Measuring the Size of the Extracellular Fluid Space Using Bromide, Iohexol, and Sodium Dilution

Is the NICE Guideline for maintenance fluid therapy in adults in hospital appropriate?

BACKGROUND AND AIMS

The National Institute for Health and Care Excellence's (NICE) Guideline for Maintenance Fluid Therapy in Adults in Hospital is widely used, but the recommendations have not been evaluated properly. In this study, we investigated whether the recommendation of providing 25-30 mL/kg/day of fluid and 1 mmol/kg each of sodium and potassium is sufficient for human needs.

METHODS

First, we calculated the distribution of fluid between the extracellular fluid volume (ECV) and intracellular fluid volume (ICV) during a cross-over infusion experiment where 12 volunteers received 25 mL/kg/day of either a high-sodium (154 mmol/L) or low-sodium (54 mmol/L) solution over 48 h. Second, urine samples from 719 volunteers and clinical patients were used to quantify their renal water conservation and excretion of sodium and potassium. Third, retrospective analysis of a diet study was used to extrapolate how large the fluid intake and the electrolyte excretion likely had been in the 719 volunteers and hospital patients who delivered urine.

RESULTS

The high-sodium fluid maintained the ECV but the ICV had decreased by 1.3 L after 48 h. The low-sodium fluid resulted in a volume deficit of 1.7 L that equally affected the ECV and the ICV. Regression equations based on the diet study suggested that the daily intake of water in the 719 subjects averaged 2.6 L and that 2 mmol/kg of sodium and 1 mmol/kg of potassium was excreted.

CONCLUSION

The NICE guideline recommends too little water and sodium for a human to adequately maintain the ECV and ICV.

CLINICAL TRIAL REGISTRATIONS

EudraCT 2016-001846-24 and ISRCTN 12215472.

Salt-sensitive trait of normotensive individuals is associated with altered autonomous cardiac regulation: a randomized controlled intervention study

Blood pressure (BP) responses to sodium intake show great variation, discriminating salt-sensitive (SS) from salt-resistant (SR) individuals. The pathophysiology behind salt sensitivity is still not fully elucidated. We aimed to investigate salt-induced effects on body fluid, vascular tone, and autonomic cardiac response with regard to BP change in healthy normotensive individuals. We performed a randomized crossover study in 51 normotensive individuals with normal body mass index and estimated glomerular filtration rate. Subjects followed both a low-Na+ diet (LSD, <50 mmol/day) and a high-Na+ diet (HSD, >200 mmol/day). Cardiac output, systemic vascular resistance (SVR), and cardiac autonomous activity, through heart rate variability and cross-correlation baroreflex sensitivity (xBRS), were assessed with noninvasive continuous finger BP measurements. In a subset, extracellular volume (ECV) was assessed by iohexol measurements. Subjects were characterized as SS if mean arterial pressure (MAP) increased ≥3 mmHg after HSD. After HSD, SS subjects (25%) showed a 6.1-mmHg (SD 1.9) increase in MAP. No differences between SS and SR in body weight, cardiac output, or ECV were found. SVR was positively correlated with Delta BP (r = 0.31, P = 0.03). xBRS and heart rate variability were significantly higher in SS participants compared to SR participants after both HSD and LSD. Sodium loading did not alter heart rate variability within groups. Salt sensitivity in normotensive individuals is associated with an inability to decrease SVR upon high salt intake that is accompanied by alterations in autonomous cardiac regulation, as reflected by decreased xBRS and heart rate variability. No discriminatory changes upon high salt were observed among salt-sensitive individuals in body weight and ECV.NEW & NOTEWORTHY Extracellular fluid expansion in normotensive individuals after salt loading is present in both salt-sensitive and salt-resistant individuals and is not discriminatory to the blood pressure response to sodium loading in a steady-state measurement. In normotensive subjects, the ability to sufficiently vasodilate seems to play a pivotal role in salt sensitivity. In a normotensive cohort, differences in sympathovagal balance are also present in low-salt conditions rather than being affected by salt loading. Whereas treatment and prevention of salt-sensitive blood pressure increase are mostly focused on renal sodium handling and extracellular volume regulation, our study suggests that an inability to adequately vasodilate and altered autonomous cardiac functioning are additional key players in the pathophysiology of salt-sensitive blood pressure increase.

