FLUID & ELECTROLYTES: PARENTERAL FLUID THERAPY
Can be complex, confusing, even intimidating—but can be mastered if the problem is
dissected
A. There are 3 components of fluid management
1. Maintenance: what we all lose normally and continuously through skin, lungs, stool,
and urine
2. Deficit: the loss incurred prior to the institution of therapy (e.g., from diarrhea for the
past 2 days)
3. Ongoing Losses: loss incurred after the institution of therapy (e.g., continued watery
stools, N-G drainage)
B. For each component,
1. First decide AMOUNT of fluid (water)
2. Then COMPOSITION (electrolytes)
1
MAINTENANCE
A. The Basics
What maintenance is: Providing fluid used up during basal metabolism
What maintenance is not: Replacement of a deficit or on-going losses (maintenance
does NOT rehydrate a child). So “2-times maintenance” is not a valid replacement
strategy
Fundamental question: Why do we need fluid to maintain homeostasis? To replace the
water used to eliminate the 2 by-products of metabolism: “heat” and “waste.” (Explains
why fluid needs are based on metabolic rate, rather than directly on weight.)
1. “Heat” (accounts for roughly half (50%) of maintenance fluids)
a. Lose heat by evaporation from skin (different from active sweating, which implies
an increased heat burden to be dissipated). These are “insensible losses” in that
you do not feel the loss of fluid as you are losing it.
b. Insensible losses also include water lost in GI secretions and water the nose
puts into inspired air to humidify air (later exhaled as water vapor)
2. “Waste” solute (roughly half (50%) of maintenance fluids)
a. Water soluble compounds (eg, nitrogenous waste  urea ) excreted in urine
b. “Sensible” not only because you feel & see the loss but also because the kidney
can dilute or concentrate the amount of water the solute is diluted in
B. AMOUNT of Maintenance
1. Since metabolic rate is not related linearly to weight, need a “system:”
2. Three "systems" used:
a. Surface area
b. Basal calorie: the driest; requires table
c. **Holliday-Segar formula (most commonly used one now) AKA 4:2:1 rule.
1) Note the difference in caloric needs between basal metabolic rate (the
amount you use at bedrest) versus the caloric need with normal activity. An
average of these is used for hospitalized children, but it will overestimate the
caloric needs of kids who have
markedly reduced activity
Table 1: COMPUTED need for “average hospitalized patient”
140
Estimated total expenditure
with normal
activity
Calories/day (ml/hr)
120
100
Weight
90
0-10 kg
11-20 kg
80
70
80
60
60
40
Basal metabolic rate
40
>20 kg
20
0
0
10
20
30
40
Weight in kilograms
2
50
60
Calories (= ml) per
hour
4 per kg
2 per each kg between 10
and 20
+ 40 for the 1st 10 kg
1 per each kg >20
+ 60 for the 1st 20 kg
Calories (= ml) per day
100 per kg
50 per each kg between
10 and 20
+ 1000 for the 1st 10 kg
20 per each kg above 20
+ 1500 for the 1st 20 kg
Table. Calories expended per day (or per hour) by weight
MAINTENANCE
3. So, 1000 calories metabolized requires 1000 ml of fluid:
Table 2: Sources of Water Loss
Source of Water Loss
Usual Losses (ml/1000 kcal metabolized)
Lung
150
Skin
300
Stool
50
Urine
500
Total
1000
Notes
a. Lungs: patients receiving humidified O2 or air may not need this
b. Skin: does not include active sweating
c. Urine: presumes basal (non-catabolic) conditions and urine that is isotonic
(neither concentrated nor dilute) = 300 mOsm/L (specific gravity of 1.010)
d. Notice that urine and insensible losses each constitute approximately half
of maintenance fluid needs. This useful guide has clinical implications:
1) An anuric patient should only receive insensible losses
2) A patient whose urine output is questionable can receive insensible losses
plus volume equal to urine output (treat urine output as “ongoing loss”)
4. Remember, maintenance is different than rehydration: Placing a dehydrated child on
“1 ½ time maintenance” generally means “lack of calculation.”
