My doctor said I should drink a lot! Recommendations for fluid intake in patients with chronic kidney disease

Water/fluid intake in Kıdney transplant recipients: An underrated topic

Although kidney transplantation (KT) is the best treatment option for end-stage kidney disease, long-term complications such as chronic kidney allograft dysfunction and cardiovascular disorders are observed. To decrease these complications, preventive measures must be applied in kidney transplant recipients (KTRs). One of these common measures is the increase of water/fluid intake although this is not evidence-based practice. Indeed, surprisingly very limited studies evaluated the impact of increased water/fluid intake on graft function, with small number of KTRs and short term follow-up. We suggest that the water/fluid intake should be personalized based on baseline graft function, time onset after KT (which water homeostasis changes), presence of hyponatremia and hypervolemia, concomitant medications, and patient willingness. Methods for estimating water/fluid intake (direct measurement, 24-h urine volume measurement, urine osmolarity) has both advantages and drawbacks and the best method has not been identified. Increase of water/fluid intake in specific conditions (in hot, and humid weather, before exercise, during Ramadan fasting) or in distinct KTRs (KTRs with de novo nephrolithiasis, frequent urinary tract infections) is not tested. Furthermore, the relationship between water/fluid intake and major cardiovascular adverse events are not known. There is no doubt that minimum amount of water/fluid intake is necessary for graft function (the amount is not known) but there is no evidence for a particular target level of water/fluid intake. In the current review, we summarize the studies assessing fluid/water intake in KTR, explained the pathophysiologic basis of water disorders in early period of KT and late after KT, elucidate conflicts and unknown issues of water intake in KTRs and suggest future research needs.

Intuitive concepts in internal medicine and their occurrence in undergraduate medical students in different semesters

Background: Dealing with errors in medical practice is of great importance for patient safety. In the natural sciences, intuitive concepts, so-called misconceptions, are increasingly coming into focus of teaching because they lead to a faulty understanding of contexts and thus to faulty scientific reasoning. In medicine, intuitive concepts still play a subordinate role. However, once intuitive concepts have been memorized, they can become firmly established and, under certain circumstances, lead to diagnostic and treatment errors in medical practice. The aim of this study was to identify potential intuitive concepts in internal medicine and to analyze their occurrence in medical students from different semesters. Methods: Eight internists from different subspecialties were asked about intuitive concepts by means of a structured interview. A total of 17 intuitive concepts were identified. Using these concepts, a multiple-choice test was created with 17 patient cases. For each case, there were four possible answers: the correct answer, an incorrect answer that included the intuitive concept, the answer "both are incorrect", and the answer "I am not sure", which is to be understood in the sense of "I do not know whether one of the three answers is correct". As an online multiple-choice test, these 17 cases were made available to all 2^nd, 6^th, and 12^th semester students (N=1170, n=418 from the 2nd semester, n=425 from the 6^th semester, and n=327 from the 12^th semester, i.e., the final year) for four weeks in June 2015. The test had to be answered within nine minutes. A mixed logistic regression model was used for evaluation. Results: Of the N=317 participating students (n=97 from the 2^nd semester, n=124 from the 6^th semester, and n=96 from the internship year, overall response rate 27.1%), on average, students from all three groups chose the intuitive concept most often, approximately 40%, although the correct answer increased toward the final year with simultaneously decreasing uncertainty and decreasing feeling of not knowing, respectively. In the final year, compared to the 2^nd semester, the intuitive concept was selected significantly more often for two questions (p<0.01). For four questions, the intuitive concept was selected significantly less frequently in the final year (p<0.01). Conclusion: Intuitive concepts can be identified in internal medicine and do not appear to be significantly reduced in students during the course of their studies. This suggests that this could also be the case for other medical subjects. Therefore, similar studies should be conducted for other medical subjects in order to identify potential sources of error in clinical work. In addition, suitable didactic methods should be developed and tested with which students learn not to succumb to intuitive concepts as far as possible in order to prevent diagnostic or therapeutic errors in later medical practice.

