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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_37_библиотеки_им_акад_М_И_Перельмана
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Closed drainage
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system
Chest tube #
Times
0700
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
0600
Urine
CHAPTER 14 Fluid and Electrolyte Management
Output
Stools
Last stool
Hematest
Type Amt. Reason
Clinitest
Gastric Blood out
Tubed
Cumul.
Color
total
Irrig.
Balance forward
Amt.
out
Cumul.
total
409
24° Totals:
Chest tube activity
B - Bubbling
F - Fluctuating
D - Draining
C - Clamped
N - No movement
Chest tube color
BL - Bloody
S - Serosanguinous
Y - Yellow
W - White or milky
Other:
FIGURE 14.3 Model intake and output sheet. (Courtesy Brenner Children’s Hospital, Winston-Salem, North Carolina.)
Urine type
VD - Void
CATH - Catheterized
CR - CREDÉ
Urine color
A - Amber
Y - Yellow
BL - Bloody
Other:
Stool type, size, and color
F - Formed
P - Pasty
LO - Loose
M - Mucus
MEC - Meconium
SDY - Seedy
SOF - Soft
W - Watery
LG - Large
MED - Medium
S - Small
T - Transitional
Y - Yellow BL - Bloody
BR - Brown G - Green
BLK - Black
Brenner Children’s Hospital • Winston-Salem, N.C. Neonatal day record
UNIT THREE Metabolic and Nutritional Care of the Neonate410
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IV Intake
#1 #2 Feedings
Blood products
0700
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
0600
Time
Bottle
Site check
Location
Line Bottle Line
IV Intake
Rate per
hour
Pump
reading
Amount
infused
Site check
Cumul.
total
Rate per
hour
Pump
Location
reading
Amount
infused
Site check
Cumul.
total
Rate per
hour
Pump
reading
Amount
infused
Cumul.
Location
total
hourly
total
Tube size:Tube:
Emesis
Amount
given
Resid.
Set
pH
Type
Amt. ordered
Cumul.
*
*
Blood products
FFP - Fresh frozen plasma
PLTS - Platelets
PRBC’s - CMV (-) Packed red
blood cells
24° Total
Brenner Children’s Hospital • Winston-Salem, N.C. Neonatal day record
Type of feeding
N - Nipple
NG - Nasogastric
OG - Oral gastric
GT - Gastrostomy
TP - Transpyloric
Other:
* Cumul. IV/feedings
FIGURE 14.3, cont’d
CHAPTER 14 Fluid and Electrolyte Management
Body weight (%)
Large
Small
Term
1-year-old
Adult
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411
Carb.
Fat
premature
infant
(2.0 kg)
Fat
Protein
Water
premature
infant
(1.0 kg)
100
Protein
80
60
Water
40
20
FIGURE 14.4 Effects of gestational age on body composition compared with older children and adults. (From Heird WC, Driscoll JM Jr,
Schullinger JN, et al. Intravenous alimentation in pediatric patients. J Pediatr. 1972;80:351.)
The ability of infants, especially those who are
premature, to remove free water and/or remove
a solute load is impaired. Once clinical signs
of fluid overload or deficit occur, it may be
difficult to regain balance. Fluid balance should
be managed prospectively; consistent assessments
and laboratory evaluations should be a part of every
initial care plan.
The effect of gestational age on body composition is striking (Fig. 14.4). Because gestational age
is a determinant of the percentage and distribution
of TBW, accurate assessment is important. In utero,
fetal fluid and electrolyte balance occurs through
feto-placental exchange. Changes in the distribution
and percentage of body water will be influenced by
intrauterine growth, maternal fluid balance, maternal
medications, maternal health conditions, and placental blood flow. For example, a preterm infant born
to a mother receiving magnesium sulfate may have
elevated serum magnesium levels at birth, which may
remain elevated for up to 3 to 5 days following birth.
Small-for-gestational-age (SGA) infants have reduced
amounts of fat, and their TBW (as a percentage of
TBM) increases. Conversely, large-for-gestational-age
(LGA) infants with an increased amount of body fat
have a lower percentage of TBW.
