Clinical biochemistry: sodium & water disorders
Disorders of sodium and water are common in clinical practice and often difficult to investigate and manage appropriately. These resources will take you through the underlying pathophysiology, clinical features, tests used in investigation, and management of hypo- and hyper-natraemia.
- The following YouTube videos outline sodium homeostasis. They are helpful, and the diagrams of the feedback loops are a good feature. However, some of the effects of sodium imbalance mentioned, such as those on the heart, are not particularly important clinically. The web pages detailing these (later) are a better reference for these aspects.
- Next is a short video on water homeostasis. This completes the overview of sodium and water homeostasis.
- We now come on to the tests used in the investigation of sodium and water disorders. Clinically, important features to pay attention to are the volume status of the patient (ie hypo-, eu-, or hypervolaemic), urine output and treatments (eg diuretics, IV fluids). The tests that are ordered are typically serum urea and electrolytes, plasma glucose, serum osmolality, urine sodium and urine osmolality. The blood samples and urine samples should be taken at the same time - this is called "paired" sampling. The links below explain the sodium and osmolality tests.
- Hyponatraemia is a common problem, particularly in primary care. The two resources below from the professional pages of Patient.co.uk and Prodigy are excellent, and give good overviews of the investigation and management of hyponatraemia in a readable format. Prodigy is well referenced and gives plenty of detail. The key to investigating many cases is to remember to gather all the appropriate clinical information before investigating biochemically - the clinical context often suggests a cause and can be very helpful in directing which investigations to request.
- Hypernatraemia can be problematic, particularly in hospitalised patients. Diagnosis can be difficult in some cases, and the hypernatraemia page below from Patient.co.uk outlines how to investigate in clear terms.
- And finally, to put this all in context, the case report on water intoxication here provides a good insight into how investigating these disorders occurs in practice. There is also an important lesson - that if a neonate is found to have severe hyponatraemia soon after birth, think about investigating the mother.
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- Duncan ColeThanks AnneMarie. Yes, I agree re the VLE - and yes, having this sort of post in Storify allows me to link to/embed it elsewhere, including the VLE, but also...Thanks AnneMarie. Yes, I agree re the VLE - and yes, having this sort of post in Storify allows me to link to/embed it elsewhere, including the VLE, but also Scoopit (I've done this), blogs etc, so very versatile which I like. Doing things once and sharing is so much more efficient! I will confess that this wasn't done all on the iPad app - the initial bit was, but I completed it on a laptop!more2013-02-13T17:24:09.349Z
- AnneMarie CunninghamImpressed that you produced this using the ipad app! I always find that a little difficult but maybe it has improved. Storify is definitely embeddable in the...Impressed that you produced this using the ipad app! I always find that a little difficult but maybe it has improved. Storify is definitely embeddable in the VLE. The benefit of having here rather than directly within the VLE is that this is accessible anywhere and can be scooped etc. Agree?more2013-02-13T15:34:44.531Z