The kinetics of isotonic and hypertonic resuscitation fluids is dependent on the sizes of the body fluid volumes

Background and Aims

The extracellular and intracellular fluid volumes (ECV and ICV) vary not only with age, gender, and body weight but also with the habitual intake of water. The present study examines whether the baseline variations in the ECV and ICV change the distribution and elimination of subsequently given infusion fluids.

Material and Methods

Twenty healthy male volunteers underwent 50 infusion experiments with crystalloid fluid for which the fluid volume kinetics was calculated based on frequent measurements of the hemodilution using mixed-effects modeling software. The results were compared with the ECV and ICV measured with multifrequency bioimpedance analysis before each infusion started. The fluids were given over 30 minutes and comprised 25 mL/kg Ringer's acetate (N = 20), Ringer's lactate, 5 mL/kg 7.5% saline, and 3 mL/kg 7.5% saline in 6% dextran 70 (these fluids, N = 10).

Results

A large ICV was associated with a small extravascular accumulation of infused fluid, which increased the plasma volume expansion and the urinary excretion. With hypertonic fluid, a large ECV greatly accelerated urinary excretion. The body weight did not serve as a covariate in the kinetic models. Albumin was recruited to the plasma during infusion of both types of fluid. The hypertonic fluids served as diuretics. The infused excess sodium and osmolality were distributed over a 35% larger space than the sum of the ECV and ICV.

Conclusion

A large ICV reduced the rate of distribution of Ringer's solution, whereas a large ECV accelerated the excretion of hypertonic saline.

The intracellular fluid compartment is smaller than commonly believed when measured by whole-body bioimpedance

OBJECTIVES

To report our data on the total body water (TBW), intracellular volume (ICV), extracellular volume (ECV), and fat-free mass (FFM) from studies using whole-body bioimpedance (BIA) with the aim of contrasting them to commonly cited reference values.

METHODS

Data were retrospectively retrieved from three single-center studies of adult healthy male volunteers and one study of women scheduled for abdominal hysterectomy where multifrequency BIA had been applied to obtain measurements of TBW, ICV, ECV, and FFM.

RESULTS

Based on measurements performed in 44 males, the TBW, ICV, ECV, and FFM represented 49.1 (4.9)%, 23.32 (3.1)%, 25.8 (2.2)%, and 67.4 (7.4)% of the BW, respectively (mean, SD). In 15 females, these volumes were 40.4 (4.5)%, 18.0 (2.1)%, 22.4 (2.6)%, and 55.6 (6.1)% per kg BW, respectively. The deviation of these measurements from the reference values increased linearly with body weight and age.

CONCLUSIONS

Body fluid volumes indicated by BIA showed that TBW amounted to 80% of the reference volume, which is 60% per kg BW in adult males. The ratio between the ICV and the ECV was approximately 1:1, while this ratio is traditionally reported to be 2:1.

Comparison between two solute equations and bioimpedance for estimation of body fluid volumes

Background

The extracellular volume (ECV) and intracellular volume (ICV) estimated by bioimpedance analysis (BIA) deviates markedly from the textbook volumes of 20% and 40% of the body weight (BW). We estimated the transcellular exchange of water by calculating solute equilibriums after fluid challenges to examine whether the BIA or the textbook volumes are likely to be most correct.

Methods

Data was retrieved from 8 healthy male volunteers who received 25 mL/kg of Ringer’s solution or 3–5 mL/kg of hypertonic (7.5%) saline over 30 min after the ECV and ICV had been estimated by BIA. The exchange of water between the ECV and the ICV was calculated according to a sodium equation and an osmolality equation. Simulations were performed, where deviating body fluid volumes were applied.