The initial (first 3 to 5 days of life) weight
loss of healthy term (up to 5% to 10% of TBM)
and preterm (up to 10% to 15% of TBM) infants
should be considered a normal physiologic loss of
infant
(3.5 kg)
Fat
Protein
Water
child
(10.5 kg)
Fat
Protein
Water
(70 kg)
Fat
Protein
Water
fluid. This loss is from the interstitial fluid (ISF).
It is not a pathologic catabolism of body tissues but a
result of the maturation of specific regulators of fluid
and electrolytes. One such example, vasopressin (antidiuretic hormone), is secreted during the early stages
of labor. This hormonal secretion contributes to renal
maturation and has an antidiuresis effect at birth.
26
After birth, contraction of the ECF compartment
occurs, followed by natriuresis, diuresis, and weight
loss.15 This weight loss is then regained over 7 to
10 days as muscle and fat, provided there is good
nutrition. Neonates often demonstrate relative
oliguria during the first 24 to 48 hours. Disease
processes, such as asphyxia, pneumonia, and respiratory distress syndrome (RDS), increase vasopressin
release; thus, the fluid and electrolyte transition
during the first few days of birth may be altered in
these conditions.
22,42,59
Neonates with RDS will also
have delayed postnatal contraction of the ECF compartment, further delaying diuresis. The onset of the
diuresis, during the first few days of life, usually coincides with the initial stages of recovery from RDS.
Despite the period of natriuresis after birth,
infants usually do not require additional sodium
during the first 24 to 48 hours of life. It is normal
to have an initial negative sodium balance, but later it
is necessary to retain sodium for appropriate growth;
additional sodium supplementation may be required.27
A review of maternal history and the intrapartum
course may be helpful in calculating the infant’s fluid
27
UNIT THREE Metabolic and Nutritional Care of the Neonate412
mEq/L
Interstitial
Plasma Intracellular
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200
180
160
140
120
100
80
60
40
20
fluid
0
Na
K
Ca
2
and Mg
2
HCO
Cl
U.A.
3
fluid
Protein
2
Mg
Org. P and Pr
FIGURE 14.5 “Gamblegram” of plasma interstitial fluid and intracellular fluid. (From Winters RW, ed. The Body Fluids in Pediatrics.
Boston: Little, Brown; 1973.)
and electrolyte requirements. For example, if the
mother received large amounts of electrolyte-free fluids
in the intrapartum period, the neonate may be hyponatremic and have an expanded ECF space at birth.
Extracellular fluid comprises both intravascu-
lar fluid (plasma) and ISF. The electrolyte compo-
sition of ISF and plasma is similar, but it is strikingly
different from ICF (Fig. 14.5). Sodium is the major
cation in ECF (both ISF and plasma) and is easily
measured. Potassium, the major cation in ICF, on the
other hand, cannot be measured readily because ICF
is not easily accessible. Because 90% of the total body
potassium is intracellular, low levels of plasma potassium are assumed to reflect low total body potassium.
Maintaining appropriate fluid and electrolyte
balance may be difficult due to the immaturity
of the neonatal renal system: (1) inability to dilute
urine secondary to lower glomerular filtration rate
(GFR) and (2) inability to concentrate urine secondary to renal tubular immaturity. The neonatal
GFR, a measure of renal function, is low in utero
but increases rapidly within a few hours after delivery and throughout the first postnatal week as renal
blood flow increases. This increased GFR is a result
34,66
of increasing cardiac output and increasing glomerular permeability.
27
GFR is independent of gestational age. It rises
rapidly during the first 6 weeks of life, increases more
slowly during infancy, and reaches adult values by 12
months of age. A VLBW infant in satisfactory condition
at 6 weeks should have a similar GFR to that of term
infants. The formation of nephrons is complete at 34 to
35 weeks’ gestation, whereas maturation of the nephrons continues beyond 40 weeks’ gestation.
15,21
The
GFR can be compromised in critically ill neonates.
In addition to fluid balance, the renal tubules are
responsible for mineral and electrolyte excretion
and reabsorption. Renal tubular function is influ-
enced by gestational age.27 At birth, immature
tubular function is associated with sodium wasting and an impaired ability to reabsorb water.28
These characteristics are exacerbated in premature infants.62 Preterm infants with immature
tubular function are more likely to experience
electrolyte imbalance.
