IV Fluid Therapy...

Our kidneys are a big deal, as they are responsible for maintaining an effective circulating volume and they also help regulate plasma osmolality. These processes are also important in maintaining electrolyte homeostasis.

Water losses lead to an increase in [Na] in the serum and in the serum osmolality, leading to the stimulation of thirst and the increased release of ADH. Essentially, patients that are alert, have access to water and who have an intact thirst mechanism, will NOT become hypernatremic, since physiology helps protect us from this issue!

Sources of water include fluid ingestion, water content in food, and water produced from the oxidation of carbohydrates.  Water loss derives from urination, GI output and insensible losses (skin, respiratory tract).

Sodium balance is tightly regulated, as the kidneys can excrete urine that is nearly free of sodium in instances where they are striving to hold on to sodium.

IV Fluid Principles

•  Maintenance Fluid: replace ongoing losses of water and electrolytes (i.e. normal physiological conditions), due to sweating, urine output, respiration and bowel movements
• Replacement therapy: correct any electrolyte abnormalities or water deficits

o   i.e. deficits due to GI, urinary, skin losses, 3^rd spacing, and bleeding

Choosing the Right Fluid for Replacement

-Depends on the type of fluid that has been lost and which electrolyte abnormalities prevail!

-Examples:

•  Hypernatremia: use a hypotonic solution
• Hyponatremia: use an isotonic solution +/- a hypertonic solution
• Blood loss: use packed RBCs and/or isotonic solution
• You may need to add KCl (i.e. 20 mEq/L or 40 mEq/L) in the setting of hypokalemia; you may need to add bicarbonate to patients with metabolic acidosis
• Dextrose solutions: should be used in hypoglycemia, or EtOH or fasting ketoacidosis. Consider administering it with insulin for patients with hyperkalemia. Avoid using in patients with uncontrolled diabetes mellitus (DM) or hypokalemia *(the administration of dextrose stimulates insulin release à which shifts K+ into the cells, making the hypokalemia worse)

Helpful Review Article:

1) This article reviews important considerations and concepts in IV fluid use:

Intravenous Fluids: It's More Than Just "Fill 'Er Up!"