Volume dynamics and volume management in intensive care unit patients / 中华危重病急救医学

Volume dynamics is a two-compartment dynamical model using hemoglobin (Hb) derived plasma diluted level as input data and urine output as input variable through consecutive repeated measurements of Hb concentration in the blood during infusion. It could be applied to evaluate and guide crystalloid fluid rehydration for patients with dehydration or hypovolemia and during anesthesia or surgery. Volume dynamics could be also used to quantificate of strains, hypovolume, and the change of fluid distribution and elimination caused by anesthesia or surgery. The factors which influence the volume resuscitation are complex, including gender, age, hemodynamic state [mean arterial pressure (MAP)], health and stress state, renal function, consciousness, surgical or anesthesia state and so on, which may affect the half-life, distribution, and volume of the fluid. This article summarizes and analyzes the pathophysiological changes of crystalloids fluid in vivo, in order to provide reference for volume management in critically ill patients.

Comparison of Fluid Kinetic Model of Normal Saline with Hartmann's Solution in Adult Volunteers

BACKGROUND: Changes in the volume of fluid space expanded by intravenous infusion of crystalloid solution have been analyzed using mathematical models. Crystalloids with similar osmolality would reveal no significant differences in distribution and elimination from the body. But each solution has different ionic composition, this can affect fluid volume kinetics. Therefore, we evaluated the fluid volume kinetics of normal saline and Hartmann's solution. METHODS: After infusion of 15 ml/kg of normal saline (n=5) and Hartmann's solution (n = 4) over 30 min and measured a serial hemoglobin concentration. The changes were expressed as fractional dilution and then plotted against time. The curves were fitted to two-volume model using non linear least square fitting process. RESULTS: Central and peripheral volume space were present. There were no significant differences between the two groups on central volume, peripheral volume and expansion ratio of fluid space per body weight and expansion ratio of peripheral volume. The expansion ratio of central volume was greater in Hartmann's solution than normal saline from 25 min to 60 min after infusion. Hartmann's solution expanded fluid space higher than normal saline on initial period. CONCLUSIONS: There were no significant differences in fluid kinetic parameters between normal saline and Hartmann's solution. However, the volume expansion effect of Hartmann's solution was more rapid than normal saline in early infusion period.

Modelling the Expandable Body Fluid Space after I.V. Fluid Infusion / 대한마취과학회지

BACKGROUND: Changes in the volume of the fluid space expanded by i.v. infusion of crystalloid solution have been analysed recently using mathematical models. The models are based on the assumption that the body strives to maintain volume homeostasis of fluid spaces and that the rate of restoration is a function of deviation from resting volume. METHODS: In this work mathematical models were developed to represent the kinetics of volume changes of fluid spaces associated with infusion of Ringer's solution. Based on the characteristics of fluid transportation, two expansion models were tested. The single-fluid space model has a single volume into which fluid is fed and from which fluid is left, and the two-fluid space model has another space in addition to the first volume so that fluid exchanges between these two spaces are possible. Volunteers (six men) were given Hartman's solution for 30 min and the changes in blood hemoglobin were detected. RESULTS: From the comparison with experimental data, the single-fluid space model was found to represent adequately in all volunteers, however, two-fluid space model was found to represent 75% of volunteers. CONCLUSIONS: These models may be useful in the description and analysis of the effects of i.v. fluid therapy.