The use of the urinary fractional excretion of
sodium (FENa) [FENa = (Urine sodium × Plasma
Cr)/(Urine Cr × Plasma sodium)] is an important
CHAPTER 14 Fluid and Electrolyte Management
mEq/L
0
0
Osmolar composition
Ionic composition
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413
of plasma
160
140
120
100
80
60
40
20
140
120
100
80
mOsm/L
60
40
20
FIGURE 14.6 Ionic and osmolar composition of plasma. (From Winters RW, ed. The Body Fluids in Pediatrics. Boston: Little, Brown;
1973.)
tool in assessing sodium balance but must be interpreted cautiously, especially shortly after birth, due to
the immaturity of renal tubular function. When using
FENa to diagnose the etiology of hyponatremia,
a value greater than 3% reflects an intrinsic renal
problem, whereas a value less than 2.5% reflects
a prerenal problem (e.g., volume depletion); both
values are higher than that expected for an adult.18 A
falsely elevated FENa may be present when excessive
sodium is lost in the urine due to prematurity or
with diuretic use.
30,69
The ability to excrete potassium is impaired
at birth, especially in low-birth-weight infants,
thus increasing their risk of hyperkalemia, particularly
when given a potassium load before establishing stable
renal function. Calcium reabsorption is also reduced
with immaturity and results in higher urinary
levels of calcium; thus, early use of loop diuretics
may lead to an increased risk of renal stones.
The capacity to concentrate urine in VLBW
infants appears limited but can be influenced by
gestational age and nutrient intake. The imma-
ture concentrating ability (maximum of approximately 600 mOsm/L) (Fig. 14.6) coupled with an
inability to rapidly excrete an acute water or sodium
load results in a narrow margin of safety when
prescribing fluid and electrolytes, especially in the
VLBW infant.
1,15,21
In general, urea is the major component of urine
osmolality (and hence specific gravity). When total
of plasma
(mOsm/L 2 [Na
parenteral nutrition is provided, urine specific gravity may rise because of a low renal threshold for
glucose and amino acids. Very preterm infants will
have glucosuria despite serum glucose levels in
the normal range. The renal protein and glucose
threshold increase with advancing gestation.
Neonatal urinary acidification is also limited, and
the threshold for bicarbonate excretion is reduced,
leading to both decreased bicarbonate retention and
acid excretion. Both physiologic and pathologic
factors can contribute to this urinary alkalinization.
Acidemia develops in premature infants due to this
limited capacity for hydrogen ion excretion. Alkaline
urine pH will precede the development of acidemia. Closely monitoring and replacing losses can
prevent the development of severe acidemia. In
more mature infants, urinary alkalinization will occur
in the setting of more acute illnesses, such as a urinary
31
tract infection or bicarbonate-losing tubular necrosis
that may occur in neonatal diagnoses associated with
acute kidney injury or with nephrotoxic medications.53 The ability to distinguish acidemia occurring from an acute illness versus a developmentally
impaired urinary acidification system is important
for proper treatment. The anion gap (serum Na+/
[serum Cl– + serum bicarbonate]) is a useful tool
in this assessment. The normal anion gap typically is less than 8. A widened anion gap is suggestive of increased production of organic acid,
in particular lactic acid (a pathologic condition),
])
Protein
U.A.
Cl
HCO
3
Na
K
2
Ca
and Mg
Glucose
2
UNIT THREE Metabolic and Nutritional Care of the Neonate414
Os
Normal
Concentration (%)
Lipemic
Plasma water
140 mEq/L
Plasma solids
1000
Urine osmolality (mOsm/L)
Urine flow (ml/kg/hr)
10
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100
75
50
25
0
FIGURE 14.7 Effects of hyperlipidemia on plasma water and plasma
sodium concentration. (From Winters RW, ed. The Body Fluids in Pediatrics.
Boston: Little, Brown; 1973.)
whereas a normal or narrow gap suggests bicarbonate loss due to the lowered threshold for
bicarbonate excretion in the neonate. Further
details are available in Chapter 8.