Results

The mean ECV measured with BIA was 24.9% of BW (p < 0.05 versus the “textbook” volume). Mean ICV measured with BIA was 22.3% of BW (p < 0.05). The sodium and osmolality equations correlated closely with respect to the translocation of water across the cell membrane (r² = 0.86). By applying the “textbook” ECV, the sodium equation indicated that Ringer’s solution exchanged negligible amounts of water, while hypertonic saline withdrew 1.4 L from the ICV to the ECV. By contrast, applying the BIA-derived ECV to the sodium equation implied that 3 L of water would be translocated from the ECV to the ICV once hypertonic saline was administered.

Conclusion

The “textbook” ECV and ICV volumes but not the BIA-derived volumes were consistent with the fluid shifts obtained by two solute equations.

Perturbed body fluid distribution and osmoregulation in response to high salt intake in patients with hereditary multiple exostoses

Background

Hereditary Multiple Exostoses (HME) is a rare autosomal disorder characterized by the presence of multiple exostoses (osteochondromas) caused by a heterozygous loss of function mutation in EXT1 or EXT2; genes involved in heparan sulfate (HS) chain elongation. Considering that HS and other glycosaminoglycans play an important role in sodium and water homeostasis, we hypothesized that HME patients have perturbed whole body volume regulation and osmolality in response to high sodium conditions.

Methods

We performed a randomized cross-over study in 7 male HME patients and 12 healthy controls, matched for age, BMI, blood pressure and renal function. All subjects followed both an 8-day low sodium diet (LSD, <50 mmol/d) and high sodium diet (HSD, >200 mmol/d) in randomized order. After each diet, blood and urine samples were collected. Body fluid compartment measurements were performed by using the distribution curve of iohexol and ¹²⁵I-albumin.

Results

In HME patients, HSD resulted in significant increase of intracellular fluid volume (ICFV) (1.2 L, p = 0.01). In this group, solute-mediated water clearance was significantly lower after HSD, and no changes in interstitial fluid volume (IFV), plasma sodium, and effective osmolality were observed. In healthy controls, HSD did not influence ICFV, but expanded IFV (1.8 L, p = 0.058) and increased plasma sodium and effective osmolality.

Conclusion

HME patients show altered body fluid distribution and osmoregulation after HSD compared to controls. Our results might indicate reduced interstitial sodium accumulation capacity in HME, leading to ICFV increase. Therefore, this study provides additional support that HS is crucial for maintaining constancy of the internal environment.

Optimal current frequency for the detection of changes in extracellular water in patients on hemodialysis by measurement of total body electrical resistance

BACKGROUND & AIMS

Measurement of total body electrical resistance (TBER) to an alternating current is useful to monitor extracellular water (ECW) in patients on hemodialysis (HD). Which current frequency is preferable is subject of ongoing debate. The aim of this study was to quantify the implications of TBER measurements at current frequencies ranging from 0 to 1000 kHz for ECW monitoring in patients on HD.

METHODS

Bioimpedance spectroscopy measurements were performed in 39 patients on HD using the Body Composition Monitor (BCM, Fresenius Medical Care). TBER data at 5, 50, 200, 500, and 1000 kHz were compared with the extrapolated TBER at 0 kHz (TBER₀) assessed by Cole-Cole analysis. Sensitivity of each TBER configuration was evaluated at individual level, by assessment of the smallest ultrafiltration (UF) volume that induced a significant change in TBER, i.e. a change in TBER ≥ 2.7%.

RESULTS

TBER precision was very high for all frequencies, with coefficients of variation of 0.25%-0.28%. Baseline TBER decreased with increasing current frequency. TBER was 2.9% lower at 5 kHz (P < 0.001), 11.6% lower at 50 kHz, and up to 22.0% lower at 1000 kHz. This pattern is attributed to a progressive increase in intracellular current conduction at higher frequencies. Sensitivity to volume changes induced by UF also decreased with increasing current frequency. At 0 and 5 kHz, an UF volume ≤ 0.5 L was sufficient to induce a significant increase in TBER in 87% of patients. This decreased to 69% at higher frequencies.

CONCLUSION

ECW monitoring by TBER requires measurement at 5 kHz or less to ensure optimal performance.

