Electrolyte abnormalities

Chapter 7
Electrolyte abnormalities


Sing Yu Moorcraft


The Royal Marsden NHS Foundation Trust, UK


Hypocalcaemia


The normal range of total calcium is usually 2.12–2.65 mmol/L (8–10 mg/dl). Hypocalcaemia is defined as a low concentration of calcium in the blood. The grade of hypocalcaemia is shown in Table 7.1.


Table 7.1 CTCAE (V4.03) grading of hypocalcaemia.


From the website of the National Cancer Institute (http://www.cancer.gov).






















Grade Criteria
1 Corrected serum calcium of < LLN – 8.0 mg/dL; < LLN – 2.0 mmol/L; ionised calcium < LLN – 1.0 mmol/L.
2 Corrected serum calcium of < 8.0–7.0 mg/dL; < 2.0–1.75 mmol/L; ionised calcium < 1.0–0.9 mmol/L; symptomatic.
3 Corrected serum calcium of < 7.0–6.0 mg/dL; < 1.75–1.5 mmol/L; ionised calcium < 0.9–0.8 mmol/L; hospitalisation indicated.
4 Corrected serum calcium of < 6.0 mg/dL; < 1.5 mmol/L; ionised calcium < 0.8 mmol/L; life-threatening consequences.
5 Death.

LLN = lower limit of normal.


Pseudohypocalcaemia


This is when variation in protein concentrations (particularly albumin) leads to fluctuations in total calcium level, but ionised calcium levels remain relatively stable. For example, patients with chronic illnesses such as cancer can have a low total plasma calcium but normal ionised calcium. Therefore calcium levels should be corrected for albumin as follows: corrected calcium (mmol/L) = measured calcium (mmol/L) + 0.02 * (40 – patient’s albumin (g/L)).


Symptoms/signs



  • Symptoms/signs: Chvostek’s sign (tapping over the facial nerve causes facial twitching), Trousseau’s sign (carpopedal spasm when brachial artery occluded), tetany, depression, perioral paraesthesiae, confusion, papilloedema.
  • ECG changes: increased QT interval, T wave inversion, heart block.

Causes



  • Tumour lysis syndrome
  • Chronic renal failure
  • Surgery:

    • Thyroid or parathyroid surgery
    • Radical neck surgery

  • Endocrine:

    • Hypoparathyroidism
    • Pseudohypoparathyroidism

  • Drugs:

    • Bisphosphonates, denosumab
    • Phosphate therapy
    • Cisplatin
    • Foscarnet
    • Calcium channel blocker overdose

  • Gastrointestinal:

    • Pancreatitis
    • Vitamin D malabsorption/deficiency
    • Re-feeding syndrome

  • Infections:

    • Sepsis
    • Toxic shock syndrome

  • Osteomalacia, bone metastases
  • Hypomagnesaemia
  • Other: acute hyperventilation, overhydration, rhabdomyolysis, low exposure to UV light, massive blood transfusion.

Management



  • Correct abnormalities in potassium and magnesium
  • Mild – moderate (calcium 1.88–2.11 mmol): oral calcium replacement:

    • For example: 1 tablet BD of Calcichew® or Adcal® (plus vitamin D if vitamin D deficient).
    • Give after meals to maximise absorption. May decrease the bioavailability of tetracyclines, fluoroquinolones, iron and atenolol.

  • Moderate to severe (calcium < 1.88 mmol/L): IV calcium replacement:

    • 10 ml of 10% calcium gluconate (2.2 mmol Ca2+) IV over 20 minutes (max 2 ml/min). The effect is short-lasting and so this can be repeated as required or dilute 100 ml of 10% calcium gluconate in 1 L of 0.9% saline or 5% glucose, start at a rate of 50 ml/hour and adjust according to response.
    • ECG monitoring should be performed (particularly in patients with heart disease or a high risk of arrhythmias).
    • Risks of IV calcium: arrhythmias, hypotension, hypercalcaemia. Use cautiously in patients on digoxin as they are more sensitive to fluctuations in serum calcium and calcium can potentiate digoxin toxicity.
    • Measure calcium regularly until within the normal range.

  • Further investigations:

    • Consider checking PTH levels in patients who are resistant to therapy (PTH is reduced or normal in hypoparathyroidism and hypomagnesaemia, but high in other causes of hypocalcaemia).
    • Serum 25-hydroxyvitamin D levels can be useful in confirming vitamin D deficiency.

Other relevant sections of this book



  • Chapter 2, sections on hypercalcaemia, tumour lysis syndrome
  • Chapter 7, sections on hyperkalaemia and hypokalaemia, hypermagnesaemia and hypomagnesaemia

References



  1. Cooper MS, Gittoes NJ. Diagnosis and management of hypocalcaemia. British Medical Journal. 2008. 336(7656): 1298–302.
  2. Ecc Committee S, Task Forces of the American Heart A. 2005 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2005. 112(24 Suppl.): IV1–203.
  3. Joint Formulary Committee. British National Formulary (online). London: BMJ Group and Pharmaceutical Press. Available from: http://www.medicinescomplete.com (accessed 1 January 2014).
  4. Nolan J, Soar J, Lockey A, Pitcher D, Gabbott D, et al. Advanced Life Support, fifth edition. Resuscitation Council (UK): London. 2008.

