The Geriatric Patient and Perioperative Management

With the increasing elderly population in the United States, it becomes increasingly important to understand the physiologic changes of aging to better tailor anesthetic management of the geriatric patient. A review of changes by system is presented below.

The CNS system shows overall decreased brain reserve and increased sensitivity to anesthetic drugs. White and gray matter decreases in mass, many neurotransmitter levels are reduced, CSF volume decreases, dura permeability increases, and the epidural space is smaller. The functional result of these changes include a decrease in MAC by 4-6% per decade after age 40, increase in perioperative delirium and postoperative cognitive dysfunction, and increased sensitivity to neuraxial anesthetics.

Cardiovascular changes include a thickened left ventricle leading to diastolic dysfunction, myocyte loss resulting in decreased contractility, increased basal sympathetic tone but decreased β-adrenergic sensitivity, and mean arterial pressure and pulse pressure increases due to vascular stiffness. Care should be taken to ensure adequate preload, optimize coronary perfusion by lowering heart rates and maintaining higher MAPs under anesthesia, and preparing for hemodynamic swings with induction and neuraxial anesthesia given decreased sensitivity to sympathomimetic drugs.

Respiratory changes include increased lung compliance but decreased chest wall compliance leading to risk of air trapping and increased work of breathing, and loss of alveolar surface area leading to worsened diffusion capacity. In terms of lung volumes, total lung capacity is unchanged, vital capacity decreases, residual volume increases, functional residual capacity (FRC) is unchanged or slightly unchanged, and closing capacity (CC) is increased. At age 44, FRC equals CC in the supine position, and at age 66 in the upright position. As FRC falls below CC, shunt occurs leading to worsened arterial oxygenation. Therefore care should be taken to adequately preoxygenate elderly patients, and consider adding PEEP during positive pressure ventilation.

Renal blood flow declines 10% per decade after age 40, but serum creatinine remains relatively unchanged due to concomitant loss of muscle mass. Therefore creatinine is not an accurate predictor of GFR in the elderly patient. Liver volume decreases 20-40% with aging, and hepatic blood flow decreases 10% per decade. Care should be taken to dose renally and hepatically cleared medications conservatively.

Understanding the physiology of aging is essential to the ability to tailor anesthetic care to the geriatric patient. In summary, the trend is toward sensitivity to many drugs, decreased cardiopulmonary reserve, and the potential for longer recovery times.

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