Acid base and electrolyte disturbance Flashcards
What is urea produced and excreted by
- Produced by liver, excretion of ammonia and breakdown products of amino acids
- Excreted in urine
When do urea levels decrease
Liver disease
When are urea levels raised
- Intravascular depletion
- Blood meal
- Renal failure
Effects of high urea levels
Urea>20 - Nausea, decreased appetite, itchiness, tiredness, smelly breath, metallic taste in mouth
Urea > 60 - Extreme ureamic frost, uraemic pericarditis, encephalopathy
What is creatinine a product of
- Breakdown product of creatinine phosphate in muscle
- Usually produced at a fairly constant rate by the body
Link between number of nephrons and creatinine levels
The less the number of nephrons the more the build up of creatinine - therefore creatinine levels are indicative of kidney function
- Creatinine is not toxic itself
How affected are creatinine levels by fluid shifts
- Less affected by fluid shifts
What can creatinine levels be used to calculate
- eGFR
- MDRD
- Cockcroft and Gault
Normal creatinine clearance rate
> 90 mls/min
CKD 1 eGFR
> 90 mls/min
CKD 2 eGFR
> 60 mls/min
CKD 3a eGFR
> 45 mls/min
CKD 3b eGFR
> 30 mls/min
CKD 4 eGFR
> 15 mls/min
CKD 5 eGFR
< 15 mls/min
Location of bulk of water and electrolytes
- Bulk of water and electrolytes are not in the serum but in the cells
- Integrated homeostatic mechanisms maintain body fluid compositions
What is glomerular filtration diminished by
- Age
- Renal disease
- Congestive heart failure
- Cirrhosis
- Nephrotic syndromes
- Volume depletion
Causes of hyponatremia - hypovolemia - renal losses >20mmol/L
- Diuretic excess
- Mineralocorticoid deficiency
- Self-losing nephropathy
- Bicarbonaturia with renal tubular acidosis and metabolic alkalosis
- Ketonuria
- Osmotic diuresis
- Cerebral salt wasting
Causes of hyponatremia - hypovolemia - extrarenal losses <20 mmol/L
- Vomiting
- Diarrhoea
- Third spacing of fluids in burns, pancreatitis and trauma
Causes of hyponatremia - euvolemia(no edema) - increase in total body water, no change in total body Na+ (>20 mmol/L)
- Glucocorticoid deficiency
- Hypothyroidism
- Stress
- Drugs
- SIADH
Causes of hyponatremia - Hypervolemia - >20mmol/L
- Acute or chronic renal failure
Causes of hyponatremia - hypervolemia - <20mmol/L
- Nephrotic syndrome
- Cirrhosis
- Cardiac failure
What is pseudohyponatremia
- A physiologically normal plasma water sodium concentration, but a reduced measured plasma sodium concentration.
