Ivan Barlow M.D.
Assistant Professor
Department of Anesthesiology
University of South Florida
Tampa, Florida
ibarlow@hsc.usf.edu
The aging process results in profound anatomic and functional
changes in virtually all major organ systems, including the
cardiovascular, respiratory and renal systems. Much attention
has been devoted to studying the effects of aging on the kidney1.
The changes in kidney function with normal aging are as dramatic
as any human organ or organ system. These changes are both structural
and functional. Microscopic examination confirms the disappearance
of the kidney's functional units with age; as many as one-half
of the glomeruli present in young adults may be gone or rendered
nonfunctional by 80 years of age. The common
denominator of these functional changes is a diminution in renal
reserve, along with constraints on the kidney's ability to respond
appropriately to challenges of either excesses or deficits.
Advanced age markedly decreases renal function reserve. Glomerular
filtration rate, normally about 125 ml/min in a young adult,
decreases to about 80 ml/min at 60 years of age and to 60 ml/min
at 80 years.3,4
Although these alterations are unlikely to be of major clinical
consequence under everyday conditions, they attain clinical
significance when residual renal function is challenged by the
superimposition of an acute illness. Clinicians of all specialties
should be familiar with these alterations because they predispose
to diverse fluid and electrolyte abnormalities and have important
implications for drug therapy in the elderly.2
The prevalence of renal disease not only increases perioperative
risk of acute renal insufficiency or failure but also affects
the duration of action of many anesthetic and adjuvant drugs.
A major pharmacokinetic consequence of age-related changes
in renal function is prolongation of the elimination half-time
of anesthetic drugs and any metabolites requiring renal clearance.3,4
Elderly patients frequently suffer from comorbid conditions
such as hypertension and heart disease, which may be additive
to the changes of aging, thereby amplifying these abnormalities.
Renal dysfunction remains a serious complication during the
perioperative period and is most likely to occur in critically
ill patients undergoing major surgery. Typically, only after
a patient has sustained renal injury are clinicians focused
on "renal protective strategies," and by then it is often too
late. Despite significant advances in hemodynamic monitoring
and hemodialysis during the past three decades, the mortality
rate from acute renal failure has not changed significantly.
Acute renal failure is in fact responsible for at least one-fifth
of all perioperative deaths among elderly surgical patients.3,4
Perioperative renal failure following trauma and thoracic or
cardiovascular surgery carries a reported incidence of 0.1%
to 50%, depending on the population analyzed and the methods
used to define renal failure, and is associated with a reported
mortality of 20 percent to 90 percent. Perioperative renal failure
accounts for one-half of all patients requiring acute dialysis.5
The precise mechanisms heralding the transition from compensated
preserved renal function to uncompensated renal failure during
the perioperative period remain poorly understood, in part because
the methods used to assess renal function are insensitive and
nonspecific.3,4
Acute tubular necrosis accounts for nearly 90 percent of the
cases of perioperative renal failure.5
Perhaps one reason for our inability to prevent renal failure
is a shift in medical populations to older and more critically
ill patients.
The wealth of data available on senescence and the kidney precludes
a complete examination of the subject in this limited space.
(For an excellent discussion on this topic, see the article
"Aging and the Kidney" by Murray Epstein, M.D.)
References:
1. Epstein M. Effects of aging on the
kidney. Fed Proc. 1979; 38:168-171.
2. Epstein M. Aging and the kidney. J
Am Soc Nephrol. 1996; 7:1106-1122.
3. Aronson S. Renal function monitoring.
In: Miller RD, ed. Anesthesia. 4th Ed. New
York: Churchill Livingstone; 1994:1293-1317.
4. Aronson S. Evaluation of Renal Function.
In: Miller RD, ed. Anesthesia. 4th Edition.
5. Wilkes BM, Mailloux LU. Acute renal failure:
pathogenesis and prevention. Am J Med. 1986; 80:1129-1136.