Fluid and Electrolytes: TUSM III Pediatric Clerkship Lecture Series

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Fluid and ElectrolytesTUSM III Pediatric
Clerkship Lecture Series

• Margaret Rounds, MD
• Baystate Medical Center
• Departments of Pediatrics
• July 26, 2004

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Objectives

• Understand maintenance fluid therapy
• Fluid composition
• Fluid rate
• Calculate fluid therapy in dehydration
• Understand differences in fluid therapy for
  hyponatremia and hypernatremia

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Parenteral Fluid Therapy

• IVF is a basic component of the care of
  hospitalized infants and children
• Fluid and electrolyte problems can be
  challenging, but can be tamed by an organized
  approach
• Useful to consider separately the following
  questions
• How much? or volume and rate
• What kind? or electrolyte constitution

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Parenteral Fluid Therapy

• IVF therapy is tailored to address differing
  clinical needs
• Maintenance
• Deficit
• Ongoing losses

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Maintenance Fluid

• Metabolism creates two by-products which must be
  actively eliminated to maintain homeostasis
• Heat dissipated by insensible losses from skin
  and lung
• Solute waste products of metabolism excreted
  into the urine

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Maintenance Fluid

• Basal Metabolic Rate does not directly relate to
  body weight
• BMR is much higher in the neonate than the adult
  and the transition is not linear
• As a result, adults need less fluid and
  electrolytes than children per kg of bodyweight

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Methods of Estimating Maintenance Fluids

• Methods of estimating basal or maintenance fluid
  requirements
• Body Surface Area
• Need to know height and weight, requires table,
  does not allow for deviations from normal
  activity
• Basal or Calorie Expenditure Method
• Requires a table, involves calculations, permits
  correction for changes in activity or injury,
  drier
• Holliday-Segar System
• Easy to remember, does not require table or
  difficult calculations, does not allow for
  deviations from normal activity

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Holliday-Segar Formula

• How does it work?
• Estimates that 1 kcal of energy requires 1 cc of
  fluid to maintain homeostasis
• Derives from fact that for each 100 kcal of
  energy expended, 50 cc of fluid are lost through
  the skin and airways, and 55 to 65 cc of fluid
  are required to generate an isosmotic urine (300
  mOsm/L)
• Heat dissipation and solute excretion each
  represent roughly 50 of maintenance needs
• Anuric patients have one-half maintenance needs

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Maintenance Electrolytes

• No electrolytes are lost in sweat or exhaled
  water vapor all electrolyte losses are urinary
• Thus, anuric patients have no maintenance sodium
  or potassium needs
• Since sodium and fluid requirements are based on
  BMR, the ratio of electrolyte to water is fixed
  and maintenance fluid requirements are the same
  for all patients (regardless of age)
• (D5 0.2 NS 20 mEq/L of K)

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Fluid Composition
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Maintenance Electrolytes

• Estimated electrolyte needs
• Na 3meq/100ml 30 meq/L
• Cl 2 meq/100ml 20 meq/L
• K 2 meq/100 ml 20 meq/L
• Maintenance fluid composition comes to D5 0.2NS
  with 20 meqKCl/L

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Clinical Practice

• Why do we give D5 0.45 NS with 20 K to kids over
  10 kg?
• ADH is increased during illness
• Many have diarrhea/vomiting as ongoing losses
• Why do we give D5 0.2 NS with 20 K to kids under
  10 kg?
• The kidney continues to mature after birth, and
  has decreased concentrating ability

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Deficit Fluid

• Definition Amount of fluid lost before treatment
  is begun
• One-time estimate additional losses after
  therapy is begun are considered on-going losses
• Methods
• Weight loss due to acute illness
• Fluid deficit (L) Preillness weight (kg)
  current weight (kg)
• Estimation of dehydration
• Fluid deficit (L) dehydration x Preillness
  weight (kg) / 100
• Clinical estimates of weight loss

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Deficit Electrolytes

• Sodium usually in pediatrics, losses are
  gastrointestinal or due to a relatively short
  period of decreased oral intake
• approximated by 0.45 NS
• Potassium deficit replacement is based on rate
  of safe replacement and not amount since danger
  of hyperkalemia is greater than hypokalemia
• Add 20 mEq potassium/L after UOP is established
• Potassium infusion rate should not exceed 1
  mEq/kg/hour unless in monitored setting