What can cause pseudohyponatremia
- Hypertriglyceridemia associated with conditions such as diabetes, obstructive liver disease, nephritic syndrome and acute pancreatitis
- Can also be caused by administering IV immunoglobulins
What is translocational hyponatraemia
Translocational hyponatremia refers to the translocation of water from the ICF compartment to the ECF compartment usually in the setting of hypertonicity, which dilutes the PNa
Potassium distribution
- Wide distribution - extracellular and intracellular
- The major intracellular cation
- Primarily distributed intracellularly (100-120mmol/L)
- Serum K = 3.2-5.1 mmol/L
Hypokalaemia causes - redistribution
- Insulin, theophylline, adrenergic use
Hypokalaemia causes - non renal loss
- Sweating, vomiting or diarrohea
Another cause of hypokalaemia
Poor diet
Causes of hypokalaemia - renal loss > 20mmol/l
- Drugs, diuretics, aminoglycosides, amphotericin
- RTA or metabolic acidosis
- Low BP bartter’s or gittlemans
- High BP
- High aldosterone normal cortisol - hyperaldosteronism
- Low aldosterone normal cortisol liddle’s
- Low aldosterone high cortisol cushing’s syndrome
Chronic hypokalaemia - cardiovascular complications
- Hypertension
- Ventricular tachyarrhythmias
Chronic hypokalaemia - endocrine complication
- Impairs insulin activity and sensitivity
Chronic hypokalaemia - muscular complication
- Impairs muscle contraction –> weakness
Chronic hypokalaemia - renal complications
- Mild tubulointerstitial fibrosis
- Renal cyst formation
- Metabolic alkalosis (increased net renal acid excretion)
- Polyuria
Chronic hypokalaemia - liver complications
- Increases renal ammonia production which may worsen hepatic encephalopathy
What does hyperkalaemia indicate
- Kidneys have a large capacity to excrete K+
- Hyperkalaemia indicates impaired renal excretion
What causes hyperkalaemia
Impaired renal excretion - CKD4/5
- Drugs impairing secretion - spironolactone, amiloride, ACE-I, ARB
- Increased K load - rhabdomyolysis, haemolysis, GI bleed
- Increased dietary intake
Pseudohyperkalaemia
- Haemolysis
During blood collection/storage
Rheumatoid/infectious mononucleosis
Hyperkalaemia - treatment
Back into cells
- Salbutamol, insulin and dextrose, sodium bicarbonate(if acidotic)
Stabilisation
- Calcium gluconate
Removal
- If passing urine, pee it out, iv fluids and diuretics
- Dialysis
Acid-base regulation
Body pH maintained 7.35-7.45
- Essential for functioning of proteins, enzymes etc
- Large net acid production - 1 mmol H+/kg
What regulates co2 tension
Resp system
What regulates HCO3 tension
Kidneys
Major sites of hCO3 recovery and H+ excretion
- Proximal tubule NaHCO3 reabsorption
- Secretion of H+ in the alpha intercalated cell of the cortical collecting duct
Sodium bicarbonate in severe metabolic acidaemia
- Depends on underlying cause
- Generally safe to give isotonic NaHCO3 1.26%
- If pH<7.2, adverse effects of acidaemia may manifest
- Removing stimulus to production of lactate/ketones will allow oxidative mechanisms to metabolise excess anion
- Diarrhoea and ingestions: NaHCO3 may be of use if acidaemia severe, and adverse effects are present
- Exogenous Na load can exacerbate fluid overload and HTN
What might metabolic alkalosis be due to
Excess alkali - kidney responds rapidly to this, so is usually transient
- K+ depletion
- Cl- depletion
Calcium
- Serum calcium tightly controlled levels 2.2-2.6mmol/l
- Absorbed by the gut
- Excreted in the urine/reabsorbed in the loop of henle and distal tubule
- Released by bone
- Controlled by PTH
Phosphate
- 0.85 to 1.6mmol/l
- Excreted by the kidneys
- Rises in renal failure/less nephrons less excretion
What are phosphate levels a good indicator of
- Malnutrition
What are high phosphate levels associated with
- Itchy skin
- Extraosseal calcification
- Soft tissues and arteries
Vitamin D and Ca and Phosphate
- Vitamin D3 from diet and skin –> liver–> 25-0H-D3 –> Kidneys –> 1,25-(OH)2-D3 –> Bone mineralisation, decrease in PTH, increase in Ca/P Gut
AKI
- Normal Na
- High K
- low bicarb
- low pH
- high urea
- high creatinine
- oliguria
- +/- fluid overload
- normal calcium, phosphate, PTH levels
What happens in ESRF
Hyperkalaemic and acidotic
- Treatment restrict K containing foods
- Sodium bicarbonate tablets
Lack of vitamin D
- Low calcium
- Treatment activated vitamin D tablets
Hyperphosphataemia
- Lack of phosphate excretion from the kidney
- Extraossial calcification
- Diet and phosphate binding tablets
