Podcast - Understanding low sodium: further assessment and management - Primary Care Guidelines | Lyssna här

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This episode makes reference to guidelines produced by North Bristol NHS Trust, Royal United Hospitals Bath NHS Trust and Royal Cornwall Hospitals NHS Trust. The content on this channel reflects my professional interpretation/summary of the guidance and I am in no way affiliated with, employed by or funded/sponsored by them.

My name is Fernando Florido and I am a General Practitioner in the United Kingdom. In this episode I go through the guidelines on hyponatraemia produced by North Bristol NHS Trust, Royal United Hospitals Bath NHS Trust and Royal Cornwall Hospitals NHS Trust, focusing on what is relevant to Primary Care only. Other guidance has also been consulted and links to all of them can be found below

I am not giving medical advice; this video is intended for health care professionals; it is only my summary and my interpretation of the guidelines and you must use your clinical judgement.

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The links to the Hyponatraemia guidelines consulted can be found here:

North Bristol NHS Trust

· https://www.nbt.nhs.uk/sites/default/files/Hyponatraemia%20in%20Primary%20Care.pdf

Royal United Hospitals Bath:

· https://www.ruh.nhs.uk/pathology/documents/clinical_guidelines/PATH-019_hyponatraemia_in_primary_care.pdf

Royal Cornwall Hospitals NHS trust:

· https://doclibrary-rcht.cornwall.nhs.uk/DocumentsLibrary/RoyalCornwallHospitalsTrust/Clinical/EndocrineAndDiabetes/ManagementOfHyponatraemiaClinicalGuideline.pdf

Greater Glasgow and Clyde:

· https://handbook.ggcmedicines.org.uk/media/1099/195-hyponatraemia-flowchart-1-final-200717e.pdf

Gloucestershire hospitals NHS Trust

· https://www.gloshospitals.nhs.uk/media/documents/Hyponatraemia.pdf

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Transcript

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Hello and welcome, I am Fernando, a GP in the UK. Today, we are looking at the further assessment and management of hyponatraemia, I have looked at the guidelines produced by North Bristol NHS Trust, and Royal United Hospitals Bath NHS Trust, as well as other guidance, focusing on what is relevant to Primary Care only. The links to the sources consulted are in the episode description. If you have not already done so, I recommend that you look at the previous episode on hyponatraemia, its classification, clinical presentation, pathophysiology and causes, which will give you a good introduction.

Right, without further ado, let’s get started.

Let’s have a look at the management of hyponatraemia.

· As we have know, acute or severe hyponatraemia can be a medical emergency and we should admit for hospital treatment anyone with either symptoms or severe hyponatraemia, understood to be a sodium below 125.

· People with asymptomatic mild hyponatraemia, that is, a sodium of between 130 and 135, can be investigated and initially managed in Primary Care.

· But, what do we do with people who are asymptomatic and who have moderate hyponatraemia, that is, a sodium of between 125 and 129? Well, these people need careful assessment because there may be a risk of the sodium falling quickly. So, in these cases, we should seek specialist advice in respect of admission or referral.

Let’s now look at the management in Primary Care.

And as a precaution, all patients with new onset hyponatraemia should have a repeat sodium checked after one week to exclude a rapidly decreasing level.

We should then assess the volume status to see if there is fluid overload or hypovolaemia. We will look at a useful flowchart later which will give us more information in that respect.

We should then review the medication and, if it could be the cause, if possible, we will stop it and repeat the sodium levels in 1-2 weeks. If the sodium level remains low after stopping the medication, we should seek specialist advice.

Of course, if the medication cannot safely be stopped, then we will discuss with the prescribing consultant.

We should also look for and investigate disorders that may cause hyponatraemia. So:

· We will look for symptoms of possible intercurrent illnesses that could play a part such as chest infections, gastrointestinal disease or UTIs.

· We will ask about fluid intake and nocturnal polyuria that could point towards primary polydipsia.

· We will enquire about possible cancer symptoms, especially lung and gastrointestinal, and arrange a chest X-ray and additional investigations if necessary. This is because these malignancies, particularly small cell lung cancer and pancreatic and colorectal cancers, are known to produce ectopic antidiuretic hormone.

