86 years old lady transferred from care home with h/o drowsiness and worsening confusion for past few days. Her past medical history included severe dementia and hypertension for which she was on medications (no diuretics). On examination she was sleepy but easily arousable. Her vital signs and lab results are as follows:
Temp. 37.0 C
PR- 94, regular
BP- 98/56 mmHg
O2 saturation: 95% on room air
Heart and lung examination were normal.
CNS examination: No focal neurological deficits
Lab results:
FBC- Normal
U&E:
Sodium- 168mmol/L
Potassium- 5.2 mmol/L
Urea- 13.8
Serum creatinine: 126
LFT- normal
CRP <2
Lactate- 2
Serum glucose: 8 mmol/L
Comments:
For most of us emergency physicians, hypernatraemia appears to be an abstruse condition and we depend on medical team to guide the management.
In the following sections I have tried to simplify the approach to the management of hypernatraemia in the emergency department. The information is based on the knowledge I gleaned from following resources
www.uptodate.com
www.bestpractice.bmj.com &
Trust guideline on management of hypernatraemia
Causes of hypernatraemia
Hypernatraemia in defined as serum sodium >145 mmol/l. There is no consensus on the cut off value for severe hypernatraemia
The main causes of hypernatraemia can be broadly divided into three categories:
Free water loss
- Osmotic diuresis (e.g., mannitol, severe hyperglycaemia etc.)
- Impaired renal concentrating abilities (Diabetes insipidus, renal or central)
- Insensible loss/ sweat (usually 500-700ml/ day in adults)
Pure water intake deficit
- Inability to drink water (most common cause in elderly) or limited excess to water
- Impaired thirst mechanism ( CNS causes)
Sodium overload
- Administration of hypertonic saline, excessive sodium bicarbonate administration for management of metabolic acidosis etc
- Ingestion of large amounts of salt
- Mineralocorticoid excess
Note:
Free water loss is the most common cause of hypernatraemia but in elderly population is inadequate water intake.
Diagnostic tests:
FBC, U&E, LFT, Serum Calcium
Serum and Urine osmolality
Urine sodium level
Management in ED:
Treatment is guided by volume status of patient, time of onset and severity of symptoms.
There is no consensus on the correction rate, but sodium level should not fall more than 10mmol/L in 24 hours. Rapid correction can cause cerebral oedema.
Strategy:
- Treatment of the underlying cause
- Calculate free water deficit
Formula:
0.4 X Ideal body weight* (serum Na+ – 140)/140 = L.
(Aim to replace 50% of this in 24 hr as glucose 5% IV as an addition to normal maintenance fluid requirements)
- Determine a suitable serum sodium correction rate
- Estimate ongoing free water loss
Note:
If the patient is hypovolemic and in shock, the intravenous volume should be restored urgently usually with 0.9% Sodium Chloride solution (prior to free water replacement).
Initial infusion rate can depend on patient’s urine output.
Free water replacement enterally or by NG tube is preferred when possible.
Monitor serum sodium 12 hourly.