Fluid and Electrolytes
Kathleen W. Bartlett, MD
August 2, 2007
Pop Quiz
SB is an 18 month old male weighing 11
kg. What would be the appropriate
maintenance IVF and rate for this patient?
Answer: D5 ¼ NS + 20 mEq KCl/L at 42
ml/hour.
Maintenance Fluids
What is the scientific basis for our
administration of IVF?
Is there evidence to support the safety and
efficacy of IVF administration in children?
What are the complications of IVF
administration in children?
Maintenance Requirements
Maintenance fluid and electrolyte needs
stem from basal metabolism.
Metabolism creates two by-products:
– Heat: dissipated through skin and
respiratory tract as “insensible losses”
– Solute: excreted in the urine
Insensible losses contribute 1/3 of fluid
needs, while urinary losses contribute 2/3.
Metabolic Rate
Not directly related to weight
Expressed in units of energy (kcals)
High in newborn period
Low in adults
Transition is not linear
Adults need less fluid per unit of body weight
than infants and children.
Fluid and electrolytes per kcal of basal
metabolism remain constant.
Basal metabolic rate, normal activity and average hospitalized patient
Roberts, K. B. Pediatrics in Review 1999;20:429-430
Copyright ©1999 American Academy of Pediatrics
General Concepts
For each 100 kcals burned, the body
needs
– 100 ml water
– 3 mEq Na
– 2 mEq K
Because we don’t have basal metabolic
rates memorized for various ages, we
have three methods to approximate these
needs for us.
Maintenance Requirements
Caloric Expenditure Method
Body Surface Area Method
Holliday-Segar Method
Maintenance requirements are over 24
hours but do not have to be given evenly
divided over each hour.
Caloric Expenditure Method
Caloric needs are based on resting energy
expenditure (=basal metabolic rate) plus activity
factors
Resting energy expenditure is based on size
Energy needs increase with injury, fever, growth,
etc; these are the “activity factors”
Uses tables to find appropriate REE, then adds
coefficients for activity factors.
Bottom Line: NOT USER FRIENDLY!
Body Surface Area Method
Requires knowledge of height and weight
Then use calculation or table to determine
BSA
Maintenance requirements are about 1500
ml/m2/day
Used exclusively by some pediatric
institutions (e.g. St. Louis Children’s
Hospital)
Holliday-Segar Method
Estimates caloric and fluid needs from
weight alone, for simplicity
Based on computed caloric expenditure in
hospitalized patients.
Can under-estimate fluid needs in fever
and injury
Method we tend to use most commonly
4,2,1 rule
Basal metabolic rate, normal activity and average hospitalized patient
Roberts, K. B. Pediatrics in Review 1999;20:429-430
Copyright ©1999 American Academy of Pediatrics
Holliday-Segar Method
Weight
ml/kg/day
ml/kg/hr
First 10 kg
100
4
Second 10 kg
50
2
Each additional 20
1
kg
e.g. 25 kg
1000+500+100 40+20+5 = 65
=1600 ml/day ml/hr (1560
ml/day)
Glucose
D5 (5% Dextrose) can run safely through a
PIV and maintains euglycemia.
5g glucose per 100 ml
at 3.4 kcals/gram
170 kcals/ liter of D5
– 1600 ml of D5 has only 272 kcals
– only 11 kcal/kg/day
Patients are malnourished when they only
receive IVF!
Electrolytes
Electrolyte Requirements:
– Na = 3 mEq per 100 kcals
= 3 mEq per 100 ml water (or 30 mEq/L)
– K = 2 mEq per 100 kcals
= 2 mEq per 100 ml water (or 20 mEq/L)
Fluid composition:
– NS = 0.9% NaCl = 154 mEq NaCl/L
– ¼ NS = 38.5 mEq NaCl/L
The commercially available fluid that most
closely approximates the electrolyte
requirements for maintenance is D5 ¼ NS + 20
mEq KCl/L.
D5 ¼ NS for infants and D5 ½ NS
for older children and adults?
The sodium concentration should NOT differ:
– Na needs are 3 mEq/100 kcals, not 3 mEq/kg.
– Na needs are not linear; they should decrease like
water needs do.
– Therefore, the ratio of Na to water should remain
constant.
Holliday and Segar argue that D5 ¼ NS with 20
mEq of KCl per liter is an appropriate
maintenance fluid for all people.
The Debate about Sodium
2004 case-control study identified 40
children who developed hyponatremia
while in the hospital.
The patients in the hospital-acquired
hyponatremia group received significantly
more free water than controls.
