Things have been a little slow at PBFluids as I have been putting my energy into NephJC the Nephrology Twitter Journal Club.
NephJC will do it’s fourth article next Tuesday and it is an article that breaks the mold. Clinical practice guidelines, like review articles and editorials are usually not included in the cannon of journal club. However we want NephJC to expand these horizons in order to tackle any document that may influence nephrology. Clinical practice guidelines probably have more influence over medicine than any single article and because of that they deserve the same critical eye that research articles do.
The Subject of this week’s NephJC is: Clinical practice guideline on diagnosis and treatment of hyponatraemia. It was published in NDT, The European Journal of Endocrinology and Intensive Care Medicine.
We excluded case series that reported on benefit if the number of participants was under 5 but included even individual case reports if they reported an adverse event.
|To interpret the guidelines to come you should major in Grade D, with a minor in Grade C.|
The clinical features of hyponatremia.
Although the more severe signs of acute hyponatraemia are well established, it is now increasingly clear that even patients with chronic hyponatraemia and no apparent symptoms can have subtle clinical abnormalities when analysed in more detail. Such abnormalities include gait disturbances, falls, concentration and cognitive deficits (13). In addition, patients with chronic hyponatraemia more often have osteoporosis and more frequently sustain bone fractures than normonatraemic persons (14, 15, 16). Finally, hyponatraemia is associated with an increased risk of death (17, 18). Whether these are causal associations or merely symptoms of underlying problems such as heart or liver failure remains unclear (19).
I wrote an editorial about that last reference for eAJKD.
There is a little blurb about pseudohyponatremia, despite telling us that this guideline will only cover hypo-osmotic hyponatremia. They point out that despite common opinion that this lab abnormality is no longer a problem that it still continues today:
Pseudohyponatraemia was seen more frequently with flame photometric measurement of serum sodium concentration than it is now with ion-selective electrodes, but despite common opinion to the contrary, it still occurs (30), because all venous blood samples are diluted and a constant distribution between water and the solid phase of serum is assumed when the serum sodium concentration is calculated (30)
Thought the “it still occurs” loses some punch when one references an 11 year old article.
They have a tidy review of the criteria for SIADH:
Interesting discussion on the rarity of hypothyroidism as a cause of hyponatremia. I was taught this as a fellow but had never seen any literature to support this pearl:
Although included in many diagnostic algorithms, hypothyroidism very rarely causes hyponatraemia (49). In 2006, Warner et al. (50) observed that serum sodium concentration decreased by 0.14 mmol/l for every 10 mU/l rise in thyroid-stimulating hormone, indicating that only severe cases of clinically manifest hypothyroidism resulted in clinically important hyponatraemia. Development of hyponatraemia may be related to myxoedema, resulting from a reduction in cardiac output and glomerular filtration rate (51).
Then they have a shout out to icodextrin-based PD fluid inducing hyponatremia. This was on my nephrology recertification boards.
I love this figure explaining how the two stimuli for ADH release, volume status and hyperosmolality, interact:
This is great writing on a subject that can be difficult to express:
Depending on the kidney’s ability to dilute urine, 50–100 mmol of solutes, such as urea and salts, are required to remove 1 l of fluid. If solute intake is low relative to water intake, the number of available osmoles can be insufficient to remove the amount of water ingested.
Guidelines for the diagnosis of the etiology of hyponatremia
Finally on page 17 of the guideline we get the first guideline: The Classification of hyponatremia, they have three different systems for classifying hyponatremia, none of them based on volume status:
|Table 5. What? No hiccups?|
- Biochemical severity
- Mild: Na 130-135
- Moderate: 125-130
- Profound: less than 125
- Acute: duration less than 48 hours
- Chronic: duration at least 48 hours
- Symptom based
- moderately symptomatic (based on Table 5)
- Severely symptomatic (based on Table 5)
Authors mostly use the terms ‘mild’, ‘moderate’ and ‘severe’ (61, 62, 63). We have chosen to replace ‘severe’ by ‘profound’ to avoid confusion with the classification based on symptoms, for which we have reserved the term ‘severe’.
In regards to symptoms, the authors explain that they very specifically excluded a category of asymptomatic:
We have purposefully omitted the category ‘asymptomatic’ as we believed this might create confusion. Patients are probably never truly ‘asymptomatic’ in the strictest sense of the word. Very limited and subclinical signs such as mild concentration deficits are seen even with mild hyponatraemia (13).
The authors defend not using volume status to categorize hyponatremia at least partly due to the pathetic job physicians do at assessing volume status:
We found two studies indicating that in patients with hyponatraemia, clinical assessment of volume status has both low sensitivity (0.5–0.8) and specificity (0.3–0.5) (89, 103). Similarly, it seems that clinicians often misclassify hyponatraemia when using algorithms that start with a clinical assessment of volume status (88). Using an algorithm in which urine osmolality and urine sodium concentration are prioritized over assessment of volume status, physicians in training had a better diagnostic performance than senior physicians who did not use the algorithm (104).
Hard to believe that nephrologists are no better at determining hypovolemia than a coin toss. Incredible.
Another interesting statement was in regards to using the urine osmolality to determine if ADH is present or not, It is clear that ADH is present when the urine osmolality is greater than serum osmolality and it is clear that ADH is absent when urine osmolality is less than 100 mOsm/Kg, but they identify a grey area from a urine osmolality of 100 to a urine osmolality that isotonic where they say one is unable to definitely say there is ADH or not. (refs: Nephron Physiology and Journal of Emergency Medicine) I found myself in that no man’s land in this case.
Urine sodium was examined as a test to separate volume depleted hypovolemia from SIADH. Urine sodium less than 30 was highly sensitive for hypovolemia (0.87-1.0) even in the one series that looked at patients on diuretics separately. However urine sodium has disappointing specificity (i.e. low urine sodium in a patient with SIADH) (0.24 to 0.83).
The authors gave cautious enthusiasm for the fractional excretion of urea less than 12% indicating SIADH. One case series had the FEUrea with a sensitivity of 0.86 and specificity of 1.0.
It is interesting though, that when they made their flow chart, the lack of precision of urine sodium, urine osmolality, physician ability to discriminate volume status are all thrown out the window. Flow charts are loved by students but never allow for the subtle Bayesian realities of clinical medicine.
They use a flow chart to map out when to use the various treatment recommendations. This seems like an intelligent to build what is essentially a table of contents for using the guidelines. Nice job.
Treatment of patients with severe symptoms from hyponatremia:
If they get better:
Never has so much been done by so many to avoid a complication that occurs in so few.
Treatment of patients with moderately severe symptoms from hyponatremia:
Treatment of patients without severe of moderately severe symptoms from hyponatremia:
Treatment of patients with chronic hyponatremia without severe or moderately severe symptoms:
|appendix 1-5 then 7 and then 6. Cause that’s how European’s count.|