Urinary Analysis of Fluid Retention in the General Population: A Cross-Sectional Study

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.

Detection of low urine output by measuring urinary biomarkers

BACKGROUND

Urine output < 1 L per 24 h is a clinical warning sign that requires attention from hospital staff, who should determine whether the low flow is due to low habitual intake of water or disease-induced dehydration. The incidence of this condition is unclear.

METHODS

A cohort of 20 healthy volunteers (mean age 42 years, range 23-62 years) recorded their food and water intakes daily for 8 days. They also collected and measured all urine and delivered first morning urine samples for analysis of osmolality and creatinine. Optimal cutoffs for these biomarkers to indicate urine output of < 1 L or 15 mL/kg during the preceding 24 h were applied with and without correction for age to cross-sectional data from 1,316 subjects in various clinical settings, including healthy volunteers, preoperative patients, patients seeking acute care at a hospital, and patients receiving institutional geriatric care.

RESULTS

The urine output amounted to < 1 L during 22 of the 159 evaluable study days and was indicated by urine osmolality > 760 mosmol/kg or urine creatinine > 13 mmol/L, which had sensitivity and specificity of approximately 80%. Days with urine output < 1 L were associated with significantly less intake of both water (-41%) and calories (-22%) compared to other days. Application of age-corrected biomarker cutoffs to the 1,316 subjects showed a stronger dependency of low urine output on age than the clinical setting, occurring in 44% of the 72 participants aged 15-30 years and 18% of the 62 patients aged 90-104 years.

CONCLUSION

Biomarkers measured in morning urine of young and middle-aged volunteers indicated urine output of < 1 L with good precision, but the cutoffs should be validated in older age groups to yield reliable results.

TRIAL REGISTRATIONS

ISRCTN12215472 at http://www.isrctn.com ; NCT01458678 at ClinicalTrials.gov, and ChiCTR-TNRC-14,004,479 at the chictr.org/en.

Concentrated urine, low urine flow, and postoperative elevation of plasma creatinine: A retrospective analysis of pooled data

Elevations of plasma creatinine are common after major surgery, but their pathophysiology is poorly understood. To identify possible contributing mechanisms, we pooled data from eight prospective studies performed in four different countries to study circumstances during which elevation of plasma creatinine occurs. We included 642 patients undergoing mixed major surgeries, mostly open gastrointestinal. Plasma and urinary creatinine and a composite index for renal fluid conservation (Fluid Retention Index, FRI) were measured just before surgery and on the first postoperative morning. Urine flow was measured during the surgery. The results show that patients with a postoperative increase in plasma creatinine by >25% had a high urinary creatinine concentration (11.0±5.9 vs. 8.3±5.6 mmol/L; P< 0001) and higher FRI value (3.2±1.0 vs. 2.9±1.1; P< 0.04) already before surgery was initiated. Progressive increase of plasma creatinine was associated with a gradually lower urine flow and larger blood loss during the surgery (Kruskal-Wallis test, P< 0.001). The patients with an elevation > 25% also showed higher creatinine and a higher FRI value on the first postoperative morning (P< 0.001). Elevations to > 50% of baseline were associated with slightly lower mean arterial pressure (73 ± 10 vs. 80 ± 12 mmHg; P< 0.005). We conclude that elevation of plasma creatinine in the perioperative period was associated with low urine flow and greater blood loss during surgery and with concentrated urine both before and after the surgery. Renal water conservation-related mechanisms seem to contribute to the development of increased plasma creatinine after surgery.

Quantifying the daily intake of water from morning and spot urine samples; retrospective analysis of a clinical trial in volunteers

BACKGROUND

The hydration status can be indicated by biomarkers in the urine. However, the sensitivity and specificity of single measurements of biomarkers in morning urine and spot urine samples to quantify previous and current daily water ingestion is unclear.

METHODS

The water content of food and liquid consumed by 20 volunteers (mean age 42 years) was calculated daily for two weeks. The volunteers increased their consumption of water by approximately 30% during the second week. They measured their excreted urine volume and sampled the morning urine and 24-h collections of urine for analysis of osmolality and creatinine during the first four days of both weeks (N = 157). The same biomarkers of hydration were measured in spot samples taken at every voiding on the other days (N = 762). Receiver operating characteristic (ROC) curves were used to study the ability of pre-specified ranges of biomarkers to quantify the water intake.

