Thomas J. Ebert, M.D., Ph.D.
Professor of Anesthesiology
The Medical College of Wisconsin
and VA Medical Center, Milwaukee, WI 53295
tjebert@mcw.edu
Three general anesthetics, isoflurane, desflurane and sevoflurane,
are commonly employed in the elderly. All three show a similar
decline in MAC with age that is about 6 percent per decade.
In healthy and generally younger patients and volunteers, these
anesthetics enjoy reasonably similar properties of maintaining
cardiac output, despite dose related decreases in myocardial
contractility, blood pressure and systemic vascular resistance.
The maintenance of cardiac output is more dependent on increases
in heart rate with isoflurane than with either sevoflurane or
desflurane. Although there is limited data comparing these anesthetics
in the elderly, some general observations are worth commenting
on. First, with increasing age, there are well described changes
in cardiac, vascular and autonomic function. There is a reduction
in the maximum attainable heart rate due to a decrease in the
response to beta adrenergic receptor stimulation and an increased
dependence on late diastolic filling due to a reduction in diastolic
compliance of the heart. The decreased cardiac response to beta
adrenergic stimulation also compromises the baroreflex-mediated
heart rate increase to hypotension.
There is a general perception that the elderly have a larger
decrease in blood pressure at a given concentration of a volatile
anesthetic than younger patients. The hard science to support
this frequent observation is generally lacking. In one study,
1 MAC isoflurane decreased cardiac output in elderly patients
compared to younger patients. The mechanism appears to be more
related to a lack of an increase in heart rate during isoflurane
in the elderly. Because cardiac output was reduced, the decrease
in blood pressure was greater in the elderly. Certainly other
factors may account for the perceived greater hemodynamic sensitivity
of the elderly. First, the age related impairment of reflex
heart rate responses to hypotension in the elderly and the further
depression of the other components of the baroreflex by the
volatile anesthetics are likely to act in concert to compromise
blood pressure in the elderly. Secondly, because all volatile
anesthetics reduce myocardial contractility, any underlying
cardiac pathology might exaggerate the expected myocardial effect
of the anesthetics. Third, many elderly patients are relatively
volume contracted. Therefore, the direct effects of volatile
anesthetic to cause vascular relaxation might enhance the blood
pressure decrease during anesthesia by several mechanisms: cardiac
filling pressures might be reduced thereby compromising the
preload dependent, "stiff" ventricle of the elderly and vascular
relaxation of narrowed arterioles might result in exaggerated
decreases in vascular resistance.
One should also consider the fact that the elderly have a higher
incidence of other disease processes and a higher frequency
of concurrent medications. For example, both diabetes and hypertension
are more prevalent in the elderly. These disease processes have
substantial effects on the autonomic nervous system, baroreflex
function and vascular pathology. The use of a volatile anesthetic
in these patients should exaggerate hemodynamic responses. Concurrent
medications, such as beta-adrenergic blocking drugs, might further
impair reflex heart rate and cardiac output increases of the
elderly during blood loss. Thus, the perception that volatile
anesthetics are associated with heightened blood pressure decreases
in the elderly is likely correct and can be attributed to multiple
factors including cardiovascular and autonomic changes with
age, concurrent disease processes and medications.
References:
- Latson TW, Ashmore TH, Reinhart DJ, et al. Autonomic reflex
dysfunction in patients presenting for elective surgery is
associated with hypotension after anesthesia induction. Anesthesiology.
1994; 80:326-337.
- Bullington J, Mouton Perry SM, Rigby J, et al. The effect
of advancing age on the sympathetic response to laryngoscopy
and tracheal intubation. Anesth Analg. 1989; 68(5):603-608.
- Lakatta EG. Cardiovascular aging research: The next horizons.
J Am Geriatr Soc. 1999; 47:613-625.
- Ebert, TJ. Cardiovascular aging: Anesthetic implications.
Fifteenth Annual Refresher Course Lectures and Clinical Update
Program. American Society of Anesthesiologists. 1999; No.
521.
- Ebert TJ, Muzi M, Berens R, et al. Sympathetic responses
to induction of anesthesia in humans with propofol or etomidate.
Anesthesiology. 1992; 76:725-733.
- Burgos LG, Ebert TJ, Asiddao C, et al. Increased intraoperative
cardiovascular morbidity in diabetics with autonomic neuropathy.
Anesthesiology. 1989; 70:591-597.
- Seymour DG, Vaz FG. A prospective study of elderly general
surgical patients: II. Post-operative complications. Age
Ageing. 1989; 18(5):316-326.
- Seymour DG, Pringle R. Post-operative complications in
the elderly surgical patient. Gerontology. 1983; 29(4):262-270.