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Interventions for promoting adherence to fluid intake and dietary salt restriction in people with end‐stage kidney disease

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Versión publicada: 27 noviembre 2014 Historial de versiones

https://doi.org/10.1002/14651858.CD011410

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Abstract

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

This review aims to look at the benefits and harms of non‐pharmacologic interventions to improve adherence to dietary salt and fluid restriction in people with ESKD, including those in the pre‐dialysis stage and those receiving HD or PD.

Background

Description of the condition

Volume overload is a common complication in end‐stage kidney disease (ESKD) (Blake 2011; Wabel 2008). Hypervolaemia, as measured by various methods, including isotope dilution, bioimpedance, relative plasma volume monitoring, biochemical markers and clinical symptoms, is associated with hypertension, left ventricular (LV) hypertrophy and mortality in the dialysis population (Agarwal 2010a; Chazot 2012; Konings 2002; Paniagua 2010; Tzamaloukas 1995; Wizemann 2009). Although not a measure of underlying volume status, interdialytic weight gain (IDWG) has also been associated with all‐cause and cardiovascular mortality (Foley 2002; Kalantar‐Zadeh 2009; Kimmel 2000; Saran 2003).

Volume status in ESKD is dependent on several factors, including sodium and fluid intake, cardiac function, residual kidney function, dialysate composition and ultrafiltration volume (K/DOQI 2006). In ESKD, salt intake restriction is especially important because renal sodium excretion becomes inadequate (Khandelwal 2003). Excess dietary sodium raises extracellular osmolality, leading to a) movement of water from the intracellular compartment to the extracellular compartment, thereby resulting in volume expansion, and b) stimulation of thirst. Because fluid intake is inextricably linked to salt intake, dietary advice should focus on salt restriction, with fluid restriction as a corollary (Agarwal 2010b; Tomson 2001).

Description of the intervention

There are a number of strategies to optimise volume status in people with ESKD, including diuretic therapy and adjusting the dialysis prescription. For people on haemodialysis (HD) this includes adjusting dialysate sodium content, increasing frequency and duration of dialysis sessions, and increasing the ultrafiltration rate. For people on peritoneal dialysis (PD), the number of daily exchanges and solution strengths can be increased to enhance fluid removal. However, the cornerstone of volume management is dietary restriction of salt and fluid intake, and guidelines from various regions differ in their sodium intake recommendations, ranging from < 65 mmol/d to < 110 mmol/d (Ash 2006; Blake 2011; Fouque 2007; Jindal 2006; K/DOQI 2002; K/DOQI 2006; Levin 2008; MacGregor 2011; Mactier 2009; Pollock 2005). A multi‐intervention approach to volume control is often used. Centres in Tassin, France have achieved blood pressure (BP) control in 98% of their cohort using a combination of dietary salt restriction, long dialysis sessions, dialysate sodium of 138 mmol/L and intensive ultrafiltration (Charra 1992). Similarly, centres in Izmir, Turkey utilized a dry weight reduction strategy with salt restriction and intensive ultrafiltration, which was associated with lower LV mass, better LV function, and less intradialytic hypotension compared to an antihypertensive‐based strategy (Kayikcioglu 2009).

Adherence is a behaviour that is influenced by multiple factors related to the patient, the treatment or condition, the health care providers and the clinical care setting (Viswanathan 2012). Several educational, psychological, cognitive, behavioural and organizational‐level interventions to enhance adherence to dietary salt and fluid restriction have been studied.

How the intervention might work

Interventions to improve adherence are often based on theoretical models that address health behaviour change, such as the health belief model, social cognitive theory, and self‐regulation theory (Bandura 1986; Becker 1974; Leventhal 1980; Welch 2005).

Why it is important to do this review

Non‐adherence to fluid restriction, as measured by IDWG above a threshold value, is common in the HD population, ranging from 10% to 60% in previous studies (Denhaerynck 2007), and such non‐adherence may have a negative impact on survival (Leggat 1998; Saran 2003). In a study conducted in people on PD, non‐adherence to salt restriction and fluid restriction was found in 74% and 76% of people with symptomatic fluid gain, respectively (Tzamaloukas 1995). Although guidelines have emphasised the role of the dietician in nutritional assessment and counselling, as well as the involvement of multidisciplinary teams, they have not included specific strategies to improve adherence.

Objectives

This review aims to look at the benefits and harms of non‐pharmacologic interventions to improve adherence to dietary salt and fluid restriction in people with ESKD, including those in the pre‐dialysis stage and those receiving HD or PD.

