Fluids, Electrolytes, and Acid–Base Balance

Maintenance IV Fluid (MIVF) and Electrolyte Requirements

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Daily Fluid Requirements

Kilograms of Body Weight–Based Method (Pediatrics. 1957;19:823)

  • 1–10 kg: 100 mL/kg/d and
  • 10–20 kg: 50 mL/kg/d and
  • >20 kg: 20 mL/kg/d

BSA-Based Method (Pediatrics. 1960;25:496)

  • See “BSA Nomogram and Calculations” in Chapter 1 for BSA calculation.
    • BSA (m2) × 1500–1600 mL/m2/d = Daily requirement

  • Examples (22-kg child):
    • Daily (body weight–based method): (100 mL/kg/d × 10 kg) + (50 mL/kg/d × 10 kg) + 20 mL/kg/d × 2 kg) = 1540 mL/d (divide by 24 for hourly rate = 64 mL/h)
    • Daily (BSA-based method): 0.84 m2 × 1600 mL/m2/d = 1344 mL/d (divide by 24 for hourly rate = 56 mL/h)

Glucose

  • Included in IV fluids to prevent protein catabolism, 3–4 mg/kg/min (not calorically adequate; see TPN section in Chapter 4 for parenteral nutrition).
    • D5W = 5% glucose solution = 5 g glucose/dL = 5 g glucose/100 mL = 50 mg/mL water

Sodium (Na)

  • Maintenance: 2–3 mEq/kg/d
    • Normal saline (NS) = 0.9% saline = 154 mEq/L; ½ NS = 0.45% saline = 77 mEq/L; ¼ NS = 0.225% saline = 38 mEq/L
  • For 1x MIVF, the following saline concentrations approximate maintenance Na: D1/4NS for 0–20 kg and D1/2NS for >20 kg

Potassium (K)

  • Maintenance is age dependant.
    • Infant; 2–3 mEq/kg/d
    • Child: 1–2 mEq/kg/d
    • Adolescent: 1 mEq/kg/d
    • Adult: 0.5–1.0 mEq/kg/d
    • K should always be added if anticipated duration of IVF greater than 24 h
    • When providing 1x MIVF, adding KCl 20 mEq/L to IVF will approximate daily maintenance for all ages

Modifications to Maintenance Daily Fluid Requirements:

  • Calculations above are for 1x MIVF, assuming an average, hospitalized patient with caloric demands 20% to 30% above resting energy expenditure.
  • Any perturbation affecting fluid intake or output or energy demand or /utilization directly affects daily MIVF needs

Increased Mivf Needs

  • ↑ Fluid losses: Renal (renal tubular injury, hyperglycemia, diuretic administration, mannitol administration, diabetes insipidus), GI (vomiting, diarrhea, NG suction, burns (see Critical Care chapter)
  • ↑ Energy expenditure: Fever (↑ 12% for each °C over 37°C), radiant warmer, hyperthyroidism, hypermetabolic states

Decreased Mivf Needs

  • ↓ Fluid losses: Anuric or oliguric renal failure, SIADH, ventilation with humidified air (decreases insensible loss)
  • ↓ Energy expenditure: Coma, sedation, paralysis, hypothermia, hypothyroidism

Replacement of Fluid Deficits

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  • All calculations are based on the condition at the time of initiation of fluids; ongoing losses must be addressed as observed.
  • End points to follow in all patients: Clinical improvement, weight gain, urine output.
  • Bicarbonate administration should be avoided for initial replacement and then utilized only in extreme cases (serum HCO3 <8).
    • [Desired HCO3 (24 mEq/L) – current HCO3] × 0.5 × [wt in kg] = HCO3 to administer slowly over hours to days

Weight-Based Determination of Degree of Dehydration

  • Percentage of total body weight lost acutely is attributable to loss of body fluid Infant (<15 kg): ≤5% mild, 6–10% moderate, ≥11% severeOlder child (≥15 kg): ≤3% mild, 6% moderate, ≥9% severe
  • Example (child with pre-illness weight of 20 kg who now weighs 19 kg):
  • Weight loss 1 kg = 1-L fluid loss/20 kg body wt = 5% dehydration

