Managing advanced chronic kidney disease: A primary care guide

OTHER ASPECTS OF CKD CARE

Bone mineral disorders

Patients with CKD develop secondary hyperparathyroidism, hyperphosphatemia, and (in advanced CKD) hypocalcemia, all leading to disorders of bone mineral metabolism.

Traditionally, it has been thought that decreased production of 1,25-dihydroxyvitamin D by dysfunctional kidneys leads to decreased suppression of the parathyroid gland and to secondary hyperparathyroidism. The major long-term adverse effect of this is a weakened bone matrix resulting from increased calcium and phosphorus efflux from bones (renal osteodystrophy).

The discovery of fibroblast growth factor 23 (FGF-23) has improved our understanding of the physiology behind disordered bone mineral metabolism in CKD. FGF-23, produced by osteoblasts and osteocytes, acts directly on the kidney to increase renal phosphate excretion. It also suppresses 1,25-dihydroxyvitamin D levels by inhibiting 1-alpha-hydroxylase,⁶⁵ and it stimulates parathyroid hormone secretion. FGF-23 levels rise much earlier in CKD than do parathyroid hormone levels, suggesting that abnormalities in phosphorus balance and FGF-23 may be the earliest pathophysiologic changes.⁶⁶

The initial treatment of bone mineral disorders is to some extent guided by laboratory values. Phosphate levels higher than 3.5 or 4 mg/dL and elevated FGF-23 levels have been associated with increased mortality rates in CKD patients.^{18,19,67–69} All patients should also have their 1,25-dihydroxyvitamin D level checked and supplemented if deficient. In many patients with early stage 3 CKD, this may correct secondary hyperparathyroidism.⁷⁰

Serum phosphorus levels should be kept in the normal range in stage 3 and 4 CKD,⁷¹ either by restricting dietary phosphorus intake (< 800 or < 1,000 mg/day) or by using a phosphate binder, which is taken with meals to prevent phosphorus absorption from the gastrointestinal tract. Current US recommendations are to allow graded increases in parathyroid hormone based on the stage of CKD (Table 2).⁷¹ However, these targets are still an area of uncertainty, with some guidelines suggesting that wider variations in parathyroid hormone can be allowed, so there may be wider variation in clinical practice in this area.⁷² If the serum phosphorus level is in the goal range but parathyroid hormone levels are still high, an activated vitamin D analogue such as calcitriol is recommended, although with the emerging role of FGF-23, some experts also call for early use of a phosphate binder in this group.

The treatment of bone mineral disorders in CKD is fairly complex, and we recommend that it be done by or with the close direction of a nephrologist.

Recommendations on bone disorders

• Check levels of calcium, phosphorus, 25-hydroxyvitamin D, and parathyroid hormone in all patients whose estimated GFR is less than 60 mL/min/1.73 m², with frequency of measurements based on the stage of CKD.⁷¹
• Replace vitamin D if deficient.
• Treat elevated phosphorus levels with a protein-restricted diet (nutrition referral) and a phosphate binder.
• Treat elevated hyperparathyroid hormone levels with a vitamin D analogue once phosphorus levels have been controlled.
• Refer patients with an elevated phosphorus or parathyroid hormone level to a nephrology service for consultation before initiating medical therapy.

Anemia is common, treatment controversial

The treatment of anemia attributed to CKD has been a topic of controversy over the past decade, and we recommend that it be done with the guidance of a nephrologist.

Anemia is common in CKD, and declining kidney function is an independent predictor of anemia.⁷³ Anemia is a risk factor for left ventricular hypertrophy, cardiovascular disease,⁷⁴ and death in CKD.⁷⁵

The anemia of CKD is attributed to relative erythropoietin deficiency and bone marrow resistance to erythropoietin, but this is a diagnosis of exclusion, and other causes of anemia must be ruled out. Iron deficiency is a common cause of anemia in CKD, and treatment of iron deficiency may correct anemia in more than one-third of these patients.^76,77

Erythropoiesis-stimulating agents such as epoetin alfa (Procrit) and darbepoetin (Aranesp) are used to treat renal anemia. However, the target hemoglobin level has been a subject of debate. Three prospective trials^78–80 found no benefit in raising the hemoglobin level to normal ranges using these agents, and several found an association with higher rates of stroke and venous thrombosis. The US Food and Drug Administration suggests that the only role for these agents in CKD is to avoid the need for transfusions. They should not be used to normalize the hemoglobin level. The target, although not explicitly specified, is suggested to be around 10 g/dL.⁸¹

