Question 5.1

Highest mark
8.0
Pass rate
76%
Other SAQs in this topic:
Other SAQs in this paper:

A 75-yr-old woman on Indapamide for Hypertension presented with seizures after a 7- day history of increasing lethargy. She was unwell, had dry mucus membranes and decreased skin turgor with a BP 88/50. Her serum sodium was 103 mmol/L. Outline your fluid management and discuss relevant physiology.

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College Answer

a) This woman requires Hypertonic Saline for her hyponatremic encephalopathy.

b) She also requires isotonic fluid therapy (e.g. 0.9 % NaCl) to correct her Hypovolemia

Once volume repletion crosses the hypovolemic threshold for the adaptive excessive ADH

release that would have occurred (in part explaining her hyponatremia), there would be a

feed-back inhibition of the excess ADH release leading to massive aquaresis and the

increased free water excretion would help correct hyponatremia

Discussion

Why is this old woman hyponatremic?

This is a symptomatic hypovolemic hyponatremia, likely due to renal losses of both sodium and free water, associated with the use of indapamide (a thiazide diuretic).

Fluid management:

  • replacement of sodium (raising the serum level at a rate of 0.5-1 mmol/L per hour)
  • hypertonic saline infusion
  • replacement of free water.
  • Isotonic saline infusion

Relevant physiology:

  • Hypovolemia has resulted in excess ADH release in spite of hypo-osmolarity, because the baroreceptor reflex is a stronger stimulus for ADH release than the osmoreceptor reflex.
  • The excess ADH results in free water retention, which counteracts the attempts to increase sodium concentration with hypertonic saline
  • Once volume is restored, ADH release will decrease, and dilute diuresis will ensue
  • This loss of free water will assist the attempts to correct hyponatremia with hypertonic saline
  • Thus, volume replacement must occur together with sodium replacement.

References

For all electrolyte abnormality questions, I refer to the Electrolyte Quintet series from the Lancet. In the sodium article by Kumar, there is a table (Pane 2) from which the college answer for 5.2(b) seems to be derived (with a couple of changes). I have used that panel as my model answer.


Sumit Kumar, Tomas Berl. Sodium.  The Lancet, Volume 352, Issue 9123, 18 July 1998, Pages 220-228


SM Lauriat, T Berl: The Hyponatremic patients: practical focus on therapy. J Am Soc Nephrol 1997; 8: 1599–1607.

 

 

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