Transcript Fluid and Electrolytes

Basic Fluid Management
…with references to the Harriet Lane
(because you have it with you)
Julie Story Byerley, MD, MPH
Why does fluid management
matter?
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It’s basic pediatrics.
Pediatricians are supposed to be the experts of
fluid management.
It matters to just about every inpatient.
Fluid is often extremely effective therapy.
Incorrect fluid management can seriously hurt
patients.
It’s not always as simple as you might think –
but you can make it simple.
Outline
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Maintenance requirements
Management of dehydration
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Normonatremic
Hyponatremic
Hypernatremic
A few little pearls
Maintenance requirements
Chapter 10, Harriet Lane, p. 233
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The two functions of maintenance fluids include
 Solute excretion in urine
 Heat dissipation through insensible losses of water
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Insensible losses are about 2/3 skin and 1/3 lungs
Each can be considered as about 50% when
maintenance needs are exactly met and urine
concentration is 1.010
The kidneys are usually smart – insensible losses come
first (less adjustable) and the kidneys can then adjust
how much water is in the urine
Maintenance Requirements
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Caloric Expenditure Method
Holliday-Segar Method
Body Surface Area Method
Remember that maintenance requirements
are over about 24 hours, and don’t have
to be given evenly divided over each hour
Caloric Expenditure Method
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Water and electrolyte needs parallel
caloric needs
Caloric needs depend on activity
For each 100 kcals,
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100-120 cc water,
2-4 MEq Na, and
2-3 MEq K are needed
Average Caloric Needs
See page 436 in Harriet Lane (table 20-1)
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At normal activity
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Infants approx. 100 kcal/kg/d
4-6yo approx. 90 kcal/kg/d
7-10yo approx. 70 kcal/kg/d
Teens approx. 50 kcal/kg/d
Caloric needs are based on resting energy expenditure and activity
Resting energy expenditure (REE) is based on size
Energy needs increase with injury, fever, growth, etc.
See p. 435 in Harriet Lane
 REE (Resting Energy Expenditure)
+ REE X (Mtn + Injury + Activity + Growth)
Don’t memorize it, just get the concept
Example, Caloric Expenditure Method
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10 yo boy with injuries and fever, 30kg
= REE + REE x (Mtn + Activ + Fever + Inj + Growth)
= 40 + 40 x(0.2 + 0.1 + 0.13 + 0.4 + 0.5)
= 40 + 40 x(1.33)
= 93 kcal/kg/d = 2790 kcal/d
Therefore, he needs 2790 cc water per day
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water needs parallel caloric needs
3 MEq Na/(100 kcals) = 84 MEq Na total per day
2 MEq K/(100 kcals) = 56 MEq K total per day
The Math – what fluid?
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D5 is standard
2790 cc of D5 has only 474 kcals
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only 16 kcal/kg/d
people are malnourished when they only
receive IVF!
84 MEq Na/ 2790 cc = X / 1000; X = 30
Quarter NS = 38.5 MEq Na/L
56 MEq K/ 2790 cc = Y / 1000; Y = 20
Try D5 quarter NS with 20 KCl at 116 cc/hour
More fluid than using the 4:2:1 rule (70cc/h);
necessary because of injuries and fever
Holliday-Segar Method
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Estimates caloric and fluid needs from
weight alone
Can over-estimate fluid needs for infants
and under-estimate fluid needs in fever
and injury
Method we tend to use most commonly
4,2,1 rule
Holliday-Segar Method
Weight
cc/kg/d
cc/kg/h
First 10 kg
100
4
Second 10 kg
50
2
Each additional
kg
Ex: 25 kg
20
1
1600 cc/d
(1000+500+100)
65 cc/h
Holliday-Segar Method
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Electrolyte Requirements
Na – 3 MEq per 100 cc water
K - 2 MEq per 100 cc water
Example, 25 kg kid, 1600 cc/d
48 Meq Na, 32 Meq K
48/1600 = X/1000; X = 30
(Remember that quarter NS has 38.5 MEq/L Na)
32/1600 = Y/ 1000; Y= 20
D5 quarter NS with 20 MEq/L KCl (as Cl is your anion to
fill with)
Sodium
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Since the ratio of electrolytes needed to amount of
water does not change, the Na concentration in MIVF
does not need to change based on weight
Often people use D5 ¼ NS for small babies and D5
1/ NS for bigger kids and adults
2
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This can give adults more sodium than needed
This error is based on the fact that fluid needs decrease as
size increases
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Na should be calculated based on kcals, (therefore cc’s not kg)
We decrease water needs as weight increases (the 4,2,1 rule),
but we tend to calculate Na needs as 3 MEq per kg per day.
