Kinetics of crystalloid fluid in hyperglycemia; an open-label exploratory clinical trial.

BACKGROUND: Infusion with 0.9% saline is a mainstay in the treatment of severe hyperglycemia, but the kinetics of the saline volume in this setting has not been studied. METHODS: An intravenous infusion of 1 L of 0.9% saline over 30 minutes was given on 31 occasions to 17 patients with hyperglycemia due to poorly controlled diabetes (mean age 51 years). A two-volume kinetic model was fitted to serial data on the hemodilution and urinary excretion, using mixed-effects modeling software. RESULTS: Plasma glucose was 36 ± 9 mmol/L on arrival to the hospital. The central volume of distribution (the plasma) was only 2.38 L (mean; 95% confidence interval 1.73-3.04) on the day of admission. Uptake into a remote compartment, believed to be the cells, amounted to 300 mL of the first liter of saline, although only small amounts of insulin were given. Plasma glucose, plasma bicarbonate, urine glucose, and plasma creatinine served as covariates in the kinetic model and mathematically affected the urinary excretion. For example, elimination of the infused fluid tripled from an increase in plasma glucose from 5 to 35 mmol/L and doubled from a reduction in plasma bicarbonate from 24 to 5 mmol/L. CONCLUSIONS: The excretion of 0.9% saline was increased depending on the degree of hyperglycemia. The kinetics was characterized by glucose-accelerated diuresis, and an intracellular uptake that occurred at two thirds the urine flow rate. These data could help to determine appropriate volumes and rates of infusion of crystalloids in hyperglycemia.

Establishing the Therapeutic Index of Fluid Resuscitation in the Septic Patient: A Narrative Review and Meta-Analysis.

This comprehensive review comparatively evaluates the safety and benefits of parenteral fluids used in resuscitation with a focus on sepsis. It also provides a random-effects meta-analysis of studies comparing restrictive resuscitation and usual care in sepsis with the primary outcome of mortality. In the septic patient, fluid therapy remains a complex interplay between fluid compartments in the body, the integrity of the endothelial barrier, and the inflammatory tone of the patient. Recent data have emerged describing the pharmacokinetics of fluid resuscitation that can be affected by the factors just listed, as well as mean arterial pressure, rate of infusion, volume of fluid infusate, nature of the fluid, and drug interactions. Fluid overload in sepsis has been associated with vasodilation, kidney injury, and increased mortality. Restrictive resuscitation after the initial septic insult is an emerging practice. Our search strategy of Medline databases revealed six randomized studies with 706 patients that examined restrictive resuscitation in sepsis. Results of this meta-analysis demonstrated no differences in mortality with restrictive resuscitation compared with usual care (30.6% vs 37.8%; risk ratio 0.83, 95% confidence interval 0.66-1.05, respectively) but was limited by the small number of studies and larger quantities of pre-randomization fluids. Another approach to address fluid overload is active (diuresis) de-resuscitation strategies that may shorten the need for mechanical ventilation and intensive care unit length of stay. Data suggest that colloids may confer mortality benefit over saline in the most severely ill septic patients. Compared with isotonic saline, balanced resuscitation fluids are associated with a lower incidence of acute kidney injury and mortality. The benefits of balanced resuscitation fluids are most evident when higher volumes of fluids are used for sepsis. Clinicians should consider these pharmacotherapeutic factors when selecting a fluid, its quantity, and rate of infusion.

Understanding volume kinetics.