C. COMPOSITION of Maintenance
1. Virtually all electrolyte loss is urinary. So, for every 1000 calories metabolized, 1000
mL of water, ~30 mEq of Na and ~20 mEq of K + are needed. (see the chart below).
a. What, then, should the composition of maintenance fluid be (for all ages &
weights)?
b. Answer: D5 ¼ NS with 20 mEq/L KCl. Let’s dissect that:
1. Normal Saline (NS) consists of 154 mEq of Na for every 1000 mL (See
table on p4)
2. Note that 32 mEq/L is about ¼ of 154 mEq/L
3. Since there is no K+ in NS, you need to specifically add it.
4. D5 ¼ NS applies to all ages & weights because the ratio of 32 mEq Na per
1000 mL of water is constant. Once you have figured out how much water
is needed for maintenance, the amount of Na is straightforward.
Table 3: Sources of Water & Electrolyte Loss
Source of Loss
Water (ml/L)
Sodium (mEq/L)
Potassium (mEq/L)
Lungs
Skin
Stool
Urine
150
300
50
500
0
1
1
30
0
2
2
20
Total
1000
32
24
c. When does D5 ¼ NS with 20 mEq/L KCl not apply?
1. An anuric patient needs no sodium or potassium for maintenance
2. When urine output is compromised by renal disease, the ratio of Na:water
will change
3. When urine output is compromised by ADH secretion (inappropriate), the
ratio of Na:water will also change
3
MAINTENANCE
D. Summary of Maintenance
1. Determine AMOUNT (ml)
a. Estimate caloric expenditure using the 4:2:1 rule
b. convert kcal = ml, unless vital organs are compromised
2. Determine COMPOSITION (electrolytes)
a. D5 ¼ NS with 20 mEq/L KCl, unless kidneys are compromised
4. Determine RATE:
a. In the hospital, fluid and electrolytes generally are given evenly over 24 hours
b. This is a convention for our convenience. Not necessary to do it this way,
particularly when maintenance is being provided orally. In the real world, we get
our maintenance fluids unevenly (e.g., how many times did you get up last night
to drink water?)
c. Again, note that speaking of "twice maintenance" is commonly talked about on
the inpatient wards but does not have any physiologic basis unless your
metabolic needs suddenly doubled.
Table 4: Composition of Frequently Used IV Fluids
Liquid
Carbohydrates
(g/100 mL)
Na
(mEq/L)
K+
(mEq/L)
Cl
(mEq/L)
NS (0.9 % NaCl)
154
154
½ NS (0.45% NaCl)
77
77
¼ NS (0.225% NaCl)
38
38
38
38
D5 ¼ NS (0.22% NaCl)
5
Lactated Ringer’s
(LR)
D5W
3% NS
5
HCO3
(mEq/L)
130
4
109
28
0
0
0
0
513
513
DEFICIT
A. AMOUNT
"% dehydration" refers to % of body weight lost. You can assume any acute weight
loss is fluid, since weight loss >1% of body weight per day virtually has to be fluid.
There are two methods of estimating % body weight loss
1. Weight change (e.g., today’s weight in the ED – weight in the office 3 days ago)
2. Clinical estimate
a. Based on thirst, decreased urination (with increased spec gravity),
moistness of mouth, skin turgor, fontanelle, pulse rate, blood pressure,
perfusion
b. Note difference between infant and adolescent (adult)
4
DEFICIT
Table 6: Estimating the % of dehydration
Clinical Data
Dry mucous
membranes,
Oliguria
Hemodynamic Severity of
Infant
Adolescent
Changes
Est.
fluid
loss
Est.
fluid loss
Dehydration
Normal
Marked oliguria, Tachycardia
Poor skin turgor,
Sunken fontanel,
Tachycardia
Hypotension,
Poor perfusion
Hypotension,
Poor perfusion
Problems in Assessment
Mild
5%
(50 ml/kg)
3%
(30 ml/kg)
Oral mucosa may be dry in
chronic mouth breathers
Frequency and amount of
urination may be difficult to
assess during diarrhea, esp.
in infant girls
Moderate
10%
(100 ml/kg)
6%
(60 ml/kg)
Oliguria: See above
Turgor affected by serum
[Na+]**
Heart rate affected by fever,
[Na+]**, underlying disease
Severe
15%
(150 ml/kg)
9%
(90 ml/kg)
Both may be affected by
[Na+]**, underlying disease
**[Na+] >150mEq/L gives falsely low estimate of severity; [Na+] <130mEq/L exaggerates clinical estimate of
severity
B. COMPOSITION
Depends on 3 things:
a. Time period of loss
b. Type of fluid lost (e.g., diarrhea, vomiting)
c. Current electrolytes
1. Time period of loss
a. "Hyperacute" loss over hours: most of the loss is from the extra-cellular fluid
(ECF). Therefore, the child needs a fluid similar to ECF, such as Ringers
lactate (LR) or normal saline (NS)
b. "Acute" loss over few days: time for equilibration between ECF and ICF
means less sodium lost, more potassium. This is what you will deal with most
of the time.
