Acute hypernatraemia and Diabetes Insipidus

Question 1

What are signs/symptoms of hypernatraemia?

Answer 1

Lethargy, thirst, weakness, irritability, confusion, coma, fits + signs of dehydration

Question 2

What are causes of hypernatraemia?

Answer 2

Water loss in excess of Na loss
Fluid loss without water replacement - darrhoea, vomit, burns)
Diabetes insipidus - suspect if large volume of urine
Osmotic diuresis
Primary aldosteronism - BP high, potassium low
Iatrogenic - incorrect IV fluids - excess saline

Question 3

Management of hypernatraemia?

Answer 3

Water orally if possible
Glucose 5% IV 1L/6h guided by urine output and plasma sodium.
Use 0.9% saline if hypovolaemic since this causes less marked fluid shifts and is hypotonic in a hypertonic patient.
Avoid hypertonic solutions.

Question 4

Signs of underfilled fluid balance?

Answer 4

Tachycardia
Pstural hypotension
Reduced capillary refill
Reduced ruine output
Cool peripheries
Dry mucous membranes
Reduced skin turgot
sunken eyes

Question 5

Signs of overfilled fluid balance?

Answer 5

Raised JVP - indicates central venous pressure
Piting oedema of sacrum, ankles or even legs and abdomen
Tachypnoea
Bibasal crepitations
Pulmonary oedema on CXR

Question 6

Emergency management of diabetes insipidus?

Answer 6

Urgent plasma U&E, serum and urine osmolalities
Monitor urine output carefully and check u&E twice a day initially
IVI to keep up with urine output. If severe hypernatraemia - do not lower Na rapidly as this may cuase cerebral oedema
Use 0.9% saline to reduce Na at < 12mmol/L per day
Desmopressin IM 2mcg as therapeutic trial (replacement for ADH

Question 7

What is diabetes insipidus?

Answer 7

Passage of large volumes (>3L/day) of dilute urine due to impaired water resorption by the kidney because of reduced ADH secretion from the posterior pituitary (cranial DI) or impaired response of the kidney to ADH (nephrogenic DI)

Question 8

What are symptoms of DI?

Answer 8

Polyuria, polydipsia, dehydration, hypernatraemia symptoms,

Question 9

What are causes of cranial DI? Nephrogenic?

Answer 9

Congenital
Tumour - pituitary
Trauma
Infection

Metabolic - hypokalaemia, drugs - demeclocycline (ADH antagnoinsst), chronic renal disease

Question 10

How to diagnose DI?

Answer 10

8 hour water deprivation test
If urine volume is >3L/day
Fluid deprivation for 8h
Weight hourly - if 3% weight lost during test, order serum osmolality - if >300msomol/kg
If urine is dilute urine osmolality < 600msoml/kg give despmopressin and allow to drink. Measure urine osmolality hourly for next 4h.
IF >600mOsmol/kg, normal. If urine >600mOsmol/kg after desmopressine, cranial DI, if no increase in urine osmolality after desmopressin, nephrogeni DI.

Question 11

How to treat cranial DI?

Answer 11

MRI head
TEst ant. pit function
Give desmopressin - synthetic analogue of ADH

Question 12

How to treat nephrogenic DI?

Answer 12

Treat cause
Bendroflumethiazide
NSAIDs lower urine volume and plasma Na by inhibiting prostaglandin synthase - prostaglandins locally inhibit ADH action.

Question 13

In emergency management, how often check sodium? How would you administer desmopressin and what dose?

Answer 13

twice daily

IM 2mcg