Hypernatraemia

Question 1

What is the definition of hypernatraemia

Answer 1

Defined as a serum sodium >145 mmol/L

Usually only significant if concentration >155mol/L or rapid rise >20mmol/L in 24hours

Question 2

What are the 6 D’s of hypernatraemia?

Answer 2

NEARLY ALWAYS DUE TO LOSS OF H20 than Na+ gain
6 D’s of hypernatremia:
• DEHYDRATION
• DIARRHOEA
• DIURETICS/LAXATIVES
• DIURESIS OSMOTIC e.g hyperglycaemia: beware pseudohyponatremia, mannitol, uraemia, high protein feeding, osmotic diuretics
• DIABETES INSPIDIGNUS
○ Central: brain, pituitary surgery or brain injuries
○ Nephrogenic: inherited or acquired e.g lithium, demeclocycline, vaptans
• DOCTORS (IATROGENIC)
○ E.g infusions of large IV NaHC03 (8.4%), excessive NaCL, haemodialysis
• DROWNING
○ Ingestion of large sea water
• DISEASE: CONN’S, CUSHINGS

Question 3

What are the clinical features of hypernatraemia when acute?

Answer 3

Acute <48hours
	• Mild: signs of dehydration
		○ Decreased salivation
		○ Dry mucous membranes and skin
	• Moderate symptoms
		○ Confusion 
		○  Irritability, restlessness
		○ Lethargy
		○ Weakness
		○ Hyperreflexia
	• Severe symptoms:
		○ Focal neurological
		○ Seizures
		○ Altered consciousness 
		○ Stupor 
		○ Coma

Question 4

What are the clinical features of hypernatraemia when chronic?

Answer 4

Chronic >48hours
• Often asymptomatic or non specific mild symptoms
• Commonly: signs of dehydration
• Rarely: irritability, anorexia, nausea, weakness and/or altered mental status
Can occasionally be associated with intracerebral or subarachnoid haemorrhage

Question 5

what brain problem can be due to hypernatraemia?

Answer 5

Intracerebral or subarachnoid haemorrhage

Question 6

How do you assess someone with hypernatraemia

Answer 6

Fluid & medication history

Assess patient’s fluid status (useful parameters include observations, capillary refill time & JVP, postural hypotension, peripheral oedema & urine output)

Bloods: U&Es, glucose, electrolytes: magnesium, calcium

Consider urine & sodium osmolalities, however, interpretation requires endocrinology or senior input

Question 7

What is hypovolaemic hypernatraemia?

Answer 7

Both water + salt are lost but water> salt

• Losses might be gastrointestinal, skin (sweating/burns)
• Or from the kidneys
• Osmotic diuresis due to uncontrolled hyperglycaemia (e.g. in DKA or HHS)
• Loop diuretics
• Less commonly: early acute tubular necrosis

Question 8

What is normvolaemic hypernatraemia?

Answer 8

Loss of purely water, resulting in the sodium concentration going up. If the patient’s unable to keep up with intake, then they will develop hypovolaemia

Impaired thirst/water intake causing dehydration (hypothalamic lesions, dementia, decreased access to water)

Diabetes insipidus (central/nephrogenic): this can lead to severe acute hypernatraemia (i.e. <48h)

Question 9

What is hypervolaemic hypernatraemia?

Answer 9

• Due to administration of high sodium load from hypertonic sodium chloride or other drugs or excessive oral intake (in drugs, in error)
• Hypertonic dialysis
• Hyperaldosteronism (look out for hypokalaemia & hypertension)

Question 10

How should you manage hypernatraemia

Answer 10

Those who are hypovolaemia need volume resuscitation
1. Stop H2O loss
• Depending on the cause
○ Anti-emetic for vomiting
○ Stopping diuretics
○ Treating diarrhoea
○ Fever control
○ Treat underlying conditions e.g desmopressin for CDI, insulin for hyperglycaemia
2. Calculate the H2O deficit- this is what you must replace
3. Encourage enteral replacement orally or via NG tube if difficulty with swallow
○ Aim to replace 1/3 of the water deficit in addition to usual fluid maintenance in the first 24 hours
4. If you need to give IV- then use 0.9% NaCl (unless hypervolaemic hypernatraemia) (giving dextrose 5% too fast) may result in hyperglycaemic induced diuresis
5. Check the serum Na+ 12hrly in first 24hrs then daily, it should NOT fall >8-10mmol/L in 24hrs

Question 11

How slowly should it fall?

Answer 11

NOT MORE THAN 8-10MMOL/L in 24hrs- odema

Question 12

When should you get senior help!

Answer 12

Senior help:
Hypernatremia due to acute water loss- should be in HDU
Correction should be with 5% Dextrose at a rate 3-6 mL/kg/hr with monitoring of plasma sodium every 1-2 hours
Aim to correct sodium in 24-48 hours
Hypernatremia in neonates and young children
If hypernatremia is due to central or nephrogenic DI, specialist input should be sought early

Question 13

What is acute hypernatraemia associated with?

Answer 13

• Intracranial haemorrhage
○ Cell dehydration and shrinkage of the brain tissue can cause intracranial vessels to rupture
○ Haemorrhages may lead to irreversible neurological deficits
• Osmotic demyelinating syndrome
○ Demyelinating brain lesions from acute rise in sodium levels and serum osmolality
○ More commonly due to overcorrection of hyponatraemia
• Rhabdomyolysis
Severe hypernatremia can damage the cell membranes of the muscle cells

Question 14

What is chronic hypernatraemia associated with?

Answer 14

• Cerebral edema: can develop from the rapid correction of chronic hypernatremia
Hypervolaemia complications: secondary to hypernatremia correction- with large volume IV fluid administration e.g non cardiogenic pulmonary edema