title: The half-life of infusion fluids: An educational review.
abstract: An understanding of the half-life (T1/2) of infused fluids can help prevent iatrogenic problems such as volume overload and postoperative interstitial oedema. Simulations show that a prolongation of the T1/2 for crystalloid fluid increases the plasma volume and promotes accumulation of fluid in the interstitial fluid space. The T1/2 for crystalloids is usually 20 to 40 min in conscious humans but might extend to 80 min or longer in the presence of preoperative stress, dehydration, blood loss of <1 l or pregnancy.The longest T1/2 measured amounts to between 3 and 8 h and occurs during surgery and general anaesthesia with mechanical ventilation. This situation lasts as long as the anaesthesia. The mechanisms for the long T1/2 are only partly understood, but involve adrenergic receptors and increased renin and aldosterone release. In contrast, the T1/2 during the postoperative period is usually short, about 15 to 20 min, at least in response to new fluid.The commonly used colloid fluids have an intravascular persistence T1/2 of 2 to 3 h, which is shortened by inflammation. The fact that the elimination T1/2 of the infused macromolecules is 2 to 6 times longer shows that they also reside outside the bloodstream. With a colloid, fluid volume is eliminated in line with its intravascular persistence, but there is insufficient data to know if this is the same in the clinical setting.
authors.affiliation: From the Research Unit, Södertälje Hospital, Södertälje, and Section for Anaesthesia, Linköping University, Linköping, Sweden.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Hahn
authors.forename: Gordon
authors.initials: G
authors.lastname: Lyons
mesh_terms: D000758:Anesthesia; D000077324:Crystalloid Solutions; D005440:Fluid Therapy / Q000009:adverse effects; D006207:Half-Life; D006801:Humans; D007262:Infusions, Intravenous; D007552:Isotonic Solutions; D010952:Plasma Substitutes; D012121:Respiration, Artificial; D012996:Solutions / Q000008:administration & dosage / Q000493:pharmacokinetics
chemical_list: D000077324:Crystalloid Solutions; D007552:Isotonic Solutions; D010952:Plasma Substitutes; D012996:Solutions