Can you spot SIADH?

Syndrome of inappropriate antidiuretic
hormone secretion (SIADH) occurs when
there’s a continuous, inappropriate action
or excessive secretion of antidiuretic hor

mone (ADH), specifically the hormone
arginine vasopressin (AVP), which is pro

duced in the hypothalamus and secreted
by the posterior pituitary gland. AVP
controls the conservation and release of
water in the body. SIADH occurs even in
the presence of an increased or normal
plasma volume and results in hypo

osmolality and hyponatremia (blood se

rum sodium levels less than 135 mEq/L).
In SIADH, hyponatremia isn’t the result
of a sodium deficiency; rather, it’s caused
by an excess of water.


SIADH is often thought of as a manifes

tation of another disease or condition, as
a symptom rather than a cause. SIADH is
associated with diseases/conditions that
affect the osmoreceptors of the hypothal

amus, which detect changes in osmotic
pressure. These osmoreceptors cause an
afferent neurologic signal to be sent to
the hypothalamus, which then triggers re

lease of ADH from the posterior pituitary
gland to regulate blood concentration
(see Understanding SIADH).

According to the Mayo Clinic, causes
of SIADH include medications, such as
hydrochlorothiazide, methotrexate, cip

rofloxacin, cisplatin, haloperidol, and
amphetamines; central nervous system
disturbances; cancers/tumors; lung dis

eases; surgical procedures, such as for
traumatic brain injury and exploratory
laparotomy; HIV/AIDS; and congestive
heart failure (CHF).

SIADH in children occurs due to water
imbalance caused by medication admin

istration, such as chemotherapy; brain
tumors; or fluid imbalances.


SIADH is the leading cause of hypona

tremia in hospitals, with approximately
one-third of all hyponatremia cases being
directly attributed to it.

Complications of SIADH are related
to the magnitude and rate of hyponatre

mia development. Onset can be acute,
develop in less than 48 hours, and lead
to potentially life-threatening complica

tions. However, if hyponatremia is chron

ic and has developed slowly over many
days or weeks, complications are often
subtle and can be easily overlooked.
Whether acute or chronic, hyponatremia
is a serious electrolyte imbalance that
studies show leads to increased morbid

ity and mortality both inside the hospital
and out.

July/August 2018 Nursing made Incredibly Easy! 21

patho puzzlerCopyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
Mild complications generally associ

ated with chronic SIADH and a serum
sodium level of greater than 125 mEq/L

memory problems
muscle cramps
weight gain
decreased urine output.
Severe complications of SIADH are
more often associated with an acute onset
of hyponatremia and a serum sodium level
of less than 120 mEq/L. These complica

tions are more advanced and related to
systemic water intoxication. Neurologic
complications develop because of osmoti

cally induced cerebral edema. Monitoring
for cardiac and pulmonary complications
is essential because vascular congestion

Understanding SIADH
Source: Nurse’s 5-Minute Clinical Consult: Diseases. Philadelphia: PA: Lippincott
Williams & Wilkins; 2006.
fluid shift
Increased renal tubule permeability
Excessive ADH secretion
filtration rate
Increased water retention and expanded extracellular fluid volume
Decreased sodium
reabsorption in
proximal tubule

stresses both the heart and lungs. In severe
SIADH, complications can include:

cerebral edema, leading to brain

noncardiogenic pulmonary edema

The diagnosis of SIADH can be challeng

ing because there’s no single definitive
test for it. Often, SIADH will be first
suspected due to abnormally low serum
sodium levels discovered during routine
blood chemistry for another condition.
Note that patients with serum sodium
levels below 120 mEq/L are at a high
risk for seizures. Although hyponatre

mia can be found in nearly all patients
with SIADH, a low serum sodium level
isn’t sufficient to act as a positive test for
SIADH. The primary reason for this is be

cause other common conditions can lead
to hyponatremia, such as gastrointestinal
illness (with corresponding vomiting and
diarrhea) and adrenal insufficiency.

Uric acid levels can be used as a gen

eral indicator. SIADH will often cause
uric acid levels to be low. This presents
in around 70% of SIADH cases, whereas
patients with salt depletion present in
around 40% of cases.