c. "Chronic" loss over weeks: time to equilibrate further, so the composition of
what is lost will look more like the ICF (i.e., even less sodium lost and more
total body potassium depletion)
2. Type of fluid lost
a. Most sources of fluid loss (diarrhea, vomiting, DKA) approximate the amount of
sodium in ½ NS (see table below) (80 mEq is about ½ of the 154 mEq in NS)
Table 7: Electrolyte Loss for Various Sources of Dehydration
Cause of Deficit
5
+
+
"Usual" Deficit of [Na ]
"Usual" Deficit of [K ]
Diarrhea
Isotonic dehydration
Hypotonic dehydration
Hypertonic dehydration
80 mEq/L
100 mEq/L
20 mEq/L
80 mEq/L
80 mEq/L
10 mEq/L
Pyloric stenosis
80 mEq/L
100 mEq/L
DEFICIT
3. Current electrolytes will modify your fluid regimen
a. Sodium is key
1) 135 - 150 = isotonic
2) >150 = hypertonic
3) <135 = hypotonic
b. Isotonic: no modifications
c. Hypertonic dehydration
1) Amount of deficit is usually underestimated by physical examination since
intravascular volume and circulation are bolstered (at the expense of
intracellular water)
2) Skin is often described as "doughy"
3) Decreasing sodium too quickly can cause serious problems – the preferred
method is to add replace the deficit and 2 days of maintenance over 48
hours.
4) Do not confuse salt poisoning with hypernatremic dehydration.
d. Hypotonic dehydration
1) Amount of deficit may be overestimated by physical examination
2) Increasing sodium too quickly can cause serious problems – If forced to act
(eg, because of seizures), calculate Na to raise serum [Na+] to ~125 (out of
seizure range) and give rapidly as 3% solution followed by severe water
restriction.
a) Amount of 3% NaCl (in ml) to give if patient is hyponatremic and seizing:
= (125 mEq/L – actual serum Na) x (wt in Kg) x 0.6 L/kg
3) NOTE: Hyponatremia more often represents excess of water than
insufficiency of sodium!
e. Anions
1) When considering replacement fluids, consider what anion was likely lost.
On the ward, K+ is often provided as KCl by default – but this does not
always make sense
i.
Diarrhea: the child loses bicarb. Therefore, replace the K+ as
KAcetate.
ii.
DKA: the child may be hypophosphatemic. Therefore, replace the K+ as
Kphos
iii.
Profuse vomiting (eg, pyloric stenosis): the child loses chloride.
Therefore, replace the K+ as KCl.
2) “Normal saline” contains the same amount of Cl as Na which is not
physiologic. Ringer’s lactate contains 130 mEq/L Na & 100 mEq/L Cl (see
table 4)
C. RATE
1. Hippocrates: "Those bodies which have been slowly emaciated should be slowly
recruited; and those which have been quickly emaciated should be quickly
recruited."
2. I can't do better than that!
6
DEFICIT
D. Summary/Example of Deficit
Joey, a 15 kg child comes in with vomiting & diarrhea for 3 days. He has dry mucous
membranes, tachycardia, decreased wet diapers, and poor skin turgor. His capillary
refill and blood pressure are normal
1. The first step is to support circulation  give Ringers lactate or normal saline at 20
ml/Kg = 300 mL
a. 20 ml/Kg is chosen because it is frequently enough to support circulation but
generally not so much as to produce congestive failure
b. If the first 20 ml/Kg isn't enough, give more until HR, perfusion return to normal:
the goal is stable circulation.
c. Sad that we mix units: We speak of dehydration in % but rehydration in ml/Kg;
note that 20 ml/Kg = 2%. Helps in guessing what changes to expect: If a child
is “15% dehydrated,” will the child be “fluid resuscitated” with a single bolus of
20 ml/Kg? (Hint: 15% - 2% = 13%)
2. Determine AMOUNT (ml)
a. Two options for estimating the amount of deficit include weight change or
clinical signs. Joey’s clinical signs point to 10% dehydration  10% of 15 kg =
1.5 liter. If you already gave him a 300 mL (20/kg) bolus, there are 1200 mL
remaining to give.