Na needs are not linear. They should decrease like water
needs do.
Many argue that D5 ¼ NS with 20 K is an
appropriate maintenance fluid for all people.
Body Surface Area Method
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Method not used as frequently, but often
taught in nephrology
More difficult to use with small children
To calculate the BSA you need to know
height
Maintenance requirements are about 1500
ml/m2/day
Dehydration
Background
 Dehydration complicates many
acute illnesses
 Accurate assessment is important
 Consequences of underestimation
 Consequences of over-estimation
 Practice guidelines for evaluation
and management
Dehydration
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Initial resuscitation
Determining deficit
Adding in maintenance
Ongoing losses (don’t forget!)
Estimating degree of
dehydration…traditional teaching
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Recent weight changes
Physical exam findings
Dehydration
Turgor
Cap refill
Mucus membranes
Eyes
Tears
Fontenelle
CNS
Pulse
Urine output
Mild (5%)
Normal
Brisk (< 2 sec)
Moist
Normal
Present
Flat
Consolable
Regular
Normal
Moderate (10%)
Tenting
2-4 sec
Dry
Deep set
Reduced
Irritable
Slight increase
Decreased
Severe (15%)
None
>4 sec
Parched/cracked
Sunken
None
Sunken
Lethargic/obtunded
Increase
Anuric
Caveats…traditional teaching
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The previous chart applies to babies. For adults
it should be scaled back to 3%, 6%, and 9%.
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Older kids show symptoms at a lower % dehydration
Hyponatremic dehydration looks worse clinically
– exaggerated hemodynamic instability
Hypernatremic dehydration looks better clinically
– circulation maintained at the expense of
intracellular volume
Systematic Review of the
Published Data on History, PE,
and Labs in Dehydration
Mike Steiner, Darren DeWalt, Julie Byerley,
2002-3
Historical Factors
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Previous visit to PCP, or previous trial of
clears provided minimal but some increase
in the likelihood of dehydration
Physical exam signs less helpful than
previously taught
Delayed Capillary Refill
Sensitivity
Specificity
LR Positive
LR Negative
0.60 (0.300.91)
0.85
(0.72-0.98)
4.1
(1.7-9.8)
0.6
(0.4-0.8)
 Limitations:
 Inter-rater agreement only slight to fair
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Kappa 0.01-0.35
Site of application, lighting and ambient
temperature
Abnormal Skin Turgor
Sensitivity
Specificity
LR Positive
LR Negative
0.58
(0.40-0.75)
0.76
(0.59-0.93)
2.5
(1.5-4.2)
0.7
(0.6-0.8)
 Limitations:
 Inter-rater agreement fair to moderate
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Kappa 0.36-0.55
Hypernatremia increases false negatives
Abnormal Respirations
Sensitivity
Specificity
LR Positive
LR Negative
0.43
(0.3-0.6)
0.79
(0.7-0.9)
2.0
(1.5-2.7)
0.7
(0.6-0.9)
 Limitations:
 Inter-rater agreement of only chance to fair
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Kappa –0.04 to 0.40
Varying measurements and definitions
Less Useful Signs
Sign
Comment
Sunken Eyes
Pooled LR of 1.7
Dry MM
Pooled LR of 1.7
Weak Pulse
LR ranged from not significant to 3.1
sensitivity low (0.04-0.25), specificity high (0.89 to 1)
Cool Extremity
LR ranged from not significant to 18.8
Absent tears
Pooled LR CI crosses 1.0
Abnormal overall
appearance
Pooled LR CI crosses 1.0
Tachycardia
Pooled LR CI crosses 1.0
Weak Cry
CI for LR crosses 1.0.