PBPK Simulation-Based Evaluation of Ganciclovir Crystalluria Risk Factors: Effect of Renal Impairment, Old Age, and Low Fluid Intake

Dosing guidance is often lacking for chronic kidney disease (CKD) due to exclusion of such patients from pivotal clinical trials. Physiologically based pharmacokinetic (PBPK) modelling supports model-informed dosing when clinical data are lacking, but application of these approaches to patients with impaired renal function is not yet at full maturity. In the current study, a ganciclovir PBPK model was developed for patients with normal renal function and extended to CKD population. CKD-related changes in tubular secretion were explored in the mechanistic kidney model and implemented either as proportional or non-proportional decline relative to GFR. Crystalluria risk was evaluated in different clinical settings (old age, severe CKD and low fluid intake) by simulating ganciclovir medullary collecting duct (MCD) concentrations. The ganciclovir PBPK model captured observed changes in systemic pharmacokinetic endpoints in mild-to-severe CKD; these trends were evident irrespective of assumed pathophysiological mechanism of altered active tubular secretion in the model. Minimal difference in simulated ganciclovir MCD concentrations was noted between young adult and geriatric populations with normal renal function and urine flow (1 mL/min), with lower concentrations predicted for severe CKD patients. High crystalluria risk was identified at reduced urine flow (0.1 mL/min) as simulated ganciclovir MCD concentrations exceeded its solubility (2.6–6 mg/mL), irrespective of underlying renal function. The analysis highlighted the importance of appropriate distribution of virtual subjects’ systems data in CKD populations. The ganciclovir PBPK model illustrates the ability of this translational tool to explore individual and combined effects of age, urine flow, and renal impairment on local drug renal exposure.

A practical guide to diagnosis and assessment of chronic kidney disease for the non-nephrologist

Chronic kidney disease (CKD) is common. People with CKD have a wide range of comorbidities and, therefore, the majority of non-nephrologists will care for people with CKD. This paper aims to provide a brief overview of the diagnosis and management of CKD for the non-nephrologist. Identifying those with CKD and optimising treatment is essential as CKD has a direct association with adverse patient outcomes. There are modifiable factors where interventions may delay progression of CKD, including: smoking cessation, dietary advice, hypertension management, renin-angiotensin system blockade, glycaemic control and relieving urinary outflow obstruction. Complications, such as renal anaemia, metabolic acidosis, CKD-related mineral bone disease, hyperkalaemia and gout, are best managed in conjunction with nephrology input. The progression of CKD is often variable and nonlinear, but person-centred intervention can delay progression of CKD, reduce morbidity and mortality, and allow time for preparation for renal replacement therapy, ultimately providing the best possible personalised care.

Water Intake, Water Balance, and the Elusive Daily Water Requirement

Water is essential for metabolism, substrate transport across membranes, cellular homeostasis, temperature regulation, and circulatory function. Although nutritional and physiological research teams and professional organizations have described the daily total water intakes (TWI, L/24h) and Adequate Intakes (AI) of children, women, and men, there is no widespread consensus regarding the human water requirements of different demographic groups. These requirements remain undefined because of the dynamic complexity inherent in the human water regulatory network, which involves the central nervous system and several organ systems, as well as large inter-individual differences. The present review analyzes published evidence that is relevant to these issues and presents a novel approach to assessing the daily water requirements of individuals in all sex and life-stage groups, as an alternative to AI values based on survey data. This empirical method focuses on the intensity of a specific neuroendocrine response (e.g., plasma arginine vasopressin (AVP) concentration) employed by the brain to regulate total body water volume and concentration. We consider this autonomically-controlled neuroendocrine response to be an inherent hydration biomarker and one means by which the brain maintains good health and optimal function. We also propose that this individualized method defines the elusive state of euhydration (i.e., water balance) and distinguishes it from hypohydration. Using plasma AVP concentration to analyze multiple published data sets that included both men and women, we determined that a mild neuroendocrine defense of body water commences when TWI is ˂1.8 L/24h, that 19⁻71% of adults in various countries consume less than this TWI each day, and consuming less than the 24-h water AI may influence the risk of dysfunctional metabolism and chronic diseases.