3.
Determine COMPOSITION (electrolytes)
a. Amount of Na deficit depends on the mechanism of loss (see table 7). Joey
has diarrhea, so he is likely losing 80 mEq of Na per liter of fluid. Normal Saline
is 154 mEq per liter and 80 is about ½ that. Therefore the fluid of choice is D5
½ NS.
4. Put it together and write your fluid orders:
a. 300 mL LR bolus
b. D5 ½ NS + 20 mEq/L Kacetate @ 150/hr x 8 hours (the remaining 1200 mL
8 hours)
c. D5 ¼ NS + 20 mEq/L Kacetate @ 78/hr x 16 hours (It is not enough to replace
deficit; Joey still needs his daily maintenance fluid of 1250 mL [100/kg for the
first 10 kg = 1000 mL + 50/kg for the last 5 kg = 250 mL]. Since we used up 8
hours to replace Joey’s deficit, we can give 24 hrs worth of maintenance over
the remaining 16 hours  1250 ml
16 hours = 78 ml/hr)
5. HINTS
a. In "usual" situation, my bias is to rehydrate promptly, since the child will feel
better when rehydrated and be less nauseous with ketones washed out,
increasing the likelihood of oral intake being successful
b. If you estimate the child’s dehydration to be ~10% and give 20 ml/Kg (2%) as
bolus, then remainder of deficit is 8%. You can give this over 8 hours @ 10
ml/Kg/hr (1% per hour), math you can do in your head! Then give the entire
day’s maintenance over the subsequent 15 or 16 hours (instead of 24) and you
will have calculated and delivered appropriate rehydration without the need of
complex calculations! (See example later in handout.)
7
ONGOING LOSSES
A. Basic concept of ongoing losses
1. All of the above calculations are approximate; guidelines which in no way can replace
careful monitoring of the patient  therefore you MUST reassess your patient.
2. Note, however, that no single, simple sign or test infallibly reflects fluid and
electrolyte balance
3. The following measures are listed in rough order of practical value, considering
degree of ease, availability, invasiveness, time to perform, and cost
Table 8: SIGNS AND TESTS TO MONITOR STATE OF HYDRATION
Sign or Test
1. Physical signs of dehydration (PE)
2. Body weight
3. Urine volume
4. Urine specific gravity
5. I & O, with direct measure of all
losses
6. Urea nitrogen (BUN)
7. Hematocrit
8. Concurrent serum & urine
osmolalities
9. Serum electrolyte concentrations
Problem
May be deceiving if [Na+] abnormal, may be influenced by fever (esp
pulse)
Can be fooled by "third spacing"
Output also low in SIADH, renal failure
Concentrating ability of infant kidney limited; SG also high in SIADH,
renal failure; SG low in pyelonephritis, ATN
Must estimate maintenance; cannot measure "third space" loss
GFR severely reduced before BUN rises; elevated by blood in GI tract;
infant normally lower than adult; may mean renal disease
Useful serially but not as single value and not if patient is actively
bleeding
Good for detecting SIADH problem
By themselves, say little about state of hydration
4. Frequency of monitoring must be individualized, depending on the present severity
of the disorder and the potential rate of change. Once daily is rarely sufficient.
Thoughtful reassessment and attention to detail are key.
B. AMOUNT (fluid)
1. Measure what you can (e.g., stool output in diapers)
2. Estimate what you must (e.g., amount of emesis)
3. In some situations, may also want to consider "ongoing gains:" e.g., fluids used to
deliver medications
8
ONGOING LOSSES
C. COMPOSITION (electrolyte)
1. Estimate from table:
Table 9: Electrolyte Loss in Ongoing Losses
Fluid
Sodium (mEq/L)
Gastric
Bile
Ileostomy
Diarrheal
Sweat: Normal
Sweat: Cystic fibrosis
Burns
20-80
120-140
45-135
10-90
10-30
50-130
140
Potassium (mEq/L)
5-20
5-15
3-15
10-80
3-10
5-25
5
Chloride (mEq/L)
100-150
80-120
20-115
10-110
10-35
50-110
110
2. Measure (lab) if profuse or prolonged
3. Also consider "ongoing gains" in situations such as heart-, brain-, or kidneycompromised patients who require salt restriction and whose IV meds require
NaCl as diluent
D. RATE
1. If a child has significant ongoing losses (profuse diarrhea) or does not seem to be
getting better despite seemingly adequate fluid therapy, you can replace ongoing
losses mL for mL.
