22-35: The Kidney & Aging

After 40 years of age, GFR declines annually by an average rate of 0.8 mL/min/1.73 m² (though some older patients show little or no change) and is accompanied by a decline in renal mass that spares medulla relative to cortex. In an attempt to maintain GFR, renal blood flow decreases, causing a resultant increase in arteriolar resistance and increased filtration fraction. Serum creatinine values may remain relatively constant if muscle mass decreases in parallel with the decrease in GFR; a stable creatinine in the face of significant weight loss suggests progression of kidney disease.

Renal tubular changes include impaired sodium handling, decreased concentrating and diluting abilities, and impaired acidification. Thus, older patients are more prone to volume overload, dysnatremias, and acidosis. Decreased renin synthesis and 1alpha-hydroxylase activity are also observed. These abnormalities can result in hyperkalemia, hypocalcemia, and elevated PTH activity.

More adverse drug reactions occur in older patients. Three main pharmacokinetic changes occur: (1) altered volume of distribution, (2) altered drug half-life, and (3) altered elimination. The latter two are directly related to impaired renal clearance of drug. The SPRINT Trial showed that more intensive blood pressure control in nondiabetic patients 75 years of age and older with CKD decreases overall cardiovascular morbidity and mortality. However, patients in the intensive arm (less than 120 mm Hg) required 2.8 medications versus 1.8 medications in the standard control arm (systolic blood pressure less than 140 mm Hg).

Roughly half of patients starting dialysis are 65 years or older. Hemodialysis and peritoneal dialysis are both reasonable options for older adults with ESKD, though hemodialysis may be preferred among those with functional impairment who cannot independently manage their treatments or receive assistance from a responsible caretaker. There is no clear evidence of survival benefit with dialysis among patients over the age 80 or those 75 and older with heart disease and other comorbidities (eg, stroke, functional limitations). In these patients, optimizing medications and carefully monitoring dietary intake—a practice called "supportive kidney care"—is increasingly recognized as offering similar life expectancy while preserving quality of life relative to initiation of dialysis.

Kidney transplantation is being offered to older individuals more often as it appears to offer survival benefit even those over 65 years. Over the age of 75, however, there is not a clear survival benefit. The most common transplant complications in this population are infection and CVD. A reduced corticosteroid requirement with the introduction of steroid-sparing agents has lowered infection rates.