A 76 yo woman is sent in from the nursing home with myoclonic jerks. She has a past medical history of slight dementia and seizures. Her GCS is 13-14/15. On arrival she has constant myoclonic jerks. Initial Blood tests reveal the following:
You make the diagnosis of hypernatraemia. What causes it? How do we correct it?
Hypernatraemia is defined as Na>145mmol/L.
Na>180 mmol/L are associated with high mortality.
Causes of Hypernatraemia
Lets think of this simply; its either too much water out or not enough water in. In more detail:
- Decrease in water intake: This can be for a variety of reasons, from not having water to not being able to communicate thirst, to disordered thirst perception.
- Increased water loss, more than salt loss
- Losses from GIT or Skin
- Renal Disease affecting concentrating ability
- Diabetes insipidus
- Inadequate salt intake
- Mineralcorticoid: Primary Hyperaldosteronism
- Glucocorticoid: Cushings
How The Patient Presents
The hypernatraemic patient presents with a range of symptoms that include:
How to correct the Hypernatraemia.
The answer is SLOWLY over 24 hours, with a maximum drop of 12mmol/L over the 24 hours. Rapid correction can result in cerebral oedema and seizures.
- Calculate total body water: Weight x (0.5 for males) or (0.45 for females)
- Calculate how much fluid will need to lower the Na
- (Na content in fluid -Patient Na)/(TBW + 1)
- Divide this into the number of mmol/L we need to reduce in 24 hours.
The Na was 165 and we wish to use 5% Dextrose which has zero sodium in it, on our 60kg woman
TBW = 0.45 x x60 =27L
Let’s reduce the Na by 10 mmol/L over 24 hours
Amount of 5% needed is 10/5.9L= 1.7 L- add to this any other expected losses.
Sodium Content of common IV fluids
|Fluid Type||0.9% NaCl||0.45% NaCl/ 4% Glucose||0.18% NaCl/4% Gluc||5% Glucose||Hartmann's||Ringer's Lactate|
|Na Content mmol/L||154||77||31||0||131||130|