Plasma volume expansion resulting from intravenous glucose tolerance test

Abstract

Objective: To quantify the degree of plasma volume expansion that occurs during an intravenous glucose tolerance test (IVGTT).

Methods: Twenty healthy volunteers (mean age, 28 years) underwent IVGTTs in which 0.3 g/kg of glucose 30% was injected as a bolus over 1 min. Twelve blood samples were collected over 75 min. The plasma glucose and blood hemoglobin concentrations were used to calculate the volume distribution (V(d)) and the clearance (CL) of both the exogenous glucose and the injected fluid volume.

Results: The IVGTT caused a virtually instant plasma volume expansion of 10%. The half-life of the glucose averaged 15 min and the plasma volume expansion 16 min. Correction of the fluid kinetic model for osmotic effects after injection reduced CL for the infused volume by 85%, which illustrates the strength of osmosis in allocating fluid back to the intracellular fluid space. Simulations indicated that plasma volume expansion can be reduced to 60% by increasing the injection time from 1 to 5 min and reducing the glucose load from 0.3 to 0.2 g/kg.

Conclusion: A regular IVGTT induced an acute plasma volume expansion that peaked at 10% despite the fact that only 50-80 mL of fluid were administered.

Figure 1

(a) Change in plasma glucose concentration. (b) Dilution of venous plasma calculated from changes in the blood hemoglobin concentration in response to an intravenous injection of 0.3 g/kg of glucose over 1 min. Each experiment is represented by a thin line and the modeled average by a thick line.

Figure 2

(a) Simulation showing the plasma volume expansion that would ensue if the injection time was increased to 5 min (left) from 1 min (right) for an IVGTT dose of 0.2 g/kg and 0.3 g/kg of glucose, respectively. (b) Simulation of the plasma glucose level if the glucose load was decreased to 0.2 g/kg (left) from 0.3 g/kg (right) in surgical patients (solid line) and in volunteers (broken line). The kinetic data for volunteers were taken from the present study, and those for surgery (V _d  =  9.1 L and CL  =  0.21 L/min) were derived from [7].