Introduction
The term “geriatrics” was coined in English by Ignatz L. Nascher in 1909 from the Greek words gêras, meaning “old age” and atrós, meaning “physician.” Aging is a normal physiological process which is associated with progressive fall in the function of all end organs, and these changes are highly variable between person to person. The prevalence of chronic health conditions increases with age. The physiological changes and their anesthetic considerations in each organ system require a proper understanding.
Physiological Changes in Old Age
Physiological changes in various organ systems are briefly discussed below:
A decrease in the volume of white matter and gray matter due to neuronal loss.
A decrease in the cerebral blood flow by up to 10 to 20%.
Reduction in the levels of neurotransmitters such as serotonin, dopamine, acetylcholine, and norepinephrine.
A decrease in the minimum alveolar requirement (MAC) of general anesthetics.
Neuraxial system: Shrinkage of epidural space, diminished cerebrospinal fluid (CSF) volume, and reduced diameter of myelinated fibers: These physiological changes make aged individuals more sensitive to neuraxial blocks.
Diminished arterial elasticity due to media fibrosis, leading to an increase in systolic pressure and afterload.
A decrease in the number of myocytes and an increase in left ventricular (LV) wall thickness, leading to a reduction in myocardial contractility.
Diminished beta-adrenergic activity, leading to a decrease in heart rate and baroreceptor reflex.
Sclerosis of aortic valves and calcification of mitral valves.
A decrease in the lung tissue elasticity, leading to an increase in closing capacity and residual volume.
Ventilation/perfusion mismatch, leading to decrease in PaO2.
A decrease in chest wall compliance and respiratory muscle function, causing increased work of breathing.
A decrease in the number of glomeruli and renal perfusion.
A decrease in glomerular filtration rate (GFR) and creatinine clearance.
A gradual increase in blood urea nitrogen (BUN) with aging.
Relatively unchanged serum creatinine due to a decrease in muscle mass. Hence, serum creatinine levels poorly predict renal function in geriatric individuals.
Impairment in sodium conservation, concentrating ability, and thirst response predispose aged to dehydration and hyponatremia.
A decrease in hepatic volume by up to 20 to 40% and a reduction in hepatic blood flow.
Decrease in phase I metabolism of drugs.
Endocrine system and metabolic function:
A decrease in oxygen consumption with age.
Impaired thermoregulation and decrease in heat production predispose the aged to hypothermia.
Decreased total body water due to reduced muscle mass and increased body fat.
Reduction in muscle mass and skin atrophy.
Frail skin may cause damage to veins during cannulation.
Arthritis of various joints causing difficulty in positioning the patients.
Degenerative changes in the cervical spine, causing restriction of neck extension and complicating airway management.
Anesthetic Considerations
Preoperative Evaluation
Look for chronic health diseases which may have significant anesthetic implications. Table 26.1 summarizes the major system-wise comorbid illnesses encountered in the elderly.
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