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RENAL > Electrolytes & Fluid Balance > Flashcards

Electrolytes & Fluid Balance Flashcards

1
Q

what is hypernatremia usually due to and what does it cause (2)

A

water deficit
1. cellular dehydration (osmotic drag)
2. vascular shear stress (bldding & thrombosis)

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2
Q

what are the symptoms of hypernatremia

A
  • thirst
  • apathy
  • irritability
  • weakness
  • confusion
  • seizures
  • hyperreflexia
  • spasticity
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3
Q

what are the 4 broad categories of hypernatremia

A
  1. hypovolaemia
  2. euvolaemic
  3. hypervolaemic
  4. diabetes insipidus
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4
Q

what are causes of hypovolaemic hyernatremia

A
  • renal free water losses: osmotic diuresis (NG feed), loop diuretics, intrinsic renal disease
  • non-renal free water losses: excess sweating, burns, diarrhoea, fistula
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5
Q

what are causes of euvolaemic hyernatremia

A
  • renal losses: DI, hypodipsia
  • extra-renal losses: insensible, resp
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6
Q

what are causes of hypervolaemic hyernatremia

A
  • primary hyperaldosteronism
  • Cushing’s
  • hypertonic dialysis
  • hypertonic sodium bicarbonate
  • NaCl tablets
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7
Q

what is a differential for DI

A

psychogenic polydipsia

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8
Q

what type of urine does DI cause

A

dilute urine
urine osmolality <300

polydipsia and polyuria but not always hypernatraemic

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9
Q

what are the 2 mechanisms of DI and their causes

A

1. impaired release of ADH (cranial DI)
- trauma/post-op
- tumours
- cerebral sarcoid/TB
- infection e.g. meningitis
- cerebral vasculitis e.g. SLE/Wegner’s

2. resistance to ADH (nephrogenic DI)
- congenital
- drugs e.g. Li, amphotericin, demeclocycline
- hypokalaemia
- hypercalcaemia

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9
Q

what is the general treatment of hypernatraemia

A

free water

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10
Q

what are the symptoms of hyponatremia

A
  • decreased perception
  • gait disturbances
  • yawning
  • nausea
  • reversible ataxia
  • headache
  • confusion
  • seizures
  • coma
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11
Q

what are the 5 broad causes of hyponatremia

A
  1. pseudohyponatremia
  2. hypovolaemic hyponatremia
  3. euvolaemic hyponatremia
  4. SIADH
  5. hypervolaemic hyponatremia
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12
Q

when does pseudohyponatremia occur (4)

A
  • high lipids
  • myeloma
  • hyperglycaemia
  • uraemia
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13
Q

what are appropriate investigations into hyponatremia

A
  • plasma osmolality: if raised or normal = pseudohyponatremia
  • urine sodium: if <20 then non-renal salt losses, if >40 then
    SIADH
  • TSH and 9am cortisol
  • Calcium, albumin, glucose, LFT
  • CT chest or head if SIADH suspected
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14
Q

what are the causes of hypovolaemic hyponatremia

A
  1. renal loss: urine Na+ >20mmol/L
    - diuretics
    - osmotic diuresis
    - Addison’s (mineralocorticoid deficiency)
  2. non-renal loss: urine Na+ >20mmol/L
    - diarrhoea
    - vomiting
    - sweating
    - third space losses e.g, burns, bowel obstruction, pancreatitis
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15
Q

what is the treatment of hypovolaemic hyponatremia

A

give IV fluids 0.9% NaCl at 1-3ml/kg/hour
- give K if necessary

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16
Q

what are the causes of euvolaemic hyponatremia

A
  • hypothyroidism
  • primary polydipsia if urine osmolality < 100
  • glucocorticoid deficiency – adrenal
    insufficiency
  • SIADH
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17
Q

what type of urine does SIADH produce

A

low serum osmolality - inappropriately concentrated urine > 100
- urine Na >20

Diagnosis of elimination – normal renal, thyroid, adrenal function

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18
Q

what is the management of SIADH

A
  • fluid restrict <800ml/day
  • PO NaCl
  • amy give furosemide
  • demeclocycline induces DI which reverses ADH effect or alternatively Tolvaptan
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19
Q

what are the causes of hypervolaemic hyponatremia (3)

A
  • CCF
  • nephrotic syndrome
  • liver cirrhosis
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20
Q

what is the treatment of hypervolaemic hyponatremia

A

fluid restrict
consider furosemide

21
Q

what is the risk of correcting hyponatremia too rapidly

A

Too rapid correction of chronic hyponatraemia leads to
central pontine/osmotic myelinosis
- Aim to correct <12mmol/L/day

22
Q

what is the treatment of acute hyponatremia

A

if symptomatic and within 48hrs:
- 3% hypertonic saline IV boluses ± furosemide

23
Q

what is the treament of chronic hyponatremia (3)

A

if >48hrs and symptomatic:
- hypertonic saline boluses if having seizures
- isotonic saline and furosemide: aim to correct 8mmol/L in 24 hours

if asymptomatic:
- water restriction and stop offending drug

if dehydrated:
- Na and water restriction and diuretics

24
Q

what are causes of hyperkalaemia

A
  • CKD
  • K rich diet w CKD: dried fruit, potatoes, oranges, tomatoes
  • drugs: ACEi, ARBs, spironolactone, LMWH, cyclosporin, calcineurin, high dose trimethoprin
  • hypoaldosteronism
  • Addison’s
  • rhabdomyolysis
  • rare: hyperkalaemic periodic paralysis, Gordon’s syndrome
  • artifact hyperkalaemia – haemolysis, leucocytosis,
    thrombocytosis
25
Q

what is hypoerinaemic hypoaldosteronism
- features
- causes
- treatment

A

type IV renal tubular acidosis
- features: hypochloraemic acidosis, hyperK
- seen in increased age/dec eGFR clasically in: diabetes nephropathy, acute GN, NSAIDs
- often hypertensive with increased extra-cellular fluid
volume (renin often down-regulated by fluid overload)
- treatment: low K diet, loop diuretic

