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Background: Crystalloid fluid requires 30 min for complete distribution throughout the extracellular fluid space and tends to cause long-standing peripheral edema. A kinetic analysis of the distribution of Ringers acetate with increasing infusion rates was performed to obtain a better understanding of these characteristics of crystalloids. Methods: Data were retrieved from six studies in which 76 volunteers and preoperative patients had received between 300 ml and 2375 ml of Ringers acetate solution at a rate of 20-80 ml/min (0.33-0.83 ml/min/kg). Serial measurements of the blood hemoglobin concentration were used as inputs in a kinetic analysis based on a two-volume model with micro-constants, using software for nonlinear mixed effects. Results: The micro-constants describing distribution (k(12)) and elimination (k(10)) were unchanged when the rate of infusion increased, with half-times of 16 and 26 min, respectively. In contrast, the micro-constant describing how rapidly the already distributed fluid left the peripheral space (k(21)) decreased by 90% when the fluid was infused more rapidly, corresponding to an increase in the half-time from 3 to 30 min. The central volume of distribution (V-c) doubled. Conclusion: The return of Ringers acetate from the peripheral fluid compartment to the plasma was slower with high than with low infusion rates. Edema is a normal consequence of plasma volume expansion with this fluid, even in healthy volunteers. The results are consistent with the view that the viscoelastic properties of the interstitial matrix are responsible for the distribution and redistribution characteristics of crystalloid fluid.

BackgroundDuring fluid infusion therapy, plasma proteins are diluted and leak from the intravascular space, which alters the colloid osmotic pressure (COP) and potentially affects coagulation. We hypothesised that acetated Ringers and starch solution, alone or in combination, influence these mechanisms differently. Materials and methodsOn different occasions, 10 male volunteers were infused with 20ml/kg acetated Ringers and 10ml/kg 6% hyroxyethyl starch 130/0.4 (Voluven((R))) alone or in combination (first with starch solution followed by Ringers solution). Blood samples were collected every 30-min for measurements of COP, blood haemoglobin, platelets, and plasma concentrations of albumin, immunoglobulins (IgG and IgM), coagulation factor VII (FVII), fibrinogen, cystatin C, activated partial thromboplastin time (APTT) and prothrombin international normalised ratio (PT-INR). Changes were compared with the haemoglobin-derived plasma dilution. ResultsThe COP increased by 8.4% (SD 3) with starch and decreased by 26.2% (7.9) with Ringers. These infusions diluted the plasma by 23.4% (5.3) and 18.7% (4.9) respectively. The COP changes in the combined experiment followed the same pattern as the individual infusions. Albumin and IgG changes in excess of the plasma dilution were very subtle. The intravascular contents of the IgM and platelets decreased, whereas FVII, fibrinogen and cystatin C increased. PT-INR increased by 1/3 of the plasma dilution, whereas changes in APTT did not correlate with the plasma dilution. ConclusionsThe starch increased COP and only minor capillary leak occurred in healthy volunteers. The fluid-induced plasma dilution correlated with mild impairment of the extrinsic coagulation pathway but not of the intrinsic pathway.

Background Plethysmographic measurement of haemoglobin concentration (SpHb  ), pleth variability index (PVI), and perfusion index (PI) with the Radical-7 apparatus is growing in popularity. Previous studies have indicated that SpHb  has poor precision, particularly when PI is low. We wanted to study the effects of a sympathetic block on these measurements.

Methods Twenty patients underwent hand surgery under brachial plexus block with one Radical-7 applied to each arm. Measurements were taken up to 20 min after the block had been initiated. Venous blood samples were also drawn from the non-blocked arm.

Results During the last 10 min of the study, SpHb  had increased by 8.6%. The PVI decreased by 54%, and PI increased by 188% in the blocked arm (median values). All these changes were statistically significant. In the non-blocked arm, these parameters did not change significantly.

Conclusions Brachial plexus block significantly altered SpHb  , PVI, and PI, which indicates that regional nervous control of the arm greatly affects plethysmographic measurements obtained by the Radical-7. After the brachial plexus block, SpHb  increased and PVI decreased.

OBJECTIVE:

The purpose of this study was to examine the isovolumetric distribution kinetics of crystalloid fluid during cardiopulmonary bypass.