The Sodium Paradox: Dysnatremia and Mortality in Patients Implanted With Extracorporeal Mechanical Circulatory Support Devices

INTRODUCTION

Dysnatremia, abnormal serum sodium levels, has long been used as a marker for disease progression in heart failure patients. Classically, hyponatremia is associated with increased fluid volume in heart failure and is often a result of neuroendocrine dysfunction and poor cardiac output. Recent studies have noted that dysnatremia and hypernatremia are predictive of worsened outcomes in critical care and renal disease populations. We investigated the relationship between dysnatremia and postoperative outcomes in patients implanted with extracorporeal mechanical circulatory devices.

METHODS

A total of 97 patients who underwent implantation with the CentriMag mechanical circulatory assist system were included in this retrospective study. Patients were divided into 2 groups based on preoperative serum sodium level cutoff of 135 mEq/L. Outcomes and mortality were compared between groups.

RESULTS

The mean age for the study population was 56.21 ± 15.13 years, and 57 patients (58.8%) were male. The mean time on CentriMag support was 22.7 days. Patients with serum sodium levels ≤135 mEq/L were noted to have significantly worsened indicators of preoperative cardiac function. However, patients with serum sodium levels >135 mEq/L had significantly shorter postoperative survival ( P = .006). When entered into a multivariate Cox proportional hazards model, sodium was an independent predictor for increased risk of mortality (hazard ratio: 1.224; 95% confidence interval: 1.009-1.485; P = .040).

CONCLUSION

Our results indicate that elevated preoperative sodium in patients undergoing implantation of a temporary mechanical circulatory support system is predictive of worsened postoperative survival.

Daily fluid intake and outcomes in kidney recipients: post hoc analysis from the randomized ABCAN trial

Generous and even excessive fluid intake is routinely recommended to kidney transplant recipients despite minimal evidence to support this practice. We hypothesized that increased fluid intake, ascertained by 24-h urine volume output, may adversely affect graft outcomes as it would impose an extra workload on a limited number of nephrons. Kidney transplant recipients who were randomized to losartan vs. placebo in the Angiotensin II Blockade for Chronic Allograft Nephropathy (ABCAN) trial (n = 153) underwent baseline, five-yr biopsies, and annual iothalamate glomerular filtration rate assessment. Recipients with higher urine volume at randomization had higher urinary sodium and also higher urinary protein. The proportion using diuretics or CNI based regimens were similar across urinary volume tertiles. The highest urinary volume tertile (>2.56 L/d) did not predict the development of interstitial volume doubling or end-stage renal disease (ESRD) from interstitial fibrosis/tubular atrophy (OR = 3.52, 95% CI 0.4, 31.24, p = 0.26), interstitial volume doubling or all-cause ESRD (OR = 7.04, 95% CI 0.66, 74.87, p = 0.11), and was not associated with the conventional endpoint of doubling serum creatinine, all-cause ESRD, or death (OR = 0.89, 95% CI 0.21, 3.71, p = 0.87). These results suggest that the current practice of liberal fluid intake may not be beneficial in low risk and mostly Caucasian transplant recipients.

"Drink at least 8 glasses of water a day to be healthy???"

The saying "drink at least 8 glasses of water per day to be healthy" has had little supporting evidence. The purpose of this article was to briefly introduce the role of hydration in health in order to explore in more detail recent observational studies of hyperhydration in chronic kidney disease (CKD) in man. The Modification of Diet in Renal Disease study initially noted a negative association between increasing urine output and progression of CKD that was absent when corrected for baseline variables. Recently, data from 2 different cross-sectional populations found those with the highest fluid intake had a significantly lower risk of CKD. In a longitudinal, community-based cohort study adjusted for baseline variables, decline in kidney function was significantly slower in those with higher versus lower baseline urine volume. These new and contradictory results underline the need for a randomized controlled study to test the hypothesis that increased fluid intake will slow renal decline.