RESULTS

The biomarkers in the morning urine obtained during normal fluid intake quantified the water consumption with an average area under the ROC curve (AUC) of 0.72 for osmolality and 0.66 for creatinine. Spot urine yielded an AUC of 0.74 for osmolality and 0.70 for creatinine. The AUCs obtained for days of increased fluid intake were approximately 10% lower. Large intakes (3-4 L daily) were identified with a sensitivity of 50-80% and low intakes (< 1.5-2 L) with a sensitivity of 20-50%, while false positives occurred in approximately 10%.

CONCLUSION

Biomarkers in morning urine and spot urine samples distinguished between large and small daily water intakes. Osmolality was slightly superior to creatinine. The indications were less useful during days of increased fluid intake.

Renal Water Conservation and Plasma Creatinine in Colorectal Cancer Surgery: A Single-Group Clinical Study

Elevation of plasma creatinine after surgery is associated with postoperative morbidity and mortality. We studied whether lengthy surgery might induce renal conservation of water strong enough to exceed the renal capacity to excrete creatinine. Colorectal cancer surgery was performed via laparoscopy in 126 patients. Blood and urine were sampled before surgery, in the postoperative care unit, and 1 day after surgery. The Fluid Retention Index (FRI), which is a composite index of renal water conservation, was calculated. The mean FRI before surgery was 2.4, indicating that patients were well-hydrated. The FRI increased to 2.8 after surgery, and further to 3.5 on the first postoperative day. Plasma creatinine increased in 66 (52%) of the patients while plasma proteins were diluted by 15%. Patients with urinary creatinine > 8.5 mmol/L before surgery were more likely to later show elevation of plasma creatinine (68 vs. 46%, P < 0.04). The final FRI was higher in those with perioperative elevation of plasma creatinine (median 3.7 vs. 3.4; P < 0.01) and a similar difference was found for the final urinary creatinine concentration (8.5 vs. 7.2 mmol/L; P < 0.01). The gastrointestinal recovery time was prolonged when >2 L of Ringer's had been infused during the surgery. We conclude that colorectal surgery initiated a process of renal water conservation that extended into the postoperative period. The water conservation was more intense and the urinary concentration of creatinine was higher in those who had a perioperative rise in plasma creatinine.

Dehydration before Major Urological Surgery and the Perioperative Pattern of Plasma Creatinine: A Prospective Cohort Series

Preoperative dehydration is usually found in 30–50% of surgical patients, but the incidence is unknown in the urologic population. We determined the prevalence of preoperative dehydration in major elective urological surgery and studied its association with postoperative outcome, with special attention to plasma creatinine changes. We recruited 187 patients scheduled for major abdominal urological surgery to participate in a single-center study that used the fluid retention index (FRI), which is a composite index of four urinary biomarkers that correlate with renal water conservation, to assess the presence of dehydration. Secondary outcomes were postoperative nausea and vomiting (PONV), return of gastrointestinal function, in-hospital complications, quality of recovery, and plasma creatinine. The proportion of dehydrated patients at surgery was 20.4%. Dehydration did not correlate with quality of recovery, PONV, or other complications, but dehydrated patients showed later defecation (p = 0.02) and significant elevations of plasma creatinine after surgery. The elevations were also greater when plasma creatinine had increased rather than decreased during the 24 h prior to surgery (p < 0.001). Overall, the increase in plasma creatinine at 6 h after surgery correlated well with elevations on postoperative days one and two. In conclusion, we found preoperative dehydration in one-fifth of the patients. Dehydration was associated with delayed defecation and elevated postoperative plasma creatinine. The preoperative plasma creatinine pattern could independently forecast more pronounced increases during the early postoperative period.

Preoperative Concentrated Urine Increases the Incidence of Plasma Creatinine Elevation After Major Surgery

Background: Postoperative elevation of plasma creatinine is a frequent complication to major surgery. A rise by 50% fulfills the criterion for Acute Kidney Injury. We studied the relationship between concentrated urine before surgery, which is usually a sign of chronically low intake of water, and the perioperative change in plasma creatinine.

Methods: The creatinine concentration was measured in plasma and urine just before and at 6 h, 1 day, and 2 days after major abdominal surgery in a consecutive series of 181 patients. Receiver operating curve analysis was used to find the optimal cut-off to separate concentrated from diluted urine.

