Download Clinical update no. 424 15 October 2015

Clinical update no. 424
15 October 2015
From N Engl J Med: A 72-year-old man with
long-standing heart failure and ischaemic
heart disease is admitted to the hospital.
Management has been a low-sodium diet,
enalapril 2.5 mg bd, carvedilol 6.25 mg bd,
hydrochlorothiazide 25 mg bd. He is 70kg,
with a 2kg weight gain from a clinic visit the
previous week.
He has been more short of breath with a
cough. Temp 38.3 C, BP 122/78, HR 78, RR
32. Examination findings are posterior rhales
IV fluids are isotonic or hypotonic based on
the Na and K concentration. Dextrose is
metabolised and does not affect tonicity.
on the right, with no wheeze or rhonchi. There
Giving hypotonic maintenance IV fluids is
is no peripheral oedema or visceromegally.
associated with hyponatraemia. There are
Na 133, K 3.3, Cl 94, pCO2 30, creatinine 145
(eGFR 42). CXR shows right lower lobe
pneumonia and IV antibiotics are given.
over 100 reports of iatrogenic deaths or
permanent neurologic impairment from
hyponatraemic encephalopathy. Acutely ill
patients may have excess antidiuretic
What is the best strategy for maintenance
hormone (ADH; or AVP) which impairs
intravenous fluids to support this patient?
excretion of free water.
Rapid volume expansion with 0.9% saline as
compared with balanced electrolyte solutions
Options given included: oral fluids, IV saline at
may result in complications.
60 or 80 ml/hr, 0.45% saline, K replacement
and changing the diuretic to spirinolactone.
See the full text for details and other useful
clinical scenarios on fluid replacement.
The safest maintenance fluid is 5% dextrose
in 0.9% saline at 100 - 120 ml/hr in adults.
In children the calculation is 100 ml/kg/24
hours for the first 10 kg of body weight, plus
The risk is for more severe hyponatraemia
and fluid overload, with CCF and renal
50 ml/kg between 10-20kg, plus 20 ml/kg
above 20 kg.
impairment. Dosing adjustments for
Hypotonic fluids should be administered only if
antibiotics and other medications is required.
there is a specific indication (such as renal
Tachypnoea at rest with a risk of tiring makes
H2O loss in diabetes insipidus), and they
giving oral fluids unwise. IV fluid with 5%
should be avoided if hyponatraemia is
dextrose in a solution of 0.9% saline plus 20
present. In patients at risk for cerebral
mmol KCL/litre at 60 ml/hr (75%
oedema, Na should be kept at >140 mmol/kg.
maintenance) would be appropriate. Avoid
hypotonic fluids. Adjust for the volume given
with IV medications. Risk of further renal
Virtually all studies evaluating hospital-
impairment and hyperkalaemia with the ACE
acquired hyponatraemia have shown that it is
inhibitor is a concern which could be
related to giving hypotonic fluids. Hypotonic
exacerbated by changing to a potassium
fluids should not be given to children.
sparing diuretic.
Available at http://www.heti.nsw.gov.au/programs/emergency-medicine-training/emergencymedicine-training-test/educational-resources/em-clinical-updates/
Early symptoms of hyponatraemic
rise in serum Na if given for hyponatraemia
encephalopathy are headache, nausea,
from SIADH, where the correct approach is
vomiting, and generalized weakness,
fluid restriction.
progressing to seizures and pulmonary
oedema which can be of abrupt onset. Chronic
hyponatraemia can give subtle neurologic
impairment with gait disturbances and falls. It
can be difficult to correct with fluid restriction
and isotonic fluids are relatively ineffective.
Balanced Salt Solutions as Compared
with 0.9% Saline 0.9% saline has a nonphysiological chloride concentration, and a low
pH when packed in plastic bags but not glass.
Large volumes may lead to hyperchloraemic
metabolic acidosis and acute kidney injury.
Alternatives such as Hartmann’s solution
contain calcium and may be incompatible with
blood products and some medications. There
Hypotonic fluids (5% dextrose in 0.18 or
is no ideal balanced solution. Hartmann’s and
0.45% saline) should be avoided.
Plasmalyte may reduce complications from
Water and electrolyte replacement in children
advocating hypotonic fluids is based on
calculations made in the 1950s based on
calorie and energy requirements, are opinion
based, and have no evidence to support them.
The routine practice of giving hypotonic
fluids (Na <130 mmo/L) should be
abandoned for both adults and children.
Nevertheless practice guidelines continue to
recommend hypotonic fluids.
large volumes of 0.9% saline, though the
evidence for that is limted. There are
insufficient data to suggest that 0.9% saline is
unsafe as a maintenance fluid.
Dextrose is provided in maintenance fluids to
limit tissue catabolism, but it does not provide
complete nutritional support. These solutions
can be hyperosmolar nut not hypertonic, since
the dextrose is rapidly metabolized
The default maintenance solution for adults is
5% dextrose in a solution of 0.9% saline
administered at 100-120 ml/hr.
A hypotonic fluid may be required if there is a
Concerns over giving isotonic fluids and the
risk of sodium and fluid overload are not
supported by a large body of evidence.
clinically significant renal concentrating defect
with ongoing free-water losses or to aid in the
correction of established hypernatraemia.
Isotonic fluids were superior for the
Studies evaluating maintenance fluid for
prevention of hyponatraemia. Fluid restriction
oedematous states are lacking.
with hypotonic fluids was not effective in
preventing hyponatraemia.
Isotonic fluids are most appropriate for the
vast majority of hospitalised patients. This
includes children in a range of medical and
A common practice is to add 20 mmol/L of
KCl, but evidence for this is lacking unless
treating hypokalaemia.
Enlarge Table for composition of fluids
postoperative settings.
There needs to be caution with renal disease,
heart failure, and cirrhosis, and studies had
notable exclusions. Isotonic fluids should not
lead to hypernatraemia or fluid overload in
most patients, though volume requirements
should not be exceeded. Giving 0.9% saline
can induce a diuresis and lead to an excessive
Available at http://www.heti.nsw.gov.au/programs/emergency-medicine-training/emergencymedicine-training-test/educational-resources/em-clinical-updates/