Sunken fontanelle
LR actually below one, CI crosses 1.0
Combinations of Signs
 Vega evaluated the standard dehydration
table
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‘Severe’ classification
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LR 3.4 for 5% dehydration
‘Mild or ‘Moderate’ classification
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No increase in likelihood of dehydration
 Gorelick found an LR of 4.9 when 3/10
signs of dehydration present
Results: Laboratory Tests
 BUN
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Study of hospitalized patients with gastroenteritis
 BUN >45, specificity: 1.00, LR positive of 46.1
BUN cutoffs of 8, 18, and 27 yielded mixed results in
four other studies
 Acidosis
 One study found no statistical increase in likelihood
 Four studies found significant positive LRs between
1.5 and 3.5
Discussion
 Poor to moderate inter-observer agreement
 History and parental report have limited
value
 Best individual tests
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Prolonged capillary refill
Abnormal skin turgor
Abnormal respirations
 Groups of positive signs are helpful
 Extremely abnormal lab tests are helpful
Implications
 Focus on symptoms and signs with
proven utility
 Ability to estimate exact degree of
dehydration is limited
 Support change to ‘none, some, or
severe’ classification scheme
Oral Rehydration
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Recommended by the AAP, WHO, and CDC
Appropriate for mild-moderate (some)
dehydration
Goal is 50-100 cc/kg over 4 hours for
mild-moderate dehydration
5 cc every 1-2 minutes
Solution containing 40-60 MEq/L Na
The Fluid Used Matters
Solution
Pedialyte
Rehydralyte
WHO
Gatorade
Apple juice
Gingerale
Coke
CHO (g/dL)
2.5
2.5
2
5.9
12
9
11
Na (mEq/L)
45
75 (1/2/NS)
90
21
0.4
3.5
4
K (mEq/L)
20
20
20
2.5
26
.1
.1
mOsm
250
310
310
377
700
565
656
Fluid Management in Shock
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Initial boluses of 20 cc/kg over 30 min
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20 cc/kg is 2% of body weight – therefore it should
take a 10% dehydrated baby to only 8% dry
One bolus is not enough when someone is 15% dry
Use isotonic solutions (NS, LR)
Consider blood, other fluids and/or pressors in
special circumstances
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Trauma or blood loss
Nephrotic syndrome
Septic and cardiogenic shock
Fluid Composition
Fluid
CHO
Cal/L Na
D5W
5
170
g/100cc
NS
154
(0.9%
NaCl)
LR
K
0-10
0-340 130
Cl
CO3
Ca
28
3
154
4
109
Rehydration
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First resuscitate out of shock – restore perfusion
Calculate maintenance, including ongoing losses,
and deficit
Run maintenance as usual
Replace ongoing losses
Typical is to replace deficit over 24 hours
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Half in first 8 hours
Other half over 16 hours
Where the dehydration comes
from…traditional teaching
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In a brief duration of illness (<3 days), 80% of
the deficit is typically from the ECF
More than 3 days of illness and the deficit from
the ICF increases to about 40% (therefore 60%
from ECF)
This matters because ECF contains a lot of
sodium (135-145 mEq), and intracellular fluid
contains a lot of potassium (150MEq)
But remember…“No walls, no sparks”
Example Calculations, normal Na
(See table 10-7 in Harriet Lane on page 237.)
7 kg infant with 10% dehydration that accumulated over >3d.
24 Hours
H2O
Na
K
Maintenance
(Hol.-Seg.)
