Normal Saline Infusion Calculator

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Background material

Derivation of Normal Saline infusion - serum level prediction
"Simplistic approach based on common physiologic variables"

Normal Saline (0.9%)
1) Infusion rate (ml/hr) / 1000 x 154 meq/L = Number of meq/hr.

2) Serum Na+ increase per hour = meq/hr /((Vd L/kg) x (Weight (kg)))
Vd (Volume of distribution) = 0.6 L/kg Male or 0.5 L/kg Female

3) Total predicted serum sodium increase =
(Serum Na+ increase per hour ) x Number of hours infused.

Example calculation:

80 kg Male. Baseline serum sodium level: 132 meq/L. 0.9 % NS infused at 150 ml/hr for 12 hours. Calculate the projected serum sodium level after the completion of the 12 hour infusion.

1) (150 ml/hr) / 1000 x 154meq = 23.1 meq/hr.

2) 23.1 meq/hr /(0.6 x 80kg) = 0.48 meq/hr serum level increase.

3) Total predicted serum sodium increase =
0.48 meq/hr x 12 hrs = 5.76 meq.

4) Predicted serum level = 132 + 5.76 = 137.76 meq/L

Actual serum sodium level obtained will depend on the patient's volume status, renal function, concomitant disease state(s), concurrent drug therapy and urine output.