Hormones, including antidiuretic hormone,
aldosterone, atrial natriuretic factor, and parathyroid
hormone, are involved in regulating the neonatal
fluid and electrolyte balance, yet the specific roles
are not well defined. Most hormonal effects occur
by modifying renal function through a change
in either GFR or renal tubular permeability. For
example, the increased osmolality that occurs in
dehydration is a trigger for antidiuretic hormone
release, leading to changes in the permeability
of the distal tubule and collecting duct. This
change results in more water reabsorption and
thus more concentrated urine.
Osmolality can be satisfactorily estimated in many
clinical settings by the following formula (Fig. 14.7):
molality
Osmotic forces are responsible for apparently
low plasma electrolyte concentrations in some common clinical settings. For example, in hyperglycemia, the plasma sodium concentration reported by
the laboratory is usually low, but the total effective
osmolality may be normal. An analogous situation
plasma
Na
=
Na
121 mEq/L
2 N a
151
mEq/L
BU N (mg / dL) 2.8
plasma
Na
151
mEq/L
e (mg / dL) 18
Glucos
400
250
Na
150
100
50
25
10
0.1 0. 2 0.3 0.4 0.51.0 2.0 3.0 5.0
FIGURE 14.8 Normal urine flow rates. (From Jones MD, Gresham EL,
Battaglia FC. Urinary flow rate and urea excretion rates in newborn infants. Biol
Neonate. 1972;21:322.)
exists for the less frequent condition of hyperlipidemia, in which low laboratory plasma sodium
values are reported with a normal osmolality (Fig.
14.8). Low laboratory values for plasma sodium
(pseudohyponatremia) can be present in the
setting of hyperlipidemia or hyperglycemia. This
occurs because the increase in plasma solids (lipids)
causes a lower plasma water content, resulting in
water displacement and hence a lower sodium concentration per liter of whole plasma.
Osmotic forces largely determine shifts in the
internal redistribution of water in hydration disturbances. An example of changes in osmolality occurs
in preterm infants who undergo insensible water
loss because of skin immaturity, decreased body
fat, and a large surface-to-volume ratio leading to
increased evaporation. This water loss from the
interstitial space results in a hyperosmolar extracellular compartment exhibited by hypernatremia and
occasionally hyperkalemia and hyperglycemia.
15
Another key concept in fluid and electrolyte
balance involves insensible water losses (IWLs) that
occur via pulmonary and cutaneous routes and
are influenced by the factors listed in Table 14.1.
However, IWL varies greatly depending on
gestational age and birth weight (Table 14.2).
The neonate’s environment also can affect the fluid
balance. Radiant warmer usage decreases the
CHAPTER 14 Fluid and Electrolyte Management
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415
TABLE
14.1
NaCl 1 2 2
Glucose 1 1 1
CaCl
TABLE
14.2
DECREASE IWL INCREASE IWL
Heat shield or double-walled
incubators
Plastic blankets
Clothes
High relative humidity (ambient
ventilator gas)
Emollient use
EXAMPLES OF OSMOTIC FORCE
mM N mOsm
2
1 3 3
FACTORS THAT INFLUENCE INSENSIBLE
WATER LOSS (IWL)
Inversely related to gestational age
and weight
Respiratory distress
Ambient temperature above
thermoneutral
Fever
Radiant warmer
Phototherapy
Activity
neonate’s radiant heat loss but can increase IWL
by 50% to 200%, resulting in hypernatremic
dehydration.40 Incubators reduce radiant heat
loss via their double-walled Plexiglas design.
Modern incubators provide sterile humidity (80% or greater) and are very effective in
decreasing IWL by reducing evaporative heat
loss. Internal incubator humidification was discon-
tinued in the 1970s when it was associated with
Pseudomonas infections.41 Presumably, the nature of
Pseudomonas promoted its stability and growth in the
water humidification reservoirs. However, present
humidification designs provide for direct heating of
water in an external reservoir to a temperature that
kills most organisms. The water is transformed into
vapor, rather than mist, and carried in a gaseous state
by the incubator’s convective air flow, thus reducing
the possibility of airborne bacterial transfer.