Example: 8 hours after admission, a 2 year old with rotavirus gastroenteritis has
400 mL of measured stool losses and no unmeasured emesis. Your order could
state: Replace stool output mL for mL with ½ NS + 20 mEq/L Kacetate every 4 h.
2. For convenience, I prefer to administer replacement "piggy-back," separate from
maintenance, since it simplifies calculations: keep separate bag of appropriate
composition hung with orders to infuse volume equal to the loss at specified
interval.
PUTTING IT TOGETHER: AN EXAMPLE
An infant who now weighs 10 kg has had diarrhea for 3 days. Clinical findings support
the estimate of 10% fluid deficit: dry mucous membranes, poor skin turgor, markedly
decreased urine output, and tachycardia; BP is normal and adequate peripheral
perfusion is shown by compression-release of the nail beds. Serum [Na] is 136 mEq/L,
[K] 4 mEq/L, [Cl] 104 mEq/L, [HCO3] 18 mEq/L.
A. Let’s do AMOUNT first (then Composition)
1. Deficit: 10% of 10 kg = 1000 mL
2. Maintenance: Since infant’s weight is 0-10 Kg, use 100 kcal/Kg/day x 10Kg =
1000kcal/day = 1000ml/day
3. Ongoing losses: Amount to be determined as course progresses (weigh diapers)
o Resuscitative portion of deficit: 20 ml/Kg x 10 Kg = 200 ml as bolus (usually given
over about 30-60 minutes)
o Remainder of deficit: 800 ml (1000 deficit – 200 bolus) given over 8 hrs = 100 mL/hr
o Maintenance: “Behind” on replacing maintenance, so need to give first day supply
(24 hours worth) = 1000ml in 15-16 hours = 60 mL/hr.
o Ongoing losses: Will add as needed
9
PUTTING IT TOGETHER: AN EXAMPLE
B. Now, address COMPOSITION: (We’ll do the detailed calculations as a demonstration)
1. Deficit: (from Table 7): 80 mEq Na x 1 liter = 80 mEq Na
2. Maintenance: 30 mEq Na x 1 liter = 30 mEq Na
3. Ongoing losses: Based on reassessment
o Resuscitative portion of deficit: you gave 200 mL (0.2 L) of Ringer's lactate (130
mEq/L Na, 4 mEq/L K)  0.2 L x 130 mEq = 26 mEq Na
o Remainder of deficit: (Na): 80 mEq (deficit) - 26 mEq (given in Ringer's) = 54 mEq.
o 54 mEq in 800 ml (remainder of deficit fluid) = 68 mEq/L. The closest standard fluid
is
D5 ½ NS (77 mEq/L)
o Acceptable shortcut: Once having made these calculations for different children, it
becomes clear that D5 ½ NS is the deficit-replacement fluid for isotonic dehydration.
o Maintenance: D5 ¼ NS (38 mEq/L) + 20 mEq/L KAcetate
C. Summary
1. Ringer's lactate
200 ml
x 30 minutes
2. D5 ½ NS + 20 mEq/L KAcetate
@ 100 ml/hr
x 8 hours
3. D5 ¼ NS + 20 mEq/L KAcetate
@ 60 ml/hr
x 16 hours
4. D5 ¼ NS + 20 mEq/L KAcetate
@ 40 ml/hr
thereafter until the child is
drinking again
D. Notes
1. You can use the observed weight and apply the estimated % deficit without having
to calculate the “pre-dehydration” weight. For example, this 10 Kg child, if “10%
dehydrated,” must have originally weighed 11.1 Kg. The difference in amount isn’t
worth the added step in calculation.
2. Only sodium needs are calculated in this example: the amount and rate of
potassium administered is governed by safety, and full replacement is not achieved
acutely. Once urine output is assured and it is thus considered safe to administer
potassium, 20 to 40 mEq/L is added to the replacement solutions.