Results: Urine creatinine of 11.3 mmol/L before the surgery started was exceeded in one third of the patients and associated with greater increase in plasma creatinine at 6 h (median 21 vs. 10%) and at 1 day postoperatively (21 vs. 7%; P < 0.0001). Elevation of plasma creatinine of >25% occurred in 41% and 19% in those with high and low urine creatinine, respectively (P < 0.001) and an increase by >50% in 16% and 10% (P = 0.27). Patients with high urine creatinine before surgery failed to further concentrate their urine during the perioperative period, which is normally associated with intensified renal fluid conservation.

Conclusion: High urinary concentration of creatinine before surgery should be considered as a risk factor for postoperative elevation of plasma creatinine. The mechanism is probably that the renal threshold is then more easily reached.

Plasma concentrations of syndecan-1 are dependent on kidney function

BACKGROUND

Elevated plasma concentrations of syndecan-1 and heparan sulfate in studies of trauma, sepsis, and major surgery are commonly assumed to indicate acute glycocalyx degradation. We explored a possible role of the kidneys for these elevations.

METHODS

Plasma and urine concentrations of syndecan-1, heparan sulfate, and biomarkers of inflammation were measured over 5 hours in 15 hospital patients treated for post-burn injury. The renal clearances of syndecan-1 and heparan sulfate (CL_R ) were calculated and their influence on the plasma concentration predicted by simulation.

RESULTS

The urine/plasma concentration ratio was 0.9 (0.3-3.0) for syndecan-1 and 2.8 (2.0-4.3) for heparan sulfate. The CL_R varied 250-fold for syndecan-1 and 10-fold for heparan sulfate. Multiple linear regression analysis showed that CL_R for syndecan-1 was positively associated with the creatinine clearance (P < .0032) and the urine flow (P < .015). CL_R for heparan sulfate increased with interleukin-6 (P < .003) and the urine flow (P < .01). Simulations suggested that a change in CL_R from the mean of the highest 3 to the lowest three values would double plasma syndecan-1 within 4 hours and cause a 7-fold rise after 24 hours. A similar change in CL_R for heparan sulfate would triple the plasma level within 24 hours, even if no increased shedding of the glycocalyx takes place.

CONCLUSIONS

The renal elimination of syndecan-1 and heparan sulfate varied greatly. A change in kidney function, which is common after trauma and major surgery, might alone induce several-fold changes in their plasma concentrations.

Renal water conservation and the volume kinetics of fluid-induced diuresis: A retrospective analysis of two cohorts of elderly men

Renal water conservation after an overnight fast mirrors the habitual intake of liquid. The hypothesis in the present study was that water conservation influences the diuretic response to infusion of two types of crystalloid fluid. Twenty-three elderly male patients (mean age 72 years) underwent a total of 46 intravenous infusions of 1.0 or 1.5 L of either hypotonic non-electrolyte fluid (glycine 1.5%) or isotonic electrolyte fluid (Ringer's acetate or 0.9% saline). Urine osmolality (used to indicate renal water conservation) and plasma creatinine were measured before the infusions started. A two-volume model was fitted to repeated measurements of the blood haemoglobin concentration and the urinary excretion, using mixed-effects modelling software. Urine osmolality was examined as a potential covariate to the fixed kinetic parameters. The results show that distribution and redistribution of infused fluid occurred twice as fast for the non-electrolyte fluids as for the electrolyte-containing fluids, while the urine flow showed less difference. For both types of fluid, high urine osmolality served as a statistically significant covariate to the rate constant describing urinary excretion. Simulations showed that a high pre-infusion urine osmolality doubled the time required for the kidneys to excrete 50% of a 30-minute infusion. High plasma creatinine independently prolonged the elimination of non-electrolyte fluid. The use of 0.9% saline instead of Ringer's prolonged the excretion of electrolyte-containing fluid. In conclusion, renal water conservation is a determinant of the diuretic response to crystalloid fluid, regardless of whether the fluid contains electrolytes, and it should be considered in fluid balance studies.