26
Q

what are 3 routes of treating hyperkalaemia

A

1. Stabilizing the myocardium to prevent arrhythmias
- 10mls of 10% Calcium Gluconate over 5-10
minutes

2. Shifting potassium back into the intracellular space
- IV fast acting insulin (actrapid): 10 units and IV glucose/dextrose 50% 50mls
- Sodium Bicarbonate: 500mls of 1.4% Sodium Bicarbonate (only effective at driving potassium intracellullarly if the patient is acidotic)
- Salbutamol 5-10mg via nebulizer

3. Eliminating Potassium From the Body
- Calcium Resonium: 15-45g orally or rectally, mixed with sorbitol or lactulose
- Furosemide: 20-80mg depending on hydration status
- Dialysis: if resistant to medical treatment

27
Q

what can causes a falsely elevated potassium (pseudohyperkalaemia)

A

haemolysis during sampling - may need to repeat sample

28
Q

what are symptoms of hypokalaemia

A
  • fatigue
  • constipation
  • proximal muscle weakness
  • paralysis
  • cardiac arrythmias
  • HTN
29
Q

what are 6 categories of causes of hypokalaemia

A
  • pseudohypokalaemia
  • extra-renal losses
  • redistribution
  • refeeding syndrome
  • endocrine
  • renal losses
30
Q

what are extra-renal loss causes of hypokalaemia

A
  • inadequate PO intake
  • gut losses e.g. vomiting, NG, Zollinger-Ellison, ileostomy
31
Q

what are redistributive causes of hypokalaemia

A
  • delirium tremens
  • beta agonists
  • insulin
  • caffeine
  • theophylline
  • doxazosin
32
Q

what are endocrine causes of hypokalaemia

A
  • primary hyperaldosteronism
  • cushing’s
  • secondary hyperaldosteronism: liver failure, heart failure, nephritic syndrome
33
Q

what are renal loss causes of hypokalaemia

A
  • direutics
  • RTA
  • tubulopathies e.g. Bartters, Liddles, Gittelmans
  • glucocorticoids
  • liquorice
  • hypoMg
34
Q

what is the treatment of hypokalaemia

A
  • Replace magnesium
  • Oral K replacement
  • IV K replacement (Usually in 0.9% NaCl - avoid in dextrose as induces further hypokalaemia)
35
Q

what are causes of rhabdomyolysis

A
  • seizures
  • collapse/coma
  • ecstasy
  • crush injury
  • McArdle’s syndrome
  • drugs: statins esp when co-prescribed with clarithromycin
36
Q

what are features of rhabdomyolysis

A
  • AKI w disproportionately raised Cr
  • elevated CK at least x5 upper limit of normal
  • myogloblinuria
  • hypocalcaemia
  • elevated phosphate
  • hyperK
  • metabolic acidosis
37
Q

how is rhabdomyolysis treated

A

IV fluids to maintain good urine output

38
Q

what can acute severe hyponatremia lead to

A

seizures
resp distress
coma
death

39
Q

what intervention should be considered in acute severe hyponatremia with neurological compromise

A

hypertonic saline to prevent cerebral oedema

senior decision and should be done only under close supervision

40
Q

what does a urine osmolality < 100mosmol/Kg suggest

A

primary polydipsia or inappropriate administration of IV fluids

41
Q

what does urine sodium < 30mmol/L suggest

A

low effective arterial volume
- either due to true dehydration or where pt are clinically overloaded but have intra-vascular depletion i.e. CCF, cirrhosis

42
Q

what diagnosis should be considered if urine sodium >30mmol/L and patient is euvolaemic

A

SIADH

43
Q

what diagnosis should be considered if urine sodium >30mmol/L and patient is dehydrated

A
  • Addison’s disease
  • renal and cerebral salt-wasting
  • hx of vomiting
44
Q

at what point can SIADH be diagnosed

A

after exclusion of hypothyroidism, total salt depletion and ACTH deficiency

45
Q

what clinical syndrome can SIADH appear identical to and why

A

ACTH deficiency as it causes reduced excretion of free water since cortisol deficiency leads to increased vasopressin activity

46
Q

what are the biochemical hallmarks of DI

A
  • high serum osmolality > 295 mosmol/kg
  • low urine osmolality < 300 mosmol/kg
  • high urine volume > 3L per 24 hours
47
Q

what investigation may be useful in partial DI

A

WDT (water deprivation test)
- pt w frank DI will have unacceptable thirst and lose significant weight due to water loss (stop test in this case)
- then give synthetic vasopressin (DDAVP)

48
Q

what results would you expect once DDAVP has been administered in WDT

A
  • cranial DI: DDAVP leads to reduced urine volume and cinreased urine osmolality
  • nephrogenic DI: no response
49
Q

what can over treatment with DDAVP lead to

A

dilutional hyponatremia
- commonly characterised by hedache and reduced cognitive ability

50
Q

what are some specific measures used to treat nephrogenic DI

A
  • low salt, low protein diet
  • diuretics
  • NSAIDs

RENAL (7 decks)

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