Hypernatremia

Question 1

What are the causes of Hypernatremia?

Answer 1

Hypovolaemia – Renal Fluid Loss (Osmotic Diuresis/Diuretics) or Extra-Renal Fluid Losses (GI, Burns etc)
Euvolaemic – Diabetes insipidus (Patients maintain fluid levels with increased oral fluid intake and so are not dehydrated) or Reduced thirst (common in the elderly)
Hypervolaemic – Inappropriate Saline infusion, Cushing’s, Hyperaldosteronism

Question 2

What will you find in a histroy taking of Hypernatremia?

Answer 2

Symptoms:
Lethargy
Thirst
Weakness
Irritability
Confusions
Coma
Seizures
Dehydration 

Risk Factors:
Diabetes - may lead to hyperglycaemia resulting in glycosuria causing an osmotic diuresis (Can also occur with a ketonuria)
History of diarrhoea or vomiting
Nephrogenic Diabetes insipidus - Hypercalcaemia, Lithium Toxicity (Drugs)
Neurogenic Diabetes insipidus - CNS injury or tumour symptoms
Recent hospital admission with fluid admission

Specific Questions to ask:
Polyuria, Polydipsia, Nocturia – Diabetes Insipidus

Question 3

What will you find on examination of a patient with Hypernatremia?

Answer 3

Examination - to assess fluid status to help differentiate between hypovolemic, hypervolemia or euvolemic causes 
End of the bed:
Reduced Skin turgidity 
Hands:
Tachycardia
Hypo-tension with Postural Drop 
Increased Capillary refill time 
Cool peripheries
Face:
Dry Mucous Membranes
Sunken Eyes 
Abdomen:
Reduced urine output
Legs:
Cool peripheries

Examination findings of fluid overload 
Neck:
Raised JVP
Chest:
Tachypnoea
Bibasil Crepitation’s
Pulmonary Oedema on CXR
Legs:
Pitting oedema in sacrum/ankles/legs

Question 4

What investigation will you order in Hypernatremia

Answer 4

Bedside:
Urine osmolality/Urinary Sodium can help to differentiate the cause if the patient is hypovolaemic as will assess where fluids have been lost from - Raised Urinary Osmolarity/Sodium indicates renal fluid loss while reduced Urinary Osmolarity/Sodium indicates non-renal fluid loss.
Very low urine osmolarity - indicates diabetes insipidus as the underlying cause (In Euvolemia)

Bloods:
U&E - Will show high Na, may also show raised Urea and creatinine in dehydration. If Hypokalaemia, alkalosis and Hypotension present, consider hyperaldosteronism
Serum Osmolarity - Used to assess fluid status
LFT - Albumin will be raised in dehydration
FBC - Haemoglobin raised in dehydration
Glucose - Rule out Glycosuria
Renin and aldosterone levels - Aldosterone raised in Hyperaldosteronism

Special Tests:
Water Deprivation Test – Diagnostic test for Diabetes Insipidus. Patient is deprived of fluids for 8 hours while measuring urine osmolarity. Osmolarity should rise with reduced fluid intake (saving water). If it does not this is a positive test

Question 5

What is the treatment of Hypernatremia ?

Answer 5

Lifestyle:
If Euvolemic/Hypovolaemic try to increase oral fluid intake, if not able to meet their requirements then IV Fluids may be used to supplement this

Medical: If oral fluid intake not adequate
Euvolaemic – Slow Dilution of Na with Dextrose (1L/6hrs)
Hypovolaemic - Fluid replacement with saline (Patient require fluids to increase volume, the extra fluid dilutes the extra Na so this will not worsen the problem)
Hypervolemia – Slow Dilution of Na with Dextrose (1L/6hrs), as patient is already hypervolaem9ic they may require furosemide to limit fluid overload
Treat the underlying cause – Renal Failure may require Renal Replacement therapy

Question 6

What is Hypernatremia?

Answer 6

Normal sodium levels are between 135 and 145. Any value above 135 is hypernatraemic. Hypernatremia can be due to incorrect fluids (Increasing Na levels) or Fluid loss (In excess of Na loss, increasing its effective concentration)