Signs of Dehydration after Hip Fracture Surgery: An Observational Descriptive Study

Background and Objectives: Dehydration might be an issue after hip fracture surgery, but the optimal tools to identify the dehydrated condition have not been determined. The aim of the present study was to compare the characteristics of elderly postoperative patients who were classified as dehydrated according to the methods used in the clinic. Materials and Methods: Thirty-eight patients aged between 65 and 97 (mean, 82) years were studied after being admitted to a geriatric department for rehabilitation after hip fracture surgery. Each patient underwent blood analyses, urine sampling, and clinical examinations. Results: Patients ingested a mean of 1,008 mL (standard deviation, 309 mL) of fluid during their first day at the clinic. Serum osmolality increased significantly with the plasma concentrations of sodium, creatinine, and urea. Seven patients had high serum osmolality (≥300 mosmol/kg) that correlated with the presence of tongue furrows (p < 0.04), poor skin turgor (p < 0.03), and pronounced albuminuria (p < 0.03). Eight patients had concentrated urine (urine-specific gravity ≥ 1.025) that correlated with a low intake of liquid and with a decrease in body weight during the past month of −3.0 kg (25–75 th percentiles, −5.1 to −0.9) versus +0.2 (−1.9 to +2.7) kg (p < 0.04). Conclusions: Renal fluid conservation of water, either in the form of hyperosmolality or concentrated urine, was found in 40% of the patients after hip fracture surgery. Hyperosmolality might not indicate a more severe fluid deficit than is indicated by concentrated urine but suggests an impaired ability to concentrate the urine.

Effects of diet, habitual water intake and increased hydration on body fluid volumes and urinary analysis of renal fluid retention in healthy volunteers

Purpose

To increase our knowledge about the causes and physiological consequences of concentrated urine, the relevance of which in the general population is uncertain.

Methods

Twenty healthy volunteers (mean age 42 years) recorded all intake of food and water for 2 weeks. During the 2nd week, they increased their daily consumption of water by 716 mL (32%). The volunteers delivered a 24-h and a morning urine sample for analysis of osmolality and creatinine during the first 4 days of both weeks, and a sample each time they voided on the other days. The water content of food and liquid was calculated and the body fluid volumes were measured by bioimpedance. Haemodynamic stability was assessed with the passive leg-raising test.

Results

There was a curvilinear correlation between the daily intake of water and biomarkers measured in the 24-h collection of urine (coefficient of determination 0.37–0.70). Habitual low intake of water was associated with larger body fluid volumes. The increased fluid intake during the 2nd week was best reflected in the 24-h collection (−15 and −20% for the osmolality and creatinine, respectively, P < 0.002), while morning urine and body fluid volumes were unchanged. Increased fluid intake improved the haemodynamic stability in volunteers with a low intake of water (< median), but only in those who had minimally concentrated morning urine.

Conclusions

The 24-h collection reflected recent intake of fluid, whereas the morning urine seemed to mirror long-term corrections of the fluid balance. Concentrated urine was associated with larger body fluid volumes.

Long Intravascular Persistence of 20% Albumin in Postoperative Patients

BACKGROUND

Albumin may persist intravascularly for a shorter time in patients after major surgery than in healthy volunteers due to a surgery-induced breakdown (shedding) of the endothelial glycocalyx layer.

METHODS

In this nonrandomized clinical trial, an IV infusion of 3 mL/kg of 20% albumin was given at a constant rate during 30 minutes to 15 patients on the first day after major open abdominal surgery (mean operating time 5.9 h) and to 15 conscious volunteers. Blood samples and urine were collected during 5 h and mass balance calculations used to estimate the half-lives of the administered albumin molecules and the induced plasma volume expansion, based on measurements of hemodilution and the plasma albumin concentration.

RESULTS

At the end of the infusions, albumin had diluted the plasma volume by 13.3% ± 4.9% (mean ± SD) in the postoperative patients and by 14.2% ± 4.8% in the volunteers (mean difference -0.9, 95% CI, -4.7 to 2.9; 1-way ANOVA P = .61), which amounted to twice the infused volume. The intravascular half-life of the infused albumin molecules was 9.1 (5.7-11.2) h in the surgical patients and 6.0 (5.1-9.0) h in the volunteers (Mann-Whitney U test, P = .26; geometric mean difference 1.2, 95% CI, 0.8-2.0). The half-life of the plasma volume expansion was 10.3 (5.3-17.6; median and interquartile range) h in the surgical patients and 7.6 (3.5-9.0) h in the volunteers (P = .10; geometric mean difference 1.5, 95% CI, 0.8-2.8). All of these parameters correlated positively with the body mass index (correlation coefficients being 0.42-0.47) while age and sex did not affect the results.

CONCLUSIONS

Twenty percent albumin caused a long-lasting plasma volume expansion of similar magnitude in postoperative patients and volunteers.

Fluid volume kinetics of 20% albumin

AIMS

A population kinetic model was developed for the body fluid shifts occurring when 20% albumin is given by intravenous infusion. The aim was to study whether its efficacy to expand the plasma volume is impaired after major surgery.