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Ongoing losses Fluid and Electrolytes

• Fluid abnormal losses that occur after the
  one-time determination of a deficit
• Diarrhea, vomiting, NG aspirates, polyuria
• Measured and replaced cc for cc
• Electrolytes
• Consult tables for electrolyte composition of
  on-going losses
• GI losses 0.45 NS
• Transudates 0.9 NS
• Radiant losses sodium free

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Overview of Parenteral Rehydration Strategy

• Phase I (immediate) If the patient is
  hemodynamically unstable or in shock, one or
  more boluses of 20 cc/kg isotonic fluid (0.9NS
  or LR) should be given in the first 30 minutes
• Phase II (deficit, maintenance, ongoing fluid
  replacement)
• Calculate fluid deficit
• Calculate maintenance fluid
• Give ½ of deficit therapy maintenance over
  first 8 hours and remainder of deficit
  maintenance over next 16 hours (or replaced
  deficit over 1st 8 hrs and 24 hrs of maint fluids
  over next 16 hrs.)
• Adjust above based on consideration of ongoing
  losses likely to be encountered

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Case 1

• A 5 month male old infant is brought to your ER
  with 4 day history of vomiting, diarrhea, and
  reduced oral intake. UOP is markedly reduced. On
  exam, the infant is fussy but consolable. He
  pushes you away when you try to examine him.
  Weight is 6.3 kg (5-25th ile), BP is 90/55 (50th
  ile), HR is 190 (gt95th ile). The fontanelle is
  slightly sunken and his skin turgor is
  diminished. The cardiopulmonary, abdominal, and
  neurologic exams are normal. He has stopped
  vomiting but refuses to drink.

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Case 1 Solution ACombined Deficit/Maintenance

• Bolus 140 cc (20 cc/kg) of NS given for
  hemodynamic instability
• Deficit Fluid
• No preillness weight, so must estimate
• Oliguria, tachycardia, no shock ? 10 dehydrated
• Deficit 10 x 7kg wt loss / 100 0.7L or 700cc
• (alternatively 10cc/kg weight loss x 7 kg 700
  cc)
• Maintenance Fluid
• Holliday-Segar 4 cc/kg for first 10 kg 7 kg x
  4 cc/kg 28 cc/hr
• Note Should use preillness weight to calculate
  deficit (6.3 kg x 100)/(100-10) 7 kg

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Case 1 Solution A Combined Deficit/Maintenance

• First 8 hours
• Maintenance
• 28 cc/hr x 8 hours 224 cc
• In theory D5 0.2 NS 20 mEq KCl/L
• In practice D5 0.45 NS 20 mEq KCl/L
• Half Deficit 700/2 350 cc of 0.45 NS
• Total Fluid 574 cc/ 8 hour 71.8 cc/hr
• IVF 75 cc/hr of D5 0.3 NS 20 mEq KCl/L
• In practice, we would give D5 ½ NS 20 K
• ADH is increased
• We usually choose between ¼ NS and ½ NS

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Case 1 Solution A Combined Deficit/Maintenance

• Next 16 hours
• Maintenance
• 28 cc/hr x 16 hours 448 cc
• In theory D5 0.2 NS 20 mEq KCl/L
• In practice D5 0.45 NS 20 mEq KCl/L
• Half Deficit 700/2 350 cc of 0.45 NS
• Total Fluid 798 cc/ 16 hour 49.9 cc/hr
• IVF 50 cc/hr of D5 0.45 NS 20 mEq KCl/L

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Case 1 Solution B Sequential Deficit/Maintenance

• Bolus 140 cc (20 cc/kg) of 0.9 NS
• First 8 hours
• Remainder of Deficit 20 cc/kg bolus represents
  2 of body weight. Since infant was 10
  dehydrated, the remainder of deficit after the
  bolus is 8 (or 80 cc/kg). This can be replaced
  over next 8 hours at 1/hr.
• 1/hr 10 cc/kg/hr 70 cc/hr
• IVF (Deficit) D5 0.45 NS 20 mEq/L KCl