Factors associated with 24-hour urinary volume: the Swiss salt survey

Background

Low 24-hour urine volume (24UV) may be a significant risk factor for decline in kidney function. We therefore aimed to study associated markers and possible determinants of 24UV in a sample of the Swiss population.

Methods

The cross-sectional Swiss Salt Study included a population-based sample of 1535 (746 men and 789 women) individuals from three linguistic regions of Switzerland. Data from 1300 subjects were available for the present analysis. 24UV was measured using 24-hour urine collection. Determinants of 24UV were identified using multivariable linear regression models.

Results

In bivariate analysis, 24UV was higher in women compared to men (2000 ml/24 h [interquartile range (IQR): 1354, 2562] versus 1780 ml/24 h [IQR: 1244, 2360], p = 0.002). In multivariable regression analyses, independent associated markers of 24UV were female sex (β = 280, 95% confidence interval [CI]: 174, 386, p < 0.0001), fluid intake (β = 604, 95% CI: 539, 670, p < 0.0001), sodium excretion (β = 4.2, 95% CI: 3.4, 4.9, p < 0.0001) age (β = 6.6, CI: 3.4, 9.7, p < .0001), creatinine clearance (β = 2.4, CI: 0.2, 4.6, p = 0.04), living in the German-speaking part of Switzerland (β = 124, CI: 29, 219, p = 0.01), alcohol consumption (β = 41, CI: 9, 73, p = 0.01 for increasing categories of alcohol consumption), body mass index (β = −32, CI: -45, -18, p < 0.0001), current smoking (β = −146, CI: -265, -26, p = 0.02), and consumption of meat and cold cut (β = −56, CI: -108, -5, p = 0.03).

Conclusion

In this large population-based, cross-sectional study, we found several strong and independent correlates for 24UV. These findings may be important to improve our understanding in the development of chronic kidney disease.

Vasopressin: a novel target for the prevention and retardation of kidney disease?

After several decades during which little attention was paid to vasopressin and/or urine concentration in clinical practice, interest in vasopressin has renewed with the availability of new, potent, orally active vasopressin-receptor antagonists--the vaptans--and with the results of epidemiological studies evaluating copeptin (a surrogate marker of vasopressin) in large population-based cohorts. Several experimental studies in rats and mice had previously shown that vasopressin, acting via vasopressin V2 antidiuretic receptors, contributes to the progression of chronic kidney disease; in particular, to autosomal dominant polycystic kidney disease. New epidemiological studies now suggest a role for vasopressin in the pathogenesis of diabetes mellitus and metabolic disorders via activation of hepatic V1a and/or pancreatic islet V1b receptors. The first part of this Review describes the adverse effects of vasopressin, as revealed by clinical and experimental studies in kidney diseases, hypertension, diabetes and the metabolic syndrome. The second part provides insights into vasopressin physiology and pathophysiology that may be relevant to the understanding of these adverse effects and that are linked to the excretion of concentrated nitrogen wastes and associated hyperfiltration. Collectively, the studies reviewed here suggest that more attention should be given to the vasopressin-thirst-urine concentration axis in clinical investigations and in patient care. Whether selective blockade of the different vasopressin receptors may provide therapeutic benefits beyond their present indication in hyponatraemia requires new clinical trials.

Dysnatraemia in heart failure

AIMS

To investigate in detail the correlates of dysnatremia, and to estimate its differential prognostic relevance in patients with heart failure with reduced or preserved LVEF. Background Hyponatraemia has been shown to carry important prognostic information in patients with heart failure with reduced left ventricular ejection fraction (LVEF). However, exact serum sodium cut-off levels are not defined and the implications for heart failure with preserved ejection fraction (HF-pEF) are unclear. The prognostic value of hypernatraemia has not been investigated systematically. Therefore, the aim of this study was to investigate in detail the correlates of dysnatraemia, and to estimate its differential prognostic relevance in patients with heart failure with reduced or preserved LVEF.