Unraveling the Contribution of Fluid Therapy to the Development of Augmented Renal Clearance in a Piglet Model

Augmented renal clearance (ARC) observed in the critically ill pediatric population has received an increased attention over the last years due to its major impact on the disposition and pharmacokinetics of mainly renally excreted drugs. Apart from an important inflammatory trigger, fluid administration has been suggested to contribute to the development of ARC. Therefore, the primary objective of this study was to evaluate the effect of continuous intravenous fluid administration on renal function using a conventional piglet animal model and to quantify the impact of fluid administration on the pharmacokinetics of renally excreted drugs. At baseline, twenty-four piglets (12 treatment/12 control; 7 weeks old, all ♂) received the marker drugs iohexol (64.7 mg/kg body weight (BW)) and para-aminohippuric acid (10 mg/kg BW) to quantify glomerular filtration rate and effective renal plasma flow, respectively. In addition, the hydrophilic antibiotic amikacin (7.5 mg/kg BW) was administered. Following this baseline measurement, the treatment group received fluid therapy as a constant rate infusion of 0.9% saline at 6 mL/kg/h over 36 h. After 24 h of fluid administration, the marker drugs and amikacin were administered again. When comparing both groups, a significant effect of fluid administration on the total body clearances of iohexol (p = 0.032) and amikacin (p = 0.0014) was observed. Clearances of iohexol and amikacin increased with on average 15 and 14%, although large interindividual variability was observed. This led to decreased systemic exposure to amikacin, which was manifested as decrease in area under the plasma concentration-time curve from time 0 h to infinity from 34,807 to 30,804 ng.h/mL. These results suggest that fluid therapy is a key factor involved in the development of ARC and should be taken into account when administering mainly renally excreted drugs. However, further research is necessary to confirm these results in children.

Understanding Volume Kinetics: The Role of Pharmacokinetic Modeling and Analysis in Fluid Therapy

Fluid therapy is a rapidly evolving yet imprecise clinical practice based upon broad assumptions, species-to-species extrapolations, obsolete experimental evidence, and individual preferences. Although widely recognized as a mainstay therapy in human and veterinary medicine, fluid therapy is not always benign and can cause significant harm through fluid overload, which increases patient morbidity and mortality. As with other pharmaceutical substances, fluids exert physiological effects when introduced into the body and therefore should be considered as "drugs." In human medicine, an innovative adaptation of pharmacokinetic analysis for intravenous fluids known as volume kinetics using serial hemoglobin dilution and urine output has been developed, refined, and investigated extensively for over two decades. Intravenous fluids can now be studied like pharmaceutical drugs, leading to improved understanding of their distribution, elimination, volume effect, efficacy, and half-life (duration of effect) under various physiologic conditions, making evidence-based approaches to fluid therapy possible. This review article introduces the basic concepts of volume kinetics, its current use in human and animal research, as well as its potential and limitations as a research tool for fluid therapy research in veterinary medicine. With limited evidence to support our current fluid administration practices in veterinary medicine, a greater understanding of volume kinetics and body water physiology in veterinary species would ideally provide some evidence-based support for safer and more effective intravenous fluid prescriptions in veterinary patients.

Electrolyte-based calculation of fluid shifts after infusing 0.9% saline in severe hyperglycemia

Background

Early treatment of severe hyperglycemia involves large shifts of body fluids that entail a risk of hemodynamic instability. We studied the feasibility of applying a new electrolyte equation that estimates the degree of volume depletion and the distribution of infused 0.9% saline in this setting.

Methods

The new equation was applied to plasma and urinary concentrations of sodium and chloride measured before and 30 min after a 30-min infusion of 1 L of 0.9% saline on two consecutive days in 14 patients with severe hyperglycemia (mean age 50 years). The extracellular fluid (ECF) volume was also estimated based on the volume dilution kinetics of chloride.

Results

On day 1, the baseline ECF volume amounted to 11.5 L. The saline infusion expanded the ECF space by 160 mL and the intracellular fluid space by 375 mL. On day 2, the ECF volume was 15.5 L, and twice as much of the infused fluid remained in the ECF space. The chloride dilution kinetics yielded baseline ECF volumes of 11.6 and 15.2 L on day 1 and day 2, respectively. No net uptake of glucose to the cells occurred during the two 1-h measurement periods despite insulin administration in the intervening time period.

