Volume Kinetic Analysis Research Articles

Diuretic responses to Ringer's solution and 20% albumin at different arterial pressures.

Intravenous volume loading is a common treatment when hypovolemia is a potential cause of oliguria. We studied whether the effectiveness of Ringer's solution and 20% albumin in inducing diuresis differs depending on the mean arterial pressure (MAP). For this purpose, volume kinetic analysis was performed based on urine output and hemoglobin-derived plasma dilution obtained during and after 136 infusions of Ringer and 85 infusions of 20% albumin. Covariance analysis quantified the diuretic response at different arterial pressures. The results show that the diuretic response to a known plasma volume expansion was greater for Ringer's solution above a MAP of 70 mmHg, while 20% albumin was significantly more effective at lower pressures (p < 0.03). Simulations of the urinary output in response to infusion of a predefined fluid volume yielded superior efficacy for 20% albumin when the MAP was low, while Ringer's was similarly effective when the MAP averaged 100 mmHg. In conclusion, urine output in response to plasma volume expansion with 20% albumin was similar to, or even stronger, than that of Ringer's solution when the MAP was below 70 mmHg.

Fluid distribution during surgery in the flat recumbent, Trendelenburg, and the reverse Trendelenburg body positions.

The distribution and elimination of infused crystalloid fluid is known to be affected by general anesthesia, but it is unclear whether changes differ depending on whether the patient is operated in the flat recumbent position, the Trendelenburg ("legs up") position, or the reverse Trendelenburg ("head up") position. Retrospective data on hemodilution and urine output obtained during and after infusion of 1-2 L of Ringer's solution over 30-60 min were collected from 61 patients undergoing surgery under general anesthesia and 106 volunteers matched with respect to the infusion volume and infusion time. Parameters describing fluid distribution in the anesthetized and awake subjects were compared by population volume kinetic analysis. General anesthesia decreased the rate constant for urine output by 79% (flat recumbent), 91% (legs up) and 91% (head up), suggesting that laparoscopic surgery per se intensified the already strong anesthesia-induced fluid retention. General anesthesia also decreased the rate constant governing the return of the distributed fluid to the plasma by 32%, 15%, and 70%, respectively. These results agree with laboratory data showing a depressive effect of anesthetic drugs on lymphatic pumping, and further suggest that the "legs up" position facilitates lymphatic flow, whereas the "head up" position slows this flow. Both Trendelenburg positions increased swelling of the "third fluid space". General anesthesia caused retention of infused fluid with preferential distribution to the extravascular space. Both Trendelenburg positions had a modifying influence on the kinetic adaptations that agreed with the gravitational forces inflicted by tilting to body.

Accelerated lymph flow from infusion of crystalloid fluid during general anesthesia

BackgroundKinetic analysis of crystalloid fluid yields a central distribution volume (Vc) of the same size as the expected plasma volume (approximately 3 L) except during general anesthesia during which Vc might be only half as large. The present study examined whether this difference is due to influence of the intravascular albumin balance.MethodsA population volume kinetic analysis according to a three-compartment model was performed based on retrospective data from 160 infusion experiments during which 1–2.5 L of crystalloid fluid had been infused intravenously over 20–30 min. The plasma dilution based on blood hemoglobin (Hb) and plasma albumin (Alb) was measured on 2,408 occasions and the urine output on 454 occasions. One-third of the infusions were performed on anesthetized patients while two-thirds were given to awake healthy volunteers.ResultsThe Hb-Alb dilution difference was four times greater during general anesthesia than in the awake state (+ 0.024 ± 0.060 versus − 0.008 ± 0.050; mean ± SD; P < 0.001) which shows that more albumin entered the plasma than was lost by capillary leakage. The Hb-Alb dilution difference correlated strongly and positively with the kinetic parameters governing the rate of fluid transfer through the fast-exchange interstitial fluid compartment (k12 and k21) and inversely with the size of Vc. Simulations suggest that approximately 200 mL of fluid might be translocated from the interstitial space to the plasma despite ongoing fluid administration.ConclusionsPronounced plasma volume expansion early during general anesthesia is associated with a positive intravascular albumin balance that is due to accelerated lymphatic flow. This phenomenon probably represents adjustment of the body fluid volumes to anesthesia-induced vasodilatation.

