Challenges in the evaluation of hyponatremia Meera Ladwa (SpR Endocrine&Diabetes) Dr Steve Hyer

 One of the commonest electrolyte disorders encountered in hospital patients  Best understood as an imbalance between sodium and water  Most commonly, a relative excess of water SODIUM WATER

 27 year old male  Known chronic paranoid schizophrenia  Taking citalopram and depot flupentixol  Brought into A+E with generalised tonic clonic seizures  Given 4mg IV lorazepam in resus

 Venous blood gas: - Na K 4.0 Initial thoughts – Hyponatremia-induced seizures secondary to medications

 Received hypertonic saline on HDU  Subsequent investigations found the following:  Serum osmolality of 231 mOsm/kgH2O  Urine osmolality of 79 mOsm/kgH2O  What is the diagnosis?

A very simple guide to hyponatremia  Question 1.  Is this hypotonic hyponatremia? Serum osmolality  NORMAL ( ):  Pseudohyponatremia secondary to elevated glucose, lipids, or protein  HIGH (>295)  Hyperglycemia, hypertonic infusions such as mannitol.  LOW (<285)  Hypotonic hyponatremia

A very simple guide to hyponatremia  Question 2:  Is there impaired water excretion? Urine osmolality  LOW (<100) – The kidneys have no problem excreting water. So the problem is too much water intake.  HIGH (>300) – The kidneys cannot maximally dilute the urine. There is a problem with water excretion.

 Primary Polydipsia leading to water intoxication  His kidneys have responded normally to a low serum sodium. There has been complete suppression of ADH, and therefore a maximally dilute urine.  After 3 days of fluid restriction 1L/day, serum sodium was 132 and he was ready for discharge.

 Telephone call from GP: “Please could you help with this 53 year old lady. She has a long history of depression and agoraphobia. She takes venlafaxine and mirtazapine...”

 “Recently she has been generally unwell with lethargy, nausea and anorexia. Her serum sodium is 118mmol/L. Could this be medication related?”  “Her serum osmolality is 264 mOsm/kg H2O”  “Her urine osmolality is 520 mOsm/kgH2O with a urine sodium of 60mmol/L.”  “Her thyroid function is normal.”

A very simple guide to hyponatremia  Question 3. Are the kidneys trying to hold on to sodium?  Urine sodium  Low (<10) EITHER: Hypovolemia (dehydration, vomiting, diarrhea, sweating) OR: Cirrhosis, heart failure, nephrotic syndrome The common factor is renal hypoperfusion

A very simple guide to hyponatremia  Question 4 Can we exclude endocrine causes?  Urine sodium  High (>20) You need to decide between: -SIADH -Diuretics -Hypothyroidism -Adrenal insufficiency

A very simple guide to hyponatremia  Check TFTs and a random cortisol  Check the drug history Random cortisol: If high (>550nmol/L) then you can reasonably exclude adrenocortical insufficiency as the cause of hyponatremia

 A few days later: “Her random cortisol is 38nmol/L”

 Hyponatremia due to adrenal insufficiency  Treatment with fluid replacement and hydrocortisone will reverse the hyponatremia

 Hyponatremia is very common, but appropriate evaluation and management is not always easy.  Outline of a basic guide to approaching hyponatremic patients - Clinical assessment plus serum osmo, urine osmo, urine sodium, TFTs, cortisol and drug hx  Don’t forget the cortisol!