Methods

Criteria for considering studies for this review

Types of studies

All randomised controlled trials (RCTs) and quasi‐RCTs (RCTs in which allocation to treatment was obtained by alternation, use of alternate medical records, date of birth or other predictable methods) looking at non‐pharmacologic interventions to improve adherence to dietary salt or fluid restriction in people with ESKD will be eligible for inclusion.

Types of participants

Adults aged 18 years and over with ESKD (chronic kidney disease stage 5 (K/DOQI 2002)), including those who are in the pre‐dialysis stage, or receiving chronic HD or PD.

Types of interventions

Studies assessing strategies to improve adherence to dietary salt and fluid restriction in comparison to a control arm will be included. Head‐to‐head comparisons of interventions or comparison to routine care are acceptable.  Examples of interventions include:

  • Cognitive behavioural therapy

  • Patient educational interventions (oral education, interactive modules, posters, booklets, videos)

  • Behavioural contracting

  • Telephone contacts with nurses

  • Hypnotherapy

  • Self‐efficacy training

  • Coaching

  • Motivational interviewing

  • Telemetric body weight monitoring

Types of outcome measures

Primary outcomes

  1. All‐cause mortality

  2. Fatal cardiovascular events (myocardial infarction (MI), stroke, sudden death, congestive heart failure, arrhythmias)

  3. Non‐fatal cardiovascular events (MI, stroke, congestive heart failure, arrhythmias)

  4. Quality of life (any measure, as reported by study authors, for example the Short Form 36 Health Survey)

Secondary outcomes

  1. Measures of volume status or changes in body volume, including:

    1. IDWG or daily weight gain (absolute weight gain or per cent of post‐dialysis weight, at end of intervention, or change between beginning and end of intervention)

    2. Bioimpedance measurements of extracellular fluid volume (ECV), in litres, or expressed as volume excess, in litres or % above normal ECV, at end of intervention, or change between beginning and end of intervention

  2. Symptomatic intradialytic hypotension (number of events and number of patients with events), defined as a  decrease in systolic BP (SBP) by ≥ 20 mm Hg or a decrease in mean arterial pressure (MAP) by ≥ 10 mm Hg, associated with abdominal discomfort, yawning, sighing, nausea, vomiting, muscle cramps, restlessness, dizziness, fainting or anxiety (K/DOQI 2005)

  3. BP control

    1. SBP, in mm Hg, at end of intervention, or change between beginning and end of intervention; or number of patients achieving BP target. In HD studies, pre‐HD SBP measurements will be used

    2. Diastolic BP (DBP), in mm Hg, at end of intervention, or change between beginning and end of intervention; or number of patients achieving BP target. In HD studies, pre‐HD DBP measurements will be used.

    3. MAP, in mm Hg, at end of intervention, or change between beginning and end of intervention; or number of patients achieving BP target

  4. LV mass index, in g/m², at end of intervention, or change between beginning and end of intervention

  5. Nutritional status:

    1. Albumin in g/L, at end of intervention, or change between beginning and end of intervention

    2. Prealbumin in mg/L, at end of intervention, or change between beginning and end of intervention

    3. Normalized protein catabolic rate in g/kg/d, at end of intervention, or change between beginning and end of intervention.

Search methods for identification of studies

Electronic searches

We will search the Cochrane Renal Group's Specialised Register through contact with the Trials' Search Co‐ordinator using search terms relevant to this review. The Cochrane Renal Group’s Specialised Register contains studies identified from the following sources.

  1. Monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL)

  2. Weekly searches of MEDLINE OVID SP

  3. Handsearching of renal‐related journals and the proceedings of major renal conferences

  4. Searching of the current year of EMBASE OVID SP

  5. Weekly current awareness alerts for selected renal journals

  6. Searches of the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

Studies contained in the Specialised Register are identified through search strategies for CENTRAL, MEDLINE, and EMBASE based on the scope of the Cochrane Renal Group. Details of these strategies, as well as a list of handsearched journals, conference proceedings and current awareness alerts, are available in the Specialised Register section of information about the Cochrane Renal Group. We will also search CINAHL and PsycINFO.

Searching other resources

  1. Reference lists of review articles, relevant studies and clinical practice guidelines.

  2. Letters seeking information about unpublished or incomplete studies to investigators known to be involved in previous studies.

Data collection and analysis

Selection of studies

The search strategy described will be used to obtain titles and abstracts of studies that may be relevant to the review. The titles and abstracts will be screened independently by two authors, who will discard studies that are not applicable, however studies and reviews that might include relevant data or information on studies will be retained initially. Two authors will independently assess retrieved abstracts and, if necessary the full text, of these studies to determine which studies satisfy the inclusion criteria.