A Slow-Exchange Interstitial Fluid Compartment in Volunteers and Anesthetized Patients: Kinetic Analysis and Physiology.

Physiological studies suggest that the interstitial space contains 2 fluid compartments, but no analysis has been performed to quantify their sizes and turnover rates. Retrospective data were retrieved from 270 experiments where Ringer's solution of between 238 and 2750 mL (mean, 1487 mL) had been administered by intravenous infusion to awake and anesthetized humans (mean age 39 years, 47% females). Urinary excretion and hemoglobin-derived plasma dilution served as input variables in a volume kinetic analysis using mixed-models software. The kinetic analysis successfully separated 2 interstitial fluid compartments. One equilibrated rapidly with the plasma and the other equilibrated slowly. General anesthesia doubled the rate constants for fluid entering these 2 compartments (from 0.072 to 0.155 and from 0.026 to 0.080 min -1 , respectively). The return flows to the plasma were impeded by intensive fluid therapy; the rate constant for the fast-exchange compartment decreased from 0.251 to 0.050 when the infusion time increased from 15 to 60 minutes, and the rate constant for the slow-exchange compartment decreased from 0.019 to 0.005 when the infused volume increased from 500 to 1500 mL. The slow-exchange compartment became disproportionately expanded when larger fluid volumes were infused and even attained an unphysiologically large size when general anesthesia was added, suggesting that the flow of fluid was restrained and not solely determined by hydrostatic and oncotic forces. The dependence of the slow-exchange compartment on general anesthesia, crystalloid infusion rate, and infusion volume all suggest a causal physiological process. Kinetic analysis supported that Ringer's solution distributes in 2 interstitial compartments with different turnover times. The slow compartment became dominant when large amounts of fluid were infused and during general anesthesia. These findings may explain why fluid accumulates in peripheral tissues during surgery and why infused fluid can remain in the body for several days after general anesthesia.

Do volatile anaesthetics depress urine output?

Urine output is markedly reduced by isoflurane, but it is unclear whether the decrease is a specific effect of volatile anaesthetics. Therefore, this study compared the diuretic response to crystalloid volume loading during surgical procedures performed with volatile anaesthetics or intravenous anaesthesia. Data from two clinical trials in which patients were randomized between isoflurane and propofol anaesthesia (open thyroid surgery, n = 29) and between sevoflurane and propofol anaesthesia (open hysterectomy; n = 25) were analysed. Urine volume was measured and the diuretic response to volume loading with 1.7-1.8 L of Ringer's solution over 30 min was studied by population volume kinetic analysis. The kinetic method used 631 measurements of plasma dilution based on blood haemoglobin and plasma albumin and 138 measurements of urine output to quantify the diuretic response to volume loading in the four study groups. The urine output after 150 min of thyroid surgery was 132 (77-231) mL in the propofol group and 218 (80-394) mL in the isoflurane group ( P = 0.50; median and interquartile range). The corresponding volumes were 50 (45-65) mL for propofol and 60 (34-71) mL for sevoflurane at 90 min in the hysterectomy patients ( P = 0.81). The kinetic analysis, which corrected for differences in infused volume, body weight, and plasma volume expansion, did not reveal any statistically significant differences in diuretic response to volume loading between the two inhaled anaesthetics and intravenous anaesthesia. Isoflurane and sevoflurane did not affect urine output more strongly than propofol.

