Kristalloida

Kristalloida are aqueous solutions containing small solutes such as mineral salts or sugars that readily diffuse through tissues and capillary walls. They are used to replace or maintain body fluids and are distinguished from colloids, which contain larger molecules that stay longer in the vascular space. Common kristalloida include normal saline (0.9% sodium chloride), Lactated Ringer’s solution, Plasma-Lyte, and dextrose-containing fluids (for example 5% dextrose in water). They are further classified by tonicity as isotonic, hypotonic, or hypertonic.

Isotonic kristalloida have roughly the same osmolality as blood and are the most commonly used for fluid resuscitation and routine maintenance. Examples include normal saline and balanced solutions like Lactated Ringer’s or Plasma-Lyte. Hypotonic kristalloida have lower osmolality and may be used for free water replacement, but can cause shifts of water into cells. Hypertonic kristalloida have higher osmolality and can draw water into the intravascular space; they are used selectively in certain conditions such as severe hyponatremia or raised intracranial pressure.

Physiology and use: kristalloida distribute quickly between intravascular and interstitial compartments. After a bolus, only a portion remains in the vascular space over time, which influences dosing and duration of effect. They are widely used for initial fluid resuscitation in dehydration, surgery, and various forms of shock, as well as for maintenance therapy.

Risks and considerations: potential edema, electrolyte imbalances (notably sodium and chloride), and dilutional effects on coagulation with large volumes. Choice of solution depends on the clinical scenario, patient physiology, and comorbidities.