### Introduction

### Materials and Methods

### Patient population

### Study procedure

_{2}0.5 of O

_{2}and air. Vasopressors were not used during the study period. To achieve and maintain stable fluid space dilution, 2, 3.5 and 5% of target dilution, infusion rates for administration of loading and maintenance volumes were selected from nomograms for fluids (Figs. 1, 2 and 3) [7]. Infusion rate for loading volume in each patient was determined at the middle portion of nomograms (convex portion) except for both extremes. Target values of 2, 3.5, and 5% were chosen to evaluate the predictive performances of fluid kinetic models under consideration of patient safety during operation. These patients were randomly assigned to one of three fluid groups (Hartmann's solution [H group, n = 23], Voluven® [Fresenius Kabi, Bad Homburg, Germany, V group, n = 28], and Hextend® [Hospira, Lake Forest, IL, X group, n = 28]) in a sequence with one of the target dilution. After invasive arterial blood pressure monitoring was established, patients received each loading and maintenance volume of fluid predetermined by nomograms for 60 min using an infusion pump (Baxter Flo-Gard 6201, San Diego, CA). Four arterial blood samples for hemoglobin measurement were obtained at preset intervals; before infusion, 10, 20 and 30 min after loading volume of fluid (t-0, t-10, t-20, t-30, respectively). Hemoglobin was measured by Gem Premier 3000 (Instrumentation Laboratory, Lexington, MA, USA). Efforts to finish the study before surgical incision was carried out. If surgical incision began before completion of the study, further samplings were not gathered. Hemoglobin concentration higher than baseline value (t-0) were discarded assuming sampling error. As a result, 22 samples for error, 25 samples for t-30 (15 for H group, 6 for V group, 4 for X group) were missing and then, 61 samples from H group, 118 samples from V group and 98 samples from X group were collected and used to evaluate predictive performance of fluid kinetic models.

### Calculation of volume kinetics

*V*: target volume,

*v*: an expandable BFS,

*Hb*: baseline hemoglobin concentration,

_{o}*Hb*: hemoglobin concentration at time t,

_{t}*Hct*: baseline hematocrit. The BFS dilution based on the model and blood volume dilutions (

_{0}*Hb*/

_{o}*Hb*- 1) were calculated from fractional changes of arterial hemoglobin concentration. Characteristics of parameters were shown in Table 2.

_{t}### Predictive performance

_{ij}represents the target BFS at the

*j*th sampling point from the

*i*th patient, whereas measured

_{ij}is the measured BFS.

_{i}):

_{i}): where

*N*is the number of PE in the

_{i}*i*th individual.

*i*th patient, as the slope acquired from the linear regression of that individual's the |PE

_{ij}|s against time: where t

_{ij}is the time at which the corresponding PE

_{ij}was determined.

### Relationship between blood volume dilution and target dilution of body fluid space

*Hb*/

_{o}*Hb*- 1) in each fluid group. Relationship between blood volume dilution and target dilution of body fluid space was analyzed in each group.

_{t}### Statistical analysis

### Results

### Discussion

*k*) and the other being a dilution-dependent mechanism governed by a constant (

_{b}*k*). In a previous study, the model demonstrated the volume effect of Hartmann's solution increases according to hypovolemic status by showing a reduction of the elimination rate constant [13].

_{r}