Peter Reuter, MD, PhD
General anesthesia has been around since the mid-1800s, and every year millions of people undergo procedures that require general anesthesia. What may be surprising to most people is the fact that after using anesthetic drugs for approximately 170 years, we still don’t know how they act exactly. We can explain how they block or suppress pain signals, but we still don’t have a sufficient explanation as to how they induce unconsciousness that can be reversed. We have evidence that they act on nerve cells or neurons in a way that interferes with the regulation of sleep, attention, and memory, and there is speculation that they disrupt communication between different parts of the brain, which somehow causes unconsciousness.
Initially patients undergoing general anesthesia were mostly younger patients because of the risks associated with the procedure, especially the stress put on the cardiovascular and respiratory systems. However, over time anesthesia has become safer for all patients and surgeons started to perform elective procedures on patients that would have been excluded because of their advanced age in the first part of the last century. Combined with an increasing number of people living into their 70s, 80s, and 90s the number of older people undergoing general anesthesia has skyrocket in the last 50 years.
In the early 1980s reports surfaced that described patients going through a state of confusion, hallucinations and memory loss after general anesthesia. The patients couldn’t respond to normal questions, such as how they were feeling, and often replied with nonsensical answers. Over time this state was termed Postoperative Delirium. When doctors started to look into the cause for this state they couldn’t find a relationship to the kind of anesthetic used or the duration of the anesthesia. There were, however, first indications that the delirium wasn’t always just a transitional state that lasts a few hours only, but could linger for months and, in rare cases, even for years.
What makes it difficult to identify the underlying cause, if the anesthetic isn’t to blame, is the fact that the stress of the general anesthesia is just one of many stresses the patients are under during their time in the hospital. Just being hospitalized for an acute or chronic ailment and the changes that come with that, such as loss of privacy, inability to sleep properly, changes to the diet or having to change or take new medications, can sometimes cause patients to become confused, depressed, irritable or even delusional. Two factors that have been isolated by various researchers are age and the type of surgery performed. We now know that patients above 70 years of age are more prone to develop Postoperative Delirium. The risk increases even more if they already suffer from mental deficits, such as dementia, before the anesthesia. Even patients who had just mild symptoms, such as forgetting appointments or to take their medication on time, were shown to be more likely to go through the delirium. Major surgeries that sometimes last for hours and that require the patients to stay in the hospital overnight or longer, also carry an increased risk for developing the syndrome. Studies have shown that half of patients older than 60 go through a state of confusion and disorientation after heart bypass or heart valve replacement surgery. Hip replacement surgery, which is usually faster and an elective procedure that can be done when the patient is physically and mentally ready, has a far lower incidence for the same age group.
Studies have also shown that some type of regional anesthesia can increase the risk for Postoperative Delirium as well. Normally, regional anesthesia uses an anesthetic drug to block nerve signals from a certain area of the body, such as the legs, from reaching the spinal cord. The patient loses feeling in the area, but is of course alert. However, patients are often given a sedative drug, such as propofol, to calm them down and reduce the stress of the situation. If the amount of those sedative drugs is sufficiently high patients go through a state of general anesthesia during at least some part of the procedure without them, and often the anesthetist, being aware of that.
Not only are older patients more susceptible to developing Postoperative Delirium, it often lasts longer and is more severe. Having older patients show signs of a mental slowdown (performing poorly on word recall test for example) three months after major surgery is not uncommon, with the time until complete recovery easily stretching to six to twelve months. One of the reasons could be that the nerve cells in older patients get more easily overwhelmed by anesthetic drugs and take a much longer time to recover their preoperative function. There is also speculation that some of the connections between different parts of the brain that get disrupted by general anesthetics, may take longer to be restored in older brains or may not be restored completely leading to lingering aftereffects.
One way to lower the risk for Postoperative Delirium is to make sure the patients are well nourished and especially well hydrated before surgery. Chronic dehydration, due to an aging thirst center that doesn’t alert the older patients any more of a lack of water, is a common problem among older people and can on its own lead to mental confusion. A more surprising find was that family and friends can play an important role in preventing and minimizing Postoperative Delirium. Patients that are accompanied by relatives or friends or who receive visits from them postoperatively have lower rates of confusion and better outcomes overall than patients that are unaccompanied and don’t have visitors. How these social interactions help prevent and treat Postoperative Delirium is unclear, however, the benefits are so tangible that more and more hospitals encourage relatives to stay with older patients before and after general anesthesia.
* Note for Medical Scribe students: Please see definitions below.
© Peter Reuter 2015
General anesthesia: https://www.youtube.com/watch?v=vRlk73BbQ8o
Anesthesia: The word itself means lack of feeling or freedom from pain, but is generally used to describe a method that reduces pain and feeling in a certain area (local anesthesia), region of the body (regional anesthesia) or the body as whole (general anesthesia). It is based on the application of substances (anesthetics) that interfere with the transmission of signals in nerves to the central nervous system (brain and spinal cord). Because of the lack of sensation and numbing of pain doctors can operate on patients using one of those techniques.
Unconsciousness: A state during with a person is not consciously aware of stimuli from the environment or its own body and is unable to respond. It can be a reversible state, such as coma or general anesthesia, or a permanent stage with no recovery.
Cardiovascular System: Consists of the heart (cardio-) and blood vessels (vascular). Its task is to supply sufficient amounts of blood to any part of the body at any time and under any conditions. To do that it has to pump a sufficient amount of blood, which can be 4-5 times more under physical stress than at rest, while generating an adequate blood pressure to push the blood through 50,000 miles or more of blood vessels.
Respiratory system: Consists of upper and lower airways that transport air into and out of the lungs and the lungs where the exchange of oxygen (into the blood) and carbon dioxide (out of the blood) happens. The task of the respiratory system is to supply sufficient amounts of oxygen regardless of how much the body needs and to remove poisonous carbon dioxide from the blood.
Delirium: Also known as acute confusional state. A serious, but usually temporary and reversible, state of impaired brain function with confusion and sometimes hallucinations and hyperactivity. Can be seen I high fever, intoxication (chronic alcoholism often leads to delirium tremens), and other disorders.
Dementia: General term to describe a decline in mental abilities that is severe enough to effect daily life. Dementia is not a disease itself, but a symptom of other diseases and can also be considered part of a normal decline in higher age, which it is also often called senility. The most well known type of dementia is dementia caused by Alzheimer’s disease.
Heart bypass: Surgical procedure to bypass a blocked blood vessel (coronary artery) be connecting the area before the blockage and the area behind the blockage by inserting a healthy blood vessel (graft) from another area of the same patient. Originally the surgery required to stop the heart from beating during the procedure and surgeons had to use external pumps to keep blood flowing through the body. Nowadays the procedure is done on the beating heart.
Heart valve replacement: Heart valves regulate the flow of blood thought he heart, just like valves regulate the inflow and outflow of air and gasoline in car engines. Defective heart valve that either don’t open properly (stenosis) or fail to close completely (regurgitation) effect the flow of blood and put extra stress on the heart, which can lead to heart attacks and death in the long term. Heart valves can be replaced using mechanical valves, animal valves (pigs) or donated human valves.
Propofol: A short-acting anesthetic used to induce or maintain anesthesia. It became infamous when it was discovered that the late Michael Jackson had received propofol iv injections to combat his insomnia, which may have caused or contributed to his death.