Essentials of Geriatric Neuroanesthesia

Hemanshu Prabhakar, Charu Mahajan, Indu Kapoor, Hemanshu Prabhakar, Charu Mahajan, Indu Kapoor

• Publisher: CRC Press
• Year: 2019
• Print ISBN:
  9781032519050
• eBook ISBN:
  9781351046459
• Topic: Medicine
• Subtopic: Anesthesiology & Pain Management

The book covers topics ranging from basic sciences (developmental changes in neuroanatomy and neurophysiology and effects of neuropharmacology) to special situations such as brain death, ethical issues and palliative care. It discusses various neurological surgical problems and their challenges along with common problems such as Alzheimer's and Parkinson's disease. A section on Pain covers all possible modalities for relieving pain in this patient population followed by the important issue of palliative care. The book addresses the issue of cognition decline, common in this group. The fact that basic sciences are included along with clinical sciences makes it a unique read for the audience.

1

Neuroanatomy: Age-related changes

Vasudha Singhal

Introduction

The aging brain

The spine

Conclusion

References

Introduction

The advancement of medical technology, combined with better access to treatment and focus on preventive strategies, has led to an extension of the human lifespan. There is therefore a trend toward an increase in the aged population worldwide. Aging is a physiological process characterized by degenerative changes in the structure and function of every organ system in the body. The age-related limitation of the functional reserve of an elderly patient during times of stress, such as that which occurs at the time of surgery, leads to an increase in perioperative morbidity. An in-depth knowledge of the age-related changes in the brain and its function helps the neuroanesthesiologist to better comprehend the implications of anesthesia in elderly neurosurgical patients.

The aging brain

Aging affects the brain at all levels, from molecules, vasculature, and morphology to cognition. With increasing age, the brain shrinks in size and the aging vasculature predisposes to cardiovascular diseases and strokes. Progressive white matter lesions and dementia due to cellular death in regions of the cortex lead to cognitive decline. Changes in the levels of neurotransmitters and hormones result in functional deficits in the elderly, such as a short sleep span, decreased motor activity, mood flattening, altered endocrine function, and declining mental status. The anatomical changes seen in different parts of the brain are delineated in “The Brain” section.

The skull

The skull forms the bony skeleton of the head that protects the brain from external injury. With age, bone remodeling affects the shape of the skull and cortical thickness. Significant cortical thinning occurs in the outer and inner tables of the frontal, occipital, and parietal bones in the elderly (1). In a study evaluating the morphological changes in the skull using three-dimensional geometric analysis from computed tomographic images, it was found that there is a relative expansion of the lateral portions of the skull, primarily in the inferior parietal and temporal regions (2). The anterior and middle cranial fossae compress inward with age, with relative bilateral widening along the lateral edges. This particular structural arrangement alters the biomechanical response of the brain to a head impact and makes the frontal and temporal regions of the brain relatively vulnerable to injury in the elderly.

The brain

Most brain structures decline in volume with age, but at highly different rates. The average rate of decline in the volume and weight of the brain is estimated to be ∼5% per decade after the age of 40, and the rate increases with age, especially after the age of 70 (3). This volumetric brain reduction is mostly due to shrinkage of neurons, and reduction in the dendritic spines and total number of the neuronal synapses, rather than neuronal loss. Also, the length of the myelinated axons is reduced by as much as 50% (4).

Age effects on gray matter

A large variety of cross-sectional studies using the magnetic resonance (MR) imaging indicate that the gray matter is reduced with age, and this reduction is somewhat greater in the cortical than in the subcortical structures (5–8). The regional cortical volume decreases with age, with the greatest effects seen in the frontal cortex, followed by the temporal areas, posterior association areas, and occipital areas. The primary sensory regions seem to be relatively preserved (9–11). Among the subcortical brain structures, the pattern of changes is highly heterogenous, with the putamen, thalamus, and accumbens being the most affected. The limbic structures—the hippocampus and amygdala—are substantially affected with age as well. The brain stem is probably the best preserved of all brain structures in healthy aging (12).

The cerebrospinal fluid (CSF) compartments, including the ventricular systems, increase in volume with age, partly due to atrophy in other brain areas like the deep white matter.

From the interpretation of various cortical studies using automated techniques, it is hypothesized that the brain areas which are the latest to develop phylo- and ontogenetically are the first to be affected by normal aging (“last in–first out”). The effects of aging are thus strongest in the frontal and prefrontal areas. As a result, executive functions like working memory, behavioral control, decision making, etc., that rely heavily on the frontal neural circuits (e.g., the frontostriatal circuits) are among the cognitive functions to be most affected by advancing age (13,14). These circuits are involved in various neurodegenerative disorders, such as Alzheimer’s disease and Parkinson’s disease, as well as in the pathogenesis of neuropsychiatric disorders such as schizophrenia and depression.

It may be remembered, however, that certain memory performances such as procedural, primary, and semantic memory are well preserved with age, as opposed to episodic and working memory. Cognitive retraining for neural recruitment in the aging brain, also called “compensatory scaffolding,” by engaging in social, leisure, and cognitive activities as well as regular exercise, may be used to prevent age-related decline in elderly patients (15).

Age effects on white matter

White matter loss starts at a later stage in the aging brain but is more rapid than gray matter loss, and ultimately exceeds it (16). Myelin breakdown is an aspect of healthy aging, and this breakdown contributes to the loss of white matter volume in the elderly. White matter changes play a causal role in cognitive performance in aging, including mental speed, episodic memory function, executive and flexible cognition, and nonv...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Contents
• Foreword
• Acknowledgment
• Contributors
• 1. Neuroanatomy: Age-related changes
• 2. Neurophysiology: Age-related changes
• 3. Neuropharmacology: Age-related changes
• 4. Preanesthetic evaluation
• 5. Neurosurgery: Supratentorial tumors
• 6. Neurosurgery: Posterior fossa surgery
• 7. Neurosurgery: Cerebrovascular diseases
• 8. Neurosurgery: Neuroendocrine lesions
• 9. Neurosurgery: Spine surgery
• 10. Neurosurgery: Minimally invasive neurosurgery
• 11. Neurosurgery: Functional neurosurgery
• 12. Neuromonitoring
• 13. Positions in neurosurgery
• 14 .Neurotrauma: Geriatric neurotrauma
• 15. Neurointensive care: Postoperative management
• 16. Neurointensive care: Sedation and analgesia in the ICU
• 17. Neurointensive care: Postoperative cognitive dysfunction
• 18. Special considerations: Electroconvulsive therapy
• 19. Special considerations: Alzheimer’s disease
• 20. Special considerations: Parkinson’s disease
• 21. Fluids and electrolyte management
• 22. Palliative care in geriatric patients with neurological diseases
• 23. Brain death and ethical issues: Death by neurological criteria
• Index