TABLE 10-7 -- ISONATREMIC DEHYDRATION CALCULATIONS *

Example: 7-kg infant with 10% dehydration (≥3 days). Serum Na+ = 137. Illness weight = 6.3 kg.

 

H2 O (mL)

Na+ (mEq)

K+ (mEq)

Maintenance

700

21

14

DEFICIT

700

 

 

0.6 0.7 L 145 =

 

61

0.4 0.7 L 150 =

 

42

24-HOUR TOTAL

1400

82

56

FLUID SCHEDULE

 

 

 

First 8 hr⅓ maintenance

233

7

5

+ deficit

350

31

21

First 8-hr total

583

38

26

Exact calculations: 583 mL/8 hr = 73 mL/hr; 38 mEq Na+ /0.583 L = 65 mEq/L; 26 mEq K+ /0.583 L = 45 mEq/L)

Next 16 hr⅔ maintenance

467

14

9

+ deficit

350

30

21

NEXT 16-hr total

817

44

30

Exact calculations: 817 mL/16 hr = 51 mL/hr; 44 mEq Na+ /0.817 L = 54 mEq/L; 30 mEq K+ /0.817 L = 37 mEq/L)

A convenient fluid for this patient would be D5 NS + 40 mEq/L KCl or potassium acetate to run at 75 mL/hr for the first 8 hours and the same fluid at 50 mL/hr over the next 16 hours.

* In the absence of hypokalemia, 20 to 30 mEq/L of potassium is commonly used and is usually adequate; monitor carefully for hyperkalemia and adequate urine output if high concentrations of potassium are used. Potassium infusion rates should not exceed 1.0 mEq/kg/hr. If rate exceeds 0.5 mEq/kg/hr, the patient should be placed on a cardiorespiratory monitor.





TABLE 10-8 -- HYPONATREMIC DEHYDRATION CALCULATIONS *

Example: 7-kg infant with 10% dehydration (≥3 days). Serum Na+ = 115. Illness weight = 6.3 kg.

 

H2 O (mL)

Na+ (mEq)

K+ (mEq)

Maintenance

700

21

14

DEFICIT

700

 

 

Na+ 0.6 0.7 L 145

 

61

Excess Na+ deficit (135-115) 0.6 7

 

84

K+ 0.4 0.7 L 150

 

42

24 HR TOTAL

1400

166

56

FLUID SCHEDULE

First 8 hr⅓ maintenance

233

7

5

+ deficit

350

73

21

First 8-HR TOTAL

583

80

26

Exact calculations: 583 mL/8 hr = 73 mL/ hr; 80 mEq Na+ /0.583 L = 137 mEq/L ; 26 mEq K+ /0.583 L = 45 mEq/L

Next 16 hr⅔ maintenance

467

14

9

+ deficit

350

72

21

NEXT 16-HR TOTAL

817

86

30

Exact calculations: 817 mL/16 hr = 51 mL/hr; 86 mEq Na+ /0.817 L = 105 mEq/L; 30 mEq K+ /0.817 L = 37 mEq/L

A convenient fluid for this patient would be D5 NS + 40 mEq/L KCl or potassium acetate to run at 75 mL/hr for the first 8 hours and D5 NS and 40 mEq/L KCl or potassium acetate at 50 mL/hr over the next 16 hours.

* In the absence of hypokalemia, 20 to 30 mEq/L of potassium is commonly used and is usually adequate; monitor carefully for hyperkalemia and adequate urine output if high concentrations of potassium are used. Potassium infusion rates should not exceed 1.0 mEq/kg/hr. If rate exceeds 0.5 mEq/kg/hr, the patient should be placed on a cardiorespiratory monitor.





TABLE 10-9 -- HYPERNATREMIC DEHYDRATION CALCULATIONS

Example: 7-kg infant with 10% dehydration (≥3 days). Serum Na+ = 155. Illness weight = 6.3 kg.

 

H2 O (mL)

Na+ (mEq)

K+ (mEq)

24-hr maintenance

  700

21

14

DEFICIT

Free water 4 mL/kg 7 kg (155-145)

  280

 

 

Solute fluid

  420

 

 

  0.6 0.42 145

 

37

  0.4 0.42 150

 

25

24-HOUR TOTAL

1400

58

39

FLUID SCHEDULE

First 24 hr 24-hr maintenance

700

21

14

Free-water deficit

140

Solute fluid deficit

420

37

25

FIRST DAY TOTAL

1260

58

39

Calculations: 1260 mL/24hr = 53 mL/hr; 58 mEq Na+ /1.26 L = 46 mEq/L; 39 mEq K+ /1.26 L = 31 mEq/L)

An appropriate initial fluid for this patient would be D5 NS with 30 mEq/L KCl or potassium acetate to run at 50 mL/hr for the first 24 hours. Follow serum Na+ and adjust fluid composition and rate based on clinical response. The second half of the free-water deficit may be replaced subsequently over the next 24 hours, or more rapidly depending on the rate of decline of serum Na+ (avoid decline of >15 mEq/L in 24 hours).

 

TABLE 10-10 -- DEFICITS OF WATER AND ELECTROLYTES IN SEVERE DEHYDRATION

Condition

H2 O (mL/kg)

Na+ (mEq/kg)

K+ (mEq/kg)

Cl (mEq/kg)

DIARRHEAL DEHYDRATION

Hyponatremic

[Na+ ] * <130 mEq/L

100-120

1015

8-15

1012

Isotonic

[Na+ ] * = 130-150 mEq/L

100-120

8-10

8-10

8-10

Hypernatremic

[Na+ ]* >150 mEq/L

100-120

2-4

0-6

0-3

PYLORIC STENOSIS

100-120

8-10

10-12

10-12

DIABETIC KETOACIDOSIS

100

8

6-10

6

From Hellerstein S. Pediatr Rev 1993; 14(3):103-115.

*[Na] refers to the serum or plasma sodium concentration.