Conclusions

The electrolyte equation was feasible to apply in a group of hyperglycemic patients. The ECF space was 3 L smaller than expected on admission but normal on the second day. Almost half of the infused fluid was distributed intracellularly.

Effect of high-salt diet on blood pressure and body fluid composition in patients with type 1 diabetes: randomized controlled intervention trial

INTRODUCTION

Patients with type 1 diabetes are susceptible to hypertension, possibly resulting from increased salt sensitivity and accompanied changes in body fluid composition. We examined the effect of a high-salt diet (HSD) in type 1 diabetes on hemodynamics, including blood pressure (BP) and body fluid composition.

RESEARCH DESIGN AND METHODS

We studied eight male patients with type 1 diabetes and 12 matched healthy controls with normal BP, body mass index, and renal function. All subjects adhered to a low-salt diet and HSD for eight days in randomized order. On day 8 of each diet, extracellular fluid volume (ECFV) and plasma volume were calculated with the use of iohexol and 125I-albumin distribution. Hemodynamic measurements included BP, cardiac output (CO), and systemic vascular resistance.

RESULTS

After HSD, patients with type 1 diabetes showed a BP increase (mean arterial pressure: 85 (5) mm Hg vs 80 (3) mm Hg; p<0.05), while BP in controls did not rise (78 (5) mm Hg vs 78 (5) mm Hg). Plasma volume increased after HSD in patients with type 1 diabetes (p<0.05) and not in controls (p=0.23). There was no significant difference in ECFV between diets, while HSD significantly increased CO, heart rate (HR) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in type 1 diabetes but not in controls. There were no significant differences in systemic vascular resistance, although there was a trend towards an HSD-induced decrease in controls (p=0.09).

CONCLUSIONS

In the present study, patients with type 1 diabetes show a salt-sensitive BP rise to HSD, which is accompanied by significant increases in plasma volume, CO, HR, and NT-proBNP. Underlying mechanisms for these responses need further research in order to unravel the increased susceptibility to hypertension and cardiovascular disease in diabetes.

TRIAL REGISTRATION NUMBERS

NTR4095 and NTR4788.

Understanding volume kinetics

The distribution and elimination kinetics of the water volume in infusion fluids can be studied by volume kinetics. The approach is a modification of drug pharmacokinetics and uses repeated measurements of blood hemoglobin and urinary excretion as input variables in (usually) a two-compartment model with expandable walls. Study results show that crystalloid fluid has a distribution phase that gives these fluids a plasma volume expansion amounting to 50%-60% of the infused volume as long as the infusion lasts, while the fraction is reduced to 15%-20% within 30 minutes after the infusion ends. Small volumes of crystalloid barely distribute to the interstitium, whereas rapid infusions tend to cause edema. Fluid elimination is very slow during general anesthesia due to the vasodilatation-induced reduction of the arterial pressure, whereas elimination is less affected by hemorrhage. The half-life is twice as long for saline than for Ringer solutions. Elimination is slower in conscious males than conscious females, and high red blood cell and thrombocyte counts retard both distribution and re-distribution. Children have faster turnover than adults. Plasma volume expansions are similar for glucose solutions and Ringer's, but the expansion duration is shorter for glucose. Concentrated urine before and during infusion slows down the elimination of crystalloid fluid. Colloid fluids have no distribution phase, an intravascular persistence half-life of 2-3 hours, and-at least for hydroxyethyl starch-the ability to reduce the effect of subsequently infused crystalloids. Accelerated distribution due to degradation of the endothelial glycocalyx layer has not yet been demonstrated.

