Sodium abnormalities: hyponatraemia and SIADH Flashcards
How common is hyponatraemia in hospitals?
30% of in patients
What are the -early signs of hyponatraemia -late signs of hyponatraemia
- early: headache, nausea, vomiting and general malaise. - later signs: confusion, agitation and drowsiness.
What are the signs of acute severe hyponatraemia?
seizures, respiratory depression, coma and even death, and requires urgent treatment under senior supervision.
How do you investigate hyponatraemia?
- Full history and examination - Drug history> Thiazide diuretics cause - Hydration staus - Serum and urine osmolality, urine sodium, thyroid function and an assessment of cortisol reserve (0900 cortisol or synacthen test).
What is the diagnostic approach to hyponatraemia depending on whether it’s acutely severe or mild/moderate? What is more important in hyponatraemia: the absolute sodium value or the rate of change of sodium?
In acute severe hyponatraemia with neurological compromise= hypertonic saline to prevent cerebral oedema. Senior decision Mild or moderate hyponatraemia = follow diagnostic algorithm THE RATE OF CHANGE OF SODIUM IS MORE IMPORTANT THAN ASOLUTE VALUE, eg someone can have chronic hyponatraemia and be fine and someone can have a sudden drop and be very unwell. Note: Mild => 130 mmol/L Moderate => 125-29 mmol/L Severe => <125mmol/L
What is the diagnostic algorithm to hyponatraemia?
Confirmation of low serum osmolality is important to exclude NON-hypo-osmolar hyponatraemia, e.g hyperglycaemia (so low sodium levels but high osmolarity) Once hypotonic hyponatraemia has been confirmed, urine osmolality should be checked: Urine osmolality < 100mosmol/Kg = primary polydipsia/inappropriate administration of IV fluids Urine osmolality > 100 msomol/Kg = urine sodium will guide the differential diagnosis.
After confirming urine osmolality of > 100 msomol/Kg, and then measuring urine sodium levels, what does a urine sodium of more than 30 mmol/L suggest?
low effective arterial volume: - True dehydration e.g gastrointestinal (GI) salt loss - Intra-vascular depletion i.e congestive cardiac failure, cirrhosis or nephrotic syndrome despite clinical overload
After confirming urine osmolality of > 100 msomol/Kg and then measurine sodium levels, and if the urine sodium is > 30mmol/L and the patient is euvolaemic, which 2 diagnoses should be considered? What about if the patient is dehydrated?
SIADH (ACTH deficiency must be excluded first) If urine sodium is > 30 mmol/L AND patients are dehydrated think about - Addisons disease (look for pigmentation), - - renal and cerebral salt-wasting History of vomiting should be considered vomiting causes loss of hydrogen ions and a metabolic alkalosis, which is corrected by the renal excretion of sodium bicarbonate. Severe hypothyroidism may cause hyponatraemia, although the mechanism is unclear.
What are the 3 features of SIADH?
low serum osmolality (< 275 momol/kg), urine osmolality > 100 mosmol/kg and urine Na > 30 mmol/l.
What 3 diagnoses must you exclude first before you diagnose someone with SIADH?
SIADH can ONY be diagnosed after excluding -hypothyroidism - total salt depletion - ACTH deficiency
How is SIADH treated? (hypovolaemic hyponatraemia and hypervolaemic hyponatraemia)
Cause-specific treatment fluid restriction are the key aspects of management of SIADH. - HYPOvoluaemic hyponatraemia - Fluid replacement with normal saline - HYPERvoluaemic hyponatraemia - specialist treatment of cirrhosis, nephrotic syndrome or CCF Drug treatment of SIADH = demeclocycline (reduces renal response to ADH but unpredictable pharmacokinetics and side effects), ADH antagonists.
Why does ACTH deficiency appear identical to SIADH?
ACTH deficiency appears identical to SIADH because it causes reduced excretion of free water, since cortisol deficiency leads to increased ADH activity.
What are the 5 categories of causes of SIADH?
-Malignancy eg lung/GI -Drugs eg NSAIDs -Pulmonary eg Pneumonia -CNS eg trauma -Miscallenous eg idiopathic, HIV If no cause for SIADH is found, cross-sectional imaging or bowel investigation > search for an underlying malignancy. Idiopathic SIADH is a diagnosis of exclusion.
DOES THE PATIENT HAVE SEVERE SYMPTOMS - COMA/SEIZURES
YES - CONSIDER IMMEDIATE HYPERTONIC SALINE
NO - MEASURE URINE OSMOLALITY, THEN DIAGNOSTIC PATHWAY, THEN CAUSE SPECIFIC TREATMENT.