Hyperkalaemia and hypokalaemia


Hyperkalaemia


The normal range of potassium is usually 3.5–5.0 mmol/L. Hyperkalaemia is defined as an elevated concentration of potassium in the blood. The grade of hyperkalaemia is shown in Table 7.2.


Table 7.2 CTCAE (V4.03) grading of hyperkalaemia.


From the website of the National Cancer Institute (http://www.cancer.gov).






















Grade Criteria
1 > ULN – 5.5 mmol/L.
2 > 5.5–6.0 mmol/L.
3 > 6.0–7.0 mmol/L; hospitalisation indicated.
4 > 7.0 mmol/L; life-threatening consequences.
5 Death.

ULN = upper limit of normal.


Symptoms/signs



  • Symptoms/signs: arrhythmias, sudden death, weakness, paraesthesiae, depressed tendon reflexes.
  • ECG changes: flattened or absent P wave, wide QRS complex, tall-tented T wave, VF/VT, first degree heart block, ST segment depression, bradycardia.

Causes



  • Artefact, for example due to haemolysis, delay in sample analysis, high WCC or platelet count.
  • Oliguric renal failure.
  • Tumour lysis syndrome.
  • Drugs: excess potassium therapy, potassium-sparing diuretics, ACE inhibitors, digoxin.
  • Other: Addison’s disease, metabolic acidosis, burns, massive blood transfusion, haemolysis, rhabdomyolysis.

Management



  • General management:

    • Perform an ECG
    • Stop all potassium containing drugs
    • Assess severity of hyperkalaemia:

      • Mild: 5.5–6 mmol/L
      • Moderate: 6.1–6.4 mmol/L
      • Severe: ≥ 6.5 or ECG changes or symptomatic

    • Low potassium diet (see hypokalaemia section for more details on potassium containing foods)
    • If the patient is hypovolaemic, give fluids to enhance urinary potassium excretion

  • If potassium > 6.5 mmol/L or ECG changes:

    • Give 10 ml of 10% calcium gluconate (2.2 mmol Ca2+) IV over two minutes repeated as necessary for cardioprotection (does not reduce the potassium level). If the patient is on digoxin, rapid administration of calcium gluconate can cause myocardial digoxin toxicity. Therefore in these patients calcium gluconate should be given slowly over 20 minutes in 100 ml of 5% glucose.
    • Insulin and glucose: for example 10 units of short-acting insulin (e.g. Actrapid®) and 250 ml of 10% glucose over 30–60 minutes (or 50 ml of 50% glucose IV over 5–15 minutes, preferably via a central line). Onset of action in 15–30 minutes, maximum effect at 30–60 minutes. Glucose should be checked 30 minutes after administration of insulin and then hourly for six hours as delayed hypoglycaemia can occur.
    • Give 2.5–10 mg nebulised salbutamol (adjunct use only). Onset of action in 15–30 minutes. Use with caution in patients with tachycardia or ischaemic heart disease.
    • Calcium resonium: there is little evidence for efficacy and it often causes constipation, leading to increased reabsorption of potassium.
    • Consider dialysis.
    • Consider IV sodium bicarbonate if patient is acidotic (pH 7.1–7.3), for example due to diabetic ketoacidosis.
    • Check potassium at least twice daily until < 6 mmol/L.

Hypokalaemia


Hypokalaemia is defined as a low concentration of potassium in the blood. The grade of hypokalaemia is shown in Table 7.3.


Table 7.3 CTCAE (V4.03) grading of hypokalaemia.


From the website of the National Cancer Institute (http://www.cancer.gov).






















Grade Criteria
1 < LLN – 3.0 mmol/L.
2 < LLN – 3.0 mmol/L; symptomatic; intervention indicated.
3 < 3.0–2.5 mmol/L; hospitalisation indicated.
4 < 2.5 mmol/L; life-threatening consequences.
5 Death.

LLN = lower limit of normal.


Symptoms/signs



  • Signs/symptoms: arrhythmias, cramps, tetany, muscle weakness, hypotonia, fatigue.
  • ECG changes: prolonged PR interval, ST depression, flattened T waves, prominent U wave (after T wave).

Causes



  • Gastrointestinal: vomiting, diarrhoea, pyloric stenosis, intestinal fistulae.
  • Endocrine: Cushing’s syndrome, Conn’s syndrome.
  • Drugs: cisplatin, diuretics, laxatives, steroids, adrenaline, high dose penicillin, amphotericin B, insulin.
  • Renal tubular failure.
  • Other: magnesium depletion, alkalosis, poor dietary intake, purgative abuse.

Management


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Jun 13, 2016 | Posted by in ONCOLOGY | Comments Off on Electrolyte abnormalities

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