41
Because added environmental humidity
reduces transcutaneous evaporative water loss,
an extremely preterm infant managed in humidity needs less fluid than those managed without
humidity to achieve the same water balance. A
relative humidity of 80% can reduce water loss
to one tenth of the water loss of a preterm infant
receiving care in 50% humidity.40 This reduction
in evaporative water loss affects the management of
fluid requirements and the electrolyte balance in
premature infants. For infants with a birth weight
of less than 1000 g, the use of humidity at 70%
to 80% in the first week of life results in lower
fluid intake and improved electrolyte balance
and growth velocity. A decreased risk of severe
BPD has also been reported in extremely lowbirth-weight (ELBW) infants cared for in humidified incubators.36 Despite these improvements, the
optimal level and duration of humidification have
yet to be determined.
The ability to provide the proper fluid and electrolyte balance is determined by assessing initial
fluid status, renal function, and estimated insensible
fluid losses. Frequent assessment of fluid balance
remains essential in preventing fluid deficit or overload, which can be difficult to correct once it has
occurred.
ETIOLOGY
The causes of common electrolyte problems and
common clinical syndromes are discussed under
Treatment later in this chapter.
PREVENTION
Prevention of fluid and electrolyte imbalance in neonates begins with knowing how to calculate fluid and
electrolyte requirements correctly. The estimated
metabolic rate forms the reference base for all calculations. The metabolic rate (and hence oxygen
consumption) normally increases steadily over the
first weeks of life, so changes in water and electrolyte requirements should be anticipated.
If the daily caloric requirement is approxi-
mately 100 kcal/kg/day, the physiologic basis of
metabolic rate may be used to calculate needs;
however, most institutions determine an infant’s
daily fluid need on a milliliters per kilogram (mL/kg)
basis, which is modified by factors that influ-
ence IWL and is usually adjusted depending on
body weight, clinical composition, serum chemistry
results, and urine volume and composition (Fig.
14.9; see also Table 14.2).
UNIT THREE Metabolic and Nutritional Care of the Neonate416
Urine
Composition
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Volume
Parenteral fluid IN OUT
Composition
Body
weight
changes
FIGURE 14.9 Basic scheme for monitoring and modifying fluid therapy.
Balance
Preterm infants have lower metabolic rates
than those of term infants.8 SGA infants may
have higher metabolic rates than those of preterm
infants of similar weight,7 which may be because
of their relatively large ratio of brain to body
mass. Infants with congenital heart disease,44 as
well as infants in the immediate postoperative
period,48 also have higher metabolic rates com-
pared with appropriate-for-gestational-age (AGA)
infants. Both SGA and preterm infants, especially
VLBW infants, should be expected to require more
frequent assessment and modification of requirements.
Preterm infants, however, are subject to other
problems that may diminish the influence of this
metabolic rate when calculating fluid needs. SGA
infants may require less water per kilogram than
either preterm or term AGA infants due to their
increased extracellular volume.45 Input should
be recorded every hour. Output should be
recorded hourly in critically ill infants but may
be recorded every 4 to 6 hours in infants who
require minimal stimulation. The smallest infants
require frequent fluid balance monitoring, so if
output is unusually large, intake can be adjusted
immediately. If fluid intake lags behind losses, critically ill infants may develop hypernatremia and may
not tolerate “catching up.” Continuous monitoring
is necessary to ensure that fluid is administered in
appropriate amounts. Current infusion pumps can
accurately infuse volumes of 0.01 mL/hr and
must be used for the smallest, sickest infants.
Requirements for fluid and electrolytes are
divided into maintenance and deficit needs.
Maintenance indicates the infant remains in a
zero-balance state and can be subdivided into (1)
normal loss, which consists of water and electrolyte
loss through stool, urine, and insensible (lung and
skin) routes; and (2) abnormal or increased losses,
Stool
Abnormal loss
Insensible loss
Body
fluid
chemistries
Volume
such as gastrointestinal/diarrhea, ostomy, and chest
tube drainage.
All diapers should be preweighed using a
gram scale and marked with dry/tare weight.
After each stool or void, the diaper is reweighed;
the difference equals the amount of loss. For
example, if the dry weight is 20 g and the wet
weight is 26 g, the difference is 6 g, or 6 mL of
stool or urine. All losses should be calculated to
the nearest milliliter.
