Volume kinetic analysis of fluid retention after induction of general anesthesia.

Background: Induction of general anesthesia increases the hemodilution resulting from infusion of crystalloid fluid, which is believed to be due to slower distribution caused by arterial hypotension. When normal distribution returns is not known.

Methods: An intravenous infusion of 25 mL kg of Ringer's lactate was infused over 30 min to 25 volunteers just after induction of general anesthesia for open abdominal hysterectomy. A two-volume model was fitted to the repeated measurements of the blood hemoglobin concentration and the urinary excretion using mixed-effects modelling software. Individual-specific covariates were added in sequence.

Results: Distribution of infused fluid was interrupted during the first 20 min of the infusions. During this time 16.6 mL kg of lactated Ringer's had been infused, of which virtually all remained in the circulating blood. Thereafter, the fluid kinetics was similar to that previously been found in awake volunteers except for the elimination rate constant (k), which remained to be very low (0.86 × 10 min). Redistribution of infused fluid from the interstitium to the plasma occurred faster (higher k) when the arterial pressure was low. No covariance was found between the fixed parameters and preoperatively concentrated urine, the use of sevoflurane or propofol to maintain the anesthesia, or the plasma concentrations of two degradation products of the endothelial glycocalyx, syndecan-1 and heparan sulfate.

Conclusions: Induction of general anesthesia interrupted the distribution of lactated Ringer's solution up to when 16.6 mL kg of crystalloid fluid had been infused. Plasma volume expansion during this period of time was pronounced.

Trial Registration: Controlled-trials.com (ISRCTN81005631) on May 17, 2016 (retrospectively registered).