Data extraction and management

Data extraction will be carried out independently by two authors using standard data extraction forms. Studies reported in non‐English language journals will be translated before assessment. Where more than one publication of one study exists, reports will be grouped together and the publication with the most complete data will be used in the analyses. Where relevant outcomes are only published in earlier versions these data will be used. Any discrepancy between published versions will be highlighted.

Assessment of risk of bias in included studies

The following items will be independently assessed by two authors using the risk of bias assessment tool (Higgins 2011) (see Appendix 2).

  • Was there adequate sequence generation (selection bias)?

  • Was allocation adequately concealed (selection bias)?

  • Was knowledge of the allocated interventions adequately prevented during the study (detection bias)?

    • Participants and personnel

    • Outcome assessors

  • Were incomplete outcome data adequately addressed (attrition bias)?

  • Are reports of the study free of suggestion of selective outcome reporting (reporting bias)?

  • Was the study apparently free of other problems that could put it at a risk of bias?

Measures of treatment effect

For dichotomous outcomes (death, cardiovascular events, episodes of intradialytic hypotension), results will be expressed as risk ratio (RR) with 95% confidence intervals (CI). Where continuous scales of measurement are used to assess the effects of treatment (IDWG, BP, LV mass index, quality of life measures), the mean difference (MD) will be used, or the standardised mean difference (SMD) if different scales have been used. For continuous data, the preferred data will be the difference between beginning and end of treatment, but if this is not available, the end of treatment data will be extracted. If data are reported at more than one time point during the study, all data will be extracted. 

Unit of analysis issues

If outcome data for a study are reported for more than one period of follow‐up, we will perform subgroup analyses for different periods of follow‐up (≤ 6 weeks, > 6 weeks to 12 weeks, > 12 weeks). If a study has more than two intervention arms, the control group sample size will be split by the number of subgroup comparisons for that study. For cluster RCTs, we will use the method of multiplying the standard error of the effect estimate (from an analysis ignoring clustering) by the square root of the design effect (Higgins 2011).

Dealing with missing data

Any further information required from the original author will be requested by written correspondence (e.g. emailing corresponding author/s) and any relevant information obtained in this manner will be included in the review. Evaluation of important numerical data such as screened, randomised patients as well as intention‐to‐treat (ITT), as‐treated and per‐protocol (PP) population will be carefully performed. Attrition rates, for example drop‐outs, losses to follow‐up and withdrawals will be investigated. Issues of missing data and imputation methods (for example, last‐observation‐carried‐forward (LOCF)) will be critically appraised (Higgins 2011). 

Assessment of heterogeneity

Heterogeneity will be analysed using a Chi² test on N‐1 degrees of freedom, with an alpha of 0.05 used for statistical significance and with the I² test (Higgins 2003). I² values of 25%, 50% and 75% correspond to low, medium and high levels of heterogeneity.

Assessment of reporting biases

If possible, funnel plots will be used to assess for the potential existence of small study bias (Higgins 2011).

Data synthesis

Data will be pooled using the random‐effects model but the fixed‐effect model will also be used to ensure robustness of the model chosen and susceptibility to outliers.

Subgroup analysis and investigation of heterogeneity

If a sufficient number of studies are identified, subgroup analysis will be used to explore possible sources of heterogeneity. The following subgroups will be explored.

  1. Dialysis modality: pre‐dialysis, HD and PD

  2. Type of adherence‐enhancing therapy: behavioural, educational, cognitive, organizational

  3. Endpoint measurement at different time points: ≤ 6 weeks, > 6 to 12 weeks, > 12 weeks

  4. Age: < 50 years versus > 50 years

  5. Sex: males versus females

  6. Education level: >12 years versus < 12 years of education

  7. Diabetic versus non‐diabetic participants, and proportion of diabetic participants in the study

  8. Hypertensive (SBP > 140 mm Hg and/or DBP > 90 mm Hg) versus non‐hypertensive participants, and proportion of hypertensive participants in the studies

  9. Time on dialysis: < 6 months versus > 6 months

  10. Studies with high versus low risk of bias

  11. Geographical area: North America, Latin America, Asia, Europe

Sensitivity analysis

We will perform sensitivity analyses in order to explore the influence of the following factors on effect size.

  • Repeating the analysis excluding unpublished studies

  • Repeating the analysis taking account of risk of bias

  • Repeating the analysis excluding any very long or large studies to establish how much they dominate the results

  • Repeating the analysis excluding the cluster‐randomised studies