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In this lesson we’re going to cover Diabetes Insipidus. This is something I’ve seen quite a few times working in the Neuro ICU. Now, this is a bit of a misnomer. It was originally named diabetes because they noticed polyuria and polydipsia, which are signs of diabetes mellitus. But, Insipidus actually means “undefined” – so they weren’t sure exactly what was going on, just that it was similar. But now we know it has nothing to do with blood sugar at all.
Diabetes Insipidus is actually caused by decreased action of antidiuretic hormone. Remember that diuresis means to urinate, anti means no, so antidiuretic hormone makes you not pee, or it makes the kidneys retain water. In Diabetes Insipidus, something is causing decreased antidiuretic hormone – either hyposecretion by the pituitary gland, which sits at the base of the brain here. Or it could be that the body just isn’t responding to the ADH anymore. Either way we have a LACK of ADH action. So instead of retaining water, the patient will begin losing excessive amounts of water in their urine. This is extreme, guys. They could put out anywhere from 4 to 30 liters of urine in one day. That leads to excessive dehydration and volume depletion. Usually this is neurogenic – something is usually going on in the brain like a stroke or a tumor. Both of these things could cause swelling and put pressure on the pituitary gland. It could also be caused by infection or pituitary surgery. There’s actually a surgery that we see quite often in the Neuro ICU where they actually go through the nose and remove the pituitary gland. It’s called a transsphenoidal hypophysectomy. Obviously if we were to remove the pituitary gland, we wouldn’t get enough secretion, right?
So we begin to see this excessive diuresis. The kidneys can’t hold onto the water and they just dump water like crazy. Patients will put out extreme amounts of urine and it’s very dilute. It’s nearly like water. So we’ll see a urine specific gravity of less than 1.006. When it comes to specific gravity, water is 1.0, and urine is normally around 1.010 to 1.025. So the lower that number gets, the more dilute and like water it is. With all that water loss, patients will also be very thirsty. This is where it began to mimic Diabetes Mellitus. Because of the excessive water loss, we see a decreased intravascular volume so the patient gets very hypotensive. And if you remember from the hemodynamics lesson, when the blood pressure goes down, the heart rate goes up to compensate, so we see tachycardia. Now, remember the kidneys are dumping tons and tons of water. So the blood becomes very concentrated and the patient’s sodium level will be extremely high. This can put the patient at risk for seizures and other neuro complications because of the severe cellular dehydration. They may be lethargic, or even comatose. Again, this may also have a neurogenic source, so you could see symptoms of that as well.
So, how do we manage Diabetes Insipidus. Well we want to replace the lost volume. Except in this case we are replacing water loss. So we want them to drink Free Water. This means plain, regular water – no tea or juice or soda – just water. If they can’t take PO, we could insert an NG tube and give them free water flushes that way, or we could replace the water in the IV. We can’t give straight water in the IV, so we give D5W, this is 5% Dextrose in Water. Once it’s in the body, the dextrose gets used up and it is essentially like giving them water. We can also replace some of the hormones they have lost. One option is DDAVP or Desmopressin – this is a synthetic form of ADH and can help improve ADH levels and stop diuresis. The other is vasopressin, which also mimics ADH and is a potent vasoactive drug. We usually give this in the ICU in the form of a titrated IV infusion, whereas the DDAVP can be given PO. We need to monitor their urine output and specific gravity every hour and report any hourly output above 200 to the provider. We keep a really close eye on the specific gravity during treatment so we can see if the kidneys are able to concentrate urine like they should. And of course we monitor their weight daily. We have to make sure we use the same scale, same clothes or linens, same time every day so we can be consistent. Remember that 1 kg of body weight equals 1 liter of fluid, so we need to keep a close eye on the weight.
So, this is probably relatively obvious, but our priority nursing concepts for a patient with Diabetes Insipidus are fluid & electrolytes, hormone regulation, and intracranial regulation. We need to monitor their electrolytes and replace water and hormones. And remember this is not only likely a neurological issue, but that hypernatremia and cellular dehydration can cause seizures or neuro changes, so we want to watch that as well. Make sure you check out the care plan attached to this lesson to see more detailed nursing interventions and rationales.
So let’s recap. Diabetes Insipidus is a decreased secretion of antidiuretic hormone from the posterior pituitary gland. It could be caused by some sort of neurological issue or by surgery or removal of the pituitary gland. It leads to excessive diuresis and water loss, which causes very dilute urine, hypernatremia and cellular dehydration. We want to replace that free water and replace hormones with meds like Vasopressin or DDAVP. And we want to make sure we maintain strict intake and output and measure their urine output and specific gravity regularly.
So those are the basics of Diabetes Insipidus. You’ll see that SIADH is the exact opposite of this, so make sure you check out that lesson as well. Now, go out and be your best selves today. And, as always, happy nursing!