Anesthesia Student Survival Guide.pdf - Index of

374 ● AnesthesiA student survivAl Guide
cognitive dysfunction at baseline, which can be elicited during the preoperative
examination by performing a simple mini-mental status examination. The
incidence of postoperative cognitive dysfunction has been stated to be approximately
30% in the immediate postoperative period and 12% after 3 months.
Postoperative cognitive dysfunction may be related to increased age, extended
duration of anesthesia, low level of education, prior exposure to anesthetics,
postoperative infection, respiratory complications, and prior stroke. Patients
with postoperative cognitive dysfunction at discharge have been shown to have
higher mortality rates during the first year after surgery.
Pharmacokinetic and Pharmacodynamic Changes
With age, there is a progressive change in the constitution of the various body
compartments. Total body water diminishes, fat stores increase, and serum
albumin decreases. As a result, the volume of distribution of the administered
drugs decreases, leading to an increase in drug concentration at the receptor
sites. As the lipid stores are increased, lipid-soluble drugs (e.g. morphine) may
have a prolonged duration of action. A decline in liver and renal function may
also slow down drug metabolism and excretion. Because of these changes, the
dosages of most medications should be decreased in the elderly, and the dosing
interval should be increased (Table 23.3).
Anesthetic Management
Preoperative Examination
The purpose of the preoperative examination is to (1) determine the baseline
physical and mental status of the patient, and (2) identify and optimize any
medical comorbidities prior to undergoing a surgical procedure. The elderly
patient has on average three or more comorbid conditions at any given time.
Table 23.3 Comparative elimination half-life of drugs.
Young Old
fentanyl 250 min 925 min
Alfentanil 90 min 130 min
diazepam 24 h 72 h
Midazolam 2.8 h 4.3 h
vecuronium 16 min 45 min