Hoorn EJ, Geary D, Robb M, Halperin ML, Bohn D. Acute
hyponatremia related to intravenous fluid administration in hospitalized children:
an observational study. Pediatrics. 2004 May;113(5):1279-84.
Why hyponatremia?
ADH (anti-diuretic hormone) increases in
response to stress:
– surgery, pain, fever, nausea, bronchiolitis,
meningitis, pneumonia, CLD, or in response
to certain drugs
When ADH increases, renal solute load is
excreted in a smaller volume of urine.
In this setting hypotonic fluid
administration can lead to free water
overload and hyponatremia.
Why hyponatremia?
Estimating caloric need in illness is difficult – it
could be much less than in healthy children.
Insensible losses may have been overestimated.
The authors argue for isotonic fluid (D5NS) as
the maintenance fluid for post-op pts and when
Na < 138.
Other authors have advocated isotonic fluid for
all patients.
Where is the evidence?
2006 systematic review found 6 studies comparing
isotonic to hypotonic fluid for hospitalized children.
– 3 observational studies, 2 “unmasked” RCTs, and one nonrandomized, controlled trial.
– 4 studies done in post-op surgical patients, 1 in patients with
gastroenteritis, and 1 case-control.
Hypotonic IVF increased the odds of developing serum
Na < 136 (OR 17.22; 95% CI 8.67 to 34.2).
Greater patient morbidity in hyponatremia group
(seizures, pulmonary edema, nausea/vomiting)
Studies poorly designed and heterogeneous, making
bias possible.
Authors recommend isotonic fluids as “more
physiological, and therefore a safer choice.”
Choong K, et al. Hypotonic versus isotonic saline in hospitalised children: a
systematic review. Arch Dis Child. 2006 Oct;91(10):828-35.
Problems with isotonic fluid for
maintenance
May lead to excessive sodium loading in
patients with cardiac or renal disease (not
observed in any of studies included in
systematic review).
Does not treat SIADH (fluid restriction
more appropriate).
Does not correct hypovolemia which may
be causing appropriate ADH secretion.
Holliday MA; Friedman AL; Segar WE; Chesney R; Finberg L. Acute hospital-induced
hyponatremia in children: a physiologic approach. J Pediatr 2004 Nov;145(5):584-7.
Conclusion about sodium
Iatrogenic hyponatremia is a real and
preventable medical error.
Do not use maintenance fluids to replace
deficits (i.e. giving a patient 2 x MIVF).
Giving a bolus of isotonic solution in
volume-depleted children may decrease
ADH secretion.
However, isotonic fluid will not prevent
hyponatremia in patients with SIADH.
Conclusion about sodium
For now continue to use Holliday-Segar method
for maintenance fluid while
– Following serum sodium
– Being mindful of situations that lead to increased
ADH.
“…no one fluid rate or composition is suitable for
all patients, and the administration of any
intravenous fluid should be considered an
invasive procedure, requiring close monitoring.”
Moritz MJ, Ayers JC. “Hospital acquired hyponatremia: why are there still deaths
[commentary]? Pediatrics. 2004;113:1395-96.
Dehydration
Diarrhea
Acute gastroenteritis is common in children.
Average of 1.3-2.3 episodes of diarrhea per child
per year for children younger than 5 in the U.S.
1.5 million pediatric office visits
>200,000 hospitalizations
300 preventable deaths
Rotavirus is most common cause (1/3 of all
hospitalizations) and costs $250 million per year
in direct medical costs.
Dehydration
Assessment of dehydration
Initial resuscitation
Determining deficit
Adding in maintenance
Ongoing losses
Assessment of dehydration
Recent weight changes (gold standard)
Physical exam findings
Dehydration
Mild (5%)
Moderate (10%)
Severe (15%)
Turgor
Normal
Tenting
None
Cap Refill
Brisk (<2 secs)
2-4 seconds
>4 seconds
Mucous membranes
Moist
Dry
Parched/cracked
Eyes
Normal
Deep set
Sunken
Tears
Present
Reduced
None
Fontanel
Flat
CNS
Consolable
Irritable
Lethargic/Obtunded
Pulse
Regular
Slightly increased
Increased
Urine output
Normal
Decreased
Anuric
Sunken
Is this child dehydrated?