METHODS

An intravenous infusion of 3 mL/kg 20% albumin over 30 minutes was given to 15 volunteers and to 15 patients on the 1^st day after major open abdominal surgery. Blood samples and urine were collected during 5 hours. Mixed-effect modelling software was used to develop a fluid volume kinetic model, using blood haemoglobin and urine excretion the estimate body fluid shifts, to which individual-specific covariates were added in sequence.

RESULTS

The rise in plasma albumin expanded the plasma volume in excess of the infused volume by relocating noncirculating fluid (rate constant k₂₁ ), but it also increased losses of fluid from the kinetic system (k_b ). The balance between k₂₁ and k_b maintained the rise in plasma albumin and plasma volume at a virtual steady-state for almost 2 hours. The rate constant for urinary excretion (k₁₀ ) was slightly reduced by the preceding surgery, by a marked rise in plasma albumin, and by a high preinfusion urinary concentration of creatinine. The arterial pressure, body weight, and plasma concentrations of C-reactive protein and shedding products of the endothelial glycocalyx layer (syndecan-1, heparan sulfate, and hyaluronic acid) did not serve as statistically significant covariates.

CONCLUSIONS

There were no clinically relevant differences in the kinetics of 20% albumin between postoperative patients and volunteers.

Signs of Dehydration in Nursing Home Residents

OBJECTIVES

Although dehydration can affect mental and physical health, there is no clear, consistent, and reproducible diagnostic tool for this condition in older people. We applied multiple methods to detect dehydration with the aim of assessing the value of using urine analysis for this purpose.

DESIGN

Nonrandomized cohort study.

SETTING AND PARTICIPANTS

Sixty nursing home residents, aged 64-103 (mean 84) years.

METHODS

Sampling of morning urine, blood analyses, and clinical examination. A previously validated algorithm summarized the urine specific gravity, osmolality, creatinine, and color to a Fluid Retention Index (FRI).

RESULTS

The cut-off for renal fluid conservation consistent with dehydration (FRI ≥ 4.0) was reached by 51% of the cohort. No statistically significant linear correlation was found between FRI and serum osmolality (mean 307.5 mOsmol/kg) or plasma sodium (mean 139 mmol/L), but the subjects reported less thirst with increasing FRI scores (linear correlation r = -0.35; P < .03). Clinical examinations of mucous membranes and tongue furrows did not correlate with other markers of dehydration. Subjects with sunken eyes had higher C-reactive protein (P < .02) and lower albumin (P < .002) concentrations in plasma than the others, while impaired skin turgor only correlated with age (P < .04).

CONCLUSIONS/IMPLICATIONS

Renal fluid conservation consistent with dehydration was found in half of the nursing home residents, which could partially be accounted for by decreased thirst. Clinical examinations probably reflected the physical status and age more than dehydration. The lack of correlation between the serum osmolality and the FRI, both of which are purported to be gold standards for dehydration, raises questions about whether a gold standard exists.

Minimal shedding of the glycocalyx layer during abdominal hysterectomy

Background

Surgery with and without hypervolaemia may cause shedding (breakdown) of the endothelial glycocalyx layer, but the severity of this problem is unclear.

Methods

In this preliminary report of a larger clinical trial, the plasma and urine concentrations of three biomarkers of glycocalyx shedding (syndecan-1, hyaluronic acid and heparan sulfate) were measured in seven patients before, during, and after open hysterectomy. The fluid therapy consisted of 25 ml/kg (approximately 2 l) of Ringer’s lactate, which was infused over 30 min when the surgery started. The resulting plasma volume expansion at the end of the infusion was estimated from the haemodilution.

Results

The mean plasma concentration of syndecan-1 was 21.7 ng/ml before surgery and averaged 19.7 ng/ml during and after the surgery. The plasma concentration of hyaluronic acid decreased from 38.0 to 27.7 ng/ml (P < 0.05), while heparan sulfate increased from 3.4 to 5.5 μg/ml (P < 0.05). The urine concentrations of syndecan-1 decreased significantly, while they increased for hyaluronic acid and heparan sulfate. Despite the vigorous fluid load, the urine flow did not exceed 1 ml/min.

Conclusions

No clear evidence was found for shedding of the endothelial glycocalyx layer when 2 l of Ringer’s lactate was infused over 30 min during abdominal hysterectomy. Urine analyses yielded patterns of changes that differed from those in plasma.

Trial registration

ISRCTN81005631. Registered May 17, 2016.