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Department of Anesthesiology - Residents Section
Anesthesia Knowledge - Elderly Anesthesia
Anesthesia for the Elderly
Age-related concomitant diseases
Emergency surgery particularly dangerous because it doesn't allow for optimization and control of co-existing disease.
Psychological factors play important role: fear of the loss of independence, etc.
Brain size decreases, weight is about 20% less by age of 80. Attrition of neurons, particularly those that synthesize neurotransmitters. Requirements for the drugs that act on CNS decreases.
CBF decreases proportionally. Autoregulation of cerebrovascular resistance in response to changes in MAP remains intact. Knowledge base, comprehension, and long-term memory are preserved.
Slowing of electrical conduction along efferent motor pathways. Increase in number of cholinergic receptors at the neuromuscular junction, it offsets the age-related decrease in the number and density of the motor neurons.
Autonomic Nervous System
Adrenal gland tissue mass and cortisol secretion decreases by 15% by 80 years. Responsiveness of beta-adrenergic receptors decreases, so inotropic and chronotropic responses to beta-agonists decreases. Alpha-adrenergic and muscarinic receptor activity practically unchanged. Baroreceptors responses are dampened, thus hypotension on induction.
SBP increases because of poor compliance of arterial walls. Heart rate decreases, AV block common, cardiac output decrease comes from decreased requirement for perfusion and metabolism by age-related decrease in muscle mass and tissue mass for organs with initially high intrinsic metabolic rate. SV and EF unaffected, but ability to increase HR in response to stress is impaired. Myocardial compliance decreased, passive LV filling decreased. Diastolic dysfunction is common, especially if dysrhythmia present.
CHF is common and usually associated with systemic hypertension and/or CAD. Dyastolic dysfunction is the principal cause of CHF, especially in people over 80.
Loss of tissue elasticity, loss of lung elastic recoil. Diffuse V/Q mismatch during anesthesia due to loss of alveolar architecture and anesthetic-induced depression of active hypoxic pulmonary vasoconstriction. Supplemental oxygen necessary to prevent arterial hypoxemia. The ventilatory response to hypoxemia or hypercapnia is decreased. Transient apnea and episodic breathing under influence of opioids is common.
Emphysema-like increase in lung compliance because on the elastic recoil decrease. Chest wall compliance decreased. Resultant net pulmonary compliance almost unchanged.
Functional residual capacity progressively increases, vital capacity decreases as residual volume increases. Work of breathing increased. Infections are more common.
Progressive loss of renal tissue mass, decreased RBF(as much as 50%). Serum creatinine usually unchanged due to declining skeletal muscle mass. Urine concentrating ability decreased, sodium concentrating ability decreased, hyponatremia is common.
Liver tissue mass decreases progressively (about 40% by age of 80), hepatic blood flow decreased proportionally. Microsomal and non-microsomal enzyme activity unchanged. Age-related loss of hepatic tissue mass is thought to be the primary reason for the delayed metabolism and prolonged pharmacologic effects of opioids. Production of albumin decreases, resulting in decreased plasma protein binding of some drugs.
Motility decreased, gastric emptying delayed, gastroesophageal sphincter tone decreased. Prone to aspiration.
DM and hypothyroidism are common. Subclinical hypothyroidism (increase in plasma concentration of TSH) is present in more than 13% healthy elderly, especially females.
Skin and musculoskeletal systems
Epidermis atrophy, decrease in elasticity, results in pronness to ulceration and skin breakdown. Osteoporosis, osteoarthritis, rheumatoid arthritis are common.
MAC for inhaled anesthetics decreases progressively (as much as 30% from young adult values).
Less consistency observed in opioids, barbiturates and benzodiazepines pharmacodinamics. Possibly, delayed clearance responsible for decreased dose requirements.
Non-depolarizers have prolonged time of onset and duration of action, if elimination is dependent on renal or hepatic clearance, but dose rerquirements are similar to young adults.
Decreased segmental dose requirements for epidural anesthesia.
Increased variations in pharmacodynamics and pharmacokinetics lead to increased incidence in adverse drug reactions. Changes in volume of distribution are common.
Causes of increased elimination half-times of drugs.
Increased volume of distribution:
Thiopental. Sensitivity increased due to decreased volume of distribution, and as a result, higher plasma concentration delivered to the brain. Brain sensitivity doesn't change with age. Dose decrease by 15% in 80 years old as compared to 20 years old to achieve the same effect.
Propofol. Brain sensitivity doesn't change. Volume of distribution decreased, thus plasma concentration increased. Dose decrease by 15% advisable to produce unconsciousness. Lean body mass is the better predictor of propofol dose than age alone.
Midazolam. Big difference in intrinsic brain sensitivity to the drug requires decrease in dose by 30% to 60% in 60-year-old and 80-year-old respectively, as compared to 20-year-old.
Fentanyl. Dose decreased by 50% in 85 y.o. as compared to 20 y.o. to produce the same effect due to pharmacodynamic changes. Alfentanyl. Pharmacokinetics doesn't change with age. Dose decrease by 50% due to pharmacodynamic changes and increased brain sensitivity to any concentration.
Sufentanyl. Highly bound to alpha-1-acid glycoprotein, as it is increased in the elderly, free fraction of the drug is decreased with age, thus suggesting the decrease in potency. However, clinical experience suggests that brain sensitivity to opioids in elderly is increased, thus dose should not be altered.
Neuromuscular blocking drugs.
Pancuronium. Decrease in renal function slows clearance.
Vecuronium. Slight decrease in clearance suggests about 10% decrease in dose. Changes in sensitivity of the neuromuscular junction to neuromuscular blockers do not occur.
Atracurium and Cisatracurium. Both ester hydrolysis and Hoffman elimination are not affected by age. Intrinsic potency of the drugs is not affected either.
Management of anesthesia
Fast and complete recovery of mental function is of utmost importance.
Preoperative evaluation and preparation.
Co-existing diseases. Alcoholism possible.
Changes in mental function - cardiac or pulmonary pathology should be excluded.
Drug history, interactions.
Detailed explanation to reduce anxiety, rather than benzodiazepines, in the preoperative period.
Glycopyrrolate, doesn't cross blood-brain barrier, good antisialagogue.
Mechanical changes associated with aging:
All these changes may be associated with potential problems in the management of general anesthesia.
Drug selection is dictated by changes in dose requirements and desire for the prompt awakening.
Acceptable alternative in alert and cooperative patient for TURP, hip fracture, GYN procedures, inguinal hernia repair. T8 level recommended. Regional anesthesia for hip fracture decreases perioperative blood loss and decreases the incidence of postoperative DVT. Higher levels of sensory blockade may occur.
Epidural anesthesia is good, too. More gradual decrease in systemic BP than that which associated with spinal anesthesia. Slightly lower dose might be considered.
Postoperative mental dysfunction (delirium)
One of the most common complications in elderly. Incidence about 10%-15% in elderly undergoing surgery. Interval delirium occurs after a lucid interval of one or more days after an operation and is the most frequent form of postoperative delirium in elderly patients. Emergence delirium occurs within minutes of regaining consciousness and is more often present in children.
Clinical features include disorders of attention, cognition, sleep-wake cycle, and psychomotor behavior. Symptoms are usually increased during periods of darkness. Disorientation of time, place, and person are common. Delirious patients may endanger themselves by inflicting self-injury or pulling out medical catheters.
Ophthalmologic, cardiac, and hip surgery are commonly associated with postoperative delirium.
No difference in incidence of delirium after general or regional anesthesia.
Etiologic factors in postoperative delirium