Water balance, diabetes Insipidus and hyponatraemia Flashcards
How much fluid is in ECF?
1/3 of total body water
14L
How much fluid is in intravascular fluid?
1/4 ECF
3.5L
How much fluid is in interstitial fluid?
3/4 ECF
10.5L
How much fluid in ICF?
2/3 total body water
28L
What is the main cation in ECF?
Na+
What is the main cation in ICF?
K+
What is the main anion in ECF?
Cl-
What is the main anion in ICF?
(PO3-)4 and organic anions
What is the release of vasopressin (ADH) controlled by?
- Osmoreceptors in hypothalamus controls release day to day
- Baroreceptors in brainstem and great vessels release ADH in emergencies
What is osmolality?
concentration per kilo
- in plasma very similar to osmolarity but concentration slightly different
What are the features of diabetes insipidus (AVP deficiency and resistance)?
- polyuria
- polydypsia
- no glycosuria
How would you diagnose diabetes insipidus?
- measure urine volume
- DI unlikely if urine volume <3L/day
- serum osmo >300 AND urine osmo<200
Why would you measure copeptin?
- Copeptin can be measured to measure AVP as it is cleaved when vasopressin is synthesised
- Measuring vasopressin is difficult as it is quickly metabolised and unstable
Define hyponatraemia
Definition: serum sodium <135 mmol/l
What is a biochemically severe hyponatraemia?
serum sodium <125 mmol/l
What are the normal bounds for serum sodium?
serum sodium 135-144mmol
What is considered acute hyponatremia?
<48 hours
What are causes of cranial diabetes insipidus (DI) - (lack of vasopressin)?
- Idiopathic
- Trauma
- Tumours
- Genetic
- Vascular – aneurysms, infarction
What is considered chronic hyponatremia?
> 48 hours
How would you manage cranial DI?
- Treat any underlying condition
- Desmopressin
- Tablets
- Nasal spray
- Injection
What are the signs and symptoms of cranial DI?
- Headache
- Lethargy
- Anorexia and abdominal pain
- Weakness
- Confusion/ hallucinations
What are some tests for hyponatraemia?
- Plasma osmolality
- Urine osmolality
- Plasma glucose
- Urine sodium
- Cortisol