METHODS AND RESULTS

One thousand consecutive patients with heart failure of any cause and severity from the Würzburg Interdisciplinary Network for Heart Failure registry were included. Non-linear models for the association between serum sodium and mortality risk were calculated using restricted cubic splines and Cox proportional hazard regression. Median follow-up time for survivors was 5.1 years. Results Independent correlates of dysnatraemia included guideline-recommended medication for chronic heart failure, indicators of renal function, and reverse associations with established cardiac risk factors. Overall mortality was 56%. Both hyponatraemia (n = 72) and hypernatraemia (n = 98) were associated with a significantly increased mortality risk: hazard ratio (HR) 2.10, 95% confidence interval (CI) 1.60-2.77; and HR 1.91, 95% CI 1.49-2.45, respectively. A U-shaped association of serum sodium with mortality risk was found. Prognosis was best for patients with high normal sodium levels, i.e. 140-145 mmol/L.

CONCLUSIONS

Both hypo- and hypernatraemia indicate a markedly compromised prognosis in heart failure regardless of LVEF. Sodium levels within the reference range carry differential information on survival, with serum levels of 135-139 mmol/L indicating an increased mortality risk.

Urine volume and change in estimated GFR in a community-based cohort study

BACKGROUND AND OBJECTIVES

The effect of increased fluid intake on kidney function is unclear. This study evaluates the relationship between urine volume and renal decline over 6 years in a large community-based cohort.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This prospective cohort study was undertaken in Canada from 2002 to 2008. We obtained 24-hour urine samples from adult participants with an estimated GFR (eGFR) ≥60 ml/min per 1.73 m(2) at study entry. Percentage annual change in eGFR from baseline was categorized as average decline <1% per year, between 1% and 4.9% (mild-to-moderate decline) or ≥5% (rapid decline).

RESULTS

2148 participants provided valid 24-hour urine samples, grouped as <1 L/d (14.5%); 1 to 1.9 L/d (51.5%); 2 to 2.9 L/d (26.3%); and ≥3 L/d (7.7%). Baseline eGFR for each category of urine volume was 90, 88, 84, and 87 ml/min per 1.73 m(2), respectively. Overall, eGFR declined by 1% per year, with 10% demonstrating rapid decline and 40% demonstrating mild-to-moderate decline. An inverse, graded relationship was evident between urine volume and eGFR decline: For each increasing category of 24-hour urine volume, percentage annual eGFR decline was progressively slower, from 1.3%, 1.0%, 0.8%, to 0.5%, respectively; P = 0.02. Compared with those with urine volume 1 to 1.9 L/d, those with urine volume ≥3 L/d were significantly less likely to demonstrate mild-to-moderate decline (adjusted odds ratio 0.66; 95% confidence interval 0.46 to 0.94) or rapid decline (adjusted odds ratio 0.46; 95% confidence interval 0.23 to 0.92); adjusted for age, gender, baseline eGFR, medication use for hypertension (including diuretics), proteinuria, diabetes, and cardiovascular disease.

CONCLUSIONS

In this community-based cohort, decline in kidney function was significantly slower in those with higher versus lower urine volume.

Prevalence and determinants of physical activity and fluid intake in kidney transplant recipients

BACKGROUND AND SIGNIFICANCE

Self-care for kidney transplantation is recommended to maintain kidney function. Little is known about levels of self-care practices and demographic, psychosocial, and health-related correlates.

AIM

To investigate patients' self-reported exercise and fluid intake, demographic and psychosocial factors associated with these self-care practices, and health-related quality of life.

METHODS

Eighty-eight of 158 kidney recipients from two academic medical centers completed a semi-structured interview and surveys 2 months post-transplant.

