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Repeated crystalloid boluses led to progressively weaker plasma volume expansion.

Researchers conducted a retrospective study published in June 2025 issue of Annals of Intensive Care to evaluate whether repeated bolus infusions of crystalloid and colloid fluids produced consistent increases in plasma volume to support the assumptions of goal-directed fluid therapy.  

They characterized the volume kinetics of crystalloid fluid in 103 anesthetized individuals, while hydroxyethyl starch parameters for colloid fluid were sourced from existing literature. Simulations modeled plasma volume responses to 3 boluses of crystalloid at 4 mL/kg and colloid at 2–4 mL/kg, each infused over 7 minutes. A 5-minute interval was maintained between boluses to allow for hemodynamic evaluation.  

The results showed that crystalloid fluid produced a reduced plasma volume response with repeated bolus infusions, with the second and third boluses increasing plasma volume by only 51% and 36% of the first bolus, respectively. This attenuation persisted when preceded by a 60-minute infusion at 5 mL/kg/h or 10 mL/kg/h of crystalloid. Placement in the Trendelenburg position (head down) lessened the attenuation. Blood loss enhanced plasma volume expansion but did not eliminate attenuation. Colloid fluid did not exhibit any attenuation in plasma volume response.  

Investigators concluded that repeated crystalloid boluses resulted in diminished plasma volume expansion, potentially limiting accurate assessment of fluid responsiveness, a limitation not observed with colloid fluid. 

Source: annalsofintensivecare.springeropen.com/articles/10.1186/s13613-025-01495-3