Salt-sensitive blood pressure rise in type 1 diabetes patients is accompanied by disturbed skin macrophage influx and lymphatic dilation-a proof-of-concept study

Type 1 diabetes patients are more prone to have hypertension than healthy individuals, possibly mediated by increased blood pressure (BP) sensitivity to high salt intake. The classical concept proposes that the kidney is central in salt-mediated BP rises, by insufficient renal sodium excretion leading to extracellular fluid volume expansion. Recent animal-derived findings, however, propose a causal role for disturbance of macrophage-mediated lymphangiogenesis. Its relevance for humans, specifically type 1 diabetes patients, is unknown. The present study aimed to assess responses of type 1 diabetes patients to a dietary salt load with regard to BP, extracellular fluid volume (using precise iohexol measurements), and CD163+ macrophage and lymphatic capillary density in skin biopsies. Also, macrophage expression of HLA-DR (a proinflammatory marker) and CD206 (an anti-inflammatory marker) was assessed. Type 1 diabetes patients (n = 8) showed a salt-sensitive BP increase without extracellular fluid volume expansion. Whereas healthy controls (n = 12), who had no BP increase, showed increased skin CD163+ and HLA-DR+ macrophages and dilation of lymphatic skin vasculature after the dietary salt load, these changes were absent (and in case of HLA-DR more heterogenic) in type 1 diabetes patients. In conclusion, we show that salt sensitivity in type 1 diabetes patients cannot be explained by the classical concept of extracellular fluid volume expansion. Rather, we open up a potential role for macrophages and the lymphatic system. Future studies on hypertension and diabetes need to scrutinize these phenomena.

Extracellular fluid volume is associated with incident end-stage kidney disease and mortality in patients with chronic kidney disease

Volume overload has been shown to be an independent risk factor for mortality in patients receiving chronic dialysis, but data in non-dialysis patients are scarce. Therefore we evaluated the prognostic value of extracellular fluid (ECF) volume for chronic kidney disease (CKD) progression and mortality in a prospective hospital-based cohort with CKD stage 1-4 (NephroTest Study). ECF (scaled to body surface area) and the measured glomerular filtration rate (mGFR) were determined using the distribution volume and clearance of 51Cr-EDTA, respectively. Cause-specific Cox and linear mixed-effect regression models were used to analyze the association of ECF with end-stage kidney disease (ESKD) and mortality, and with mGFR decline, respectively. The 1593 patients were mean age 58.8 years, 67% were men, mean mGFR of 43.6 mL/min/1.73m² and mean ECF 15.1 L/1.73m². After a median follow-up of 5.3 years, ESKD occurred in 324 patients and 185 patients died before ESKD. In multivariable analysis, ECF was significantly associated with the risk of ESKD (hazard ratio per 1L/1.73m² increase: 1.14; 95% confidence interval [1.07; 1.21]) and with a faster GFR decline (adjusted mean difference in mGFR slope per 1L/1.73m² increase -0.14 [-0.23; -0.05] mL/min/year). The relationship of ECF with mortality was non-linear and not significant (per 1L/1.73m² increase 0.92, [0.73; 1.16]), below 15L/1.73m², but significant (1.28; [1.14-1.45]) above 15L/1.73m². Thus, in this large cohort of carefully phenotyped patients with CKD, ECF was an independent risk factor of CKD progression and mortality. Hence, close monitoring and treatment of fluid overload are important for the clinical management of patients with non-dialysis CKD.

Flavonoid compounds from the red marine alga Alsidium corallinum protect against potassium bromate-induced nephrotoxicity in adult mice

Potassium bromate (KBrO₃ ), an environmental pollutant, is a well-known human carcinogen and a potent nephrotoxic agent. Currently, natural products have built a well-recognized role in the management of many diseases induced by pollutants. As potent natural sources of bioactive compounds, marine algae have been demonstrated to be rich in novel secondary metabolites with a broad range of biological functions. In this study, adults male mice were orally treated for 15 days with KBrO₃ (0.5 g/L) associated or not with extract of Alsidium corallinum, a red Mediterranean alga. In vitro study demonstrated that algal extract has antioxidant efficacy attributable to the presence of flavonoids and polyphenols. Among these, Liquid chromatography-mass spectrometry analysis showed A. corallinum is rich in kaempferol, apigenin, catechin, and quercetin flavonoids. In vivo study showed that supplementation with the alga significantly prevented KBrO₃ -induced nephrotoxicity as indicated by plasma biomarkers (urea, uric acid, and creatinin levels) and oxidative stress related parameters (malondialdehyde, superoxide dismutase, catalase, glutathione peroxidase, reduced glutathione, vitamin C, hydrogen peroxide, protein oxidation products) in kidney tissue. The corrective effect of A. corallinum on KBrO₃ -induced kidney injury was also supported by molecular and histopathological observations. In conclusion, it was established that the red alga, thanks to its bioactive compounds, effectively counteracts toxic effects of KBrO₃ and could be a useful coadjuvant agent for treatment of this pollutant poisonings. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1475-1486, 2017.