RESULTS

Most patients were sedentary (76%) with a quarter exercising either regularly (11%) or not at current recommendations (13%). One-third (35%) reported drinking the recommended 3 L of fluid daily. Multivariate analyses indicated that private insurance, high self-efficacy, and better physical functioning were significantly associated with engaging in physical activity (p < 0.05); while male gender, private insurance, high self-efficacy, and not attributing oneself responsible for transplant success were significant predictors of adherence to fluid intake (p < 0.05). Despite the significance of these predictors, models for physical activity and fluid intake explained 10-15% of the overall variance in these behaviors. Multivariate analyses indicated that younger age, high value of exercise, and higher social functioning significantly (p < 0.05) predicted high self-efficacy for physical activity, while being married significantly (p < 0.05) predicted high self-efficacy for fluid intake.

CONCLUSION

Identifying patients at risk of inadequate self-care practice is essential for educating patients about the importance of self-care.

Longitudinal analysis of physical activity, fluid intake, and graft function among kidney transplant recipients

Self-care is recommended to kidney transplant recipients as a vital component to maintain long-term graft function. However, little is known about the effects of physical activity, fluid intake, and smoking history on graft function. This longitudinal study examined the relationship between self-care practices on graft function among 88 new kidney transplant recipients in Chicago, IL and Albany, NY between 2005 and 2008. Participants were interviewed, completed surveys, and medical charts were abstracted. Physical activity, fluid intake, and smoking history at baseline were compared with changes in estimated glomerular filtration rate (eGFR) (every 6 months up to 1 year) using bivariate and multivariate regression analysis, while controlling for sociodemographic and clinical transplant variables. Multivariate analyses revealed that greater physical activity was significantly (P < 0.05) associated with improvement in GFR at 6 months; while greater physical activity, absence of smoking history, and nonwhite ethnicity were significant (P < 0.05) predictors of improvement in GFR at 12 months. These results suggest that increasing physical activity levels in kidney recipients may be an effective behavioral measure to help ensure graft functioning. Our findings suggest the need for a randomized controlled trial of exercise, fluid intake, and smoking history on GFR beyond 12 months.

Risk factors for end-stage renal disease: 25-year follow-up

BACKGROUND

Few cohort studies have focused on risk factors for end-stage renal disease (ESRD). This investigation evaluated the prognostic value of several potential novel risk factors for ESRD after considering established risk factors.

METHODS

We studied 177 570 individuals from a large integrated health care delivery system in northern California who volunteered for health checkups between June 1, 1964, and August 31, 1973. Initiation of ESRD treatment was ascertained using US Renal Data System registry data through December 31, 2000.

RESULTS

A total of 842 cases of ESRD were observed during 5 275 957 person-years of follow-up. This comprehensive evaluation confirmed the importance of established risk factors, including the following: male sex, older age, proteinuria, diabetes mellitus, lower educational attainment, and African American race, as well as higher blood pressure, body mass index, and serum creatinine level. The 2 most potent risk factors were proteinuria and excess weight. For proteinuria, the adjusted hazard ratios (HRs) were 7.90 (95% confidence interval [CI], 5.35-11.67) for 3 to 4+ on urine dipstick, 3.59 (2.82-4.57) for 1 to 2+ on urine dipstick, and 2.37 (1.79-3.14) for trace vs negative on urine dipstick. For excess weight, the HRs were 4.39 (95% CI, 3.38-5.70) for class 2 to class 3 obesity, 3.11 (2.51-3.84) for class 1 obesity, and 1.65 (1.39-1.97) for overweight vs normal weight. Furthermore, several independent novel risk factors for ESRD were identified, including lower hemoglobin level (1.33 [1.08-1.63] for lowest vs highest quartile), higher serum uric acid level (2.14 [1.65-2.77] for highest vs lowest quartile), self-reported history of nocturia (1.36 [1.17-1.58]), and family history of kidney disease (HR, 1.40 [95% CI, 1.02-1.90]).

CONCLUSIONS

We confirmed the importance of established ESRD risk factors in this large cohort with broad sex and racial/ethnic representation. Lower hemoglobin level, higher serum uric acid level, self-reported history of nocturia, and family history of kidney disease are independent risk factors for ESRD.