Saline

Saline is a general term for a solution that contains salt dissolved in water. In medical contexts, saline most often refers to sodium chloride solutions used for intravenous administration or irrigation. The common preparation is normal saline, a 0.9% w/v solution of NaCl in water. It is roughly isotonic with body fluids, minimizing net movement of water across cell membranes.

Other saline solutions differ in concentration. Half-normal saline is 0.45% NaCl and is hypotonic relative to blood. Hypertonic saline, such as 3% or 5% NaCl, draws water out of cells and is used in specific settings, for example to reduce brain swelling or to treat severe hyponatremia, under careful supervision.

Saline works by dissociating into sodium and chloride ions. It is widely used as an intravenous crystalloid fluid for resuscitation, hydration, and electrolyte maintenance. It is also employed for wound cleansing, nasal irrigation, and as a sterile rinse during medical procedures.

Safety considerations include the risk of hypernatremia, hyperchloremic acidosis, or fluid overload with excessive or inappropriate use, especially in kidney disease or heart failure. Sterile, preservative-free saline is standard for injections; multi-dose vials may contain preservatives that are avoided in some patients.

Beyond medicine, saline describes saltwater or briny water with dissolved salts, such as seawater or saline lakes, where the term denotes substantial salt content.