Hyponatremia Flashcards
Definition?
Hyponatraemia is defined as a serum sodium concentration of <135 mmol/L.
RF?
- Older
- Hospitalisation
- SSRI use
- Thiazide diuretic use
- Underlying conditions
- Meds
- Ecstasy use
DDX?
• Hypertonic hyponatremia-hyperglycaemia
• Pseudohyponatremia-artefact
Other causes
Epidemiology ?
Age:
Sex:
Ethnicity:
P:
Aetiology?
hypovolaemic
euvolaemic
hypervolaemic
hypovolaemic?
• Gastrointestinal fluid loss (e.g., severe diarrhoea or vomiting)
• Third spacing of fluids (e.g., pancreatitis, severe hypoalbuminaemia)
• Salt-wasting nephropathy
• Cerebral salt-wasting syndrome (a rare cause of hyponatraemia resulting from urinary salt wasting; elevated brain natriuretic peptide has been implicated)
Mineralocorticoid deficiency.
euvolaemic?
- Medications (e.g., vasopressin, diuretics, antidepressants, opioids). The most common are thiazide diuretics and antidepressants[10]
- Syndrome of inappropriate antidiuretic hormone: can result from malignancy (e.g., small cell lung cancer, gastrointestinal tract cancers); central nervous system disorders (e.g., subarachnoid haemorrhage, meningitis, encephalitis); pulmonary disease (e.g., pneumonia); or other non-specific causes (e.g., medications, pain, nausea, stress, general anaesthesia). It can also be idiopathic
- High fluid intake: can result from intense/prolonged physical activity (e.g., marathon running, military training, wilderness exploration);[11]surgery; primary polydipsia (also referred to as psychogenic polydipsia); or potomania, which is caused by a low intake of solutes and electrolytes with relatively high fluid intake
- Medical testing: although less common, euvolaemic hyponatraemia related to excessive fluids can occur in the setting of medical testing such as cardiac catheterisation or colonoscopy.
hypervolaemic?
• Acute kidney injury/chronic kidney disease (low sodium levels in advanced kidney disease or dialysis patients is due to relatively higher water versus salt intake with poor excretion due to underlying kidney disease)
• Congestive heart failure
• Cirrhosis
Nephrotic syndrome.
CP?
- N and V
- Confusion, seizures , coma
- Low urine output
- Weight changes
- Orthostatic hypotension
- Abnormal JVP
- Poor skin turgor
- Dry mucous membranes
- Oedema
- Rales on auscultation
Pathophys?
- Low sodium conc in blood
- Losing more sodium than water or gaining more water than sodium
- Hypervolaemic-
- CHF, cirrhosis, nephrotic syndrome-fluid leaks into interstitium-oedema
- Lower circulating volume is reduced so water is retained and some sodium via RAAS-more water follows sodium
- Hypovolaemic
- Small decrease in total body water and more loss in sodium-
- Diarrhoea and vomiting-loss of electrolytes being absrobed
- Diuretics-more loss into urine
- Cerebral salt wasting-injury disrupts SNS and regulation of kidneys-disproportionate loss of sodium
- Euvolaemia-
- Increased water and normal sodium-no fluid into interstitium and so no oedema
- Dilute urine-adrenal insufficiency, hypothyroidism,polydipsia, potomania
- Conc-SIADH
- Pseudo
- Both are normal, but there is an excess of lipids, proteins-affect lab results of sodium measures
• Symptoms
Cerebral oedema-water moves into ICF-swell and damage and die-or increased ICP or herniation of brainstem
Investigations-first line?
- Serum electrolytes-Na <135 mmol/L,hyperglycaemia, over-hydration
- Serum osmolality-
- Serum osmolality <275 mmol/kg: indicates hypotonic hyponatraemia.
- Serum osmolality >295 mmol/kg: indicates hypertonic hyponatraemia.
- Urine sodium-
- In hypovolaemic hyponatraemia, urine sodium concentration >20 mmol/L indicates renal sodium loss (e.g., diuretics), and ≤20 mmol/L indicates non-renal sodium loss (e.g., gastrointestinal losses).
- In hypervolaemic hyponatraemia, urine sodium concentration >20 mmol/L indicates acute kidney injury/chronic kidney disease or diuretic use, and ≤20 mmol/L indicates congestive heart failure, cirrhosis, or nephrotic syndrome.
- In euvolaemic hyponatraemia, urine sodium concentration is >20 mmol/L in most patients; however, patients with a concomitant low sodium intake may have a low urinary sodium.
- Urine osmolality-
- High (≥300 mmol/kg): indicates syndrome of inappropriate antidiuretic hormone (SIADH) due to the inappropriate dilution of plasma as a result of pathological vasopressin release,[1]or may also be due to medication-related effects.
- Intermediate (150-300 mmol/kg): indicates potomania or a partial effect of medications or mild SIADH in conjunction with high fluid intake.
- Low (<100-150 mmol/kg): indicates primary polydipsia.
- Urine flow rate
- Electrolyte-free water excretion
- Hormones-thyroid, adrenal
Investigations-second line?
CT tumours
underlying cause
Management overall?
Correct the underlying cause; never base treatment on Na+concentration alone. The presence of symptoms, the chronicity of the hyponatraemia, and state of hydration are all important. Replace Na+and water at the same rate they were lost.
Management chronic?
Asymptomatic chronic hyponatraemia, fluid restriction is often sufficient if asymptomatic, although demeclocycline (adhantagonist) may be required. If hypervolaemic (cirrhosis,ccf), treat the underlying disorder first.
Management acute?
Acute or symptomatic hyponatraemia, or ifdehydrated, cautious rehydration with 0.9% saline may be given, but do not correct changes rapidly ascentral pontine myelinolysis2may result. Maximum rise in serum Na+15mmol/L per day if chronic, or 1mmol/L per hour if acute. Consider using furosemide when not hypovolaemic to avoid fluid overload.
