Introduction:
Anesthesia and surgery have been associated with cognitive changes. Cognitive dysfunction is a short-term effect due to anesthesia, but the elderly population tends to be affected by long-term cognitive dysfunction. The complications that occur due to the pharmacological effects of anesthesia are post-operative cognitive dysfunction (POCD) and postoperative delirium (POD). Post-operative delirium is another complication characterized by inattention and cognitive disturbance.
What Are the Cognitive Functions?
Cognitive function refers to mental abilities like learning, reasoning, thinking, remembering, problem-solving, attention, and decision-making. Four of the main cognitive functions are sensation, feeling, thinking, and intuition. The frontal lobes, basal ganglia, and cerebellum of the brain have been involved in cognitive and motor skills.
What Is Post-operative Cognitive Dysfunction?
POCD (postoperative cognitive dysfunction) is defined as an impairment in the mental processing of information, perception, and memory. POCD is reflected as an objective decline of cognitive functions even after the expected period of normal recovery due to anesthesia. The changes in the behavior of the patient are most commonly observed and reported by the family members and caregivers. However, it is quite difficult to find an obvious cognitive decline. Studies state that general anesthesia acts through several receptor proteins to regulate neuronal activities, producing effects like amnesia (memory loss), analgesia (painless feeling), immobilization, and sedation (state of calmness).
How Is It Caused?
The mechanism of cognitive disturbance is due to neuroapoptosis, in which early exposure to anesthesia results in long-lasting impairments in the communication between neurons and the neuronal circuits being formed. Other mechanisms like neuroinflammation, calcium dysregulation, and mitochondrial dysfunction are also involved in neurocognitive decline. Therefore, exposure to anesthesia in the aged brain can be risky and result in long-lasting cognitive function impairments. The following drugs have been proven to be associated with cognitive disturbances:
-
The use of Ketamine as a sedative has shown post-operative hallucinations (feeling or sensing something which is not actually present) in certain patients.
-
The effect of Isoflurane on POCD has been widely investigated compared to other potent agents like Sevoflurane and Desflurane. However, it is still being studied, and further research is going on.
-
Inhalational anesthetics such as Nitrous oxide have been associated with POCD and delirium (a confused state without awareness of self).
-
The opioid is shown to cause memory loss, inability to concentrate, hallucinations, drowsiness, and euphoria (state of extreme happiness) or dysphoria (state of disappointment or uneasiness).
What Are the Potential Risk Factors for Causing the Cognitive Decline?
-
Patients who have pre-existing mental conditions and psychiatric disorders.
-
Patients with conditions like hyperglycemia and hypertension. Hyperglycemia refers to increased blood glucose levels, and hypertension refers to increased blood pressure.
-
Patients who are under certain medications may interact with general anesthesia.
-
Patients who are addicted to alcohol.
-
Patients who are suffering from sleep disorders.
-
Patients with diseases like a stroke or coronary artery disease. A stroke is a cerebrovascular accident due to blockage of blood supply to the brain, and that causes paralysis and other mental problems. Coronary artery disease refers to the narrowing or blockage of arteries and causes restriction of blood supply to the heart.
-
Patients who are suffering from dementia. Dementia is characterized by a group of conditions that causes cognitive disturbances and interfere with memory, reasoning, and thinking.
How to Diagnose POCD?
A series of neurocognitive tests are done to diagnose this condition. These help to test the memory and learning prior to surgery and compare them with the results obtained post-operatively. The patients are assessed on their daily activities of living, and objective testing on execution, learning and memory, and other social functions are carried out to diagnose this condition.
What Is the Treatment for POCD?
Most often, the patients will regain the lost function in a few months' time. In some patients alone, it can last for several months or years. As of now, there are no known treatments or medications to treat this condition. It can be managed pre, intra, and post-operatively.
How to Manage POCD?
-
Pre-operative Management: Older patients often have other geriatric problems, and the risk of developing delirium is significantly increased in patients with pre-operative cognitive impairment and depression. Patients with functional impairments and those taking certain psychotropic medications also tend to develop neurocognitive disorders. In the presence of these risk factors, the perioperative physician should consider referral to either a primary care physician, geriatrician, or mental health specialist for optimization or prehabilitation prior to the surgical procedure.
-
Intraoperative Management: Since general anesthesia targets the central nervous system, regional anesthesia is preferred. Regional anesthesia refers to anesthetizing a large part of the body, such as a limb or one-half of the body, while the patient is awake. Whereas in general anesthesia, the patient is unconscious during the procedure. Regional anesthesia is often accompanied by sedation at levels comparable to general anesthesia. Sedation refers to the use of sedative drugs to put the patient in a relaxed and calm manner. Dexmedetomidine, used for sedation, has been proven to decrease the incidence of delirium in patients. The use of processed electroencephalograms to guide the anesthetic management will reduce the risk of postoperative delirium and postoperative neurocognitive decline.
-
Postoperative Management: Administration of opioids has been associated with the development of POD (postoperative delirium). Hence opioid-sparing pain management is done in intensive care units. Acetaminophen and COX2 (cyclooxygenase) inhibitors have also been suggested as a part of a pain management strategy to reduce POD. COX2 inhibitors have also been shown to reduce post-operative opioid utilization and pain reduction in patients older than 60 years of age. Nonpharmacologic interventions to manage POCD and POD include a calm environment and reorientation tools such as a calendar, familiar items, family members, and the removal of restraint devices. Pharmacologic interventions are done for those who pose a threat to themselves. The effective drugs include Dexmedetomidine and Haloperidol to control the severity of delirium.
Conclusion:
The use of general anesthesia has been associated with postoperative cognitive dysfunction. The selection of anesthetics to be used and their possible interactions with other drugs should be assessed prior to the surgery. Management should be done at all stages of the surgery, like pre and post-operatively for the well-being of the patient.