Body fluid kinetics is changed by a rise in plasma glucose

Glucose is an osmotically active molecule and, therefore, rapid changes in plasma glucose might redistribute water volume between the body fluid compartments in a yet unknown way. To study this issue, population volume kinetic analysis was applied to repeated measurements of plasma glucose, blood hemoglobin, and urine output during and after 84 intravenous infusions of 2.5 % glucose with 70 mmol of sodium and in 9 control experiments using Ringer's solution. Forty-nine infusions were given to healthy volunteers, 11 to patients undergoing surgery, and 24 to patients with type 2 diabetes. The results showed that a rise in plasma glucose without marked glucosuria accelerated the distribution of fluid while the return of extravascular fluid to the plasma was strongly retarded. High plasma glucose also decreased the urine output, which was probably due to sodium retention. The summary effect was that fluid-induced plasma volume expansion subsided within 30 min after an infusion ended while extracellular fluid volume remained increased for several hours. Accumulation of fluid was most pronounced in the patients with type 2 diabetes and in the surgical patients. Plasma glucose, HOMA-IR, and Ouicki values did not correlate with any of the kinetic parameters. In conclusion, a rise in plasma glucose conserved infused fluid in the body and promoted peripheral accumulation. A specific effect of type 2 diabetes further decreased the urine flow.

Evidence of serial connection between the plasma volume and two interstitial fluid compartments

BackgroundKinetic analysis of fluid volume shifts can identify two interstitial fluid compartments with different turnover rates, but how they are connected to the bloodstream is unknown. MethodsRetrospective data were retrieved from 217 experiments where 1.5 L of Ringer's solution (mean) had been administered by intravenous infusion over 30 min to awake and anesthetized humans (mean age 40 years). Urinary excretion and hemoglobin-derived plasma dilution served as input variables in a volume kinetic analysis using mixed models software. Possible modes of connection between the two interstitial fluid compartments and the bloodstream were judged by covariance analysis between kinetic rate constants, physiological variables, and time factors. ResultsThe return flow of already distributed fluid to the plasma via a fast-exchange interstitial compartment was inhibited ongoing infusion of fluid (−38 %), which was probably due to increase of the venous pressure during volume loading. Ongoing infusion also greatly retarded the entrance of fluid to the slow-exchange compartment (−85 %), which suggests that infused Ringer's first had to enter the fast-exchange compartment. A high mean arterial pressure markedly increased the urine output and, to a lesser degree, also the rate of entrance of fluid to the fast-exchange compartment. Moreover, a high blood hemoglobin concentration retarded the rate of entrance of fluid to the fast-exchange compartment. ConclusionsThe fast-exchange but not the slow-exchange interstitial fluid compartment was affected by intravascular events, which suggests that only the fast-exchange compartment is directly connected to the circulating blood.

Interstitial washdown during crystalloid fluid loading in graded hypovolemia -A retrospective analysis in volunteers.

"Interstitial washdown" is an edema-preventing mechanism that implies a greater redistribution of interstitial albumin occurs whenever the capillary filtration is increased. To study the effect of interstitial washdown on fluid distribution in normovolemic and hypovolemic volunteers. Capillary filtration was increased by infusing 25 mL/kg Ringer's acetate intravenously over 30 min 10 male just after withdrawal of 0, 450, and 900 mL of blood. Population volume kinetic analysis was used to assess the effects of washdown and hemorrhage on fluid distribution, using the difference in plasma dilution based on hemoglobin and albumin as biomarker of washdown. Blood withdrawal during 10-15 min recruited 100-150 mL of fluid of high albumin content to the plasma, which was probably lymph. The albumin recruitment was temporarily reduced during the fluid loading but increased from 40 min post-infusion and was then greater when preceded by hemorrhage. Simulations suggested that interstitial washdown decreased the extravascular fluid volume by 200 mL over 3 h. The plasma volume and urinary excretion both increased by approximately half this amount. Blood loss without hypotension probably recruited lymph to the plasma, but interstitial washdown played no major role in determining the distribution of crystalloid fluid after hemorrhage.

Volume kinetic analysis of two crystalloid fluid bolus rates in anesthetized cats

Volume kinetic analysis of two crystalloid fluid bolus rates in anesthetized cats

Interstitial washdown and vascular albumin refill during fluid infusion: novel kinetic analysis from three clinical trials

