Section 13. Fluids and Electrolytes

Hypotonic Fluids

D5W

Fluid maintenance

May impair glucose control in diabetes; provides free water to all compartments

• Maintenance dosing according to the 4:2:1 rule:

• 4 mL/kg/hr for 1–10 kg
• Add 2 mL/kg/h for 10–20 kg
• Add 1 mL/kg/h for every kg over 20 kg

½ NS—0.45% NaCl

(Na+ 77 mEq/L, Cl− 77 mEq/L)

Fluid maintenance

Hyponatremia with long-term use; increased risk of IV infiltration vs. isotonic

Isotonic Fluids

NS—0.9% NaCl

(Na+ 154 mEq/L; Cl− 154 mEq/L)

Fluid replacement; hypovolemia, shock

Monitor for fluid overload; hyperchloremic metabolic acidosis with large volumes

• Dose varies widely depending on patient fluid status and clinical situation

LR

(Na+ 130 mEq/L, Cl− 109 mEq/L

Lactate 28 mEq/L, K+ 4 mEq/L

Ca++ 3 mEq/L)

Fluid replacement; hypovolemia

Lactate converted to bicarbonate in the liver, may accumulate in cirrhosis leading to lactic acidosis

Hypertonic Fluids

3% NaCl

(Na+ 513 mEq/L, Cl− 513 mEq/L)

Severe symptomatic hyponatremia

Osmotic demyelination syndrome with too-rapid correction (>12 mEq/L/d for acute hyponatremia, >8 mEq/L/d for chronic hyponatremia)

• Initial rate = desired serum [Na+] increase per hour (mEq/h) × patient weight (kg) (example: ↑ Na+ by 1 mEq/L/h in 70 kg patient = 70 mL/h infusion, Am J Med. 2007;120(11A):S1)
• Alternate calculation: Effect of 1 L 3% saline on serum [Na+] = (513 – serum Na+)/(TBW+1), where TBW = 0.6 × weight (kg) for males, 0.5 × weight (kg) for females, rate to raise 1 mEq/L/hr = 1/(Effect of 1 L 3% saline on serum [Na+])

Hyponatremia

3% saline

Acute hyponatremia with severe symptoms

Infusion rate = desired [Na+] ↑ per hour (mEq/h) × weight (kg) (see Table 13.1.1)

• Limit serum [Na+] correction to ≤12 mEq/L/d for acute, ≤8 mEq/L/d for chronic hyponatremia to prevent osmotic demyelination
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