biostudies-literatureUnknown15Hahn RG<h4>Introduction</h4>The interstitial space harbours two fluid compartments linked serially to the plasma. This study explores conditions that lead to fluid accumulation in the most secluded compartment, termed the "third space".<h4>Methods</h4>Retrospective data was collected from 326 experiments in which intravenous crystalloid fluid was administered to conscious volunteers as well as a small group of anaesthetized patients. The urinary excretion and plasma dilution derived from haemoglobin served as input variables in nine population volume kinetic analyses representing subtly different settings.<h4>Results</h4>An infusion of 250-500 mL of Ringer's solution expanded only the central fluid space (plasma), whereas the infusion of 500-1,000 mL extended into a rapidly exchanging interstitial fluid space. When more than 1 L was infused over 30 min, it was distributed across plasma and both interstitial fluid compartments. The remote space, characterized by slow turnover, abruptly accommodated fluid upon accumulation of 700-800 mL in the rapidly exchanging space, equivalent to an 11%-13% volume increase. However, larger expansion was necessary to trigger this event in a perioperative setting. The plasma half-life of crystalloid fluid was 25 times longer when 2,000-2,700 mL expanded all three fluid compartments compared to when only 250-500 mL expanded the central space (14 h versus 30 min).<h4>Conclusion</h4>As the volume of crystalloid fluid increases, it apparently occupies a larger proportion of the interstitial space. When more than 1 L is administered at a high rate, there is expansion of a remote "third space", which considerably extends the intravascular half-life.Frontiers in physiology1439035https://www.ebi.ac.uk/biostudies/studies/S-EPMC11387178biostudies-literatureSequential recruitment of body fluid spaces for increasing volumes of crystalloid fluid.PMC11387178Hahn RGfalseSequential recruitment of body fluid spaces for increasing volumes of crystalloid fluid.<h4>Introduction</h4>The interstitial space harbours two fluid compartments linked serially to the plasma. This study explores conditions that lead to fluid accumulation in the most secluded compartment, termed the "third space".<h4>Methods</h4>Retrospective data was collected from 326 experiments in which intravenous crystalloid fluid was administered to conscious volunteers as well as a small group of anaesthetized patients. The urinary excretion and plasma dilution derived from haemoglobin served as input variables in nine population volume kinetic analyses representing subtly different settings.<h4>Results</h4>An infusion of 250-500 mL of Ringer's solution expanded only the central fluid space (plasma), whereas the infusion of 500-1,000 mL extended into a rapidly exchanging interstitial fluid space. When more than 1 L was infused over 30 min, it was distributed across plasma and both interstitial fluid compartments. The remote space, characterized by slow turnover, abruptly accommodated fluid upon accumulation of 700-800 mL in the rapidly exchanging space, equivalent to an 11%-13% volume increase. However, larger expansion was necessary to trigger this event in a perioperative setting. The plasma half-life of crystalloid fluid was 25 times longer when 2,000-2,700 mL expanded all three fluid compartments compared to when only 250-500 mL expanded the central space (14 h versus 30 min).<h4>Conclusion</h4>As the volume of crystalloid fluid increases, it apparently occupies a larger proportion of the interstitial space. When more than 1 L is administered at a high rate, there is expansion of a remote "third space", which considerably extends the intravascular half-life.2024-01-01T00:00:00Z20242026-06-02T23:38:26.793Z2025-04-05T18:43:07.117ZS-EPMC113871783926362710.3389/fphys.2024.1439035