Systematic review of the published data on
history, PE, and labs in dehydration revealed:
– Poor to moderate inter-observer agreement
– History and parental report have limited value
– Best individual tests
Prolonged capillary refill
Abnormal skin turgor
Abnormal respirations
– Groups of positive signs are most helpful
– Extremely abnormal lab tests are helpful
Steiner MJ, DeWalt DA, Byerley JS. Is this child dehydrated? JAMA. 2004
Jun 9;291(22):2746-54.
Conclusions
Focus on symptoms and signs with proven
utility.
Ability to estimate exact degree of
dehydration is limited.
Support change to “none (<3%), some (39%), or severe (>9%)” classification
method recommended by CDC and WHO.
WHO assessment of
dehydration
King CK, Glass R, Bresee JS, Duggan C. Managing acute gastroenteritis among
young children. MMWR. November 21, 2003/52 (RR16):1-16.
Fluid management in shock
Initial boluses of 10 - 20 ml/kg given quickly
– 20 ml/kg is 2% of body weight – therefore it should
reduce 10% dehydration to 8% dehydration.
– One bolus is not enough to replace a deficit when
someone is dehydrated.
– Reassessment is key!
Use isotonic solutions (NS, LR)
Consider blood, other fluids and/or pressors in
special circumstances
– Trauma or blood loss, nephrotic syndrome, septic and
cardiogenic shock
Fluid Composition
Fluid
CHO
KCal/L Na
5
170
K
Cl
CO3
Ca
28
3
g/100cc
D5W
154
NS
154
(0.9%
NaCl)
LR
0-10
0-340 130
4
109
IV Rehydration
First resuscitate out of shock – restore perfusion
Calculate maintenance, including ongoing
losses, and deficit
Run maintenance as usual
Replace ongoing losses
Typically replace deficit over 24 hours
– Half in first 8 hours
– Other half over 16 hours
Replacement should be done in relation to the
rate that the loss occurred
Where the deficit is coming from—
the traditional teaching
For a brief duration of illness (<3 days),
80% of the deficit is from the extracellular
fluid space (ECF)
After more than 3 days of illness, the
deficit from the ICF increases to about
40% (therefore 60% from ECF)
ECF contains a lot of Na (135-145 mEq);
ICF contains a lot of K (150 mEq)
Case # 1
JW is a previously healthy 6 mo male who
presents with a 4-day history of low-grade fever,
vomiting and diarrhea. He has been unable to
tolerate PO. Mom reports that he has lost 1 ½
lbs since his well-child check last week.
On exam, he weighs 7 kg. He is mildly
tachycardic and tachypneic. He is listless. He
has a slightly sunken fontanelle, dry mucous
membranes and delayed CR (~3 secs).
Example Calculations, normal Na
7 kg infant with 10% dehydration that accumulated over >3d.
24 Hours
H2O
Na
K
Maintenance
(Hol.-Seg.)
700
21
14
Deficit
(8% of 7 kg)
560
ECF (60%)
336
ICF (40%)
224
Total
49
(145 MEq/L
x 0.336 L)
34
(150 MEq/L x
0.224 L)
1260ml 70mEq 48 mEq
First 8 hours
MIVF for the first 8 hours + 50% of the deficit
1/
3
Maint
½ Deficit
Total
H2O
Na
K
233
7
5
280
513
24
31
17
22
513/8 =
64 ml/hr
31/0.513= 22/0.513=
60 mEq
43 mEq
Na/L
K/L
Roughly D5 ½ NS (77 mEq/L) + 40 mEq KCl/L at 64 ml/hr
Next 16 hours
MIVF for 16 hours + other 50% of the deficit.
H2O
Na
K
467
14
9
½ Deficit
280
24
17
Total
747
38
26
747/16=
47 ml/hr
38/0.747= 26/0.747=
51 mEq/L 35 mEq/L
2/
3 Maint
Roughly D5 ¼ NS (38.5 mEq/L) + 30 mEq KCl/L at 47 ml/hr
Simplified – fluid choice, normal Na
(Roberts’ method)
Usually after boluses with NS or LR, D5 ½ NS is
an appropriate rehydration fluid
After urine output is assured, give K as 20
MEq/L
– That is usually safe
– Often you don’t need to fully replete K losses acutely
– Watch the rate of fluids regarding K and don’t give
more than 1 mEq/kg/hr
Roberts, KB. Fluid and electrolytes: parenteral fluid therapy. Pedatr. Rev.
2001;22:380-387.
