Renal Disease And Wasting

Question 1

Role of sodium in CKD: normal homeostasis, dietary advice for CKD (and how to assess), importance of restricting

Answer 1

• normal homeostasis: high sodium is detected by osmoreceptors which causes release of vasopressin (makes thirsty) and ADH (retains water). Sodium retained by kidneys. When diluted, will release
• need to restrict to 5g of salt per day for CKD, can assess this through FFQ, diet diaries
• important to restrict as can lead to interdialytic weight gain (putting strain on heart), Na overload: osmotically active (increases ECV and causes hypertension) or osmotically inactive (exchanges for K+ in cells and increases ISF volume causing vasoconstriction and hypertension)

Question 2

Potassium restriction in CKD

Answer 2

• too high potassium can affect electrical conduction of the heart
• high potassium foods are considered to be >200 mg (bananas, oranges, pears)
• advise to over boil vegetables and throw water oht

Question 3

Phosphate restriction in CKD and consequences

Answer 3

• too high phosphate causes precipitation out of areas with low blood flow (such as skin causing ulcers), severe phosphate deposition could cause calcification of the arteries
• foods high in phosphate: milk, cheese, meat, prepared sauces
• can use phosphate binders but these are large and chalky, and difficult to swallow

Question 4

Why do those with CKD lose weight? Disturbances in hunger hormone profiles

Answer 4

• those with CKD have increased satiety hormones: leptin (from AT), obestatin (stomach), PYY (from the colon during constipation)
• they also have des-acyl ghrelin which is an anorexiogenic peptide version of ghrelin (increases satiety)
• inflammatory cytokines can also enter the brain at the 3rd ventricle through fenestrated capillaries which activate the POMC neuron and cause satiety

Question 5

Definition of protein-energy wasting

Answer 5

• catabolic and anorexic state
• decline in protein and fat stores
• increased EE
• inflammation
• oxidative stress
• can lead to sarcopenia

Question 6

Causes of protein energy wasting (PEW)

Answer 6

• anorexia and malnutrition caused by activation of POMC via IL6, TNFa
• depression/anxiety caused by POMC activation
• increased EE leading to catabolism, directly (proteasome pathway activated by metabolic acidosis), or indirectly (insulin resistance, increased myostatin)
• reduced anabolic hormones (testosterone, GH)
• anaemia
• metabolic acidosis

Question 7

Contribution of dialysis to wasting disease, why do we care about protein losses?

Answer 7

• HD leads to protein losses of ~25g per week
• PD leads to losses of ~35g per week
• CRRT (use in ITU) leads to greatest protein losses as it is on all the time
• the lower the FFM the higher the mortality

Question 8

Improving patient outcomes: dietary screening

Answer 8

• using dietary assessment (3 day diet diaries) although these are reliant on the patient
• can use SGA: scoring system for malnutrition
• biochemical parameters: serum albumin (low= malnutrition), IGF1, amino acids, protein equivalent nitrogen appearance in diasylate or urine
• body weight (although issues with fluid retention), anthropometry (although varies a lot between those taking measurements)
• hand grip strength
• body composition analysis (accounts for water in body) using BIA, single frequency provides total body water, multifrequency provides additional information on intracellular or extracellular
• dual x ray absorptiometry: 2 x ray beams show fat, FFM (including water), and bone mass

Question 9

Management of malnutrition

Answer 9

• guidance is 35 kcal/kg/day with 0.75g/kg/day protein before dialysis and 1.2g/kg/day once they start dialysis
• need regular dietary counselling and education
• if inadequate intake consider ONS, or PEG/nasogastric feeds in the short term
• intra-dialytic PN has been trialled but expensive with limited efficacy as only on HD for 4 hours
• intra-peritoneal amino acids are effective in short term but then efficacy dwindles
• need to supplement with water soluble vitamins (as overboiling foods), such as folate (which also helps with overcoming blunting of methylation pathway), B vitamins, vitamin C to stay under 50mg as could form oxalate crystals in kidneys, supplement fat soluble vitamins D and K

Question 10

Measures for preventing PEW

Answer 10

• managing metabolic acidosis by giving 22mol/L plasma bicarbonate
• supplementary endurance and resistance training during dialysis to enhance anabolism