METHODS:

Ten patients undergoing coronary artery bypass grafting participated in this prospective observational study. The blood hemoglobin and the serum albumin and sodium concentrations were measured repeatedly during the distribution of priming solution (Ringer's acetate 1470 ml and mannitol 15% 200 ml) and initial cardioplegia. The rate of crystalloid fluid distribution was calculated based on 3-min Hb changes. The preoperative blood volume was extrapolated from the marked hemodilution occurring during the onset of cardiopulmonary bypass. Clinicaltrials.gov: NCT01115166.

RESULTS:

The distribution half-time of Ringer's acetate averaged 8 minutes, corresponding to a transcapillary escape rate of 0.38 ml/kg/min. The intravascular albumin mass increased by 5.4% according to mass balance calculations. The preoperative blood volume, as extrapolated from the drop in hemoglobin concentration by 32% (mean) at the beginning of cardiopulmonary bypass, was 0.6-1.2 L less than that estimated by anthropometric methods (p<0.02). The mass balance of sodium indicated a translocation from the intracellular to the extracellular fluid space in 8 of the 10 patients, with a median volume of 236 ml.

CONCLUSIONS:

The distribution half-time of Ringer's solution during isovolumetric cardiopulmonary bypass was 8 minutes, which is the same as for crystalloid fluid infusions in healthy subjects. The intravascular albumin mass increased. Most patients were hypovolemic prior to the start of anesthesia. Intracellular edema did not occur.

BACKGROUND: Mild to moderately severe dehydration is common in the elderly, but its relationship to surgical outcome is unclear.

OBJECTIVES: To study the incidence of dehydration prior to hip fracture surgery and its relationship to postoperative complications.

DESIGN: Prospective observational study.

SETTING: Operation department and orthopaedic ward at a regional hospital.

PATIENTS: Forty-five patients [median (interquartile range) age 78 (75 to 86) years] undergoing acute hip fracture surgery.

INTERVENTIONS: A urine sample was taken on admission to the operating theatre. Complications were assessed 2 days postoperatively using a check-list.

MAIN OUTCOME MEASURES: Dehydration was considered to be present if the urinary specific gravity was 1.020 or higher, indicating renal water conservation. The number and type of postoperative complications were recorded.

RESULTS: Dehydration was present in one third of the patients. Sixty percent of these patients had at least one postoperative complication, whereas the corresponding proportion was 30% in the euhydrated patients (P <0.01). Only one patient (3%) had more than one complication in the euhydrated group compared with six patients (40%) in the dehydrated group (P <0.01). Euhydrated patients had a mean of 0.3 postoperative complications per surgery, whereas dehydrated patients scored 1.1 complications (P <0.015). The higher incidence included confusion, arterial desaturation and cardiovascular events.

CONCLUSION: Dehydration before surgery nearly quadrupled the number of postoperative complications after hip fracture repair.

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.

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⁻¹), hydroxyethyl starch 130/0.4 (10 ml kg⁻¹) 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⁻¹ whereas the 95% prediction interval was wide, ranging from −24.9 to 23.7 g l⁻¹. 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.

BACKGROUND: Patients admitted to surgery may be dehydrated, which is difficult to diagnose except when it is severe (>5% Gl116 of the body weight). We hypothesized that modest dehydration can be detected by kinetic analysis of the blood hemoglobin concentration after a bolus infusion of crystalloid fluid.

METHODS: Four series of experiments were performed on 10 conscious, healthy male volunteers. Separated by at least 2 days, they received 5 or 10 mL/kg acetated Ringer's solution over 15 minutes. Before starting half of the IV infusions, volume depletion amounting to 1.5 to 2.0 L (approximately 2% of body weight) was induced with furosemide. The elimination clearance and the half-life of the infused fluid were calculated based on blood hemoglobin over 120 minutes. The perfusion index and the pleth variability index were monitored by pulse oximetry after a change of body position.

RESULTS: Dehydration decreased the elimination clearance of acetated Ringer's solution [median (25th-75th percentile)] from 1.84 (1.23-2.57) to 0.53 (0.41-0.79) mL/kg/min (Wilcoxon matched-pair test P < 0.001) and increased the half-life from 23 (12-37) to 76 (57-101) minutes (P < 0.001). The smaller infusion, 5 mL/kg, fully discriminated between experiments performed in the euhydrated and dehydrated states, whereas the urinary excretion provided a less-reliable indication of hydration status. Dehydration decreased the perfusion index but did not affect the pleth variability index.

CONCLUSION: Dehydration amounting to 2% of the body weight could be detected from the elimination clearance and the half-life of an infusion of 5 mL/kg Ringer's solution.