Symptomatic Determination of Degree of Dehydration*

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Symptom

Mild

Moderate

Severe

Mental status

Normal and alert

Normal to fatigued, restless, or irritable

Apathetic, lethargic, unconscious

Thirst

Normal or may refuse liquids

Thirsty, eager to drink

Poor or absent desire to drink

Heart rate

Normal

Normal to tachycardic

Tachycardic → bradycardic

Quality of pulses

Normal

Normal to decreased

Weak, thready

Breathing

Normal

Normal to tachypneic

Deep

Eyes

Normal

Slightly sunken

Deeply sunken

Tears

Present

Decreased

Absent

Mouth and tongue

Moist

Dry

Parched

Skin fold

Instant recoil

Recoil in <2 sec

Recoil in >2 sec

Capillary refill

Normal

Prolonged (>2 sec)

Prolonged, minimal

Extremities

Warm

Cool

Cold, mottled, cyanotic

Urine output

Normal to decreased

Decreased

Minimal to none

Blood pressure

Normal

Orthostatic hypotension

Hypotension

*This table was developed for children with dehydration caused by GI losses; extrapolate to other clinical scenarios only as appropriate.

Reproduced with permission from Morbid Mortal Wkly Rep. 2003;52(RR-16):1.

Biochemical Classification of Dehydration

  • Clinical parameters determine the degree of dehydration, and biochemical parameters (primarily serum sodium) guide the choice of rehydration fluids.

Types of Dehydration with Associated Fluid and Sodium Deficits

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Type

Biochemical Characteristics

Deficits*

Serum Sodium (mEq/L)

Serum Osmolality (mOsm/L)

Fluid (mL/kg)

Na (mEq/kg)

Isonatremic

130–150

280–300

100–120

8–10

Hypernatremic

>150

>300

100–120

2–4

Hyponatremic

<130

<280

100–120

10–12

*Deficits shown are averages to demonstrate the relationship of fl uid (water) to sodium loss.Data from Alario AJ, Birnkrant J, eds. Practical Guide to the Care of the Pediatric Patient, 2nd ed. Elsevier Mosby;2007:223.

Correction of Hypernatremic and Hyponatremic Dehydration

  • See “Hypernatremia” and “Hyponatremia” in this chapter.

Correction of Isonatremic Dehydration (Most Common Type of Dehydration)

Oral Rehydration for Mild to Moderate Isonatremic Dehydration

  • Oral rehydration is as efficacious as IV rehydration for acute gastroenteritis and may result in shorter hospitalization; this is best with one-on-one care from adult caregiver (Cochrane Database 2006(3):CD004390, Pediatrics 1996;97(3):424).

Oral Rehydration Strategies

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Degree of Dehydration

Rehydration (Deficit Replacement)

Replacement of Ongoing Losses

Nutrition

Minimal dehydration or prevention of dehydration

Not applicable

Normal daily maintenance fluid (eg, 100 mL/ kg for <10 kg) plus 60–120 mL (<10 kg) or 120–240 mL (≥10 kg) ORS for each diarrheal stool or vomiting episode

If possible, continue with breastfeeding or age-appropriate normal diet after initial hydration, including adequate caloric intake (do not restrict diet and do not discontinue breastfeeding)

Mild to moderate dehydration

ORS 50 mL/kg (mild) to100 mL/kg (moderate) over 4 h in small, frequent aliquots (5–10 mL every 5–10 min)

Same as above

Same as above

Pediatrics 1996;97(3):424–435 and Morbid Mortal Wkly Rep 2003;53(No. RR-16).

  • Resume normal diet as soon as tolerated; do not restrict diet (eg, BRAT diet).
  • Encourage breastfeeding; do not dilute or change from standard formula.
  • Generally, a lower osmolality and lower carbohydrate content are tolerated better. Avoid antibiotics, antidiarrheals, and anticholinergics (hyoscyamine).
  • IV ondansetron may ↓ emesis (Pediatrics 2002;109:e62).
  • Oral zinc (15–30 mg/d) ↓ duration of acute or persistent diarrhea in children older than age 6 mo, especially in developing countries, where malnutrition is prevalent (Cochrane Database Syst Rev 2008(3):CD005436, Morbid Mortal Wkly Rep 2003;52 (RR-16):1).
  • Oral rehydration solution (ORS) should be WHO oral rehydration solution or a solution similar in composition.