Isotonic saline in elderly men: an open-labelled controlled infusion study of electrolyte balance, urine flow and kidney function

Isotonic saline is a widely-used infusion fluid, although the associated chloride load may cause metabolic acidosis and impair kidney function in young, healthy volunteers. We wished to examine whether these effects also occurred in the elderly, and conducted a crossover study in 13 men with a mean age of 73 years (range 66-84), who each received intravenous infusions of 1.5 l of Ringer's acetate and of isotonic saline. Isotonic saline induced mild changes in plasma sodium (mean +1.5 mmol.l(-1) ), plasma chloride (+3 mmol.l(-1) ) and standard bicarbonate (-2 mmol.l(-1) ). Three hours after starting the infusions, 68% of the Ringer's acetate and 30% of the infused saline had been excreted (p < 0.01). The glomerular filtration rate increased in response to both fluids, but more after the Ringer's acetate (p < 0.03). Pre-infusion fluid retention, as evidenced by high urinary osmolality (> 700 mOsmol.kg(-1) ) and/or creatinine (> 7 mmol.l(-1) ), was a strong factor governing the responses to both fluid loads.

Determination of extracellular fluid volume in healthy and azotemic cats

BACKGROUND

Methods for determining extracellular fluid volume (ECFV) are important clinically for cats. Bromide dilution has been studied in cats to estimate ECFV. Markers of GFR also distribute in ECFV and can be used for its measurement.

HYPOTHESIS/OBJECTIVES

The primary objective was to develop a method of determining ECFV from iohexol clearance in cats and evaluate agreement with that determined using bromide dilution. Additional objectives were to compare ECFV between azotemic and nonazotemic cats and evaluate appropriate methods of standardizing ECFV.

ANIMALS

Client-owned cats with varying renal function.

METHODS

Validation of ECFV determined from slope-intercept iohexol clearance was performed in 18 healthy nonazotemic cats. ECFV was then determined using the validated method and bromide dilution and agreement assessed. Appropriateness of standardization to body weight (BW) and body surface area (BSA) was evaluated.

RESULTS

Extracellular fluid volume determined from slope-intercept iohexol clearance and bromide dilution was 0.84 ± 0.32 L and 0.85 ± 0.19 L (mean ± SD), respectively. There were wide limits of agreement between the methods (-0.58 to 0.54 L) and therefore, agreement was considered to be poor. ECFV did not differ significantly between azotemic and nonazotemic cats (P = .177). BSA was found to be the best method for standardizing ECFV measurement in cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study developed a method for determining ECFV from slope-intercept iohexol clearance which provides simultaneous assessment of renal function and an estimate of ECFV. ECFV does not differ between azotemic and nonazotemic cats, which suggests fluid volume loss or overload is not an important clinical feature in cats with mild chronic kidney disease.

Agreement of single- and multi-frequency bioimpedance measurements in hemodialysis patients: an ancillary study of the Frequent Hemodialysis Network Daily Trial

BACKGROUND

Bioimpedance analysis (BIA) is well established to assess body composition. Agreements between single- and multi-frequency bioimpedance (SF-BIA, MF-BIS) measurements in subjects undergoing 6 or 3 times/week hemodialysis (HD) were analyzed.

METHODS

Total body water (TBW) and intra- and extracellular fluid (ICF, ECF) of subjects enrolled in the Frequent Hemodialysis Network (FHN) Daily Trial (www.clinicaltrials.gov No. NCT00264758) were measured with a Hydra 4200 at baseline (BL) and at 5 months (M5). Volumes were computed using SF (at 50 kHz) and MF approaches. Agreement was assessed by means of linear regression and Bland-Altman analysis and treatment effects by t test.

