Electrolyte Imbalances and Biochemistry Flashcards by Alex Davison

Causes of hypernatraemia?

Fluid Loss
- Diarrhoea, burns, fever, glycosuria (DM, DI)
Inadequate Intake
- Impaired thirst response in elderly or hypothalamic disease
Excess Na⁺
- Iatrogenic (excess crystalloids or Na+ containing drugs – IV Ben Pen), Conn’s syndrome

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Presentation of hypernatraemia?

Anorexia, thirst, nausea, weakness, hyperreflexia, confusion, ↓GCS

Assess volume status

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Investigations in hypernatraemia?

Daily serum Na⁺ concentrations

Renal function and electrolytes

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Management of hypernatraemia?

Mild/Euvolaemic

Encourage patient to drink water
Slow infusion 5% dextrose

Severe/Hypovolaemic

Slow infusion of 0.9% NaCl
Glucose 5% thereafter to correct water deficit

Severe/Hypervolaemic

Slow infusion of 5% glucose

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Caution in treatment of hypernatraemia?

If extracellular Na⁺ rapidly corrected, osmotic forces will drive fluid into cells, causing lysis resulting in neurological damage and death –> CENTRAL PONTINE DEMYELINATION

Aim for slow correction of Na⁺ - 10mmol/L/24h at very most. Treatment guided by volume status.

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Causes of hyponatraemia?

Usually Dilutional

Diuretics, Addison’s disease, DKA, D+V, burns
SIADH
- Malignancy (lung, pancreas, lymphoma)
- Lung infections
- CNS infections or vascular events
- Drugs (SSRIs, tricyclics, carbamazepine, antipsychotics)
- Idiopathic

Pseudohyponatraemia = taking blood from arm with IV fluids running, a lipaemic sample or osmotically active substances in blood (e.g. hyperglycaemia).

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Causes of hyponatraeima if HYPOvolaemic?

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Causes of hyponatraeima if EUvolaemic?

(ADH leads to more concentrated urine)

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Causes of hyponatraemia if oedematous?

Like SIADH but because of oedema

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Presentation of hyponatraemia?

Headache, confusion, drowsiness, seizures, coma, death

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Investigations in hyponatraemia?

Daily serum sodium concentrations, electrolytes and renal function

Blood/Urine Osmolalities

In SIADH…
- Urine = high Na+ and high osmolality (concentrated)
- Blood = low Na+ and low osmolality (concentrated)

Daily weights (1 litre = 1kg)

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Management of hyponatraemia?

Depends on volume status and underlying cause. If mild and asymptomatic, no treatment usually required.

Treat cause!

Overloaded

Fluid restrict

Hypovolaemic

Slow 0.9% NaCl – to replace lost fluid

Euvolaemic (SIADH)

Correct cause + slow 0.9% NaCl
Fluid restrict to 1 L/day. If resistant to fluid restriction, inhibition of ADH may be required –> demeclocycline.

Seizures/Coma

Hypertonic saline - SENIOR SUPPORT

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Causes of hyperkalaemia?

Reduced Renal Excretion
- AKI/CKD, drugs (potassium-sparing diuretics, ACEi, NSAIDs), Addison’s
Excess K+ Load
- Iatrogenic, massive blood transfusion
Increased Cellular Release
- Acidosis, tissue breakdown (rhabdomyolysis, haemolysis)
Pseudo-Hyperkalaemia
- Haemolysis, EDTA-contaminated sample

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Investigations in hyperkalaemia?

ECG – low flat P-wave, wide bizarre QRS complex becoming sinusoidal, tall tented T-waves, VF.
Bloods – urgent repeat U+E; if K⁺ <7mmol/L with no new ECG changes or sample is haemolysed, repeat sample, otherwise follow treatment plan. Digoxin levels – toxicity will worsen hyperkalaemia.
ABG – for acidosis if acute renal failure

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What is this?

Sine wave - pre-terminal rhythm of hyperkalaemia

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When does hyperkalaemia require management?

Serum K+ of >6.5 or hyperkalaemia with ECG changes requires immediate treatment

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Management of Hyperkalaemia?

Calcium Gluconate 10% - 10ml IV over 5 mins
- Repeat every 10 min up to 50ml until K+/ECG corrected
Insulin/Dextrose - 10 units actrapid in 100ml 20% glucose
- Check CBG before, during and after
- Check K+ decreasing at 30 mins and overall result at 2 hours
Salbutamol - 5mg neb
Calcium Resonium 15g TDS/QDS PO
- Takes 24h to work
- Constipates (give with lactulose)
Furosemide
- With IV fluids if necessary – enhances K+ excretion

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Treatment of refractory hyperkalaemia?

Haemodialysis

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Causes of hypokalaemia?

↑Renal Excretion
- Diuretics (except K+ sparing)
- Endocrine (steroids, Cushing’s, Conn’s)
- Renal tubular acidosis
- Hypomagnasaemia
Other K+ loss
- D+V
↑Cellular Uptake
- Salbutamol, insulin, alkalosis

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What is renal tubular acidosis?

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Failure of kidneys to acidify urine (normal anion gap)

Either…

Not enough bicarb absorption (proximal)
Not enough H+ excretion (distal)

Presentation and complication of hypokalaemia?

