One of the most common fears of people undergoing anesthesia and surgery is that anesthesia will cause harm, even permanent damage, to the brain. The traditional view is that anesthetic agents are rapidly metabolized (broken down) and/or excreted from the body, their effects are readily reversed, and anesthesia is therefore unlikely in the long run to cause neurologic injury.
We know that anesthetic agents affect many aspects of brain physiology, altering blood supply to the brain, metabolism, neurotransmitters, cerebrospinal fluid production, and more. These effects are being investigated in the laboratory and through the use of special imaging techniques. The picture that emerges is as complex as the brain itself, and is sometimes surprising. For instance, certain anesthetic agents seem to protect, not injure, the brain – at least in animal experiments.
More than 50 years ago, it was reported that some older people have brain problems after surgery, and recent research challenges the belief that a well-conducted anesthetic and complication-free surgical procedure is totally neurologically benign.
The term postoperative cognitive dysfunction (POCD) has been coined to describe the mental changes, (in the areas of thinking, attention and memory) that do occur in some patients after anesthesia and surgery.
Depending on when the presence of these changes is assessed, and in what population, as many of 50% of patients can show some change in cognitive function, though most patients seem to recover in time.
A large clinical study from Duke University now appears to confirm earlier findings, in an important 1998 Lancet publication, showing that significant numbers of elderly people experience long term (3 months or more) changes in higher order brain function after anesthesia and surgery. This study and similar recent research raises many questions about how and why the changes that lead to POCD occur.
1064 patients were studied. They were classified as young (18-39), middle-aged (40-59), or elderly (60 or older) and had a variety of surgeries not involving the heart. Before surgery, at discharge from the hospital, and 3 months after hospital their mental function was tested with a battery of tests. Patients were discharged from the hospital an average of 4 days after their anesthesia.
The main findings:
- At discharge from the hospital, signs of POCD were present in 30-41% of patients.
- At the 3 month mark, young and middle aged patients had recovered, but 12.7% of elderly patients (over 60) still showed cognitive impairment.
- Risk of POCD at 3 months after surgery was increased in patients aged over 60, those with a low educational level, a history of previous stroke (despite recovery from that stroke), and POCD at hospital discharge.
- Patients with POCD were more likely to die in the year after surgery.
- This is an important study (it is accompanied by an editorial) and confirms that elderly patients are at risk of POCD.
- This study cannot tell us whether POCD is due to (1) anesthesia, (2) surgery, or (3) some aspect(s) of recovery from surgery (e.g. pain, pain medication, other medications, infection, inflammation, sleep disruption, etc).
- A 22 month gap occurred between submission of the paper and eventual publication in the January 2008 edition of the journal. I wonder whether Anesthesiology’s peer reviewers were not entirely happy with the paper’s methods or conclusions.
- Controls – the patients against whom the patients getting surgery were compared – were family members. They showed approximately a 5% incidence of cognitive impairment incidence which seems pretty high.
- Young patients (age 18-39) had higher cognitive impairment rates than middle-aged patients (though not reaching statistical significance) which also seems surprising.
- The type of anesthesia used in each case is unfortunately not recorded.
Researchers suggest that, in patients who develop POCD, limited brain “reserve” has been somehow “unmasked” by anesthesia and surgery, or that anesthesia and surgery somehow accelerates the ageing process in the brain. Inflammation might be the culprit. Inflammation is part of the body’s response to the trauma of surgery but has possibly harmful effects. Previous research has shown signs of inflammation in cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) after surgery but it is not clear whether this is the cause, or the result of POCD.
The study authors speculate that patients who develop POCD may become less able to recognize their own difficulties and to take care of themselves, including accessing needed medical care, explaining the greater risk of death in these patients after hospital discharge. It has been shown in other studies that, quite apart from surgery, elderly people with cognitive decline die sooner than those without.
What you can do about it:
Not much. Not many of us are going to volunteer for surgery without anesthesia. Even if anesthesia is in some way responsible for this syndrome (not proven by this study), we do not yet know, and this study certainly doesn’t give us any clues, whether any particular type, or even dose, of anesthetic, increases the risk of long term POCD.
We don’t know of any way to protect against the development of POCD. What we can do, is what we do routinely, that is maintain measured physiology (“homeostasis”) as close to normal as possible during each case (heart and lung function in particular).
It seems intuitive that general anesthesia might be more harmful than regional or local anesthesia but this is not proven. There is some evidence that early recovery from POCD (at 1 week) is better with regional anesthesia but differences disappear at or before 3 months.
Should the elderly avoid surgery because of the risk of POCD? Every surgery should be accompanied by a careful evaluation of the risks and benefits for that patient. This study suggests that when elderly patients are assessed for surgery and are found to have a history of stroke, or have a poor educational background, extra caution is warranted. Those that develop POCD may need a prolonged period of additional support and care at home.
Monk TG, et al. Predictors of cognitive dysfunction after major noncardiac surgery. Anesthesiology 2008; 108:18–30. Link to this article here.