Disturbed electrolytes - high Na+

Question 1

define ↑Na+?

Answer 1

> 145

(Sx rare until >160)

Due to H2O loss/deficit or Na+ excess.
In general, it is rare, as the body triggers ADH then thirst to avoid this at all costs, even if it means becoming very hypervolaemic.
When it does happen, it is usually in elderly patients due to a lack of H2O intake.

Question 2

causes ↑Na+?

Answer 2

EXTRA-RENAL H2O loss/deficit:
• lack of intake: elderly, mentally ill
• loss through D, V
• skin: sweat, burns

RENAL H2O loss:
• osmotic diuresis: glycosuria inc. HHS, urea, mannitol
• diabetes insipidus (less ADH secreted, less water retained in blood)
• diuretics: loop, thiazide
• endocrine: Conn’s, Cushing’s

EXCESS Na+ intake (rare):
• excess hypertonic fluids
• sea water ingestion

Question 3

Sx and Ex ↑Na+?

Answer 3

• tired, weak
• thirsty
• signs of dehydration: ↓skin turgor, dry mouth, oliguria, tachycardia, orthostatic hypotension
• irritable, confused
• seizures, coma

Question 4

Ix ↑Na+?

Answer 4

BEDSIDE
• Urine and serum osmolality (DI)
- hypertonic urine is an appropriate renal response to ↑Na+ so suggests extrarenal fluid loss
- hypotonic urine suggests diabetes insipidus bc less ADH secreted therefore more water lost in urine

BLOODS
• U+E: check others, co-morbid imbalances
• glucose (osmotic diuresis)

Question 5

Tx ↑Na+?

Answer 5

• hypotonic fluids: 5% dextrose, 0.45% saline, or oral water

* monitor Na+ to ensure slow correction, dropping no more than 10 mmol/L/24hr

Question 6

Tx central diabetes insipidus (low ADH)?

Answer 6

desmopressin (substitute for vasopressin/ADH)

Question 7

what causes diabetes insipidus?

Answer 7

either a deficiency of antidiuretic hormone ADH (cranial) or an insensitivity (nephrogenic)

CRANIAL
• idiopathic
• post head injury
• pituitary surgery
• craniopharyngiomas
• histiocytosis X
• DIDMOAD is the association of cranial Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness (also known as Wolfram's syndrome)
• haemochromatosis

NEPHROGENIC
• genetic: the more common form affects the vasopression (ADH) receptor, the less common form results from a mutation in the gene that encodes the aquaporin 2 channel
• electrolytes: hypercalcaemia, hypokalaemia
• drugs: demeclocycline, lithium
• tubulo-interstitial disease: obstruction, sickle-cell, pyelonephritis

Question 8

Sx DI?

Answer 8

polyuria

polydipsia

Question 9

Ix + Tx DI?

Answer 9

• high plasma osmolality, low urine osmolality
(urine osmolality of >700 mOsm/kg EXCLUDES diabetes insipidus)
• water deprivation test

Tx
• nephrogenic diabetes insipidus: thiazides, low salt/protein diet
• central diabetes insipidus can be treated with desmopressin