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Case 1 Solution B Sequential Deficit/Maintenance

• Next 16 hours
• Days worth of maintenance fluid is then provided
  in next 16 hours
• 4 cc/kg/hr x 7 kg x 24 hours 672 cc Fluid
• 672 cc/16 hours 42 cc/hr
• IVF (Maintenance)
• In theory D5 0.2 NS 20 mEq/L KCl
• In practice D5 0.45 NS 20 K

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Monitoring Effectiveness of Parenteral Therapy
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Oral Rehydration Therapy

• Indications mild to moderate dehydration
• Contraindications shock, severe dehydration,
  intractable vomiting, coma, gastric distension
• Method give 5-10 cc of ORT q 5-10 minutes
• Fluids Cerealyte, Pedialyte, Naturalyte,
  Rehydralyte, WHO/UNICEF ORS (One teaspoon salt, 8
  teaspoon sugar, 1 liter water)
• Avoid soda, juice, gatorade, jello
• Lack sufficient sodium and potassium, are often
  hyperosmolar, can perpetuate diarrhea

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Disorders of Sodium

• Serum Sodium gt Osmolality lt Water
• Regulated by thirst , ADH, renal water handling
• A disruption in water balance is manifested as an
  abnormality in serum sodium
• Sodium is a functionally impermeable solute, so
  it contributes to tonicity and induces water
  movement across membranes
• Hypernatremia hyperosmolar (hypertonic)
  Hyponatremia hyposmolar (hypotonic)

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• Hypernatremia Serum Sodium gt 145 mmol/L
• Hypernatremia represents a deficit of water in
  relation to the bodys sodium stores
• Net water loss
• Common
• Hypertonic sodium gain
• Uncommon
• Usually iatrogenic

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Hypernatremia Clinical Manifestations

• Related to CNS dysfunction sequelae are
  prominent when the increase in serum sodium is
  rapid or large
• Affects the very young or very old
• Infants hyperpnea, muscle weakness,
  restlessness, high-pitched cry, insomnia,
  lethargy, or coma. Seizures are uncommon.
• Elderly often asymptomatic until Na gt 160

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Hypernatremia Management

• Approach
• Identify Cause
• Correct Hypertonicity
• Rapid Correction
• Improves prognosis in patients in whom
  hypernatremia developed acutely (sodium loading)
• Correct serum sodium by up to 1 mmol/L/hr

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Hypernatremia Management

• Slow Correction
• Prudent in patients with hypernatremia of longer
  or unknown duration
• Correct sodium by 0.5 mmol/L/hr or 10 mmol/d with
  goal of 145 mmol/L
• Others suggest adding the calculated fluid
  deficit to maintenance fluid requirements and
  giving over 48 hours
• IVF
• Only hypotonic fluids are appropriate unless
  frank circulatory collapse exists
• The more hypotonic the infusate, the lower the
  required volume to correct the hypertonicity, and
  the lower the risk of cerebral edema

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Hypernatremia Management

• Rate of infusion is calculated using the Madias
  Formula which estimates the change in serum
  sodium caused by 1 liter of any infusate. The
  required volume, and thus rate, is determined by
  dividing the change in serum sodium desired for a
  given period of time by the value obtained from
  Madias formula.

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Case 2

• A 1 week old female neonate is admitted to the
  PICU after increasing lethargy and difficulty
  with breastfeeding. Her birthweight was 3.8 kg.
  Her admission weight is 3.3 kg. On exam, the
  infant is difficult to arouse. BP is 72/62 (75th
  ile), HR is 120 (50th ile), RR is increased at
  60. The PE is unrevealing except for hypotonia
  and decreased level of consciousness. The nurse
  informs you the sodium is 165 mmol/liter.