Composition of Selected Enteral Products

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Enteral Solution

kcal/oz

CHO (g/dL)

Na (mEq/dL)

K (mEq/dL)

Ca (mg/dL)

P (mg/dL)

Approximate Osmolality

Oral Rehydration Solutions

Enfalyte

3

5

2.5

0

0

200

Pedialyte (flavored)

2.5

4.5

2

0

0

250

Rehydralyte

2.5

7.5

2

0

0

310

WHO oral rehydration solution 1975*

2.0

9.0

2

0

0

311

WHO oral rehydration solution 2006

-—

1.35

7.5

2

0

0

245

General Formulas

Boost

30

17

2.4

4.3

64

131

610–670

Human breast milk

20

7.1

0.7

1.3

17

14

260

Enfamil Lipil

20

7.4

0.8

1.9

26

29

300

Ensure

31

18

3.6

3.9

73

125

590

Jevity

32

15.5

4

4

45

76

300

Milk (1%, cow)

12.8

5.3

1.8

3.9

38

95

280

Milk (whole, cow)

18

4.6

1.8

3.7

58

93

280

Nutren 1.0

30

12.7

3.8

3.2

33

67

315–370

Nutren 2.0

60

19.6

5.7

4.9

67

134

745

Nutren Jr.

30

11

2

3.4

50

80

350

PediaSure

30

13.5

1.7

3.3

48

80

430–520

Similac Advance

20

7.3

0.7

1.8

26

28

300

Special Formulas

Neocate infant

20

7.9

1.1

2.7

42

63

375

Neocate Jr

30

10.4

1.8

3.5

50

94

610

Nepro

54

17

4.6

2.7

53

70

665

Nutramigen Lipil

20

7

1.4

1.9

32

43

270

Pregestimil

20

6.9

1.4

1.9

39

51

330

Pulmocare

45

10.6

5.7

5

53

106

475

Suplena

60

20

3.4

2.9

139

70

600

Other fluids

Apple juice (Minute Maid)

10

11.7

0.1

1

650–750

Colas and sodas (Coca-Cola Classic)

12.1

11.3

0.2

0

5.1

390–750

Chicken broth

∼1–5

25

0.8

500

Gatorade: Lemon-lime flavor

6.3

5.8

2

0.3

330

*Monitor for hypernatremia given the high sodium content; developed for rehydration (not maintenance) in areas without IV capability.

— = no information.

MMWR 2003;52(RR.16):1.16.

IV Rehydration

  • This is for patients with severe isonatremic dehydration, or oral rehydration failure and those unable to tolerate PO.
  • It is divided into the initial emergent rehydration phase and the subsequent second fluid hydration phase.
    • Initial rehydration phase (correction of hypovolemia, mental status, perfusion)
      • Done over initial 2–4 h using NS or LR (20 cc/kg boluses).
      • There is no benefit of using colloid over crystalloid fluids for resuscitation (Cochrane Database Syst Rev 2000(2):CD000567).
    • Second phase of rehydration
      • Administration of maintenance fluid needs (based on weight), replacement of any additional deficits not replaced in the initial rehydration phase (estimated by weight loss or clinical evaluation at presentation), replacement of continuing losses (strict input and output recording), correction of electrolyte imbalances.
      • Choice of fluids is based on the status of the patient’s sodium and potassium levels and the need to correct electrolyte imbalances.
        • NS to correct any residual volume deficits.
        • 1/2 NS or NS for maintenance fluids and continued loss replacement. NS is not usually maintenance fluid; however, it may be beneficial in preventing hyponatremia from hypotonic fluids in hospitalized dehydrated pts (due to ADH in this population).

Composition of Commonly Used IV Fluids

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Na (mEq/L)

Cl (mEq/L)

Lactate* (mmol/L)

K (mEq/L)

Ca (mg/dL)

Total mosm/L

ECF

142

103

1

4

8.5

290

NS (0.9%)

154

154

0

0

0

308

D5 ½ NS (0.45%)

77

77

0

0

0

432

D5 ¼ NS (0.22%)

38

38

0

0

0

355

Hypertonic saline (3%)

513

513

0

0

0

1026

LR

130

109

28

4

3

274

5% albumin

130–160

130–160

0

0

0

265

Isolyte M

36

49

20 (acetate)

35

0

390

Isolyte P

23

20

23 (acetate)

340

D5W

0

0

0

0

0

278

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Jan 9, 2019 | Posted by in PEDIATRICS | Comments Off on Fluids, Electrolytes, and Acid–Base Balance

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