The distribution and elimination kinetics of the water volume in infusion fluids can be studied by volume kinetics. The approach is a modification of drug pharmacokinetics and uses repeated measurements of blood hemoglobin and urinary excretion as input variables in (usually) a two-compartment model with expandable walls. Study results show that crystalloid fluid has a distribution phase that gives these fluids a plasma volume expansion amounting to 50%-60% of the infused volume as long as the infusion lasts, while the fraction is reduced to 15%-20% within 30 minutes after the infusion ends. Small volumes of crystalloid barely distribute to the interstitium, whereas rapid infusions tend to cause edema. Fluid elimination is very slow during general anesthesia due to the vasodilatation-induced reduction of the arterial pressure, whereas elimination is less affected by hemorrhage. The half-life is twice as long for saline than for Ringer solutions. Elimination is slower in conscious males than conscious females, and high red blood cell and thrombocyte counts retard both distribution and re-distribution. Children have faster turnover than adults. Plasma volume expansions are similar for glucose solutions and Ringer's, but the expansion duration is shorter for glucose. Concentrated urine before and during infusion slows down the elimination of crystalloid fluid. Colloid fluids have no distribution phase, an intravascular persistence half-life of 2-3 hours, and-at least for hydroxyethyl starch-the ability to reduce the effect of subsequently infused crystalloids. Accelerated distribution due to degradation of the endothelial glycocalyx layer has not yet been demonstrated.

Mechanisms of Crystalloid versus Colloid Osmosis across the Peritoneal Membrane.

Background Osmosis drives transcapillary ultrafiltration and water removal in patients treated with peritoneal dialysis. Crystalloid osmosis, typically induced by glucose, relies on dialysate tonicity and occurs through endothelial aquaporin-1 water channels and interendothelial clefts. In contrast, the mechanisms mediating water flow driven by colloidal agents, such as icodextrin, and combinations of osmotic agents have not been evaluated.Methods We used experimental models of peritoneal dialysis in mouse and biophysical studies combined with mathematical modeling to evaluate the mechanisms of colloid versus crystalloid osmosis across the peritoneal membrane and to investigate the pathways mediating water flow generated by the glucose polymer icodextrin.ResultsIn silico modeling and in vivo studies showed that deletion of aquaporin-1 did not influence osmotic water transport induced by icodextrin but did affect that induced by crystalloid agents. Water flow induced by icodextrin was dependent upon the presence of large, colloidal fractions, with a reflection coefficient close to unity, a low diffusion capacity, and a minimal effect on dialysate osmolality. Combining crystalloid and colloid osmotic agents in the same dialysis solution strikingly enhanced water and sodium transport across the peritoneal membrane, improving ultrafiltration efficiency over that obtained with either type of agent alone.Conclusions These data cast light on the molecular mechanisms involved in colloid versus crystalloid osmosis and characterize novel osmotic agents. Dialysis solutions combining crystalloid and colloid particles may help restore fluid balance in patients treated with peritoneal dialysis.

Influences of red blood cell and platelet counts on the distribution and elimination of crystalloid fluid.

BACKGROUND AND OBJECTIVE: A high number of blood cells increases the viscosity of the blood. The present study explored whether variations in blood cell counts are relevant to the distribution and elimination of infused crystalloid fluid. MATERIALS AND METHODS: On three different occasions, 10 healthy male volunteers received an intravenous infusion of 25mL/kg of Ringer's acetate, Ringer's lactate, and isotonic saline over 30min. Blood hemoglobin and urinary excretion were monitored for 4h and used as input in a two-volume kinetic model, using nonlinear mixed effects software. The covariates used in the kinetic model were red blood cell and platelet counts, the total leukocyte count, the use of isotonic saline, and the arterial pressure. RESULTS: Red blood cell and platelet counts in the upper end of the normal range were associated with a decreased rate of distribution and redistribution of crystalloid fluid. Simulations showed that high counts were correlated with volume expansion of the peripheral (interstitial) fluid space, while the plasma volume was less affected. In contrast, the total leukocyte count had no influence on the distribution, redistribution, or elimination. The use of isotonic saline caused a transient reduction in the systolic arterial pressure (P<0.05) and doubled the half-life of infused fluid in the body when compared to the two Ringer solutions. Isotonic saline did not decrease the serum potassium concentration, despite the fact that saline is potassium-free. CONCLUSIONS: High red blood cell and platelet counts are associated with peripheral accumulation of infused crystalloid fluid.