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Case 2 Solution A

• Bolus? no
• Deficit Fluid
• Deficit 3.8 kg 3.3 kg 0.5 kg or 500 cc
• Maintenance Fluid
• Holliday-Segar 4 cc/kg for first 10 kg 3.8 kg x
  4 cc/kg 15.2 cc/hr
• 48 hours needs
• Deficit 500 cc of 0.45 NS
• Maintenance 15 cc/hr x 48 hr 720 cc of D5 0.2
  NS 20 mEq KCl/L
• Total Fluid 500 cc 720 CC 1200 cc/ 48 hour
  25 cc/h
• IVF 25 cc/hr of D5 0.3 NS 20 mEq KCl/L

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Case 2 Solution B

• Deficit (Madias Formula)
• TBW (0.8 x 3.8kg) 3 L
• Retention of 1 L of 0.2 NS will reduce the serum
  sodium by 40 (34-195/31)
• The goal of therapy is to reduce the serum sodium
  by 20 mmol/L in 48 hours. Therefore, 20/40 is 0.5
  L or 500 cc of fluid is required.
• 48 hour needs
• Deficit 500 cc of D5 0.2 NS
• Maintenance 3.8 kg x 4 cc/kg 15.2 cc/hr x 48
  hr 720 cc of D5 0.2 NS 20 mEq KCl/L
• Total Fluid 500 cc 720 CC 1200 cc/ 48 hour
  25 cc/h
• IVF 25 cc/hr of D5 0.2 NS 20 mEq KCl/L

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Hyponatremia

• Serum Sodium lt 136 mmol/L
• Hypotonic hyponatremia results from an excess of
  water in relation to existing sodium stores,
  which can be decreased, normal, or increased.
• Impaired renal water excretion
• common
• Excess water intake
• uncommon

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• Adults thiazide diuretics, SIADH, polydipsia,
  and TURP
• Children GI fluid loss, ingestion of dilute
  formula, accidental ingestion of water, and
  multiple tap water enemas.

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Hyponatremia Clinical Manifestations

• Related to CNS dysfunction sequelae are
  prominent when the decrease in serum sodium is
  rapid or large
• Symptoms Headache, nausea, vomiting, muscle
  cramps, lethargy, restlessness, disorientation,
  and depressed reflexes
• If Na lt 125 mmol/L seizure, coma, brain damage,
  herniation, and death

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Hyponatremia Management

• Symptomatic Hypertonic saline therapy (can be
  combined with furosemide to limit expansion of
  ECF)
• Correct 1-2 mmol/L/hour x several hours if
  severly symptomatic
• Target for increase in serum sodium of no more
  than 8 mmol/d to prevent osmotic demyelination
• Asymptomatic Fluid therapy is guided by Madias
  Formula

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Hyponatremia Management

• Rate of infusion is calculated using the Madias
  Formula which estimates the change in serum
  sodium caused by 1 liter of any infusate. The
  required volume, and thus rate, is determined by
  dividing the change in serum sodium desired for a
  given period of time by the value obtained from
  Madias formula.

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Case 3

• A 12 year old male is found unresponsive at the
  bottom of a swimming pool. He is resuscitated in
  the field and on arrival to the ER is intubated
  and ventilated but has a spontaneous pulse. In
  the trauma room, he develops generalized
  tonic-clonic seizures. He is loaded with
  phenytoin. His stat sodium then returns at 110
  mmol/L. His weight is 45 kg, BP is 100/70
  (normal), HR is 100 (normal). On exam, he is
  unresponsive and his right pupil is sluggish.

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Case 1 Solution

• Initial management is to prevent cerebral edema
  and herniation TBW 0.6 x 45 kg 27 L
• Madias Formula Retention of 1 L of 3 NS will
  increase the serum sodium by 14.4 mmol
  (513-110)/(271)
• The goal of therapy is to increase the serum
  sodium by 5 mmol/L in 3 hours. Therefore, 5/14
  210 cc of fluid is required.
• IVF 210 cc/3 hr 70 cc/hr of 3 NS x 3 hours.

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References

• Adrogue, HJ and NE Madias. Hypernatremia. New
  England Journal of Medicine. 2000 342(20)
  1493-1499.
• Adrogue, HJ and NE Madias. Hyponatremia. New
  England Journal of Medicine. 2000 342(21)
  1581-1589.
• Choukair, MK. Fluids and Electrolytes. In
  Siberry GK and R. Iannone, ed. The Harriet Lane
  Handbook. 15th ed. St. Louis, MO Mosby 2000
  229-240.
• Roberts, KB. Fluid and Electrolytes Parenteral
  Fluid Therapy. Pediatrics in Review. 2001
  22(11) 380-387.