700
21
14
Deficit
(10% of 7 kg)
700
ECF (60%)
420
ICF (40%)
280
Total
61
(145MEq/L x
0.42L)
42
(150MEq/L x
0.28L)
1400cc 82MEq 56MEq
First 8 hours
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MIVF for 8 hours plus 50% of the deficit
H2O
Na
K
233
7
5
½ Deficit
350
31
21
Total
583
38
26
1/
3
Maint
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583/8=73 cc/h; 38/0.583=65MEqNa/L = 0.42NS
(65/154); 26/0.583=45MEqK/L
Roughly D5halfNS plus 40 KCl at 75 cc/h
Next 16 hours
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MIVF for 16 hours plus other 50% of the deficit
H2O
Na
K
467
14
9
½ Deficit
350
30
21
Total
817
44
30
2/
3
Maint
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817/16=51 cc/h; 44/0.817=54MEqNa/L =
0.35NS (54/154); 30/0.817=37MEqK/L
Roughly D5halfNS plus 40 KCl at 50 cc/h
Simplified – what fluid, normal Na
(Roberts’ method)
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Usually after boluses with NS or LR, D5halfNS is
an appropriate rehydration fluid
After urine output is assured, give K as 20
MEq/L
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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/h
Simplified – what rate
(Roberts’ method)
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If a child is 10% dehydrated Give a 20 cc/kg bolus of NS
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Next give 10 cc/kg/h of D5halfNS with 20 KCl for
8 hours
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Restores hydration 2%
Restores hydration 8%
Next give 1.5 times MIVF using D5quarterNS
with 20KCL for 16 hours
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That day’s maintenance
Example, the Robert’s method
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7kg child with 10% dehydration
Bolus of 140 cc NS
70 cc/h of D5halfNS with 20 KCL for 8
hours, then
40 cc/h of D5quarterNS with 20 KCL for 16
hours
Hyponatremia
Always measure the sodium.
Hyponatremic patients look more
dehydrated than they probably are.
Example calculation, hyponatremia
(7kg with 10% dehydration, Na 115, >3 d
duration)
Table 10-8 on p. 238
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Fluid deficit – same as before
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10% of 7 kg=700 ml total fluid deficit
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Na deficit (from dehydration) – same as before
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60% from ECF, 40% from ICF
ECF Na x 60% of total fluid deficit
145 mEq/L x .6 x .7L = 61mE
Excess Na deficit (because hyponatremic)
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(Desired Na – Actual Na) x distribution factor x wt
(CD-CA) x fD x weight
(135-115)MEq/L x 0.6L/kg x 7kg = 84 mEq Na
Replace excess Na deficit over 24 hours
Replace Na faster if symptomatic
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K deficit (same as before)
 ICF K x 40% of total fluid deficit
 150mEq/L x 0.4 x 0.7L=42 mEq
Make a table!
Component
Mainenance
Deficit
Excess Na
deficit
24 hour
totals
H2O
(mL)
Na=3mEq/100ml 700
K=2mEq/100ml
700
60% ECF x 700
= 420
40% ICF x 700 =
280
(135-115) x .6 x
7kg
1400
Na
(mEq)
21
K
(mEq)
14
61
42
84
166
56
First 8 hours, hyponatremia
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MIVF for 8 hours plus 50% of the deficit
H2O
Na
K
233
7
5
½ Deficit
350
72
21
Total
583
80
26
1/
3
Maint
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583/8=73 cc/h; 80/0.583=137MEqNa/L =
0.89NS (137/154); 26/0.583=45MEqK/L
Roughly D5halfNS plus 40 KCl at 75 cc/h
Next 16 hours, hyponatremia
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MIVF for 16 hours plus other 50% of the deficit
H2O
Na
K
467
14
9
½ Deficit
350
72
21
Total
817
86
30
2/
3
Maint
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817/16=51 cc/h; 86/0.817=105MEqNa/L =
0.68NS (105/154); 30/0.817=37MEqK/L
Roughly D5halfNS plus 40 KCl at 50 cc/h
Practical Interpretation,
Hyponatremia
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In adults, rapid correction of hyponatremia may
be associated with central pontine myelinoysis.