PREPARE FOR END-STAGE RENAL DISEASE

Discuss the options

Because the risk of developing end-stage renal disease rises dramatically once CKD reaches stage 4, all such patients should have a discussion about renal replacement therapy. They should be educated about their options for treatment (hemodialysis, peritoneal dialysis, and transplantation, as well as not proceeding with renal replacement therapy), often in a formal class. They should then be actively engaged in the decision about how to proceed. Survival and quality of life should be discussed, particularly with patients who are over age 80, who are severely ill, or who are living in a nursing facility, as these groups get limited survival benefit from starting dialysis, and quality of life may actually decrease with dialysis.^82,83

The Renal Physicians Association has created clinical practice guidelines for shared decision-making, consisting of 10 practice recommendations that outline a systematic approach to patients needing renal replacement therapy.⁸⁴

Consider preemptive kidney transplantation

Any patient thought to be a suitable candidate for renal transplantation should be referred to a transplantation center for evaluation. Studies have shown that kidney transplantation offers a survival advantage compared with chronic dialysis and should preferably be done preemptively, ie, before dialysis is required.^85–90 Therefore, patients with estimated GFRs in the low 20s should be referred for a transplantation evaluation.

If a living donor is available, the transplantation team usually waits to perform the procedure until the patient is closer to needing dialysis, often when the estimated GFR is around 15 to 16 mL/min/1.73 m². If no living donor is available, the patient can earn time on the deceased-donor waiting list once his or her estimated GFR falls to below 20 mL/min/1.7 m².

Plan for dialysis access

Patients starting hemodialysis first need to undergo a procedure to provide access to the blood. The three options are an arteriovenous fistula, an arteriovenous graft, and a central venous catheter (Figure 1).

An arteriovenous fistula is the best option, being the most durable, followed by a graft and then a catheter.⁹¹ Arteriovenous fistulas also have the lowest rates of infection,⁹² thrombosis,⁹³ and intervention to maintain patency.⁹³

The fistula is created by ligating a vein draining an extremity, most often the nondominant arm, and anastomosing the vein to an artery. The higher arterial pressure causes the vein to dilate and thicken (“arterialize”), thus making it able to withstand repeated cannulation necessary for hemodialysis.

An arteriovenous fistula typically takes 1 to 3 months to “mature” to the point where it can be used,^94,95 and, depending on the patient and experience of the vascular surgeon, a significant number may never mature. Thus, it is important to discuss hemodialysis access before the patient reaches end-stage renal disease so that he or she can be referred to a vascular surgeon early, when the estimated GFR is about 20 mL/min/1.73 m².

An arteriovenous graft. Not all patients have suitable vessels for creation of an arteriovenous fistula. In such patients, an arteriovenous graft, typically made of polytetrafluoroethylene, is the next best option. The graft is typically ready to use in 2 weeks and thus does not require as much advance planning. Grafts tend to narrow more often than fistulas and require more procedures to keep them patent.

A central venous catheter is most often inserted into the internal jugular vein and tunneled under the skin to exit in an area covered by the patient’s shirt.

Tunneled dialysis catheters are associated with higher rates of infection, thrombosis, and overall mortality and are therefore the least preferred choice. They are reserved for patients who have not had advance planning for end-stage renal disease, who do not have acceptable vessels for an arteriovenous fistula or graft, or who have refused surgical access.

Protect the fistula arm. It is recommended that venipuncture, intravenous lines, and blood pressure measurements be avoided in the nondominant upper arm of patients with stage 4 and 5 CKD to protect those veins for the potential creation of an arteriovenous fistula.⁹⁶ For the same reason, peripherally inserted central catheter lines and subclavian catheters should be avoided in these patients. If an arteriovenous fistula has already been placed, this arm must be protected from such procedures at all times.

Studies have shown that late referral to a nephrologist is associated with a lower incidence of starting dialysis with a permanent vascular access.^97,98

If the patient wishes to start peritoneal dialysis, the peritoneal dialysis catheter can usually be used 2 weeks after being inserted.