Determination of the effect of in vitro time, temperature, and tourniquet use on whole blood venous point-of-care lactate concentrations.

Abstract

The authors sought to determine the effect of in vitro time, temperature, and removable tourniquet use on changes in venous point-of-care lactate concentrations. This was a prospective randomized trial on healthy volunteers. Subjects were randomized to one of three groups: group 1 had venous lactate concentrations measured on blood drawn without a tourniquet and the sample placed in ice (-1 degrees C), group 2 had lactate concentrations measured on blood drawn without a tourniquet and the sample left at 23 degrees C, and group 3 had lactate concentrations measured on blood drawn with a tourniquet placed 5 minutes before venipuncture and the sample placed in ice (-1 degrees C). Lactate concentrations were measured on a point-of-care device at time 0, 3, 6, 9, 12, and 15 minutes in all three groups. Mean lactate concentrations were analyzed using a two-way repeated-measures analysis of variance. Eighty subjects were randomized, with complete data available in 63 (21 per group). Over the 15-minute period, lactate concentrations increased 10% (0.14 +/- 0.12 mmol/L) in group 1, 25% (0.33 +/- 0.003 mmol/L) in group 2, and 6% (0.08 +/- 0.22 mmol/L) in group 3. No significant differences in mean lactate concentrations were found between any group or time point by analysis of variance (p > 0.90). A 50% relative increase in lactate concentrations between time 0 and 15 minutes occurred in zero of 21 subjects in group 1, four of 21 in group 2, and one of 21 in group 3 (p = 0.05 group 1 vs. group 2, Fisher's exact test). Whole blood point-of-care lactate concentrations in healthy subjects do not change significantly over 15 minutes at either -1 degrees C or 23 degrees C, and the use of a tourniquet has no appreciable effect on lactate concentrations.