SIADH: Diagnosis and Treatment

by Carlo Raj, MD

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    00:01 Let’s talk further about SIADH.

    00:03 History and physical for sure; findings, here you go.

    00:07 Euvolemic patient, what does that mean? What’s eu- mean, the prefix? It means normal.

    00:13 You’ve heard of euthyroid, here we have euvolemia, what does that mean? Even though you know for a fact your patient has, for whatever reason, increased ADH functioning, you’re going to reabsorb more water from the collecting duct and one would think that your patient, for sure, has pitting edema.

    00:32 Nope, because how much sodium would you have in your interstitium compared to a patient who has right-sided heart failure and strictly transudate? Decreased sodium and SIADH.

    00:45 Your patient is not going to present with pitting edema or significant pitting edema.

    00:52 Serum sodium levels and plasma osmolarity, ridiculously low.

    00:57 What about urine osmolarity? High.

    01:04 Plasma osmolarity? Low.

    01:07 Urine sodium? Low...

    01:11 Low BUN, serum uric acid, everything is being diluted, diluted, diluted.

    01:19 Now, at the very bottom of this, it’s important, SIADH cannot be diagnosed without excluding hypothyroidism and adrenal insufficiency.

    01:30 Once again, keep in mind that whenever you are dealing with ADH, other endocrine dysfunctions, especially thyroid and the adrenals, are important for you to make sure that you rule out.

    01:44 What do you want to do? Always come to the underlying cause.

    01:50 If your issue was a lung cancer, completely different steps of management.

    01:55 If your patient was on drugs, which is carbamezapine, obviously remove the offending agent.

    02:02 Whatever it may be, you want to keep things in mind, pulmonary disease and treatment, cessation of drugs, hormonal replacement and adrenal insufficiency or even perhaps hypothyroidism.

    02:12 Things...

    02:13 These are things that you are paying attention to when dealing with SIADH.

    02:17 Restrict free water intake.

    02:19 Here, once again, caution must be exercised with patients with SIADH secondary to subarachnoid haemorrhage due to exacerbation of the vasospasms and infarction from the drop in blood pressure.

    02:33 Keep that in mind.

    02:34 So, if your patient, extremely important clinical point, is the fact that if there is going to be head trauma and it’s due to subarachnoid haemorrhage, be very, very careful because if there is going to be ADH and vasospasm, it only makes matters worst up in the brain.

    02:54 That’s a huge clinical point that you can use for every single board that is ever presented to you.

    03:02 Restrict your free water intake please with SIADH, your patient is already extremely hypervolemic.

    03:10 Let’s talk about the use of IV saline and SIADH.

    03:15 The first thing you’re thinking to yourself, “Dr. Raj, you just said your patient is hypervolemic, you said-you said restrict free water intake.” That is correct.

    03:25 Free water is not sodium, is it? No, it’s free water.

    03:30 If your patient’s hypervolemic and already is reabsorbing too much water, why would you want to give more free water? So, that does not help you with management.

    03:40 Now, that free water that you are reabsorbing from the collecting duct, does what to sodium? Hyponatremia.

    03:51 You want to make sure that you replenish the sodium.

    03:55 What’s IV saline? Oh, Na, here you go… sea of-sea of IV saline.

    04:01 Now, if you want to... objective is to increase the sodium concentration, what you want to keep in mind for your board exam is the following that electrolyte concentration of fluid given must exceed the electrolyte concentration of the urine and not simply the plasma because here the plasma is not going to be a proper indicator as to how much sodium is actually in your patient, but if you’re able to measure your sodium urine or urine sodium then that is what is going to be your actual control or your measurement.

    04:36 IV saline, why? Because your patient is hyponatremic.

    04:41 However, the only thing that you want to worry is the fact with any time you’re giving IV saline, whatever the indication may be, dehydration, maybe SIADH, so and so forth, is that you never give it rapidly because if doing so then you’re always worried about an interesting side effect, but nonetheless, incredibly significant called central pontine myelinolysis.

    05:03 SIADH pharmacologically… high salt in conjunction with loop diuretic.

    05:08 Remember, you are trying to get rid of this.

    05:10 Now, is all the loop diuretic going to be effective? Well, it all depends, but sodium is going to be incredibly important.

    05:18 Vasopressin receptor antagonists is what you’re thinking about here.

    05:23 Why? Because there’s too much SIADH, we’ll talk about these in a second, and you have a particular V2 receptor blocker known as conivaptan and this is then given as IV only, V2 receptor blocker.

    05:39 Pharmacologically speaking, with vaptan as being a V2 receptor blocker, we have an oral analog known as tolvaptan and interesting enough, you have demeclocycline and lithium.

    05:55 Stop here for one second.

    05:56 The boards will ask you the following.

    05:58 Here’s a-Here’s a patient that requires demeclocycline, here is a patient that is bipolar taking lithium.

    06:03 This, ladies and gentlemen, will bring about nephrogenic diabetes insipidus that we do know.

    06:11 Now, your patient has SIADH and the patient with SIADH where there’s too much V2 receptor activity, wouldn’t you want to then induce nephrogenic diabetes insipidus? And that’s the thinking that you must have here when dealing with demeclocycline and lithium.

    06:31 Antagonize ADH in action and can be used in a rare patient who cannot be treated with vaptan the drugs mentioned above.

    06:42 Steps of management… restrict free water intake.

    06:47 IV saline is important so that you...

    06:50 replenishes sodium.

    06:51 Get rid of that fluid if you’re thinking about loop diuretic, but once again keep in mind of the sodium levels.

    06:57 V2 receptor blockers and these are your vaptan drugs: conivaptan, IV, tolvaptan, your PO oral.

    07:07 If these are refractory, then you start thinking about drugs such as demeclocycline and lithium.

    About the Lecture

    The lecture SIADH: Diagnosis and Treatment by Carlo Raj, MD is from the course Pituitary Gland Disorders.

    Included Quiz Questions

    1. Euvolemia, low plasma osmolarity, low serum sodium
    2. Euvolemia, high plasma osmolarity, low serum sodium
    3. Hypovolemia, low plasma osmolarity, low serum sodium
    4. Hypovolemia, low plasma osmolarity, high serum sodium
    5. Hypervolemia, low plasma osmolarity, low serum sodium
    1. Hypothyroidism
    2. Diabetes mellitus
    3. Adrenal hyperplasia
    4. Sheehan's syndrome
    5. Hyperparathyroidism
    1. Electrolyte concentration of administered fluid is less than that of the plasma.
    2. Free water intake is restricted.
    3. Intravenous saline, if indicated, is administered gradually to avoid central pontine myelinolysis.
    4. Electrolyte concentration of administered fluid is greater than that of the urine.
    5. Hypertonic saline is rarely indicated.
    1. It diminishes the responsiveness to antidiuretic hormone.
    2. It increases the secretion of antidiuretic hormone.
    3. It increases the responsiveness to antidiuretic hormone.
    4. It diminishes the secretion of antidiuretic hormone.
    5. It increases reabsorption of sodium from the distal convoluted tubules.

    Author of lecture SIADH: Diagnosis and Treatment

     Carlo Raj, MD

    Carlo Raj, MD

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