Hypernatraemia

Question 1

Hypernatraemia is a relatively rare presentation seen in clinical practice. It is serum sodium > …mmol/L, however symptoms of hypernatraemia are normally only seen when [Na+] >…mmol/L.

Answer 1

Hypernatraemia is a relatively rare presentation seen in clinical practice. It is serum sodium > 145mmol/L, however symptoms of hypernatraemia are normally only seen when [Na+] > 160mmol/L.

Question 2

However, hypernatraemia in surgical patients also has impacts on peri-operative outcomes, with even mild hypernatraemia associated with increased … and … rates.

Answer 2

However, hypernatraemia in surgical patients also has impacts on peri-operative outcomes, with even mild hypernatraemia associated with increased morbidity and mortality rates. A cohort study of over 20,000 patients with pre-operative hypernatraemia demonstrated higher 30-day mortality rates than the control patients (5.2% vs 1.3%).

Question 3

Hypovolaemic Hypernatremia - causes (4)

Answer 3

Diuretics (common)
Mainly from loop diuretics
Dehydration / fluid restriction (common)
Includes diarrhoea, vomiting, burns, or febrile illness
Acute tubular necrosis
Due to the early polyuric stage
Hyperosmolar states
Includes HHS (hyperosmolar hyperglycaemic state)

Question 4

Diuretics (common)
Mainly from loop diuretics
Dehydration / fluid restriction (common)
Includes diarrhoea, vomiting, burns, or febrile illness
Acute tubular necrosis
Due to the early polyuric stage
Hyperosmolar states
Includes HHS (hyperosmolar hyperglycaemic state)

Can all cause what type of hypernatraemia?

Answer 4

Hypovolaemic Hypernatremia

Question 5

Euvolemic Hypernatremia - cause

Answer 5

Diabetes insipidus (DI)

Question 6

Diabetes insipidus (DI) can cause what type of hypernatremia?

Answer 6

Euvolemic Hypernatremia

Question 7

Hypervolaemic Hypernatremia - causes (2)

Answer 7

Excessive hypertonic saline administration (common)
Steroid excess
Conn’s syndrome or Cushing’s syndrome

Question 8

Excessive hypertonic saline administration (common)
Steroid excess
Conn’s syndrome or Cushing’s syndrome

Can cause what type of hypernatraemia?

Answer 8

Hypervolaemic Hypernatremia

Question 9

Hypernatremia is generally asymptomatic, although mild cases can result in ….

Answer 9

Hypernatremia is generally asymptomatic, although mild cases can result in excessive thirst. However, in severe cases, progression of symptoms can result in weakness, lethargy, irritability, confusion, seizures and coma.

In cases where [Na+]>180, neurological defects can appear, including ataxia, tremor, coma, and seizures.

Question 10

Hypernatremia is generally asymptomatic, although mild cases can result in excessive thirst. However, in severe cases, progression of symptoms can result in …. (6)

In cases where [Na+]>180, neurological defects can appear, including ataxia, tremor, coma, and seizures.

Answer 10

Hypernatremia is generally asymptomatic, although mild cases can result in excessive thirst. However, in severe cases, progression of symptoms can result in weakness, lethargy, irritability, confusion, seizures and coma.

In cases where [Na+]>180, neurological defects can appear, including ataxia, tremor, coma, and seizures.

Question 11

In cases where [Na+]>180, neurological defects can appear, including …, tremor, coma, and …

Answer 11

In cases where [Na+]>180, neurological defects can appear, including ataxia, tremor, coma, and seizures.

Question 12

Taking a thorough clinical history is the most important tool in evaluating the cause of hypernatraemia. A metabolic panel of bloods should be taken, including serum glucose, potassium, chloride, urea, and creatinine. A … … … will also help assess for any associated acid-base disturbance.

Answer 12

Taking a thorough clinical history is the most important tool in evaluating the cause of hypernatraemia. A metabolic panel of bloods should be taken, including serum glucose, potassium, chloride, urea, and creatinine. A venous blood gas will also help assess for any associated acid-base disturbance

Question 13

Urine … can aid the diagnosis when uncertain; hypernatraemia stimulates hypothalamic ADH release which leads to concentration of urine:

Answer 13

Urine osmolality can aid the diagnosis when uncertain; hypernatraemia stimulates hypothalamic ADH release which leads to concentration of urine:

If both hypothalamic and renal function are intact, the urine osmolality in the presence of hypernatraemia should be above 600mOsmol/kg, this is typically seen in extra-renal causes of hypernatraemia
If the urinary osmolality is less than 600mOsmol/kg despite hypernatraemia, it may indicate an ADH or renal dependent mechanism, such as osmotic diuresis or diabetes insipidus

Question 14

If both hypothalamic and renal function are intact, the urine osmolality in the presence of hypernatraemia should be … 600mOsmol/kg, this is typically seen in extra-renal causes of hypernatraemia

If the urinary osmolality is … than 600mOsmol/kg despite hypernatraemia, it may indicate an ADH or renal dependent mechanism, such as osmotic diuresis or diabetes insipidus

Answer 14

If both hypothalamic and renal function are intact, the urine osmolality in the presence of hypernatraemia should be above 600mOsmol/kg, this is typically seen in extra-renal causes of hypernatraemia

If the urinary osmolality is less than 600mOsmol/kg despite hypernatraemia, it may indicate an ADH or renal dependent mechanism, such as osmotic diuresis or diabetes insipidus

Question 15

Diabetes Insipidus - what is this?

Answer 15

Diabetes Insipidus (DI) is the disorder characterised by excessive excretion of dilute urine (5-20L/day) and an increased thirst response. It can be classified as:

Cranial DI– impaired anti-diuretic hormone secretion from the posterior pituitary
Often occurs after pituitary surgery or following head trauma
Nephrogenic DI– impaired response of the renal tubules to anti-diuretic hormone

Question 16

Diabetes Insipidus - presentation

Answer 16

Patients will present with symptoms of polyuria (+compensatory polydipsia). Diagnosis of DI can be confirmed by doing a water deprivation test, whereby the patient is deprived of fluids for up to eight hours (or 5% loss of body weight), following which desmopressin is given

Normal: Urine Osmolality >600mOsm before desmopressin test
Cranial DI: Urine Osmolality increases >600mOsm after desmopressin test
Nephrogenic DI: Urine Osmolality does not increase after desmopressin test

Question 17

It is important not to correct the serum sodium concentration too rapidly - why?

Answer 17

It is important not to correct the serum sodium concentration too rapidly due to the risk of cerebral oedema (in chronic hypernatraemia, the aim is to lower the serum sodium level by 10 mmol/L/day). When replacing any fluid deficits, enteral free water replacement is preferred where possible (including administration via nasogastric tube if needed)

Question 18

Hypernatraemia key points

Answer 18

Hypernatraemia is defined as a serum sodium > 145mmol/L
Common causes include dehydration, vomiting, diarrhoea, burns, and excessive saline administration
Most cases are asymptomatic yet neurological defects can present in severe cases
Even mild hypernatraemia may be associated with an increased risk of morbidity and mortality
Do not correct serum sodium concentrations too rapidly, due to the risk of cerebral oedema