The term deficit refers to previously incurred
losses. These should be uncommon in the newborn
but can occur when there are unrecognized losses,
such as “third space” or interstitial losses with NEC
(see later discussion). In older neonates, deficits
may occur with disorders that have an insidious or
delayed onset, such as renal tubular dysfunction or
nonvirilizing congenital adrenal hyperplasia.
Deficits are best estimated by body weight
comparisons. Weight loss greater than 10% to
15% in 1 week should be considered excessive,
although in VLBW infants it can be difficult
to maintain within 10% to 15% of birth weight
during the first week of life.71 Infants who are
SGA have less weight loss compared with AGA
infants72 in the first 10 days after birth. Growth
charts assist with calculations of weight loss and/
or gain and help consider the normal physiologic
weight loss that occurs during the first several days
after birth when calculating an infant’s fluid needs.
The initial choice of parenteral solution depends
on the weight and postnatal age of the infant
(Table 14.3). Also important is whether the infant
is in an incubator with a heated humidified environment or under a radiant warmer without a
plastic blanket or heat shield. Uncovered VLBW
infants under radiant warmers demonstrate
IWLs of up to 170 mL/kg/day,27 and the use
CHAPTER 14 Fluid and Electrolyte Management
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417
TABLE
14.3
WEIGHT (g) RANGES OF WATER LOSS DAY 1* DAYS 2–3* DAYS 4–7*
Less than 1250 IWL
1250–1750 IWL
More than 1750 IWL
Increment for phototherapy: 20–30 mL/kg/day if patient is in open warmer and has radiant phototherapy. No adjustment if baby is in humidified environment and/or has fiberoptic phototherapy source.
Increment for radiant warmer: 20–30 mL/kg/day.
Maintenance solutes: glucose: 7–12 g/kg/day (4–8 g/kg in VLBW infants)
*Adjustment based on a urine flow rate of 2–5 mL/kg/hr and a stable weight.
†
May be reduced by 30% if the infant is on a ventilator.
IWL, Insensible water loss; VLBW, very-low-birth-weight.
GUIDELINES FOR FLUID (mL/kg/day) AND SOLUTE PROVISION BY PATIENT WEIGHT AND DAYS OF
AGE
†
Urine 50–100
Stool 5–10
TOTAL 95–280 120 140 150–175
†
Urine 50–100
Stool 5–10
TOTAL 75–160 90 110 130–140
†
Urine 50–100
Stool 5–10
TOTAL 70–150 80 90 100–200
Na: 1–4 mEq/kg/day (2–8 mEq/kg/day in VLBW infants)
K: 1–4 mEq/kg/day
Cl: 1–4 mEq/kg/day
Ca: 1 mEq/kg/day
40–170
20–50
15–40
of radiant warmers should thus be avoided if
possible. Maintenance of water and glucose
needs in larger infants on the first day of life
can usually be met by a 10% glucose solution
infused at 60 to 80 mL/kg/day, which provides
an acceptable glucose infusion of about 4.2
to 5.5 mg/kg/min. The infusion rate can be
gradually increased over 4 to 5 days to 120 to
140 mL/kg/day using principles of monitoring
discussed later in this chapter.
All sick infants require IV access for fluid
administration. Placement of an IV line is the most
common procedure in the neonatal intensive care
unit (NICU).50 The IV equipment should include
(1) a needle or catheter, (2) connecting tubing, and
(3) an infusion pump.
Electrolytes such as sodium and potassium
are usually omitted for the first 1 to 2 days
of life and then added as the salt of acetate,
chloride, or phosphate in amounts of 1 to 4
mEq/kg/day. Mildly acidotic and VLBW infants
may be given their sodium requirements as sodium
acetate.5 Potassium should never be added to
IV fluid until urine flow and renal function
have been assessed. The initial requirement for
calcium is 1 mEq/kg/day (20 mg/kg/day), but
5
this rises to a maintenance requirement of 3 to
4 mEq/kg/day (about 60 to 80 mg/kg/day) of
elemental calcium, preferably given as calcium
gluconate (about 600 to 800 mg/kg/day).65 This
maintenance is most important in VLBW infants
and those who are severely ill. Careful observa-
tion of peripheral IV sites with the infusion
of IV fluids containing calcium is critical due
to the risk of tissue necrosis associated with
infiltration.