3. Sequential replacement of deficit and maintenance fluids is demonstrated in the
example; the method is convenient, illustrates the approach in the outline, and
results in an appealing stepwise, progressive decrease in the amount of fluid and
concentration of sodium from resuscitation to maintenance.
10
PUTTING IT TOGETHER: AN EXAMPLE
a. Recall that for children who are “10% dehydrated,” giving a bolus of 20 ml/Kg
(2% of body weight) leaves 8% that needs to be replaced: You should not go
directly to maintenance rate or a maintenance solution. If you provide the 8%
replacement over 8 hours, you are giving 1% of body weight per hour
(10ml/kg/hr). Look how simple the math becomes!
b. Many clinicians prefer to combine deficit and maintenance replacement and/or to
proceed more slowly; that method also works and is preferred in hypernatremic
dehydration.
c. Many residents learn (and teach) that you should give half the deficit in the first 8
hours and the other half in the next 16 hours along with maintenance fluid. This
is much more work (in terms of calculations) than necessary. For example, had
you done that for the example, you would have divided the 800 ml deficit (after
the resuscitation phase) into halves and planned to give 400 ml in the first 8
hours and the other 400 ml in the next eight hours. You then would have had to
figure out 8 hours of maintenance to give along with the first half of the deficit
and 16 hours of maintenance to give with the second half. Once you did all of
that you would have come out with 400+320=720 ml for the first 8 hours and
400+640=1040 for the next 16 hours. Compare that to just replacing the deficit
in 8 hours (800 ml) and finishing the day’s maintenance in 16 hours (1000 ml):
Deficit + Maintenance Method:
“Easy” Sequential Method:
11
1st 8 hours
720 ml
800 ml
next 16 hours
1040 ml
1000 ml
ANSWERS TO THE PROBLEMS
1. a. 5 Kg: 100 mL/Kg/d x 5 Kg = 500 mL/d OR 4 mL/Kg/hr x 5 Kg = 20 mL/hr
b. 30 Kg: (100x10)+(50x10)+(20x10) = 1700 mL/d OR (4x10)+(2x10)+(1x10) = 70 mL/hr
c. 50 Kg: (100x10)+(50x10)+(20x30) = 2100 mL/d OR (4x10)+(2x10)+(1x30) = 90 mL/hr
So why isn’t the rate for 30 Kg six times the rate as for 5 Kg? And why isn’t the rate for 50
Kg ten times the rate as for 5 Kg? (Because basal metabolic rate per Kg declines with
age.)
2. COMPOSITION: D5 ¼ NS + 20 mEq/L K+ regardless of age or weight (based on metabolic
rate, not on age or weight).
3. Rather than use a rule about urine output, let’s calculate what urine output is expected
a. First step: Urine output should not equal intake; intake needs also to cover insensible
losses.
b. Second step: estimate urine output
1) The key is to recognize urinary losses as 50% of maintenance, presuming basal
conditions and SG of 1.010.
a) Maintenance = [(100x10) + (50x5)] = 1250 ml/d
i) 50% of 1250 ml/d = 625 ml/d
2) If you prefer to think of urine output in ml/Kg/hr, you can try to use a “rule,” but no
rule is particularly helpful, since urine output (like the amount of maintenance fluid)
is not linearly related to body weight. SO could calculate what it should be by
expressing maintenance in ml/Kg/hr and calculating 50% of that:
a) Urine: 2 ml/Kg/hr for first 10 Kg; 1 ml/Kg/hr from 10 to20 Kg; 0.5 ml/Kg/hr above
20 Kg
b) So maintenance here = [(2x10) + (1x5)] = 25 ml/hr
i) 25 ml/hr @15Kg = 1.7 ml/Kg/hr
3) Whatever way you do it, the child's urine output is not far off (particularly if the SG is
a little over 1.010):
a) The child is not oliguric.
b) Output should NOT equal intake (because of insensible losses).
c) Thank you for the consultation.
4. a. Diagnosis: Acute post-streptococcal glomerulonephritis
b. AMOUNT: Maintenance is [(100x10) + (50x10) + (20x1)] = 1520 ml/d, of which half is
needed for insensible losses (approximately 760 ml/d) and half for urine formation—if
child is making urine. So give 760 ml/d plus, if the child is not totally anuric, enough
additional fluid to replace urine output ml for ml (i.e., as an ongoing loss).
