Intravenous Fluids

Intravenous fluids can supply two things: fluid volume and electrolytes. These fluids are usually provided to: 1) acutely expand intravascular volume; 2) to correct an underlying imbalance in fluids or electrolytes or 3) to compensate for an ongoing problem that is affecting either fluid or electrolytes. For instance, a patient comes into the ER with gastroenteritis and is dehydrated from vomiting and diarrhea. Acutely, she receives a fluid bolus to expand her intravascular volume. She still cannot eat for some period, so an IV is started. Her blood chemistry shows that her electrolytes are a bit off, so the IV fluid is adjusted to bring them within normal parameters. She will remain on maintenance IV fluid until she can drink.

Acute vascular space expansion

Two IV solutions are used for acute volume expansion: Normal Saline (0.9%) and Lactated Ringer's Solution. Normal Saline is nothing more than salt water at a concentration that is isotonic with the blood (154 mM sodium). Ringer's Lactate is similar, but has small amounts of potassium. In addition, it provides lactate which is metabolized by the liver to bicarbonate and helps buffer the blood if acidosis is present. Note that these two solutions do not contain any glucose. This is because rapid (bolus) infusion of these solutions would drive blood glucose (and plasma osmolarity) up too quickly. In adults, boluses of 500 mL are common. In children above one year, boluses of 20 mL/kg are common, and 10 mL/kg is used under one year of age. In an ICU setting, multiple smaller boluses with frequent monitoring for effect are recommended. Neonates may receive 5% albumin for volume expansion, usually in 10 mL/kg boluses.

Note that while volume and electrolytes are added with IV fluids, all other components in blood are effectively diluted. Thus, the hematocrit will fall and clotting factors will be diluted. Plasma components may be required to avoid this effect. In an emergency or surgical setting, the role of IV fluids is to achieve rapid intravascular expansion. These crystalloid solutions are limited by the short staying power of their solutes. The ions will eventually redistribute or be lost through renal excretion. A longer term solution would be infusion of albumin or blood products which have some oncotic pressure by virtue of their protein content.

Maintenance Fluids

Maintenance fluids are an IV solution designed to balance the IV infusion against ongoing losses of fluid and electrolytes. The IV fluid composition and rate must be chosen to reflect these losses. If the proper solution is selected, the patient's electrolyte values should remain constant. There are several methods for calculating maintenance fluid requirements, and these are presented on the next page. Before that, however, it is necessary to also know the composition of solutions which are commonly available in hospitals.

Common IV Solutions
Solution	Glucose (g/L)	Na⁺	K⁺	Ca⁺²	Cl^-	Lactate	PO₄^-3	Mg⁺²
5% Dextrose (D₅W)	50	0	0	0	0	0	0	0
10% Dextrose (D₁₀W)	100	0	0	0	0	0	0	0
Normal Saline (NS)	0	154	0	0	154	0	0	0
D₅NS	50	154	0	0	154	0	0	0
D₅½NS	50	77	0	0	77	0	0	0
0.2% NS	0	31	0	0	31	0	0	0
3% NaCl	0	513	0	0	513	0	0	0
Ringer's Lactate (LR)	0	130	4	3	109	28	0	0
D₅LR	50	130	4	3	109	28	0	0
D₁₀ E#48	100	30	15	0	20	25	3	3
D₅ E#48	50	25	20	0	22	23	3	3
D₁₀ E#75	100	57	35	0	40	25	12	6
D₆ E#75	60	40	40	0	35	20	15	0

Note: Glucose in g/L; all ions in mEq/L.

Net Scut Home

Please direct all comments to:

Last modification: April 30, 1998