Interactions between the volume effects of hydroxyethyl starch 130/0.4 and Ringer´s acetate.

INTRODUCTION: The turnover of Ringer´s solutions is greatly dependent on the physiological situation, such as the presence of dehydration or anaesthesia. The present study evaluates whether the kinetics is affected by previous infusion of colloid fluid. METHODS: Ten male volunteers with a mean age of 22 years underwent three infusion experiments, on separate days and in random order. The experiments included 10 mL/kg of 6% hydroxyethyl starch 130/0.4 (Voluven™), 20 mL/kg of Ringer's acetate, and a combination of both, where Ringer´s was administered 75 minutes after the starch infusion ended. The kinetics of the volume expansion was analysed by non-linear least- squares regression, based on urinary excretion and serial measurement of blood haemoglobin concentration for up to 420 minutes. RESULTS: The mean volume of distribution of the starch was 3.12 L which agreed well with the plasma volume (3.14 L) estimated by anthropometry. The volume expansion following the infusion of starch showed monoexponential elimination kinetics with a half-life of two hours. Two interaction effects were found when Ringer´s acetate was infused after the starch. First, there was a higher tendency for Ringer´s acetate to distribute to a peripheral compartment at the expense of the plasma volume expansion. The translocated amount of Ringer´s was 70% higher when HES had been infused earlier. Second, the elimination half-life of Ringer´s acetate was five times longer when administered after the starch (88 versus 497 minutes, P<0.02). CONCLUSIONS: Starch promoted peripheral accumulation of the later infused Ringer´s acetate solution and markedly prolonged the elimination half-life. TRIAL REGISTRATION: ClinicalTrials.gov: NCT01195025.

Accuracy of noninvasive haemoglobin measurement by pulse oximetry depends on the type of infusion fluid.

CONTEXT: Measurement of blood haemoglobin concentration by pulse oximetry could be of value in determining when erythrocytes should be transfused during surgery, but the effect of infusion fluids on the results is unclear. OBJECTIVE: To study the effect of crystalloid and colloid fluid on the accuracy (bias) and precision of pulse oximetry haemoglobin estimation to indicate the venous haemoglobin concentration in volunteers. DESIGN: Open interventional crossover study. SETTING: Single university hospital. PARTICIPANTS: Ten male volunteers aged 18-28 (mean 22) years. INTERVENTIONS: Each volunteer underwent three infusion experiments on separate days and in random order. The infusions were Ringer's acetate (20 ml kg), hydroxyethyl starch 130/0.4 (10 ml kg) and a combination of both. RESULTS: At the end of the infusions of Ringer's acetate, pulse oximetry haemoglobin concentration had decreased more than the true haemoglobin concentration (15 vs. 8%; P < 0.005; n = 10) whereas starch solution decreased pulse oximetry haemoglobin concentration less than true haemoglobin concentration (7 vs. 11%; P < 0.02; n = 20). The same differences were seen when the fluids were infused separately and when they were combined. The overall difference between all 956 pairs of pulse oximetry haemoglobin concentration and true haemoglobin concentrations (the bias) averaged only -0.7 g l whereas the 95% prediction interval was wide, ranging from -24.9 to 23.7 g l. In addition to the choice of infusion fluid, the bias was strongly dependent on the volunteer (each factor, P < 0.001). CONCLUSION: The bias of measuring haemoglobin concentration by pulse oximetry is dependent on whether a crystalloid or a colloid fluid is infused. TRIAL REGISTRATION: ClinicalTrials identifier: NCT01195025.

Accuracy of noninvasive haemoglobin measurement by pulse oximetry depends on the type of infusion fluid.

CONTEXT: Measurement of blood haemoglobin concentration by pulse oximetry could be of value in determining when erythrocytes should be transfused during surgery, but the effect of infusion fluids on the results is unclear. OBJECTIVE: To study the effect of crystalloid and colloid fluid on the accuracy (bias) and precision of pulse oximetry haemoglobin estimation to indicate the venous haemoglobin concentration in volunteers. DESIGN: Open interventional crossover study. SETTING: Single university hospital. PARTICIPANTS: Ten male volunteers aged 18-28 (mean 22) years. INTERVENTIONS: Each volunteer underwent three infusion experiments on separate days and in random order. The infusions were Ringer's acetate (20 ml kg), hydroxyethyl starch 130/0.4 (10 ml kg) and a combination of both. RESULTS: At the end of the infusions of Ringer's acetate, pulse oximetry haemoglobin concentration had decreased more than the true haemoglobin concentration (15 vs. 8%; P < 0.005; n = 10) whereas starch solution decreased pulse oximetry haemoglobin concentration less than true haemoglobin concentration (7 vs. 11%; P < 0.02; n = 20). The same differences were seen when the fluids were infused separately and when they were combined. The overall difference between all 956 pairs of pulse oximetry haemoglobin concentration and true haemoglobin concentrations (the bias) averaged only -0.7 g l whereas the 95% prediction interval was wide, ranging from -24.9 to 23.7 g l. In addition to the choice of infusion fluid, the bias was strongly dependent on the volunteer (each factor, P < 0.001). CONCLUSION: The bias of measuring haemoglobin concentration by pulse oximetry is dependent on whether a crystalloid or a colloid fluid is infused. Trial registration ClinicalTrials identifier: NCT01195025.