Alice I. Andreasen, B.S.
University of Washington
School of Medicine
Seattle, Washington
Keith D. Knopes, M.D.
Virginia Mason Medical Center
1100 Ninth Avenue, B2-AN
Seattle, Washington 98101
anekdk@vmmc.org
Opiates were primarily used as analgesics until approximately
20 years ago, when it became known that larger doses of some
agents caused loss of consciousness (more reliably so in the
elderly as opposed to young patients). The potent and rapid-acting
opiates (fentanyl, sufentanil, alfentanil) can be used as the
sole induction agents in cardiovascular surgery where hemodynamic
stability is critical. High doses of these analgesics not only
produce loss of consciousness, they effectively blunt the blood
pressure and heart rate responses to laryngoscopy and intubation.
Opioids can be administered in lower doses by intermittent intravenous
injections or continuous infusion for maintenance of anesthesia
or as adjuvants to inhaled anesthetics.
Fentanyl in doses of 50 to 150 mcg/kg IV are usually necessary
to induce unconsciousness. Because the elimination half-life
of fentanyl is significantly longer in elderly patients compared
to young patients (roughly 945 min and 265 min, respectively),
such a dose will produce respiratory depression and analgesia
for a long time in the elderly. Transdermal fentanyl has been
used for postoperative analgesia; however, because of the increased
sensitivity to the depressant effects of opioids in the elderly,
the occurrence of respiratory depression with the usual 50-75
mcg/hr dose makes the transdermal patch method of pain control
unsuitable in opioid-naïve elderly patients. Administering
25 mcg of fentanyl with bupivacaine during spinal anesthesia
in the elderly significantly decreases pain intensity in the
post operative period. The only significant side effect of this
was pruritus; respiratory depression occurred only if benzodiazepines
were used in conjunction with the spinal fentanyl.
Alfentanil is a very rapid, short-acting synthetic derivative
of fentanyl. It has a low pKa, so much of the drug
exists in the nonionized form at physiologic pH and thus readily
crosses the blood brain barrier. It has a smaller volume of
distribution and shorter elimination half-time in comparison
to fentanyl. Alfentanil can be used as the sole induction anesthetic
(150 to 300 mcg/kg IV produces unconsciousness in approximately
45 seconds) and, at a continuous infusion of 25 to 150 mcg/kg/hr
IV, for anesthetic maintenance in combination with volatile
anesthetics. Alfentanil is a good choice for short operative
procedures in the elderly because it does not produce sustained
postoperative sedation and respiratory depression.
Opioids have a high lipid solubility and therefore a large
volume of distribution. Recovery from a single analgesic dose
of fentanyl or sufentanil may be rapid, owing to the redistribution
from the brain to lean muscle and fatty tissue. However, recovery
from a larger dose used for induction tends to be protracted
due to the saturation of the inactive tissue sites and to the
long elimination half-life of fentanyl and sufentanil (three
to six hours). In spite of the high hepatic clearance rate,
the elimination half-life is long due to the large volume of
distribution. In the elderly, there is a decreased hepatic clearance
rate, resulting in even longer half-life of elimination. Thus,
a given dose would be clinically effective for a longer period
of time. Another potential reason for the decreased requirement
of opioids when used in the elderly is an increase in sensitivity
of the brain to at least some narcotics with aging.
Lower doses of fentanyl (1 to 3ug/kg), alfentanil (10 to 20ug/kg)
or sufentanil (0.125 to 0.25 mcg/kg) are effective adjuvants
to thiopental (2 to 3 mg/kg) for induction of anesthesia because
they decrease the need for barbiturates and diminish the cardiovascular
response to laryngoscopy and intubation.
Bibliography:
- Gauzit R, Marty J, Couderc E, et al. Comparison of sufentanil
and fentanyl to supplement N20 - halothane anesthesia
for total hip arthroplasty in elderly patients. Anesth
Analg. 1991; 72:756-60.
This study of 30 elderly patients concludes that sufentanil
provides improved postoperative analgesia than fentanyl.
- Chung F, Evans D. Low-dose fentanyl: Haemodynamic response
during induction and intubation in geriatric patients. Can
Anaesth Soc J. 1985; 32(6):622-628.
Fentanyl lowers the thiopental requirement for induction
in the elderly.
- Barvais L, DâHollander A, Schmartz D, et al. Predictive
accuracy of alfentanil infusion in coronary artery surgery:
A prebypass study in middle-aged and elderly patients. J
Cardiothorac Vasc Anesth. 1994; 8(3):278-283.
This study compares various infusion schemes of alfentanil.
The scheme using the lowest clearance rate was the most accurate
in the elderly.
- Maitre PO, Ausems ME, Vozeh S, Stanski DR. Evaluating the
accuracy of using population pharmacokinetic data to predict
plasma concentrations of alfentanil. Anesthesiology.
1988; 68(1):59-67.
- Thompson JP, Bower S, Liddle AM, Rowbotham DJ. Perioperative
pharmacokinetics of transdermal fentanyl in elderly and young
adult patients. Br J of Anaesth. 1998; 81(2):152-154.
Varrassi G, Celleno D, Capogna G, et al. Ventilatory effects
of subarachnoid fentanyl in the elderly. Anaesthesia.
1992; 47(7):558-562.
- Fernandez-Galinski D, Rue M, Moral V, Castells C, Puig
MM. Spinal anesthesia with bupivacaine and fentanyl in geriatric
patients. Anesth Analg. 1996; 83(3):537-541.