Hypernatraemia

Question 1

What are classifications for Hypernatraemia?

Answer 1

• PURE (predominant) H2O LOSS
• HYPOTONIC FLUID LOSS
• SALT GAIN

Question 2

What is the prevalence of Hypernatraemia?

Answer 2

• Hospital acquired hypernatraemia is the most common form. Typically Iatrogenic
• Hypernatraemia on admission occurs more in older patients and Infections. It is less common

Question 3

What causes Pure Hypernatraemia?

Answer 3

Inadequate H2O intake + Normal fluid losses

1. EXTRA-RENAL LOSS + INADEQUATE H2O INTAKE

• Too old / young / sick to drink
• No access to H2O, e.g. nursing home
• Oesophageal obstruction
• Decreased sense of thirst (age, pathological)

2. RENAL LOSS + INADEQUATE H2O INTAKE

• Diabetes insipidus

Question 4

What is diabetes insipidus?

Answer 4

• Primary inability to concentrate urine with secondary polydipsia
• This leads to passage of large volumes of dilute urine
• Classified into Cranial Diabetes Insipidus (CDI) and Nephrogenic Diabetes Insipidus (NDI)
• CDI leads to impaired release of ADH from the posterior pituitary
• NDI leads to impaired renal response to ADH

Question 5

What causes Hypotonic Fluid Hypernatraemia?

Answer 5

Inadequate H2O intake + Hypotonic fluid losses

1. EXTRA-RENAL LOSS + INADEQUATE H2O INTAKE

• Vomiting
• Diarrhoea
• Fistula
• Excessive sweating

2. RENAL LOSS + INADEQUATE H2O INTAKE

• Osmotic diuresis
• Glucose
• Urea
• Mannitol

Question 6

What causes Salt gain Hypernatraemia?

Answer 6

Uncommon and usually iatrogenic:

• May be deliberate / accidental excessive salt intake e.g. ingestion of sea water
• Mineralcorticoid excess

Question 7

What are types of solutions given for Hypernatraemia?

Answer 7

• Crystalloid Solution
• Colloid Solution

Question 8

What are features of Crystalloid solution?

Answer 8

• Low molecular weight salts or sugars.
• Dissolve completely in water.
• Pass freely between the intravascular and interstitial space.
• Remain in the vascular space for a short time.

Question 9

What are features of Colloid Solutions?

Answer 9

• Large molecular weight substances.
• Do not dissolve completely in water.
• Do not pass freely between intravascular and interstitial compartments.
• Remain in the vascular space for a longer time.

Question 10

How is Hypernatraemia treated?

Answer 10

Hypovolaemia

• Rehydrate with Saline or Hartmann
• Check U&E after infusion and control rate dependant upon rise and symptoms.

Euvolaemia

• Treat underlying cause
• Maintain accurate fluid balance chart and measure weight
• If SIADH fluid restrict and consider Tolvaptan

Hypervolaemia

• Fluid and salt restriction
• Consider diuretics
• Treat underlying cause.