A reliable way to test whether a patient
meets the basic criteria to be considered for
SIADH is to perform these three checks:

Is the patient hyponatremic (serum
sodium level less than 135 mEq/L)?

Does the patient present with hypo
osmolality (less than 280 mOsm/kg)?

Is urine osmolality high?
If these three conditions are met, then
the distal nephrons are being acted on by
AVP. Although this is helpful, it doesn’t
indicate if AVP is being secreted inappro

priately, as may be the case with patients
with cirrhosis or CHF.

22 Nursing made Incredibly Easy! July/August 2018

Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.Some of the tests for SIADH fall into
the category of positive test by negative
finding. An example of this is when the
patient’s clinical assessment offers find

ings that don’t support decreased effec

tive intravascular volume, yet the patient
presents with hyponatremia. One simple
way to begin to isolate what’s happening
and why is to put the patient on a sodium
restriction. Patients who have SIADH will
continue to excrete sodium in their urine
that’s less than maximally dilute, regard

less of dietary restrictions.

Unfortunately, imaging still doesn’t
have a lot to offer in the way of diagnostic
tools. It’s more typically used to confirm
the existence of underlying conditions
that may cause the release of AVP, such
as CHF, or identify conditions caused by
hyponatremia secondary to SIADH, such
as hydrocephalus.


Supportive care for SIADH is determined
by a multitude of factors. Treatment is
based on:

patient health and tolerance to therapy
or medications

determination as chronic (unknown du
ration) or acute (less than 48 hours)

degree of hyponatremia (mild, moder
ate, or severe)

presentation as symptomatic or

lab values for urine osmolality and cre
atinine clearance.

Because SIADH may be the result of an
underlying cause, initial treatment may
include either addressing the primary
medical condition or adjusting or discon

tinuing current medications in the event
of a drug-induced condition. Otherwise,
hyponatremia is corrected by reduc

ing fluid retention and avoiding further
buildup by limiting fluid intake.

Fluid intake may be restricted to 500
to 1,500 mL/day. Calculations must con

sider all intake, including oral, I.V., and
metabolic production in comparison to

Signs and symptoms

Weight gain

Change in LOC
Muscle weakness and cramping
Muscle twitching
Decreased urination
water loss through urine, stool, skin,
and respiration. A rise in serum sodium
concentration is expected. However, this
nonpharmacologic approach can be dif

ficult for patients to adhere to. Taking a
daily weight measurement is important,
as is rigorous measurements of intake and

Pharmacologic approaches include 3%
sodium chloride solution, loop diuretics,
urea, demeclocycline, lithium, conivaptan,
and tolvaptan. Sodium chloride solution
administration must be closely moni

tored due to the possibility of pulmonary
edema. The loop diuretic furosemide may
be administered with 3% sodium chloride
solution to avoid edema or as a stand-alone
treatment. Note that the effectiveness of
lithium can be unreliable and may result
in renal toxicity. Adverse reactions of
conivaptan include hypotension, elevated
blood urea nitrogen, increased thirst, and
infusion-site reactions. Adverse reactions
of tolvaptan may include increased thirst,
dry mouth, and urinary frequency, along
with reports of constipation, nausea, diz

ziness, weakness, hyperglycemia, and
urinary tract infection.

Continuous venovenous hemofiltra

tion and sustained low-efficiency daily
dialysis are invasive procedures used in
the case of exceptional, cardiac-related
July/August 2018 Nursing made Incredibly Easy! 23

Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.patho puzzler
Management of SIADH is focused
on treating symptoms related to hypo

natremia, whether mild, moderate, or
advanced. Correction rates are monitored
closely regardless of treatment due to
the risk of central pontine myelinolysis
(CPM)—the dysfunction of brain cells
caused by the destruction of the myelin
sheath of nerve cells in the central por

tion of the brainstem. This adverse reac

tion can occur in relation to a rapid rise
in serum sodium levels and can lead to
decreased level of consciousness (LOC),
dysphagia, mutism, quadriparesis, and

The key to avoiding CPM is careful
and appropriate correction of the patient’s
hyponatremia based on the degree of
sodium deficiency, whether the patient is
symptomatic, and whether the hypona

tremia is acute or chronic in nature, with
frequent lab testing of serum sodium
levels. In addition to lab testing, frequent
monitoring of the patient’s neurologic sta

tus must be performed to identify changes
as early as possible. Total sodium correc

tion must not exceed 10 mEq in a 24-hour
period, with some authors recommending
an even more conservative rate of 8 mEq in
a 24-hour period.