Background and aimsIncreased capillary filtration may paradoxically accelerate vascular refill of both fluid and albumin from the interstitial space, which is claimed to be edema-preventing. We characterized this proposed mechanism, called “interstitial washdown”, by kinetic analyses of the hemodilution induced by intravenous infusion of crystalloid fluid during 3 distinct physiological states.MethodsGreater plasma dilution of hemoglobin as compared to albumin during fluid therapy indicated recruitment of albumin, which was compared to the flow of interstitial fluid to the plasma as indicated by population volume kinetic analysis. Data for the comparison were derived from 24 infusions of crystalloid fluid in conscious volunteers, 30 in anesthetized patients, and 31 in patients with ketoacidosis from hyperglycemia.Results“Interstitial washdown” increased the plasma albumin concentration by between 0.3 and 1.0 g/L in the three series of infusions. The initial albumin concentration in the interstitial fluid returning to the plasma was estimated to between 22 g/L and 29 g/L, which decreased to an average of 50–75% lower during the subsequent 2–3 h. Kinetic simulations show that pronounced washdown was associated with increased capillary filtration (high k12) and, in conscious subjects, with greater plasma and interstitial volume expansion and restricted urine flow. During anesthesia, the main effect was an increase in the non-exchangeable fluid volume (“third-spacing”).ConclusionsCrystalloid fluid accelerates lymphatic flow that moderately increases plasma albumin, but more clearly helps to maintain the intravascular volume. This “interstitial washdown” mechanism becomes exhausted after a few hours.

Model-predicted capillary leakage in graded hypotension: Extended analysis of experimental spinal anesthesia.

Crystalloid fluid infused during the induction of spinal anesthesia is involved in a complex set of physiological responses, including vasodilatation, reactive vasoconstriction, and changes in mean arterial pressure (MAP). The present evaluation compares the modeled capillary leakage in anesthetized versus nonanesthetized body regions. Ten female volunteers (mean age, 29years) received 25ml/kg of Ringer's acetate over 60min during experimental spinal anesthesia. Blood hemoglobin was measured repeatedly in the radial artery (reference), arm (cubital) vein, and leg (femoral) vein for 240min. Each pattern of data served as a dependent variable in volume kinetic analyses that used mixed models software and MAP as covariate. The capillary leakage of fluid from the plasma to the extravascular space peaked at 17ml/min when MAP was 100mmHg, and the two venous curves were virtually identical. At MAP 60mmHg, the rate was reduced to 10-12ml/min when assessed in arterial blood and leg vein blood, but only 5mmHg in blood collected from the arm vein. The distribution half-life of infused fluid was then 40min in the leg and 80min in the arm. These results suggest that vasoconstriction in nonanesthetized body regions halves the capillary leakage that is observed in vasodilated, anesthetized body regions. Graded hypotension during spinal anesthesia reduced the capillary filtration of fluid as determined by volume kinetic analysis. The effect was twice as great when venous blood was sampled from a nonanesthetized body region than from an anesthetized body region.

Can perioperative hemodilution be monitored with non-invasive measurement of blood hemoglobin?

BackgroundTrends in non-invasive measurements of blood hemoglobin (Hb) may be useful for identifying the need for transfusion in the perioperative period.MethodsCrystalloid fluid (5–20 mL/kg) was administered intravenously or by mouth to 30 volunteers and 33 surgical patients in five non-randomized clinical studies where Hb was measured on 915 occasions by non-invasive (Radical-7™) and invasive methodology. The hemodilution curves were compared by volume kinetic analysis and linear regression, with the slope and scattering of the data as key outcome measures.ResultsThe slope was 1.0, indicating unity between the two modes of measuring Hb when crystalloid fluid was infused in volunteers; however, only 40–45% of the variability in the non-invasive Hb could be explained by the invasive Hb. Patients undergoing major surgery, who showed the most pronounced hemodilution (median 24 g/L); non-invasive Hb explained 72% of the variability but indicated only half the magnitude of the invasive Hb changes (slope 0.48, P < 0.001 versus the volunteers). Simulations based on volume kinetic parameters from the volunteers showed 25% less plasma volume expansion after infusion when based on non-invasive as compared to invasive Hb, while no difference was found during infusion.ConclusionsIn volunteers the non-invasive Hb had good accuracy (low bias) but poor precision. In surgical patients the non-invasive Hb had good precision but systematically underestimated the hemodilution. Despite severe limitations, the non-invasive technology can be used to follow Hb trends during surgery if supported by occasional invasive measurements to assure acceptable quality of the hemodilution curve.Trial registrationsControlledTrials.gov NCT01195025, NCT01062776, NCT01458678, NCT03848507, and NCT01360333 on September 3, 2010, February 4, 2010, October 25, 2011, February 20, 2019, and May 25, 2011, respectively.

