Kristalloider

Kristalloider, or crystalloids, are intravenous solutions composed of water and small, osmotically active molecules such as electrolytes and sugars. Because these small solutes diffuse readily across capillary walls, crystalloids distribute quickly into the extracellular fluid and do not create long-lasting increases in oncotic pressure. They are used to restore circulating volume, treat dehydration, and support fluid therapy in surgery and critical illness.

Types include isotonic crystalloids (for example, 0.9% sodium chloride, commonly known as normal saline; balanced solutions such as lactated Ringer’s), hypotonic crystalloids (for example 0.45% saline), and hypertonic crystalloids (such as 3% saline). Isotonic solutions are most commonly used for volume resuscitation; hypotonic solutions may be used for cellular hydration; hypertonic solutions are used selectively to draw water from cells in certain neurological or brain-injury settings.

Clinical use includes resuscitation after acute volume loss from injury or illness, treatment of dehydration, maintenance fluids in adults and children, and perioperative fluid management. Crystalloids do not supply oncotic pressure, so maintaining intravascular volume often requires larger volumes and can increase the risk of interstitial edema if not carefully monitored.

Advantages include low cost and wide availability, with a favorable safety profile in many settings. Disadvantages involve the need for potentially large volumes to sustain perfusion, risk of edema, and electrolyte disturbances. Normal saline in large amounts can cause hyperchloremic metabolic acidosis; lactated or buffered solutions may be avoided in certain liver dysfunction or metabolic conditions.

Compared with colloids, crystalloids are cheaper and have fewer immediate transfusion-related risks, but they may be less efficient at maintaining intravascular volume and can contribute to tissue edema if used in excess.