Download AM disease - hyponatraemia

Note: severe hyponatraemia is a medical emergency, but Na should not be
brought down too quickly
Definition = plasma sodium < 130 mmol/L
Epidemiology
Types
Hypovolaemic (dehydrated)
Euvolaemic
Hypervolaemic
Causes
Hypovolaemic
Diuretics
Vomiting, diarrhoea, sweating
Osmotic diuresis (urea, glucose (DKA), mannitol)
Euvolaemic
Artefact (taken iv from arm)
Iatrogenic (xs iv dextrose post-op)
Psychogenic polydipsia
Hypothyroidism/Hypoadrenalism
SIADH (many causes, esp lung/cerebral pathology)
Hypervolaemic
CCF
Hepatic/Renal failure
Nephrotic symdrome
Note: many patients have more than one cause, eg CCF,
mild CRF, on diuretics
Symptoms
Nil, if mild
Depends on fluid state (ie could be thirsty and dizzy if
hypovolaemic, or c/o SOB/oedema if hypervolaemic)
If Na < 125 mmol/L, may be confused
If Na < 120 mmol/L, may be drowsy, or fit
Key questions
‘Has anyone changed your tablets in last 4-6 weeks?’
Signs
Nil, if mild
Depends on fluid state
May be confused, drowsy, or fit
Investigations
Blood
FBC, CRP, ESR
U+E, LFT, Bone
Other
CXR (causes SIADH)
Key investigation
Blood
Sodium
Other
CXR
Specialist investigations
Serum osmolality (275-285 mosmol/L)
Urinary sodium (normal 10-20 mmol/L)
Urine osmolality (70-1200; low <300; high >800
mosmol/L)
Urine osmo dec, urine Na inc
Hypoadrenalism
SIADH
Urine osmo dec, urine Na dec
Most causes hypovolaemia
Hypervolaemic causes
Treatment (first line)
Note: treatments very different, depending on
cause
Hypovolaemia (iv fluids, often half-normal
saline)
Euvolaemia (fluid restriction)
Hypervolamia (diuretics?)
Stop
Diuretics, if hypovolaemic, and thought to be
cause
Note: though in other cases giving/inc diuretics
can be treatments
Other drugs that may cause hyponatraemia (eg
SSRIs)
IV fluids (eg 5% dextrose, post op)
Admit?
Usually
Bed plan
Any medical ward (esp endocrine/DM)
± ITU, if ill, or fitting
Referral
Medical
Endocrine (renal?)
PAM
Pharmacist (drug causes)
Prognosis
Usually good (in mild cases)
2° Prevention
Monitor Na in pts with diuretcis
Don’t forget
Bring Na down slowly (<5 mmol/L/day)
Note: faster risks central pontine myelinosis
Red flags
Na < 120 mmol/L, drowsy or fitting
Local guideline (link)
National guideline (link)
Tell a story
Patient info (link)