This website caught my eye because it covers the problem of hypernatraemia from a paediatric viewpoint, with which GPs may well be involved.
Although not common in children, it can occur when there is water loss in excess of sodium loss, as can happen in diarrhoea.
The pages constitute clinical practice guidelines and embrace definition, assessment and management. A chart details fluid replacement parameters for moderate and severe hypernatraemia based on the child's weight.
This is really in-patient stuff, but I fancy the examiners would be impressed with it at an nMRCGP viva.
Why go there: it is laid out clearly.
Downside: complex in places.
Information from: Royal Children's Hospital, Melbourne, Australia.
An interesting case
Admittedly this is high-powered content, and describes a hospital case, but it makes an interesting read that will enhance your understanding of the problem.
What intrigued me is that it starts by saying that although hypernatraemia is a relatively frequent electrolyte abnormality in hospital patients, this electrolyte imbalance will not occur in patients with an intact thirst mechanism and free access to water, because we have such a powerful osmolar stimulus to drink.
Situations that can disrupt the stimulation of thirst include hypothalamic injuries, and that is what this case is about. You don't need to read the small print of the tables, just a quick skim through is enough.
This is a serious case, as severe hypernatraemia can be fatal in over 60 per cent of cases.
Why go there: the site helps understanding.
Downside: little GP relevance.
Information from: Nephrology Dialysis Transplantation.
Salt poisoning or hypernatraemia?
Given the high-profile case of a parent being accused of poisoning their child with salt, I thought it would be of interest to find out how it was possible to tell if poisoning, as opposed to disease, was the cause.
Traditionally the focus is on hypernatraemia with high urinary concentrations of sodium and chloride, but this combination may be found in children with dehydration caused by diarrhoea. The physiology of salt overload and hypernatraemic dehydration is considered, and there is an explanation of how poisoning and a disease process can be distinguished on the basis of history, examination and biochemical analysis. Perhaps the best part is reading about the two cases that were tested in court.
Why go there: it has a touch of courtroom drama.
Downside: 15 minutes to read.
Information from: British Medical Journal.
This case looks at a man who developed hypernatraemia but did not complain of thirst.
It refreshes the reader on the underlying physiology of hypernatraemia in the guise of a highly intriguing case. It also shows the complexity of the condition.
Four possible factors were looked at: a hypothalamic lesion, diabetes insipidus, unusual lesions such as occult germinoma, and finally a psychiatric cause.
Perhaps the most arresting point was the demonstration of a link between psychiatric and physiological abnormalities.
The authors concluded that a psychiatric basis to hypodipsia was the principle cause although diabetes insipidus was also partially implicated.
Why go there: a thoroughly interesting case.
Downside: takes time to comprehend.
Information from: Nephrology Dialysis Transplantation
Dr Barnard is a former GP in Fareham, Hampshire
Website of the week
Finding specific information on hypernatraemia is not easy, but it is possible to unearth the occasional site.
This one, on hypernatraemia in the elderly includes an algorithm for assessment, which is not to be missed.
The possible causes are varied, including central diabetes insipidus, excess water intake with decreased anti-diuretic hormone (water diuresis), Cushing's disease, primary hyperaldosteronism, diuretics, renal disease, excess sweating and diarrhoea.
Why go there: it has an excellent algorithm.
Information from: American Academy of Family Physicians.
Address: www.aafp.org/afp/20000615/3623.html .