Fluid escapes to the "third space" during anesthesia, a commentary.

BackgroundThe “third fluid space” is a concept that has caused much confusion for more than half a century, dividing anesthesiologists into believers and non‐believers.AimTo challenge the existence of the “third fluid space” based on analysis of crystalloid fluid kinetics.MethodsData on hemodilution patterns from 157 infusion experiments performed in volunteers and from 85 patients undergoing surgery under general anesthesia were studied by population volume kinetic analysis. Elimination of infused crystalloid fluid from the kinetic model could occur either as urine or "third space" accumulation. The latter fluid volume remained in the body, but without equilibrating with the plasma within the 3‐4 h of the experiment.ResultsThe rate constant for "third space" loss of fluid accounted for 20% of the elimination in conscious volunteers and for 75% during general anesthesia and surgery. The two elimination constants showed a reciprocal relationship, resulting in that "third‐space" losses increase when urinary excretion is restricted. The effect on the plasma volume was smaller than indicated by these figures because fluid distributed to the extravascular space continuously redistributed to the plasma. Worked‐out examples show that one‐third of an infused crystalloid volume has been confined to the "third space" after 3 h of surgery. When equilibration with the plasma eventually occurs, which is necessary for excretion of the fluid, is not known.ConclusionDuring anesthesia and surgery one third of the infused crystalloid fluid is at least temporarily unavailable for excretion, which probably contributes to postoperative weight increase and edema.

Evaluation of the Distribution and Elimination of Balanced Isotonic Crystalloid, 5% Hypertonic Saline, and 6% Tetrastarch 130/0.4 Using Volume Kinetic Modeling and Analysis in Healthy Conscious Cats.

This prospective, randomized, blinded, interventional cross-over study investigated the distribution, elimination, plasma volume expansion, half-life, comparative potency, and ideal fluid prescription of three commonly prescribed intravenous (IV) fluids in 10 healthy conscious cats using volume kinetic analysis that is novel to veterinary medicine. Each cat received 20 mL/kg of balanced isotonic crystalloid (PLA), 3.3 mL/kg of 5% hypertonic saline (HS), and 5 mL/kg of 6% tetrastarch 130/0.4 (HES) over 15 min on separate occasions. Hemoglobin concentration, red blood cell count, hematocrit, heart rate, and blood pressure were measured at baseline, 5, 10, 15, 20, 30, 40, 50, 60, and every 15 min until 180 min. Urine output was estimated every 30 min using point-of-care bladder ultrasonography. Plasma dilution derived from serial hemoglobin concentration and red blood cell count served as input variables for group and individual fluid volume kinetic analyses using a non-linear mixed effects model. In general, the distribution of all IV fluids was rapid, while elimination was slow. The half-lives of PLA, HS, and HES were 49, 319, and 104 min, respectively. The prescribed fluid doses for PLA, HS, and HES resulted in similar peak plasma volume expansion of 27–30%. The potency of HS was 6 times higher than PLA and 1.7 times greater than HES, while HES was 3.5 times more potent than PLA. Simulation of ideal fluid prescriptions to achieve and maintain 15 or 30% plasma volume expansion revealed the importance of a substantial reduction in infusion rates following initial IV fluid bolus. In conclusion, volume kinetic analysis is a feasible research tool that can provide data on IV fluid kinetics and body water physiology in cats. The rapid distribution but slow elimination of IV fluids in healthy conscious cats is consistent with anecdotal reports of fluid overload susceptibility in cats and warrants further investigation.

