## Monday, August 29, 2016

### Life Threatening Electrolytes

Slide deck (in pdf) for the above presentation:

Life threatening electrolyte abnormalities from Chew Keng Sheng

Perhaps one thing which I did not make clear in the video and the slide is the use of 3% hypertonic saline:
As 1g of Na = 17 mmol
therefore,
3% NaCl means
3 g in 100 ml
or
30 g in 1000 ml (1 L)
= (30 * 17) mmol in 1 L     [since 1 g NaCL = 17 mmol)
= 510 mmol/l
~ 500 mmol per 1000 ml (1 L)
therefore,
1 ml of 3% NaCL = 500/1000 = 0.5 mmol ------- Equation 1

Sodium deficit is
[Desired sodium - measured sodium] * Total Body water
= [Desired sodium - measured sodium] * 50% * Body weight (BW)

Now,
let say we wish to raise the serum sodium by 1 mmol/l  a.k.a. [Desired sodium - measured sodium ] = 1 mmol/l]

therefore,
[1*50%*BW] mmol/ = the amount of sodium deficit required

But we know from Equation 1, that 1 ml contains 0.5 mmol
therefore,
0.5 mmol ------- 1 ml
(0.5 * BW) mmol -------- (BW) ml

Therefore, 1 ml per kg BW of 3% hypertonic saline raises serum sodium by 1 mmol/l

However, as mentioned in the slide, the degree of serum sodium elevation may be more than expected. This is because as sodium is replaced, water re-absorption occurs initially. This removes the hypovolemic stimulus for the release of ADH. As a result, there will be greater degree of diuresis than expected.

References:
Parham WA, Mehdirad AA, Biermann KM, Fredman CS. Hyperkalemia revisited. Tex Heart Inst J. 2006;33(1):40-7. Can be accessed FREE here.

Verbalis JG, Goldsmith SR, Greenberg A, Korzelius C, Schrier RW, Sterns RH, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013;126(10 Suppl 1):S1-42. Can be accessed FREE here.