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Patient Safety Tip of the Week
July 2, 2024 Iatrogenic
Hyponatremia
Hospital-acquired hyponatremia can be a serious patient
safety issue. There are many causes of hyponatremia and the nature and severity
of symptoms of hyponatremia depend upon the rapidity with which it develops. Rapidly
progressive hyponatremia can lead to confusion, seizures, obtundation, and even
death from cerebral edema. Equally important is appropriate management of
hyponatremia, since too rapid correction can lead to osmotic demyelination
syndrome (formerly known as central pontine myelinolysis) which can have
significant neurological sequalae.
Two recent reports from Canada (ISMP
Canada 2024, Manderville
2024) found that errors in IV fluid management and monitoring were the prime
causes of hospital-acquired hyponatremia in most cases. Unintended IV infusion
of hypotonic fluids is the major culprit. The ISMP Canada article identified
cases where normal saline (alone or in combination with D5W) was ordered but
instead patients were given hypotonic solutions like ½ normal saline or D5W
alone. ISMP Canada notes that the errors were identified by nurses during routine
checks (e.g., when changing an empty IV solution bag, at change of nursing
shift, or when a patient was transferred from another unit), thus preventing harm
in most cases. But there was one incident with the patient experiencing a decreased
level of consciousness, and another incident documented the error as continuing
undetected for 3 days.
ISMP Canada noted the following contributing factors to incidents
in which an isotonic fluid was ordered, but a hypotonic IV fluid was given in
error:
·
incorrect storage of the IV solutions on the IV storage
cart (e.g., D5W½NS with 20 mmol/L KCl stocked where
NS with 20 mmol/L KCl was supposed to be stocked)
·
similar appearance of IV bag labels
·
IV fluid not included in the medication administration
record (MAR)
·
delays in the identification of possible
symptoms of hyponatremia
·
lack of laboratory monitoring that might have identified
the incorrect IV solution sooner
·
challenges in differentiating symptoms of hyponatremia
(e.g., confusion) from other conditions with similar symptoms
Manderville et al. (Manderville
2024) note that labelling of IV solutions may be misleading. The confusion
often revolves around the concepts of “tonicity” and “osmolality”. They
reviewed commonly used IV products used in Canada and the US. They found several
examples of isotonic and hypotonic IV solutions that were designated as
“hypertonic” both in the product monograph and on individual bags of IV fluid.
Of 28 products reviewed, 27 had incorrect information in their respective
monographs, labelling, or both. Of the 18 hypotonic fluids reviewed, 11 (61%)
were incorrectly labelled as “hypertonic” on the IV bag.
Manderville et al. note that tonicity is a property of a solution
with reference to a particular membrane, whereas osmolality is a property of a
solution that is independent of any membrane. Solutes such as dextrose (which
can freely enter the cell under normal conditions) contribute to the osmolality
of a solution, but they do not alter tonicity.
Pediatric patients, postoperative patients, and older adults
are the populations most at risk of hyponatremia due to use of hypotonic IV
fluids. Mandeville et al. note that issues related to antidiuretic hormone
(ADH) are often present in hospitalized patients. They often have risk factors
for non-osmotic release of ADH, including pain, nausea, stress, and certain
medications. In the setting of increased ADH, the free water available in
hypotonic IV solutions can rapidly lead to clinically significant hyponatremia.
The American Academy of Pediatrics and the Canadian Paediatric
Society recommend the use of isotonic IV solutions as the standard for fluid
maintenance in children, with the recognition that hypotonic IV solutions can
be used in specific circumstances but only with careful monitoring. That has
led some pediatric hospitals to restrict hypotonic solutions to only certain
area, like pediatric critical care units.
ISMP Canada has multiple recommendations (for hospital
systems, nurses, and pharmacists):
·
Consider incorporating an alert in CPOE systems
about the risk of acute hyponatremia with hypotonic IV fluids when these are
used for maintenance therapy, especially in pediatric patients.
·
Review the types and quantities of IV solutions
needed in clinical areas to reduce risk of selection errors. For example, the
Canadian Paediatric Society recommends that hypotonic
fluids containing less than ½ NS should not be generally available on pediatric
wards.
·
Ensure mechanisms are in place to check that the
types of IV solutions provided to nursing units are correct (e.g. bar-coding
technology).
·
Unless treating a clinical condition or a
specific fluid or electrolyte disturbance, and provided there are no
contraindications, clinicians should prescribe isotonic IV fluids, to reduce
the risk of hyponatremia. The Canadian Paediatric
Society recommends that D5W 0.9% NaCl (D5W NS) be initiated as the maintenance
fluid when serum electrolyte levels are not yet available. Hypotonic fluids
containing less than 0.45% NaCl should not be used for routine maintenance
fluid therapy.
·
Both the Canadian Paediatric
Society and the American Academy of Pediatrics recommend isotonic fluids for
routine maintenance, with the recognition that in certain specific
circumstances, hypotonic IV solutions may be used, but only with careful
monitoring.
·
Ensure regular electrolyte monitoring.
·
Regularly review the need for IV fluid therapy.
If the patient has adequate oral intake of fluids, medications, nutrients, and
calories, consider deprescribing any unneeded IV infusion. (We like this one.
All too often we continue unnecessary IV fluids, sometimes to satisfy criteria
for continued hospitalization!).
·
If acute hyponatremia is identified, avoid
overly rapid correction. (See our November 23, 2021 Patient Safety Tip of the
Week “The Perils of Hypertonic
Sodium Chloride”).
·
Nursing Teams should ensure the particular IV fluid and rate of infusion are checked against
the MAR and/or nursing care plan at the beginning of each shift.
·
Ensure that any IV fluid administered is
appropriate for the patient’s clinical status.
·
Close monitoring and documentation of vital
signs, serum electrolytes, and the patient’s volume status (intake and output)
are essential in preventing hospital-acquired hyponatremia.
·
For the pediatric population, weight should be
documented daily.
·
Immediately report any critical laboratory
results to the most responsible physician.
·
Pharmacy Teams should confirm a valid indication
and monitor electrolyte results when hypotonic fluids are prescribed for
at-risk patients.
These are just a few select recommendations. See the ISMP
Canada article itself for the full list of recommendations.
The management of acute hyponatremia is beyond the scope of
today’s column. We refer you to the excellent review on diagnosis and
management of hyponatremia by Adrogué et al. (Adrogué
2022). We also refer you to our November 23, 2021 Patient Safety Tip
of the Week “The Perils of Hypertonic
Sodium Chloride” for a discussion on use of hypertonic sodium
chloride.
References:
ISMP Canada. Reducing the Risk of Hospital-Acquired
Hyponatremia:
Intravenous Fluid Management and Monitoring. ISMP Canada
Medication Safety Bulletin 2024; 24(6): 1-6 June 18, 2024
Manderville JR, More KM, Tennankore
K. Misunderstandings about tonicity and osmolality can lead to patient harm.
Can J Hosp Pharm 2023;76(4): 324-326
https://www.cjhp-online.ca/index.php/cjhp/article/view/3417
Adrogué HJ, Tucker BM, Madias NE.
Diagnosis and management of hyponatremia: a review. JAMA 2022; 328(3): 280-291
https://jamanetwork.com/journals/jama/article-abstract/2794358
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