Impaired Kidney Function

A healthy kidney filters +- 1600litres / day of blood.

Through active processes of reabsorbing certain components (for eg protein ) and secreting others    ( for eg uric acid) the ultra-filtrate is changed into the 1.5 litres of urine excreted in an average day.

Urine volume of less than 500ml / day is called oliguria. It is impossible for such as small urine volume to eliminate all of the daily waste. The majority of the solute load consists of nitrogenous wastes, primarily the end products of protein metabolism. Urea predominates, depending on the protein content of the diet.  Renal failure is the inability to excrete the daily load of wastes.

The kidney also performs other important functions such as control of blood pressure, and production of the hormone erythropoietin (EPO) which stimulates bone marrow to produce red blood cells.

Renal disease can be ordered by degree of severity.

• kidney stones (nephrolithiasis)
• acute kidney injury (AKI )
• chronic kidney disease (CKD)
• end-stage renal disease (ESRD)

Objectives of Medical Nutrition Therapy (MNT) depend on the abnormality being treated.

• Kidney Stones

A low urine volume is the single most important risk factor for all types of nephrolithiasis. The following 5 modifiable risk factors account for more than 50% of kidney stone incidents:

• Body Mass Index (BMI); hydration / water intake; DASH (Dietary Approached To Stop Hypertension) style diet; dietary calcium intake; sugar-sweetened beverage intake.

Calcium oxalate stones are the most common (60%), with uric acid stones (5-10%), and cystine and struvite stones less common.  It is important to understand how MNT differs for each condition. Nutrition assessment is needed to determine risk factors for stone recurrence.  Accurate understanding of how dietary intake can influence the acidity or alkalinity of the urine is important.

• Acute Kidney Injury

Causes of AKI (Acute Kidney Injury) are numerous and could be due to severe dehydration, trauma, surgery, nephrotoxicity from drugs,  prostatic hypertrophy, acute glomerulonephritis, and more.

The amount of protein, energy, fluid, sodium, or potassium required,  is influenced by the underlying cause. MNT is particularly important, because the patient not only has uremia (nausea, vomiting, loss of appetite), metabolic acidosis, fluid and electrolyte imbalance, but also suffers from physiological stress ( for eg infection ) that increases protein needs.

• Chronic Kidney Disease:

CKD is characterised by a slow, steady decline in renal function. Progressive loss of renal function has been the subject of an enormous amount of clinical research and the subject of several excellent reviews ( National Kidney foundation 2018 )  MNT begins when the patient is diagnosed, with the goal of preventing, or slowing the development of the disease, and mitigating symptoms.  Diabetes is the leading risk factor for CKD followed by hypertension. With each level of CKD, a different nutrition therapy is proposed. Supporting medical treatment of the primary cause ( for eg hypertension )  and secondary symptoms ( for eg edema, hypoalbuminemia ) decrease the risk of progression. Documented guidelines are used, to ensure that the diet provides sufficient protein to maintain a positive nitrogen balance, while not overtaxing the kidneys.

Specific recommendations are also published for the dietitian to manage sodium, potassium, phosphorous, lipids, vitamins,  and probiotics in the diet.

• End Stage Renal Disease

ESRD is diagnosed when the kidney is unable to excrete waste products, maintain fluid and electrolyte balance, and produce hormones.  Uraemia develops, causing many symptoms, due to unacceptable levels of nitrogenous waste in the body.  Options for treatment include: dialysis, transplant and medical management.

During ESRD, the goal of MNT is to prevent nutrition deficiencies, control oedema and electrolytes, prevent renal osteodystrophy, and support the patient with a palatable and attractive diet.

Nutrient requirements differ at this stage from pre-dialysis goals, and need to be adjusted according to the individual patient’s clinical picture including blood results.

ESRD with Diabetes, is a common occurrence, as +- 45% of all patients starting dialysis, have diabetes. Controlling blood glucose is paramount diet therapy. The diabetic patient on dialysis often has other complications which places this patient at high nutritional risk. Lastly, the nutritional care of the patient who has received a transplanted kidney, is based on the metabolic affects of the required immunosuppressive therapy.