Fluid and Electrolyte Balance and Disorders Flashcards
What are possible causes when the urinary sodium is low?
If the urinary sodium is low and they are hyponatraemic, the sodium must not be going through the kidneys and must be leaving the body some other way…
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Sodium depletion, extra-renal loss:
- diarrhoea, vomiting, sweating
- burns
- rectal adenoma
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Water XS (patient often hypervolaemic and oedematous):
- secondary hyperaldosteronism (heart failure, liver cirrhosis)
- nephrotic syndrome
- IV dextrose
- psychogenic polydipsia
What are clinical features of hyponatraemia?
- Anorexia / Nausea
- Malaise / Weakness
- Headache / Irritability
- Confusion / Reduced GCS
- Seizures
- Also increased risk of falls in elderly
What are the ECG features of hypokalaemia?
- U waves
- Small or absent T waves
- Prolonged PR interval
- ST depression
What is the management of hypernatraemia?
- Give water orally if possible
- If not, give glucose 5% IV slowly (1L/6h) guided by urine output and plasma Na
What ECG changes occur in hyperkalaemia?
- Tall-tented T waves
- Loss of P waves
- Broad QRS complexes
Potassium and hydrogen can be thought of as competitors. Hyperkalaemia tends to be associated with acidosis because as potassium levels rise fewer hydrogen ions can enter the cells. Hypokalaemia (K+ < 2.5) can be with either alkalosis or acidosis.
What are causes of hypokalaemia with alkalosis?
- Vomiting
- Thiazide + loop diuretics
- Cushing’s syndrome
- Conn’s syndrome (primary hyperaldosteronism)
What is distal (type 1) renal tubular acidosis (RTA)?
- Failure of acid (H+) excretion
- Primary genetic disease or secondary to autoimmune disease (eg. Sjogren’s, SLE), or toxins (eg. lithium)
What is hyperkalaemia?
- K+ > 6.5 mmol/L
- Potential emergency + needs urgent assessment
- Can cause myocardial hyperexcitability → VF → arrest
- Concerns if fast irregular pulse, chest pain or ECG changes
What is the treatment for mild hyponatraemia?
- Fluid restriction sufficient
- Loop diuretics
What are the clinical features of hypernatraemia?
- Lethargy / Weakness
- Thirst
- Irritability
- Confusion / Coma
What are clinical features of hypokalaemia?
- Muscle weakness
- Hypotonia + hyporeflexia
- Cramps
- Tetany
- Palpitations
Hypokalaemia also exacerbates digoxin toxicity
What causes hypokalaemia with acidosis?
- Diarrhoea
- Renal tubular acidosis
- Acetazolamide
- Partially treated DKA
Mg deficiency may also cause hypokalaemia - normalising potassium elvle may be difficult until Mg def is corrected
Summary of hyponatraemia
Hyponatraemia may be caused by water excess or sodium depletion. Causes of pseudohyponatraemia include hyperlipidaemia (increase in serum volume) or a taking blood from a drip arm. Urinary sodium and osmolarity levels aid making a diagnosis
What are possible causes when the urinary sodium is > 20 mmol/l?
If the urinary sodium is high and they are hyponatraemic, the sodium must be going through the kidneys (so caused by things that affect kidney)
- Sodium depletion, renal loss (patient often hypovolaemic):
- diuretics: thiazdes + loops
- Addison’s disease
- diuretic stage of renal failure
- Patient often euvolaemic:
- SIADH (urine osmolality > 500)
- hypothyroidism
What are causes of hyperkalaemia?
- Acute kidney injury
- Drugs → potassium sparing diuretics, ACEi, ARBs, spironolactone, ciclosporin, heparin
- Metabolic acidosis
- Addison’s disease
- Rhabdomyolysis
- Massive blood transfusion
- Foods → salt substitutes, bananas, oranges, kiwi, avocado, spinach, tomatoes
What is iatrogenic hyponatraemia?
- If 5% glucose infused continuously without adding 0.9% saline, glucose is quickly used, rendering the fluid hypotonic and causing hyponatraemia
- Especially in those pts on thiazides, women and those undergoing physiological stress
What is Fanconi syndrome?
- Generalised impairment of proximal tubular function
- Leads to glycosuria, phosphaturia, uricosuria and tubular proteinuria
- Negative dipstick but positive urine P:CR
What is the treatment for severe hyponatraemia?
- Bolus of hypertonic saline until symptom resolution
- Can also give ADH antagonist (conviaptan)
What is the treatment for moderate hyponatraemia?
- Cautious rehydration w/ 0.9% NaCl in first 3-4 hrs to increase Na+ > 120 mmol/l
- Then fluid restriction (< 800ml/day) + loop diuretics
- Rapid correction → central pontine myelinolysis
What is the treatment for mild hypokalaemia?
- K+ > 2.5 mmol/l
- No symptoms
- Give oral K+ supplement
- Review K+ after 3 days
What is osmotic demyelination syndrome (central pontine myelinolysis)?
- AKA ‘Locked-in syndrome’
- Can occur due to overcorrection of severe hyponatraemia
- To avoid this, Na+ levels are only raised by 4-6 mmol/l in a 24hr period
- Symptoms occur after 2 days are usually irreversible
- Dysarthria / Dysphagia / Paraparesis / Seizures / Confusion / Coma
- Patients are awake but unable to move or verbally communicate
For hyperkalaemia, precipitating factors should be addressed (eg acute renal failure) and agravating drugs stopped. Treat K+ if > 6.5mmol/L or with ECG changes.
What is the acute treatment for hyperkalaemia?
- IV 10% of 10ml calcium gluconate → slowly IV; stabilises cardiac membrane; repeat dose if necessary until ECG normalises up to a max dose of 40ml
- Dextrose/Insulin infusion → 50ml of 50% dextrose + 10U soluble human insulin; shifts potassium from ECF to ICF; check BM every hour
- Nebulised salbutamol → also shifts K+
- Renal replacement therapy if underlying pathology cannot be corrected
What is Bartter’s syndrome?
- Due to impaired salt transport
- Soidum reabsorption increases further along nephron in exchange for H+ and K+
- Therefore all cause a hypokalaemic, hypochloraemic metabolic alkalosis
- Presents in childhood
- Think of Bartter’s as taking lots of furosemide
Hypernatraemia results usually when water loss is greater than Na loss.
What are causes of hypernatraemia?
- Fluid loss without water replacement (diarrhoea, vomiting, burns)
- Diabetes insipidus
- Osmotic diuresis (for diabetic coma)
- Primary aldosteronism: rarely severe, suspect if hypertensive
- Iatrogenic: incorrect IV fluid replacement (XS saline)
What is Gitelman syndrome?
Milder version of Bartter’s
What is the treatment for severe hypokalaemia?
- K+ < 2.5 mmol/l
- Dangerous symptoms
- Infuse I K+ into large vein 10-20 mmol K+ / hr
- Do not give K+ if oliguric
