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INTRODUCTION

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By 2040, over 20% of the US population will be age 65 or older. Increased age by itself does not add significant risk for poorer perioperative outcomes. However, older patients have significant comorbid conditions which form the basis of risk stratification. Most elderly patients who present for surgery have a baseline functional status that allows them to meet their daily needs. However, the physiologic stress of surgery may unmask decreased functional reserve in a number of different organ systems.

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PHYSIOLOGIC CHANGES

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Cardiovascular System

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A fundamental change of the cardiovascular system seen with aging is the stiffening of the arterial vasculature. Fibrosis of the medial layer results in decreased arterial compliance, elevated systolic blood pressure, increased afterload, and left ventricular hypertrophy. This chain of events also leads to myocardial stiffening, creating a high incidence of diastolic dysfunction in the geriatric population. Higher atrial pressures are necessary to maintain adequate end-diastolic volume. Consequently, the elderly are prone to developing hypovolemia as the aged heart is more dependent on the Frank–Starling mechanism and an adequate end-diastolic volume to maintain stroke volume. In addition, older patients rely more heavily on atrial contraction for adequate ventricular filling, predisposing the elderly to atrial enlargement and arrhythmias such as atrial fibrillation and flutter. Careful perioperative fluid management in the geriatric population is of the utmost importance. Older patients may also have subtle systolic dysfunction despite a normal ejection fraction.

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In the geriatric patient, the receptors of the autonomic nervous system have lower sensitivity, leading to impaired control of heart rate. The diminished response of adrenergic receptors is most likely due to impaired second messenger systems. This change occurs despite increased plasma levels of norepinephrine and decreased cardiac norepinephrine.

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The reflex regulation of heart rate is primarily dependent on cardiac vagal input. Attenuation of the respiratory sinus arrhythmia in older patients suggests that the parasympathetic control of the sinus node is diminished. Elderly patients have lower resting vagal tone as a result of decreased vagal outflow, decreased muscarinic receptors, and diminished receptor function. Consequently, these patients have a diminished heart rate increase to large doses of atropine compared to younger patients. As a result, geriatric patients have a decreased ability to increase heart rate in response to hypovolemia, hypotension, and hypoxemia.

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Respiratory System

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Geriatric patients develop decreased upper airway patency due to hypotonia of pharyngeal and laryngeal muscles. The risk of aspiration increases due to diminished swallowing and cough reflexes. Natural calcification of cartilage and degenerative changes of the spine lead to geometric changes to the thorax and decreased chest wall compliance. Decreases in muscle fiber cross-sectional area and changes to the neuromuscular junction also lead to decreased strength of the diaphragm and accessory respiratory muscles.

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Due to aging, the elasticity of lung tissue decreases. The corresponding increase in lung compliance predisposes the ...

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