· We will consider further blood tests such as:

o Renal function tests including eGFR and urinalysis to exclude renal disease

o Liver function tests to exclude liver disease

o Thyroid function tests to exclude hypothyroidism

9AM serum cortisol if Addison's disease is suspected.

BNP if heart failure is suspected.

o Total serum protein and serum electrophoresis as well as urine Bence-Jones protein if myeloma is suspected

· And Finally, a paired serum osmolality and urine osmolality and sodium. It is essential that both the serum and urine are sent on the same day. Let’s see what these investigations mean:

o Serum osmolality will determine whether the hyponatraemia is:

§ Pseudo-hyponatraemia, when the serum osmolality is normal

§ Hypertonic, like in hyperglycaemia, when the serum osmolality is high and

§ Hypotonic, like in true hyponatraemia, when the serum osmolality is low. In this case we will have to look at the urine results to assess further.

o Urine osmolality will determine how concentrated the urine is:

§ If the urine is very diluted and urine osmolality is <100, then ADH is not acting, like seen in primary polydipsia or high beer intake or potomania

§ If the urine osmolality is >100, then ADH is acting and we will have to look at urinary sodium to categorise it further.

o Urinary sodium will determine whether sodium is being appropriately regulated in the kidneys. So, if urine osmolality is >100 and:

§ If urinary sodium is low, that is, <30, then the kidneys are reabsorbing sodium correctly. If the patient is hypovolaemic, we will look at extrarenal losses of sodium like, for example. in excessive vomiting, diarrhoea, sweating or extensive burns. If the patient is hypervolaemic, we will consider conditions like, for example, heart failure, liver disease or nephrotic syndrome.

§ If both urine osmolality and urinary sodium are high, then it means that the kidneys are not reabsorbing sodium appropriately, like for example in Addison’s disease, salt wasting diseases and syndrome of inappropriate secretion of antidiuretic hormone. But the issue becomes more complicated depending on whether the patient is on diuretics or has CKD, so these patients are best referred for further specialist assessment.

And we should normally refer any patient in which we suspect:

· Cancer

· Primary polydipsia

· An endocrinology cause or

· Suspected Syndrome of inappropriate secretion of antidiuretic hormone.

So, let’s try and make sense to all of this by looking at this flowchart by Royal United Hospitals Bath.

So, when we find hyponatraemia

We will review the fluid status and medication and consider pseudo hyponatraemia and other possible confounding factors such as hyperglycaemia, hypertriglyceridaemia and paraproteinaemia.

If the patient is hypovolaemic

We will expect to find the typical clinical signs such as Postural hypotension, Tachycardia, Dry mucus membranes, a decreased Skin turgor, Sunken eyes and a raised urea.

And if the urinary sodium is low, that is, below 30

We will consider Extra Renal loss like, for example, Diarrhoea and vomiting, Burns, Bowel obstruction or Pancreatitis

However, if the urinary sodium is high, that is, above 30

We will consider Renal Loss, like for example, Diuretics, AKI, Renal disease, Addison’s, Congenital adrenal hyperplasia and Cerebral salt wasting disease.

In which case, admission and specialist treatment may be required.

If the patient is hypervolaemic, like in oedematous disorders

We will consider conditions like, for example, CCF, Ascites, Liver failure. Nephrotic syndrome and Low albumin states

In which case, we will treat the underlying condition, which is also likely to require specialist referral.

If the patient is euvolaemic,

We will carry out investigations such as TFTs and 9 am serum cortisol as well as Paired Serum osmolality & Urine osmolality and sodium

If the thyroid function tests are abnormal or the 9AM serum cortisol is low

We will consider hypothyroid state or Addison’s disease

And we will refer them urgently to endocrinology, as the treatment is disease specific.

On the other hand, if Serum Osm is low, Urine Osm is high and the Urinary sodium is also high, with a normal cortisol and TFTs and without contributing drugs such as diuretics

We will think of syndrome of inappropriate secretion of antidiuretic hormone

But by then we will have concluded that referral for further specialist assessment and management is needed.

So that is it, a review of the further assessment and management of hyponatraemia relevant to primary care.

We have come to the end of this episode. Remember that this is not medical advice and it is only my summary and my interpretation of the guidelines. You must always use your clinical judgement.

Thank you for listening and goodbye.

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