RESULTS

35 subjects (17 on the more frequent regimen, 26 males, 20 African-American, 48 ± 9 years, pre-HD weight 84 ± 19 kg) were studied. Assessments with SF-BIA and MF-BIS correlated significantly at BL and M5 in both arms. No proportional errors, but systematic biases over the entire range of values were found at BL and M5. Agreement did not differ between subjects randomized to either HD treatment arm at both time points. MF-BIS appears to have better precision than SF-BIA allowing the observation of a significant treatment effect by the intervention [-1.5 (95% CI -2.5 to -0.5) l] on ECF, not found for ECF SF-BIA. Precision also affected the statistical power of the SF-BIA data in the current analysis.

CONCLUSION

Both methods showed agreement without significant proportional errors regardless of HD frequency and can be used for longitudinal analyses. SF-BIA has lower precision which needs thorough consideration in the design of future trials with similar outcomes.

Comparison of fluid volume estimates in chronic hemodialysis patients by bioimpedance, direct isotopic, and dilution methods

Bioimpedance analysis (BIA) is accepted for the assessment of total-body water (TBW), intracellular fluid (ICF) and extracellular fluid (ECF). We aimed to compare precision and accuracy of single and multi-frequency-BIA to direct estimation methods (DEMs) of TBW, ECF, and ICF in hemodialysis patients. Linear regression analysis of volume estimates in 49 patients by single- and multi-frequency-BIA correlated significantly with DEMs. Bland-Altman analysis (BAA) found systemic bias for ECF single-frequency-BIA vs. ECF-DEMs. No other systematic biases were found. Proportional errors were found by BAA of ICF and ECF assessments with single- and multi-frequency bioimpedance spectroscopy compared to the DEMs. Comparisons of indirect methods (IEMs) to DEMs showed no significant differences and proportional errors. Root mean-squared-error analysis suggested slightly better accuracy and precision of ICF single-frequency-BIA vs. DEMs over ICF multi-frequency-BIA and IEMs to DEMs, and slightly better performance for ECF multi-frequency-BIA over both respective other methods. Compared to DEMs, there is slightly better accuracy for ECF multi- over single-frequency-BIA and ICF single- over multi-frequency-BIA. However the margin of differences between direct and indirect methods suggests that none of the analyzed methods served as a true "gold standard", because indirect methods are almost equally precise compared to DEMs.

Feasibility and impact of the measurement of extracellular fluid volume simultaneous with GFR by 125I-iothalamate

The feasibility, validity, and possible applications of the assessment of extracellular fluid volume (ECFV) simultaneous with glomerular filtration rate (GFR) were assessed in a series of validation studies using the constant infusion method of (125)I-iothalamate (IOT). In 48 subjects with a broad range of GFR, distribution volume (V(d)) of IOT corresponded well with V(d) bromide (16.71 +/- 3.0 and 16.73 +/- 3.2 l, respectively, not significant), with a strong correlation (r = 0.933, P < 0.01) and without systematic deviations. Reproducibility assessment in 25 healthy male subjects showed coefficients of variation of 8.6% of duplicate measurement of V(d) IOT during strictly standardized (50 mmol Na(+)/d) sodium intake. An increase in dietary sodium intake (200 mmol Na(+)/d) induced a corresponding rise in V(d) IOT of 1.11 +/- 1.5 l (P < 0.01). In 158 healthy prospective kidney donors, the impact of indexing of GFR to ECFV was analyzed. Age, gender, height, and body surface area (BSA) were determinants of GFR. Whereas GFR, GFR/BSA, and GFR/height were gender-dependent, GFR/ECFV was gender-independent and not related to height or BSA. This supports the potential of normalizing GFR by ECFV. Thus, ECFV can be simultaneously assessed with GFR by the constant infusion method using IOT. After appropriate validation, also other GFR tracers could be used for such a simultaneous estimation, providing a valuable resource of data on ECFV in renal studies and, moreover, allowing GFR to be indexed to the body fluid compartment it clears: the ECFV.