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Symptoms

Weakness, cramps, tetany, palpitations, nausea, paraesthesia

Signs

Muscle weakness, hypotonia, arrhythmias, hyporeflexia

Complications

Hypokalaemia increases risk of digoxin toxicity

Investigations in hypokalaemia?

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ECG – prolonged PR interval, depressed ST segment, small/inverted T waves, prominent U-wave
Bloods – U+E (check for other imbalances, especially ↓Mg²⁺
ABG – if alkalosis suspected

No pot and no T - long PR and a long QT

What is this?

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U wave

Management of hypokalaemia?

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>2.5, No ECG Changes

Sando-K – 2 tablets TDS for 3/7 OR
Add 20-40 mmol/L KCl to IV fluids
Monitor U+E –> replace any concurrent ↓Mg²⁺(8mmol MgSO₄ in 100ml 0.9% saline IV over 1h)

<2.5 or ECG Changes

40mmol/L KCl in 1L 0.9% saline IV over 6 hours (unless oliguric)

Do not replace K+ faster than 10mmol/h outside of HDU/ICU

Definition of hypo/hypercalcaemia?

Hyper = \>2.60 (treat at 3.0) Hypo = \<2.20

Causes of hypercalcaemia?

1. **↓Renal Excretion** * Drugs (thiazide diuretics) 2. **↑Release from Bone** * Bony mets (↑ALP) – PB KTL * Myeloma (ALP normal) * Sarcoidosis * Thyrotoxicosis 3. **Excess PTH** * Primary hyperparathyroidism (↑PTH) or tertiary hyperparathyroidism (↑↑↑PTH) 4. **Excess Vitamin D** * Excess vitamin D intake 5. **Dehydration** * Urea and albumin raised

Causes of hypercalcaemia? (mnemonic)

RHINOS * *R**enal insufficiency (2^o/3^o hyperparathyroidism) * *H**yperparathyroidism * *I**atrogenic (overuse of vitamin D, Ca2+, thiazides) * *N**eoplasms * *O**ther endocrinopathies (hyperT, Addison's) * *S**arcoidosis

Presentation of hypercalcaemia?

**If mild** - asymptomatic **Severe** - bone pain, renal colic, N+V, polyuria, altered consciousness, shortened QT interval **BONES, STONES, GROANS, PSYCHIATRIC OVERTONES**

Investigations in hypercalcaemia?

Investigate for cause if not clear * U+Es, ALP, PTH, phosphate * Myeloma screen/Bence-Jones protein * Serum ACE (if sarcoid suspected) * Isotope bone scan (if bony mets suspected) ECG - **shortened QT**. Continuous cardiac monitoring if severe hypercalcaemia

Management of hypercalcaemia?

Remove any underlying cause Restrict dietary calcium **_Rehydration_** * NaCl 0.9% --\> 1L 4-6 hourly for 24 hours; then 6 hourly for 48-72 hours with adequate K+ * Add loop diuretics once hydrated to enhance calcium excretion and prevent fluid overload (furosemide 80-100 mg OD) **_Bisphosphonates_** * Pamidronate infusion (can be started during rehydration) * Dilute with NaCl 0.9%/glucose 5% * Takes 2-4 days to have effect – max effect after 1 week

Causes of hypocalcaemia?

1. **_↑Renal Excretion_** * Loop diuretics, CKD (↑PO₄^3-), hypomagnasaemia 2. **_↑Deposition in Bone_** * Bisphosphonates 3. **_↓/Ineffective PTH_** * Hypoparathyroidism (surgical/congenital) * Pseudohypoparathyroidism (resistance to PTH) 4. **_↓Vitamin D_** * Deficiency (osteomalacia, rickets)

Presentation of hypocalcaemia?

**Symptoms** * Tetany, paraesthesia, cramps, anxiety, seizures **Signs** * Chovstek's sign * Trousseau's sign

Investigations in hypocalcaemia?

**Bloods** * U+E * PTH * Phosphate, magnesium **ECG** --\> long QT (continuous cardiac monitoring if severe)

Management of mild hypocalcaemia?

Treat cause --\> vitamin D deficiency * Load with 100,000 units colecalciferol STAT and give adcal-D3 maintenance * Monitor patients on digoxin – IV calcium can increase digoxin toxicity **_Mild_** * Oral calcium * Calcichew tablets – up to 40 mmol per day (12.6 mmol per tablet)

Management of severe hypocalcaemia?

**Calcium gluconate 10% 10 ml IV slowly over 10-30 mins** * Dilute in 40ml NaCl or 5% dextrose * Repeat until asymptomatic * Follow with infusion if required * 40ml 10% calcium gluconate in 1L dextrose/NaCl over 4-8 hours * ECG monitoring required

Biochemical profile of dehydration?

* Raised urea disproportionate to a smaller increase in creatinine * Raised haematocrit (PCV) * Low urine volume * Decreased skin turgor Dehydration affects urea more than creatinine because in dehydration a greater amount of urea is reabsorbed by the kidney - creatinine is hardly reabsorbed at all.

Biochemical profile of abnormal kidney function? (2 types)