If the child can drink, this can be done PO by writing an order for fluid restriction
If the child cannot drink, then give using IVF
c. COMPOSITION: If po, give an electrolyte free solution such as ginger ale, water, etc
(remember that insensible losses have minimal electrolytes). NOTE: To maintain basal
conditions as much as possible and minimize endogenous protein breakdown, need an
electrolyte-free, protein-free source of calories; a favorite is hard candy ("sour balls").
If IV, give D5W which wil provide both fluids and non-protein calories
12
ANSWERS TO THE PROBLEMS
5. You could consider his lack of fluids in the last 8 hours to be a “deficit,” but you could also think of it
as simply being behind on maintenance, understanding that maintenance requirements do not
need to be met continuously at an even hourly rate. You do not replace your own maintenance
losses continuously, and the convention of providing maintenance fluid and electrolytes at a
continuous rate in the hospital is simply for staff convenience. When you think about deficits, you
likely have a knee-jerk response of wanting to provide a bolus. Boluses are used to restore
intravascular volume rapidly; they contain not only a large amount of water but also a large amount
of sodium, as they are necessarily comparable to serum concentrations (to avoid fluid shifts).
Therefore, boluses should be reserved for individuals with evidence of circulatory compromise,
such as tachycardia, hypotension, or delayed capillary refill time—none of which would be expected
in this child.
a. AMOUNT:
1) 8 hours of maintenance fluid plus ongoing maintenance needs
a) Maintenance = [(100x10)+(50x3)] = 1150 ml/d or [(4x10)+(2x3)] = 46 ml/hr
b) 8 hours of maintenance not received = 8x46 = 368 ml
b. COMPOSITION: D5 ¼ NS + 20 mEq/L K+
c. RATE:
1) Could give the additional 368 ml in, say, 4 hours (92 ml/hr) added to maintenance:
92+46=138 ml/hr x 4. Then you would return to maintenance rate, 46 ml/hr
2) OR could replace deficit in 6 hours (368/6=61) along with maintenance (61 + 46 = 107
ml/hr) followed by maintenance (46 ml/hr).
3) NOTE: AMOUNT and COMPOSITION are straightforward here; choices come in selecting
rate.
6. a. Pyloric stenosis. There is evidence of greater malnutrition than is usually seen with GE reflux,
and the electrolytes indicate a profuse loss of gastric fluid, more suggestive of vomiting than of
mild regurgitation. (“Projectile vomiting” is a clue, too.)
b. Before surgery is performed, medical management needs to assure restoration of circulating
volume and return to normal electrolyte balance: Assess dehydration at 10% = 3.4 Kg.
Phase I: Resuscitation: Bolus: 20 mL/Kg (=68 mL) of normal saline (Even a fan of Ringer's
lactate like me would use normal saline in this situation, because of the chloride deficit!).
Phase II: Deficit: Since 20mL/Kg = 2% body weight, an 8% deficit remains. The easiest way to
replace it is to give 1% (10mL/Kg) per hour for 8 hours (10 mL/kg/hr = 34 mL) with D 5 ½ NS +
20-30 mEq/L KCl. The hypokalemia will resolve along with the alkalosis.
Phase III: Maintenance: You can either piggy-back the maintenance (4 mL/kg/hr =~14 mL/hr of
D5 ¼ NS+20mEq/L KCl) along with the deficit or replace deficit and then address maintenance.
To avoid worsening the hyponatremia, it is preferable to replace the deficit first, then give
maintenance. If you choose to do it that way, note that you are 8 hours behind (like problem
#5), so you would give 24 hours worth in 16 hours: 24/16 = 1½ x maintenance rate = 21 mL/hr x
16 hours; then 14 mL/hr.
1) Only when volume is restored and electrolytes are normal should the pyloromyotomy be
performed and the malnutrition addressed.
2) Consider child moderately dehydrated clinically (10%) even though the weight discrepancy
between what he should weigh and what he does way is much more than 10%. The reason
for the greater discrepancy is the lack of subcutaneous fat: ie, more than water is involved.
You only need to resolve the dehydration prior to surgery. The rest will be accomplished
through nutrition post-operatively.
3) An error commonly made is to give the bolus and then proceed to maintenance without
restoring the 8% remaining deficit. Note that you will not catch up by giving some multiple
of maintenance and that the composition of the fluid needed to replace the deficit contains
more sodium than does the maintenance solution.
