Sodium disorders:

 

Hyponatraemia:

Severity

·     Mild: 130-135

·     Mod: 125-130

·     Sev: <125

Presentation

·     Asymptomatic (if mild or gradual)

·     Cerebral oedema

o   Nausea

o   Headache

o   Confusion

o   Vomiting

o   Seizure

o   Coma

By tonicity

·     Hypotonic

o   ↑Water: heart/kidney/liver failure, SIADH, psychogenic

o   ↓Sodium: diuretics, nephropathy, CSW

·     Isotonic: pseudohypoNa (lipid, protein)

·     Hypertonic: glucose, mannitol, glycerol etc

(↑Glucose 1mM = ↑Na+ 2.5mM)

By volume status

·     Hypovolaemic:

o   Ax: urine ++, diarrhoea ++, sweat ++

o   Rx: NS

-> Beware spontaneous diuresis

·     Euvolaemic:

o   Ax: SIADH

o   Rx: FR, 3NS

·     Hypervolaemic:

o   Ax: heart/kidney/liver failure

o   Rx: FR, diuretic

 

Hypernatraemia:

Severity

·     Mild: 145-150

·     Mod: 150-170

·     Sev: >170

By volume state

·     Hypervolaemic: ↑Na > ↑TBW

o   Iatrogenic: 3NS, NaHCO3

o   Occurs in patients who cannot control water intake

o   Rx:

·     Hypovolaemic: ↓TBW > ↓Na

o   Urine: central DI, nephrogenic DI, osmotic

o   Other: sweat, vomit, diarrhoea, burns

o   N.B. % ↑Na+ = % ↓TBW

Treatment

·     Water

·     DDAVP

 

Sodium flux:

Hyponatraemia

Pathophysiology:

·     Direct effect: brain cells swell

·     Fast compo: ↑Na+ and K+

·     Slow compo: ↑idiogenic osmoles

·     Rapid treatment: brain cells shrink -> osmotic demyelination

o   Occurs 2-3 days after correction

o   Pons is most susceptible location

o   Catastrophe

Recommend if severe:

·     First hour: ↑5mM max: 150mL 3NS q20 mins, check Na+ in between

·     First day: ↑10mM max

Hypernatraemia

Pathophysiology:

·     Direct effect: brain cells shrink

·     Fast compo: ↓Na+ and K+

·     Slow compo: ↓idiogenic osmoles

·     Rapid treatment: brain cells swell -> cerebral oedema

·     ±Spontaneous diuresis -> osmotic demyelination

Recommend if severe: (probably)

·     First hour: ↓5mM max: ~1.5L 5% dextrose

·     First day: ↑10mM in 24h

 

SIADH:

Features

·          ADH excess -> inappropriate water retention

·          Common

Diagnosis

·          Fluid status: euvolaemic, oliguric

·          Blood test: Osm <280, Na <135

·          Urine test: Osm >100, Na >40
(inappropriately concentrated)

Cause

·          Peri-op (general anaesthesia, pain, stress response)

·          Acute illness (neuro, resp)

·          Drugs (e.g. anti-depressant)

·          Cancer

Treatment

·          Treat underlying cause

·          Fluid restriction 0.5-1L/day (contraindicated in SAH!)

·          Hypertonic saline if Na >125

o   Too fast: central pontine myelinolysis

·          Drugs uncommon (frusemide, demeocycline, conivaptan)

 

CSW:

Features

·          Voodoo -> inappropriate natriuresis

·          Uncommon

Diagnosis

·          Fluid status: hypovolaemic, polyuric

·          Watery blood: Osm <280, Na <135

·          Salty urine: Osm >100, Na >140, ↑Hct

Cause

·          Neurosurgical problem

Treatment

·          Treat the underlying cause

·          Replace deficit

o   Saline – hypertonic > normal

o   Too fast: central pontine myelinolysis

 

Central DI:

Features

·          ADH deficiency -> inappropriate water loss

o   Polyuric phase (day 2-5)

o   Antidiuretic phase (day 6-10)

o   Permanent DI

DDx Neurosurgery

·          Fluid +++

·          Mannitol

·          Steroid-induced glycosuria

Diagnosis

·          Polyuria >200mL/h for 2 hours

·          Blood test: Osm >290, Na >150

·          Urine test: Osm <150

Cause

·          Central: pituitary aurgery, TBI, idiopathic

·          Nephro: CKD, electrolytes, toxicity

Treatment

·          Replace deficit

o   = TBW x (Na - 140) / 140

·          Desmopressin

o   Indications: severe (>500mL/h) or prolonged (>24h)

o   IV: 1-2mcg BD (0.3mcg/kg is for vWD + bleeding)

o   PO: 200mcg TDS

 

 

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