Anesthesia and Alzheimer’s Disease - a Review

Introduction

Alzheimer’s disease is a disorder of the brain that has a major effect on memory, language, and thinking ability. It starts mild and gradually worsens over time, making it difficult for them to communicate or perform routine tasks. Anesthesia is the use of certain medications or techniques to medically induce a temporary state of unconsciousness so that the patient does not perceive pain. This is done for surgeries and other painful interventions.

For patients with Alzheimer's disease, medical management involving surgery is challenging, especially when anesthesia is required. This article aims to explain the relationship between Alzheimer's disease and anesthesia, diving into the effects, risks, and clinical considerations.

What Is Alzheimer’s Disease?

Alzheimer's disease is a neurodegenerative disease characterized by progressive loss of memory and thinking ability. It is common in the elderly and is not a normal part of aging. It significantly impacts day-to-day life and the completion of tasks. It is both incurable and progressive.

The exact cause is unknown, but the most common risk factor known is aging, which is above 60 years of age, and the onset is sporadic primarily. There are links connecting it to genetic and environmental factors. There has been growing research trying to connect the dots between Alzheimer's and various risk factors, and it has been seen that developing a healthy lifestyle may reduce the risk considerably.

The pathological part of the disease includes the deposition of beta-amyloid and the formation of neurofibrillary tangles, leading to damage to neurons. Plaques develop in the areas of dealing with memory and thinking.

Diagnosis is mainly determined by clinical examination, imaging studies, and lumbar puncture.

The management is mainly based on pharmacological therapy to modulate neurotransmitters in the brain like cholinesterase inhibitors, etc. Secondary symptoms are managed appropriately.

What Is the Relationship Between Alzheimer’s and Anesthesia?

The relationship between Alzheimer's and anesthesia has been a topic of extensive research. Some studies suggest there is a risk of developing dementia or Alzheimers in older individuals after anesthesia exposure. The exact underlying mechanism is still unclear.

Alzheimer's disease and anesthesia share a potential relationship, which includes:

• Post-operative Cognitive Dysfunction

After surgery with anesthesia, a significant decline in cognitive function is noticed, which can affect the memory and brain function of the patient. Usually, it is transient, but for some individuals, it can be long-lasting.

There is increased risk in individuals who are:

• Elderly: Aging is a common risk factor, and individuals above 65 are more susceptible.

• Existing Cognitive Dysfunction: Dementia, Alzheimer's, mild impairment

• Complex Surgery: Surgeries that take longer and involve major organs like the heart or complicated bone involvement have a higher risk of developing this dysfunction.

• The possible mechanisms include:

  • Neuroinflammation:

    • An inflammatory response may be initiated in the brain due to anesthesia and surgery stress.

• Microglial Activation: The immune cells in the brain, microglia, are activated in response to surgical stress and anesthesia reactions. These can release proinflammatory cytokines.

• Blood-Brain Barrier Disruption: Due to surgery, the barrier may be disrupted, allowing inflammatory mediators to enter the brain.

• Amyloid and Tau Pathology

  • Amyloid beta and tau protein phosphorylation may develop as a response to certain anesthesia agents.

  • Isoflurane, a commonly used anesthetic inhalational agent, promotes aggregation of beta-amyloid in animals.

  • Similarly, anesthetic agents play a role in neurofibrillary tangle formation by increasing tau protein phosphorylation.

All these factors show a marked contribution of anesthesia usage in the pathophysiology of Alzheimer's disease.

• Cognitive Effects and Neurotransmitter Imbalance

Anesthesia agents can have a marked effect on the neurotransmitter receptors and affect the balance in the brain. This leads to a significant decline in cognitive function after a procedure under anesthesia.

What Are the Clinical Considerations While Using Anesthesia?

1. Preoperative Assessment

A proper assessment before planning any surgery can significantly affect the recognition of the patients at risk. To reduce the risk of cognitive decline in such patients, it is advised to keep the anesthesia and surgery duration to the required minimum. Attempts are made to maintain optimal post-operative conditions and good cognitive engagement.

1. Anesthesia Agent Selection

Different anesthesia agents have impacts on brain function. Choosing anesthesia agents that have minimal effect on brain function is crucial for patients with dementia and Alzheimer’s disease.

• Isoflurane

It is a commonly used inhalational anesthetic agent; it has shown aggregation of beta-amyloid in studies. Hence, in patients with dementia and Alzheimer's, it must be considered as it can exacerbate the disease.

• Propofol

Commonly used intravenous anesthetic agents mediated by gamma-aminobutyric acid (GABA) receptors have a rapid onset and shorter action. In patients with dementia and Alzheimers, it is generally considered better as it has less cognitive impairment compared to other anesthetic agents. Studies are saying it has a certain degree of neuroprotective effects, too. Also, since it has a shorter duration of action, it is more preferred in surgical procedures for patients with Alzheimers.

• Dexmedetomidine

It is a highly selective alpha 2 adrenergic agonist sedative agent. It is convenient and helpful for critically ill patients, as it has the most minor complications, like respiratory depression. In patients with Alzheimer's, it can be used as it has neuroprotective effects and helps preserve cognitive function. There are limited long-term studies of the use of this in patients with Alzheimer's, but overall, it emerges to be a promising alternative to traditional sedatives and anesthetics.

1. Postoperative Monitoring

Monitoring the patients for memory loss and cognitive changes like delirium is necessary. The patient must be advised to start moving as much as medically possible and engage in activities with families to support recovery.

What Are the Future Directions in This Regard?

There has been significant research aiming to understand the pathogenesis and linkage between anesthesia agents and Alzheimer's disease, which includes:

• Animal Models: The long-term effects of anesthesia must be studied in models depicting Alzheimer's pathology.

• Preventive Techniques: Developing new anesthesia agents, modifying dosages, and introducing newer neuroprotective strategies can significantly help.

Conclusion

As research continues evolving and introducing newer anesthesia agents and approaches, the exact mechanism of linkage between the two can help improve patient care, reduce post-operative complications, and slow disease progress.