Water content of the endothelial glycocalyx layer estimated by volume kinetic analysis

BackgroundThe water volume of the endothelial glycocalyx layer has been estimated at 0.7 to 1.7 L using tracer methods of unclear value. The present study attempts to measure this fluid volume by analyzing the kinetics of a crystalloid fluid load.MethodsAn intravenous infusion of approximately 1 L of Ringer’s acetate was administered to 35 healthy volunteers, and the central volume of distribution of the water volume was calculated from the urinary excretion and frequent measurements of the fluid-induced hemodilution using mixed-effects modeling software. Comparisons were made with the plasma volume derived from three published anthropometric regression equations based on isotope measurements. In a second analysis, up to 2.5 L of Ringer’s was administered to 60 volunteers selected from a cohort of 160 to have as similar hematocrits as possible to the volunteers whose data were used to create the anthropometric equations.ResultsVolume kinetics showed that the infused crystalloid fluid occupied a larger central fluid space than was estimated with the isotope measurements. The first analysis of the 35 subjects indicated a mean difference of 0.51 L in males and 0.49 L in females. The second, larger analysis showed a mean excess volume of 0.43 L, which was approximately 15% of the circulating plasma volume.ConclusionsA crystalloid fluid load expands a 0.4–0.5 L larger central fluid space than the circulating plasma volume. The excess volume is probably located in the glycocalyx layer.

Volume kinetic analysis of fluid retention after induction of general anesthesia

BackgroundInduction of general anesthesia increases the hemodilution resulting from infusion of crystalloid fluid, which is believed to be due to slower distribution caused by arterial hypotension. When normal distribution returns is not known.MethodsAn intravenous infusion of 25 mL kg− 1 of Ringer’s lactate was infused over 30 min to 25 volunteers just after induction of general anesthesia for open abdominal hysterectomy. A two-volume model was fitted to the repeated measurements of the blood hemoglobin concentration and the urinary excretion using mixed-effects modelling software. Individual-specific covariates were added in sequence.ResultsDistribution of infused fluid was interrupted during the first 20 min of the infusions. During this time 16.6 mL kg− 1 of lactated Ringer’s had been infused, of which virtually all remained in the circulating blood. Thereafter, the fluid kinetics was similar to that previously been found in awake volunteers except for the elimination rate constant (k10), which remained to be very low (0.86 × 10− 3 min− 1). Redistribution of infused fluid from the interstitium to the plasma occurred faster (higher k21) when the arterial pressure was low. No covariance was found between the fixed parameters and preoperatively concentrated urine, the use of sevoflurane or propofol to maintain the anesthesia, or the plasma concentrations of two degradation products of the endothelial glycocalyx, syndecan-1 and heparan sulfate.ConclusionsInduction of general anesthesia interrupted the distribution of lactated Ringer’s solution up to when 16.6 mL kg− 1 of crystalloid fluid had been infused. Plasma volume expansion during this period of time was pronounced.Trial registrationControlled-trials.com (ISRCTN81005631) on May 17, 2016 (retrospectively registered).

Population-based volume kinetics of Ringer's lactate solution in patients undergoing open gastrectomy.

In order to maintain stable blood pressure and heart rate during surgery, anesthesiologists need to administer the appropriate amount of fluid with appropriate fluid type to the patient, then quantifying how fluid is distributed and eliminated from the body is useful for establishing a fluid administration strategy. In this study we characterized the volume kinetics of Ringer's lactate solution in patients undergoing open gastrectomy. When propofol and remifentanil reached a pseudosteady state at the target concentration and blood pressure was stabilized following surgical stimulation, enrolled patients were administered 1000 mL of Ringer's lactate solution for 20 min, followed by continuous infusion at a rate of 6 mL/kg/h until the time of the last blood collection for volume kinetic analysis. Arterial blood samples were collected to measure the hemoglobin concentration at different time points. The change in hemoglobin-derived plasma dilution induced by the administration of Ringer's lactate solution was evaluated by nonlinear mixed effects modeling. Three hundred and twenty-three plasma dilution data points from 27 patients were used to determine the pharmacokinetic characteristics of Ringer's lactate solution. A two-volume model best described the pharmacokinetics of Ringer's lactate solution. The mean arterial pressure (MAP) and body weight (WT) were significant covariates for the elimination clearance (kr) and central volume of distribution at baseline (Vc0), respectively. The parameter estimates were as follows: kr (mL/min) = 124 + (MAP/70)14.2, Vc0 (mL) = 0.95 + 3440 × (WT/63), Vt0 (mL) = 2730, and kt (mL/min) = 181. A higher MAP was associated with a greater elimination clearance and, consequently, less water accumulation in the interstitium. As body weight increases, volume expansion in the blood vessels increases.