Simplified Rate (Roberts’ method)
If a child is 10% dehydrated:
Give a 20 ml/kg bolus of NS
– Restores hydration 2%
Next give 10 ml/kg/hr of D5 ½ NS with 20 KCl
for 8 hours
– Restores hydration 8%
Next give 1.5 times MIVF using D5 ¼ NS with
20 KCl for 16 hours
– The whole day’s maintenance
Case #1 using Roberts’ Method
7 kg child with 10% dehydration
Bolus of 140 ml NS
70 ml/hr of D5 ½ NS with 20 KCL for 8
hours, then
40 ml/hr of D5 ¼ NS with 20 KCL for 16
hours
Hyponatremia
Hyponatremic patients appear more dehydrated
than they are.
Risk of rapid correction is central pontine
myelinolysis.
Correct the Na fast only if the patient is
symptomatic (seizing or particularly irritable)
For asymptomatic patients, the goal should be to
increase the Na no faster than 1 mEq/L per hour.
Now suppose JW has Na=115
Fluid deficit is the same.
Na deficit from dehydration is the same.
K deficit is the same.
Excess Na deficit:
– (Desired Na – Actual Na) x distribution factor x wt
– (135-115) mEq Na/L x 0.6 L/kg x 7 kg = 84 mEq Na
Make a table!
Component

Maintenance Na=3mEq/100ml

K=2mEq/100ml
Deficit
60% ECF x 700
= 420
40% ICF x 700 =
280
Excess Na
(135-115) x .6 x
deficit
7kg
24 hour
totals
H2O
(mL)
700
Na
(mEq)
21
K
(mEq)
14
700
61
42
84
1400
166
56
First 8 hours—hyponatremia
MIVF for the first 8 hours + 50% of the deficit
1/
3
Maint
½ Deficit
Total
H2O
Na
K
233
7
5
350
583
72
80
21
26
583/8 =
73 ml/hr
80/0.583= 26/0.583=
137 mEq 45 mEq
Na/L
K/L
Roughly D5 ½ NS (77 mEq/L) + 40 mEq KCl/L at 73 ml/hr
Next 16 hours
MIVF for 16 hours + other 50% of the deficit.
H2O
Na
K
467
14
9
½ Deficit
350
72
21
Total
817
86
30
817/16=
51 ml/hr
86/0.817= 30/0.817=
105 mEq/L 37 mEq/L
2/
3 Maint
Roughly D5 ½ NS (77 mEq/L) + 30 mEq KCl/L at 51 ml/hr
Hypernatremia
Hypernatremic patients may appear less
dehydrated than they really are.
In hypernatremia, rehydrate more slowly to
avoid fluid shifts that could cause cerebral
edema or intracranial bleeding
The hypernatremic dehydrated patient is still
total body sodium depleted, but in addition has
lost free water
Free water losses must be calculated and
subtracted from total deficit to calculate the
solute deficit.
Now JW has Na=155
Same fluid deficit and maintenance requirements
FW deficit= [Na]actual – [Na]desired x 1000 ml/L x 0.6L/kg = ml/kg
[Na]actual
FW deficit= (155-145) ÷ 155 x 0.6 L/kg x 7 kg= 0.270 L
Replace free water deficit evenly over 48 h
– Give only half of deficit in first 24 hours.
Subtract the free water deficit from the total deficit when
calculating Na and K deficits from dehydration.
Decrease Na by less than 15 MEq/L/day
Follow electrolytes closely
Table for Hypernatremia, first 24 h
H2O
Na
K
MIVF
700
21
14
Free water
deficit =
270cc/2 days
135
Def remaining
(solute) =420cc
(700-270=430)
ECF (60%)
ICF (40%)
Total, 24 hr
258
172
37
1265
58
27
41
Fluid Choice—hypernatremia
1265 ml/ 24 hours = 53 ml/ hr
58/1.265 = 46 mEq/L Na
41/1.265 = 32 mEq/l K
Roughly D5 ½ NS with 30 KCl at 53 ml/hr –
Could also use D5 ¼ NS (half is more
conservative)
Practical approach to
hypernatremia
Still bolus the hypernatremic patient with
NS if needed.
To lower the Na slowly, start with D5 ½ NS
and remeasure.
The calculations almost always come out
to something near ¼ NS, so that is also a
reasonable starting point.
The important thing is to follow the sodium
carefully and adjust as necessary.
Conclusions
Intravenous fluid is very important therapy, but a
frequent source of medical error.
Think about isotonic maintenance fluids in
patients at risk for SIADH.
Treat hypovolemia carefully—do not just
increase the rate of maintenance fluids.
Hyponatremia and hyponatremia require extra
caution with fluid calculations.
Reassess frequently and follow electrolytes.