Volume kinetic analysis of fluid retention after induction of general anesthesia

Abstract

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 − 1 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 − 1 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 10), which remained to be very low (0.86 × 10 − 3 min − 1). Redistribution of infused fluid from the interstitium to the plasma occurred faster (higher k 21) 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 − 1 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).

Distribution of Crystalloid Fluid Infused During Onset of Anesthesia-Induced Hypotension: A Retrospective Population Kinetic Analysis

“…Acetated Ringer's seemed to distribute more rapidly than lactated Ringer's, but this difference lost signi cance in the nal model. In accordance with a previous study (Hahn & Nemme, 2020), the distribution (k 12 ) was hypothesized to be turned off for a period of time after the induction; therefore, time periods of 3, 5-6, 9-10, 15, 20, and 25 min were tested. The amount of uid infused up to those timepoints was also evaluated, but none of those variables was strong enough for inclusion in the model.…”

“…The reason is probably that the infusion of 1.1 L of Ringer's did not ll up the vasodilated cardiovascular system su ciently to allow a resumption of the normal exchange of uid with the extravascular space. In a previous study, this "turning point" was reached when 16.6 mL kg − 1 of Ringer's (1.25 L) had been administered (Hahn and Nemme, 2020). This probably corresponds to the anesthesia-induced expansion of the part of the blood volume that is sometimes called "unstressed" and which denotes the amount of venous blood that does not increase the transmural pressure (Gelman, 2008).…”

“…A larger proportion of infused uid is also known to remain in the plasma when hypotension has just been induced (Hahn, 1992). A recent uid kinetic study in which the uid was given only after the induction showed an arrested distribution of the excessive uid-induced hemodilution that resolved only 20 min later (Hahn and Nemme, 2020).…”

Fluid escapes to the “third space” during anesthesia, a commentary

“…Data were obtained on 85 patients from four studies of laparoscopic and open surgery associated with low-grade blood loss. [23][24][25][26] Here k 10 was only 3.2 × 10 −3 min −1 (95% CI, 2.4-3.9) while k b increased to 10.1 × 10 −3 min −1 (95% CI, 8.3-12.0), that is, three times higher than the urine flow rate (Figure 2). Simulations suggest that half of the excess fluid in the plasma volume would then be excreted after 225 min while as much as 80% of the fluid load would remain in the body after 6 hours.…”

“…These parameters change markedly in patients subjected to general anesthesia. Data were obtained on 85 patients from four studies of laparoscopic and open surgery associated with low‐grade blood loss 23‐26 . Here k 10 was only 3.2 × 10 −3 min −1 (95% CI, 2.4‐3.9) while k b increased to 10.1 × 10 −3 min −1 (95% CI, 8.3‐12.0), that is, three times higher than the urine flow rate (Figure 2).…”