The Use of a Noninvasive Hemoglobin Monitor for Volume Kinetic Analysis in an Emergency Room Setting

Distribution and clearance of an infused bolus can be studied by repetitive sampling of invasive total hemoglobin (tHb) using volume kinetic equations. Pulse CO-oximetry, a recent advancement in patient monitoring that allows for the continuous and noninvasive estimation of hemoglobin concentration (SpHb), would greatly facilitate the scientific and clinical use of the volume kinetic parameters. In the present study, we examined whether serial measurements of SpHb in an emergency room setting can be used to calculate distribution volume (V) and clearance (Cl) rate of an infused bolus. This was a prospective, observational study of patients in 2 age groups admitted for various reasons to the emergency room of a tertiary care center. IV catheters were placed in both arms of the subjects to induce plasma volume expansion by infusion of a buffered crystalloid glucose solution and for withdrawing venous blood samples for analysis of tHb at 0, 5, 10, 15, 30, 45, 60, 75, and 90 minutes after start of infusion. During these interventions, subjects were simultaneously monitored by pulse CO-oximetry for measurement of SpHb (Masimo Radical-7, Rev E ReSposable Sensor). Bias, precision, and limits of agreement were calculated in Bland-Altman plots to compare the accuracy of SpHb with invasive tHb measurements. Using volume kinetic (pharmacokinetics for fluids) equations, V and Cl were determined. Thirty patients (14 from the young group with a mean age of 30 years, and 16 from the geriatric group with mean age of 84 years) were enrolled in the study. When all data were included, this yielded 242 data pairs with a bias of -0.47 (95% confidence interval, -0.62 to -0.32) between SpHb and tHb. However, 5 patients were omitted because of low quality signals, leaving 193 hemoglobin data pairs for further analysis. Bias was then -0.24 (95% confidence interval, -0.39 to -0.09). The biases show that the device on average slightly underestimates tHb values. The precision of SpHb decreases when the low signal quality indicator is present. For the 27 subjects for whom the V and Cl were calculated, there were no significant differences in the estimation of the distribution volumes using either tHb or SpHb values. Clearance constants were also estimated, but with less accuracy. Our data show that SpHb by pulse CO-oximetry may be used to calculate volume of distribution in an emergency room setting.

Low doses of esmolol and phenylephrine act as diuretics during intravenous anesthesia

IntroductionThe renal clearance of infused crystalloid fluid is very low during anaesthesia and surgery, but experiments in conscious sheep indicate that the renal fluid clearance might approach a normal rate when the adrenergic balance is modified.MethodsSixty females (mean age, 32 years) undergoing laparoscopic gynecological surgery were randomized to control group and received only the conventional anesthetic drugs and 20 ml/kg of lactated Ringer's over 30 mins. The others were also given an infusion of 50 μg/kg/min of esmolol (beta1-receptor blocker) or 0.01 μg/kg/min of phenylephrine (alpha1-adrenergic agonist) over 3 hours. The distribution and elimination of infused fluid were studied by volume kinetic analysis based on urinary excretion and blood hemoglobin level.ResultsBoth drugs significantly increased urinary excretion while heart rate and arterial pressure remained largely unaffected. The urine flows during non-surgery were 43, 147, and 176 ml in the control, esmolol, and phenylephrine groups, respectively (medians, P < 0.03). When surgery had started the corresponding values were 34, 65 and 61 ml (P < 0.04). At 3 hours, averages of 9%, 20%, and 25% of the infused volume had been excreted in the three groups (P < 0.01). The kinetic analyses indicated that both treatments slowed down the distribution of fluid from the plasma to the interstitial fluid space, thereby preventing hypovolemia.ConclusionsEsmolol doubled and phenylephrine almost tripled urinary excretion during anesthesia-induced depression of renal fluid clearance.

Use of a noninvasive hemoglobin monitor for volume kinetic analysis in an emergency room setting

s and Programme: EUROANAESTHESIA 2011: The European Anaesthesiology Congress: Monitoring: Equipment and Computers