13
FLUID & ELECTROLYTES: TAKE HOME MESSAGES
1. When planning to rehydrate a dehydrated child, it is easiest if you consider separately the
a. Fluid (ie, amount of water) vs. Electrolytes (ie, composition of fluid)
1) Estimate the amount of fluid first, then think about composition
b. Deficit vs. Maintenance vs. Ongoing Losses
2. For maintenance, both fluids AND lytes are based on metabolic rate-- not directly to weight.
Rule of thumb is as follows:
-Amount:
Weight
ml/Kg/d or ml/Kg/hr
Example (ml/Kg/d)
0- 10 Kg
100
4
7 Kg: 100x7 = 700
11-20 Kg
50
2
15 Kg: 100x10 + 50x5 =1250
>20 Kg
20
1
25 Kg: 100x10 + 50x10 + 20x5 = 1600
-Composition: always ¼ NS + 20 mEq/L K+ (either as KCl, KPhos, or Kacetate).
3. Assessment of dehydration: The rule of 5-10-15 (mild dehydration = 5%, moderate
dehydration = 10%, severe dehydration = 15%) applies to infants. For adolescents and
adults, the rule is 3-6-9 (mild dehydration = 3%, moderate dehydration = 5-6%, severe
dehydration = 7-9%). (For young school-age children, the rule is somewhere in between,
but, in practice, we often ignore the distinction from infants and use 5-10-15 in this age
group.)
4. Front load your fluid replacement. This is especially true in severely dehydrated kids
5. Consider Oral Rehydration for kids who are mild-moderately dehydrated
6. "Fluid resuscitation:" Note that 20 ml/Kg = 2%. Implications: if you estimate an infants's
degree of dehydration to be 15% (and you are right), he will not "normalize" with 20 ml/Kg
but will improve to 13% -- and still be tachycardic, etc. To rapidly return him to
cardiovascular sufficiency, he will need 3 boluses of 20 ml/Kg (as recommended in PALS).
7. Composition of rehydration fluid: To correct isotonic dehydration (i.e., serum [Na+ ] is
normal), calculations will result in: a bolus of Ringer's lactate or normal saline; followed by
several hours (6-8) of D5 ½ NS + 20 mEq/L KAcetate; followed by D5 ¼ NS + 20 mEq/L
KAcetate.
8. On-going losses: If likely to be significant, measure and replace.
9. Monitoring rehydration: The things we forget most often are the simple ones (which are
also the most helpful): e.g., the physical examination (to see if the signs of dehydration
have improved); urine specific gravity.
14
Appendix: What’s wrong with 1 ½ time maintenance?
A child comes in with moderate (10%) dehydration. You start D5 ½ NS at 1 ½ time
maintenance, thinking that this will be a good estimate of maintenance + fix his
dehydration. The next morning, the attending is unhappy when you mention “1 ½ times
maintenance.” Is it just semantics? Won’t this usually work out the same as if you had
calculated it?
No. Look at the two examples below:
10 kg child who is 10% dehydrated from acute diarrhea
Water
Sodium
Maintenance
~1000 mL
30 mEq
Deficit
Total
(4:2:1 rule = 4 ml/hr * 10 kg * 24 hr
in a day)
(based on usual maintenance
needs Table 3 )
1000 mL
80 mEq
(10% of 10 kg)
(based on electrolyte losses
Table 7)
2000 mL
110 mEq Na
Using simply 1 ½ times maintenance:
Using D5 ¼
1440 mL
Using D5 ½
1440 mL
55 mEq Na
110 mEq Na
If you use 1 ½ time maintenance, you will not give enough water (using D5 ¼ would
also not give enough salt)
40 kg child who is 5% dehydrated from acute diarrhea
Water
Sodium
Maintenance
~1900 mL
57 mEq
Deficit
Total
(4:2:1 rule)
(based on usual maintenance
needs Table 3 )
2000 mL
160 mEq
(5% of 40 kg)
(based on electrolyte losses
Table 7)
3900 mL
217 mEq Na
Using simply 1 ½ times maintenance:
Using D5 ¼
2880 mL
Using D5 ½
2880 mL
110 mEq Na
220 mEq Na
If you use 1 ½ time maintenance, you will not give enough water (using D5 ¼ would
also not give enough salt)
15