Geriatric Anesthesia Considerations

Emergency surgery, surgical site, and ASA status increase the anesthetic risk for thoracic, intraperitoneal (colon surgery), and major vascular procedures.

Common co-existing diseases are systemic hypertension (SBP >180, DBP >110), DM, CVD, pulmonary, neurological, and renal disease

MAC decreases by 6% per year after age 40

System Changes in the Elderly

Decreased ability to increase heart rate in response to hypovolemia, hypotension, or hypoxia

Decreased lung compliance

Decreased arterial oxygen tension

Impaired ability to cough

Decreased renal tubular function

Increased susceptibility to hypothermia

Cardiovascular

Reduced arterial compliance

• Increased afterload, elevated SBP, left ventricular hypertrophy
• Fibrosis/calcification of valves is common
  • Fibrosis of the conduction system and loss of the SA node cells increase the risk of dysrhythmias (A fib/Aflutter - loses 20-30% of CO)

Decreased adrenergic activity

• Lower resting HR, lower maximal HR, decreased baroreceptor reflex leading to decreased CO

Diastolic dysfunction

• Left shift on the pressure-volume curve leads to increased pressure for the same volume, possibly leading to pulmonary congestion
• The has poor exercise tolerance, HTN, CAD, cardiomyopathy, DM, CRF, aortic stenosis, A fib
  • May complain of dyspnea, cough, or fatigue

Respiratory

Decreased elasticity leading to over-distention of alveoli (reduced surface area for gas exchange) and collapse of small airways

• Increases residual volume and closing capacity (the volume of air in the lungs at which small airways begin to close)
• When closing capacity exceeds FRC, some airways close during normal tidal breathing, leading to a mismatch of ventilation and perfusion

Increased anatomical and physiological dead space

Decreased arterial oxygen tension

• Due to reduced pulmonary capillary blood volume

Increased chest wall rigidity

Decreased muscle strength

• Weak cough

15% loss of functional alveolar surface area by age 70

Central Nervous System

Decreased CNS activity due to loss of neurons, decreased cerebral metabolic oxygen consumption, decreased blood flow, reduced number of receptor sites for neurotransmitter action, and decreased synthesis of neurotransmitters

Higher incidence of post-op delirium and cognitive dysfunction

Delirium is usually transient

• At risk are those aged 70 or older with a history of delirium/alcohol abuse, use of narcotic analgesics, and depression
• Drugs associated with delirium are sedative-hypnotics, narcotics, and anticholinergics

Cognitive dysfunction is usually more persistent, leading to delayed recovery, prolonged hospital stays, nursing home placement, and mortality

Renal and Hepatobiliary

Decreased renal flow due to decreases in cardiac output due to aging

Decreased ability to dilute and concentrate urine and conserve Na

Decreased elimination of drugs

Higher risk of fluid overload

Hepatic function changes minimally

Endocrine

Decreased response to ADH in hypovolemia and hypotension

ADH still responds to serum osmolarity

Decreased pancreatic function, monitor glucose levels

Anesthesia Implications

Exaggerated BP drop during general anesthesia induction due to lower cardiac reserve

Prolonged circulation time delays the onset of IV drugs but speeds induction with inhalational agents (more can get on the train)

Longer preoxygenation period

Edentulous patients may be more challenging to mask ventilate

Arthritis of the temporomandibular joint or cervical spine can indicate difficult intubation

Higher inspired O2 to offset hypoxemia and reduced gas exchange efficiency

Possible use of PEEP to offset the development of atelectasis in the dependent lung areas leading to shunts (perfusion, no ventilation)

There is a higher risk for aspiration due to decreased protective laryngeal reflexes with age

Optimal pain control to enhance pulmonary function post-op

Decreased renal blood flow increases the intraop risk of renal insufficiency or failure

Decreased circulation volume leads to higher initial drug concentrations

Protein binding: Less protein and thus more drugs competing for the receptor sites equals more free drug available (think smaller dose)

Possible prolonged elimination of drugs due to decreased renal and hepatic function

Hypothermia may lead to

• Slower metabolism and excretion of drugs
• Shivering, which can increase O2 consumption up to 400% and cause ischemia/arterial hypoxemia

Continue beta-blockers to decrease myocardial oxygen consumption by reducing HR and contractility

Propofol

• Negative inotropic and vasodilatory effects can exaggerate the decrease in BP

Etomidate

• Preserves cardiac function, about half the dose for 80yr old

Versed

• Increased potency, decreased clearance = longer duration

Opioids

• Decreased volume leading to longer elimination half-times along with decreased hepatic function

NMB

• Clearance decreased for drugs dependent on renal or hepatic (Vecuronium/Rocuronium)
• Clearance unchanged for drugs using Hoffman elimination

Regional

• Exaggerated response to block

Preventing delirium

• Avoid hypoxemia and hypo/hypercapnia
• Provide good pain control