Chapter 12 The Aging Kidney and Renal Disease

NUTRITIONAL RISKS IN KIDNEY DISEASE

The primary comorbid conditions that often lead to nutrition risk and need to be addressed in CKD include protein-energy wasting (PEW), hypertension, renal osteodystrophy, and anemia. These comorbid conditions may be present in older adults at any stage of CKD (5). A brief summary of each of these condi- tions follows.

PROTEIN-ENERGY WASTING PEW is a known risk factor for mortality and morbidity in chronic dialysis clients (11). A multitude of factors contribute to malnutrition in this population (see Box 12.1). Nutrition strategies to correct malnutrition may include liberalization of the diet, use of enteral supple- ments or nutrition support, renal multivitamins, gastro- intestinal medications, and assistance with meals (eg, home-delivered meals, home care services), to name a few. RDNs must ensure that protein and energy needs are met. Close monitoring of food intake, weight records, assessment of laboratory values, and early medical nutrition intervention will result in better out- comes for these clients.

BOX 12.1 Risk Factors for Malnutrition ●

Dietary restrictions ● Catabolic illness

● Loss of nutrients during dialysis ● Blood loss

● Poor appetite

● Malabsorption/abnormal metabolism ● Social, physical, or psychological factors ● Knowledge deficit

HYPERTENSION

Hypertension is common among older adults with CKD. Those on hemodialysis should limit sodium intake to 2 to 3 g daily. Those on peritoneal dialysis may liberalize sodium restriction to approximately 3 g per day (7,8). These are guidelines, and each indi- vidual’s requirement will depend on blood pressure and fluid status.

RENAL OSTEODYSTROPHY Clients with kidney disease at all stages are at risk for renal osteodystrophy or weak, brittle bones, as well as secondary hyperparathyroidism (12). In healthy indi- viduals, the kidneys play the key role in calcium and

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phosphorus balance by activating vitamin D in the kidneys. Vitamin D, in turn, aids in calcium absorption. As kidney function deteriorates, the body loses its ability to activate vitamin D, and serum calcium levels decrease. This drop in serum calcium triggers the release of parathyroid hormone (PTH), which then trig- gers a response that allows calcium to be drawn from the bones to supply serum calcium. Prevention of renal osteodystrophy is most important because once the condition occurs, remineralization is nearly impossible (13).

It is important that clients with CKD have normal serum levels of corrected total calcium. Hypocalcemia may cause secondary hyperparathyroidism and adverse effects on bone mineralization. Because calcium is bound to protein, calcium levels may appear falsely low if the client has hypoalbuminemia. Ideally, an ionized calcium should be drawn to determine a more accurate calcium level (13). In the clinical setting, another way to assess the calcium level is to calculate a “corrected calcium.” Although not as accurate as an ionized calcium, it is a good indicator of the approxi- mate calcium level. Only the serum albumin and the actual calcium levels are required to calculate the esti- mated or corrected calcium level. The formula to deter- mine “corrected calcium” follows (6):

Corrected serum calcium = [(4 – Albumin level) × 0.8] + Calcium level

where calcium and albumin levels are measured in mg/dL.

Example: If a client has a calcium level of 8.8 mg/dL and an albumin level of 3.1 mg/dL, the calculations could be as follows:

4 – 3.1 = 0.9 0.9 × 0.8 = 0.72 0.72 + 8.8 = Corrected calcium of 9.52 mg/dL

Current understanding suggests that abnormalities in serum phosphorus and elevated PTH levels cause soft-tissue calcification and increase the risk of cardio- vascular death in the end-stage renal disease population (14). Hyperphosphatemia is a common occurrence in CKD and another risk factor for renal osteodystrophy and bone disease. A low-phosphorus diet should be ini- tiated to maintain the serum phosphorus in a range of 3.5 to 5.5 mg/dL. Dietary phosphate should be restricted to 10 to 12 mg of phosphorus per gram of protein or approximately 800 to 1,000 mg/d (13). This limits the amounts of some foods that can be con- sumed, such as milk products, whole grains, nuts and legumes, cola, and chocolate. The serum calcium-phos- phorus product should be maintained at less than