Causes and symptoms of hyponatraemia in palliative care
Patients with palliative care needs often develop hyponatraemia. It is usually a marker of advanced disease, indicating a poor prognosis and a need to revisit the patient’s goals of care and advance care plan.
Hyponatraemia may not be recognised because symptoms are nonspecific and can mimic other consequences of life-limiting illnesses. Symptoms include headache, confusion, nausea, vomiting, anorexia, muscle weakness and cramps. Mild cases may be relatively asymptomatic, particularly if the serum sodium concentration drops slowly (eg over weeks to months). More severe cases result in delirium, seizures and coma, particularly when the sodium concentration drops rapidly over hours to daysBraun, 2015Spasovski, 2014.
Hyponatraemia is frequently associated with the syndrome of inappropriate antidiuresis (SIAD)Ellison, 2007. SIAD results in the retention of water and is characterised by low serum osmolality and hyponatraemia, in the presence of concentrated urine and normal extracellular fluid volume. SIAD is often (but not always) associated with ‘inappropriately’ elevated levels of arginine vasopressin (AVP) (also known as antidiuretic hormone [ADH]), or tumour production of AVP analogues. SIAD may also be:
- a physiological response to the stress of illness and low blood volume
- an adverse effect of drugs (eg tricyclic antidepressants, opioids, dopamine antagonists, selective serotonin reuptake inhibitors [SSRIs], carbamazepine, nonsteroidal anti-inflammatory drugs, some anticancer drugs)
- caused by pulmonary or cerebral disease.
Diuretics are a common cause of hyponatraemia but should not be stopped without carefully considering the balance of harms to benefits of doing so; see Principles of medication rationalisation in palliative care for guidance. If the approach is unclear, seek specialist palliative care advice.