35
UNIT THREE Metabolic and Nutritional Care of the Neonate418
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Factors that influence IWL must be identified
early and maintenance needs adjusted appropriately to prevent problems with water and electrolyte balance. Humidified incubators significantly
decrease the IWL of ELBW infants. They require
less fluid intake, have lower percentage of weight
loss, and have fewer episodes of hypernatremia than
infants cared for in a nonhumidified incubator.36
Management of VLBW infants presents special,
complex problems, and continued research is
needed. The following observations may be helpful:
• Total fluid requirements should typically start
at 100 to 120 mL/kg/day at birth, although
some authors suggest as low as 80 mL/kg/
12,46,67
day,
and often need to be increased by
20 to 40 mL/kg/day over days 2 to 6 of life,
typically plateauing at 150 to 160 mL/kg/day.
Higher fluid requirements may be necessary for
VLBW infants managed on a radiant warmer or
in nonhumidified incubation. Careful restric-
tion of fluids, without allowing dehydration,
has been shown to decrease the risk of PDA
and NEC.10 A lower risk of BPD has also
been associated with early appropriate weight
loss in ELBW infants.
36,72
Careful restriction of
fluids allows for the normal contraction of extracellular fluid and appropriate weight loss while
maintaining physiologic needs.
10,25,46
• Cumulative weight loss plateaus at 10% to
15% of birth weight by postnatal day 3 to 5.
• Sodium requirements (including medications)
are 2 to 3 mEq/kg/day after 24 to 48 hours
of age and may reach a maximum of 4 to 5
mEq/kg/day during the first few weeks of life.
18
• Maintaining serum glucose concentrations (60
to 150 mg/dL) in VLBW infants may initially
require relatively less glucose than that of term
or near-term infants because their own endogenous glucose production may not be effectively
suppressed. However, in order to preserve
endogenous stores of glucose (e.g., glycogen)
in clinical practice, the preterm infant may
need up to 8 to 9 mg/kg/min of glucose,
whereas the term infant requires about 6 mg/
kg/min.19 In VLBW infants, a gradual increase
in the glucose infusion rate to 11 to 12 mg/
kg/min by the end of the first week of life is
usually well tolerated.5 The glucose concentra-
tion of the fluids administered may need to be
changed, sometimes frequently, to maintain an
appropriate serum glucose concentration. With
the larger initial fluid requirements of very tiny
babies, lower glucose concentrations, sometimes down to D5W (5 mg% or 5 mg/dL)
in IV fluids, are often prescribed for ELBW
infants as the initial fluid. As anticipated, infants
weighing less than 1000 g are the most difficult to
manage without inducing excessive weight loss,
hypernatremia, or hyperglycemia, especially those
stabilized under radiant warmers. They may have
greatly increased IWL with fluid requirements in
the range of 175 to 200 mL/kg/day or greater. By
the end of the first week of life, as the epithelium
cornifies, their daily requirements decrease to 120
to 150 mL/kg/day. When enteral caloric intake
is low (fewer than 50 kcal/kg/day), neonates
will require administration of IV fluids, which
should be provided as parenteral nutrition43
containing glucose, amino acids, lipids, vitamins,
and micronutrients in order to support growth
(see Chapter 17).
DATA COLLECTION
Parenteral therapy should be based on the following principles: (1) assess the patient’s clinical
status for maintenance needs, factors that modify
IWL, and confounding medical or surgical disorders; (2) calculate short-term (12 to 24 hours)
fluid and electrolyte needs; (3) initiate therapy at
the proper site and infusion rate; and (4) monitor and adjust the fluid infusion rate and content
based on clinical and biochemical data.
History
Factors influencing IWL (see Table 14.2) include
gestational age, birth weight, and postnatal age.
When the patient’s condition changes, it is important to detail the change to evaluate the potential
effect of the new condition on fluid and electrolyte
balance and requirements. Thus, NEC may be associated with an acute need for additional volume
expansion–type fluids because of “third space losses,”
whereas with acute renal failure, anuria should
prompt clinical reassessment and usually indicates
the need for reducing daily fluid administration.
Signs and Symptoms
Weight, urine output (Box 14.1), and serum
sodium concentration (Box 14.2) are the best
overall clinical guides to assess whether therapy is
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