Accuracy and vigilance

SIADH needs to be accurately diag

nosed and then controlled and moni

tored appropriately. As always, safety is
paramount. Your vigilance is crucial for

patients with this

key points

Nursing considerations
Maintain strict input and output, with daily Children’s Hospital of
weights; fluid restriction of 500 to 1,500 mL/day
Philadelphia. Syndrome
Monitor for urine retention and assess for of inappropriate antidi
uretic hormone secretion

signs and symptoms of dehydration
(SIADH). www.chop.
Perform hourly neurologic checks; assess edu/conditions-diseases/
for changes in LOC

Monitor vital signs and lab values for urine secretion-siadh.
osmolality, creatinine clearance, and blood
Corona G, Giuliani C,
urea nitrogen Verbalis JG, Forti G, Maggi
M, Peri A. Hyponatremia

improvement is associated with a reduced risk of
mortality: evidence from a meta-analysis. PLoS One.

Cuesta M, Thompson CJ. The syndrome of inappropriate
antidiuresis (SIAD). Best Pract Res Clin Endocrinol Metab.

Decaux D, Musch W. Clinical laboratory evaluation of
the syndrome of inappropriate secretion of antidiuretic

Gross P. Clinical management of SIADH. Ther Adv
Endocrinol Metab. 2012;3(2):61-73.

Mayo Clinic. Hyponatremia.

Medline Plus. Central pontine myelinolysis.
Mosby’s Dictionary of Medicine, Nursing, and Health
Professions. 10th ed. St. Louis, MO: Elsevier; 2016.

Mujtaba B, Sarmast AH, Shah NF, Showkat HI, Gupta RP.
Hyponatremia in postoperative patients.


Nardone R, Brigo F, Trinka E. Acute symptomatic sei

zures caused by electrolyte disturbances. J Clin Neurol.

Pfennig CL, Slovis CM. Electrolyte disorders. In: Marx JA,
Hockberger RS, Walls RM, et al., eds. Rosen’s Emergency
Medicine: Concepts and Clinical Practice. 8th ed. St. Louis,
MO: Elsevier; 2014.

Pillai BP, Unnikrishnan AG, Pavithran PV. Syndrome of
inappropriate antidiuretic hormone secretion: revisiting
a classical endocrine disorder. Indian J Endocrinol Metab.
2011;15(suppl 3):S208-S215.

Sahay M, Sahay R. Hyponatremia: a practical approach.
Indian J Endocrinol Metab. 2014;18(6):760-771.

Thomas CP. Syndrome of inappropriate antidiuretic
hormone secretion workup.

University of Rochester Medical Center. Antidiuretic

University of Rochester Medical Center. Syndrome of
inappropriate antidiuretic hormone secretion in children.


Verbalis JG, Goldsmith SR, Greenberg A, et al. Diagnosis,
evaluation, and treatment of hyponatremia: expert
panel recommendations. Am J Med. 2013;126(10 suppl 1):

At Northern Arizona VA Medical Center in Prescott, Ariz., Jean
Brennan is a Geriatrics and Extended Care Clinical Nurse Educator,
Sabra Carpenter is an LPN, Jessica Florence is an RN, Jennifer
Hemphill is a Nurse Manager, Ramona Hicks is a Charge RN, Kim
Rooper is a Nursing Officer of the Day, Jason Sewell is an RN, and
Kimber Wagner-Hines is a Charge RN.

The authors have disclosed no financial relationships related to this


24 Nursing made Incredibly Easy! July/August 2018

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