With respect to hyponatraemia:
a) Outline the classification and underlying causes. (50% marks)
a) Outline the specific treatment of severe hyponatraemia (i.e. sodium level < 120 mmol/L and/or associated with significant adverse symptoms). (50% marks)
a)
Classify hyponatraemia:
Further subdivide hypotonic:
Serum Na+ < 135 mmol/L
What is serum osmolality? |
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Low (< 285 mOsm/kg) |
Normal (285 – 295 mOsm/kg) |
High (> 295 mOsm/kg) |
Pseudohyponatraemia Hyperlipidaemia Hyperproteinaemia |
Hyperglycaemia Hypertonic infusions Mannitol Glucose |
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What is volume status? |
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What is urinary [Na+]? |
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< 20 mmol/L |
> 20 mmol/L |
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Hypovolaemic |
Vomiting Diarrhoea Skin losses excess sweating 3rd space losses Burns Pancreatitis |
Obstruction Diuretics Renal tubular acidosis Adrenal insufficiency |
Normovolaemic |
Water intoxication Decreased solute intake |
Renal failure Hypothyroidism Adrenal insufficiency SIADH Cerebral salt wasting |
Hypervolaemic |
Cirrhosis Heart failure Nephrotic syndrome |
Acute renal failure Chronic renal failure |
b)
Management is divided into
Emergency treatment of sodium level
If the patient is symptomatic, then the serum sodium level needs to be urgently elevated by approximately 2- 4% e.g. 2.5 – 5 mmol/L (these are rough figures).
This is done by giving a specific sodium dose, which is usually in the form of hypertonic saline (e.g. 3%) to avoid any more excess water, over a brief period e.g. 30 minutes.
It is calculated by the following formula.
Sodium dose = Total body water x desired change in sodium level
For example in a 70 kg man, a total of 200 ml of 3% saline will raise the serum sodium by 2.5 mmol/L
Short-term sodium management
Once symptoms have resolved, the aim is to correct the sodium level by roughly 0.5 – 1.0 mmol/L per hour over the next 24 hours. And how this is done depends on the underlying cause.
Specific treatment of underlying cause:
a)
Mindlessly regurgitate the hyponatremia algorithm? Don't mind if I do. This is the "classical" approach:
In word form:
b)
In the management of severe (symptomatic) hyponatremia, the college were clearly after some sort of hypertonic saline protocol. The fact that the hyponatremia is being described as "severe" and "symptomatic" suggests that simple fluid restriction was not going to cut it. However, the alternative smust be mentioned. Thus:
Where it comes to a discussion of hyptertonic saline, the college recommend rapid corection of symptomatic hyponatremia, which is followed by slow correction of asymptomatic hyponatremia. This is consistent with the recent European guidelines (Spasovski et al, 2014). The guideline development group felt that the risk of brain oedema outweighs the risk of osmotic demyelination syndrome. Specifically, they recommend the infusion of 150ml of 3% saline over 20 minutes, then checking the sodium, and then repeating the infusion.
Spasovski, Goce, et al. "Clinical practice guideline on diagnosis and treatment of hyponatraemia." European Journal of Endocrinology 170.3 (2014): G1-G47.
David M., Arnold S. Berns, and Anthony D. Ivankovich. "Isotonic hyponatremia following transurethral prostate resection." Journal of clinical anesthesia 2.1 (1990): 48-53.