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
Start with NS boluses and then D5NS or
D5halfNS
Follow Na carefully
Hypernatremia
Always measure the sodium
Hypernatremia
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In hypernatremia, rehydrate more slowly to avoid fluid
shifts that could cause cerebral edema or intracranial
bleeding
Remember that the hypernatremic patient doesn’t
always look as dry as they are because the intravascular
volume is protected
The hypernatremic dehydrated patient is still 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
Example calculation, hypernatremia
(7kg with 10% dehydration, Na 155, >3 d
duration)
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Table 10-9 on p. 239
Same fluid deficit, maintenance fluid and electrolytes as before, in
isotonic dehydration example
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FW deficit
=(measured Na – ideal Na)x 4cc/kg x wt
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FW def = (155-145) x 4 x 7 = 280 cc
Replace free water deficit evenly over 48 h
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Give only half of FW deficit in first day
Drop Na less than 15 MEq/L/day
Follow lytes closely – every 4 hours at first
Subtract the free water deficit from the total
deficit to determine Na deficit
Chart for Hypernatremia, first 24 h
H2O
Na
K
MIVF
700
21
14
Free water
deficit =
280cc/2 days
140
Def remaining
(solute) =420cc
(700-280=420)
ECF (60%)
ICF (40%)
Total, 24 hr
252
168
37
1260
58
25
39
Fluid choice, Hypernatremia
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Need in 24 hours,
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1260 cc water
58 Meq Na
39 MEq K
1260/24 = 52.5 cc/h
58/1.260 = 46 MEqNa/L = 0.3 NS (46/154)
39/1.260 = 31MEqK/L
Roughly D5halfNS with 30KCl at 50 cc/h – could
also use D5quarterNS – half is more
conservative
Practical Interpretation,
Hypernatremia
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Still bolus the hypernatremic patient with NS if
needed
You want to lower the Na slowly so you can start
with D5halfNS and remeasure
The calculations almost always come out to
something near quarter NS, and you should not
give more dilute fluid than that, so that is also a
reasonable starting point
The important thing is to follow the sodium
carefully and adjust as necessary
Practical Approach,
Replacing the Deficit
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Isotonic dehydration
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Hyponatremic dehydration
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3/4 or NS
Hypernatrmic dehydration
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1/2 NS
1/4 NS
Follow I/O’s, weights, lytes carefully – q 4
hours, you can follow on VBGs
Even Easier…Run Maintenance
and Deficit Separately
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Maintenance (calculate using Holliday-Segar)
Y in Deficit
Ongoing losses (calculate by shift or anticipate)
Use the same calculations as above to calculate
the deficit, but hang different fluids
Generally easier to manage than having unusual
fluids mixed by pharmacy
Ongoing losses
Don’t forget losses into third spaces
 Pay attention to In-Out sheets
 Replace shift to shift if output is large
 Check electrolytes on output prn
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Ongoing losses!
Fluid
Gastric
Illeostomy
Diarrhea
Burns
Na
20-80
45-135
10-90
140
K
5-20
3-15
10-80
5
Cl
100-150
20-115
10-110
110
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Usually replace GI losses with half normal
Radiant losses are usually just water
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See table 10-11, p.240, for other specific situations
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Special situations
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Symptomatic hyponatremia (sz’s)
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10-12mL/kg of 3% saline over 60 minutes
Increased insensible losses
When the kidneys are not smarter than
you!
Electrolyte abnormalities
THE END
Other Equations, Anion Gap
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Anion gap = Na – (Cl + HCO3)
Normal gap 12 +/- 4
AG increased in acid production or decreased
acid excretion
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Ketones, lactic acidosis, inborn errors of metabolism
Renal failure
AG normal in hyperchloremic acidosis
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GI loss of bicarb
Renal loss of bicarb
Other Equations, Osmolality
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Osmolality is number of particles per liter
Approximated by:
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2(Na) + (glu/18) + (BUN/2.8)
Where glucose and BUN are in mg/dl
Normal is 285-295
A Pearl about Blood Transfusion
See p. 319 in Harriet Lane (table 15.7)
 Vol PRBC needed to transfuse =
EBV (cc) multiplied by (desired HCT –
actual HCT)/ HCT of PRBCs
Ex: Transfuse a 6 mo old with HCT 20%
with 87.5 cc to get their HCT to 30%
cc PRBC = 75cc/kg(7kg)(.10)/0.60
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