POCD. This inconsistency is due to major variations in the methods. Many researchers focused solely on subjective cognitive complaints or intelligence or general cognition as measured by a screening test such as the Mini Mental Status Examination. The problem is that these measures are insensitive to subtler cognitive changes. Intelligence tests generally have high test-retest reliability even with fairly major cerebral events (in other words, it usually takes major damage to the brain to significantly affect general intelligence). Brief general cognitive tests are usually quite reliable over time but they are insensitive to change because they are so shallow and broad. Minor or specific declines are important to measure because they can cause impairment in everyday functioning.

Even though POCD research has varied in quality, researchers and doctors are confident that POCD is a real effect. Any older adults (POCD researchers typically use age 60 as the threshold for “old adulthood”) who are undergoing major cardiac or non-cardiac surgery should be aware that mild to moderate cognitive deficits can occur following surgery. The cause is generally unknown. The good news is that there is little evidence that these deficits in general last longer than a few months.

References

&NA;, . (2006). The Role of Postoperative Analgesia in Delirium and Cognitive Decline in Elderly Patients Survey of Anesthesiology, 50 (5), 263-264 DOI: 10.1097/01.sa.0000238941.61799.e6

Lewis, M., Maruff, P., Silbert, B., Evered, L., & Scott, D. (2006). Detection of Postoperative Cognitive Decline After Coronary Artery Bypass Graft Surgery is Affected by the Number of Neuropsychological Tests in the Assessment Battery The Annals of Thoracic Surgery, 81 (6), 2097-2104 DOI: 10.1016/j.athoracsur.2006.01.044

&NA;, . (2008). Predictors of Cognitive Dysfunction After Major Noncardiac Surgery Survey of Anesthesiology, 52 (3), 135-136 DOI: 10.1097/01.SA.0000307885.46705.f5

&NA;, . (2007). Postoperative Cognitive Dysfunction After Noncardiac Surgery Survey of Anesthesiology, 51 (6) DOI: 10.1097/sa.0b013e31815c0ff1

Rasmussen, L. S., Larsen, K., Houx, P., Skovgaard, L. T., Hanning, C. D., & Moller, J. T. (2001). The assessment of postoperative cognitive dysfunction. Acta Anaesthesiol Scand, 45, 275-289.